Search

Biochar (BC) has garnered extensive attention as a carbon sequestration solution. This study comprehensively reviews of the effects of BC on the buildup, protection, stabilization, and mineralization of soil organic carbon (SOC). The input of BC-derived carbon alters soil carbon quality by changing SOC content and aromaticity. BC also affects processes controlling substrate accessibility, such as physical protection of SOC by soil aggregates and organo-mineral interaction. Changes in soil carbon quality and physicochemical properties further alter carbon source availability and microbial habitat, thereby affecting the microbial decomposition of SOC. Of particular importance is the soil aggregation process, which regulates the distribution and turnover of microbial necromass and SOC fraction in different aggregates. The "microbial carbon pump" concept framework highlights the pivotal role of microbial necromass in the formation of soil stable carbon pool. BC can affect the accumulation and decomposition of microbial necromass carbon in the bulk soil and different aggregates, thereby changing the soil carbon pool composition and stability. The newly proposed "mineral carbon pump" hypothesis further emphasizes the crucial role of organo-mineral interaction in stabilizing SOC. Further research is required to understand the role of viable microbial biomass and dead microbial necromass in SOC turnover, as well as the extent and mechanism of the interaction between BC and soil minerals. Long-term ecosystem effects of BC, as well as the resilience of BC-soil system to climate change, need to be clarified to determine the rationality of BC application in the context of global change. [ABSTRACT FROM AUTHOR]

To achieve long‐term increases in soil organic carbon (SOC) storage, it is essential to understand the effects of carbon management strategies on SOC formation pathways, particularly through changes in microbial necromass carbon (MNC) and dissolved organic carbon (DOC). Using a 14‐year field study, we demonstrate that both biochar and maize straw lifted the SOC ceiling, but through different pathways. Biochar, while raising SOC and DOC content, decreased substrate degradability by increasing carbon aromaticity. This resulted in suppressed microbial abundance and enzyme activity, which lowered soil respiration, weakened in vivo turnover and ex vivo modification for MNC production (i.e., low microbial carbon pump "efficacy"), and led to lower efficiency in decomposing MNC, ultimately resulting in the net accumulation of SOC and MNC. In contrast, straw incorporation increased the content and decreased the aromaticity of SOC and DOC. The enhanced SOC degradability and soil nutrient content, such as total nitrogen and total phosphorous, stimulated the microbial population and activity, thereby boosting soil respiration and enhancing microbial carbon pump "efficacy" for MNC production. The total C added to biochar and straw plots were estimated as 27.3–54.5 and 41.4 Mg C ha−1, respectively. Our results demonstrated that biochar was more efficient in lifting the SOC stock via exogenous stable carbon input and MNC stabilization, although the latter showed low "efficacy". Meanwhile, straw incorporation significantly promoted net MNC accumulation but also stimulated SOC mineralization, resulting in a smaller increase in SOC content (by 50%) compared to biochar (by 53%–102%). The results address the decadal‐scale effects of biochar and straw application on the formation of the stable organic carbon pool in soil, and understanding the causal mechanisms can allow field practices to maximize SOC content. [ABSTRACT FROM AUTHOR]

Biochar is a promising amendment to promote cadmium (Cd) sorption and fixation in agricultural soil, where microplastics are emerging contaminants in soil. Herein, a greenhouse pot experiment was conducted to elucidate the effects on Cd availability in a soil–plant system by biochar and fresh/aged microplastics application. The fresh microplastics led to an obvious increase in soil Cd availability and Cd uptake by wheat plant, while the aged microplastics increased the available Cd in soil but had no effect on Cd uptake by wheat plant, which was likely attributed to the blocking effect of the aged microplastics on Cd transportation from the soil to the wheat plant. Unexpectedly, biochar had increased Cd availability and Cd uptake. The increased soil soluble Cd was because of both decreased soil pH and elevated dissolved organic matter (DOM) content resulted by biochar addition. Also, the unchanged Cd adsorption of the soil was likely responsible for the increased tested soil Cd availability. In addition, the combined effects of a greater decrease in soil pH, an increase in soil DOM content, and a reduction in Cd adsorption after the addition of microplastics to biochar‐amended soil resulted in a significant increase (ranging from 2.63% to 47.73%) in Cd availability compared to soil treated with biochar alone. Moreover, fresh microplastics inhibited wheat growth, and greater inhibition effect was observed for their aged ones. The biochar elevated the wheat biomass; however, the coexistence of microplastics and biochar decreased the wheat plant biomass compared with biochar alone, due to the negative influence of microplastics in plant growth. [ABSTRACT FROM AUTHOR]

Phosphorus (P) in biochar serves as both a P source for plant growth and a contributor to water eutrophication, thus prioritizing the efficient management of P in biochar. This study employed solid- and solution- state 31 P-nuclear magnetic resonance and X-ray diffraction analyses to explore the impact of feedstock and heating treatment temperature (HTT) on P species of biochars. The effects of ambient temperature, coexisting anions, pH and nutrient solution on P release were also investigated to study the effect of various environmental factors on P release from biochars. P species in both plant- and manure- derived biochars were dominated by inorganic orthophosphate and pyrophosphate (mainly calcium-bound-phosphates). The HTT of biochar showed a negative impact upon its pyrophosphate content. Compared with plant biochars, manure biochars contained higher P but had a lower release degree. Release of P from biochars was controlled by diffusion-dissolution process and was enhanced by higher ambient temperature, co-existing anions, and both acidic and alkaline conditions but inhibited by coexisting Hoagland nutrients. Anion-induced increase in P release was more significant for plant biochars than manure biochars. These findings help to adjust favorable environmental conditions for the full utilization of P in biochars. [ABSTRACT FROM AUTHOR]

The stability of biochar is a major determinant of its potential for carbon sequestration. In previous studies, the biochar stability was evaluated by analyzing the oxidation resistance property of biochar, for which, K 2 Cr 2 O 7 /H 2 O 2 oxidation and thermogravimetric analysis (TGA) were widely used to measure the high oxidation resistance of biochars. In this study, rice straw (RI)- and swine manure (SW)-derived biochars produced at different heating treatment temperatures (HTTs) and their corresponding de-ashed biochars and iron-biochars were selected to investigate the effect of minerals on these biochars stability. There was a significantly positive correlation between carbon remaining values (CRVs) obtained after K 2 Cr 2 O 7 /H 2 O 2 oxidation and ash (mineral) contents of biochars ( p  < 0.05). Moreover, the decreasing CRVs of most biochars were observed after de-ashing treatment. These K 2 Cr 2 O 7 /H 2 O 2 oxidation results indicated that endogenous minerals in biochars can protect biochars from chemical oxidation. On the other hand, the R 50 (C recalcitrance index) values of iron-biochars (33.3–57.4%) were lower than those of corresponding biochars (38.6–60.8%), indicating that Fe-bearing mineral formed in biochars can promote the thermal decomposition of biochars. In H 2 O 2 oxidation, the different change trend of CRVs between biochars produced at 450 °C and biochars produced at 600 °C after iron mineral treatment showed that the effect of exogenous Fe-bearing mineral on biochar stability was related to biochar category regulated by HTTs. This study indicated that endogenous minerals could increase biochar stability, and exogenous Fe-bearing minerals had dissimilar effects on different kinds of biochars, which critically regulates the potential of biochar for long-term carbon sequestration. [ABSTRACT FROM AUTHOR]

Chemical composition and pollutant sorption of biochar-derived organic matter fractions (BDOMs) are critical for understanding the long-term environmental significance of biochar. Phenanthrene (PHE) sorption by the humic acid-like (HAL) fractions isolated from plant straw- (PLABs) and animal manure-based (ANIBs) biochars, and the residue materials (RES) after HAL extraction was investigated. The HAL fraction comprised approximately 50% of organic carbon (OC) of the original biochars. Results of XPS and 13 C NMR demonstrated that the biochar-derived HAL fractions mainly consisted of aromatic clusters substituted by carboxylic groups. The CO 2 cumulative surface area of BDOMs excluding PLAB-derived RES fractions was obviously lower than that of corresponding biochars. The sorption nonlinearity of PHE by the fresh biochars was significantly stronger than that of the BDOM fractions, implying that the BDOM fractions were more chemically homogeneous. The BDOMs generally exhibited comparable or higher OC-normalized distribution coefficients ( K oc ) of PHE than the original biochars. The PHE log K oc values of the fresh biochars correlated negatively with the micropore volumes due to steric hindrance effect. In contrast, a positive relationship between the sorption coefficients ( K d ) of BDOMs and the micropore volumes was observed in this study, suggesting that pore filling could dominate PHE sorption by the BDOMs. The positive correlation between the PHE log K oc values of the HAL fractions and the aromatic C contents indicates that PHE sorption by the HAL fractions was regulated by aromatic domains. The findings of this study improve our knowledge of the evolution of biochar properties after application and its potential environmental impacts. [ABSTRACT FROM AUTHOR]

The oxidation of biochar in the natural environment has been widely observed. However, its influence on the sorption of hydrophobic organic compounds (HOCs) by biochars, especially biochars with high contents of minerals, remains poorly understood. In this study, sorption of phenanthrene (PHE) by grass straw-based biochars (GRABs) and animal waste-based biochars (ANIBs) produced at 450 °C before and after oxidation with HNO 3 was investigated. The biochar samples were characterized using elemental analysis, X-ray photoelectron spectroscopy, 13 C nuclear magnetic resonance, and CO 2 adsorption. Characterization results demonstrate that HNO 3 treatment of biochars caused O enrichment, loss of alkyl C, and rise of aromaticity. The organic C-normalized surface area (CO 2 -SA/OC) of both GRABs and ANIBs generally increased after oxidation. The sorption nonlinearity of PHE by the biochars was weakened after HNO 3 treatment. The sorption capacity of PHE by oxidized GRABs was consistently elevated compared with the untreated samples, indicating that the high sorption capacity of PHE by GRABs may be maintained for a long time after being added into soils. By contrast, PHE sorption by ANIBs was unchanged or attenuated after oxidation. Polar groups facilitated the sorption of PHE by GRABs, while inhibited that by ANIBs. Pore-filling and π-π electron donor-acceptor interactions regulated PHE sorption by GRABs. Our results imply that GRABs are promising sorbents for environmental applications in view of their long-lasting sorption capacity. [ABSTRACT FROM AUTHOR]

Pyrogenic humic acid (HA) is released into the environment during the large-scale application of biochar. However, the biogeochemistry of pyrogenic organic matter (PyOM) fractions and their sorption of hydrophobic organic compounds (HOCs) are poorly understood in comparison with natural organic matter (NOM) fractions. HA and humin (HM) fractions isolated from soils and the oxidized biochars were characterized. Sorption of phenanthrene (PHE) by these fractions was also examined. The characterization results demonstrate that pyrogenic HAs are different from natural HAs, with the former having lower atomic H/C ratios, more abundant aromatic C, and higher concentrations of surface carboxylic groups. Compared with the fresh biochars, the Koc of PHE on their oxidized biochars, pyrogenic HA, and HM fractions were undiminished, which is encouraging for the use of biochar in soil remediation. The PyOM fractions exhibited stronger nonlinear sorption than the NOM fractions. In addition, the PyOM fractions had higher sorption capacity than the NOM fractions due to their low polar C content and high aryl C content. The results obtained from this work will shed new light on the impact of the addition of biochar on the biogeochemistry of soil organic matter and on the fate of HOCs in biochar-amended soil. [ABSTRACT FROM AUTHOR]

A pot experiment was conducted to investigate the effects of biochars on the availability of heavy metals (Cd, Cu, Mn, Ni, Pb, and Zn) to ryegrass in an alkaline contaminated soil. Biochars only slightly decreased or even increased the availability of heavy metals assesses by chemical extractant (a mixture of 0.05 mol L −1 ethylenediaminetetraacetic acid disodium, 0.01 mol L −1 CaCl 2 , and 0.1 mol L −1 triethanolamine). The significantly positive correlation between most chemical-extractable heavy metals and the ash content in biochars indicated the positive role of ash in this extraction. Biochars significantly reduced the plant uptake of heavy metals, excluding Mn. The absence of a positive correlation between the chemical-extractable heavy metals and the plant uptake counterparts (except for Mn) indicates that chemical extractability is probably not a reliable indicator to predict the phytoavailability of most heavy metals in alkaline soils treated with biochars. The obviously negative correlation between the plant uptake of heavy metals (except for Mn) and the (O + N)/C and H/C indicates that biochars with more polar groups, which were produced at lower temperatures, had higher efficiency for reducing the phytoavailability of heavy metals. The significantly negative correlations between the plant uptake of Mn and ryegrass biomass indicated the “dilution effect” caused by the improvement of biomass. These observations will be helpful for designing biochars as soil amendments to reduce the availability of heavy metals to plants in soils, especially in alkaline soils. [ABSTRACT FROM AUTHOR]

Sorption behavior of propiconazole (PROPI) by plant-residue derived biochars (PLABs) and animal waste-derived biochars (ANIBs) obtained at three heating treatment temperatures (HTTs) (300, 450 and 600 °C) (e.g., BCs300, BCs450, and BCs600) and their corresponding de-ashed BCs450 was investigated. PLABs belonged to high- or medium-C biochars and ANIBs were low-C biochars. Surface C concentrations of the tested biochars were generally higher than their corresponding bulk C. Surface polar groups were mainly composed of O-containing groups of minerals within biochars. The nonlinearity coefficients ( n ) of propiconazole (PROPI) sorption isotherms ranged from 0.23 to 0.64, which was significantly and negatively related to organic carbon (OC)–normalized CO 2 -surface area (CO 2 -SA/OC) of biochars. This correlation along with the positive relationship between CO 2 -SA/OC and aromaticity indicates that pore-filling in nanopores within aromatic C dominate nonlinear PROPI sorption. HTTs or C contents do not necessarily regulate PROPI sorption. Removal of minerals from BCs450 elevated PROPI sorption because minerals may exert certain influence on sorption via impacting spatial arrangement of polar groups and/or organic matter (OM)–mineral interactions. This study helps to better understand sorption behavior of PROPI to biochars and evaluate the potential role of biochar in water treatment systems. [ABSTRACT FROM AUTHOR]

Fourteen metal/metalloid elements and sixteen polycyclic aromatic hydrocarbons (PAHs) within biochars were quantified to investigate how heat treatment temperatures (HTTs) and feedstocks affect their concentration and composition. Concentrations and composition of metals/metalloids were strongly dependent upon feedstocks rather than HTTs. HTTs significantly affected concentrations and composition of PAHs. The highest concentration of PAHs was observed for plant residue-derived biochars (PLABs) produced at 450 °C and the opposite result was for animal waste-derived bichars. High mineral content was responsible for depolymerization of organic matter (OM), which facilitated high production of PAHs. High HTTs pyrolysis or combustion PAHs (COMB) of PLABs possibly blocks their micropores derived from other components within OM and leads to a decline of CO 2 -surface areas (CO 2 -SAs). Concentration of ∑COMB or individual PAH was affected by biochar properties, including composition and contents of functional groups, ash content, and CO 2 -SAs. PLABs produced at 600 °C were recommended for low toxicity. [ABSTRACT FROM AUTHOR]

The carbon sequestration potential of biochar depends on its stability in the soil and its priming effect on native soil organic carbon mineralization, which could be expected to be in turn affected by biochar processing, aging and soil clay content. This study applied stable carbon isotopes (δ13C) to quantify the mineralization of fresh and aged biochar pyrolyzed at 300, 450, and 600 °C and their priming effects on native soil organic carbon in two types of soils with different clay contents. At the end of the incubation, the total carbon loss of biochar-amended soil was 16–53% lower than that of unamended soil and the lowest carbon loss was found in soils amended with 600 °C biochar. Regardless of soil type, the proportion of biochar-carbon (carbon in the biochar) mineralized decreased with increasing pyrolysis temperature. For fresh biochar, the proportion of carbon mineralized was 13–47% higher in the sandy loam soil than in the sandy clay loam soil at the end of the incubation. However, soil type had a minimal effect on the mineralization proportion of aged biochar-carbon. The dissolved organic carbon increased after fresh and aged biochar was added to the sandy clay loam, but not the sandy loam, suggesting less carbon hydrolysis and solubilization from native soil organic carbon and biochar in the sandy loam soil. Moreover, biochar amendment increased the enzyme activities in sandy clay loam soil and either increased or had no effect on those in sandy loam soil. Fresh biochar had no effect on native soil organic carbon mineralization after it was applied, although a negative priming effect was observed after two−7 wk. For aged biochar, a negative priming effect was found for both soils. These findings demonstrated that biochar was more stable in clayey soils, and biochar produced at higher temperature indeed showed high soil carbon sequestration potential. [Display omitted] • Biochar was more stable in sandy clay loam soil than in sandy loam soil. • Fresh biochar had no priming effect on soil organic carbon in the early stage. • Fresh/aged biochar had a negative priming effect on soil organic carbon. • Both fresh and aged biochar addition reduced carbon loss from soil. [ABSTRACT FROM AUTHOR]

Abstract: The spatial arrangement of biochar and the exact underlying interaction mechanisms of biochar and hydrophobic organic compounds both remain largely unknown. The sorption of dibutyl phthalate (DBP) and phenanthrene (PHE) to plant- and manure-derived biochars in both single- and bi-solute systems was investigated. The significant positive relation between surface polarity and ash content suggests that minerals benefit the external distribution of polar groups on particle surfaces. PHE and DBP sorption by the biochars was regulated by their surface polarity. The PHE generally displayed a pronounced enhancement of DBP sorption, likely resulting from the formation of biochar–PHE–DBP complexes, suggesting that DBP and PHE had different sorption sites on the biochars. The enhancement of Cd2+ (a soft Lewis acid) on DBP sorption implied that π–π interactions should not dominate DBP sorption by biochars. The influence of Cd2+ on PHE sorption by biochars would depend on the balance between suppressive sorption by Cd2+ PHE bonding and enhanced sorption by Cd2+-complexed functionalities, and the amounts of Cd2+ adsorbed by biochars determined the relative role of increased sorption by Cd2+ in the overall PHE sorption. [Copyright &y& Elsevier]

Abstract: Molecular variations among different biochar categories translate into differences in their ability to function as sorbents to three phthalic acid esters (PAEs) representing a gradient in hydrophobicity. The sorption capacity (K OC) for all three PAEs was the greatest for amorphous biochars (heat treatment temperature HTT=400°C), followed by biochars produced at 300°C, and was best explained by the hydrophobicity of the sorbate. Greater alkyl C content and higher polarity of grass chars versus wood chars prepared at similar temperatures explained both (a) the difference in sorbent strength between feedstocks and (b) the maximum in sorbent strength at relatively low HTTs (300–400°C). Hydrophobic partitioning into ‘soft’ alkyl carbon and specific H-bonding involving char-bound O and N groups jointly account for high affinities of PAEs for low-HTT biochars. The results highlight the influence of feedstocks and HTTs on PAEs sorption strength and mechanism. [Copyright &y& Elsevier]

Sorption of two herbicides, fluridone (FLUN) and norflurazon (NORO), by two types of biochars, whole sediment, and various soil/sediment organic matter (OM) fractions including nonhydrolyzable carbon (NHC), black carbon (BC) and humic acid (HA) was examined. The single-point organic carbon (OC)-normalized distribution coefficients (K OC) of FLUN and NORO at low solution concentration (C e =0.01S W, solubility) for HA, NHC, and BC were about 3, 14, and 24 times and 3, 16, and 36 times larger than their bulk sediments, respectively, indicating the importance of different OM fractions in herbicide sorption. This study revealed that aliphatic moieties of the hydrothermal biochars and aromatic moieties of NHC samples, respectively, were possibly responsible for herbicide sorption. The hydrothermal biochar and condensed OM (i.e., NHC and BC) showed relatively high or similar herbicide sorption efficiency compared to the thermal biochar, suggesting that the hydrothermal biochar may serve as an amendment for minimizing off-site herbicide movement. [Copyright &y& Elsevier]

Abstract: Biochars produced at different heat treatment temperatures (HTT) are molecularly distinct and thus expected to show variable sorbent characteristics. We investigated the difference in sorption behavior of norflurazon (NORO) and fluridone (FLUN) to biochars from wood and grass feedstocks produced at different HTT. Amorphous biochars (HTT=400°C) exhibited the highest sorption parameter (K OC) for the two herbicides, emphasizing the importance of amorphous structural arrangement of aromatic moieties in these chars. Negative correlation between biochar aromaticity and isotherm nonlinearity (n) suggests that the n values were related mainly to total aromatic C content, not to that in the individual phases. Sorption of FLUN and NORO to low-temperature biochars (HTT=400°C) was about 1100 times and 6400 times greater, respectively, than a sediment sample, confirming that applications of low-temperature biochars to arable soils may reduce the mobility of FLUN and NORO, thus preventing unwanted herbicide leaching and subsequent contamination of sensitive water bodies. [Copyright &y& Elsevier]

Abstract: Thermal and hydrothermal biochars were characterized, and adsorption of bisphenol A (BPA), 17α-ethinyl estradiol (EE2) and phenanthrene (Phen) was determined to investigate the sorption characteristic difference between the two types of biochars. Thermal biochars were composed mostly of aromatic moieties, with low H/C and O/C ratios as compared to hydrothermal ones having diverse functional groups. Single-point organic carbon-normalized distribution coefficients (logK OC) of EE2 and BPA of hydrothermal biochars were higher than thermal biochars, while Phen logK OC values were comparable among them. X-ray diffraction and solid state nuclear magnetic resonance results suggested that hydrothermal biochars consisted of more amorphous aliphatic-C, possibly being responsible for their high sorption capacity of Phen. This study demonstrated that hydrothermal biochars could adsorb a wider spectrum of both polar and nonpolar organic contaminants than thermally produced biochars, suggesting that hydrothermal biochar derived from poultry and animal waste is a potential sorbent for agricultural and environmental applications. [Copyright &y& Elsevier]

• Stability of biochar was related with both biochar and soil properties. • Positive priming effect was common for manure biochar and sandy soil. • Manure-based and low temperature biochar more intensely promoted soil aggregation. • Influential mechanisms of biochar on HS amount and composition were proposed. Extensive application of biochar to soil exerts a profound effect on organic carbon (OC) in soils. However, the impact of biochar on the content and composition of OC has not been comprehensively summarized. This review provided a detailed examination on the stability of biochar and its effect on the amount, composition and turnover of soil OC, with key limitations and issues recognized. The direct input of labile and stable OC of biochar to soil OC pool, and indirect effects of biochar on soil OC by affecting soil physicochemical and biological properties were discussed. Both low stability of biochar and biochar-induced strong positive priming effect on OC mineralization were commonly observed in sandy soil added with biochar produced from manure at low temperature. The stable OC of biochar was composed of both aromatic OC and the OC fractions stabilized by soil minerals. Biochar mainly increased the formation of macro-aggregates, and this promotion was more intense for clayey soil added with manure-based low temperature-biochar. Additionally, potential influential mechanisms were proposed to explain the effect of biochar addition on amount and composition of humic substances in soils. This review will shed lights on the effect of biochar application on the amount, composition and turnover of native soil OC, and improve the understanding of the ecological effect of biochar on the soil functions. [ABSTRACT FROM AUTHOR]

The effects of soil minerals and microplastics on the stability of biochar (BC) have not been clearly clarified. Here, the mineralization of BC produced at low and high temperatures (L-BC and H-BC) and their artificial soils made of quartz, smectite and kaolinite, respectively, was investigated. BC and BC artificial soils were incubated with or without polyethylene (PE) over 180 d, and the CO 2 emission, molecular composition and microbial community structure were assessed. Minerals, especially quartz, had relatively more protection to H-BC than to L-BC. Moreover, smectite preserved aliphatic C of L-BC, and kaolinite protected its aromatic C and aliphatic C. Smectite and kaolinite likely had comparable ability to protect BCs. Quartz protected the aromatic C of H–BCs by adsorbing the hydrophobic aromatic C. Minerals also led to the shift of the dominant bacteria from r-strategists to K-strategists, which alleviated degradation of labile carbon and reduced the CO 2 emissions. PE decreased the CO 2 emissions of L-BC as well as its artificial soils and the opposite effect was observed for H-BC. PE enhanced the aromatic C associated with minerals within H-BC artificial soils, and inhibited the mineralization of H-BC. PE degradation by fungi (Aspergillus) could be largely responsible for the rise in CO 2 emissions of H-BC artificial soils. This study addressed the different effect of minerals and PE in the process of BC mineralization and provided the basis for elucidating the stability mechanism of BC in soil, which would be helpful for establishment of BC carbon sequestration policy. [Display omitted] • Minerals led to the shift of bacteria from r-to K-strategists in biochar (BC). • Quartz preserved aromatic C while smectite preserved aliphatic C in BC. • Kaolinite preserved aromatic/aliphatic C in BC. • Polyethylene promoted the accumulation of aromatic C in BC-mineral association. • Polyethylene increased CO 2 emission of biochar-mineral system due to fungi shift. [ABSTRACT FROM AUTHOR]

Biochars produced from rice straw, wheat straw and swine manure at 300, 450 and 600 °C were added to soil at 1, 5, 10, or 20% levels to determine whether they would predictably reduce the pore water concentration of imidacloprid, isoproturon, and atrazine. The sorption capacity of the mixtures increased with increasing biochar amounts. The enhanced sorption capacity could be attributed to the increased organic carbon (OC) content and surface area (SA) as well as the decreased hydrophobicity. Biochar dominated the overall sorption when its content was above 5%. The OC contents of the mixtures with 10% and 20% biochar were generally lower than the predicted values. This implies possible interaction between soil components and biochar and/or the effect of biochar oxidation. For soils amended with biochars produced at 300 °C, the N 2 SA (N 2 -SA) values were underestimated. The predicted CO 2 SA (CO 2 -SA) values of the mixtures at the biochar content of 10% and 20% were generally higher than the experimental values. Sorption of imidacloprid to the soils amended with biochar at 10% and 20% levels, excluding the soils amended with rice (SR300) and wheat (SW300) straw-derived biochar produced at 300 °C, was lower than the predicted value. For SR300 and SW300, the intrinsic sorption capacity of biochar was enhanced by 1.3–5.6 times, depending on the biochar, solute concentration, and biochar dose. This study indicates that biochars would be helpful to stabilize the soil contaminated with imidacloprid, isoproturon, and atrazine, but the sorption capacity of the mixtures could exceed or fall short of predicted values without assuming a cross-effect between soil and biochar. [ABSTRACT FROM AUTHOR]

Sorption behavior of acetochlor (ACE), dibutyl phthalate (DBP), 17α-Ethynyl estradiol (EE2) and phenanthrene (PHE) with biochars produced from three feedstocks (maize straw (MABs), pine wood dust (WDBs) and swine manure (SWBs)) at seven heat treatment temperatures (HTTs) was evaluated. The bulk polarity of these biochars declined with increasing HTT while the aromaticity and CO 2 -surface area (CO 2 -SA) rose. The surface OC contents of biochars were generally higher than bulk OC contents. The organic carbon (OC)-normalized CO 2 -SA (CO 2 -SA/OC) of biochars significantly correlated with the sorption coefficients ( n and log K oc ), suggesting that pore filling could dominate the sorption of tested sorbates. SWBs had higher log K oc values compared to MABs and WDBs, due to their higher ash contents. Additionally, the log K oc values for MABs was relatively greater than that for WDBs at low HTTs (≤400 °C), probably resulting from the higher CO 2 -SA/OC, ash contents and aromaticity of MABs. Surface polarity and the aliphatic C may dominate the sorption of WDBs obtained at relatively low HTTs (≤400 °C), while aromatic C affects the sorption of biochars at high HTTs. Results of this work aid to deepen our understanding of the sorption mechanisms, which is pivotal to wise utilization of biochars as sorbents for hazardous organic compounds. [ABSTRACT FROM AUTHOR]

Biochar of low-medium temperature may contain abundant dissolved organic carbon (BDOC), affecting its priming effect and carbon sequestration potential in soils. However, the direct and quantitative evidence for such impacts remains lacking. This study conducted incubation experiments on maize straw-derived 300/450 °C biochar, BDOC-extracted biochar residues and BDOC, and applied δ13C analysis to quantify biochar's mineralization and their priming effects on native soil organic carbon in a paddy soil. BDOC contained abundant lipid-, protein-, carbohydrate-like species, serving as nutrients for the metabolism of microorganisms, and thus enhanced native soil organic carbon's mineralization by 15–20%. After BDOC extraction, 300 °C biochar-trigged priming effect shifted from a positive (3.7 mg CO 2 –C kg−1 soil) to a negative state (−14.4 mg CO 2 –C kg−1 soil), and 450 °C biochar-induced negative priming effect increased by 31%; biochar's mineralization also decreased by 41–65%. Overall, after BDOC extraction, the net carbon balance in biochar-amended soils reduced by 7–8%. Furthermore, BDOC shifted the dominant priming mechanisms of biochar mainly by enhancing soil macro-aggregates while reducing sorptive protection for native soil organic carbon. Its extraction reduced the amount of soil macro-aggregates by 16–25% but enhanced the sorption affinity of native soil organic carbon by biochar by 68–122%. Additionally, after BDOC extraction, the microbial communities in biochar-amended soils contained more fungi and G+-bacteria. These findings proved that BDOC extraction appears a feasible strategy to enhance the short-period carbon sequestration potential of biochar. [Display omitted] • Biochar-DOC (BDOC) increased SOC mineralization by 15–20% mainly through co-metabolism. • BDOC reduced net carbon balance of biochar by 7–8%. • BDOC existence shifted the dominant priming mechanisms of biochar. • BDOC enhanced macroaggregates by 16–25% but reduced sorption for SOC by 68–122%. • Soils with BDOC-extracted residual biochar were dominated by fungi and G+-bacteria. [ABSTRACT FROM AUTHOR]

The soil near tailings areas is relatively barren and contaminated by multi-metal(loid)s, seriously threatening the safety of crop production. Here, biochar and nano-hydroxyapatite (nHAP) were combined to improve the sterilized and unsterilized polymetallic contaminated soil, and soil incubation and soybean pot experiments were designed. Results showed that biochar and nHAP not only increased soil C, N, and P but also effectively reduced multi-metal bioavailability, wherein the combined application of the two amendments had the best effect on metal immobilization. The synergistic effect of the two amendments decreased the acid-soluble contents of Co, Cu, Fe, and Pb in rhizosphere soils up to 86.75%, 80.69%, 89.09%, and 96.70%, respectively. The ameliorant reduced the accumulation of metal(loid)s in soybean plants, and rhizosphere microorganisms inhibited the migration of soil metals to plants. Additionally, biochar and nHAP regulated the rhizosphere soil microbial community. The rhizosphere soil of the sterilization group tended to prioritize the restoration of the original dominant bacteria. As, Pb, Fe, Urease, OM, TN, and TP were the critical environmental variables affecting rhizosphere soil bacterial communities. Therefore, combining biochar and nHAP is an environmentally friendly strategy to reduce polymetallic mobility in tailings soil and crops and improve soil microbial community structure. [Display omitted] • Biochar and nHAP combined immobilization of soil multi-metal(loid)s in mining area. • Biochar and nHAP effectively reduced the metal(loid) content in soybean plants. • Biochar and nHAP improved rhizosphere soil bacterial community. • Rhizosphere microorganisms can inhibit the migration of soil metals to plants. • As, Pb, Fe, Urease, OM, TN, and TP are the key factors affecting bacteria. [ABSTRACT FROM AUTHOR]

In order to successfully apply biochar to soil remediation such as immobilizing contaminants and sequestering carbon, the prerequisite is to maintain its strong sorption capacity for contaminants and stability after long-term aging. Simulated diagenesis was performed here to mimic real geochemical aging process of biochars with different mineral content. The results showed that biochars exhibited increasing aromaticity, thermal and chemical oxidation resistance, microporosity, but declined surface and total polarity after direct diagenesis. The involvement of minerals during diagenesis further increased the surface Fe, Al, and Si content, as well as surface polarity and thermal stability compared to direct diagenesis. Other property changes induced by mineral involvement were dependent on original biochar structure and mineral type. Diagenetic treatment slightly improved the sorption capacity of 450 and 600 °C biochars, regardless of mineral amendment. Only marginal effects were observed relating to their sorption capacity, while the structure of 250 °C biochars was most profoundly affected during diagenesis. Consequently, the simulated geochemical aging had positive effects on biochars long-term stability and ability to immobilize pollutants. [Display omitted] • Biochars (BCs) produced at different temperatures were subjected to diagenesis. • Diagenetic BCs had higher aromaticity, surface area, stability but lower polarity. • Diagenetic treatment induced the greatest structural changes for 250 °C BCs. • Diagenesis increased the imidacloprid sorption capacity of 450 and 600 °C BCs. • The effects of minerals depended on the BCs structure and mineral type. [ABSTRACT FROM AUTHOR]

In recent years, researchers have sought ways to efficiently convert biomass wastes into biochars with potential for environmental application. Fe and Al salts are reactive constituents that participate in biochar formation. However, their influences on the properties of biochar and its application on contaminant removal and carbon mitigation remain unknown. In this study, FeCl 3 and AlCl 3 were added to two typical biomass wastes (rice straw and poultry litter) during pyrochar and hydrochar production. The effects of Al (Ⅲ) and Fe (Ⅲ) on the molecular characteristics, stability, and adsorption efficiency of biochars for polar and nonpolar contaminants were explored. Results showed that Al (Ⅲ) and Fe (Ⅲ) significantly changed the properties of biochar. Al (Ⅲ) facilitated the carbonization of 250 °C pyrochar, but suppressed that of hydrochar and 450 °C pyrochar. Fe (Ⅲ) enhanced the formation of aromatic structures of both pyrochar and hydrochar, but reduced the abundance of lignin- and condensed aromatics-like species in their dissolved organic carbon fractions. Furthermore, Fe (Ⅲ) increased the stability and adsorption efficiency of pyrochar and hydrochar for both polar and nonpolar contaminants. These findings provide new insights into the design of functional biochar from biomass wastes with high stability and adsorption efficiency for organic contaminants. • Al (Ⅲ) and Fe (Ⅲ) were added to biomass during pyrochar and hydrochar production. • Effect of Al (Ⅲ) on thermal conversion of biochar depended on pyrolysis conditions. • Fe (Ⅲ) enhanced the formation of aromatic structure of both pyrochar and hydrochar. • Fe (Ⅲ) improved the stability and adsorption efficiency of biochar. [ABSTRACT FROM AUTHOR]

Plant-residue derived biochars from walnut shell, corn cob, corn straw, and rice straw obtained at three heat treatment temperatures (HTTs) (250 °C, 400 °C, and 600 °C) were applied in an incubation experiment to investigate how feedstocks, HTTs, and biochar properties affect the quantity of microorganisms, microbial community shift, enzyme activity, and biodegradation of polycyclic aromatic hydrocarbons (PAHs) in an aged contaminated soil. The microbial quantities (bacteria and fungi) and enzyme activities (catechol 2,3-dioxygenase and ligninolytic enzymes) generally decreased with the increase in HTTs. Microbial quantities had significantly positive correlations with the aliphatic carbon (C) ( p  < 0.01) but negative correlations with the aromatic C of biochars ( p  < 0.01). Similar findings were observed with enzyme activities, which had significantly positive correlations with microbial quantities ( p  < 0.05). Meanwhile, there were significantly positive correlations between C23O activity and bacterial quantity ( p  < 0.01) and between ligninolytic enzyme activities and the quantity of fungi ( p  < 0.05). These results indicate that the increase in recalcitrant aromatic C in biochars that occurs with the increase in HTT is unfavorable for the microbial growth and enzyme activity in the soil studied. Generally, application of biochars had little influence on the biodegradation rates of total PAHs. However, the effects of biochars on the biodegradation rates of major individual PAH (e.g., Nap, Phe, Pyr, and Chr) depended on both the types of biochars and the PAH properties such as benzene ring number and angular pattern of the ring linkage. [ABSTRACT FROM AUTHOR]

Despite the abundance of diagenetically derived organic materials in the environment, the effects of diagenesis on the structure and some of the associated properties (e.g., stability and sorption behavior) of organic matter (OM) remain unclear. Here, subcritical water treatment, suggested previously to mimic the diagenesis process, was chosen to further investigate the impact of diagenesis on OM compositions, stability and sorption of selected hydrophobic organic compounds. Humic acids and biochars were selected as representatives of natural and engineered OM, respectively. To examine the impact of mineral constituents on the diagenesis of OM, de-ashed samples, as well as samples amended with minerals (kaolinite, calcite and calcium dihydrogen phosphate), were included in the diagenesis treatment system. Comparison of OM composition before and after treatment indicated that simulated diagenesis resulted in lower bulk polarity, higher surface polarity and aromaticity and greater microporosity. Thermal analysis and chemical oxidation suggested that as a result of the increase in aromaticity and decrease in O/C ratio of OM, the resistance of OM to thermal and chemical oxidation was enhanced after simulated diagenesis. Moreover, our diagenesis treatment of OM induced stronger sorption nonlinearity and higher sorption capacity, for phenanthrene. Additionally, minerals protected the structure of OM from being changed by simulated diagenesis. Consequently, with regard to the susceptibility of OM to oxidative decay, the presence of minerals mitigated the increase in chemical stability imparted by simulated diagenesis but, on the other hand, protected OM from degradation. [ABSTRACT FROM AUTHOR]

The HNO 3 treatment was used to chemically modify the biochars produced from wheat straw (WH) and cow manure for U(VI) removal from aqueous solution. Macroscopic experiments proved that the enrichment of U(VI) on the biochars was regulated by surface complexation and electrostatic interactions. FTIR and XPS analyses confirmed that the highly efficient adsorption of U(VI) was due to the carboxyl groups on the biochar surfaces. The reducing agents of the R-CH 2 OH groups facilitated U(VI) adsorption on the untreated biochars. Owing to the higher contents of surface COO groups and more negative surface charge, the modified biochars showed enhanced U(VI) adsorption ability than the untreated ones. The maximum adsorption capacity of U(VI) by the oxidized WH was calculated to be 355.6 mg/g at pH 4.5 and 298 K, which was an improvement of 40 times relative to the untreated WH and was higher than that of most carbon-based adsorbents. [ABSTRACT FROM AUTHOR]

Assessing biochar's ability to resist oxidation is fundamental to understanding its potential to sequester carbon. Chemical oxidation exhibits good performance in estimating the oxidation resistance of biochar. Herein, oxidation resistance of 14 types of biochars produced from four feedstocks at different pyrolysis conditions (hydrothermal versus thermal carbonization) was investigated via hydrogen peroxide oxidation with varying concentrations. The oxidation resistance of organic carbon (C) of hydrochars was relatively higher than that of 250 °C pyrochars (P250) but was comparable to that of 450 °C pyrochars (P450). Both hydrochars and P450 from ash-rich feedstocks contained at least three different C pools (5.9–18.3% labile, 43.2–56.5% semi-labile and 26.9–45.9% stable C). Part (< 33%) of aromatic C within 600 °C pyrochars (P600) was easily oxidizable, which consisted of amorphous C. The influence of pyrolysis temperature upon oxidation resistance of biochars depended on the feedstock. For ash-rich feedstock (rice straw, swine manure and poultry litter), the oxidation resistance of biochars was determined by both aromaticity and mineral components, and mineral protection was regulated by pyrolysis conditions. The amorphous silicon within hydrochars and P450 could interact with C, preventing C from being oxidized, to some extent. Nevertheless, this type of protection did not occur for P250 and P600. [ABSTRACT FROM AUTHOR]

Pyrogenic dissolved organic matter (pyDOM) is the photolabile fraction in the dissolved organic matter pool. However, the molecular changes and reactive oxygen species generation of pyDOMs under continuous irradiation, and how these vary with feedstock type and pyrolysis temperature, are not well understood. In this study, the soluble fractions of 300 and 450 ºC biochars (pyDOM300 and pyDOM450) were subjected to photo-irradiation. PyDOM450 was of higher aromaticity, molecular variety, but lower unsaturation than pyDOM300. The molecular weight, aromaticity, and double bond equivalents of pyDOMs generally decreased after photo-irradiation. The degradation pattern of pyDOMs can be divided into two stages. In the initial 24 h, pyDOM300 degraded faster than pyDOM450, with the more profound transformation of condensed aromatics and carbohydrate into aliphatic/proteins, lignins, and tannins in pyDOM300. After 720 h irradiation, however, the degradation ratio of pyDOM450 (36.2–43.9%) exceeded that of pyDOM300 (23.7–30.3%), with the initially preserved condensed aromatics in pyDOM450 further transforming into aliphatic/proteins and tannins. This was potentially attributed to the generation of more reactive oxygen species (·OH and 1O 2) in pyDOM450. This study uncovered the photodegradation mechanisms of pyDOMs at molecular scale and helped to understand their cycling and effects on environment. [Display omitted] • PyDOM450 had higher aromaticity and molecular variety than pyDOM300. • The aromatic and fluorescent components in pyDOMs were prior to photodegradation. • PyDOM300 degraded more in 24 h irradiation but less after 720 h than pyDOM450. • The condensed aromatics in pyDOM300 were more photolabile than that of pyDOM450. • PyDOM450 generated more ·OH and 1O 2 than pyDOM300 after 24 h. [ABSTRACT FROM AUTHOR]

Highlights: [•] Sorption of PAEs in young and old leachates on AC, CNTs, and biochars were compared. [•] Carbonaceous sorbents had higher sorption of PAEs in YL than those in OL. [•] Young DOM slightly increased the sorption of DEP and DBP, but old DOC was contrary. [•] CNTs had remarkable lower sorption of PAEs in old leachates relative to AC. [Copyright &y& Elsevier]

As a promising soil amendment, biochar has demonstrated its potential for influencing soil nutrient transformations. The effects of biochar on soil phosphorus (P) transformations have received much less attention than its effects on carbon cycling. A review of the literature reveals that biochar applications to soils may have notable effects on the abundance, speciation, availability, and leaching loss of soil P. However, a comprehensive and systematic understanding of the biochar-induced environmental behavior of soil P has not been obtained so far. Therefore, in this review, we analyzed and identified the known and potential mechanisms through which biochar affects P behavior in soils: (1) biochar as a source of P provides soluble and exchangeable P to soil; (2) biochar enhances the availability of endogenic soil P by influencing P-related complexation and metabolism effects; and (3) biochar affects P leaching losses directly or indirectly by adsorbing P, improving P retention by soil, and facilitating P assimilation by plants. By presenting a broad and detailed illustration of P behaviors in biochar-amended soils, this paper suggests that the application of biochar to soils will help enlarge soil P pools, increase soil P availability, and decrease P leaching losses from soil. Additional studies are needed to further elucidate the long-term effects of biochar addition on soil P transformations, explore how biochar-derived dissolved organic matter (BDOM) affects the mobility and availability of soil mineral-associated P, and examine the transport of particulate P in biochar-amended soils. Unlabelled Image • Soil endogenic P availability will be enhanced by biochar application. • P leaching loss from soil can be reduced by biochar application. • Long-term field studies on P behaviors in biochar-amended soils are needed. • The transport of particulate P in biochar-amended soils remains to be explored. [ABSTRACT FROM AUTHOR]

• Minerals in biochars played key role in microbial activity in coking plant soil. • Rice straw pyrolyzing at 600 °C (RS6) effectively removed PAHs in coking plant soil. • Acidobacteria genera contributed to effective removal of PAHs in RS6-treated soil. • Mineral-rich biochar was recommended to remediate heavily PAH-contaminated soil. Twelve types of biochars were applied in a heavily contaminated soil from a coking plant to gain insights into the mechanism responsible for the microbial response to the addition of different biochar types into soil and biodegradation removal of polycyclic aromatic hydrocarbons (PAHs). The biochars primarily influenced the bacterial community at the genus level, while they strongly affected the fungal community not only at the genus level but also at the class and phylum levels. Principal component analysis (PCA) indicated that the inorganic minerals in biochars played a key role in stimulating microbial abundance (bacteria) and diversity (bacteria and fungi) in soil from the coking plant, and significantly negative correlations between the residual concentrations of PAHs in biochar-treated soils and the ash contents in biochars (generally, p < 0.05 for PAHs with 3–6 rings) were observed. These findings further suggested a positive effect of the inorganic minerals of biochars on stimulating changes in microorganisms, which could contribute to the biodegradation of PAHs in soil from the coking plant. Generally, the addition of biochars to the soils increased the biodegradation percentages of individual PAHs by 3.0–60.3% compared to those of the control. Among these biochars, rice straw-derived biochar pyrolyzed at 600 °C (RS6) effectively degraded PAHs from soil, with increasing biodegradation percentages of individual PAHs from 40.00% to 58.84%. This result was likely attributed to that the substantially specific Acidobacteria-related genera in RS6-treated soil were detected, which contributed to the effective biodegradation of PAHs. Accordingly, biochars pyrolyzed at a relatively high heating temperature with rice straw feedstock containing relatively high mineral nutrients are recommended for application to heavily PAH-contaminated soils. [ABSTRACT FROM AUTHOR]

In recent decades, great attention has been given to developing methods for targeted modification of biochar with innovative properties to improve its remediation efficacy. This study investigated the sorption performance of animal manure-derived hydrochar and pyrochar modified with oxidizing agents (H 2 O 2) and alkaline (NaOH) solutions for U(VI). Characterization results showed that H 2 O 2 and NaOH modification provided more carboxyl and hydroxyl groups, respectively, on sample surface. NaOH treatment remarkably increased specific surface area by three to six times. H 2 O 2 and NaOH impressively improved the maximum adsorption capacity (Q max) of biochar for U(VI), and NaOH modification induced a higher enhancement. Among different biochar types, pyrochar produced at a medium-high temperature not only showed the highest Q max but also the strongest improvement. After NaOH modification, its Q max (221.4 mg/g) was roughly 5-fold higher than that of original sample, showing that with NaOH modification, the pyrochar produced from animal manure under a medium-high thermal temperature might be a promising candidate as a sorbent for U(VI) remediation. In addition, the obvious shift in the XPS spectrum and pore structure of sample after U(VI) loading, along with the semi-quantification of the contribution of surface complexation mechanism, demonstrated that additional carboxyl and hydroxyl groups and higher SSA jointly explained more efficient U(VI) adsorption. This study not only proposes a promising adsorbent for U(VI) in nuclear wastewater, but also provides a way for the efficient recycling of animal manure wastes. Image 1 • Animal manure-derived hydrochar and pyrochar were modified by H 2 O 2 and NaOH. • NaOH modification impressively increased the CO 2 -SSA by 3–4 times. • Each modification improved the Q max for U(VI), and NaOH caused a higher enhancement. • 450 °C pyrochar not only showed the highest Q max but also the strongest improvement. • More surface COOH/C–OH and higher SSA of modified biochar caused the higher Q max. [ABSTRACT FROM AUTHOR]

• Biochar reduced uptake of thiamethoxam (THI) and metabolite clothianidin (CLO) by Chinese chive. • Biochar increased persistence of THI in soil, but reduced bioavailable content. • Biochar increased the sorption capacity of soil to THI and CLO. • Biochar increased soil microbial diversity, but decrease the biodegradation of THI. Information about the effect of biochar on the environmental fate of pesticide thiamethoxam (THI) in soil-vegetable ecosystems is limited. Therefore, the influence of a wood-derived biochar produced at 450 °C (BC450) on the uptake of THI by Chinese chive (Allium tuberosum) and its dissipation in soil was investigated using a 42-day pot experiment. BC450 addition decreased THI uptake and its metabolite clothianidin (CLO) by 22.8 % and 37.6 %, respectively. However, the half-life of THI in soil rose from 89.4–120 days, indicating that BC450 increased soil THI's persistence. The decreased bioavailability and increased persistence of THI resulted mainly from the higher sorption capacity of BC450 to THI and CLO, which, in turn, enhanced the soil sorption capacity. Consequently, the application of BC450 increased the soil microbial diversity and altered the structure of the microbial community. Although the abundance of Actinobacteria associated with the biodegradation of THI, increased the persistence of THI in the BC450-amended soil, mainly due to the decrease in bioavailable THI. Our findings provide valuable information about the effect of biochar on the fate of THI and its metabolites in agricultural soil and will help to guide the practical application of biochar to remediate soils contaminated with neonicotinoid pesticides. [ABSTRACT FROM AUTHOR]