Biochar-coupled Fe3O4@SiO2/TiO2/g-C3N4 composites were successfully constructed through simple sol–gel and calcination methods. The composites efficiently removed high-concentration toxic tetracycline (TC) by means of ·OH and ·${\rm O}_2^{-}$, whose removal rate exhibited 91.88% during 3 h, and the degradation rate constant reached up to 0.0068 min−1. The excellent performance can be attributed to the high specific surface area, enhanced visible light response, the introduction of magnetic nanoparticles and biochars expediting charge transfer, Z-scheme heterojunction enhancing the spatial separation of photo-generate carriers and, importantly extraordinary adsorption capacity of 147.96 mg g−1. Moreover, the composites showed the most excellent efficiency under the calcination temperature of 450 ℃, and exhibited good stability with tolerance to a wide range of pH and anions. Interestingly, a synergistic photocatalytic effect was discovered in the TC/Cr(VI) combined pollution systems, resulting in significantly improved removal of Cr(VI). Besides, the photocatalytic mechanism and degradation path of tetracycline were also elucidated. All these findings suggested the as-synthesized catalyst was an excellent photocatalyst for removal of TC/Cr(VI)-contaminated water.
Biochar (BC) and nanoparticle-decorated biochar (NPs@BC) have emerged as potential high-performance function materials to facilitate simultaneous soil remediation and agricultural production. Therefore, there is an urgent need to incorporate environmental sustainability and human health targets into BC and NPs@BC selection and design processes. In contrast to extensive research on the preparation, modification, and environmental application of BC to soil ecosystems, reports about the adapted framework and material selection strategy of NPs@BC under environmental and human health considerations are still limited. Nevertheless, few studies systematically explored the impact of NPs@BC on soil ecosystems, including soil biota, geochemical properties, and nutrient cycles, which are critical for large-scale utilization as a multifunctional product. The main objective of this systematic literature review is to show the high degrees of contaminant removal for different heavy metals and organic pollutants, and to quantify the economic, environmental, and toxicological outcomes of NPs@BC in the context of sustainable agriculture. To address this need, in this review, we summarized synthesis techniques and characterization, and highlighted a linkage between the evolution of NPs@BC properties with the framework for sustainable NPs@BC selection and design based on environmental effects, hazards, and economic considerations. Then, research advances in contaminant remediation for heavy metals and organic pollutants of NPs@BC are minutely discussed. Eventually, NPs@BC positively acts on sustainable agriculture, which is declared. In the meantime, evaluating from the perspective of plant growth, soil characterizations as well as carbon and nitrogen cycle was conducted, which is critical for comprehending the NPs@BC environmental sustainability. Our work may develop a potential framework that can inform decision-making for the use of NPs@BC to facilitate promising environmental applications and prevent unintended consequences, and is expected to guide and boost the development of highly efficient NPs@BC for sustainable agriculture and environmental applications.
Carbon-based materials have been widely used in gaseous pollutant removal because of their sufficient surface functional groups; however, its removal efficiency for elemental mercury (Hg0) is low. In this study, we fabricated biomass using a chelated coupled pyrolysis strategy and further constructed the regulated adsorption sites for gaseous Hg0 uptake. A series of Mnδ-N2O2/BC with different manganese cluster sizes demonstrated that manganese clusters anchored on biochar acted as highly active and durable adsorbents for Hg0 immobilization, which increased the adsorption efficiency of Hg0 by up to 50%. Shrimp- and crab-based biochar adsorbents exhibited excellent Hg0 removal because of their chitosan-like structure. In particular, small Mn clusters and oxygen species around the defect led to a boost in the Hg0 adsorption by carbon. The results of density functional theory calculation revealed that the presence of oxygen in the carbon skeleton can tune the electrons of small-sized Mn clusters, thereby promoting the affinity of mercury atoms. The newly developed Mnδ-N2O2/BCshrimp had an adsorption capacity of 7.98–11.52 mg g−1 over a broad temperature range (50–200 °C) and showed a high tolerance to different industrial flue gases (H2O, NO, HCl, and SO2). These results provide novel green and low-carbon disposal methods for biomass resource utilization and industrial Hg0 emission control.
Although research on biochar has received increasing attention for environmental and agricultural applications, the significance of nanobiochar for environmental pollutant remediation is poorly understood. In contrast to bulk biochar, nanobiochar has superior physicochemical properties such as high catalytic activity, unique nanostructure, large specific surface area and high mobility in the soil environment. These unique characteristics make nanobiochar an ideal candidate for pollution remediation. Thus far, the research on nanobiochar is still in its infancy and most of the previous studies have only been conducted for exploring its properties and environmental functions. The lack of in-depth summary of nanobiochar’s research direction makes it a challenge for scientists and researchers globally. Hence in this review, we established some key fabrication methods for nanobiochar with a focus on its performance for the removal of pollutants from the environment. We also provided up-to-date information on nanobiochar’s role in environmental remediation and insights into different mechanisms involved in the pollutant removal. Although, nanobiochar application is increasing, the associated drawbacks to the soil ecosystem have not received enough research attention. Therefore, further research is warranted to evaluate the potential environmental risks of nanobiochar before large scale application.
Although composting is a very effective way to dispose agricultural wastes, its development is greatly limited by the low compost quality and greenhouse gas emissions. At present, there is a lack of effective means to solve these two problems simultaneously. Here, the effects of three additives of compound microbial agent, biochar and biochar carried microbial agent on the composting performance, nitrogen transformation, greenhouse gas and ammonia emissions, and bacterial communities were investigated in sheep manure composting during 28 days. Results showed that biochar carried microbial agent prolonged the thermophilic stage and promoted compost maturity. At the same time, it was confirmed by the increase of the decomposition of organic nitrogen and the transformation of NH4+-N to NO3−-N. Besides, adding biochar carried microbial agent decreased CH4, NH3 and N2O emissions by 65.23%, 42.05% and 68.64%, respectively. The gas emissions were mainly correlated to Chloroflexi, Myxococcota, Acidobacteriota, Firmicutes, and Gemmatimonadota. Redundancy analysis showed that EC and TKN were closely related to bacterial community. Therefore, biochar carried microbial agent is recommended as an effective additive to enhance compost quality and reduce gas emissions during sheep manure composting.
Biochar addition has been widely used in the field to mitigate soil nitrous oxide (N2O) emissions, and can be considered as a potential method to reduce N2O emissions during vermicomposting. However, excessive biochar addition may inhibit earthworms’ activity. Thus, it is crucial to clarify the optimum addition volumes of biochar during vermicomposting. This study evaluated the impact of addition of various amounts of biochar (0, 5, 10, 15, 20 and 25% of total amount of feedstock) on earthworms’ (Eiseniafetida) activity, N2O emission and compost quality during vermicomposting. Compared with the treatment without biochar added, 5% of biochar application significantly increased earthworm total biomass (from 177.5 to 202.2 g pot−1), and cumulative burrowing activity (from 47.0% to 52.2% pixel per terrarium). The increased earthworms activity stimulated the vermicomposting process and led to the best quality of compost, which showed the highest total nutrient content (5.38%) and a significantly higher germination percentage of seeds (88%). Although N2O emissions were slightly increased by 5% biochar addition, a non-significant difference was found between the treatment with 5% biochar and the treatment without biochar added. On the contrary, 20% and 25% biochar addition not only lowered N2O emissions, but also significantly decreased the quality of compost. The results suggest that 5% biochar application is an appropriate amount to improve the quality of compost without significant N2O emissions.
As a bioproduct from the thermal decomposition of biomass, biochar has various applications in diversified field. In this study, a bibliometric analysis was conducted to visualize the current research status and trends of biochar research. A total of 5535 documents were collected from the Web of Science Core Collection and subjected to visualization analysis for the biochar field's development in 2021 with CiteSpace software. The visual analysis results demonstrate that the number of publications expanded dramatically in 2021, and the growth trend would continue. China and USA were the most contributing countries in biochar research in terms of the number of publications. Based on the keyword co-occurrence analyses, “Biochar for toxic metal immobilization”, “Biochar-based catalyst for biofuel production”, “Biochar for global climate change mitigation”, “Biochar for salinity and drought stress amelioration”, “Biochar amendment in composting”, and “Biochar as additives in anaerobic digestion” were the main research trends and hotspots in this field in 2021. This indicates that the biochar research was multidisciplinary. Regarding the research hotspots, the employment of biochar as heterogeneous catalysts for biofuel production gained great attention in 2021. On the contrary, bioremediation using functional bacteria immobilized on biochar and biochar-assisted advanced oxidation process were well-studied but with less frequency than other topics in 2021. Furthermore, the future research was proposed for green and sustainable applications of biochar. This review provides a comprehensive overview of the research frontiers, the evolution of research hotspots, and potential future research directions in the biochar field.
Due to the poor surface/interfacial interaction and the large gaps in the size and microstructure between biomass and clay mineral, it was difficult to adjust the structure and performance of biochar/clay mineral composites at the molecular level. Herein, oil shale semi-coke composed of multi-minerals and organic matters was used as a promising precursor to prepare biochar/clay mineral nanocomposites via phosphoric acid-assisted hydrothermal treatment followed by KOH activation for removal of organic pollutants from aqueous solution. The results revealed that the nanocomposites presented well-defined sheet-like morphology, and the carbon species uniformly anchored on the surface of clay minerals. With the changes in the pore structure, surface charge and functional groups after two-step modification, the nanocomposites exhibited much better adsorption property toward organic pollutants than the raw oil shale semi-coke, and the maximum adsorption capacities of methylene blue, methyl violet, tetracycline, and malachite green were 165.30 mg g−1, 159.02 mg g−1, 145.89 mg g−1, and 2137.36 mg g−1, respectively. The adsorption mechanisms involved electrostatic attraction, π–π stacking and hydrogen bonds. After five consecutive adsorption–desorption, there was no obvious decrease in the adsorption capacity of malachite green, exhibiting good cyclic regeneration performance. It is expected to provide a feasible strategy for the preparation of biochar/clay mineral nanocomposites with the excellent adsorption performances for removal of organic pollutants based on full-component resource utilization of oil shale semi-coke.
Modified biochar with higher electron transport and adsorption capabilities could significantly improve the performance of anaerobic ammonia oxidation (anammox). However, there are few related investigations on the reinforcement of anammox through iron-modified Enteromorpha prolifera biochar (IMEPB). In this study, with the addition of the IMEPB in the anammox system, the enhancing process of anammox performance was studied, the improving feasibility of anammox was evaluated, and the reinforcing mechanism of anammox was elucidated. The results showed that the optimal iron−charcoal ratio (Fe:C) and IMEPB dosage were 1:10 and 10 g L−1, respectively. Under the optimal conditions, when the nitrogen loading rate gradually increased to 0.557 (kg m−3 day−1), the nitrogen removal efficiency and nitrogen removal rate of the anammox process supplemented with IMEPB increased by 11%, and the specific anammox activity increased by 23.8%. Compared with the control, the secretion of extracellular polymeric substances (EPS) of anammox bacteria supplemented IMEPB increased by 24.4%, greatly improving the stability of the anammox system. Meanwhile, EPS secretion further promoted the microbial activity of anammox bacteria, achieving a 19% increase in the abundance of Candidatus Brocadia. These findings demonstrate the potential mechanism of IMEPB in improving anammox, provide new insights into recycling E. prolifera, and provide a novel reinforcement strategy for anammox. In the future, adding IMEPB may be a vital measure for the practical application of anammox in coastal areas.
Biochar is a carbon-containing material prepared through thermal treatment of biomass in limited supply of oxygen, and used for an array of applications including waste management, climate change mitigation, soil fertility improvement, bio-energy production, and contaminant remediation. The data related to biochar, its production, and the wide applicability were collected using Web of Science Core Collection Database (on 25/10/2022), while bibliometric network analysis was performed using VOSviewer software to analyse year-wise, author-wise, country-wise, and journal-wise publication trends, construct keyword co-occurrence maps, and identify research areas receiving greater focus. Further, the applications of biochar were reviewed and mechanistic insights were provided. Some of the findings include: > 50% of documents (> 13,000) getting published in the past 3 years, > 90% of documents (> 21,000) being research articles, ~ 50% of publications (> 10,000) being related to environmental sciences, pyrolysis being the most widely used (~ 40% articles) production technique (followed by carbonization, gasification, combustion, and torrefaction), China being the most active country in terms of publications (> 11,000), and biochar being mostly used for removing contaminants (followed by soil improvement, waste management, energy production, and climate change mitigation). Various strengths, weaknesses, opportunities, and threats (SWOT analysis) of biochar production and wide-ranging applicability were identified. Lastly, gaps were identified including the need for performing elaborate life cycle assessments, exploring machine learning and artificial intelligence for upgrading conversion technology and producing application-specific biochar, and investigating mechanistic aspects of soil-biochar interactions and nano-scale transformation of biochar. The study covers a broad spectrum of biochar applicability to identify areas receiving lesser attention, which could guide the future researchers for augmenting biochar research.
The influence of biochar-released dissolved organic matter (BDOM) on the transcription of gene (DEG) in Pseudomonas stutzeri and Shewanella putrefacien during sulfamethoxazole (SMX) and chloramphenicol (CAP) biodegradation under visible light was investigated in this study. The results indicated that BDOM components would be nutrients for bacterial amplification and growth under the culture conditions of xenon lamp irradiation and avoiding light, especially BDOM from low temperatures. Additionally, visible light irradiation would improve the saturated fatty acid by stimulating the cell membrane of the microorganism, thus promoting the biodegradation of antibiotics through altering P. stutzeri and S. putrefaciens reoxidative and catabolism processes and significantly inhabiting the copy number of their genes. Moreover, the upregulated genes and enzymes related to SMX and CAP-metabolic and catabolic processes were enriched, which were involved in the pathways of biodegradation, further improving biodegradation efficiency. In particular, interaction network analysis between the top 100 dominant functional genes from P. stutzeri and S. putrefaciens and the molecular types of BDOM, e.g., CHO, CHON, and CHOS (p < 0.05), indicated that the genes of molecular function showed a high positive or negative correlation with the CHO type of BDOM. The results revealed that the CHO type of BDOM affected the functional genes of molecular function, cellular component, and biological process from P. stutzeri and S. putrefaciens, influencing the biodegradation of SMX and CAP. This study provided an basis for BDOM playing a role in antibiotic removal from the aqueous solution using biochar combined with photobiodegradation.
To contribute to the reduction of methane emissions, using low-cost biochar as adsorbents for capturing and storing methane in oil and gas fields is investigated. This work presents results of methane adsorption on four biochars made from forestry wastes in comparison with the results of three commercial activated carbons. Although the adsorption capacity of the biochars is lower by over 50% than that of the activated carbons, thelow-cost and potential environmental benefits provide the incentive to the investigation. Moreover, it is shown that biochar can store more methane than vessels of compressed gas up to the pressure of 75 bar, suggesting the possibility of avoiding high-pressure gas compression and heavy vessels for cost savings in oil and gas fields. The thermodynamic and kinetic behaviors of the adsorption are studied and implications for the targeted application are discussed.
Hydrothermal carbonization (HTC) technology has increasingly been considered for biomass conversion applications because of its economic and environmental advantages. As an HTC conversion product, hydrochar has been widely used in the agricultural and environmental fields for decades. A CiteSpace-based system analysis was used for conducting a bibliometric study to understand the state of hydrochar environmental application research from 2011 to 2021. Researchers had a basic understanding of hydrochar between 2011 and 2016 when they discovered hydrochar could apply to agricultural and environmental improvement projects. Keyword clustering results of the literature published in 2017–2021 showed that soil quality and plant growth were the major research topics, followed by carbon capture and greenhouse gas emissions, organic pollutant removal, and heavy metal adsorption and its bioavailability. This review also pointed out the challenge and perspective for hydrochar research and application, namely: (1) the environmental effects of hydrochar on soils need to be clarified in terms of the scope and conditions; (2) the influence of soil microorganisms needs to be investigated to illustrate the impact of hydrochar on greenhouse gas emissions; (3) combined heavy metal and organic contaminant sorption experiments for hydrochar need to be conducted for large-scale applications; (4) more research needs to be conducted to reveal the economic benefits of hydrochar and the coupling of hydrochar with anaerobic digestion technology. This review suggested that it would be valuable to create a database that contains detailed information on how hydrochar got from different sources, and different preparation conditions can be applied in the environmental field.
The nanoscale biochar (N-BC) generated during the production and weathering of bulk biochar has caused significant concerns for its cotransport with contaminants spreading the contamination. In this study, the cotransport behaviors of N-BC with Cd2+ under variable solution chemistry were investigated for the first time, which can pose environmental contamination risks but have received little attention. The column experiment results showed that increasing ionic strength (IS) or decreasing pH retarded the transport of N-BC but promoted the transport of Cd2+ in their individual transport. In cotransport scenarios, Cd2+ facilitated the deposition of N-BC on the quartz sand with increasing IS or decreasing pH by providing additional sorption sites and led to the ripening of N-BC via cation bridging. N-BC retarded the transport of Cd2+ under all conditions. However, lower pH and higher IS could facilitate the release of Cd2+ from the immobile N-BC. The cotransport modeling results demonstrated that the Cd2+ adsorption on and desorption from the immobile N-BC controlled the retention and release of Cd2+ under variable pH and IS, while the influence of mobile N-BC on Cd2+ transport was minor. This study provided new insight for evaluating the potential contamination-spreading risks and suggested that rational use of biochar with great caution is necessary.
To improve the phosphorus (P) recovery efficiency from livestock wastewater, a novel MgO doped mildewed corn biochar with thermal pre-puffing treatment (Mg-PBC) and without pre-puffing (Mg-BC) was synthesized and tested. The thermal-puffing pretreatment improved the effectiveness of metal soaking and MgO dispersion. P recovery time with Mg-PBC (7 h) was significantly shorter than that with Mg-BC (12 h). Moreover, Mg-PBC showed significantly higher P recovery capacity (241 mg g−1) than Mg-BC (96.6 mg g−1). P recovery capacity of the Mg-PBC fitted to the Thomas model was 90.7 mg g−1, which was 4 times higher than that of Mg-BC (22.9 mg g−1) under column test conditions. The mechanisms involved in P recovery included precipitation, surface complexation, and electrostatic interaction. After adsorption, both Mg-BC and Mg-PBC showed relatively low regeneration abilities. The P loaded Mg-BC (Mg-BC-P) and Mg-PBC (Mg-PBC-P), the later particularly, obviously increased the available P content and promoted plant growth. The release of P increased with time in the Mg-PBC-P treated soil, while it decreased with time in the P fertilizer treated soil. A cost–benefit analysis revealed that thermal-puffing pretreatment greatly increased the profit of MgO doped biochar from −0.66 to 5.90 US$ kg−1. These findings highlight that biomass pre-puffing is a feasible treatment to produce MgO modified biochar and to recover P from livestock wastewater, and that the Mg-PBC-P can be used as a slow-release P fertilizer.
The dynamic effect of biochar amendment in contaminated soil on the bioavailability of polycyclic aromatic hydrocarbons (PAHs) and microbial communities and how it comprehensively affects PAH biodegradation remain unclear. This study investigated the effects of wheat straw-derived biochars obtained at 300 and 500 °C at different amendment levels (0.03% and 0.3%) on the mineralization kinetics of phenanthrene with different initial concentrations (2 and 20 mg kg−1) in soil by indigenous microorganisms. The results revealed that the addition of biochar inhibited both the rates and extents of mineralization in low-concentration phenanthrene-contaminated soil (PLS) by 38.9–78.3% and 23.9–53.6%, respectively. This was because biochar amendment in the PLS greatly reduced the bioavailable fraction of phenanthrene for degradation owing to its strong sorption and also decreased that to specific degrading bacterial genera, which hindered their growth and reduced their abundances by 1.37–36.6%. However, biochar addition into the soil contaminated with high concentrations of phenanthrene (PHS) resulted in its effective mineralization and enhanced mineralization rates and extents at high amendment levels by 32.4–86.7% and 32.0–44.7%, respectively. This was because biochar amendment in the PHS significantly promoted the abundances of the total bacterial communities (29.9–80.4%) and potential degrading genera (1.89–25.9%) by providing nutrients and stimulated the specific PAH-degradative nidA gene abundance by 1–2 times. These findings will guide the use of biochar to remediate soils with different PAH pollution levels based on the two roles that they play (i.e., immobilizing PAHs or facilitating PAH degradation).
Crystal morphology of metal oxides in engineered metal-biochar composites governs the removal of phosphorus (P) from aqueous solutions. Up to our best knowledge, preparation of bio-assembled MgO-coated biochar and its application for the removal of P from solutions and kitchen waste fermentation liquids have not yet been studied. Therefore, in this study, a needle-like MgO particle coated tea waste biochar composite (MTC) was prepared through a novel biological assembly and template elimination process. The produced MTC was used as an adsorbent for removing P from a synthetic solution and real kitchen waste fermentation liquid. The maximum P sorption capacities of the MTC, deduced from the Langmuir model, were 58.80 mg g−1 from the solution at pH 7 and 192.8 mg g−1 from the fermentation liquid at pH 9. The increase of ionic strength (0–0.1 mol L−1 NaNO3) reduced P removal efficiency from 98.53% to 93.01% in the synthetic solution but had no significant impact on P removal from the fermentation liquid. Precipitation of MgHPO4 and Mg(H2PO4)2 (76.5%), ligand exchange (18.0%), and electrostatic attraction (5.5%) were the potential mechanisms for P sorption from the synthetic solution, while struvite formation (57.6%) and ligand exchange (42.2%) governed the sorption of P from the kitchen waste fermentation liquid. Compared to previously reported MgO-biochar composites, MTC had a lower P sorption capacity in phosphate solution but a higher P sorption capacity in fermentation liquid. Therefore, the studied MTC could be used as an effective candidate for the removal of P from aqueous environments, and especially from the fermentation liquids. In the future, it will be necessary to systematically compare the performance of metal-biochar composites with different metal oxide crystal morphology for P removal from different types of wastewater.
Biochar has various agricultural applications, including the promising use as a carrier for beneficial microorganisms. However, most recent research has demonstrated the possible attachment or immobilization of a single bacterial species onto biochar rather than a consortium of microbes for biotechnological applications. Thus, an assessment on the potential of oil palm kernel shell (OPKS) biochar as a biofilm-producing Bacillus consortium carrier through optimization study on the operating and environmental factors influencing the biofilm adhesion was conducted using response surface methodology (RSM) and the subsequent soil stability and storage potential of the formulation. The highest Bacillus population was observed at temperature 33 °C, agitation speed of 135 rpm, at a neutral pH of 7.5 with 10% (w/w) of sago starch as the co-carbon source. The adhesion of Bacillus on OPKS biochar following the optimized conditions fitted pseudo-second order (PSO) of kinetic modelling (R2 = 0.998). The optimized formulation was subjected to storage in different temperatures and in vitro soil incubation which revealed that the Bacillus biofilm-adhered OPKS biochar may be stored up to 4 months with minimum range of live Bacillus viability reaching 107 CFU g-1 of biochar which is within the minimum range of acceptable biofertilizer viability (106 CFU mL-1). Formulation that is viable in room storage can be easily incorporated into current agricultural distribution networks that do not have refrigeration. This work highlighted the physicochemical and soil stability qualities of optimized Bacillus consortium adhesion on biochar for agricultural usage.
Article Highlights
| • | Integration of biochar with Bacillus consortium biofilms served as novel organic fertilizer in agriculture. |
| • | The biochar-integrated Bacillus biofilms persisted in challenging temperature and environment. |
| • | Biochar-integrated Bacillus biofilm fertilizer fostered the attainment of the Sustainable Development Goals |
Excess phosphorus (P) in water can lead to eutrophication and upset ecological balance. In this study, biochar with ultrathin two-dimensional nanosheets from the natural mesocarp of shaddock was chosen as the carrier. The highly dispersed and small particle size of La(OH)3 on the surface of the nanosheets (MSBL3) was successfully achieved using chemical impregnation for the adsorption of P in aqueous solution, and the maximum adsorption capacity was 260.0 mg P g−1 [La]. The differences in surface crystallization of La(OH)3 on biochar at different La loadings were analyzed using the high-precision characterization methods. After six adsorption–desorption cycles, MSBL3 retained 76.7% of its initial performance in terms of the P adsorption capacity. The preparation of 1 g of MSBL3 costs about RMB 1, and it could reduce the P concentration in 2.6 ton of Laoyu River water to below the eutrophication threshold; and the inhibitory effect of MSBL3 on the eutrophication of water bodies was confirmed by the growth state of water hyacinth. Furthermore, 0.1 M MSBL3 could inhibit Escherichia coli and Staphylococcus aureus up to 98.7% and 85.0%, respectively, which indicates that MSBL3 can be used to recover P from water and also to improve water quality. In addition, the growth of the maize seedlings verified that the P-absorbed MSBL3 waste is a good soil fertilizer and can solve the problem of post-treatment of the adsorbent. In conclusion, MSBL3 prepared in this study is a promising P sorbent for application.
Torrefaction operation is an essential pathway for solid biofuel upgrading, and good hydrophobicity of torrefied biochar is conducive to its storage. Herein, a two-stage treatment of torrefaction followed by modification by hexadecyltrimethoxysilane was adopted to improve the moisture resistance performance of biochar. This two-stage treatment process led to a longer torrefied microalgal biochar preservation time (60–200% improved) and great superhydrophobicity and superlipophilicity. Therefore, the modified microalgal biochar could significantly adsorb leaking oil for environmental remediation and further improve the calorific value of the biochar. The obtained results indicated that the oil adsorption capacity of modified microalgal biochar was correlated to torrefaction temperature and oil species. Specifically, the oil adsorption capacity was enhanced up to 70–80% from the modification process when comparing to raw microalga. Increasing the torrefaction temperature enhanced the adsorption quantity of the modified microalgal biochar. By adsorbing the oil, the calorific value of oilchar, namely, biochar with adsorbed oil, could be higher than 40 MJ kg− 1. Furthermore, the pyrolysis and combustion characteristics suggested that biochar stability gradually rose as the torrefaction temperature increased. By comprehensively analyzing and comparing the fuel performance of the modified microalgal biochar with previous literature, the obtained modified microalgal biochar possessed better fuel properties and environmental sustainability.
| • | Annual Low-rate biochar strategy showed higher rice yields than High Single in the 6th year. |
| • | Higher total carbon, pH, and Ca2+ led to higher rice yields in Annual Low than High Single. |
| • | Higher aromatic carbon loss in High Single contributed to lower inert organic carbon. |
The literature has shown that biochar can serve as potential amendment to achieve sustainable agriculture and environment. The accessibility and availability of cheap feedstock are considered as important constraint factors for the widespread application of biochar in agriculture. Marginal lands are widely distributed globally, several times larger than arable land, and hold little value for food production due to poor soil conditions. However, these lands are suitable for growing plants, which can be used as feedstock for biochar production. The salt-affected lands, as one of the main marginal lands, are particularly suitable for cultivating diverse varieties of halophytes that can be pyrolyzed into biochar, bio-gas, and bio-oil. The halophyte-derived biochar is useful to produce a desirable acid soil conditioner due to its high ash and rich bases, and improves soil characteristics under extreme saline conditions. Additionally, syngas and bio-oil hold potential benefits as fuels and industrial raw materials. This study introduces an innovative management technique for marginal lands such as salt-affected land, which can provide all-round benefits in food production, land management, vegetation coverage, carbon sequestration, and climate change mitigation.
Long-term consumption of tea with high fluoride (F) content has a potential threat to human health. The application of different amounts of biochar to reduce F accumulation in tea leaves has been little studied. In this study, a pot experiment was conducted to investigate the effect of biochar amounts (0, 0.5%, 2.5%, 5.0%, 8.0%, and 10.0%, w/w) on tea F content during the tea plant growth. Changes in tea quality, soil F fraction, and soil properties caused by biochar and the relationship with tea F accumulation were also considered. The results showed that the application of biochar amendment significantly reduced water-soluble F contents in tea leaves compared to CK (without biochar), especially in the 8.0% treatment (72.55%). Overall, biochar contributed to improving tea polyphenols and caffeine, but had no significant impact on free amino acids and water leachate. Compared with CK, 5.0–10.0% biochar significantly increased soil water-soluble F content due to the substitution of F− with OH− under high pH. Additionally, biochar applied to tea garden soil was effective in decreasing the soil exchangeable aluminum (Ex-Al) content (46.37–91.90%) and increasing the soil exchangeable calcium (Ca2+) content (12.02–129.74%) compared to CK, and correlation analysis showed that this may help reduce F enrichment of tea leaves. In general, the application of 5.0–8.0% biochar can be suggested as an optimal application dose to decrease tea F contents while simultaneously improving tea quality.
This work demonstrated that Enteromorpha biochar with introduced iron (SFB900-3) could activate peroxymonosulfate (PMS) efficiently for NTP remediation. It removed 83.9%–95.1% of NTP in 60 min under a wide pH range from 3.15 to 8.95. Density functional theory (DFT) calculations revealed the synergistic relationship between internal Fe single atoms and introduced Fe compounds—Fe3C. The adsorption capacity of SFB900-3 for persulfate improved from −0.953 eV to −4.214 eV, and the Bader charge analysis showed that Fe atoms as active sites (0.658 e) enhanced the adsorption capacity more than carbon (0.050 e). Moreover, the energy barrier for PMS dissociation reduced from 0.072 eV to −5.372 eV due to the longer length of O–O bond under the synergistic effect of Fe single atom and Fe3C which increased from 1.467 Å to 3.890 Å. The quenching experiment confirmed that 1O2 was the main active substance in NTP degradation and its contribution rate was 88.2%, which was further verified by EPR detection. The effect factor experiments proved that the SFB900-3/PMS system had stable and efficient activity for NTP removal, which remained at 73.6% removal rate after three rounds of tests. This work provided novel guidance for constructing efficient and stable biochar-based materials for organic pollutant remediation.
Microbially induced calcite precipitation (MICP) technique utilizes ureolytic bacteria to decompose urea and generate carbonate ions for metal combination. MICP can remediate heavy metal (e.g., Cd) contaminated soils while maintaining or even improving soil functions, but its efficiency in agricultural soil practical application still needs to be enhanced. Here, we constructed a biochar-bacteria (2B) partnership in which biochar provides high nutrition and diverse sorption sites. Using the 2B system, Cd immobilization effectiveness and the underlying mechanism were examined along with the soil properties and soil functions. Results showed that compared to the single biochar and ureolytic bacteria systems, soil Cd mobility was reduced by 23.6% and 45.8% through co-precipitating with CaCO3 as otavite (CdCO3) in the 2B system, whereas soil fertility, bacterial diversity, and richness increased by 11.7–90.2%, 5.4–16.1%, and 6.8–54.7%, respectively. Moreover, the abundances of Proteobacteria and Firmicutes were enhanced in the 2B system. Notably, Sporosarcina and Bacillus (Firmicutes genus) that carry the ureC gene were boosted in the system, further implicating the microbiological mechanism in reducing Cd migration and its bioavailability in soil. Overall, the constructed 2B system was efficient in soil Cd immobilization by strengthening the ureolytic bacteria growth and their nutrient supply in the bacteria-rich soil ecosystem.
Metal-free porous biochars are popularly utilized as catalysts for peroxydisulfate (PDS) activation. The enhancement effect of PDS activation of porous biochars fabricated by employing both hard template and alkali metal activating agent has not been explored completely. In addition, the role of the inherent carbon defect in PDS activation has not been clearly elucidated. Hence, a series of carbonaceous catalysts were fabricated using a sole template (KCl), a sole activating agent (Na2S2O3) or a combination of template and activating agent (KCl/Na2S2O3, KCl/KHCO3, KCl/NaHCO3, and KCl/Na2C2O4), to systematically investigate the effect of specific surface area (SSA) and intrinsic defect of porous biochar on its PDS activation ability. The biochar synthesized by KCl and Na2S2O3 (SK-C) exhibited the optimum degradation performance. The SK-C was found to possess an interconnected hollow cage with three-dimensional mesh structure showing the largest surface area, pore volume and C-sp3 edge defect content among all the catalysts, which explained its paramount catalytic ability. The SSA and C-sp3 content together can determine the catalytic performance in a quantitative relationship. The single electron transfer pathway from SDZ to inner-sphere bound SK-C/PDS* was the protagonist of pollutant oxidation. The degradation intermediates were detected and recognized and their toxicities were evaluated. This study for the first time comprehensively identified the synergistic effect between the SSA and inherent defects on improving the catalytic performance of biochar for PDS activation to removal contaminants.
• FeN3-doped biochar was first proposed for GHGs mitigation in paddy fields.
• FeN3-doped biochar exhibited excellent GHGs adsorption ability.
• FeN3-doped biochar improved physico-chemical adsorption ability for GHGs.
Due to large specific surface area, abundant functional groups and low cost, biochar is widely used for pollutant removal. The adsorption performance of biochar is related to biochar synthesis and adsorption parameters. But the influence factor is numerous, the traditional experimental enumeration is powerless. In recent years, machine learning has been gradually employed for biochar, but there is no comprehensive review on the whole process regulation of biochar adsorbents, covering synthesis optimization and adsorption modeling. This review article systematically summarized the application of machine learning in biochar adsorbents from the perspective of all-round regulation for the first time, including the synthesis optimization and adsorption modeling of biochar adsorbents. Firstly, the overview of machine learning was introduced. Then, the latest advances of machine learning in biochar synthesis for pollutant removal were summarized, including prediction of biochar yield and physicochemical properties, optimal synthetic conditions and economic cost. And the application of machine learning in pollutant adsorption by biochar was reviewed, covering prediction of adsorption efficiency, optimization of experimental conditions and revelation of adsorption mechanism. General guidelines for the application of machine learning in whole-process optimization of biochar from synthesis to adsorption were presented. Finally, the existing problems and future perspectives of machine learning for biochar adsorbents were put forward. We hope that this review can promote the integration of machine learning and biochar, and thus light up the industrialization of biochar.
Biochar application and conservation tillage are significant for long-term organic carbon (OC) sequestration in soil and enhancing crop yields, however, their effects on native soil organic carbon (native SOC) without biochar carbon sequestration in situ remain largely unknown. Here, an 11-year field experiment was carried out to examine different biochar application rates (0, 30, 60, and 90 Mg ha−1) on native SOC pools (native labile SOC pool I and II, and native recalcitrant SOC) and microbial activities in calcareous soil across an entire winter wheat–maize rotation. The proportions of C3 and C4-derived native SOC mineralization were quantified using soil basal respiration (SBR) combined with 13C natural isotope abundance measurements. The results showed that 39–51% of the biochar remained in the top 30 cm after 11 years. Biochar application rates significantly increased native SOC and native recalcitrant SOC contents but decreased the proportion of native labile SOC [native labile SOC pool I and II, dissolved organic carbon (DOC), and microbial biomass carbon (MBC)]. Biochar application tended to increase the indicators of microbial activities associated with SOC degradation, such as SBR, fluorescein diacetate hydrolysis activity, and metabolic quotient (qCO2). Meanwhile, higher biochar application rates (B60 and B90) significantly increased the C4-derived CO2 proportion of the SBR and enhanced C4-derived native SOC mineralization. The effect of the biochar application rate on the content and proportion of native SOC fractions occurred in the 0–15 cm layer, however, there were no significant differences at 15–30 cm. Soil depth also significantly increased native labile SOC pool I and II contents and decreased qCO2. In conclusion, the biochar application rate significantly increased native SOC accumulation in calcareous soil by enhancing the proportion of native recalcitrant SOC, and biochar application and soil depth collectively influenced the seasonal turnover of native SOC fractions, which has important implications for long-term agricultural soil organic carbon sequestration.
In this study, the synchronous magnetized carbonization method was utilized for preparing photocatalysis ZnO-Fe@SC heterostructure, which exhibited degradation efficiency 99.14% (60 min) for malachite green (200 mg/L) and could still maintain good performance after 5 cycles. The prepared ZnO-Fe@SC was analyzed using UV–Vis DRS, PL, SEM, TEM, BET, FTIR, XPS and VSM, and LC–MS for degradation products. The results indicate that photocatalyst has favorable magnetic properties, chemical stability and low charge carriers (e−/h+) recombination rate. The modification of bimetals enables the composite photocatalyst to enhance the intensity of photogenerated electron transition. Moreover, quenching experiment revealed that the photo-generated holes (h+) and superoxide radicals (·O2−) were the dominant active species during the photocatalytic process, which degraded malachite green into small molecules by demethylation, deamination, ring-opening reactions as deducted from LC–MS analysis. ZnO-Fe@SC was prepared using a green, safe, low cost and operable synthetic method, which has a broad market potential in the field of environmental remediation.
Root-knot nematodes (RKNs) are obligate endoparasites that feed on their host plants to complete its life cycle, representing a major threat to agriculture and economy worldwide. The development of new management strategies becomes essential as effective chemical nematicides are progressively being restricted. Hence, we analysed grape pomace-derived biochars, pyrolysed at 350 °C (BC350) and 700 °C (BC700), focusing on their potential for RKN control. The thermal treatment of grape pomace caused an increase in the concentration of carbon and plant macro- and micronutrients, which were largely present in a water-soluble form. Synchrotron radiation-based Fourier transform infrared microspectroscopy data showed a general loss of carboxylic functional groups during pyrolysis, partially contributing to the alkalinisation of both biochars, mostly in BC700. Scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy analysis revealed a highly porous structure filled with different crystals composed of elements such as K, Ca, Mg, P, Si or Al, which could be a suitable environment for the growth of microorganisms. Biochar-derived aqueous extracts showed phytotoxicity to tomato seedlings at high concentrations, and disappeared upon dilution, but no toxic effect was observed on the nematode’s infective stage. However, the infective and reproductive traits of a Meloidogyne javanica population in tomato were significantly reduced (i.e. egg masses and eggs per plant) in washed-biochar-treated soil in pots (0.75%; BC350W). Therefore, the large amount of grape waste generated after wine production can be transformed into a valuable product such as biochar, effective for RKNs control, thus reducing the waste management problem and contributing to a circular economy.
The structural reconstruction mechanism of lignin and cellulose-derived biochars during direct graphitization under ultra-high temperatures was intensively investigated. It was demonstrated that cellulose-derived char was almost composed of carbon microcrystallites, whereas lignin-derived char reserved some of its skeleton structures, and such structural difference played a vital role in the morphology of formed graphitic layers. The results illustrated that the graphitized lignin-derived sample under 2800 ℃ had graphitic degree of 89.53%, interlayer spacing of 0.3363 nm and electronic conductivity of 104.6 S cm−1, while cellulose-derived sample had graphitic degree of 76.74%, layer distance of 0.3374 nm, and electronic conductivity of only 48.8 S cm−1. Combined with the results of structural analysis of the chars derived from lignin and cellulose, it was inferred that the stable and aromatic ring containing skeleton structure in lignin was beneficial to the ring-enlarging reconstruction and the formation of large areas of continuous graphitic layers during graphitizing process, leading to high electronic conductivity. Meanwhile, the interwoven microcrystallites in cellulose-derived char strongly restricted the expanding of continuous lamellar graphitic areas even at such ultra-high temperature, causing the formation of turbostratic structure with numerous structural defects as well, and finally resulting in relatively lower electronic conductivity. This work is expected to provide theoretical guidance for preparing high-performance functional carbon materials from lignocellulosic biomass.
Carbon-based solid acids have been successfully employed as acidic catalysts for pollutant mitigation in wastewater. To fully tap the potentials of commercially viable carbons for the preparation of solid acids and enhance their catalytic performances is a challenging problem. In this work, three commercialized carbons including biochar, activated carbon and graphite were preprocessed (ball-milling, Hummer exfoliation, HNO3 soaking, and microwave heating in HNO3, etc.), sulfonated, and evaluated as solid-acid catalysts for tylosin mitigation. Graphite-originated solid acid performed the best through a balling-milling preprocess, while biochar-originated solid acids behaved well under all preprocessing treatments, in which 40 mg L−1 of tylosin was mitigated within 8 min by 1 g L−1 of biochar-originated solid acids. The biochar solid acid through the ball-milling preprocess presented high total acidity and large amounts of –SO3H groups, due to dramatically increased surface area and the rise of activation groups (hydroxyl, alkyl and alkoxy groups, etc.) facilitating electrophilic reaction. In addition, decreased particle size and aromaticity and increased structural defects also contributed. Theoretical calculation of average local ionization energy (ALIE) of condensed aromatic model molecules with substituted activation groups confirmed the promoting effects on sulfonation from strong to weak were 8.40–9.06 eV. These findings have deepened the knowledge in tuning carbon surface chemistry for better sulfonation, thus strengthening catalytic degradation of tylosin. The value of this study is in pulling a clear thread for maneuvering solid-acid catalysts using carbons, which holds a novel promise for rationally functionalizing biochar-based catalysts for the remediation of macrolide antibiotics in polluted water.
Herein, a biochar-based composite (Ti3C2Tx@biochar-PDA/PEI) was constructed by decorating Ti3C2Tx and polydopamine on coconut shell biochar via electrostatic self-assembly method. Different characterization techniques were applied to explore the structure, morphology and composition of the sorbents. It was found that the higher porosity and diverse functional groups were conducive for Ti3C2Tx@biochar-PDA/PEI to capture radionuclides, and the water environmental conditions made a great contribution to the adsorption process. The process of removing U(VI)/Cs(I) well complied with the Langmuir isotherm and Pseudo-second-order equations, which indicated that the single layer chemical adsorption occurred on the solid liquid interface. Meanwhile, this produced composite exhibited superior removal performance under complex co-existing ion environment, and the maximum adsorption amounts of U(VI) and Cs(I) reached up to 239.7 and 40.3 mg g−1. Impressively, this adsorbent still exhibited good adsorption performance after three cycles of regeneration. The spectral analysis and DFT calculation demonstrated that adsorption of U(VI) might be a chemical process, while the adsorption of Cs(I) should be ion exchange or electrostatic attraction. This study demonstrated the potential application of Ti3C2Tx@biochar-PDA/PEI as an effective remediation strategy for radioactive wastewater cleanup.
Grasslands (natural, semi-natural and improved) occupy approximately one-third of the terrestrial biosphere and are key for global ecosystem service provision, storing up to 30% of soil organic carbon (SOC). To date, most research on soil carbon (C) sequestration has focused on croplands where the levels of native soil organic matter (SOM) are typically low and significant potential exists to replenish SOM stocks. However, with the renewed push to achieve “net zero” C emissions by 2050, grasslands may offer an additional C store, utilising tools such as biochar. Here, we critically evaluate the potential for biochar as a technology for increasing grassland C stocks, identifying a number of practical, economic, social and legislative challenges that need to be addressed before the widescale adoption of biochar may be achieved. We critically assess the current knowledge within the field of grassland biochar research in the context of ecosystem service provision and provide opinions on the applicability of biochar as an amendment to different types of grassland (improved, semi-improved and unimproved) and the potential effect on ecosystem provision using a range of application techniques in the topsoil and subsoil. We concluded that the key question remains, is it possible for managed grasslands to store more C, without causing a loss in additional ecosystem services? To address this question future research must take a more multidisciplinary and holistic approach when evaluating the potential role of biochar at sequestering C in grasslands to mitigate climate change.
In the past few decades, numerous studies have been conducted to promote the use of biochar as a soil amendment and most recently, for compacted geo-engineered soils. In general, the definite trends of biochar effects on water retention and fertility of soils have been confirmed. However, the biochar effects on hydraulic conductivity, particularly unsaturated hydraulic conductivity of soil-biochar mix remain unclear, making it difficult to understand water seepage in both agricultural and geo-engineered infrastructures in semi-arid regions. This study examines the unsaturated hydraulic conductivity function derived based on the measurements of soil water characteristic curves of soil with biochar contents of 0%, 5% and 10%. A new parameter “biochar conductivity factor (BCF)” is proposed to evaluate the inconsistency in reported biochar effects on soil hydraulic conductivity and to interpret it from various mechanisms (inter- and intra- pore space filling, cracking, aggregation, bio-film formation and piping/internal erosion). The impact of biochar content on unsaturated hydraulic conductivity appears to reduce as the soil becomes drier with minimal effect in residual zone. Qualitative comparison of near-saturated hydraulic conductivity with test results in the literature showed that the BCF is generally higher for smaller ratio of sand to fine content (clay and silt). Moreover, the particle size of biochar may have significant influence on soil permeability. Future scope of research has been highlighted with respect to biochar production for its applications in agriculture and geo-environmental engineering. Long term effects such as root decay and growth, aggregation and nutrient supply need to be considered.
One of the challenges of promoting accelerated carbonation curing (ACC) of concrete as a carbon sequestration strategy is ensuring that carbonation will not deteriorate mechanical strength. This study examined the mechanical strength, water sorptivity and carbonation efficiency of ten types of mortar containing dry or pre-soaked biochar subjected to internal and/or external carbonation. The results obtained enabled a typology of ACC to be proposed, in which the carbon dioxide absorption of mortar containing various types of CO2-dosed biochar ranged between 0.022% and 0.068% per unit dosage hour. In particular, the mortar containing dry biochar dosed with carbon dioxide was the top candidate for concurrently increasing both compressive strength (54.9 MPa) and carbon dioxide absorption (0.055% per unit dosage hour). Mortar containing pre-soaked biochar dosed with carbon dioxide was identified as a strategy that achieved the highest carbonation efficiency (0.068% per unit dosage hour), but it also reduced compressive strength (45.1 MPa). Collectively, the proposed typology offers a useful overview of the different ways by which biochar can be used to tune ACC in mortar, according to any technical constraints and/or intended functions of the carbonated concrete components.
Whether biochar produced as a by-product of energy generation from the papermill industry, and often disposed in landfills, can be gainfully applied to commercial croplands has not been investigated. The objective of this study was to investigate the physical and hydraulic properties of soils in commercial cotton fields managed as no-till systems following repeated applications of biochar generated as a waste of a papermill plant. Undisturbed cores and disturbed soil samples were collected from 0–5 and 5–10 cm layers from five commercial no-till fields in Mississippi, USA that received 6.7 Mg ha−1 year−1 biochar for 0, 2, 3, 5 or 10 years. A number of physical, hydraulic, and chemical properties of these samples were measured in the lab. The results showed that biochar reduced the degree of soil compactness and increased soil aggregation and structural stability index. The findings were particularly apparent for the 10 years of consecutive application, which increased soil aggregate stability by up to 67%, reduced bulk density from 1.40 to 1.26 g cm−3, and reduced degree of compactness from 73.2% to 62.8%. Biochar increased soil porosity but much of this increase (55%) occurred for small pores (< 0.5 μm) with little effect on storage pores (0.5–50 μm) or transmission pores (> 50 μm). Consequently, biochar increased soil field capacity by up to 26%, but PAW increased by only 17%. Biochar significantly increased soil physical quality index score in the 0–5 cm layer from 0.16 to 0.26 and the increase was positively correlated with the number of years of application. The results suggest biochar generated as a byproduct of papermill could be land-applied in real-world crop production systems to improve soil health as an alternative to disposal in landfills.
Carbon materials (e.g., pyrogenic carbon (PyC)) are widely used in agricultural soils and can participate in various biogeochemical processes, including iron (Fe) cycling. In soils, Fe(II) species have been proposed as the main active contributor to produce reactive oxygen species (ROS), which are involved in various biogeochemical processes. However, the effects of PyC on the transformation of different Fe species in soils and the associated production of ROS are rarely investigated. This study examined the influence of PyC (pyrolyzed at 300–700 °C) on Fe(II)/Fe(III) cycling and hydroxyl radical (·OH) production during redox fluctuations of paddy soils. Results showed that the reduction of Fe(III) in soils was facilitated by PyC during anoxic incubation, which was ascribed to the increased abundance of dissimilatory Fe(III)-reducing microorganisms (biotic reduction) and the electron exchange capacity of PyC (abiotic reduction). During oxygenation, PyC and higher soil pH promoted the oxidation of active Fe(II) species (e.g., exchangeable and low-crystalline Fe(II)), which consequently induced higher yield of ·OH and further led to degradation of imidacloprid and inactivation of soil microorganisms. Our results demonstrated that PyC accelerated Fe(II)/Fe(III) cycling and ·OH production during redox fluctuations of paddy soils (especially those with low content of soil organic carbon), providing a new insight for remediation strategies in agricultural fields contaminated with organic pollutants.
Biochar and biochar-based materials have been studied extensively in multidisciplinary areas because of their outstanding physicochemical properties. In this review article, biochar and biochar-based materials in the removal of environmental pollutants, hydrogen generation and carbon dioxide capture were summarized and compared. The interaction mechanisms were discussed from the experimental results and characterization analysis. The high porous structures, active surface sites, (co)doping of single metals/nonmetals, and incorporation of metal oxides or other materials improved the high activity of biochar-based materials in their applications. However, there are still some challenges such as: (1) the fact that H2 generation with high selectivity or the produced syngas to meet the real application requirement in industrial is the main challenge in H2 production; (2) the fact that the selective capture of CO2 with high stability, high adsorption capacity and recyclability at low-cost should be considered and focused on; (3) the sorption-(photo)degradation of the organic chemicals; and (4) the fact that the sorption-reduction-extraction/solidification of metals/radionuclides are efficient methods for the elimination of environmental pollutants. In the end, the perspectives, challenges and possible techniques for biochar-based materials’ real application in future were described.
The development of sustainable and functional biocomposites remains a robust research and industrial claim. Herein, the efficiency of using eco-friendly biochar as reinforcement in Additive Manufacturing (AM) was investigated. Two AM technologies were applied, i.e., vat photopolymerization (VPP) and material extrusion (MEX). A standard-grade resin in VPP and the also eco-friendly biodegradable Polylactic Acid (PLA) in the MEX process were selected as polymeric matrices. Biochar was prepared in the study from olive trees. Composites were developed for both 3D printing processes at different biochar loadings. Samples were 3D-printed and mechanically tested after international test standards. Thermogravimetric Analysis and Raman revealed the thermal and structural characteristics of the composites. Morphological and fractographic features were derived, among others, with Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). Biochar was proven to be sufficient reinforcement agent, especially in the filament MEX process, reaching more than 20% improvement at 4 wt.% loading in tensile strength compared to the pure PLA control samples. In the VPP process, results were not as satisfactory, still, a 5% improvement was achieved in the flexural strength with 0.5 wt.% biochar loading. The findings prove the strong potential of biochar-based composites in AM applications, too.
Advanced treated municipal wastewater is an important alternative water source for agricultural irrigation. However, the possible persistence of chemical and microbiological contaminants in these waters raise potential safety concerns with regard to reusing treated wastewater for food crop irrigation. Two low-cost and environmentally-friendly filter media, biochar (BC) and zero-valent iron (ZVI), have attracted great interest in terms of treating reused water. Here, we evaluated the efficacy of BC-, nanosilver-amended biochar- (Ag-BC) and ZVI-sand filters, in reducing contaminants of emerging concern (CECs), Escherichia coli (E. coli) and total bacterial diversity from wastewater effluent. Six experiments were conducted with control quartz sand and sand columns containing BC, Ag-BC, ZVI, BC with ZVI, or Ag-BC with ZVI. After filtration, Ag-BC, ZVI, BC with ZVI and Ag-BC with ZVI demonstrated more than 90% (> 1 log) removal of E. coli from wastewater samples, while BC, Ag-BC, BC with ZVI and Ag-BC with ZVI also demonstrated efficient removal of tested CECs. Lower bacterial diversity was also observed after filtration; however, differences were marginally significant. In addition, significantly (p < 0.05) higher bacterial diversity was observed in wastewater samples collected during warmer versus colder months. Leaching of silver ions occurred from Ag-BC columns; however, this was prevented through the addition of ZVI. In conclusion, our data suggest that the BC with ZVI and Ag-BC with ZVI sand filters, which demonstrated more than 99% removal of both CECs and E. coli without silver ion release, may be effective, low-cost options for decentralized treatment of reused wastewater.
Immobilized microbial technology has been widely used in wastewater treatment, but it has been used less frequently for soil remediation, particularly in sites that are co-contaminated with organic compounds and heavy metals. In addition, there is limited knowledge on the efficiency of remediation and microbial preferences to colonize the immobilized carriers. In this study, biochar immobilized with Sphingobium abikonense was introduced to remediate soils that were co-contaminated with phenanthrene (PHE) and copper (Cu), and the mechanisms of microbial assemblage were investigated. The immobilized microbial biochar maintained a degradation rate of more than 96% in both the first (0–6 d) and second (6–12 d) contamination periods. The addition of biochar increased the proportion of Cu bound to organic matter, and Fe–Mn oxide bound Cu in the soil. In addition, both Cu and PHE could be adsorbed into biochar pellets in the presence or absence of immobilized S. abikonense. The presence of biochar significantly increased the abundance of bacteria, such as Luteibacter, Bordetella and Dyella, that could degrade organic matter and tolerate heavy metals. Notably, the biochar could specifically select host microbes from the soil for colonization, while the presence of S. abikonense affected this preference. The autonomous selection facilitates the degradation of PHE and/or the immobilization of Cu in the soil. These results provide a green approach to efficiently and sustainably remediate soil co-contaminated with PHE and Cu and highlight the importance of microbial preference colonized in immobilized carriers.
| 1. | A new biochar fertilizer was developed by incorporating hydrotalcite and starch. |
| 2. | HS-BCF exhibited better water-retention and slow-release performance than BCF. |
| 3. | The nutrient release of HS-BCF was diffusion and relaxation-controlled mechanism. |
| 4. | The enhanced P durability of HS-BCF was partially due to the binding of hydrotalcite. |
Nonradical oxidation based on peroxydisulfate (PDS) activation has attracted increasing attention for selective degradation of organic pollutants. Herein, topological defects were introduced into biochar (BC) via removing N atoms in N-doped BC (NBC) in an attempt to improve the nonradical catalytic performance. Compared to the pristine BC and NBC, the introduction of topological defects could achieve up to 36.6- and 8.7-times catalytic activity enhancement, respectively. More importantly, it was found that the catalytic activity was dominated by topological defects, which was verified by the significant positive correlation between the pseudo-first-order rate constants and the content of topological defects. Theoretical calculations suggested that topological defects enhanced the electron-donating ability of BC by reducing the energy gap, which made the electrons transfer to PDS molecules more easily. As a result, holes were generated after the carbon defects lost electrons, and induced a nonradical oxidation process. Benefiting from the merits of nonradical oxidation, the developed BC/PDS system showed superior performance in removing electron-rich contaminants in the presence of inorganic anions and in the actual environments. This study not only provides a potential avenue for designing efficient biochar-based catalysts, but also advances the mechanism understanding of nonradical oxidation process induced by carbon defects.
Salt-affected soils urgently need to be remediated to achieve the goals of carbon neutrality and food security. Limited reviews are available on biochar performance in remediating salt-affected soils in the context of carbon neutrality and climate change mitigation. This work summarized the two pathways to achieve carbon neutrality during remediating salt-affected soils using biochars, i.e., biochar production from sustainable feedstock using thermal technologies, application for promoting plant productivity and mitigating greenhouse gas (GHG) emission. Converting biomass wastes into biochars can reduce GHG emission and promote carbon dioxide removal (CDR), and collection of halophyte biomass as biochar feedstocks, development of biochar poly-generation production systems with carbon neutrality or negativity could be promising strategies. Biochar can effectively improve plant growth in salt-affected soils, showing that the grand mean of plant productivity response was 29.3%, via improving physicochemical characteristics, shifting microbial communities, and enhancing plant halotolerance. Moreover, biochar can mitigate GHG emission via inducing negative priming effect, improving soil properties, changing microbial communities associated with carbon and nitrogen cycle, direct adsorption of GHG. However, biochar also may pose negative effects on plant growth because of stress of toxic compounds and free radicals, and deterioration of soil properties. The promoted GHG emission is mainly ascribed to positive priming effect, and provision of labile carbon and inorganic nitrogen fractions as microbial substrates. Finally, this review pointed out the gaps in the current studies and the future perspectives. Particularly, the development of “carbon neutral” or “carbon negative” biochar production system, balancing the relationship of biochar effectiveness and functionality with its environmental risks and costs, and designing biochar-based GHG adsorbents would be important directions for remediating salt-affected soils to achieve carbon neutrality and abate climate change.
Biochar with a highly accessible specific surface area can display a higher performance when it is used as the cathode of lithium-ion capacitors. Facing the complex composition and diversity of biomass precursors, there is a lack of a universally applicable method to construct hierarchical porous biochar controllably. In this work, a multi-stage activation strategy combining the feature of different activation methods is proposed for this target. To confirm the porous characteristic in prepared samples, N2 adsorption–desorption and transmission electron microscope were used. As the optimal sample, BC-P3K4S had the highest specific surface area of 3583.3 m2 g−1. Evaluated as the electrode for a lithium-ion capacitor, BC-P3K4S displayed a capacity of 139.1 mAh g−1 at 0.1 A g−1. After coupling it with pre-lithiated hard carbon, the full device exhibited a high energy density of 129.3 W h kg−1 at 153 W kg−1. The work outlined herein offers some insights into the preparation of hierarchical porous biochar from complex biomass by multistep activation method.
Plant–biochar interaction has been recognized to affect the hydraulic properties of landfill cover soils, while its influence on landfill gas emission is rarely studied. This study investigated the coupled effects of biochar and vegetation on gas permeability and emission in unsaturated landfill cover through an integrated theoretical modelling and laboratory investigation. First, a gas permeability model was developed for vegetated coarse-grained soils with biochar addition. Then, a well-instrumented laboratory column test and two tests from the literature, considering bare, grass, biochar and grass + biochar conditions, were used for model validation. Finally, a numerical parametric study was conducted to investigate the influence of root growth and drought conditions on the gas emission rate. Results showed that the developed model can satisfactorily capture the gas permeability of unsaturated soils at various degrees of saturation. The lowest water retention capacity, the highest gas permeability and gas emission rate after 24 months of growth were observed in the grassed column. However, adding biochar in vegetated soils can maximize the water retention capacity and decrease the gas permeability, resulting in the lowest gas emission rate. The measured gas emission rates for the four cases meet the recommended value by the design guideline. The parametric study showed that the increased root depth from 0.2 m to 0.4 m improved the gas emission rate by 170% in the grass case but decreased by 97% in the grass + biochar case. Under the severe drought condition with soil suction around 500 kPa, the gas emission rate in the grassed case exceeded the design value by 18%, while those in the biochar cases were far below the allowable value. Therefore, peanut shell biochar should be considered to amend the grassed landfill cover using coarse-grained soils as it can significantly improve engineering performance in reducing gas emissions under extreme drought conditions.
The charosphere is a thin soil one surrounding the biochar with highly active biochemical functions. Yet, little is known about the spatial and temporal distribution of charosphere hotspots. In this study, repacked soil cores were incubated with a central layer of biochar (pristine or acid-modified) with or without nitrogen (N) additions for 30 days and sliced at the millimeter scale for analyzing soil pH, mineral N, bacterial and fungal communities as well as the putative functions. We aimed to determine gradient distributions (in millimeter scale) of charosphere affected by biochar under different N additions. Our results showed narrower gradient changes (3 mm) of microbial community composition and wider shifts (6 mm) in pH and inorganic N contents in charosphere. The pristine biochar increased the soil pH up to 1.5 units in the charosphere, and subsequently boosted the relative abundance of Proteobacteria, Acidobacteria, and Zygomycota. With N addition, both the biochar site and charosphere were observed with decreased complexity of microbial networks, which might imply the limited microbial functionality of charosphere. These results will advance the understanding and prediction of biochar’s environmental impacts in soil.
Biochar can change the availability and morphology of soil Cd. However, the influence of biochar on Cd chemical form and subcellular fraction in rice is poorly understood, particularly under different irrigation methods. A pot experiment of biochar application combined with two irrigation methods (continuous flooding and intermittent irrigation, CF and II) was conducted. The Cd accumulation, chemical form and subcellular fraction in rice organs and the associated physiological responses were examined. Biochar significantly reduced soil available Cd (30.85–47.26% and 32.35–52.35%) under CF and II but increased the Cd content (30.4–63.88% and 13.03–18.59%) in brown rice. Additionally, the Cd content in shoots/grains under II was higher than that under CF. Biochar elevated the Cd soluble fraction in roots while lowered the cell wall fraction under both irrigation methods, whereas the opposite result was observed in leaves. Biochar increased water-, ethanol-, and NaCl-extractable Cd in roots meanwhile increased ethanol-extractable Cd in leaves under both irrigation methods. Moreover, the total amount of water-, ethanol-, and NaCl-extractable Cd in rice roots was higher under II than under CF. Related hormones and antioxidant enzymes may also be involved in biochar-mediated Cd accumulation in rice grains. Thus, changes in Cd chemical form and subcellular fraction in the root and leaf are the main mechanisms of biochar-induced rice grains Cd accumulation.
Various human activities have led to multiple contamination of natural water systems. The present study investigated the effect of a novel multifunctional biochar to treat nutrients, oil, and harmful algae in water. Specifically, magnesium (Mg) and biosurfactant rhamnolipid (RL) were incorporated into biochar, including Mg-biochar, RL-biochar, and Mg-RL-biochar. Their adsorption efficiency on phosphate and total petroleum hydrocarbons (TPH) was evaluated in separate batch studies. Also, the inhibition effect of RL-modified biochars on cyanobacteria was investigated. The results showed that Mg-impregnated biochar showed high adsorption capacity on phosphate (118 mg g−1), while RL-modified biochar significantly reduced TPH (especially aromatic and light aliphatic fraction) with adsorption capacity of 44.4 mg g−1. The inhibition effects of biochar composites on algae in water without contaminants were in order of Mg-RL-biochar > RL-biochar > biochar with biomass reduction ranging 61–64%. Overall, Mg-RL-biochar was suggested based on this study due to its ability to remove PO43− and TPH, and inhibit the growth of toxic algae.
Highly efficient isomerization of glucose to fructose is essential for valorizing cellulose fraction of biomass to value-added chemicals. This work provided an innovative method for preparing Mg-biochar and Mg–K-biochar catalysts by impregnating either MgCl2 alone or in combination with different K compounds (Ding et al. in Bioresour Technol 341:125835, 2021, https://doi.org/10.1016/j.biortech.2021.125835 and KHCO3) on cellulose-derived biochar, followed by hydrothermal carbonization and pyrolysis. Single active substance MgO existing in the 10Mg–C could give better catalytic effect on glucose isomerization than the synergy of MgO and KCl crystalline material present in 10Mg–KCl–C. But the catalytic effect of 10Mg–C was decreased when the basic site of MgO was overloaded. Compared to other carbon-based metal catalysts, 10Mg–KHCO3–C with 10 wt% MgCl2 loading had excellent catalytic performance, which gave a higher fructose yield (36.7%) and selectivity (74.54%), and catalyzed excellent glucose conversion (53.99%) at 100 °C in 30 min. Scanning electron microscope–energy dispersive spectrometer and X-Ray diffraction revealed that the distribution of Mg2+ and K+ in 10Mg–KHCO3–C was uniform and the catalytic active substances (MgO, KCl and K2CO3) were more than 10Mg–C (only MgO). The synergy effects of MgO and K2CO3 active sites enhanced the pH of reaction system and induced H2O ionization to form considerable OH− ions, thus easily realizing a deprotonation of glucose and effectively catalyzing the isomerization of glucose. In this study, we developed a highly efficient Mg–K-biochar bimetallic catalyst for glucose isomerization and provided an efficient method for cellulose valorization.
Rapid development in industrialization and urbanization causes serious environmental issues, of which acid rain is one of the quintessential hazards, negatively affecting soil ecology. Liming has been investigated for a long time as the most effective amendment to alter the adverse effects of soil acidity resulting from acid rain. Herein, this study tested the biochar produced from invasive plants as an alternative amendment and hypothesized that biochar can maintain better availability of macronutrients under acid rain than liming by improving soil chemical and biological properties. Therefore, a pot experiment was conducted to compare the effects of lime and biochar at two rates (1% and 3%) on soil available nitrogen (N), phosphorous (P) and potassium (K) under simulated acid rain of two pH levels (4.5: pH4.5 and 2.5: pH2.5) as compared with tap water (pH7.1) as a control treatment. Biochar was produced using different invasive plants, including Blackjack (Biden Pilosa), Wedelia (Wedelia trilobata) and Bitter Vine (Mikania micrantha Kunth). Liming decreased the availability of soil N, P, and K by 36.3% as compared with the control due to the great increment in soil pH and exchangeable calcium (Ca2+) by 59% and 16-fold, respectively. Moreover, liming reduced the alpha diversity of soil bacteria and fungi by 27% and 11%, respectively. In contrast, biochar at different types and rates resulted in a fourfold increment in the available N, P, and K as an average under acid rain (pH4.5 and pH2.5) owing to maintaining a neutral pH (6.5–7), which is the most favorable level for soil microbial and enzymatic activites, and the bioavailability of soil nutrients. Furthermore, biochar caused balanced increments in Ca2+ by threefold, cation exchange capacity by 45%, urease activity by 16%, and fungal diversity by 10%, while having a slight reduction in bacterial diversity by 2.5%. Based on the path, correlation, and principal component analyses, the exchangeable aluminum was a moderator for the reductions in macronutrients’ availability under acid rain, which decreased by 40% and 35% under liming and biochar, respectively. This study strongly recommended the use of biochar from invasive plants instead of lime for sustainable improvements in soil properties under acid rain.
The use of inorganic nitrogen (N) fertilizers has increased drastically to meet the food requirements of the world's growing population. However, the excessive use of chemical nitrogen fertilizer has caused a series of soil and environmental problems, such as soil hardening, lower nitrogen use efficiency (NUE), nitrate pollution of water sources, nitrous oxide emissions, etc. In this review, we aimed to elaborate and discuss the role of engineered biochar in inducing the stability of water-stable macroaggregates, improving inorganic N transformation, and utilization efficiency to address the current uncertainties of nitrogen loss and maintaining soil and water quality. Firstly, we elucidated the characteristics of engineered biochar in improving biochar quality to work as a multifunctional player in the ecosystem and promote resource utilization, soil conservation, and ecosystem preservation. Secondly, we discussed how the engineered biochar modulates the stability of water-stable macroaggregates and soil inorganic nitrogen transformation to enhance plant response under various toxic or deficient nitrogen conditions in the soil. Thirdly, the role of engineered biochar in biological nitrogen fixation, mediating nirK, nirS, and nosZ genes to promote the conversion of N2O to N2, and decreasing denitrification and N2O emission was reviewed. Altogether, we suggest that engineered biochar amendment to soil can regulate soil water-stable macroaggregates, reduce N input, improve nitrogen metabolism, and finally, NUE and crop growth. To the best of our knowledge, this is the first time to evaluate the combined interactions of "engineered biochar × soil × NUE × crop growth,” providing advantages over the increasing N and water utilization and crop productivity separately with the aim of enhancing the stability of water-stable macroaggregates and NUE together on a sustainable basis.
Goethite nanoparticles modified biochar (FBC) could address the weak effectiveness of conventional biochar commonly to process heavy metal(loids) (HMs) co-contamination with different charges. However, few studies have focused on the change of soil mechanical properties after stabilization. In this study, FBC was synthesized to stabilize simultaneously arsenic (As (V)) (anions) and cadmium (Cd (II)) (cations) in co-contaminated soils. Batch adsorption, leaching toxicity, geotechnical properties and micro-spectroscopic tests were comprehensively adopted to investigate the stabilization mechanism. The results showed that FBC could immobilize As (V) mainly through redox and surface precipitation while stabilizing Cd (II) by electrostatic attraction and complexation, causing soil agglomeration and ultimately making rougher surface and stronger sliding friction of contaminated soils. The maximum adsorption capacity of FBC for As (V) and Cd (II) was 31.96 mg g−1 and 129.31 mg g−1, respectively. Besides, the dosages of FBC required in contaminated soils generally were approximately 57% higher than those in contaminated water. FBC promoted the formation of small macroaggregates (0.25–2 mm) and the shear strengths of co-contaminated soils by 21.40% and 8.34%, respectively. Furthermore, the soil reutilization level was significantly improved from 0.14–0.46 to 0.76–0.83 after FBC stabilization according to TOPSIS method (i.e., technique for order preference by similarity to an ideal solution). These findings confirm the potential of FBC in immobilizing As (V) and Cd (II) of co-contaminated soils and provide a useful reference for green stabilization and remediation of HMs co-contaminated sites.
Increased biogas residue related to the rapid development of anaerobic fermentation has become an urgent environmental problem. The pyrolysis of biogas residue into biochar is one of the most promising treatments. In this study, biochar derived from biogas residue was prepared, and the degradation efficiency of phenol by permanganate (KMnO4) increased from 25.3% to 73.4% in 60 min in the presence of biogas residue biochar (BRB). KMnO4 reacted with BRB to produce intermediate manganese dioxide (MnO2), while BRB was activated. The specific surface area increased by 132.25%, and the oxygen-containing functional groups C=O, C−O, and COOH increased after the reaction. The generated MnO2 complexed with BRB to form MnO2@BRB. The newly formed MnO2@BRB catalyzed KMnO4 to remove phenol, which explains the high removal efficiency of phenol. A significant removal rate was also observed for antibiotics and chlorophenols, which suggested that the KMnO4/BRB system has a relatively high ability to oxidize organic pollutants. In addition, the co-existing metal ions and the natural environment had little influence on the removal efficiency of the KMnO4/BRB system. This work provides a novel technology for the resource utilization of biogas residue and improved organic pollutant removal efficiency of KMnO4 in the presence of BRB.
Soil harbors a huge diversity of microorganisms and serves as the ecological and social foundation of human civilization. Hence, soil health management is of utmost and consistent importance, aligning with the United Nations Sustainable Development Goals. One of the most hazardous contaminants in soil matrix is potentially toxic elements (PTEs), which can cause stress in soil indigenous microorganisms and severely jeopardize soil health. Biochar technology has emerged as a promising means to alleviate PTE toxicity and benefit soil health management. Current literature has broadly integrated knowledge about the potential consequences of biochar-amended soil but has focused more on the physical and chemical responses of the soil system than microbiological attributes. In consideration of the indispensable roles of soil microbials, this paper first introduces PTE-induced stresses on soil microbials and then proposes the mechanisms of biochar’s effects on soil microbials. Finally, microbial responses including variations in abundance, interspecific relationships, community composition and biological functions in biochar-amended soil are critically reviewed. This review thus aims to provide a comprehensive scientific view on the effect of biochar on soil microbiological health and its management.
| • | Biochar had higher efficiency than conventional filter media. |
| • | Biochar had high efficiencies in removing copper, iron, aluminium, and total coliforms. |
| • | Biochar in mixed beds substantially improved haze and colour removal. |
Biochar has been considered an effective approach as soil amendment for decreasing incidences of disease and regulating microbial populations in continuous-cropping soil. Although researches have extensively focused on changes of soil microbes and unbalance of nutrition in continuous-cropping soil, the relationship between soil properties and pathogens by biochar application remains poorly understood. In this study, we applied ITS ribosomal RNA gene profiling to analyze tobacco root microbiota of biochar and non-biochar treatment in a 3-year continuous-cropping tobacco field, comparing firstly planting tobacco as control. We found that biochar application decreased the relative abundance of the soil fungal pathogens (Ceratobasidium and Monosporascus), which are the prime pathogens of tobacco root rot in continuous-cropping soil. Using RDA, co-occurrence and PLS-PM approaches, we provided evidence that there was a negative correlation between fungal genera (especially for Ceratobasidium and Monosporascus) and soil polyphenol oxidase (PPO) activity (R2incidence rate = − 0.930, R2disease index = − 0.905, both p < 0.001). The PPO was up-regulated by different biochar treatment intensities. Together, we demonstrated that biochar in continuous-cropping soil regulated the soil PPO activity to suppress pathogens, and further decrease incidence of root rot. Notably, biochar application forward continuous cropping was more effective for the continuous-cropping soil improvement than the other treatments. The data should help in appropriate timing of biochar application for alleviating continuous-cropping obstacle.
The Climate Change Conference of Parties (COP) 21 in December 2015 established Nationally Determined Contributions toward reduction of greenhouse gas emissions. In the years since COP21, it has become increasingly evident that carbon dioxide removal (CDR) technologies must be deployed immediately to stabilize concentration of atmospheric greenhouse gases and avoid major climate change impacts. Biochar is a carbon-rich material formed by high-temperature conversion of biomass under reduced oxygen conditions, and its production is one of few established CDR methods that can be deployed at a scale large enough to counteract effects of climate change within the next decade. Here we provide a generalized framework for quantifying the potential contribution biochar can make toward achieving national carbon emissions reduction goals, assuming use of only sustainably supplied biomass, i.e., residues from existing agricultural, livestock, forestry and wastewater treatment operations. Our results illustrate the significant role biochar can play in world-wide CDR strategies, with carbon dioxide removal potential of 6.23 ± 0.24% of total GHG emissions in the 155 countries covered based on 2020 data over a 100-year timeframe, and more than 10% of national emissions in 28 countries. Concentrated regions of high biochar carbon dioxide removal potential relative to national emissions were identified in South America, northwestern Africa and eastern Europe.
| • | Heteroatom-doped wood-derived biochar was assisted in situ growth of NiFe-LDH. |
| • | NiFe-LDH@NC exhibited excellent bifunctional activity and stability toward ORR/OER. |
| • | The ZAB achieved a peak power density of 123 mW cm−2 and a cycling stability of 270 h. |
Biochar has the potential to provide a multitude of benefits when used in soil remediation and increasing soil organic matter enrichment. Nevertheless, the intricated, hydrophobic pores and groups weaken its water-holding capacity in dry, sandy soils in arid lands. In order to combat this issue, starch-carbon-based material (SB), sodium alginate-carbon-based material (SAB), and chitosan-carbon-based material (CB) have been successfully synthesized through the graft-polymerization of biochar (BC). A series of soil column simulations were used to scrutinize the microstructure of the carbon-based material and explore its water absorption properties and its effects on sandy soil water infiltration, water retention, and aggregation. The results indicated that SB, SAB, and CB achieved water maximum absorption rates of 155, 188, and 172 g g−1, respectively. Considering their impact on sandy soils, SB, SAB, and CB lengthened infiltration times by 1920, 3330, and 3880 min, respectively, whilst enhancing the water retention capabilities of the soil by 18%, 25%, and 23% in comparison to solely adding BC. The utilization of these innovative materials notably encouraged the formation of sandy soil aggregates ranging from 2.0 to 0.25 mm, endowing the aggregates with enhanced structural stability. Findings from potting experiments suggested that all three carbon-based materials were conducive to the growth of soybean seeds. Thus, it is evident that the carbon-based materials have been fabricated with success, and they have great potential not only to significantly augment the water retention capacities and structural robustness of sandy soils in arid areas, but also to bolster the development of soil aggregates and crop growth. These materials possess significant application potential for enhancing the quality of sandy soils in arid and semi-arid regions.
Root and tuber crops are important sources of food and provide income for millions of people worldwide besides an observed high demand for organically produced harvests. Hence, recent attention has been given to utilizing biochar, a carbon-rich material produced from the pyrolysis of organic materials, which improves soil structure, water-holding capacity, and nutrient availability, as an amendment to produce organic root and tuber crops. These effects are caused by the formation of organic coatings on the surface of biochar, which decreases hydrophobicity and increases the ability to retain nutrients, acting as a slow-release mechanism delivering nutrients dependent on plant physiological requirements. However, comprehensive studies on the impact of biochar application on root and tuber crop growth, productivity, and effectiveness in eliminating soil parasites have not been extensively studied. Thus, the purpose of this review is to explore the use of biochar and biochar-based soil amendments and their potential applications for improving the growth, yield, and efficacy of controlling parasitic nematodes in a wide range of root crops. Most of the studies have investigated the effects of biochar on cassava, sweet potatoes, and minor root crops such as ginger and turmeric. It has been observed that biochar application rates (5–20 t ha−1) increase the vine length and the number of leaves, tubers, and tuber weight. The addition of biochar demonstrates the ability to control plant-parasitic nematodes in a rate-dependent manner. While biochar has shown promising results in improving crop growth and yield of limited root and tuber crops based on a few biochar types, ample opportunities are around to evaluate the influence of biochar produced in different temperatures, feedstock, modifications and controlling parasitic nematodes.
Drying and rewetting (DRW) events cause the release of colloidal phosphorus (Pcoll, 1–1000 nm) in leachate, and biochar is considered an effective inhibitor; however, the microbial mechanism remains elusive. In this study, three successive DRW cycles were performed on the soil columns to assess the effect of biochar addition on Pcoll content and its possible associates, including phosphatase-producing microbial populations (phoD- and phoC-harboring microbial communities) and alkaline/acid phosphatase (ALP/ACP) activities. Results showed that the biochar addition significantly decreased the Pcoll by 15.5–32.1% during three DRW cycles. The structural equation model (SEM) confirmed that biochar addition increased phoD- and phoC-harboring microbial communities and ALP/ACP activities, which reduces the release of Pcoll into leachate. In addition, the manure biochar was more effective than the straw biochar in promoting competition and cooperation in the co-occurrence network (2–5% nodes increased on average), and the key taxa Proteobacteria and Cyanobacteria were identified as the dominant species of potential ALP/ACP activities and Pcoll content. Our findings provide a novel understanding of biochar reducing Pcoll loss from the phosphatase perspective by regulating the phoD- and phoC-harboring communities during DRW events.
Biochars with a high affinity for phosphorus (P) are promising soil amendments for reducing P in agricultural runoff. Poultry litter (PL) is an abundant biochar feedstock. However, PL-derived biochars are typically high in soluble P and therefore require chemical modification to become effective P sorbents. This study investigated the effect of magnesium (Mg) activation on extractable P (EP) and P sorption capacities of PL-derived biochars. Biochar was produced at 500–900 °C from PL activated with 0–1 M Mg. Three differentially aged PL feedstocks were evaluated (1-, 3–5-, and 7–9-year-old). Increased Mg activation level and pyrolysis temperature both resulted in EP reductions from the biochars. Specifically, biochars produced at temperatures ≥ 700 °C from PL activated with ≥ 0.25 M Mg had negligible EP. X-ray diffractograms indicated that increased Mg loading favored the formation of stable Mg3(PO4)2 phases while increasing temperature favored the formation of both Mg3(PO4)2 and Ca5(PO4)3OH. Maximum P sorption capacities (Pmax) of the biochars were estimated by fitting Langmuir isotherms to batch sorption data and ranged from 0.66–10.35 mg g−1. Average Pmax values were not affected by PL age or pyrolysis temperature; however, biochars produced from 1 M Mg-activated PL did have significantly higher average Pmax values (p < 0.05), likely due to a greater abundance of MgO. Overall, the results demonstrated that Mg activation is an effective strategy for producing PL-derived biochars with the potential ability to reduce P loading into environmentally sensitive ecosystems.
The intensification of estrogen non-point source pollution has drawn global attention due to their contribution to ecological environment problems worldwide, and it is critical to develop effective, economic and eco-friendly methods for reducing estrogens pollution. To address the agglomeration and oxidation of nano zero-valent iron (nZVI), biochar-nanoscale zero-valent iron composite (nZVI-biochar) could be a feasible choice for estrogens removal. This study summarized biochar and nZVI-biochar preparation, characterization, and unusual applications for estrone (E1), 17β-estradiol (E2), and estriol (E3) removal. The properties of biochar and nZVI-biochar in characterization, effects of influencing factors on the removal efficiency, adsorption kinetics, isotherm and thermodynamics were investigated. The experiment results showed that nZVI-biochar exhibited the superior removal performance for estrogens pollutants compared to biochar. Based on the quasi-second-order model, estrogens adsorption kinetics were observed, which supported the mechanism that chemical and physical adsorption existed simultaneously on estrogens removal. The adsorption isotherm of estrogens could be well presented by the Freundlich model and thermodynamics studies explained that nZVI-biochar could spontaneously remove estrogens pollutants and the main mechanisms involved π-π interaction, hydrophobic interaction, hydrogen bonding and degradation through ring rupture. The products analyzed by GC–MS showed that estrogens degradation was primarily attributed to the benzene ring broken, and Fe3+ promoted the production of free radicals, which further proved that nZVI-biochar had the excellent adsorption performances. Generally, nZVI-biochar could be employed as a potential material for removing estrogens from wastewater.
Due to anthropogenic activities, heavy metal (HM) pollution in soils has increased, resulting in severe ecological problems and posing a constant threat to human health. Among various remediation methods, bacterial remediation is a relatively clean, efficient, and minimally negative approach. However, bacterial agents face multiple environmental stresses, making them challenging to achieve long-lasting and stable restoration effects. To address this issue, supportive organic substances such as biochar can be added to the soil with bacteria. According to bibliometric studies, integrating biochar and bacteria is extensively researched and widely used for HM-contaminated soil remediation. By integrating biochar and bacteria, heavy metals in the soil can be remediated, and soil conditions can be improved over time. Bacteria can also better promote plant growth or contribute effectively to phytoremediation processes when assisted by biochar. However, the remediation agents integrating biochar and bacteria are still some distance away from large-scale use because of their high cost and possible environmental problems. Therefore, further discussion on the interaction between biochar and bacteria and the integration approach, along with their remediation efficiency and environmental friendliness, is needed to achieve sustainable remediation of HM-contaminated soils by integrating biochar and bacteria. This paper discusses the potential mechanisms of biochar-bacteria-metal interactions, current advancements in biochar-bacteria combinations for HM-contaminated soil treatment, and their application in sustainable remediation, analyzes the interaction between biochar and bacteria and compares the remediation effect of different ways and feedstocks to integrate biochar and bacteria. Finally, future directions of biochar-bacteria combinations are presented, along with evidence and strategies for improving their commercialization and implementation.
Due to the rising need for clean and renewable energy, green materials including biochar are becoming increasingly popular in the field of energy storage and conversion. However, the lack of highly active and stable electrode materials hinders the development of stable energy supplies and efficient hydrogen production devices. Herein, we fabricated stable, conductive, and multifunctional chitosan microspheres by a facile emulsion crosslinking solution growth and hydrothermal sulphuration methods as multifunctional electrodes for overall water splitting driven by supercapacitors. This material possessed three-dimensional layered conductors with favorable heterojunction interface, ample hollow and porous structures. It presented remarkably enhanced electrochemical and catalytic activity for both supercapacitors and overall water electrolysis. The asymmetric supercapacitors based on chitosan biochar microsphere achieved high specific capacitance (260.9 F g−1 at 1 A g−1) and high energy density (81.5W h kg−1) at a power density of 978.4 W kg−1. The chitosan biochar microsphere as an electrode for electrolyze only required a low cell voltage of 1.49 V to reach a current density of 10 mA cm−2, and achieved excellent stability with 30 h continuous test at 20 mA cm−2. Then, we assembled a coupled energy storage device and hydrogen production system, the SCs as a backup power source availably guaranteed the continuous operation of overall water electrolysis. Our study provides valuable perspectives into the practical design of both integrated biochar-based electrode materials and coupled energy storage devices with energy conversion and storage in practical.
Biochar has been shown to improve soil properties and plant productivity in soils with inherently low fertility. However, little has been reported for upland corns under dry and wet precipitation regimes. This study investigates the effect of biochar addition on a range of soil physicochemical, biological, and hydrological properties, and corn growth and productivity under agrometeorological drought and wet conditions. Here, experiments were laid out in a randomized complete block design with three replications at two sites during 2017 and 2018 in South Korea. Treatments included (i) CN: control (ii) IF: inorganic fertilizer (N–P–K) at 145–30–60 kg ha−1; (iii) BS: barley straw at 5 t ha−1; (iv) CWBC: corn waste biochar at 5 t ha−1; (v) CWBC + IF: corn waste biochar + inorganic fertilizer; (vi) CWBC + BS: corn waste biochar + barley straw. The year 2017 was relatively dry, whereas the year 2018 was wet. Despite drought conditions in the year 2017, biochar facilitated soil water conservation. However, higher precipitation in 2018 increased the quantity and distribution of soil water and nutrients in the top 15 cm. Biochar reduced soil bulk density, and increased porosity, cation exchange capacity and total organic carbon in both years but increased total bacterial counts during the dry year only. Bacterial population was generally higher under wet conditions. Similarly, more soil CO2 was emitted in the wet year than in the dry year. Results further indicated that biochar can enhance corn biomass and grain yield regardless of precipitation conditions. The grain index was, however, affected by rainfall and was significantly different across treatments in the year 2018 only. All biomass, grain yield, and grain index were highest in CWBC + IF treatment and lowest under CN treatment. Indeed, biochar addition appeared to improve soil quality and soil conditioning effects in the drought and wet years, ameliorating soil and plant properties. Overall, biochar can improve water and nutrients storage, availability, and uptake, and therefore corn productivity during hydrological extremes.
Herein, we report the synthesis of interconnected hierarchical pore biochar (HTB) via an ice-templating strategy using bio-waste (tofukasu). The abundance of N- and O-containing functional groups in tofukasu makes it easy to form hydrogen bonds with water molecules and water clusters, resulting in nano-micro structures like ice clusters and snow crystals during freezing process. More importantly, tofukasu will be squeezed by micron-scale snow crystals to form coiled sheet-like structures, and its surface and interior will be affected by needle-like ice nanocrystals from several nanometers to tens of nanometers to form transverse groove needles and mesopores. The ice crystals are then removed by sublimation with tofukasu, leaving the interconnected pore structure intact. Therefore, the ice template synthesis strategy endowed the interconnected hierarchical pore structure of HTB with a large specific surface area (SBET, 733 m2⋅g−1) and hierarchical porosity (30.30% for mesopores/total pore volume ratio), which is significantly higher than the normal dry treated tofukasu biochar (TB), which had a SBET of 436 m2⋅g−1 and contained 1.53% mesopores. In addition, the sheet-like structure with interconnected pores of HTB favors high exposure of active sites (N- and O-containing functional groups), and a fast electron transport rate. As a result, HTB had an excellent adsorption capacity of 159.65 mg⋅g−1, which is 4.7 times that of typical block biochar of TB (33.89 mg⋅g−1) according to Langmuir model. Electrochemical characterization, FTIR and XPS analysis showed that the mechanism of Cr(VI) removal by HTB included electrostatic attraction, pore filling, reduction and surface complexation.
Biochar is a potential porous carbon to remove the contaminants from aquatic environments. Herein, N-doped hierarchical biochar was produced by the combined approach of ammonia torrefaction pretreatment (ATP) and alkali activation. ATP could not only incorporate N element into poplar wood, but obtain the loose structure of poplar wood. The highest surface area of N-doped hierarchical biochar was 2324.61 m2 g−1 after ammonia wet torrefaction pretreatment, which was higher than that of activation carbon (1401.82 m2 g−1) without torrefaction pretreatment, the hierarchical biochar (2111.03 m2 g−1) without ammonia atmosphere. The N-doped hierarchical biochar presented the highest adsorption capacity (564.7 mg g−1) of methyl orange (MO), which was 14.64-fold of that on biochar without N doping. In addition, the pseudo-second-order and Langmuir model fitted well with the adsorption kinetics and isotherms of the N-doped hierarchical biochar. The incorporation of nitrogen element could not only tune the distribution of surface electrons on biochar, but optimize the ambient condition of adsorption active sites as well. The adsorption of MO might occur on the N-/O-containing functional groups through the electrostatic interaction, the π-π dispersion interaction, and the hydrogen bonding. The density functional theory showed that the graphitic-N and pyridinic-N were the dominant adsorption active sites.
Metalloid pollution, including arsenic poisoning, is a serious environmental issue, plaguing plant productivity and quality of life worldwide. Biochar, a carbon-rich material, has been known to alleviate the negative effects of environmental pollutants on plants. However, the specific role of biochar in mitigating arsenic stress in maize remains relatively unexplored. Here, we elucidated the functions of biochar in improving maize growth under the elevated level of sodium arsenate (Na2AsO4, AsV). Maize plants were grown in pot-soils amended with two doses of biochar (2.5% (B1) and 5.0% (B2) biochar Kg−1 of soil) for 5 days, followed by exposure to Na2AsO4 ('B1 + AsV'and 'B2 + AsV') for 9 days. Maize plants exposed to AsV only accumulated substantial amount of arsenic in both roots and leaves, triggering severe phytotoxic effects, including stunted growth, leaf-yellowing, chlorosis, reduced photosynthesis, and nutritional imbalance, when compared with control plants. Contrariwise, biochar addition improved the phenotype and growth of AsV-stressed maize plants by reducing root-to-leaf AsV translocation (by 46.56 and 57.46% in ‘B1 + AsV’ and ‘B2 + AsV’ plants), improving gas-exchange attributes, and elevating chlorophylls and mineral levels beyond AsV-stressed plants. Biochar pretreatment also substantially counteracted AsV-induced oxidative stress by lowering reactive oxygen species accumulation, lipoxygenase activity, malondialdehyde level, and electrolyte leakage. Less oxidative stress in ‘B1 + AsV’ and ‘B2 + AsV’ plants likely supported by a strong antioxidant system powered by biochar-mediated increased activities of superoxide dismutase (by 25.12 and 46.55%), catalase (51.78 and 82.82%), and glutathione S-transferase (61.48 and 153.83%), and improved flavonoid levels (41.48 and 75.37%, respectively). Furthermore, increased levels of soluble sugars and free amino acids also correlated with improved leaf relative water content, suggesting a better osmotic acclimatization mechanism in biochar-pretreated AsV-exposed plants. Overall, our findings provided mechanistic insight into how biochar facilitates maize’s active recovery from AsV-stress, implying that biochar application may be a viable technique for mitigating negative effects of arsenic in maize, and perhaps, in other important cereal crops.
Fertilizer-intensive agriculture is a leading source of reactive nitrogen (Nr) emissions that damage climate, air quality, and human health. Biochar has long been studied as a soil amendment, but its influence on Nr emissions remains insufficiently characterized. More recently, the pyrolysis of light hydrocarbons has been suggested as a source of hydrogen fuel, resulting in a solid zero-valent carbon (ZVC) byproduct whose impact on soil emissions has yet to be tested. We incorporate carbon amendment algorithms into an agroecosystem model to simulate emission changes in the year following the application of biochar or ZVC to the US. fertilized soils. Our simulations predicted that the impacts of biochar amendments on Nr emissions would vary widely (− 17% to + 27% under 5 ton ha−1 applications, − 38% to + 18% under 20 ton ha−1 applications) and depend mostly on how nitrification is affected. Low-dose biochar application (5 ton ha−1) stimulated emissions of all three nitrogen species in 75% of simulated agricultural areas, while high-dose applications (20 ton ha−1) mitigated emissions in 76% of simulated areas. Applying zero-valent carbon at 20 ton ha−1 exhibited similar effects on nitrogen emissions as biochar applications at 5 ton ha−1. Biochar amendments are most likely to mitigate emissions if applied at high rates in acidic soils (pH < 5.84) with low organic carbon (< 55.9 kg C ha−1) and inorganic nitrogen (< 101.5 kg N ha−1) content. Our simulations could inform where the application of carbon amendments would most likely mitigate Nr emissions and their associated adverse impacts.
Biochar wettability and ability to accumulate moisture inside the porous space are crucial for improving soil fertility, regulating soil water balance, and regulating nutrients. However, a long-term interaction of biochar with agricultural soils may drastically alter the wetting properties and, eventually, influence water holding capacity and the structure of soils. In this work, the structure and wetting properties of biochar samples after 6-year long exposure to a sandy loam Spodosol with a crop rotation and mineral fertilizers application were studied. It was found that the elemental composition of the aged biochars was richer and more "soil-like", which is explained by the presence of the mineral crust on the biochar surface. The temporal evolution of biochar in the soil without any mineral fertilizer application resulted in significant improvement of its surface wettability due to the effects of various environmental factors. The lateral surface of biochar after 6-year interaction with the soil changes into a loose porous layer in a form of grooved base filled with adherent mineral soil and clay particles. Contrary, the application of the mineral fertilizer to the soil resulted in decreased wettability of the biochar lateral surfaces due to a decrease in the polar component of surface energy and the crusting of the surface with fine material, which blocks the pore space of the biochar. As a result, water capacity of the biochar from the treatment with the fertilizer decreased compared to the biochar samples collected from the soil without the fertilizer application. The radial biochar surfaces of both types of samples collected from the soil were open vessels filled with soil particles that slow down complete wetting and water absorption. The treatment of the biochar samples with surfactants drastically increased wettability of lateral surface and water absorption capacity of control samples as compared to the samples collected from the soil. The obtained results support the idea that the hydrophilisation of biochar caused by the adhesion of soil particles and treatment of its pore surface with surfactants, can improve the water-holding capacity of the sandy loam Spodosol in the plant-available range of soil water.
Applying biochar amendment and manure in tea plantation ecosystems can diminish soil acidification and degradation. However, the impact of these practices on soil respiration and associated mechanisms remains unclear. In this study, we combined a two-year field experiment and laboratory analyses based on soil properties, functional genes, and microbial co-occurrence networks to explore the determinants of soil respiration intensity in a subtropical tea plantation with biochar amendment and manure application. The results showed that the effect of biochar amendment on soil respiration was unconspicuous. Although biochar amendment increased bacterial richness and Shannon index, biochar amendment did not alter the abundance of species associated with C-cycling functional genes. Besides directly adding recalcitrant C to the soil, biochar also indirectly enhanced C sequestration by weakly increasing soil carbon dioxide (CO2) emissions. However, replacing mineral fertilizer with manure significantly stimulated soil respiration in the tea plantation, resulting in a 36% increase in CO2 emissions over two years. The increase in CO2 emissions under the manure treatment was mainly attributed to the increased soil labile C pool, the activity of hydrolytic enzymes (e.g., cellobiohydrolase and acetylglucosaminidase), and the relative abundance of functional genes associated with the C-cycle. This may also be related to the application of manure that increased the abundance of Gemmatimonadetes and altered ecological clusters in bacterial co-occurrence networks. Our correlation network analysis suggested that Gemmatimonadetes might be the potential hosts for C-cycling genes due to their strong positive correlation with the abundance of C-cycling genes. Overall, these findings provide new insights into soil respiration under biochar amendment and manure application in tea plantations and broaden the options for carbon sequestration in soils.
Biochar, as a potential CO2 adsorbent, is of great significance in addressing the problem of global warming. Previous studies have demonstrated that the CO2 adsorption performance of biochar can be improved by nitrogen and sulfur doping. Co-doping can integrate the structure and function of two elements. However, the physicochemical interaction of nitrogen and sulfur during doping and the CO2 adsorption process remains unclear in co-doped biochar. In this study, the heteroatom-doped biochar was prepared with different additives (urea, sodium thiosulfate, and thiourea) via hydrothermal carbonization, and the physicochemical interaction of nitrogen and sulfur in co-doped biochar was investigated extensively. The findings revealed that nitrogen and sulfur competed for limited doped active sites on the carbon skeleton during the co-doping process. Interestingly, thiourea retained the amino group on the surface of biochar to a great extent due to carbon–sulfur double bond breaking and bonding, which facilitated the formation of pore in the activation process. Significantly, co-doping had no significant improvement effect although nitrogen and sulfur doping separately enhanced the CO2 adsorption performance of biochar by 11.9% and 8.5%. The nitrogen-containing and sulfur-containing functional groups in co-doped biochar exhibited mutual inhibition in the process of CO2 adsorption. The findings of this study will have pertinent implications in the application of N/S co-doped biochar for CO2 adsorption.
Icing of wind turbine blades will seriously hinder the development of the wind power industry, and the use of biomass resources to solve the icing problem is conducive to promoting the synergistic development of biomass and wind energy. In this study, ice-phobic coatings with photothermal and anti-corrosion properties were prepared by surface modification pyrolysis and hydrothermal reaction with rice straw biogas residue as raw material. The erosion of KOH and the surface modification of MoS2 produced a rough structure of the material, and the high-temperature pyrolysis and hydrothermal reaction promoted the dehydrogenation and decarboxylation reactions, which reduced the number of oxygen-containing functional groups and decreased the surface energy of the material. The ice-phobic coating has superhydrophobic properties with a contact angle of 158.32°. Due to the small surface area in contact with water, the coating was able to significantly reduce the icing adhesion strength to 53.23 kPa. The icing wind tunnel test results showed that the icing area and mass were reduced by 10.54% and 30.08%, respectively, when the wind speed was 10 m s−1 and the temperature was − 10 °C. Photothermal performance tests showed that the MoS2-loaded material had light absorption properties, and the coating could rapidly warm up to 58.3 ℃ under xenon lamp irradiation with photothermal cycle stability. The loading of MoS2 acts as a physical barrier, reducing the contact of corrosive media with the substrate, thus improving the anti-corrosion of the coating. This study has practical application value and significance for the development of the anti-icing field under complex environmental conditions.
In the last few decades, sulfonated carbon materials have garnered significant attention as Brønsted solid acid catalysts. The sulfonation process and catalytic activity of sulfonated biochar can be influenced by the aromaticity and degree of condensation exhibited by biochar. However, the relationships between the aromaticity, sulfonating ability, and resultant catalytic activity are not fully understood. In this study, biochar samples pyrolyzed at 300–650 °C exhibiting different aromaticity and degrees of condensation were sulfonated and employed as sulfonate-bearing solid catalysts for hydrolytically removing tylosin. They exhibited excellent hydrolytic performance and their kinetic constants were positively correlated with the total acidity and negatively correlated with their aromaticity. This study has uncovered the relationship between the structure, properties, sulfonating ability, and subsequent hydrolytic performance of biochar samples. It was observed that the aromaticity of biochar decreased as the pyrolysis temperature increased. Lower pyrolysis temperatures resulted in a reduced degree of condensation, smaller ring size, and an increased number of ring edge sites available for sulfonation, ultimately leading to enhanced catalytic performance. These findings provide valuable insights into the fundamental chemistry behind sulfonation upgrading of biochar, with the aim of developing functional catalysts for mitigating antibiotics in contaminated water.
Biochar has a large specific surface area, well-developed pore structure, abundant surface functional groups, and superior nutrient supply capacity, which is widely available and environmentally friendly with its advantages in waste resource utilization, heavy metal(loid) remediation, and carbon storage. This review focuses on the interactions between biochar (including raw biochar, functional biochar (modified/ engineered/ designer biochar), and composite biochar) and rhizosphere during the remediation of soil contaminated with heavy metal(loid)s (Pb, As, Cd, Hg, Co, Cu, Ni, Zn, Cr, etc.) and the effects of these interactions on the microbial communities and root exudates (enzymes and low-molecular-weight organic acids (LMWOAs)). In terms of microorganisms, biochar affects the composition, diversity, and structure of microbial communities through the supply of nutrients, provision of microbial colonization sites, immobilization of heavy metal(loid)s, and introduction of exogenous microorganisms. With regard to root exudates, biochar provides electron transfer support between the microorganisms and exudates, regulates the secretion of enzymes to resist the oxidative stress stimulated by heavy metal(loid)s, ameliorates rhizosphere acidification caused by LMWOAs, and promotes the activity of soil enzymes. The roles and mechanisms of biochar on rhizosphere soils are discussed, as well as the challenges of biochar in the remediation of heavy metal(loid)-contaminated soils, and the issues that need to be addressed in future research are foreseen.
Biochar has gained significant attention in agricultural and environmental research over the last two decades. This comprehensive review evaluates the effects of biochar on soil organic carbon (SOC), emission of non-CO2 greenhouse gases, and crop yield, including related mechanisms and major influencing factors. The impacts of biochar on SOC, methane and nitrous oxide emissions, and crop yield are controlled by biochar and soil properties and management practices. High-temperature biochar produced from lignin-rich feedstocks may decrease methane and nitrous oxide emissions in acidic soils and strengthen long-term carbon sequestration due to its stable aromatic structure. In contrast, low-temperature biochar from manure may increase crop yield in low-fertility soils. Applying biochar to farmlands in China can increase SOC content by 1.9 Pg C and reduce methane and nitrous oxide emissions by 25 and 20 Mt CO2-eq year−1, respectively, while increasing crop yields by 19%. Despite the increasing evidence of the positive effects of biochar, future research needs to explore the potential factors that could weaken or hinder its capacity to address climate change and secure crop production. We conclude that biochar is not a universal solution for global cropland; however, targeted applications in fields, landscapes, or regional scales, especially in low fertility and sandy soils, could realize the benefits of biochar as a climate-smart measure.
Highlights
| • | The findings of research on biochar's effects on soil C sequestration, GHG mitigation, and crop production were summarized. |
| • | The factors influencing the impact of biochar on soil functioning were reviewed. |
| • | The effects of biochar on soil C sequestration and GHG mitigation in farmlands of China were quantified. |
The extensive use of neonicotinoids on food crops for pest management has resulted in substantial environmental contamination. It is imperative to develop an effective remediation material and technique as well as to determine the evolution pathways of products. Here, novel ball-milled nitrogen-doped biochar (NBC)-modified zero-valent iron (ZVI) composites (named MNBC-ZVI) were fabricated and applied to degrading neonicotinoids. Based on the characterization results, NBC incorporation introduced N-doped sites and new allying heterojunctions and achieved surface charge redistribution, rapid electron transfer, and higher hydrophobicity of ZVI particles. As a result, the interaction between ZVI particles and thiamethoxam (a typical neonicotinoid) was improved, and the adsorption–desorption and reductive degradation of thiamethoxam and ·H generation steps were optimized. MNBC-ZVI could rapidly degrade 100% of 10 mg·L−1 thiamethoxam within 360 min, its reduction rate constant was 12.1-fold greater than that of pristine ZVI, and the electron efficiency increased from 29.7% to 57.8%. This improved reactivity and selectivity resulted from increased electron transfer, enhanced hydrophobicity, and reduced accumulation of iron mud. Moreover, the degradation of neonicotinoids occurred mainly via nitrate reduction and dichlorination, and toxicity tests with degradation intermediates revealed that neonicotinoids undergo rapid detoxification. Remarkably, MNBC-ZVI also presented favorable tolerance to various anions, humic acid, wastewater and contaminated soil, as well as high reusability. This work offers an efficient and economic biochar-ZVI remediation technology for the rapid degradation and detoxification of neonicotinoids, significantly contributes to knowledge on the relevant removal mechanism and further advances the synthesis of highly reactive and environmentally friendly materials.
Pyrolysis is an effective technology for treating and utilizing biogas residue. To explore the phosphorus (P) supply capacity of the biochar generated from biogas residue of Eichhornia Crassipes, the P speciation of E. crassipes biogas residue and biomass during pyrolysis (300–700 °C) was analyzed by combining sequential chemical extraction, 31P nuclear magnetic resonance (NMR) and P K-edge X-ray absorption near edge structure (XANES) spectroscopy. Pyrolysis treatment promoted the conversion of amorphous Ca-P phases in biogas residue and biomass into crystalline hydroxyapatite (HAP) phase, which matched the formation of stable HCl-P pools in the biochar derived from biogas residue (AEBs, 22.65–82.04%) and biomass (EBs, 13.08–33.52%) in the process of pyrolysis. Moreover, the total P contents in AEBs (19.43–28.92 mg g−1) were higher than that of EBs (3.41–5.26 mg g−1), indicating that AEBs had a great P reclamation potential. The P release kinetics from AEBs and EBs in water were evaluated via an incubation experiment for 360 h. The P release from both AEBs and EBs conformed to the pseudo-second order kinetics model (R2 > 0.93), but their P release behaviors were different. The P release of AEBs conformed to the diffusion-re-adsorption model, while that of EBs accorded with the diffusion-dissolution model. The diffusive gradients in thin-films (DGT) analysis showed that AEBs could significantly increase soil available P content as compared with EBs. Hence, the biochar produced from biogas residue of E. crassipes via pyrolysis has a good application potential as a P fertilizer.
Magnetite-functionalized biochar (MBC) is a promising engineered material for remediation of antibiotic-contaminated fields. However, sorption mechanisms of ionizable organic compounds such as sulfonamide antibiotics (SAs) on MBC are still unclear. This study employed four representative SAs including sulfamethazine (SMT), sulfamerazine (SMR), sulfadiazine (SDZ), and sulfamethoxazole (SMX), to compare the difference in sorption on MBC. Results showed that the sorption capacities and affinities of the four SAs varied with their substituents, hydrophobic properties, and dissociation constants (pKa). Synergistic effect during co-pyrolysis with Fe3+ enhanced the sorption performance of MBC towards SAs compared to original BC. Spectral methods confirmed structural changes of MBC such as the variance in oxygen-containing groups and defective/graphitized phases. Results of modeling pH-dependent sorption revealed that H-bonding or π-bond assisted H-bonding determined the sorption affinities and capacities of SAs. In particular, the SAs with lower pKa were thermodynamically favorable to form H-bonding with MBC via proton exchange with water molecules. Quantum calculation results quantified the contributions of H-bonding strengths and found that the energies of H-bonding were correlated with affinities of SAs. Moreover, contributions of oxygen-containing groups instead of minerals dominated the H-bonding energies. Mechanistic insights from this study can be valuable in exploring engineered BC composites for practical application in field remediation.
Plants regulate root exudates to form the composition of rhizosphere microbial community and resist disease stress. Many studies advocate intervention with biochar (BC) and exogenous microbe to enhance this process and improve plant defenses. However, the mechanism by which BC mediates exogenous microorganisms to enhance root exudate-soil microbial defensive feedback remains unclear. Here, a BC-based Bacillus subtilis SL-44 inoculant (BC@SL) was prepared to investigate the defensive feedback mechanism for plants, which enhanced plant growth and defense more than BC or SL-44 alone. BC@SL not only strengthened the direct inhibition of Rhizoctonia solani Rs by solving the problem of reduced viability of a single SL-44 inoculant but also indirectly alleviated the Rs stress by strengthening plant defensive feedback, which was specifically manifested by the following: (1) increasing the root resistance enzyme activities (superoxide dismutase up to 3.5 FC); (2) increasing the abundance of beneficial microbe in soil (0.38–16.31% Bacillus); and (3) remodeling the composition of root exudates (palmitic acid 3.95–6.96%, stearic acid 3.56–5.93%, 2,4 tert-butylphenol 1.23–2.62%, increasing citric acid 0.94–1.81%, and benzoic acid 0.97–2.13%). The mechanism reveals that BC@SL can enhance the positive regulatory effect between root exudates and microorganisms by optimizing their composition. Overall, BC@SL is a stable and efficient new solid exogenous soil auxiliary, and this study lays the foundation for the generalization and application of green pesticides.
The widespread organic pollutants in wastewater are one of the global environmental problems. Advanced oxidation processes (AOPs) are widely used because of their characteristics of high efficiency and strong oxidation. However, AOPs may have some defects, such as incomplete mineralization of organic pollutants and the generation of toxic by-products during the degradation process, thus it is essential to seek efficient and green wastewater treatment technologies. Coupling different AOPs or other processes is beneficial for the mineralization of pollutants and reduces ecological risks to the environment. It is worth noting that carbonaceous materials (CMs) have received widespread attention and application in the degradation of organic pollutants in water by advanced oxidation coupling processes (C-AOPs) due to their excellent physicochemical properties in recent years. However, the behaviors and mechanisms of C-AOPs based on CMs on the degradation of organic pollutants are still unknown. Therefore, it is essential to comprehensively summarize the recent research progress. In this review, the applications of different CMs in C-AOPs were reviewed first. Secondly, the synergistic mechanisms of the C-AOPs based on different CMs were discussed. Then, toxic intermediates were explored and important toxicity assessment methods were proposed. Finally, the application potential of the C-AOPs in the future and the challenges were proposed. This review provides an important reference for the application and optimization of the C-AOPs in organic wastewater treatment in the future.
Numerous studies have unequivocally demonstrated that biochar and, to a lesser degree, earthworms can independently improve soil fertility and crop productivity, although information about their co-application effects on soil characteristics is limited. In this review, (1) earthworm biomarkers and underlying influencing factors, as well as the changes in the amended soil quality in response to co-application of earthworms and biochar are presented, (2) the functional interactions between earthworms and biochar in soil are summarized; (3) the principles governing the synergetic effects of biochar and earthworms on soil quality enhancement are probed; and (4) alternative strategies to optimize the efficacy of earthworm and biochar amendments are provided. It is noteworthy that while low doses of biochar can have a positive effect on various earthworm biomarkers, including growth and reproduction, restoration of the intestinal environment, and the mitigation of cellular organelle toxicity and genetic damage, high biochar dosages can yield adverse effects. Conversely, earthworms play a crucial role in distributing biochar particles deeper into the soil matrix, bolstering carbon sequestration potential, and enhancing the persistence and efficiency of biochar utilization. Moreover, earthworms stimulate the production of soil extracellular enzymes by microorganisms, which are pivotal to the processing, stabilization, and decomposition of soil organic matter, as well as nutrient cycling in terrestrial ecosystems. Additionally, they enhance the binding affinities of these enzymes to biochar. Significantly, changes in earthworm biomarkers in response to biochar integration are predominately governed by biochar properties and dosage, contact time, and soil type.
Sludge biochar, a carbonized product of raw sludge, contains porous architectures that can act as epicenters for adsorbing external molecules through physical or chemical bonding. Sludge biochar also immobilizes innate micropollutants, which is advantageous over conventional sludge disposal methods. To date, numerous strategies have been discovered to improve sludge biochar morphology, but the influential factors, pore tuning mechanisms, and process feasibility remain imprecise. This knowledge gap limits our ability to design a robust sludge-based biochar. Herein, we present state-of-the-art sludge biochar synthesis methods with insight into structural and chemical transformation mechanisms. Roadblocks and novel concepts for improving sludge biochar porous architecture are highlighted. For the first time, sludge biochar properties, adsorption performances, and techno-economic perspectives were compared with commercial activated carbon (AC) to reveal the precise challenges in sludge biochar application. More importantly, sludge biochar role in carbon sequestration is detailed to demonstrate the environmental significance of this technology. Eventually, the review concludes with an overview of prospects and an outlook for developing sludge biochar-based research.
| • | Highly efficient P-absorber with honeycomb structure and high specific surface area (2093.1 m2 g-1) was prepared. |
| • | LCB had an adsorption capacity of up to 280.4 mg P g-1 La-1 and its reusability was outstanding. |
| • | LCB maintained good P-removal effect at a solution pH of 3~10 and can be used in a wide range of applications. |
The biochar amendment plays a vital role in maintaining soil health largely due to its effects on soil microbial communities. However, individual cases and the variability in biochar properties are not sufficient to draw universal conclusions. The present study aimed to reveal how the biochar application affects soil microbial communities. Metadata of 525 ITS and 1288 16S rRNA sequencing samples from previous studies were reanalyzed and machine learning models were applied to explore the dynamics of soil microbial communities under biochar amendment. The results showed that biochar considerably changed the soil bacterial and fungal community composition and enhanced the relative abundances of Acidobacteriota, Firmicutes, Basidiomycota, and Mortierellomycota. Biochar enhanced the robustness of the soil microbial community but decreased the interactions between fungi and bacteria. The random forest model combined with tenfold cross-validation were used to predict biomarkers of biochar response, indicating that potentially beneficial microbes, such as Gemmatimonadetes, Microtrichales, Candidatus_Kaiserbacteria, and Pyrinomonadales, were enriched in the soil with biochar amendment, which promoted plant growth and soil nutrient cycling. In addition, the biochar amendment enhanced the ability of bacteria to biosynthesize and led to an increase in fungal nutrient patterns, resulting in an increase in the abundance and diversity of saprophytic fungi that enhance soil nutrient cycling. The machine learning model more accurately revealed how biochar affected soil microbial community than previous independent studies. Our study provides a basis for guiding the reasonable use of biochar in agricultural soil and minimizing its negative effects on soil microecosystem.
Bio-tar extra-produced from biomass pyrolysis is prone to pose a threat to environment and human health. A novel N-doped porous electrode from bio-tar was produced under dual-activation of urea and KOH in this study. One-pot dual-activation played significant roles in N-functional group and micro-mesoporous structure, which resulted in the carbon material with the highest of nitrogen content (4.08%) and the special surface area (1298.26 m2·g−1). Specifically, the potential mechanisms of pore formation and N-doping in the one-pot dual-activation strategy were also proposed as a consequence, the one-pot dual-activated carbon material displayed excellent electrochemical performance with the highest capacitance of 309.5 F·g−1 at 0.5 A·g−1, and the unipolar specific capacitance remained with cyclic characteristics of 80.1% after 10,000 cycles in two-electrode symmetric system. Furthermore, the one-pot dual-activation strategy could create a profit of $1.64–$2.38 per kilogram of bio-tar processed without considering the initial investment and labor costs, which provides new perspectives for the utilization of waste bio-tar.