Compositions and sorptive properties of crop residue-derived chars

Remediation of cadmium contaminated water and soil using vinegar residue biochar

This study investigated a new biochar produced from vinegar residue that could be used to remediate cadmium (Cd)-contaminated water and soil. Aqueous solution adsorption and soil incubation experiments were performed to investigate whether a biochar prepared at 700 °C from vinegar residue could efficiently adsorb and/or stabilize Cd in water and soil. In the aqueous solution adsorption experiment, the Cd adsorption process was best fitted by the pseudo-second-order kinetic and Freundlich isotherm models. If the optimum parameters were used, i.e., pH 5 or higher, a biochar dosage of 12 g L^-1, a 10 mg L^-1 Cd initial concentration, and 15-min equilibrium time, at 25 °C, then Cd removal could reach about 100%. The soil incubation experiment evaluated the biochar effects at four different application rates (1, 2, 5, and 10% w/w) and three Cd contamination rates (0.5, 1, and 2.5 mg kg^-1) on soil properties and Cd fractionation. Soil pH and organic matter increased after adding biochar, especially at the 10% application rate. At Cd pollution levels of 1.0 or 2.5 mg kg^-1, a 10% biochar application rate was most effective. At 0.5 mg Cd kg^-1 soil, a 5% biochar application rate was most efficient at transforming the acid extractable and easily reducible Cd fractions to oxidizable and residual Cd. The results from this study demonstrated that biochar made from vinegar residue could be a new and promising alternative biomass-derived material for Cd remediation in water and soil.

Pine sawdust biomass and biochars at different pyrolysis temperatures change soil redox processes

To date, no investigation has been carried out to explore the effects of biochars produced at different pyrolysis temperatures on the dynamics of redox potential (E_H) and pH in a contaminated floodplain soil. Thus, we aimed to quantify the dynamics of E_H and pH in contaminated flooded soils treated with 70tha^-1 of pine sawdust biomass (S&BM) and biochars pyrolyzed at 300°C (S&BC300) and 550°C (S&BC550) and pre-incubated for 105days in an automated biogeochemical microcosm system. Microbial community composition was also determined via analyzing phospholipid fatty acid (PLFA).We found that BC300 and BC550 treatments substantially decreased (3-6.5%) and BM increased (~37%) the mean of soil E_H compared to the untreated contaminated soil (CS).·The largest E_H decline in S&BC550 was at the rate of -80mVh^-1 at 10h while it was observed at 25h in S&BC300 and 20-25h in S&BM or CS, respectively. At high E_H, a higher total PLFA biomass and microbial groups in the CS (71-87%) were found in comparison to treated soils. Higher aromaticity and ash content in BC550 than BC300 and BM led to the greater PLFA biomass and microbial groups which contributed to higher capacity of accepting and donating electrons in soil slurry and were probably one reason for the largest decrease in E_H. Pine sawdust biomass and BCs have a noticeable influence in soil biogeochemical processes relevant to fluctuating redox conditions.

Influence of potassium hydroxide activation on characteristics and environmental risk of heavy metals in chars derived from municipal sewage sludge

To investigate the influence of KOH activation on characteristics and environmental risk of heavy metals in chars, sludge was pyrolyzed with varying amount of KOH. The analyzation of characteristics and potential ecological risk evaluation of heavy metals were conducted by surface area analyzer, FTIR, XRD and BCR sequential extraction. The activated chars have higher surface area and lower content of silica compared to those without being activated. The activation of KOH promoted residual fraction of Cd, meanwhile, Zinc, Cr, Ni and Mn were converted to relatively unstable fractions (F2 and F3). The results of risk assessment indicated that the potential ecological risk level of Cd was reduced in activated chars, while risk level of Zn, Cr, Ni and Mn were increased after pyrolysis with KOH activation. The potential ecological risk of heavy metals in activated chars was further declined, and the risk level transformed from moderate to low.

Comparison of carbonized materials from wastes of different origin for nonylphenol removal by adsorption

The application of carbonized materials (CMs) from solid wastes for the control of hydrophobic organic contaminants is a promising way to treat wastes. In this paper, the physicochemical properties of CMs prepared from industry (fly ash and sewage sludge), plant (rice straw and bamboo fragments), and livestock (chicken manure) were analyzed, their adsorption capacities for nonylphenol were studied, and the relationship between the adsorption capacity and the physicochemical properties of different types of CMs was investigated. The results showed that the adsorption capacities of CMs prepared from plant solid wastes (rice straw and bamboo fragments) far exceeded those of the industrial and livestock solid wastes. The parameter K_f obtained by the Freundlich model showed a significant and positive correlation with carbon content (C%), carboxyl content, specific surface area (SSA), and pore volume, and a negative correlation with ash content (ash%). Compared with CMs produced by the other two types of solid wastes, CMs from the plant solid wastes had the characteristics of a large SSA, rich pore structure (especially mesoporous) and high aromaticity (high C%), which were the main reasons for their superior adsorption capacity. The results could provide a scientific basis for the utilization of solid wastes.

Kinetic and isothermal adsorption-desorption of PAEs on biochars: effect of biomass feedstock, pyrolysis temperature, and mechanism implication of desorption hysteresis

Biochar has the potential to sequester biomass carbon efficiently into land, simultaneously while improving soil fertility and crop production. Biochar has also attracted attention as a potential sorbent for good performance on adsorption and immobilization of many organic pollutants such as phthalic acid esters (PAEs), a typical plasticizer in plastic and presenting a current environmental issue. Due to lack of investigation on the kinetic and thermodynamic adsorption-desorption of PAEs on biochar, we systematically assessed adsorption-desorption for two typical PAEs, dimethyl phthalate (DMP) and diethyl phthalate (DEP), using biochar derived from peanut hull and wheat straw at different pyrolysis temperatures (450, 550, and 650 °C). The aromaticity and specific surface area of biochars increased with the pyrolysis temperature, whereas the total amount of surface functional groups decreased. The quasi-second-order kinetic model could better describe the adsorption of DMP/DEP, and the adsorption capacity of wheat straw biochars was higher than that of peanut hull biochars, owing to the O-bearing functional groups of organic matter on exposed minerals within the biochars. The thermodynamic analysis showed that DMP/DEP adsorption on biochar is physically spontaneous and endothermic. The isothermal desorption and thermodynamic index of irreversibility indicated that DMP/DEP is stably adsorbed. Sorption of PAEs on biochar and the mechanism of desorption hysteresis provide insights relevant not only to the mitigation of plasticizer mobility but also to inform on the effect of biochar amendment on geochemical behavior of organic pollutants in the water and soil.

Incorporation of corn straw biochar inhibited the re-acidification of four acidic soils derived from different parent materials

The effect of corn straw biochar on inhibiting the re-acidification of acid soils derived from different parent materials due to increased soil pH buffering capacity (pHBC) was investigated using indoor incubation and simulated acidification experiments. The incorporation of the biochar increased the pHBC of all four soils due to the increase in soil cation exchange capacity (CEC). When 5% biochar was incorporated, the pHBC was increased by 62, 27, 32, and 24% for the Ultisols derived from Tertiary red sandstone, Quaternary red earth, granite, and the Oxisol derived from basalt, respectively. Ca(OH)₂ and the biochar were added to adjust the soil pH to the same values, and then HNO₃ was added to acidify these amended soils. The results of this simulated acidification indicated that the decrease in soil pH induced by HNO₃ was lower for the treatments with the biochar added than that of the treatments with Ca(OH)₂ added. Consequently, the biochar could inhibit the re-acidification of the amended acid soils due to the increased resistance of the soils to acidification when the pH of amended soil was higher than 5.5. The inhibiting effectiveness of the biochar on soil re-acidification was greater in the Ultisol derived from Tertiary red sandstone due to its lower clay and organic matter contents and CEC than the other three soils. The incorporation of the biochar also decreased the potentially reactive Al, i.e., exchangeable Al, organically bound Al, and sorbed hydroxyl Al, compared with the treatments amended with Ca(OH)₂. Therefore, the incorporation of corn straw biochar not only inhibited the re-acidification of amended acid soils through increasing their resistance to acidification but also decreased the potential of Al toxicity generated during re-acidification.

UV modification of biochar for enhanced hexavalent chromium removal from aqueous solution

This study was conducted to understand the effects of ultraviolet (UV) irradiation on the physicochemical properties and the hexavalent chromium (Cr(VI)) removal ability of biochar. Structural and morphological analysis showed that UV irradiation increased the specific surface area of biochar and added a large amount of oxygen-containing functional groups (e.g., carboxyl, lactonic, and hydroxyl) to biochar's surface. Batch sorption experimental results showed that UV-modified biochar (UVBC) produced at the pyrolysis temperature of 300 °C, the irradiated time of 24 h, and the irradiation distance of 40 mm exhibited excellent Cr(VI) removal ability (from 1.11 mg/g for BC to 20.04 mg/g for UVBC, a 18.1-fold increase). The adsorption kinetics and adsorption isotherm data agreed well with the pseudo-second-order model and Freundlich model, respectively. Experimental and modeling results suggest that the oxygen-containing functional groups and specific surface areas of biochars were notably increased by UV irradiation, which enhanced Cr(VI) adsorption by surface complexation. X-ray photoelectron spectroscopy (XPS) analysis of UVBC before and after reaction with Cr(VI) showed that reduction occurred during Cr(VI) adsorption. The energy consumption of UV modification is 2.7 MJ per gram of UVBC produced, which is comparable to that in activated carbon. The results showed that the method of UV modification of biochar is a very novel and effective method for the adsorption of Cr(VI) in solution.

Comprehensive Adsorption Studies of Doxycycline and Ciprofloxacin Antibiotics by Biochars Prepared at Different Temperatures

This paper comparatively investigated the removal efficiency and mechanisms of rice straw biochars prepared under three pyrolytic temperatures for two kinds of tetracycline and quinolone antibiotics (doxycycline and ciprofloxacin). The influencing factors of antibiotic adsorption (including biochar dosage, pH, background electrolytes, humic acid, initial antibiotics concentration, contact time, and temperature) were comprehensively studied. The results suggest that biochars produced at high-temperature [i.e., 700°C (BC700)], have higher adsorption capacity for the two antibiotics than low-temperature (i.e., 300-500°C) biochars (BC300 and BC500). Higher surface area gives rise to greater volume of micropores and mesopores, and higher graphitic surfaces of the BC700 contributed to its higher functionality. The maximum adsorption capacity was found to be in the following order: DOX > CIP. The π-π EDA interaction and hydrogen bonding might be the predominant adsorption mechanisms. Findings in this study highlight the important roles of high-temperature biochars in controlling the contamination of tetracycline and quinolone antibiotics in the environment.

Peanut straw biochar increases the resistance of two Ultisols derived from different parent materials to acidification: A mechanism study

The mechanisms for increasing soil pH buffering capacity (pHBC) and soil resistance to acidification by peanut straw biochar were investigated by undertaking indoor incubation and simulated acidification experiments using two Ultisols derived from tertiary red sandstone and quaternary red earth. The biochar increased the pHBC and resistance of the two Ultisols to acidification. The addition of 3% biochar increased the pHBC of the two Ultisols by 76% and 25%, respectively. The increased resistance of the soils to acidification led to the inhibition to decrease in soil pH and the activation of soil Al during acidification. The protonation of carboxyl groups on the biochar surface was the main mechanism responsible for resisting acidification of the Ultisols when the pH was between 4.5 and 7.0. The higher soil pH (>6.0) after biochar application and the large number of carboxyl groups on the biochar surface were essential if biochar was to significantly increase the resistance of soils to acidification.

Preparation of biochar from Enteromorpha prolifera and its use for the removal of polycyclic aromatic hydrocarbons (PAHs) from aqueous solution

EP-biochar was produced from Enteromorpha prolifera (EP) at temperatures of 200-600°C under limited-oxygen conditions and then activated using HCl and HF. To optimize the sorption of pyrene (PYR) and benzo[a]pyrene (BaP), the effect of the pyrolysis temperature was studied, and the results showed that EP-biochar produced at 500°C gave the highest removal efficiency. The physiochemical properties of EP-biochar pyrolyzed at 500°C were characterized. The examination indicated that the surface area of EP-biochar was 205.32m²/g. The effect of the EP-biochar dosage and initial solution pH on the adsorption were studied in batch adsorption experiments. Kinetic studies indicated that the adsorption processes of PYR and BaP agreed well with a pseudo second-order kinetic model. The sorption equilibrium data were well described by the Langmuir model. Desorption experiments were conducted to test the strength of binding interactions of EP-biochar. The results showed that PYR and BaP were difficult to dissolve in water after adsorption. Regeneration experiments demonstrated that the biochars regenerated at 200°C retained approximately 48% and 40% of their initial PYR and BaP uptake.

Phosphorus-loaded biochar changes soil heavy metals availability and uptake potential of maize (Zea mays L.) plants

Biochar (BC) was produced by pyrolyzing the date palm leaf waste at 600 °C and then loaded with phosphorus (P) via sorption process. Greenhouse pot experiment was conducted to investigate the application effects of BC and P-loaded biochar (BCP) on growth and availability of P and heavy metals to maize (Zea mays L.) plants grown in contaminated mining soil. The treatments consisted of BC and BCP (at application rates of 5, 10, 20, and 30 g kg^-1 of soil), recommended NK and NPK, and a control (no amendment). Sorption experiment showed that Langmuir predicted maximum P sorption capacity of BC was 13.71 mg g^-1. Applying BCP increased the soil available P, while BC and BCP significantly decreased the soil labile heavy metals compared to control. Likewise, heavy metals in exchangeable and reducible fractions were transformed to more stable fraction with BC and BCP applications. The highest application rate of BCP (3%) was most effective treatment in enhancing plant growth parameters (shoot and root lengths and dry matter) and uptake of P and heavy metals by 2-3 folds. However, based on metal uptake and phytoextraction indices, total heavy metals extraction by maize plants was very small for practical application. It could be concluded that using P-loaded biochar as a soil additive may be considered a promising tool to immobilize heavy metals in contaminated mining areas, while positive effects on the biomass growth of plants may assist the stabilization of contaminated areas affected by wind and water erosion.

Engineered/designer biochar for the removal of phosphate in water and wastewater

During the past decade, biochar has attracted immense scientific interest for agricultural and environmental applications. A broad range of biochars with advantageous properties (e.g., high surface area, flexible architecture, and high porosity) has been developed for pollution abatement. Nevertheless, biochar suffers from certain drawbacks (e.g., limited sorption capacity for anions and poor mechanical properties) that limit their practical applicability. This review focuses on recent advancements in biochar technology, especially with respect to its technical aspects, the variables associated with removing phosphates from water, and the challenges for such abatement. The attention paid to the specific remediation of phosphate from water using biochar is limited (n=1114 - Scopus) compared to the application of biochar to other common water pollutants (n=3998 - Scopus). The subject warrants immediate rigorous research because of the undesirable effects of excess phosphate in water bodies. This review will thus facilitate the construction of a roadmap for further developments and the expansion of this challenging area of research.

Quantification and characterization of chemically-and thermally-labile and recalcitrant biochar fractions

The C:N ratios of biochar labile fractions is important for assessing biochar stability and N cycling in soil. Here we compare chemically and thermally labile fractions for nine biochars produced from five biomass feedstocks using four production techniques. Biochar fractionation methods included proximate analysis, hot water extraction, acid and base extractions (0.05 M, 0.5 M, 1 M, 2 M, 3 M, and 6 M of either H₂SO₄ or NaOH), and oxidation with 15% H₂O₂ and 0.33 M KMnO₄ (pH 7.2). Results show chemical addition reactions cause underestimation of mass of the labile fraction for chemical extraction and oxidation procedures but not the thermal procedure. Estimates of C and N in labile and recalcitrant fractions were not adversely affected by addition reactions, because solvents were independent of C or N. Results indicate that herbaceous biochars may be a source of N fertility while hardwood biochars may immobilize N during the first few years after biochar application to soils.

Response surface methodology optimization for sorption of malachite green dye on sugarcane bagasse biochar and evaluating the residual dye for phyto and cytogenotoxicity

In the present study, sorption and detoxification of malachite green (MG) dye was executed using biochar resulting after pyrolysis of agro-industrial waste at 400, 600 and 800 °C. Maximum sorption of MG dye (3000 mg/L) was observed on the sugarcane bagasse biochar (SCB) prepared at 800 °C. The interactive effects of different factors like dye concentration, time, pH and temperature on sorption of MG dye were investigated using response surface methodology (RSM). Optimum MG dye concentration, contact time, temperature and pH predicted through Box-Behnken based RSM model were 3000 mg/L MG dye, 51.89 min, 60 °C and 7.5, respectively. ANOVA analysis displayed the non-significant lack of fit value (0.4566), whereas, the predicted correlation coefficient values (R² 0.8494) were reasonably in agreement with the adjusted value (R² 0.9363) demonstrating highly significant model for MG dye sorption. The applicability of this model was also checked through F- test (30.39) with lower probability (0.0001) value. Furthermore, the characterization of SCB was performed using fourier transform infra-red spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscope (SEM), Brunauer-Emmett-Teller surfaces (BET), total organic carbon (TOC) and atomic absorption spectroscopy (AAS). Phyto-toxicity and cytogenotoxicity studies showed successful removal of MG dye using SCB. In addition, the batch sorption studies for reutilization of SCB revealed that the SCB was effective in removal of MG for five repeated cycles. This technology would be effective for treating the toxic textile effluent released from the textile industries.

Morphology, molecular structure, and stable carbon isotopic composition of black carbon (BC) in urban topsoils

Urban soils contain significant amounts of black carbon (BC) from biomass and fossil fuel combustion and regard to be a pool of BC. BC in urban soils has multiple effects on environmental processes in urban system, such as global climate change, air quality, and public health. Urban topsoil samples (0-10 cm) were collected from Anshan, Liaoning Province, northeast China, which is one of the most important old steel industrial bases in China. The BC in urban topsoils was extracted using the density method. Their chemical composition, morphology, molecular structure, and stable carbon isotopic composition were examined using elemental analysis, scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), X-ray diffraction (XRD), and stable carbon isotope (δ¹³C). Elemental analysis shows that carbon content in the BC of studied soils ranged from 64.5 to 78.4%, with the average more than 70%. The O/C atomic ratio of BC is on average 0.18. The BC particle displays different morphology, including porous spherical, irregular porous fragmentary, and blocky shapes. The porous spherical BC particles has atomic molar O/C ratio determined by SEM-EDS ranging from 0.04 to 0.37. XRD indicates that BC exists in mainly combining with mineral phases hematite (Fe₂O₃), kaolinite (Al₂Si₂O₅(OH)₄), quartz (SiO₂), and calcite (CaCO₃). The FTIR spectra of BC particles show major bands at approximately 3400 cm^-1 (O-H), 2920 cm^-1 (C = H), 1600 cm^-1 (C = C), 1230 cm^-1 (C = O), and 1070 cm^-1 (C = O). The stable carbon isotope (δ¹³C) of BC ranges from -24.48 to -23.18‰ with the average of -23.79 ± 0.39‰. The concentration of BC in the industrial area is significantly (p < 0.05) higher than that in the roadside area. The BC of industrial area is characterized by porous spherical structure, suggesting that they are mainly derived from fossil fuel combustion. Results indicated that a combination of atomic O/C ratio, porous structure, and stable carbon isotopic (δ¹³C) of BC could reflect effectively the origin of BC in urban topsoils. It could conclude that BC in Anshan urban topsoil was mainly from fossil fuel combustion.

Adsorption of heavy metals from aqueous solution by UV-mutant Bacillus subtilis loaded on biochars derived from different stock materials

Two kinds of biochars, one derived from corn straw (CBC) and one from pig manure (PBC), were used as the carriers of a bacterium (B38) to adsorb heavy metals in solution. CBC exhibited high affinity to Hg(II), while PBC showed large adsorption capacity of Pb(II). After loading with B38, the sorption capacity of the co-sorbents were enhanced for Pb(II), but weakened for Hg(II). In a binary system, the overall adsorption capacity to Hg-Pb (CBC+B38, 136.7mg/g; PBC+B38, 181.3mg/g) on co-sorbents was equal to the sum of the single-component values for Hg(II) and Pb(II). Electrostatic interactions and precipitation are the major mechanisms in the adsorption of Hg(II). In contrast, cation-π interactions and precipitation were involved in the sorption process of Pb(II). Moreover, the sorption sites of Hg(II) and Pb(II) partially overlapped on the biochar surface, but were different on co-sorbents. Hence, the co-sorbents have an advantage over the biochar alone in the removal of heavy metal mixtures.

Physical modification of biochar to expose the inner pores and their functional groups to enhance lead adsorption

Biochars have been successfully used to treat wastewater and contaminated soils. The efficiency of biochar as a biosorbent of heavy metals can be increased by reducing the particle size, exposing the inner pores and their functional groups. In this study, the empty fruit bunch biochar (EFBB) of oil palm was separated into three particle sizes, fine (F-EFBB < 50 μm), medium (M-EFBB 250–500 μm) and coarse (C-EFBB > 2000 μm) to compare their physical and chemical characteristics and their adsorption capacity for lead. Results revealed that the F-EFBB had greater surface area and exposed more micropores compared to the other particle sizes. Similarly, the F-EFBB had the most oxygen containing functional groups, CEC, and negative charges as measured by the zeta potential. The F-EFBB had the highest adsorption capacity for Pb, followed by M-EFBB and C-EFBB with the lowest. Therefore, the F-EFBB are able to adsorb more heavy metals as compared to M-EFBB and C-EFBB, as suggested by the more favourable physical and chemical characteristics.

Biochars have been successfully used to treat wastewater and contaminated soils.

Review on utilization of biochar for metal-contaminated soil and sediment remediation

Biochar is a carbon-neutral or even carbon-negative material produced through thermal decomposition of plant- and animal-based biomass under oxygen-limited conditions. Recently, there has been an increasing interest in the application of biochar as an adsorbent, soil ameliorant and climate mitigation approach in many types of applications. Metal-contaminated soil remediation using biochar has been intensively investigated in small-scale and pilot-scale trials with obtained beneficial results and multifaceted effects. But so far, the study and application of biochar in contaminated sediment management has been very limited, and this is also a worldwide problem. Nonetheless, there is reason to believe that the same multiple benefits can also be realized with these sediments due to similar mechanisms for stabilizing contaminants. This paper provides a review on current biochar properties and its use as a sorbent/amendment for metal-contaminated soil/sediment remediation and its effect on plant growth, fauna habits as well as microorganism communities. In addition, the use of biochar as a potential strategy for contaminated sediment management is also discussed, especially as regards in-situ planning. Finally, we highlight the possibility of biochar application as an effective amendment and propose further research directions to ensure the safe and sustainable use of biochar as an amendment for remediation of contaminated soil and sediment.

Characterization of modified biochars prepared at low pyrolysis temperature as an efficient adsorbent for atrazine removal

In this study, biochars (BC, ZnBC, and PBC) produced from wheat straw at relatively lower pyrolysis are successfully fabricated using different pretreatment techniques (without and with ZnCl₂ or H₃PO₄). The specific surface area (SSA), elemental analysis, and Fourier transform infrared spectra (FTIR) are used to analyze physicochemical properties of unmodified and modified biochars. ZnBC and PBC show higher specific surface area and more micropore structure than pure BC. Kinetic models (pseudo-first order, pseudo-second order, and intra-particle diffusion) as well as isotherm models (Langmuir and Freundlich) are applied to analyze adsorption behavior. Adsorption on biochars can be better fitted by the pseudo-second-order and intra-particle diffusion models, indicating that micropores and mesopores play important roles on adsorption process and chemisorption is dominant. The adsorption process is also affected by physical and chemical adsorption. In conclusion, biochar is a low-cost, effective, and environment-friendly adsorbent implicating in the environment for pesticide removal. Graphical abstract.

Removal of acenaphthene from water by Triton X-100-facilitated biochar-immobilized Pseudomonas aeruginosa

By adding the nonionic surfactant Triton X-100 and using biochar as an immobilization carrier, a Triton X-100-facilitated biochar-immobilized Pseudomonas aeruginosa (TFBIP) material was prepared using the sorption method and was used to treat acenaphthene in water. The results showed that a low concentration of Triton X-100 simultaneously promoted the sorption capacity of the biochar and the degradation activity of P. aeruginosa, thereby significantly enhancing the removal of acenaphthene from water by the immobilized P. aeruginosa material. Compared with the control without Triton X-100, a low concentration of Triton X-100 significantly increased the acenaphthene removal rate by 20–50%. The optimal conditions for preparing the TFBIP were a loading time of 24 h, the use of a bacterial suspension with a concentration of OD₆₀₀ = 0.2, and a Triton X-100 concentration of 10 mg L⁻¹. The optimized TFBIP material could efficiently remove acenaphthene from water at temperatures of 10–50 °C, pH values of 4.5–10.5, and NaCl concentrations of up to 0.2 mol L⁻¹. The new TFBIP material can be used for the treatment of wastewater and may also be directly used for the remediation of soils contaminated with organic pollutants.

A new efficient PAH-degrading bacterial material was produced by using biochar as an immobilization carrier and adding nonionic surfactant.

Comprehensive Adsorption Studies of Doxycycline and Ciprofloxacin Antibiotics by Biochars Prepared at Different Temperatures

This paper comparatively investigated the removal efficiency and mechanisms of rice straw biochars prepared under three pyrolytic temperatures for two kinds of tetracycline and quinolone antibiotics (doxycycline and ciprofloxacin). The influencing factors of antibiotic adsorption (including biochar dosage, pH, background electrolytes, humic acid, initial antibiotics concentration, contact time, and temperature) were comprehensively studied. The results suggest that biochars produced at high-temperature [i.e., 700°C (BC700)], have higher adsorption capacity for the two antibiotics than low-temperature (i.e., 300-500°C) biochars (BC300 and BC500). Higher surface area gives rise to greater volume of micropores and mesopores, and higher graphitic surfaces of the BC700 contributed to its higher functionality. The maximum adsorption capacity was found to be in the following order: DOX > CIP. The π-π EDA interaction and hydrogen bonding might be the predominant adsorption mechanisms. Findings in this study highlight the important roles of high-temperature biochars in controlling the contamination of tetracycline and quinolone antibiotics in the environment.

Sorption of tetracycline on biochar derived from rice straw and swine manure

Biochar is an efficient and cost-effective sorbent for removing contaminants from aqueous environments. In this study, biochar samples derived from rice straw (R) and swine manure (M) pyrolyzed at 400 °C (R400 and M400) and 600 °C (R600 and M600) were used to adsorb tetracycline from an aqueous solution. The adsorption of tetracycline on both types of biochar included multi-step adsorption processes that were well described by the pseudo-second-order kinetics model (R² > 0.99). The adsorption equilibrium of tetracycline on rice straw and swine manure derived biochar was reached after 24 h and 36 h respectively. The solution pH affected the adsorption processes by changing the surface charges of tetracycline and biochar. Adsorption isotherms fitted both the Langmuir and Freundlich models well. The adsorption capacity was higher in biochar derived from rice straw than in biochar derived from swine manure, and increased with increasing pyrolysis temperature. Thermodynamic analysis revealed a spontaneous and endothermic tetracycline adsorption process. The values of the adsorption coefficient (K_d) were on the order of 10³ for R600 and 10²–10³ for the other three types of biochar. These experiments indicate that R600 can be used as an inexpensive adsorbent to remove tetracycline from aqueous solutions, but swine manure derived biochar needs more improvement to be a suitable adsorbent.

Comparing the adsorption ability of biochar from swine manure and rice straw on tetracycline and investigating the relative mechanisms involved in the process.

Biochar production and applications in soil fertility and carbon sequestration – a sustainable solution to crop-residue burning in India

A sustainable solution to crop residues burning by converting residues into biochars is provided.

Study of the mechanism of remediation of Cd-contaminated soil by novel biochars

This article used novel non-magnetized and magnetized biochars prepared under a CO2 atmosphere returned to Cd-contaminated soil and compared these to the effects of conventional biochars prepared under a N2 atmosphere with regard to Cd-contaminated soil remediation. A pot experiment with lettuce (Lactuca sativa) was conducted to investigate the relative soil remediation effects of these biochars. The soil used for the pot experiment was spiked with 20 mg kg-1 Cd and amended with 5% of a biochar before sowing. Through these research works, some important results were obtained as follows: (1) applying biochar treated by pyrolysis under a CO2 atmosphere can obtain the best remediation effect of Cd-contaminated soil that the content of cadmium in the lettuce roots, stems, and leaves was reduced 67, 62, and 63%, respectively; (2) the magnetic biochar aggregation for the soil is weak, so the heavy metal cadmium in the soil could not be immobilized well by the magnetic biochar; (3) The remediation mechanism of novel biochars is that biochar includes a large number of organic functional groups (-C-OH, -C=O, COO-) that can act in a complexing reaction with heavy metal Cd(II) and the inorganic salt ions (Si, S, Cl, etc.) that can combine with cadmium and generate a stable combination.

Synthesis of biochar from residues after biogas production with respect to cadmium and nickel removal from wastewater

The objective of the study was to investigate the ability of biochars prepared under different temperatures (400 °C and 600 °C) from the residue of biogas production (RBP) for the adsorption of cadmium (Cd(II)) and nickel (Ni(II)) ions from aqueous solution. Furthermore, the RBP biochars adsorption capacity was compared with adsorption capacity of biochar produced from wheat straw at 600 °C (BCS600). The kinetics of the adsorption, the sorption isotherms, the influence of solution pH and the interfering ions (chlorides and nitrates) were investigated. The desorption of Cd(II) and Ni(II) by hydrochloric and nitric acid from biochars was also investigated. The different types of feedstock used for biochar (BC) preparation (RBP and biomass) determined the physico-chemical properties of biochars and hence their adsorption abilities. Generally, biochars produced from RBPs (regardless of temperature) had the greater capacity to adsorb Cd(II) and Ni(II) than the biochar produced from wheat straw. Of the tested models (Freundlich and Langmuir), the Langmuir model was demonstrated to be the best to describe the sorption of Cd(II) and Ni(II). For the kinetic study, the adsorption process proceeded the fastest for BCU400 than BCU600. Furthermore, BCU600 was the most resistant to the influence of interfering ions on adsorption. For the desorption study, BCU400 was characterized by the highest reproducibility of the surface. The comparison of the results obtained in each adsorption step between RBP biochars and BCS600 suggested that the residue from biogas production could be successfully applied for the removal of Cd(II) and Ni(II) ions from aqueous solutions.

Kinetic, isotherm and thermodynamic studies with linear and non-linear fitting for cadmium(II) removal by black carbon of pine cone

In this study, black carbon from pine cone (BCPC) and acidic-modified BCPC (MBCPC) powder as a popular agricultural waste in the southeast of Iran were used for cadmium removal from aqueous solutions. The effect of various factors, such as surface chemistry and dosage of adsorbent, contact time, size of particles, initial concentration of cadmium, temperature, and pH of aqueous solutions, was investigated. The results show cadmium removal with usage of the mentioned adsorbents increased after acidic modification. It was noteworthy in this work that the removal percentage of pollutant was above 90% for suggested biosorbents. The obtained experimental data for optimum conditions were selected to model the adsorption behavior of the materials with usage of six isotherm equations via non-linear fitting method and the residual root mean square error estimation for each model. The adsorption of cadmium preferably fitted Khan and Langmuir-Freundlich isotherms for BCPC and MBCPC adsorbents, respectively. The kinetic studies via linear fitting method proved the second-order kinetic was the applicable model for the adsorption process. Thermodynamic studies show the adsorption process of cadmium onto BCPC and MBCPC was spontaneous and endothermic.

Mechanisms for Increasing the pH Buffering Capacity of an Acidic Ultisol by Crop Residue-Derived Biochars

The effects and underlying mechanisms of crop residue-derived biochars on the pH buffering capacity (pHbuff) of an acidic Ultisol, with low pHbuff, were investigated through indoor incubation and simulated acidification experiments. The incorporation of biochars significantly increased soil pHbuff with the magnitude of the increase dependent on acid buffering capacity of the biochar incorporated to the soil. Cation release, resulting from the protonation of carboxyl groups on biochar surfaces and the dissolution of carbonates, was the predominant mechanism responsible for the increase in soil pHbuff at pH 4.0-7.0 and accounted for >67% of the increased pHbuff. The reaction of protons with soluble silica (Si) in biochars derived from rice straw and corn stover also accounted for ∼20% of the pHbuff increase due to H₃SiO₄^- precipitation. In conclusion, the incorporation of crop residue-derived biochars into acidic soils increased soil pHbuff with peanut stover biochar being the most effective biochar tested.

Bio-butanol sorption performance on novel porous-carbon adsorbents from corncob prepared via hydrothermal carbonization and post-pyrolysis method

A series of porous-carbon adsorbents termed as HDPC (hydrochar-derived pyrolysis char) were prepared from corncob and used for the 1-butanol recovery from aqueous solution. The influences of pyrolysis temperature on properties of the adsorbents were systematically investigated. The results showed that hydrophobicity, surface area, and pore volume of HDPC samples increased with an increase in pyrolysis temperature. Furthermore, the adsorption mechanism of 1-butanol on the adsorbents was explored based on correlation of the samples properties with adsorption parameters extracted from the 1-butanol adsorption isotherms (K_F and Q_e12). Overall, the 1-butanol adsorption capacity increased with a decrease in polarity and an increase in aromaticity, surface area and pore volume of HDPC samples. However, at different pyrolysis temperature, the factors causing the increase of 1-butanol adsorption on the adsorbents are variable. The kinetic experiments revealed that the pores played a vital role in the 1-butonal adsorption process. The intraparticle diffusion model was used to predict the adsorption kinetic process. The simulation results showed that intraparticle diffusion was the main rate-controlling step in the 1-butanol adsorption process.

Sorption of tetracycline on biochar derived from rice straw under different temperatures

Biochars produced from the pyrolysis of waste biomass under limited oxygen conditions could serve as adsorbents in environmental remediation processes. Biochar samples derived from rice straw that were pyrolyzed at 300 (R300), 500 (R500) and 700°C (R700) were used as adsorbents to remove tetracycline from an aqueous solution. Both the Langmuir and Freundlich models fitted the adsorption data well (R² > 0.919). The adsorption capacity increased with pyrolysis temperature. The R500 and R700 samples exhibited relative high removal efficiencies across a range of initial tetracycline concentrations (0.5mg/L-32mg/L) with the maximum (92.8%–96.7%) found for adsorption on R700 at 35°C. The relatively high surface area of the R700 sample and π–π electron-donor acceptor contributed to the high adsorption capacities. A thermodynamic analysis indicated that the tetracycline adsorption process was spontaneous and endothermic. The pH of solution was also found to influence the adsorption processes; the maximum adsorption capacity occurred at a pH of 5.5. These experimental results highlight that biochar derived from rice straw is a promising candidate for low-cost removal of tetracycline from water.

Removal of Copper (II) by Biochar Mediated by Dissolved Organic Matter

The effects of humic acid (HA) and fulvic acid (FA) on Cu²⁺ adsorption on biochar were investigated, with mechanisms confirmed by excitation-emission matrix spectroscopy, Fourier transform infrared spectroscopy, and scanning electron microscopy. HA loading enhanced Cu²⁺ adsorption on biochar, with the maximum enhancement of 55.0% occurring at an HA loading of 100 mg-C/L. The adsorbed HA introduced many additional functional groups to biochar, thus enhancing Cu²⁺ adsorption, which decreased at HA concentrations >100 mg-C/L due to self-association of HA at high loading concentrations. In contrast, FA loading caused no enhancement on Cu²⁺ adsorption on biochar. FA was adsorbed through H-bonding with the functional groups of biochar, which set up a competition with Cu²⁺ for adsorption on biochar. The functional groups occupied by adsorbed FA were offset by the newly introduced functional groups of FA, thus there was no net increase in the amount of Cu²⁺ adsorption upon FA loading. These findings imply that, because of the enhanced adsorption of HA-loaded biochar, the amount of Cu²⁺ immobilized would increase by 28.2% for mature compost and 31.9% for fresh compost if there exist interaction between biochar and HA compared with the amounts immobilized by non-interactive HA and biochar.

Comparative adsorption of Pb2+ and Cd2+ by cow manure and its vermicompost

Organic waste has great potential for use as an amendment to immobilize heavy metals in the environment. Therefore, this study investigates various properties of cow manure (CM) and its derived vermicompost (CV), including the pH, cationic exchangeable capacity (CEC), elemental composition and surface structure, to determine the potential of these waste products to remove Pb²⁺ and Cd²⁺ from solution. The results demonstrate that CV has a much higher pH, CEC and more irregular pores than CM and is enriched with minerals and ash content but has a lower C, H, O and N content. Adsorption isotherms studies shows that the adsorption of Pb²⁺ and Cd²⁺ onto either CM or CV follows a Langmuir model and presents maximum Pb²⁺ and Cd²⁺ adsorption capacities of 102.77 mg g^-1 and 38.11 mg g^-1 onto CM and 170.65 and 43.01 mg g^-1 onto CV, respectively. Kinetic studies show that the adsorption of Pb²⁺ onto CM and CV fits an Elovich model, whereas the adsorption of Cd²⁺ onto CM and CV fits a pseudo-second-order model. Desorption studies indicate that CV is more effective than CM in removing Pb²⁺ and Cd²⁺. FTIR analysis demonstrates that the adsorption of Pb²⁺ and Cd²⁺ onto CM mainly depends on existed aliphatic alcohol, aromatic acid as well as new produced carbonates, whereas that onto CV may be contributed by the existed aliphatic alcohol, aromatic acids as well as some carbonates and phosphates. Thus, vermicomposting disposal of cow manure with destination mineral addition may broaden the way of its recycle and environmental usage.

Biochar-based water treatment systems as a potential low-cost and sustainable technology for clean water provision

Approximately 600 million people lack access to safe drinking water, hence achieving Sustainable Development Goal 6 (Ensure availability and sustainable management of water and sanitation for all by 2030) calls for rapid translation of recent research into practical and frugal solutions within the remaining 13 years. Biochars, with excellent capacity to remove several contaminants from aqueous solutions, constitute an untapped technology for drinking water treatment. Biochar water treatment has several potential merits compared to existing low-cost methods (i.e., sand filtration, boiling, solar disinfection, chlorination): (1) biochar is a low-cost and renewable adsorbent made using readily available biomaterials and skills, making it appropriate for low-income communities; (2) existing methods predominantly remove pathogens, but biochars remove chemical, biological and physical contaminants; (3) biochars maintain organoleptic properties of water, while existing methods generate carcinogenic by-products (e.g., chlorination) and/or increase concentrations of chemical contaminants (e.g., boiling). Biochars have co-benefits including provision of clean energy for household heating and cooking, and soil application of spent biochar improves soil quality and crop yields. Integrating biochar into the water and sanitation system transforms linear material flows into looped material cycles, consistent with terra preta sanitation. Lack of design information on biochar water treatment, and environmental and public health risks constrain the biochar technology. Seven hypotheses for future research are highlighted under three themes: (1) design and optimization of biochar water treatment; (2) ecotoxicology and human health risks associated with contaminant transfer along the biochar-soil-food-human pathway, and (3) life cycle analyses of carbon and energy footprints of biochar water treatment systems.

Mechanisms of metal sorption by biochars: Biochar characteristics and modifications

Biochar produced by thermal decomposition of biomass under oxygen-limited conditions has received increasing attention as a cost-effective sorbent to treat metal-contaminated waters. However, there is a lack of information on the roles of different sorption mechanisms for different metals and recent development of biochar modification to enhance metal sorption capacity, which is critical for biochar field application. This review summarizes the characteristics of biochar (e.g., surface area, porosity, pH, surface charge, functional groups, and mineral components) and main mechanisms governing sorption of As, Cr, Cd, Pb, and Hg by biochar. Biochar properties vary considerably with feedstock material and pyrolysis temperature, with high temperature producing biochars with higher surface area, porosity, pH, and mineral contents, but less functional groups. Different mechanisms dominate sorption of As (complexation and electrostatic interactions), Cr (electrostatic interactions, reduction, and complexation), Cd and Pb (complexation, cation exchange, and precipitation), and Hg (complexation and reduction). Besides sorption mechanisms, recent advance in modifying biochar by loading with minerals, reductants, organic functional groups, and nanoparticles, and activation with alkali solution to enhance metal sorption capacity is discussed. Future research needs for field application of biochar include competitive sorption mechanisms of co-existing metals, biochar reuse, and cost reduction of biochar production.

Bio- and hydrochars from rice straw and pig manure: Inter-comparison

Conversion of rice straw (RS) and pig manure (PM) into chars is a promising disposal/recycling option. Herein, pyrolysis and hydrothermal carbonization were used to produce bio- and hydrochars from RS and PM, affording lower biochar (300-700°C) and hydrochar (180-300°C) yields at higher temperatures within the specified range. The C contents and C/N ratios of RS chars were higher than those of PM ones, with the opposite trend observed for yield and ash content. C and ash contents increased with increasing temperature, whereas H/C, O/C, and (O+N)/C ratios decreased. The lower H/C ratio of biochars compared to that of hydrochars indicated greater stability of the former. KCl was the main inorganic fraction in RS biochars, whereas quartz was dominant in PM biochars, and albite in PM hydrochars. Thus, RS is more suitable for carbon sequestration, while PM is more suitable for use as a soil amendment substrate.

Impact of different feedstocks derived biochar amendment with cadmium low uptake affinity cultivar of pak choi (Brassica rapa ssb. chinensis L.) on phytoavoidation of Cd to reduce potential dietary toxicity

Biochar has become eco-friendly amendment used for phytoavoidation with low cadmium (Cd) accumulating cultivars of crops to ensure food safety in Cd contaminated soils. In this study, biochar with different waste feedstock material were evaluated for their effectiveness on essential trace metals mobility, Cd bioavailability and its accumulation in two contrasting Cd accumulating cultivars of pak choi (Brassica rapa ssp. chinensis L.) grown in Cd contaminated Mollisol soil. A greenhouse experiment was conducted with plants grown in Cd contaminated soil that had been amended with biochar derived from barley straw, tomato green waste, chicken manure, duck manure and swine manure at application rate of 0%, 2.5% and 5.0% (w/w). The results showed that soil pH was significantly increased by all treatments. Biochar increased plant dry biomass, micronutrients bioavailability with significant differences in the Cd sorption capacity, with the effectiveness higher with increasing biochar application rate. However, tomato green waste (TGW) and chicken manure (CM) derived biochar were more effective than the other biochar in reducing Cd mobilization in soil by 35-54% and 26-43% and reduced its accumulation in shoots of pak choi cultivars by 34-76% and 33-72% in low Cd accumulator cultivar and 64-85% and 55-80% in high Cd accumulator cultivar than the control. Overall, results indicate that TGW and CM biochar can efficiently immobilize Cd, thereby reducing bioavailability in Cd contaminated Mollisol soil to ensure food safety.

Removal of hydrogen sulfide generated during anaerobic treatment of sulfate-laden wastewater using biochar: Evaluation of efficiency and mechanisms

Removal of hydrogen sulfide (H₂S) from biogas was investigated in a biochar column integrated with a bench-scale continuous-stirred tank reactor (CSTR) treating sulfate-laden wastewater. Synthetic wastewater containing sulfate concentrations of 200-2000mg SO₄^2-/L was used as substrate, and the CSTR was operated at an organic loading rate of 1.5g chemical oxygen demand (COD)/L·day and a hydraulic retention time (HRT) of 20days. The biochar was able to remove about 98.0 (±1.2)% of H₂S for the ranges of concentrations from 105-1020ppmv, especially at high moisture content (80-85%). Very high H₂S adsorption capacity (up to 273.2±1.9mg H₂S/g) of biochar is expected to enhance the H₂S oxidation into S⁰ and sulfate. These findings bring a potentially novel application of sulfur-rich biochar as a source of sulfur, an essential but often deficient micro-nutrient in soils.

Preparation of biochar by simultaneous carbonization, magnetization and activation for norfloxacin removal in water

Activated magnetic biochar (AMB) was prepared with corn stalks, reed stalks, and willow branches by simultaneous carbonization, magnetization, and activation, and used for norfloxacin removal in water. The exploration results showed that the zeta potential was positively charged at pH 2-10. These prepared activated magnetic biochars have a large specific surface area (>700m²·g^-1) and pore volume (>0.3cm³·g^-1). The quasi-second-order kinetic adsorption equation could better describe the adsorption of NOR on AMB. The Langmuir isotherm showed the better fitting results on AMB. The AMB showed the strong adsorption of NOR, and the saturated adsorption capacity of corn activated magnetic biochar was the highest, 7.6249mg·g^-1. The adsorption of NOR on AMB was a spontaneous endothermic process. The effect of pH on the adsorption behaviors of NOR on AMB was not obvious, and AMB had a good adsorption effect on NOR in a wide pH range.

A Direct Observation of the Fine Aromatic Clusters and Molecular Structures of Biochars

Biochar is a promising carbon material to improve soil quality and relieve global warming by adding it into soil. Though biochar has been used for millennia as a soil ingredient, fundamental studies on the structure of biochar have only recently attracted great interest, and molecular-level structures are being pursued. In this study, by applying solvent exfoliation, high-resolution transmission electron microscopy with Cs-correction and quadrupole time-of-flight mass spectroscopy, we report, for the first time, an atomic-level observation of the fine aromatic cluster and molecular structure of the exfoliated biochars. The observed aromatic clusters are generally smaller than 5 nm and decorate the graphene-like aggregates at different depths. The Stone-Wales transformation in the dispersed biochars was observed, which is critical to form carbon nanotubes, fullerenes, and other carbon nanostructures in the natural environment. In addition, the C-C bond length decreases as the pyrolysis temperature increases from 500 to 700 °C, indicating that aliphatic carbon transforms into aromatic carbon. The quaternary structure of biochar, including heterogeneous phases, graphene-like aggregates, nanosized aromatic clusters, and atomic arrangements, is conceptualized to enhance our knowledge of the biochar structure, which greatly aids in understanding the novel functions of biochar and offers a molecular guide for potential applications of biochar.

Synthesis optimization of oil palm empty fruit bunch and rice husk biochars for removal of imazapic and imazapyr herbicides

Imidazolinones are a family of herbicides that are used to control a broad range of weeds. Their high persistence and leaching potential make them probable risk to the ecosystems. In this study, biochar, the biomass-derived solid material, was produced from oil palm empty fruit bunches (EFB) and rice husk (RH) through pyrolysis process. Feedstock and pyrolysis variables can control biochar sorption capacity. Therefore, the present study attempts to evaluate effects of three pyrolysis variables (temperature, heating rate and retention time) on abilities of biochars for removal of imazapic and imazapyr herbicides from soil. Response surface methodology (RSM) was used for optimizing the variables to achieve maximum sorption performance of the biochars. Experimental data were interpreted accurately by quadratic models. Based on the results, sorption capacities of both biochars raised when temperature decreased to 300 °C, mainly because of increased biochars effective functionality in sorption of polar molecules. Heating rate of 3°C/min provided optimum conditions to maximize the sorption capacities of both biochars. Retention time of about 1 h and 3 h were found to be the best for EFB and RH biochars, respectively. EFB biochar was more efficient in removal of the herbicides, especially imazapyr due to its chemical composition and higher polarity index (0.42) rather than RH biochar (0.39). Besides, higher cation exchange capacity (CEC) values of EFB biochar (83.90 cmol_c/kg) in comparison with RH biochar (70.73 cmol_c/kg) represented its higher surface polarity effective in sorption of the polar herbicides.

Biochar soil amendment on alleviation of drought and salt stress in plants: a critical review

Drought and salt stress negatively affect soil fertility and plant growth. Application of biochar, carbon-rich material developed from combustion of biomass under no or limited oxygen supply, ameliorates the negative effects of drought and salt stress on plants. The biochar application increased the plant growth, biomass, and yield under either drought and/or salt stress and also increased photosynthesis, nutrient uptake, and modified gas exchange characteristics in drought and salt-stressed plants. Under drought stress, biochar increased the water holding capacity of soil and improved the physical and biological properties of soils. Under salt stress, biochar decreased Na⁺ uptake, while increased K⁺ uptake by plants. Biochar-mediated increase in salt tolerance of plants is primarily associated with improvement in soil properties, thus increasing plant water status, reduction of Na⁺ uptake, increasing uptake of minerals, and regulation of stomatal conductance and phytohormones. This review highlights both the potential of biochar in alleviating drought and salt stress in plants and future prospect of the role of biochar under drought and salt stress in plants.

Characterization of hard- and softwood biochars pyrolyzed at high temperature

A wide range of waste biomass/waste wood feedstocks abundantly available at mine sites provide the opportunity to produce biochars for cost-effective improvement of mine tailings and contaminated land at metal mines. In the present study, soft- and hardwood biochars derived from pine and jarrah woods at high temperature (700 °C) were characterized for their physiochemical properties including chemical components, electrical conductivity, pH, zeta potential, cation-exchange capacity (CEC), alkalinity, BET surface area and surface morphology. Evaluating and comparing these characteristics with available data from the literature have affirmed the strong dictation of precursor type on the physiochemical properties of the biochars. The pine and jarrah wood feedstocks are mainly different in their proportions of cellulose, hemicellulose and lignin, resulting in biochars with heterogeneous physiochemical properties. The hardwood jarrah biochar exhibits much higher microporosity, alkalinity and electrostatic capacity than the softwood pine. Correlation analysis and principal component analysis also show a good correlation between CEC-BET-alkalinity, and alkalinity-ash content. These comprehensive characterization and analysis results on biochars' properties from feedstocks of hardwood (from forest land clearance at mine construction) and waste pine wood (from mining operations) will provide a good guide for tailoring biochar functionalities for remediating metal mine tailings. The relatively inert high-temperature biochars can be stored for a long term at mine closure after decades of operations.

Effects of different types of biochar on methane and ammonia mitigation during layer manure composting

Biochar, because of its unique physiochemical properties and sorption capacity, may be an ideal amendment in reducing gaseous emissions during composting process but there has been little information on the potential effects of different types of biochar on undesired gaseous emissions. The objective of this study was to examine the ability and mechanism of different types of biochar, as co-substrate, in mitigating gaseous emission from composting of layer hen manure. The study was conducted in small-scale laboratory composters with the addition of 10% of one of the following biochars: cornstalk biochar, bamboo biochar, woody biochar, layer manure biochar and coir biochar. The results showed that the cumulative NH₃ production was significantly reduced by 24.8±2.9, 9.2±1.3, 20.1±2.6, 14.2±1.6, 11.8±1.7% (corrected for initial total N) in the cornstalk biochar, bamboo biochar, woody biochar, layer manure biochar and coir biochar treatments, respectively, compared to the control. Total CH₄ emissions was significantly reduced by 26.1±2.3, 15.5±2.1, 22.4±3.1, 17.1±2.1% (corrected for the initial total carbon) for cornstalk biochar, bamboo biochar, woody biochar and coir biochar treatments than the control. Moreover, addition of cornstalk biochar increased the temperature and NO₃^--N concentration and decreased the pH, NH₄⁺-N and organic matter content throughout the composting process. The results suggested that total volatilization of NH₃ and CH₄ in cornstalk biochar treatment was lower than the other treatments; which could be due to (i) decrease of pH and higher nitrification, (ii) high sorption capacity for gases and their precursors, such as ammonium nitrogen from composting mixtures, because of the higher surface area, pore volumes, total acidic functional groups and CEC of cornstalk biochar.

Biochar decreases nitrogen oxide and enhances methane emissions via altering microbial community composition of anaerobic paddy soil

Biochar application to agricultural soil is an appealing approach to mitigate nitrous oxide (N₂O) and methane (CH₄) emissions. However, the underlying microbial mechanisms are unclear. In this study, a paddy soil slurry was incubated anaerobically for 14d with biochar amendments produced from rice straw at 300, 500, or 700°C (B300, B500, and B700) to study their influences on greenhouse gas emissions. Illumina sequencing was used to characterize shift of soil bacterial and archaeal community composition. After peaking at day 1, N₂O emission then sharply decreased to low levels while CH₄ started to emit at day 3 then continually increased with incubation. Compared to control soil (57.9mgkg^-1 soil), B300, B500, and B700 amendments decreased N₂O peak emission to 17.9, 1.28, and 0.59mgkg^-1, mainly due to increased soil pH. In contrast, the amendments enhanced CH₄ production from 58.2 to 93.4, 62.6, and 63.4mgkg^-1 at day 14 due to increased soil dissolved organic carbon. Abundance of denitrifying bacteria (e.g., Bacilli, 7.07-13.6 vs. 16.9%) was reduced with biochar amendments, especially with B500 and B700, contributing to the decreased N₂O emissions. However, larger pore size of B500 and B700 (surface area of 68.1 and 161m²g^-1) than B300 (4.40m²g^-1) favored electron transfer between bacteria and iron minerals, leading to increased abundance of iron-reducing bacteria, (e.g., Clostridia, 48.2-50.6 vs. 33.3%), which competed with methanogens to produce CH₄, thereby leading to lower increase in CH₄ emission. Biochar amendments with high pH and surface area might be effective to mitigate emission of both N₂O and CH₄ from paddy soil.