The development of biochar has triggered a hot-spot in various research fields including agriculture, energy, environment, and materials. Biochar-based materials provide a novel approach against environmental challenging issues. Considering the rapid development of biochar materials, this review serves as a valuable platform to summarize the recent progress on the theoretical investigation and engineering applications of biochar materials in environmental remediation. For a better understanding of the structure–application relationships, the structural properties of biochar from macroscopic and microscopic aspects are summarized. The multilevel structures including elements, phases, surface chemistry, and molecular are highlighted to elucidate the multi-functional properties of biochars. Sorption, catalysis, redox reaction, and biological activity of biochar are briefly illustrated, which influence the transport, transformation, and removal of organic and inorganic pollutants in the environments. According to the multi-level structures and structure–application relationships of biochar, specific biochar-based materials and devices have been designed for practical environmental application. The important progress on the functionalization and device of biochar-based materials, including magnetic biochars, 2D and 3D biochar-based macrostructures, immobilized microorganism on biochar, and biochar-amended biofilters are highlighted. The environmental friendliness and sustainability of biochar-based materials, considering the whole cycle from synthesis to application, are evaluated.
Thallium (Tl) is an extremely harmful metal that is substantially distributed in the environment. It can threaten human health via consumption of food potentially derived from Tl-contaminated agricultural production. Little information is available on how to utilize biochar to remediate Tl contamination in agricultural soils. More efforts are urgently needed to be devoted to developing effective techniques to empower biochar with high selectivity of Tl in agricultural soils. In this review, we provided comprehensive information on Tl contamination in agricultural soils. We also discussed recent developments and assessed the current status of biochar applications. We briefly reviewed the bridge between biochar preparation technology and utilization wherein further developments can exhibit potential in terms of Tl remediation. Hence, biochar is expected to exhibit excellent Tl remediation performance in contaminated agricultural soils with promising application prospects. The obtained knowledge provides further insights into the remediation of Tl contamination in agricultural soils.
Biochar have received multidisciplinary attention because of their extraordinary physicochemical properties. In this review, the application of biochar and biochar-based materials for the efficient elimination of organic and inorganic pollutants are summarized. The sorption of organic chemicals and heavy metal ions/radionuclides, degradation/transformation of organic pollutants, and sorption–reduction–solidification of high-valent metal ions are described in detail. The interaction mechanism at molecular level from advanced spectroscopic techniques and theoretical calculations is discussed. Finally, the challenges in the application of biochar and biochar-supported materials in the immobilization of heavy metal ions and photocatalytic degradation of persistent organic pollutants in soils or wastewater are pointed out. This review is helpful for the graduate students to understand the recent works about biochar and biochar-supported materials in environmental pollutants management.
Biochar application to soil has been proposed as a potential management strategy to enhance soil carbon (C) sequestration, reduce greenhouse gas emission, improve soil quality, and increase crop productivity. The effects of biochar on soil microbial and enzyme activities are integrally linked to the potential of biochar in achieving these benefits. We conducted a global meta-analysis to assess the effects of biochar on soil microbial biomass C and nitrogen (N) and the activities of 12 enzymes, and identify key factors affecting those soil microbial properties using 964 data points from 72 papers. We found that biochar effects on enzyme activities vary widely with soil type, biochar property and the type of enzyme studied. Biochar significantly increased microbial biomass C (MBC) and urease, alkaline phosphatase and dehydrogenase activities by 21.7%, 23.1%, 25.4% and 19.8%, respectively, with no significant negative effects on any of the enzymes analyzed in this study. Biochar application was more effective in increasing MBC and enzyme activities in soils with low pH (< 6.5), TC (< 20 g kg−1), TN (< 2 g kg−1), and a fine texture (including clay, clay loam and silt clay). Biochars produced at pyrolysis temperature of 350–550 °C with a high pH (> 10) and low C/N ratio (< 50) increased MBC and urease and dehydrogenase activities. Biochar increased MBC and N-acquisition enzyme activities in the field but not in lab incubation experiments. Urease was increased in short-term studies (within 100 days of biochar application) while alkaline phosphatase was increased in long-term studies that span more than 1 year. The increase in MBC and activities of some soil enzymes in response to biochar application with no negative effects on any hydrolytic and oxidative enzymes illustrate its potential to enhance soil quality particularly in the degraded soils with low nutrient availability and fertility due to limited soil microbial and enzymatic activities. This study also shows that biochars can be designed to achieve specific properties for enhancing microbial and enzymatic activities for specific soils.
A novel α-FeOOH modified wheat straw biochar (α-FeOOH@BC) was developed and the findings of the current study showed that α-FeOOH@BC is an efficient material for the simultaneous removal of cations (Cd(II)) and anions (As(III)) from aqueous solutions. The SEM, FTIR, and XRD analysis proved that α-FeOOH@BC was covered by α-FeOOH. In the single adsorption system, the maximum adsorption capacities of α-FeOOH@BC for Cd(II) and As(III) were 62.9 and 78.3 mg/g, respectively. In the dual adsorption system, the maximum adsorption capacities of α-FeOOH@BC for Cd(II) and As(III) dropped to 39.3 and 67.2 mg/g, respectively. The adsorption capacities of Cd(II) and As(III) by α-FeOOH@BC were much higher by BC and α-FeOOH both in single and dual adsorbate system. The adsorption results were well fitted by the Langmuir and pseudo-second-order kinetics models. The Cd(II) and As(III) co-adsorption on α-FeOOH@BC had a competitive effect, and the dominant adsorption mechanisms were co-precipitation and ion exchange. Our study showed that α-FeOOH@BC could be an effective remediation material for Cd(II) and As(III) co-adsorption from aqueous environment.
Meta-analyses have shown that only about half of biochar addition studies report improved plant growth. To improve yield response, here we describe a decision support tool (DST) for selecting a biochar type and amendment rate to meet soil and crop management goals, based on soil and biochar tests values and crop requirements as reported by regional extension recommendations. Using data from a greenhouse wheat trial, we assessed whether this approach could predict changes in soil chemistry and whether it could identify soils in which amendment would stimulate crop yield. These data indicated that the DST could provide semi-quantitative predictions of biochar amendment rates needed to meet target soil pH levels, with recommended rates averaging 25% higher than were needed. The DST was better at predicting biochar application rates to provision P and K. Across six soil types, post-harvest measurements of extractable-K showed an average 104% recovery of the quantities estimated to be provisioned by conifer wood or wheat straw biochars. Extractable-P recovery averaged 101% in two sandy soils with low P-retention but was considerably lower in four soils with higher P-retention capacity. Greenhouse data also showed that wheat growth improved only when biochar alleviated pH that was substantially below critical thresholds for plant growth, and supported the principle of using crop-specific pH requirements as part of an approach for biochar decision-support. Future field trials that evaluate yield responses in several nutrient-deficient or acidified soils will be needed to provide a robust evaluation of this DST.
Salinity and acidity have affected several hundred million hectares of land throughout the globe which poses a major threat to global food security and biodiversity. Application of organic amendments for salt-affected soils has been identified as one of the most effective ways to mitigate salinity-induced problems and considered as a green technique offering twin benefits of waste load reduction and land reclamation. However, studies on reclaiming acidic-salt affected soils are limited. Therefore, this study aimed to determine the reclamation potential of biochars and organic amendments involving Gliricidia sepium biochar produced at 300 °C, 500 °C, and 700 °C, green waste compost, and municipal sewage sludge at three different amendment ratios, 1.0%, 2.5% and 5.0%. The incubation experiment was conducted for a 4-month period with different amendment ratios applied to the coastal acidic-salt affected soil. Subsamples were extracted from incubation pots after 1 and 4 months and analyzed for soil chemical parameters (pH, EC, NO3−, PO43−, total organic carbon, cation exchange capacity, sodium adsorption ratio, exchangeable sodium percentage) and microbial enzyme activity (catalase activity, and acid- and alkaline phosphatase activity). All organic amendments demonstrated enhancement of the soil properties in a significant manner. However, increasing incubation time and amendment ratio increase the changes of soil parameters by a great percentage. Therefore, the maximum amendment ratio of 5.0% and 4 months of incubation period rendered a significant improvement in the reclamation of acidic-salt affected soil. However, the biochar produced at 500 °C contributed the maximum towards the improved physicochemical and biochemical profile of acidic-salt affected soil, making it the most promising organic amendment for the reclamation of acidic-salt affected soil. The overall reclamation efficiency of organic amendments registered the following order of variation: 700 BC < Sludge < 300 BC < Compost < 500 BC.
Various materials have been extensively investigated to mimic the structures and functions of natural enzymes. We describe the discovery of a new catalytic property in the group of biochar-based carbonaceous materials, which are usually produced during biowaste thermal processing under specific conditions. The tested biochars exhibited peroxidase-like catalytic activity. Biomaterial feedstock, pyrolysis temperature, size of resulting biochar particles or biochar modification (e.g., magnetic particles deposition) influenced the peroxidase-like activity. Catalytic activity was measured with the chromogenic organic substrates N,N-diethyl-p-phenylenediamine (DPD) or 3,3′,5,5′-tetramethylbenzidine (TMB), in the presence of hydrogen peroxide. Magnetic biochar composite was studied as a complementary material, in which the presence of iron oxide particles enhances catalytic activity and enables smart magnetic separation of catalyst even from complex mixtures. The activity of the selected biochar had an optimum at pH 4 and temperature 32 °C; biochar catalyst can be reused ten times without the loss of activity. Using DPD as a substrate, Km values for native wood chip biochar and its magnetic derivative were 220 ± 5 μmol L−1 and 690 ± 80 μmol L−1, respectively, while Vmax values were 10.1 ± 0.3 μmol L−1 min−1 and 16.1 ± 0.4 μmol L−1 min−1, respectively. Biochar catalytic activity enabled the decolorization of crystal violet both in the model solution and the fish pond water containing suspended solids and dissolved organic matter. The observed biochar enzyme mimetic activity can thus find interesting applications in environmental technology for the degradation of selected xenobiotics. In general, this property predestines the low-cost biochar to be a perspective supplement or even substitution of common peroxidases in practical applications.