Compacted clay possesses a low water permeability and has been widely used in geo-environmental facilities such as landfill cover systems. Recent studies revealed the potential applications of compacted biochar-amended clay (BAC) as an alternative landfill cover soil. However, the effects of biochar on the soil water retention curves (SWRCs) of clay at low suction are not known. This study can help fill this knowledge gap by measuring the wetting and drying SWRCs of clay and BAC (20% biochar). Soils were compacted in instrumented soil columns and subjected to a wetting and drying cycle, and soil water content and suction were measured along with the soil depth. BAC was saturated faster when compared with clay. Upon drying, the soil water content of clay at 65 mm depth dropped to almost zero, while about 5% of water was retained in BAC. It showed that biochar increased the soil water retention capacity of compacted clay upon drying. SWRCs showed that biochar-clay composite possesses a higher soil water retention capacity at a low soil suction range (< 1000 kPa) compared with clay alone. It revealed the benefits of using compacted biochar-clay composite as a hydraulic barrier to minimize desiccation-induced cracks and potentially promote its serviceability, especially in arid and semi-arid regions. The composite is also a carbon sink material that can reduce landfill gas emissions and pollutant leaching.
The current study investigated the effect of biochars derived from cinnamomum woodchip, garden waste and mulberry woodchip on soil phytoavailable lead (Pb), cadmium (Cd) pools, and their uptake by Chinese cabbage (Brassica chinensis L.). The biochars were produced at 450 °C of pyrolysis temperature. The contaminated soils were collected from Yunfu (classified as Udept), Jiyuan (Ustalf) and Shaoguan (Udult) cities in China at the depth of 0–20 cm and amended with biochars at the rate of 3% w/w. After mixing the soil with biochar for 14 days, the Chinese cabbage was planted in the amended soils. Then, it was harvested on the 48th day after sowing period. In Udult soil, Chinese cabbage died 18 days after sowing period in control and soils amended with cinnamomum and mulberry biochars. Although only plants grown with the garden waste biochar treatment survived in Udult soil, amendment of garden waste or mulberry biochars at 3% w/w (450 °C) to Udult soil significantly increased (4.95–6.25) soil pH compared to other biochar treatments. In Udept and Ustalf soils, the application of garden waste and mulberry biochars significantly improved plant biomass compared to control, albeit it was dependent on both biochar and soil properties. Garden waste biochar significantly decreased soil Cd phytoavailable concentration by 26% in the Udult soil, while a decrease of soil Cd phytoavailable concentration by 16% and 9% was observed in Ustalf and Udept soils, respectively. The available phosphorus in biochar and soil pH were important factors controlling toxic metal phytouptake by the plant. Thus, the amendment of soil with biochar at 3% can effectively reduce the mobility of Cd and Pb in soil and plant uptake. However, biochar and soil properties should be well-known before being used for soil toxic metal immobilization.
Little attention has been paid to how long-term application of crop straw and its biochar affects soil phosphorus (P) transformation and carbon (C) fractions. We conducted a 7-year field experiment including control treatment (chemical fertilizer only, CK), straw return (2.25 t ha−1), and different amounts of biochar addition (11.25 t ha−1 (0.5%BC) and 22.5 t ha−1 (1.0%BC), to investigate influence of these amendments on soil C structure, P fractions, and their interaction with microorganisms. The 13C nuclear magnetic resonance and soil P sequence fractionation were applied to capture changes of soil C compositions and P pool. Compared to CK, straw and biochar amendments decreased alkyl C/O-alkyl C, which is conducive to increased soil organic C. The 0.5%BC and 1.0%BC treatments enhanced recalcitrant aromatic C by 69.0% and 131%, respectively. Compared to CK (101.2 ± 33.32 mg kg−1), the 0.5%BC and 1.0%BC treatments had a negligible effect on soil available P, while negative effects were observed in straw treatment (59.79 ± 9.023 mg kg−1). Straw and biochar amendments increased primary P and occluded P, whereas had negligible effect on organic P. Redundancy analysis and correlation analysis indicated that C compositions and P pool correlated to microbial community composition and enzyme activities, and aromatic C was the most related factor. Moreover, structural equation modeling indicated available P was most related to phosphatase activity and C composition. Our findings reveal the changes of soil P and C response under long-term crop straw and its biochar amendment, and can contribute toward improving understanding of the effect of biochar and straw return in future agriculture management.
To remove antibiotics from waste water, an alkali active porous biochar, 850BC, was prepared from corncob xylose residue. In preparation, NaOH dipping was used for silicon removal and KOH activation was operated at 850℃. Further characterization containing BET, SEM, and FTIR were confirmed. 850BC possessed a huge specific surface area of 3043 m2·g−1, developed pore structure and abundant oxygen functional groups. The adsorption performance of sulfamethoxazole on 850BC was quick and efficient, and the adsorption capacity reached 1429 mg·g−1, which was significantly higher than other adsorbents reported previously. While pseudo-second-order kinetic model and Langmuir model could better describe the adsorption, chemisorption dominated the SMX adsorption onto 850BC. In virtue of pore-filling and π–π interaction as major mechanism, a large surface area and rich oxygen-containing functional groups led to an excellent adsorption performance. Thus, this preparation method provided a biochar-based adsorbent with enhanced specific surface for efficient removal of antibiotic pollutants.
Silicate minerals constitute the main components in silicon (Si)-rich biomass, affecting the phosphorus (P) adsorption and release competencies of mineral-engineered biochar; however, the mechanisms underlying their differences remain largely unresolved. To examine these interactions, we investigated the mineralogical compositions and quantified the P-adsorption capacities of Al-, Fe-, Mn-, Zn-, and Mg-engineered biochars from Si-rich rice husk material. The potential uses of P-laden mineral-engineered biochar for P fertilizers were assessed using citric acid extraction. The results from X-ray diffraction, scanning electron microscopy, and Fourier transform infrared spectrometry revealed that mixed metal (oxyhydr)oxides and metal-silicate compounds precipitated in the biochar structure and acted as the main P adsorbents. Micro-crystalline silicates derived from the biomass-induced metal-silicate precipitates in all engineered biochars, which effectively retained the aqueous P with varying excellent capacities (25.6–46.5 mg/g) but relatively slow kinetics (48 h). The suitability of the Zn-, Mg-, Mn-, and Fe-biochars as P-recycled fertilizers was confirmed by the high amounts of citric acid extractable P (19–69% of the total P). Varying amounts of Zn, Mg, and Mn (34–47% of the total host metals) were also released from the engineered biochar through ligand-promoted dissolution. Our data shed light on the novel potential utilization of Mn-, Mg- and Zn-biochars from Si-rich biomass for P retrieval and their use for P, Mg, and micronutrient (Mn and Zn) fertilizers. Regarding the P removal capacity, the mineral-engineered biochar needed a longer adsorption period than conventional metal-engineered biochar.
The large-scale use of antibiotics is causing serious water pollution problems, and it is of great significance to develop new technologies to remove antibiotics from water. As an environmentally friendly and economical adsorption material, carbon derived from biomass is a low-cost and feasible material for removing antibiotics in sewage, but the current removal efficiencies are not high enough for large-scale practical application. In this study, poplar wood chips are used as raw material, and a magnetic biochar is prepared by co-pyrolysis of poplar wood chips and FeCl3/CaCl2 mixed molten salt. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), N2-isothermal adsorption and desorption, X-ray photoelectron spectroscopy (XPS) and scanning electron microscope (SEM) techniques showed the successful synthesis of Fe2O3/bioC composite. In-situ formed Fe2O3 makes the biochar possess the characteristic of superparamagnetic, which is conducive to the recycling of biochar. Due to the etching effect of the molten salts, rough surface was formed on Fe2O3/bioC, resulting in a maximum norfloxacin (NOR) adsorption ability up to 38.77 mg g−1 at pH 6.0. The NOR adsorption behavior on Fe2O3/bioC followed the pseudo second order kinetic model and the equilibrium data was best fitted the Langmuir model. In addition, the adsorption process of NOR on Fe2O3/bioC was thermodynamically spontaneous. The results show that this low-cost and reusable magnetic biochar has the potential for rapid and efficient removal of antibiotic from aqueous solution.
In recent years, numerous investigations have explored the use of biochar for the removal of organic and inorganic pollutants in single component systems. Biochar is a carbonaceous material produced from waste biomass, mainly by thermochemical conversion methods. This material was used as a biosorbent in various removal processes of pollutants, and its efficiency was strongly influenced by the characteristics of the biomass feedstock. This review integrates the recent works of literature to understand the biosorption behaviour of dyes onto biochar-based biosorbents. The factors influencing the biosorption process and the mechanisms describing the biosorption behaviours of the biochar have been broadly reviewed. Furthermore, the biosorption models can be used to comprehend the competence of the biochar as biosorbent for dye removal techniques.
Woody agricultural wastes have created enormous pressure on the environment. In this study, mulberry and cinnamon woodchips were reclaimed and prepared for biochars through pyrolysis technique at four different temperatures. Physicochemical properties showed that mulberry biochar exhibited higher pH, CEC and ash content than cinnamon biochar at each temperature. All biochars were utilized as adsorbents to remove cadmium (Cd) and atrazine (AT) from water. The adsorption isotherms were found to be well fitted by Freundlich and Langmuir models. The maximum adsorption capacities were 5306.41 mg/kg for Cd adsorption and 538.89 mg/kg for AT adsorption, respectively. Moreover, the principal component analysis, XPS and FTIR analysis proved that precipitation with phosphate in biochars acted as the key property that governed the adsorption capacity of Cd, whereas the porosity demonstrated a significant impact on the adsorption capacity of AT. Partial least squares (PLS) model was considered to be more favorable for predicting AT adsorption than Cd adsorption. The results of the present paper will be helpful for selecting most effective biochars from locally available woody agricultural byproducts that are optimized for contaminants removal from environment.
Biological nitrogen fixation (BNF) can help replenish available nitrogen (N) in cropland and reduce the use of chemical N fertilizers, with diazotrophs playing an important role. However, the response of diazotroph community and BNF activity in biochar amendment soil, especially in the deep soil horizon, are poorly understood. In this study, soil samples were collected from topsoil (0–20 cm) and subsoil (20–40 cm) in the field experiment (established in 2013) comprising treatments with no chemical fertilizer (CK), chemical fertilizer (NPK), biochar (BC), and biochar plus chemical fertilizers (BNPK). Here, we investigated the diazotroph community using real-time PCR and high-throughput sequencing of the nifH gene, and assessed the soil N2 fixation rate (RNfix) using acetylene reduction assay (ARA). Results showed that in the topsoil, the treatments with biochar significantly increased nifH gene copies and RNfix, which was consistent with the increased soil organic matter (SOM), total carbon-to-nitrogen ratio (C/N), dissolved organic carbon (DOC) and pH. In the subsoil, applying chemical fertilizers (NPK) strongly decreased RNfix, but had no effect on diazotroph abundance; in contrast, biochar application (BC) had no effect on RNfix, but suppressed the growth of bacteria and diazotrophs while increasing the abundance of Rhizobiales order. Diazotroph and bacterial gene copies were significantly and positively correlated in both top- and sub-soil, and they were mainly influenced by SOM and total nitrogen (TN). In addition, soil nitrate nitrogen (NO3−–N) was the major factor in shaping the vertical stratification of diazotroph community structure. Although nifH gene abundance was significantly correlated with RNfix in the topsoil, the structure equation modeling (SEM) showed the highest correlation between diazotroph community structure and RNfix. Hence, we suggested that soil carbon and nitrogen sources were the key factors correlated with changes in the vertical pattern of diazotroph abundance. Biochar induced the dominant diazotroph community succession and increased soil carbon content and pH, which contributed to the BNF activity. Changes in the BNF activity were driven by the variation in diazotroph community structure.
Dissolved organic matter plays a critical role in affecting sorption properties of biochar for organic contaminants. In this study, dissolved humic acid (DHA) as a representative of dissolved organic matter and oak sawdust-derived biochar as a sorbent were prepared and characterized. Roles of DHA in sorption of benzotriazole (BTA), an emerging organic contaminant, to biochar in different electrolyte solutions were investigated. The results revealed the dual roles of DHA in BTA sorption to biochar. On the one hand, DHA can compete for sites and/or block pores available for BTA to inhibit the adsorption of BTA to biochar. On the other hand, the sorbed DHA on biochar can serve as additional partitioning phase to promote the partition of BTA. The finding was in accordance with the site energy distribution analysis of BTA sorption that the site energy of the highest occurring frequency in the DHA-BTA system was lower than that in the DHA-free system (3.41–10.4 versus 13.1–20.1 kJ mol−1). The variation in apparent BTA sorption to biochar affected by DHA was thus a combination of changes in both its partition and adsorption properties. A modified Dual-mode model including the aqueous concentration of DHA was proposed to predict the effect of DHA on BTA sorption to biochar in different electrolyte solutions, which showed good prediction performance with most BTA sorption coefficient (Kd, L g−1) deviations within 0.1 log unit.
Tropical Arenosols may be challenging for agricultural use, particularly in semi-arid regions. The aim of this study was to evaluate the impact of the addition of increasing shares of biochar and clay on the nutrient sorption capacity of a tropical Arenosol. In batch equilibrium experiments, the sorption of ammonium-N ($\hbox {NH}_{4}^{+}{\text{-N}}$), nitrate-N ($\text {NO}_{3}^{-}{\text{-N}}$), potassium ($\text {K}^{+}$), and phosphate-P ($\text {PO}_{4}^{3-}{\text{-P}}$) was quantified for mixtures of an Arenosol with increasing shares of biochar and clay (1%, 2.5%, 5%, 10%, 100%) and the unmixed Arenosol, biochar, and clay. The mid-temperature biochar was produced from Prosopis juliflora feedstock; the clayey material was taken from the sedimentary parent material of a temporarily dry lake. Only the Arenosol–biochar mixture with 10% biochar addition and the biochar increased the $\text {NH}_{4}^{+}{\text{-N}}$ maximum sorption capacity ($q_{max}$) of the Arenosol, by 34% and 130%, respectively. The $q_{max}$ of $\text {PO}_{4}^{3-}{\text{-P}}$ slightly increased with ascending biochar shares (1–10%) by 14%, 30%, 26%, and 42%, whereas the undiluted biochar released $\text {PO}_{4}^{3-}{\text{-P}}$. Biochar addition slightly reduced $\text {NO}_{3}^{-}{\text{-N}}$ release from the Arenosol but strongly induced $\text {K}^{+}$ release. On the other hand, clay addition of 10% and clay itself augmented $q_{max}$ of $\text {NH}_{4}^{+}{\text{-N}}$ by 30% and 162%; ascending clay rates (1–100%) increased $q_{max}$ for $\text {PO}_{4}^{3-}{\text{-P}}$ by 78%, 130%, 180%, 268%, and 712%. Clay rates above 5% improved $\text {K}^{+}$ sorption; however, no $q_{max}$ values could be derived. Sorption of $\text {NO}_{3}^{-}{\text{-N}}$ remained unaffected by clay amendment. Overall, clay addition proved to enhance the nutrient sorption capacity of the Arenosol more effectively than biochar; nonetheless, both materials may be promising amendments to meliorate sandy soils for agricultural use in the semi-arid tropics.
The mechanism of oxidation and degradation effect of phytate-modified biochar catalyzed persulfate on Ponceau 2R was investigated. Chemical-structural properties of phytate-modified biochar, such as surface morphology and surface oxygen-containing functional groups were characterized. The results suggest that modified biochar has better oxidation performance than unmodified biochar, and the modified biochar generated at 500 ℃ pyrolysis temperature can catalyze peroxymonosulfate (PMS) system with high efficiency, in large pH and temperature scope. And the degradation mechanism of Ponceau 2R by biochar-catalyzed PMS generation (BC-PMS) system was researched. It revealed that PBC300 (phytate-modified biochar pyrolyzed at 300 °C), PBC500 (phytate-modified biochar pyrolyzed at 500 °C), and PBC700 (phytate-modified biochar pyrolyzed at 700 °C) may have metaphosphoric acid linked to oxygen atoms and metaphosphoric acid linked in a bridging manner on the surface of biochar, catalyzing the production of hydroxyl radicals by PMS. PBC700 catalyzes the production of singlet oxygen by PMS through its structural defects, and singlet oxygen is the main catalytic product of PBC700.
Biochars can improve soil health but have been widely shown to reduce plant-available nitrogen (N) owing to their high carbon (C) content, which stimulates microbial N-immobilization. However, because biochars contain large amounts of C that are not microbially available, their total elemental C:N ratio does not correspond well with impacts on soil N. We hypothesized that impacts on soil plant-available N would relate to biochar mineralizable-C (Cmin) content, and that C:N ratios of the mineralizable biochar component could provide a means for predicting conditions of net soil N-mineralization or -immobilization. We conducted two laboratory experiments, the first measuring biochar Cmin from respiration of isotopically labeled barley biochars manufactured at 300, 500, and 750 °C, and the second characterizing Cmin by proxy measurements for ten biochars from six feedstocks at several temperatures. For both experiments, soils were incubated with 2% biochar by mass to determine impacts to soil N-mineralization. Contrary to expectation, all the biochars increased soil N-mineralization relative to unamended soils. Also unexpected, higher temperature (500 and 700 °C) barley biochars with less Cmin stimulated more soil decomposition and more soil N-mineralization than a 350 °C barley biochar. However, across diverse biochar feedstocks and production methods, none of the biochar characteristics correlated with soil N-mineralization. The finding of improved soil N-mineralization adds complexity to the range of soil N responses that can be expected in response to biochar amendment. Because of the limited ability to predict soil N responses from biochar properties, users should monitor soil N to manage soil fertility.
Biochar is a widely known soil amendment. Here we synthesize the available information on influence of biochar application on different soil properties and crop productivity using meta-analysis. Global data on influence of biochar applications on different soil physical, chemical, microbial properties, and crop productivity were extracted from literature and statistically analyzed. Based on selection criteria, 59 studies from the literature published between 2012 and 2021 were selected for the meta-analysis. Correlations were developed between effect size of biochar application on different soil properties and crop productivity. Application of biochar increased soil pH, cation exchange capacity, and organic carbon by 46%, 20%, and 27%, respectively, with greater effects in coarse and fine-textured soils. Effects on chemical properties were variable among biochar prepared from different feedstocks. Among physical properties, biochar application reduced bulk densities by 29% and increased porosity by 59%. Biochar prepared at higher pyrolytic temperatures (> 500 ℃) improved bulk density and porosity to greater extents (31% and 66%, respectively). Biochar prepared at lower pyrolytic temperatures (< 500 ℃) had a greater effect on microbial diversity (both bacterial and fungal), with more diverse bacterial populations in medium and coarse textured soils, while fungal diversity increased in fine textured soils. Biochar applications increased crop productivity only in fine and coarse textured soil. The effect size of biochar application on crop productivity was correlated with responses to physical properties of soils. The meta-analysis highlighted the need to conduct long-term field experiments to provide better explanations for changes in biochar properties as it undergoes aging, its longer-term effects on soil properties, and timing of re-application of different biochars.
As a metal immobilizer, biochar can be used to remediate contaminated soil. Biochar’s effect on the phytoremediation process in flooded conditions under a scenario of increasing flooding frequency as global climate change is not well understood. This study investigated bamboo biochar (BBC) effects on growth and metal accumulation of Salix in multi-metal contaminated soil under non-flooded versus flooded conditions. Salix cuttings were cultivated in pots with severely contaminated soil by Cd and Zn, for 120 days, with four treatments including non-flooded treatment, flooded treatment, non-flooded with 3% BBC application (BBC/soil, w/w), and flooded with 3% BBC addition. BBC, flooding, and BBC× flooding significantly decreased the bioavailability of metals in soils (P < 0.05). The BBC addition markedly stimulated Cd concentration in leaves under non-flooded (94.20%) and flooded conditions (32.73%) but showed little effect on roots. The BBC significantly boosted Cd and Zn transport from roots to aboveground parts by 68.85% and 102.27% compared with no BBC amendment under non-flooded treatment, while showing insignificant changes under flooded treatment. Although the plant biomass was little affected, BBC significantly increased Cd and Zn accumulation in the whole plant by 52.53% and 28.52% under non-flooded while showing an insignificant impact under flooded conditions. Taken together, BBC enhanced the phytoremediation efficiency of Salix to Cd and Zn in severely polluted non-flooded soil, while flooding offset this effect. The results indicated the effects of BBC varied under different soil moisture, which should be considered in the biochar-assisted phytoremediation to variable and complex environments.
In this study, four biochars prepared from different crop residue waste i.e. sugarcane bagasse (SBB), coconut shell (CNB), paddy straw (PDB), and distilled waste of lemongrass (LGB) were evaluated for removal of Remazol Brilliant Blue R from the aqueous system. The RBBR adsorption capacities of biochar were 97–79% for SBB, 99.9–99.47% for CNB, 66.1–48% for PDB, and 78–68% for LGB, dominantly controlled by their aromaticity and mineral content. The Langmuir and Freundlich isotherms and pseudo-second-order kinetic models have described the chemisorption of RBBR on biochar surfaces. The thermodynamic data suggested that adsorption was spontaneous and endothermic. These biochars demonstrated excellent reusability (till four cycles with 50–61% regeneration). The purified water and biochar dye sludge demonstrated no phytotoxicity. The findings obtained in this study may provide supports for the potential of biochars for anionic dye removal from water and utilization of generated sludge for zero waste-producing technologies in the future.
Glycophyte biomass-derived biochars are currently concerned in most studies. However, little attention is given to the characteristics of halophyte-derived biochars. In this study, five typical halophytes of euhalophytes (Suaeda altissima, Suaeda salsa, and Kalidium foliatum), recretohalophytes (Phragmites australis), and pseudohalophytes (Tamarix chinensis) which are widely distributed in the arid and semiarid regions of northwestern China were selected for producing biochars with a slow pyrolysis process at 500 °C for 1 h. The harvested biochars were characterized in elemental content, pores, surface area, and surface charges, and then their potential value as a soil conditioner was evaluated. The results showed that the halophyte-derived biochars had variable ash and Na+ contents, ranging from 7.26 to 23.64% and 1.06 to 33.93 g kg−1 respectively. The EC value of the biochars ranged from 1.76 to 23.45 mS cm−1. The biochar derived from Suaeda altissima had a very low specific surface area (SSA), 3.50 m2 g−1, while that derived from Phragmites australis (BPA) had a very high SSA, 344.02 m2 g−1. All the biochars carried both positive and negative charges. Kalidium foliatum biochar (BKF) possessed more negative charges, while Suaeda altissima biochar (BSA) contained more positive charges. In general, the halophyte biochars had a higher ash content and lower point of zero net charge (PZNC) value, compared with the biochars derived from glycophytes, which would imply their higher potential value as an acidic soil conditioner.
Low molecular weight organic acids (LMWOAs), as active components in the rhizosphere carbon cycling, may influence the environmental behaviors of biochar colloids. This study selected the pine-wood and wheat-straw biochars (PB and WB) as two typical biochars. The effects of typical LMWOAs (oxalic acid, citric acid, and malic acid) on aggregation kinetics of PB and WB colloids were investigated under pH 4 and 6 conditions. Critical coagulation concentrations (CCCs) of both PB and WB colloids were decreased with the LMWOAs regardless of the types of biochar and the solution pH, and the most significant effect occurred in pH 4 due to more LMWOAs sorption on the biochar colloids. The different types of LMWOAs caused various CCCs changes. For example, the CCC values of PB colloids decreased from 75 mM to 56, 52, and 47 mM in the pH 4 NaCl solutions when 1 mM oxalic acid, citric acid, and malic acid were present in the suspensions, respectively. The chemical structure (functional groups) and molecular weight of LMWOAs, solution pH, and the electrophoretic mobility (EPM) of biochar co-influence the interactions between biochar colloids and LMWOAs, thus affecting the stability of biochar colloids in the presence of LMWOAs. The presence of LMWOAs accelerated the aggregation of colloidal biochar by increasing the interaction of surface bridging bonds (hydrogen bonding) and decreasing the repulsive force between colloidal biochar particles. This study showed that LMWOAs could accelerate the aggregation of biochar colloids in acidic or neutral environments and reduce the mobility of biochar colloids in soil rhizosphere.
The textural properties and surface chemistry of phosphoric acid-modified biochars (PABCs) prepared at different pyrolysis temperatures (500–700 °C) were studied based on the results obtained from XRD, SEM, BET, FT-IR, Raman, XPS and elements analyses. PABCs prepared at higher temperatures tended to possess a bigger proportion of microporous structure. The adsorption capacity and initial rate of PABCs for sulfadiazine (SDZ) were notably improved to 139.2 mg/g and 9.66 mg/(g min) as calculated from the Langmuir model. The adsorption equilibrium time was only one quarter of that without modification. The H3PO4 modification was advantageous to produce phosphate and break functional groups to form disordered carbon structure abundant of micropores. The enhancement in the adsorption of SDZ was due to the confinement effect of hydrophobic cavities from the mircoporous structure and the π–π electron–donor–acceptor interaction. Specially, PABCs exhibited stable adsorption capacities at a wide pH range (3.0–9.0) or relatively high concentrations of coexisting ions.
| • | Multiple life cycle assessments of novel urban biochar applications were performed. |
| • | Urban biochar use has better climate impact than references, when biochar stability is high and energy is low-carbon. |
| • | Biochar products lead to some shifts in environmental burdens and will create new types of urban waste. |
Mitigation of toxic contaminants from wastewater is crucial to the safety and sustainability of the aquatic ecosystem and human health. There is a pressing need to find economical and efficient technologies for municipal, agricultural, aquacultural, and industrial wastewater treatment. Nitrogen-doped biochar, which is synthesized from waste biomass, is shown to exhibit good adsorptive performance towards harmful aqueous contaminants, including heavy metals and organic chemicals. Incorporating nitrogen into the biochar matrix changes the overall electronic structure of biochar, which favors the interaction of N-doped biochar with contaminants. In this review, we start the discussion with the preparation techniques and raw materials used for the production of N-doped biochar, along with its structural attributes. Next, the adsorption of heavy metals and organic pollutants on N-doped biochars is systematically discussed. The adsorption mechanisms of contaminant removal by N-doped biochar are also clearly explained. Further, mathematical analyses of adsorption, crucial to the quantification of adsorption, process design, and understanding of the mechanics of the process, are reviewed. Furthermore, the influence of environmental parameters on the adsorption process and the reusability of N-doped biochars are critically evaluated. Finally, future research trends for the design and development of application-specific preparation of N-doped biochars for wastewater treatment are suggested.
Biochar shows significant potential to serve as a globally applicable material to remediate water and soil owing to the extensive availability of feedstocks and conducive physio-chemical surface characteristics. This review aims to highlight biochar production technologies, characteristics of biochar, and the latest advancements in immobilizing and eliminating heavy metal ions and organic pollutants in soil and water. Pyrolysis temperature, heat transfer rate, residence time, and type of feedstock are critical influential parameters. Biochar’s efficacy in managing contaminants relies on the pore size distribution, surface groups, and ion-exchange capacity. The molecular composition and physical architecture of biochar may be crucial when practically applied to water and soil. In general, biochar produced at relatively high pyrolysis temperatures can effectively manage organic pollutants via increasing surface area, hydrophobicity and microporosity. Biochar generated at lower temperatures is deemed to be more suitable for removing polar organic and inorganic pollutants through oxygen-containing functional groups, precipitation and electrostatic attraction. This review also presents the existing obstacles and future research direction related to biochar-based materials in immobilizing organic contaminants and heavy metal ions in effluents and soil.
Fabricating surface oxygen vacancies is considered to be an efficient method to improve the adsorption performance of sorbents. In this work, a bismuth oxychloride/biochar (BiOCl/BC) nanocomposite with abundant oxygen vacancies was successfully prepared by a facile ball milling method. BiOCl/BC nanocomposite was found to have excellent adsorption performance for removing reactive red-120 (RR120) from aqueous solution. The effects of key adsorption parameters, such as RR120 dye concentration, solution pH (2–10), and contact time were studied by batch adsorption test. The adsorption data were well described by the Langmuir and Freundlich isotherms and pseudo-second-order kinetic models. The 50%-BiOCl/BC (50 wt% of BiOCl in composite) exhibited the best adsorptive performance (60%), much better than the pristine BM-BC (20%). The high adsorption capacity of 50%-BiOCl/BC (Langmuir maximum capacity of 116.382 mg g−1) can be attributed to the electrostatic effect, π–π interactions, and hydrogen bond. This work provided a facile method to prepare semiconductor assisted biochar-based adsorbents, which would also contribute to the advance of environmental remediation.
There has been more than 75% rise in the number of extreme weather events such as drought and flood during 2000–2019 compared to 1980–1999 due to the adverse effects of climate change, causing significant deterioration of the soil and water quality. Simultaneously, the growing human population has been exerting pressure on available water and soil resources due to overuse or unplanned use. While greenhouse gas emissions have intensified, the fertility of agricultural soils has declined globally due to the exposure of soils to frequent flooding, desertification, and salinization (resulting from extreme weather events). The current review aims to give an overview of damages caused to the soil–plant system by extreme weather events and provide a perspective on how biochar can repair the damaged system. Biochar is known to improve soil fertility, increase crop productivity and mitigate greenhouse gas emissions via sustainable recycling of bio-waste. Beneficial properties of biochar such as alkaline pH, high cation exchange capacity, abundant surface functional groups, remarkable surface area, adequate porosity, excellent water holding capacity, and sufficient nutrient retention capacity can help repair the adverse effects of extreme weather events in the soil–plant system. This paper recommends some cautious future approaches that can propel biochar’s use in improving the soil–plant systems and promoting sustainable functioning of extreme weather-affected areas via mitigation of the adverse effects.
Biochar (BC) has gained attention for removal of toxic elements (TEs) from aqueous media; however, pristine biochar often exhibits low adsorption capability. Thus, various modification strategies in BC have been developed to improve its removal capability against TEs. Nanoscale zero-valent iron (nZVI) and iron oxides (FeOx) have been used as sorbents for TE removal. However, these materials are prone to agglomeration and also expensive, which make their usage limited for large-scale applications. The nZVI technical demerits could be resolved by the development of BC-based composite sorbents through the loading of nZVI or FeOx onto BC surface. Nano zero-valent iron modified BC (nZVIBC), FeOx-modified BC (FeOxBC) have attracted attention for their capability in removing pollutants from the aqueous phases. Nonetheless, a potential use of nZVIBC and FeOxBC for TE removal from aqueous environments has not been well-realized or reviewed. As such, this article reviews: (i) the preparation and characterization of nZVIBC and FeOxBC; (ii) the capacity of nZVIBC and FeOxBC for TE retention in line with their physicochemical properties, and (iii) TE removal mechanisms by nZVIBC and FeOxBC. Adopting nZVI and FeOx in BC increases its sporptive capability of TEs due to surface modifications in morphology, functional groups, and elemental composition. The combined effects of BC and nZVI, FeOx or Fe salts on the sorption of TEs are complex because they are very specific to TEs. This review identified significant opportunities for research and technology advancement of nZVIBC and FeOxBC as novel and effective sorbents for the remediation of TEs contaminated water.
| • | Magnesium was introduced to modify the corn stalk biochar for simultaneous adsorption of ammonium and phosphate. |
| • | Ammonium and phosphate adsorption by magnesium modified biochar involved multi-mechanisms. |
| • | Compared to the leaching performance with CF, MgB-A was more stable and maintained a long-term slow-release of ammonium and phosphate. |
| • | MgB-A could be used as a struvite carbon-based fertiliser to promote plant growth. |
| • | For the first time, phosphorus in BRC was used as the phosphorus source for MAP treatment of biogas slurry. |
| • | Nitrogen and phosphorus were mainly recovered by MAP precipitation and functional group bonding of functionalized BRC. |
| • | N-rich biogas slurry was treated with P-rich biogas residue to produce biochar-based slow-release N-P fertilizer. |
Nanoparticles are abundant in the subsurface, soil, streams, and water bodies, and are often a critical control on elemental speciation, transport and cycling in the natural environment. This review provides an overview of pyrolyzed biomass-derived nanoparticles (PBNPs), their surface properties and reactivity towards aqueous species. We focus specifically on biochar-derived nanoparticles and activated carbon-derived nanoparticles which fall under our classification of PBNPs. Activated carbon-iron (nano)composites are included in some instances where there are significant gaps in literature because of their environmental relevance. Increased use of activated carbon, along with a resurgence in the manufacture and application of biochar for water treatment and soil amendment, has generated significant concerns about the mobility and toxicity of PBNPs derived from the bulk material in environmental applications. Recent examples are discussed to highlight current progress in understanding the influence of PBNPs on contaminant transport, followed by a critical discussion of gaps and future research directions.
The development of a multifunctional oil adsorbing material which could effectively and quickly separate oily wastewater is one of the focuses in water environment restoration. In this study, bamboo charcoal (BC) was used as an improver to modify polyurethane (PU) foam. The results of scanning electron microscope (SEM) and Fourier-transform infrared spectroscopy (FTIR) revealed that the addition of BC could effectively improve the mechanical properties of PU. The adsorption data exhibited that the BC-loaded PU (BC/PU) foam composites effectively removed seven organic solvents (OSs, including octane, petroleum ether, soybean oil, chlorobenzene, 1,2-dichloroethane, n-hexane, cyclohexane), and the maximum adsorption capacity of BC/PU was 23.6 g g−1 when BC content was 5%. The order of pseudo-second-order kinetic constants and maximum adsorption capacity of seven OSs was octane < petroleum ether < soybean oil < chlorobenzene < 1, 2-dichloroethane < cyclohexane < n-hexane. Based on the experimental data and density functional theory (DFT) simulation, the adsorption mechanism of OSs on BC/PU-5 was discussed. The EHOMO and μ of OSs calculated by DFT were highly correlated with absorption affinity (K2, Qe and Qmax). Hence, the contribution of OSs to the adsorption efficiency of BC/PU-5 may be mainly due to electron donor–acceptor (EDA) interaction and non-hydrophobic interaction. In addition, the adsorption capacity did not change significantly after repeated recycling 5 times. Overall, the prepared BC/PU foam composites could be used as a potential candidate for separating OSs in engineering applications.
The hydroxyapatite-loaded swine manure derived-biocarbon was successfully prepared by pyrolysis method for the adsorption of uranium(VI). The results of the adsorption experiments displayed that the adsorption behaviors for uranium(VI) of biocarbon did almost not depend on the interfering ions except Al3+, Ca2+ and CO32−, showing the high selectivity of the composites for uranium(VI). The maximum static and dynamic removal capacity of the hydroxyapatite-biocarbon composites to uranium(VI) were 834.8 and 782.8 mg/g (pH = 3, m/V = 0.1 g/L and T = 298 K), far exceeding other reported biocarbon and hydroxyapatite materials, which indicated that the hydroxyapatite-biocarbon composites possessed an application potential in adsorption. After five cycles of adsorption–desorption processes, the removal efficiency of the hydroxyapatite-biocarbon composite for uranium(VI) was 93.2% (Ci = 5 mg/L, pH = 3, m/V = 0.1 g/L and T = 298 K), revealing that the composite had excellent stability and reusability. Moreover, the capture mechanisms of the hydroxyapatite-biocarbon composite for uranium(VI) included ion exchange and complexation, which was ascribed to the ample active adsorption sites (–OH and PO43−). Therefore, the hydroxyapatite-loaded swine manure derived-biocarbon would be a potential material to effectually separate uranium(VI) from solution.
Metal-free photocatalysts have attracted growing concern recently. Herein, the composites combining g-C3N4 with wood pulp cellulose biochar (WPBC/g-C3N4) were synthesized to effectively activate peroxymonosulfate (PMS) under visible light for the degradation of diclofenac (DCF). The incorporation of WPBC endowed g-C3N4 with enhanced visible light absorption, improved charge separation capability, reduced electrical conductivity, and increased photocatalytic and PMS activation capability. Based on quenching tests, electron paramagnetic resonance (EPR), electrochemical analysis and solvent exchange experiments, both radical and nonradical mechanisms were proposed. Radical species including ·OH, h+, ·O2– were identified to contribute to DCF degradation. The 1O2 and electron transfer were the dominant nonradical pathways for DCF degradation. Moreover, the common influencing factors were examined, and DCF concentration was the most influential factor based on principal component analysis. Generally, the composites exhibited good reusability during consecutive runs. Based on HPLC/MS analysis, four intermediates were detected and the possible DCF degradation pathway was proposed. This work provided a potential strategy based on metal-free WPBC/g-C3N4 for the photocatalytic activation of PMS to effectively degrade emerging contaminants in wastewater.
The emission of air pollutants from various industries is a major contributor to environmental pollution. The removal of these pollutants before they are discharged into the environment has become an important means of controlling air pollution. Biochar has attracted increasing attention because of its low cost, high porosity, large specific surface area, abundant surface functional groups, and high removal capacity. The physicochemical properties of biochar are greatly affected by feedstock types, preparation, and modification conditions. For this reason, the capacity and propensity of biochar for removing air pollutants are rather variable. To understand the existing research status and grasp the latest research progress, a systematic review on the removal of different air pollutants by biochar is highly needed. Based on the recent research, this paper systematically analyzes and summarizes the preparation and modification methods of biochar commonly used for the removal of six air pollutants (SO2, H2S, CO2, Hg0, VOCs, and NH3), as well as the removal performance and mechanisms. Then, the potential influencing factors (preparation parameters, physicochemical characteristics of biochar, and removal conditions) are discussed. Finally, the regeneration of biochar, suggestions, and future perspectives are proposed.
Sorption kinetics of organic compounds on biochars is important for understanding the retardation of mobility and bioavailability of organic compounds. Herein, sorption kinetics of 1,3,5-trinitrobenzene on biochars prepared from 200 to 700 °C was investigated to explore the sorption process. Loose partition matrix and condensed partition matrix were formed at relatively low and moderate temperatures, respectively. However, biochars produced at relatively high temperatures formed rich pore structures. Therefore, sorption equilibrium time of 1,3,5-trinitrobenzene increased with increasing preparation temperature from 200 to 350 °C due to the slower diffusion rate in the more condensed matrix, and then decreased when preparation temperature was higher than 400 °C because of the faster adsorption rate in the greater number of pores. Linear positive relationship between matrix diffusion rates of 1,3,5-trinitrobenzene on biochars prepared at 200, 250, 300, 350 °C and H/C ratios of biochars was observed, suggesting that the inhibition of partition process was caused by the condensed matrix in biochars. Linear positive relationships between adsorption rates (i.e., fast outer diffusion rate and slow pore diffusion rate) of 1,3,5-trinitrobenzene on biochars prepared at 400, 450, 550, 700 °C and graphite defects of biochars were observed, because the increase of graphite defects of biochars could promote the adsorption by increasing the quantity of fast diffusion channels and sorption sites. This study reveals the underlying mechanisms of sorption kinetics for organic compounds with relatively large size on biochars, which has potential guidance for the application of biochars and prediction of the environmental risks of organic compounds.
Direct chemical oxidation and pure adsorption could not effectively remove p-Arsanilic acid (p-ASA) and the released inorganic arsenic. Herein, one novel biochar supported MnFe2O4 (MFB) was synthesized and adopted for p-ASA degradation and synchronous adsorption of the generated inorganic arsenic. The MFB/persulfate (PS) system could remain effective under a wide pH range (3.0–9.0), and the released arsenic could be removed simultaneously by MFB. Mechanism investigation revealed that the functional groups of MFB (i.e. O–C=O and C=O), Fe and Mn oxides on MFB all contributed to PS activation. O2·− and 1O2 were the main reactive oxygen species (ROS) responsible for p-ASA degradation, and 1O2 was the predominant ROS. Besides, the MFB possessed superior reusability. Therefore, it is expected to develop a potential method for organic arsenic contaminants removal via an oxidation-adsorption process, and the results could also shed light on the better understanding of the PS activation mechanisms.
Hydrochar has potential applications in soil improvement and heavy metal remediation. Hydrochar would undergo the process of aging when introduced into the soil, altering its properties. However, recent studies have focused mainly on the artificial aging of hydrochar, which could not reveal the cumulative effect of multiple environmental factors. Therefore, the periodical monitoring of the property and sorption behavior of hydrochar after amending soils is necessary to better understand the multifaceted mechanisms associated with the natural aging of hydrochar. This study selected the sludge-derived hydrochar (SLHC) as a typical hydrochar and applied a 16-month rice–wheat–rice rotation to mimic the natural aging of hydrochar, focusing on changing properties and cadmium (Cd) sorption and literature contrast between aging strategies and biochar types. The porosity, O abundance, and ash content of 16-month aged SLHC increased by 37%, 47%, and 8.5%, respectively, facilitating Cd sorption due to surface complexation, pore sorption, and precipitation. The sorption percentage of Cd to SLHC was in the range of 11–14% for SLHC-A0 and increased to 17–31% for SLHC-A4 and 20–32% for SLHC-A16 after natural aging. The natural aging of SLHC induced by ash content played an essential role in Cd sorption site heterogeneity. Linear regression analysis showed that aging strategies on sorption behavior significantly differed between biochars. Thus, studies involving natural aging with multiple environmental factors are preferred over those involving chemical or biological aging. Future studies should continue to explore the mechanisms of natural aging-induced heavy metal sorption between hydrochar and pyrochar. These results improve insights to appraise the potential of SLHC as soil amendments to alleviate the adverse effects of heavy metal contamination and provide an essential basis for researchers and staff in soil management and environmental prevention.
Globally, nitrogen (N) fertilizer demand is expected to reach 112 million tonnes to support food production for about 8 billion people. However, more than half of the N fertilizer is lost to the environment with impacts on air, water and soil quality, and biodiversity. Importantly, N loss to the environment contributes to greenhouse gas emissions and climate change. Nevertheless, where N fertilizer application is limited, severe depletion of soil fertility has become a major constraint to sustainable agriculture. To address the issues of low fertilizer N use efficiency (NUE), biochar-based N fertilizers (BBNFs) have been developed to reduce off-site loss and maximize crop N uptake. These products are generally made through physical mixing of biochar and N fertilizer or via coating chemical N fertilizers such as prilled urea with biochar. This review aims to describe the manufacturing processes of BBNFs, and to critically assess the effects of the products on soil properties, crop yield and N loss pathways.
Crawfish-shell biochar (CSB) pyrolyzed at 350°C showed the highest Sb(III) adsorption and oxidation.
DFT calculations highlighted complexation, H-bonding and π–π interactions as key removal mechanisms.
Sb(III) oxidation was mainly governed by persistent free radicals and electron transfer capacity of biochar.
As cheap and renewable sources, the exploitation of biomass resources was of great value in phase change energy storage. In this study, hemp stems were converted into biochars with three-dimensional multi-level anisotropic pores through a temperature-controlled charring process, which were used as supports for polyethylene glycol (PEG6000) to form shape-stable composite phase change materials (ss-CPCMs). It is shown that the ss-CPCMs using anisotropic hemp-stem-derived biochar obtained at a carbonization temperature of 900 °C as a support has high PEG6000 loading rate (88.62wt%), large latent heat (170.44 J/g) and favorable thermal stability owning to its high surface area and hierarchical pores. The biochar-based ss-CPCM also has good light absorption ability with a maximum solar-thermal conversion efficiency of 97.70%. In addition, the different thermal conductivities in the transverse and longitudinal directions of ss-CPCMs reflect the unique anisotropic structure. This work can not only improve the high-value utilization of biochars, but also provide the ss-CPCMs with excellent performance for solar-thermal conversion and storage systems.
| • | A biochar aerogel decorated with Ru/RuS2 particles was synthesized successfully. |
| • | Plenty of defects at carbon were formed due to regulation of two kinds of biomass. |
| • | The sample required a low overpotential of 228 mV at 10 mA cm−2 in 0.5 M H2SO4. |
| • | The unique 2D/3D microstructures in biochar aerogel enhanced mass transfer ability. |
| • | A meta-analysis of biochar preparation and application methods for disease severity and plant growth is needed. |
| • | Soil application of biochar from straw at 350–600 °C and at 3–5% rate was effective in reducing disease severity. |
| • | Biochar application has better suppression effect on cash crop diseases caused by airborne pathogens. |
| • | The results of the meta-analysis are particularly useful for maximizing the effect of biochar on plant disease control. |
Biochar, possessing electron exchange capacities (EEC), is generally involved in environmental redox reactions due to the presence of redox-active moieties (RAMs). The phenomenon that chars containing comparable RAMs possess differential EEC revealed that the accessibility of RAMs is important to the redox properties. However, many studies have focused on the type of RAMs, whereas the distribution has been insufficiently investigated. Herein, we achieved nanoscale observation of electroactive moieties on the surface of six chars using a conductive atomic force microscope. For the two specific kinds of chars with submicron particles and opposite current distributions, the submicron particles took up only 1–4‰wt of biochar accounting for approximately 30–50% of electron-donating capacity (EDC), and electron-accepting capacity (EAC) became 87% and 1.40 times as before after removing submicron particles, respectively. Meanwhile, the combined impact of RAMs and surface topography (that uneven distribution of RAMs resulted in outstanding EEC by enhancing accessibility) was clarified. Furthermore, direct evidence of the link between char structure and EEC (that condensed aromatic structures were indispensable to EAC while both heteroatoms and amorphous aromatics contributed to EDC) was established. These findings can aid in understanding the functions of biochar in biotic and abiotic redox processes.
Using 15N tracer technique, we investigated the potential rates of denitrification, anaerobic ammonium oxidation, dissimilatory nitrate reduction to ammonium (DNRA), and their partitioning among nitrate reduction, as well as the N2O emission rates in a paddy soil receiving various biochar (0%, 0.03%, 0.1%, 0.5%, and 1.0%; w/w) and straw (0.1%) over six consecutive years. Results showed that except for the 1.0% amendment treatment, biochar significantly (P < 0.05) increased denitrification rates by 10.19‒75.96% compared with non-biochar amended treatment, and that biochar significantly (P < 0.05) increased DNRA rates by 1.63‒6.84 folds relative to non-biochar amended treatment. Consequently, biochar shifted more NO3– partitioning toward DNRA process, as suggested by the increased DNRA/(denitrification + DNRA) ratios from 1.60 to 13.18%. On the other hand, biochar significantly (P < 0.05) reduced N2O emission rates by 61.86–97.65% accompanied by a significant decrease in N2O/(N2O + N2) ratios (65.29–98.39%), indicating biochar amendment facilitated the reduction of N2O to N2. The promoting effects of biochar on DNRA rates and DNRA/(denitrification + DNRA) ratios were attributed to the increased carbon availability and the altered nitrate reducer communities. Collectively, our study suggests that biochar amendment in the paddy soil is helpful for N conservation by favoring nitrate partitioning toward DNRA process, which deepens our understanding of how biochar mediates N cycling in the paddy field.
Biochar and dung amendments have been extensively employed in soil remediation and fertilization of grasslands, which are the largest terrestrial sinks for methane. However, how these exogenous amendments regulate methane metabolisms at the molecular and community levels remains elusive. In this study, we investigated the functional genes and community assemblies of methanogens and methanotrophs using Geochip 5.0 and high-throughput sequencing to reveal the impacts of biochar and dung on soil methanogenesis and methane oxidation. The interactions between methane metabolic genes and other biogeochemical genes were also examined. According to Geochip microarrays, methanogenic gene mcrA decreased and increased with dung or biochar amendment, respectively; The methanotrophic gene pmoA showed a reverse but not significant tendency. Undominated processes contributed 65.51% to replace homogeneous selections as primary driving forces of methanogen assembly after dung amendment; the contribution of dispersal limitation increased to 46.13% in methanotroph assembly after biochar amendment. The diversity and association of co-occurrence networks for carbon–nitrogen cycling genes decreased after exogenous amendments. These results indicated that biochar and dung amendments prominently regulated the functional genes and community assembly involved in methane metabolisms. The co-existence patterns of methane metabolic genes and other related geochemical genes were also shaped by these amendments. This study provides the scientific reference for the development of grassland management in the context of global warming.
Biochar amendment and substituting chemical fertilizers with organic manure (organic substitution) have been widely reported to increase crop production and decrease reactive nitrogen (Nr) loss including nitrous oxide (N2O), nitric oxide (NO), and ammonia (NH3) emissions, and N runoff and leaching. However, few comprehensive evaluations have been performed on the environmental and economic aspects of biochar amendment or organic substitution. Here, we studied the comprehensive effects of biochar amendment, organic substitution, and biochar amendment combined with organic substitution on crop production, Nr loss, and net ecosystem economic benefit (NEEB) in intensive vegetable production by integrating life-cycle assessment for Nr footprints, empirical models for NH3 volatilization and N runoff and leaching derived from peer-reviewed publications and validated by the current measurements and direct field measurement for N2O and NO emissions during 5 consecutive years of vegetable crop rotations. Five fertilization treatments were applied (SN: synthetic fertilizer application; SNB: SN plus 20 t ha−1 biochar amendment; SNM: substituting 50% of chemical N fertilizer with organic manure; SNMB: SNM plus 20 t ha−1 biochar amendment; and CK: no fertilizer or biochar addition). Compared with the SN, the SNB increased vegetable yield (28.4%, p < 0.05; interannually varying from − 10 to 74.9%) and nitrogen use efficiency (29.2%, interannually varying from − 39.7 to 150.4%), and decreased field Nr loss (45.4%, p < 0.01; interannually varying from − 40.3 to 78.4%), and thus improved NEEB by 7.1%; meanwhile, the SNM increased vegetable yield (11.6%, interannually varying from − 5.4 to 27.1%) and nitrogen use efficiency (45.7%, p < 0.05; interannually varying from 2.3 to 154%), reduced field Nr loss (34.9%, p < 0.01; interannually varying from 8.4–39.0%), and thus improved NEEB by 17.8% (p < 0.05) compared to the SN, being 56.0 × 103 Chinese Yuan (CNY) ha−1 crop−1. Due to the high foreground Nr loss during organic manure production and high input costs of biochar production, the SNMB decreased the NEEB by 8.0% as compared to the SN. Moreover, the SNB and SNM improved vegetable qualities by increasing protein, soluble sugar, and vitamin C contents while decreasing nitrate content (p < 0.05). Therefore, single application of biochar amendment or organic substitution would achieve better NEEB and product quality in vegetable production.
| • | Biomass type and thermochemical conversion temperature significantly affect biochar physicochemical properties. |
| • | Biochar-based catalysts applied in Fenton-like system exhibited better performance for refractory emerging pollutants. |
| • | Biochar-matrix, metal nanoparticles of catalysts, as well as intermediates are the main risks. |
| • | Carbonization (1 h, 400 °C, N2) of mix ball-milled (10 min) waste leaves and humic acid affords weak-acid biochars. |
| • | As-prepared weak-acid biochars (–COOH, OH, amino groups) were activated solids with adsorptive and catalytic properties. |
| • | Weak-acid biochar catalyst is reusable and promotes fructose dehydration to 5-HMF in yields of 77.5% (140 °C, 60 min). |
Conversion of organic waste into engineered metal-biochar composite is an effective way of enhancing biochar’s efficiency for adsorptive capture of phosphorus (P) from aqueous media. Thus, various strategies have been created for the production of metal-biochar composites; however, the complex preparation steps, high-cost metal salt reagent application, or extreme process equipment requirements involved in those strategies limited the large-scale production of metal-biochar composites. In this study, a novel biochar composite rich in magnesium oxides (MFBC) was directly produced through co-pyrolysis of magnesite with food waste; the product, MFBC was used to adsorptively capture P from solution and bio-liquid wastewater. The results showed that compared to the pristine food waste biochar, MFBC was a uniformly hybrid MgO biochar composite with a P capture capacity of 523.91 mg/g. The capture of P by MFBC was fitted using the Langmuir and pseudo-first-order kinetic models. The P adsorptive capture was controlled by MgHPO4 formation and electrostatic attraction, which was affected by the coexisting F− and CO32− ions. MFBC could recover more than 98% of P from the solution and bio-liquid wastewater. Although the P-adsorbed MFBC showed very limited reusability but it can be substituted for phosphate fertiliser in agricultural practices. This study provided an innovative technology for preparing MgO-biochar composite against P recovery from aqueous media, and also highlighted high-value-added approaches for resource utilization of bio-liquid wastewater and food waste.
Biochar nanoparticles (BCNPs) and iron mineral nanoparticles (IMNPs), such as ferrihydrite nanoparticles (FHNPs), magnetite nanoparticles (MTNPs), and goethite nanoparticles (GTNPs), are often combined and used in soil remediation. However, the stability and interaction of nanoparticles under various environmental conditions have not been investigated previously. In this study, settling experiments, a semi-empirical model, the Derjaguin–Landau–Verwey–Overbeek (DLVO) theory, scanning electron microscopy (SEM) observations, and quantum chemical calculations were used to study the interaction and heteroaggregation of BCNPs and IMNPs. Settling of BCNPs-FHNPs and BCNPs-GTNPs was stable at neutral and alkaline pH (relative concentration of unsettled nanoparticles Cres’ = 0.679–0.824), whereas fast settling of BCNPs-IMNPs was observed at acidic pH (Cres’ = 0.104–0.628). By contrast, BCNPs-MTNPs consistently showed moderate settling regardless of the mass of magnetite at all pH (Cres’ = 0.423–0.673). Both humic acid (HA, 10 mg L−1) and ionic strength (IS, 10 and 100 mM) facilitated the settling of BCNPs-FHNPs and BCNPs-MTNPs systems, whereas the settling of BCNPs-GTNPs was sensitive only to IS. Fulvic acid (10 mg L−1) had a general stabilizing effect on the BCNPs-IMNPs systems. The results of SEM and quantum chemical calculations suggested that the interaction between BCNPs and FHNPs (-2755.58 kJ mol−1) was stronger than that between BCNPs and GTNPs (−1706.23 kJ mol−1) or MTNPs (−1676.73 kJ mol−1). The enhancement of heteroaggregation between BCNPs and IMNPs under unfavorable conditions (acidic pH, HA, and IS) was regulated by the strength of the interaction. Therefore, the enhancement of heteroaggregation of BCNPs-FHNPs was greater than that of BCNPs-MTNPs. In the BCNPs-GTNPs system, the high concentration and elongated structure of GTNPs may contribute greatly to heteroaggregation and settling with small interactions. Our results highlight the influence of pH, IS, and HA on the interaction between BCNPs and IMNPs. These results will be helpful in the application of BCNPs and IMNPs for soil remediation.
The fast increase of population results in the quick development of industry and agriculture. Large amounts of contaminants such as metal ions and organic contaminants are released into the natural environment, posing a risk to human health and causing environment ecosystem problems. The efficient elimination of contaminants from aqueous solutions, photocatalytic degradation of organic pollutants or the in-situ solidification/immobilization of heavy metal ions in solid phases are the most suitable strategies to decontaminate the pollution. Biochar and biochar-based composites have attracted multidisciplinary interests especially in environmental pollution management because of their porous structures, large amounts of functional groups, high adsorption capacities and photocatalysis performance. In this review, the application of biochar and biochar-based composites as adsorbents and/or catalysts for the adsorption of different contaminants, adsorption-photodegradation of organic pollutants, and adsorption-(photo)reduction of metal ions are summarized, and the mechanism was discussed from advanced spectroscopy analysis and DFT calculation in detail. The doping of metal or metal oxides is the main strategy to narrow the band gap, to increase the generation and separation of photogenerated e−-h+ pairs, to produce more superoxide radicals (·O2−) and hydroxyl radicals (·OH), to enhance the visible light absorption and to increase photocatalysis performance, which dominate the photocatalytic degradation of organic pollutants and (photo)reduction of high valent metals to low valent metals. The biochar-based composites are environmentally friendly materials, which are promising candidates in environmental pollution cleanup. The challenge and perspective for biochar-based catalysts are provided in the end.
The addition of biochar could mitigate the bioavailability of heavy metals during livestock manure composting. However, the main action mechanism of biochar, such as how it worked, was ambiguous. Therefore, in this study, materials (biochar, alkali modified biochar, pretreated cotton ball) were added by embedding with nylon mesh bags to explore the adsorption performance of added materials and its influence on the composting process. The results showed that embedded materials promoted the formation of humic acid and reduced the distribution proportion of bioavailable fraction of heavy metals during composting (Cu: at least 15.72%; Zn: at least 33.44%). The surface of biochar extracted from composting contained attachments, however, the attachment of heavy metal was not detected and functional groups on the materials did no change significantly. This indicated that the addition of biochar did not directly adsorb heavy metals. Most notably, the microbial network changed after embedding materials, and the succession of microbial community promoted the formation of humic acid. Ultimately, structural equation models verified that embedded materials promoted the formation of humic acid through stable microbial groups, thereby accelerating the passivation of heavy metals during composting. This study provides theoretical and technical supports for mitigating the biotoxicity of heavy metals by biochar during composting.
Hydrochar (HC) produced by the hydrothermal carbonization (HTC) of typically wet biomass is generally considered to be less effective for carbon (C) sequestration in soils compared to biochar (BC) by pyrolysis, due to a higher content of more easily decomposable C. Although the recalcitrance of HC is suggested to improve with increasing HTC production temperature, the way it interacts and becomes associated with soil organic matter (SOM) fractions of different stabilities against decomposition, may also influence its effectiveness for C sequestration in soils. In that respect, this study aimed to verify the potential of HCs from maize silage produced at different HTC temperatures (190, 210 and 230 °C) for C sequestration in a HC-amended sandy loam Podzol. To do this, we conducted a pot trial experiment and traced the fate of HC-derived C (HC-C) within different SOM fractions, namely the free- and occluded particulate organic matter (POMF and POMO, respectively) fractions and that comprising organic matter (OM) bound to clays (OMCl). Approx. 1 year after applying 5% of the different HTC temperature HCs to the soil, the SOM fractions were isolated by density fractionation for each HC treatment (HC190, HC210 and HC230) and the control (absent of HC). All fractions and the HCs were analyzed for organic C (OC) content and isotopic signatures (δ 13C). From the δ 13C signatures, the amount of HC-C and native soil organic carbon (SOC) within each fraction was calculated. Increased C contents and decreased H/C and O/C ratios were observed with increasing HTC production temperatures, which suggests a lower stability for the low temperature HC. After ca. 1 year, a loss of ~ 20–23% of the bulk soil TOC was found in the HC-amended soils. The POMF fraction of the HC-amended soils showed losses of 68–81% HC-C and 52–72% native SOC, which may be due to a positive priming effect caused by HC addition. The POMO and OMCl fractions of the HC-amended soils contained more OC than the control, indicating the integration of HC-C together with SOM within these more stable fractions, while the effect of HTC production temperature on the level of decomposition of the resultant HCs was negligible. In all HC treatments, the OMCl fraction comprised the least amount of HC-C, thus showing the weakest response to C amendment. In conclusion, long(er)-term research on the C net balance that accounts for the observed priming-induced TOC losses and the HC-C enrichment in more stable fractions is required to verify the potential of the different HCs for the purpose of C sequestration in soils.
| • | Basswood-derived free-standing thick carbon electrodes were developed for supercapacitors. |
| • | The capacitance performance was enhanced by pre-oxidation, solvothermal treatment and KOH activation. |
| • | Supercapacitors assembled from the optimized electrode exhibited good rate performance and stability. |
The development of biochar-based granule-like adsorbents suitable for scaled-up application has been attracting increasing attention in the field of water treatment. Herein, a new formable porous granulated biochar loaded with La-Fe(hydr)oxides/montmorillonite (LaFe/MB) was fabricated via a granulation and pyrolysis process for enhanced phosphorus (P) removal from wastewater. Montmorillonite acted as a binder that increased the size of the granulated biochar, while the use of Fe promoted the surface charge and facilitated the dispersion of La, which was responsible for selective phosphate removal. LaFe/MB exhibited rapid phosphate adsorption kinetics and a high maximum adsorption capacity (Langmuir model, 52.12 mg P g−1), which were better than those of many existing granulated materials. The desorption and recyclability experiments showed that LaFe/MB could be regenerated, and maintained 76.7% of its initial phosphate adsorption capacity after four adsorption cycles. The high hydraulic endurance strength retention rate of the developed material (91.6%) suggested high practical applicability in actual wastewater. Electrostatic attraction, surface precipitation, and inner-sphere complexation via ligand exchange were found to be involved in selective P removal over a wide pH range of 3–9. The thermodynamic parameters were determined, which revealed the feasibility and spontaneity of adsorption. Based on approximate site energy distribution analyses, high distribution frequency contributed to efficient P removal. The research results provide a new insight that LaFe/MB shows great application prospects for advanced phosphate removal from wastewater.
Phosphorus (P) availability, diffusion, and resupply processes can be altered by biochar addition in flooded rice rhizosphere, which controls the risk of P release to the environment. However, there are few in-situ investigations of these rhizospheric processes and effects. To explore the effects of biochar addition on soil P availability, high-resolution dialysis (HR-Peeper), diffusive gradients in thin films (DGT), and zymography techniques were used to provide direct evidence in the rice rhizosphere at the sub-millimeter scale. Long-term (9-years) field and greenhouse pot experiments demonstrated that biochar addition notably decreased the soluble/labile P and Fe concentrations in rice rhizosphere (vs. no biochar addition; CK) based on the results of Peeper, DGT, and two-dimensional imaging of labile P fluxes. DGT-induced fluxes in the soil/sediment (DIFS) model and sediment P release risk index (SPRRI) further indicated that biochar addition decreased the diffusion and resupply capacity of P from soil solid to the solution, thereby decreasing P release risk to the environment. These processes were dominated by Fe redox cycling and the hydrolysis of Al (hydro)oxides that greatly increased the unavailable P (Ca-P and residual-P). Additionally, greenhouse pot experiments (without additional biochar) showed that the previous long-term biochar addition significantly increased soil phosphatase activity, due to an adaptive-enhancing response to P decrease in the rhizosphere zone. The in-situ study on the biogeochemical reactions of P in the rice rhizosphere may provide a new and direct perspective to better evaluate the biochar addition and potential benefits to agricultural soils.
To better understand the amendment effects and mechanisms of aluminum (Al(III)) phytotoxicity mitigation by different regional crop straw biochars, wheat seedling root elongation trials were conducted. The contributions of liming effect, oxygen-containing surface functional group adsorption, and oxyanions precipitation to Al(III) phytotoxicity mitigation by Ca(OH)2, pristine and ash-free canola straw biochar were evaluated. The results indicated that biochars derived from canola straw collected from four different regions (Yingtan, Xuancheng, Nanjing, and Huaiyin) caused 22–70% wheat seedling root elongation, which might be linked to liming effect. Incorporation of the corresponding ash-free biochars caused 15–30% elongation, which could be attributed to the surface functional group adsorption. About 0–60% of changes could be explained by Al(III) precipitation with inorganic oxyanions. These findings provide new insights into the physicochemical properties, potential applications, efficiencies, and underlying mechanisms of crop straw biochar in alleviating Al(III) phytotoxicity, which is dependent on the cultivation soil, and indicate similar application of crop straw biochar for acidic soil amelioration, contaminated soil remediation, and arable soil improvement.
There have been many studies on soil quality and crop yield using different biochar application amounts, but few studies have focused on the combination of different methods and amounts of biochar application in moderately degraded Mollisols. In this study, the methods of mixing biochar evenly with the soil of the plough layer (0–20 cm depth) [homogeneous biochar application (HO)] and burying biochar above the soil plow pan (under 20 cm depth) (heterogeneous biochar application (HE)) were used to reveal how biochar application methods influenced soil quality, crop yield and agronomic characteristics in moderately degraded Mollisols (soil organic matter (SOM), 30.33 g kg−1). The biochar application amounts were 0 (control), 10 (level 1), 20 (level 2), and 40 (level 3) t ha−1 in both the HO and HE treatments. The results showed that, compared with control, HO3 significantly increased maize yield in the first year, and HO2, HO3, HE2 and HE3 continuously increased maize yield in the next three years but not significantly. HO1 and HE1 had the lowest maize yield. HO2 tended to delay maize leaf senescence. There was a positive linear relationship between soil quality index (SQI) and biochar application amount in HO. Compared with other treatments, the pH, EC, SOM, available phosphorus, sucrase and catalase activities were highest in HO3. However, the effects of HE on soil quality and crop productivity were limited at first but gradually increased with time. Overall, HO3 was beneficial for improving the soil quality and crop productivity in Mollisols for short-term cultivation (3-year), while HE showed an effect over time.
Arsenic (As) is recognized as a persistent and toxic contaminant in the environment that is harmful to humans. Biochar, a porous carbonaceous material with tunable functionality, has been used widely as an adsorbent for remediating As-contaminated water and soils. Several types of pristine and modified biochar are available, and significant efforts have been made toward modifying the surface of biochars to increase their adsorption capacity for As. Adsorption capacity is influenced by multiple factors, including biomass pyrolysis temperature, pH, the presence of dissolved organic carbon, surface charge, and the presence of phosphate, silicate, sulfate, and microbial activity. Improved As adsorption in modified biochars is attributed to several mechanisms including surface complexation/precipitation, ion exchange, oxidation, reduction, electrostatic interactions, and surface functional groups that have a relatively higher affinity for As. Modified biochars show promise for As adsorption; however, further research is required to improve the performance of these materials. For example, modified biochars must be eco-friendly, cost-effective, reliable, efficient, and sustainable to ensure their widespread application for immobilizing As in contaminated water and soils. Conducting relevant research to address these issues relies on a thorough understanding of biochar modifications to date. This study presents an in-depth review of pristine and modified biochars, including their production, physicochemical properties, and As adsorption mechanisms. Furthermore, a comprehensive evaluation of biochar applications is provided in As-contaminated environments as a guide for selecting suitable biochars for As removal in the field.
Biochar is a waste-derived material that can sequester carbon at a large scale. The development of low-carbon and sustainable biochar-enhanced construction materials has attracted extensive interest. Biochar, having a porous nature and highly functionalised surface, can provide nucleation sites for chemical reactions and exhibit compatibility with cement, asphalt, and polymer materials. This study critically reviewed the state-of-the-art biochar-enhanced construction materials, including biochar-cement composites, biochar-asphalt composites, biochar-plastic composites, etc. The efficacies and mechanisms of biochar as construction materials were articulated to improve their functional properties. This critical review highlighted the roles of biochar in cement hydration, surface functional groups of engineered biochar for promoting chemical reactions, and value-added merits of biochar-enhanced construction materials (such as humidity regulation, thermal insulation, noise reduction, air/water purification, electromagnetic shielding, and self-sensing). The major properties of biochar are correlated to the features and functionalities of biochar-enhanced construction materials. Further advances in our understanding of biochar’s roles in various composites can foster the next-generation design of carbon–neutral construction materials.
Biochar produced from pyrolysis of biomass has been developed as a platform carbonaceous material that can be used in various applications. The specific surface area (SSA) and functionalities such as N-containing functional groups of biochar are the most significant properties determining the application performance of biochar as a carbon material in various areas, such as removal of pollutants, adsorption of CO2 and H2, catalysis, and energy storage. Producing biochar with preferable SSA and N functional groups is among the frontiers to engineer biochar materials. This study attempted to build machine learning models to predict and optimize specific surface area of biochar (SSA-char), N content of biochar (N-char), and yield of biochar (Yield-char) individually or simultaneously, by using elemental, proximate, and biochemical compositions of biomass and pyrolysis conditions as input variables. The predictions of Yield-char, N-char, and SSA-char were compared by using random forest (RF) and gradient boosting regression (GBR) models. GBR outperformed RF for most predictions. When input parameters included elemental and proximate compositions as well as pyrolysis conditions, the test R2 values for the single-target and multi-target GBR models were 0.90–0.95 except for the two-target prediction of Yield-char and SSA-char which had a test R2 of 0.84 and the three-target prediction model which had a test R2 of 0.81. As indicated by the Pearson correlation coefficient between variables and the feature importance of these GBR models, the top influencing factors toward predicting three targets were specified as follows: pyrolysis temperature, residence time, and fixed carbon for Yield-char; N and ash for N-char; ash and pyrolysis temperature for SSA-char. The effects of these parameters on three targets were different, but the trade-offs of these three were balanced during multi-target ML prediction and optimization. The optimum solutions were then experimentally verified, which opens a new way for designing smart biochar with target properties and oriented application potential.
More technologies are urgently needed for combined use to effectively eliminate the effect of oil spills, an environmental problem of widespread concern. Among these technologies, sorption methods are available to remove residual oil and prevent the further spread on the water surface. In this study, biochars, prepared from different feedstock materials and pyrolysis temperatures, were screened and further modified to improve their application in the water environment. Among cornstalk biochar (CSBC), corncob biochar (CCBC), Sophora sawdust biochar (SSBC), and rice husk biochar (RHBC), the CSBC had excellent oil sorption capacity, especially prepared at 350℃ (CSBC350), which has a complete and full pore structure. Furthermore, magnetic and silane agent modifications of CSBC350 (OMBC) were performed to enhance the properties of the magnetic field controllability and hydrophobicity to increase oil sorption. The OMBC exhibited satisfactory oil sorption capacities to crude oil, diesel oil, and engine oil in the water-oil system of 8.77 g g−1, 4.01 g g−1, and 4.44 g g−1, respectively. The sorption process of CSBC350 and OMBC complied with the pseudo-second-order kinetics (R2 > 0.97) and the Langmuir isotherm models (R2 > 0.80) based on the highest regression coefficients. The sorption mechanisms are dominated by hydrophobic forces, pore intercepts, and hydrogen-bond interactions. The biochar adsorbent can availably cooperate with other physical methods to eliminate oil contaminants, which can be an outstanding fuel source for producing heat.
Biochar from bio-waste pyrolysis presents excellent CO2 sequestration capacity. This study innovated the design of cement-bonded particleboards utilizing a substantial amount of 50–70 wt.% pre-soaked biochar to render the products carbon-negative. We investigated the roles of biochar in magnesium oxysulfate cement (MOSC) system and demonstrated good mechanical and functional properties of biochar cement particleboards. In the presence of biochar, the amounts of hydration products were enriched in the cement systems as illustrated by the thermogravimetric analyses (TGA) and X-ray diffraction (XRD). We further incorporated supplementary cementitious materials (SCMs) and generated 5 Mg(OH)2⋅MgSO4·7H2O (5–1–7) phase in the MOSC system. As a result, our designs of biochar particleboards satisfied the standard requirements for flexural strength (> 5.5 MPa) and thickness swelling (< 2%). Moreover, our biochar particleboards presented a low thermal conductivity as the biochar pores disrupted thermal bridging within particleboards. We illustrated that the high dosage ratio of biochar could significantly offset the CO2 emissions of the particleboards (i.e., carbon-negative) via life cycle assessment. Noticeable economic profits could also be accomplished for the biochar particleboards. For instance, the 50BC-MOSC bonded particleboard (with 50 wt.% pre-soaked biochar as aggregate, 50 wt.% MOSC as binder) with promising mechanical properties could store 137 kg CO2 tonne−1 and yield an overall economic profit of 92 to 116 USD m−3 depending on the carbon prices in different countries. In summary, our new designs of carbon-negative biochar particleboards could curtail carbon emissions in the construction materials and promote the realization of carbon neutrality and circular economy.
Green roofs are exposed to high winds and harsh environmental conditions that can degrade vegetation and erode substrate material, with negative consequences to ecosystem services. Biochar has been promoted as an effective substrate additive to enhance plant performance, but unprocessed biochars are susceptible to wind and water erosion. Applications of granulated biochars or chemical dust suppressants are suggested as a means to mitigate biochar and substrate erosion; however, research on biochar type and chemical dust suppressant use on biochar and substrate erosion is lacking. Vegetation is a crucial factor that influences substrate erosion, yet plant responses may vary with biochar type and chemical dust suppressant; thus, the effects of possible mitigation measures on biochar and substrate erosion are unclear. We investigated the effects of surface-applied granulated and unprocessed biochars and an organic dust suppressant (Entac™) on biochar and substrate erosion on green roofs with Sedum album L. and a native plant mix. Our results show that 94% of unprocessed biochars were lost from green roofs after 2 years regardless of the Entac™ amendment, likely due to the lightweight nature and fragmentation of biochar particles. In contrast, granulation of biochars reduced the biochar erosion and total substrate erosion by 74% and 39%, respectively, possibly due to enhanced biochar bulk density and particle size and improved moisture retention of biochar-amended substrates. Additionally, Sedum album better reduced biochar and substrate erosion than the native plant mix, likely due to rapid development of high vegetation cover that reduced wind exposure and enhanced substrate moisture retention. We conclude that applications of granulated biochars can substantially reduce biochar and substrate erosion on green roofs, improving green roof sustainability.
Anaerobic digestion (AD) has been considered as a promising technique for food waste (FW) recycling. However, the accumulation of volatile fatty acids (VFAs) restricts the stability of anaerobic reactors. The present study investigated the use of biochar produced at different conditions (750 °C-30 min, 750 °C-60 min, 750 °C-120 min, 550 °C-60 min, 650 °C-60 min, 850 °C-60 min, 950 °C-60 min) for enhancing the AD of FW. Batch experiments showed that all the biochar increased the methane production rates and biochar obtained at 750 °C-60 min resulted in the highest enhancement by 21.5%. It was further showed surface oxygen-containing functional groups and graphitization degree of biochar were the critical factors for improving methane production. Microbial analysis showed that biochar addition formed different microbial communities, and Methanosaeta, Romboutsia, and norank_f_Anaerolineaceae were enriched, which might be correlated with direct interspecies electron transfer (DIET). This research showed biochar could enhance the AD of FW and also revealed the main characteristics of biochar relating with the enhancement of AD.
Biochar supported nano-scale zerovalent iron (nZVI/BC) for persulfate (PS) activation has been studied extensively for the degradation of pollutants on the lab scale, but it was rarely applied in practical soil remediation in the field. In this research, we developed a facile ball-milling method for the mass production of nZVI/BC, which was successfully applied to activate persulfate for the remediation of organic polluted soil on an in-situ pilot scale. In-situ high-pressure injection device was developed to inject nZVI/BC suspension and PS solution into the soil with a depth of 0–70 cm. The removal efficiency of target pollutants such as 2-ethylnitrobenzene (ENB, 1.47–1.56 mg/kg), biphenyl (BP, 0.19–0.21 mg/kg), 4-(methylsulfonyl) toluene (MST, 0.32–0.43 mg/kg), and 4-phenylphenol (PP, 1.70–2.46 mg/kg) at different soil depths was 99.7%, 99.1%, 99.9% and 99.7%, respectively, after 360 days of remediation. The application of nZVI/BC significantly increased the degradation rates of contaminants by 11–322%, ascribed to its relatively higher efficiency of free radical generation than that of control groups. In addition, it was found that nZVI/BC-PS inhibited soil urease and sucrase enzyme activities by 1–61% within 55 days due to the oxidative stress for microbes induced by free radicals, while these inhibition effects disappeared with remediation time prolonged (> 127 days). Our research provides a useful implementation case of remediation with nZVI/BC-PS activation and verifies its feasibility in practical contaminated soil remediation.
Numerous studies have reported the potential of silica as a biochar (BC) modifier. However, despite its high silica content, fly ash is rarely used for BC modification. Herein, modified BCs were produced by co-pyrolysis of corn stalks with alkali-fused fly ash (AFFA) at 200 and 600 °C (denoted as AFFA/BC). The Pb(II) adsorption mechanism and adsorption performance were investigated. The AFFA/BC had larger specific surface areas than the pure BC samples (2.54–137 vs. 0.50 m2 g−1) owing to their stable carbon structure. The Pb(II) adsorption capacity of AFFA/BC in water was approximately 6% higher than that of BC owing to the increased cation (Na+) exchange and new bonding sites, such as C–O and Si–O. AFFA/BC exhibited good Pb(II) adsorption performance in high-concentration simulated wastewater (pH 4–6), with a maximum adsorption capacity of 110.29 mg g−1. The Pb(II) adsorption mechanism was in accordance with the pseudo-second-order kinetic and Langmuir isotherm models. At 25 °C and pH 5, the theoretical Pb(II) adsorption capacities of AFFA200/BC and AFFA600/BC were 201.66 and 186.81 mg g−1, respectively, compared to 145.98 mg g−1 of BC. Physical adsorption, precipitation, cation exchange, and complexation were identified as the main Pb(II) adsorption mechanisms through X-ray photoelectron spectrometry.
Graphene-based composite aerogel doped with other low-cost materials can reduce the cost and promote the use in water treatment. This work prepared ball-milled biochar/reduced graphene oxide aerogel (BC/rGA) using GO and low-cost ball-milled biochar (BC) in a certain proportion with the freeze-thawing technique and sol–gel method, and applied BC/rGA on the Cr(VI) removal from aquatic environments. The characterization results showed that aerogel had a honeycomb briquette three-dimension (3D) and mesoporous structure with interconnected pores, and proved the preparation progress of aerogel in principle. Compared with GO, rGA and BC/rGA had better adsorption performance with 3D structure and well-developed pores, and BC/rGA with the mixture ratio of BC and GO of 1:4 was more appropriate. The adsorption kinetics data of rGA and BC/rGA(1:4) were fitting well with the pseudo-second-order model (R2 > 0.951), and the isotherm adsorption results were fitting the Langmuir model well (R2 > 0.974). The results demonstrated that the adsorption process was monolayer and endothermic adsorption involving chemisorption. Additionally, the adsorption capacities of rGA and BC/rGA(1:4) at solution pH 2 were 3.71 and 3.89 times greater than those at solution pH 8, respectively. High background ion strength and low temperature slightly inhibited the adsorption of Cr(VI) by both rGA and BC/rGA(1:4). The adsorption mechanisms of Cr(VI) on rGA and BC/rGA(1:4) were electrostatic interaction, reduction and ion exchange. The use of BC/rGA could reduce the cost and promote the green reuse of agricultural waste. Overall, BC/rGA could be used as a promising green adsorbent alternative for the feasible treatment of heavy metal contaminated water.
Biochar amendment of soil may ameliorate inherently infertile soils, such as in the typical coconut (Cocos nucifera L.) growth areas along tropical coasts, where, moreover, temporary moisture stress commonly occurs. We conducted a pot experiment to evaluate the effects of biochar soil amendment (1% w/w) produced from Gliricidia sepium stems (BC-Gly) and rice husks (BC-RiH) on the growth of coconut seedlings and on N and P uptake mediated by mycorrhizae under wet or dry conditions in a Sandy Regosol. The pots were divided into root and hyphal zones by a nylon mesh, where 15N labelled N and P nutrients were only provided in the hyphal zone. Under wet conditions, biochar application did not affect plant growth, while under dry conditions, the BC-Gly increased root and plant growth similar to that under wet conditions. BC-Gly increased the acidic pH of the soil to a neutral level, and the microbial community shifted towards a higher fungal abundance. The P accumulated (Pacc) in roots was higher with BC-Gly and BC-RiH under dry and wet conditions, respectively. Pacc weakly correlated with the abundance of arbuscular mycorrhizal fungi (AMF) in the hyphal zone. With BC-Gly roots showed lower N derived from fertilizer. We conclude that biochar application has no impact on crop growth under wet conditions, while under dry conditions, BC-Gly stimulates crop growth and P uptake, probably through liming induced P availability but also possibly by some enhancement of AMF growth. The shift in the fungal-oriented microbial community and reduced plant fertilizer N uptake suggested that BC-Gly acted as an additional N source.
Co-contamination of groundwater with trichloroethene (TCE) and arsenic (As) is a widespread problem in industrial sites. The simultaneous biological removal of As and TCE has not yet been developed. This study incorporated biochar into anaerobic dechlorination system to achieve a greatly accelerated dissipation and co-removal of TCE and As. Biochar eliminated microbial lag (6 days) and achieved a 100% TCE removal within 12 days even at a relatively high initial concentration (TCE: 30 mg L−1; As(V): 4 mg L−1), while without biochar, only 75% TCE was removed until day 18. Biochar adsorbed TCE and the intermediate products allowing them to be degraded on its surface gradually, maintaining a high metabolic activity of microbes. Biochar facilitated the preferential colonization of its surfaces by dechlorinating microorganisms (Clostridium and Dehalococcoides) and suppressed hydrogen-competing microorganisms (Desulfovibrio) in water. Biochar itself cannot adsorb As, however, separation of biochar carrying the As-laden microorganisms achieved 50–70% As-removal from groundwater. The biochar-amended incubations were found to be enriched with microbes possessing more crucial As-transforming genes (K00537-arsC and K07755-AS3MT), and upregulated amino acid metabolism, thus enhancing the self-detoxification ability of microorganisms to transform As(V) to As(III) or volatile organic As. This study proposes a strategy of regulating microbes’ metabolic activity by biochar to achieve simultaneous removal of coexisting contaminations, which is an important step prior to examining the feasibility of biochar application for enhanced bioremediation.
Sewage sludge (SS) is a residual/semi-solid material produced from industrial and municipal wastewater treatment processes. SS contains a high content of lipids and earth alkaline metals that can be used as catalysts for various chemical applications; however, its valorization has rarely been the focus of research. This study demonstrates that SS could be a promising raw material for biodiesel production and a biochar catalyst to promote the reaction kinetics of alkylation. Thermally induced transesterification of the SS extract (SSE) was performed in comparison with the conventional homogeneous reaction. SS biochar was fabricated via pyrolysis. The highest yield (33.5 wt.% per SSE) of biodiesel production was achieved in 1 min of reaction at 305 °C via thermally induced transesterification in the presence of SS biochar, while the yield of biodiesel from (trans)esterification with 5 wt.% H2SO4 was less than 1% even after 24 h. The reaction kinetics (< 1 min) of thermally induced transesterification was extraordinarily faster than that of conventional transesterification (3–24 h). The porous structure and high content of alkaline species in the SS biochar expedited the reaction kinetics. Consequently, the integrated/hybridized process for thermally induced transesterification and pyrolysis of the solid residue of SS was experimentally proved for the valorization of SS in this study. Considering that SS is being disposed of as a waste material and generates toxic chemicals in the environment, its valorization into value-added biodiesel and a catalyst could be an environmentally benign and sustainable technique.
Biochar applications have an enormous impact on the soil microbial community and functionality. However, the majority of the knowledge on biochar–microbe interaction derives almost exclusively from bacterial and fungal studies, while the vast majority of eukaryotic diversity, protists, are mostly neglected. Protists play important roles in the soil ecosystem as microbial predators, decomposers, photoautotrophs, pathogens, and parasites and they are essential for a healthy soil ecosystem. Toward a comprehensive understanding of the effects of biochar application, we need more studies on protists across the full breadth of eukaryotic diversity. The aim of this article is to highlight the research needs and discuss potential research ideas on biochar–protist interaction, which would advance our knowledge of biochar–microbe interaction.
| • | Biochar–microbe interaction is almost exclusively studied for bacteria and fungi. |
| • | Only a few studies are available on how soil protists react to biochar application. |
| • | More research on biochar–protist is needed for a better understanding of biochar–microbe interaction. |
Biochar (BC)-supported graphene-encapsulated zero-valent iron nanoparticle composites (BC-G@Fe0) are promising engineering nanocomposites that can be used to scavenge heavy metal from wastewater. However, the production of BC-G@Fe0 through carbothermal reduction using biomass as a carbon source remains challenging because of biomass pyrolysis complications. Here, we examined two carbothermal reduction routes for preparing BC-G@Fe0 using bamboo as the carbon source. The first route impregnated Fe ions (Fe2+/3+) into unpyrolyzed bamboo particles initially, followed by carbonization at 600–1000 °C. This process produced BC-G@Fe0 dominated by iron carbide (Fe3C), which led to low heavy metal removal efficiency (i.e., Cu2+ capacity of < 0.3 mmol g−1). In the second route, bamboo particles were pyrolyzed (600 °C) to biochar first, followed by impregnating this biochar with Fe ions, and then carbonized at 600–1000 °C. This route produces zero-valent iron nanoparticles, which resulted in high heavy metal removal capacities (i.e., 0.30, 1.58, and 1.91 mmol g−1 for Pb2+, Cu2+, and Ag+, respectively). The effects of carbonization temperature (600–1000 °C), iron source (i.e., iron nitrates, iron sulfate, ferrous chloride, and ferric chloride), and iron loading (5–40%) on the morphology, structure, and heavy metal ion aqueous uptake performance of BC-G@Fe0 were also investigated. This study revealed the formation mechanisms of BC-G@Fe0 through biomass carbothermal reduction, which could guide the application-oriented design of multifunctional iron-BC composites for water remediation.
Hydrogen sulfide (H2S) removal has been a significant concern in various industries. In this study, food waste digestate-derived biochar (DFW-BC), a by-product of food waste treatment with abundant minerals, was assessed for removing H2S from different simulated biogas containing oxygen (O2) and carbon dioxide (CO2) and under different moisture (H2O) contents (0% and 20%) of biochar. The influencing mechanisms of the gas conditions combined with the moisture contents were also investigated. The results showed an H2S removal of 1.75 mg g−1 for dry biochar under pure H2S, 4.29 mg g−1 for dry biochar under H2S + O2, 5.29 mg g−1 for humid biochar under H2S, and 12.50 mg g−1 for humid biochar under H2S + O2. For dry DFW-BC, the high Fe content was responsible for the O2 enhancement. In contrast, O2 + H2O activated the catalytic H2S oxidation of the less reactive minerals (mainly Ca). The inhibition of CO2 on H2S adsorption was not obvious for dry DFW-BC; the specific pore structure may have provided a buffer against the physisorption competition of CO2. However, when H2O was present on DFW-BC, the changes in critical biochar properties and sulfur speciation as opposed to that without H2O implied an evident occurrence of CO2 chemisorption. This CO2 chemisorption partially hindered O2 + H2O enhancement, decreasing the H2S removal capacity from 12.50 to 8.88 mg g−1. The negative effect was ascribed to mineral carbonation of CO2, neutralizing the alkaline surface and immobilizing metal oxides, which thus reduced the acceleration in H2S dissociation and activation in catalytic H2S oxidation by O2 + H2O.