Cow bone-derived biochar enhances microbial biomass and alters bacterial community composition and diversity in a smelter contaminated soil.

Bone waste could be utilized as a potential amendment for remediation of smelter-contaminated soils. Nevertheless, the influences of cow bone-derived biochar (CB) on soil microbial biomass and microbial community composition in multi-metal contaminated mining soils are still not clearly documented. Hence, the cow bone was used as feedstock material for biochar preparation and pyrolyzed at two temperatures such as 500 °C (CB500) and 800 °C (CB800), and added to a smelter soil at the dosage of 0 (unamended control), 2.5, 5, and 10% (w/w); then, the soil treatments were cultivated by maize. The CB effect on soil biochemical attributes and response of soil microbial biomass, bacterial communities, and diversity indices were examined after harvesting maize. Addition of CB enhanced total nutrient contents (i.e., total nitrogen up to 26% and total phosphorus P up to 27%) and the nutrients availability (i.e., NH4 up to 50%; NO3 up to 31%; Olsen P up to 48%; extractable K up to 18%; dissolved organic carbon up to 74%) in the treated soil, as compared to the control. The CB500 application revealed higher microbial biomass C (up to 66%), P (up to 41%), and bacterial gene abundance (up to 76%) than the control. However, comparatively a lower microbial biomass nitrogen and diversity indices were observed in the biochar (both with CB500 and CB800) treated soils than in the unamended soils. At the phylum level, the highest dose (10% of CB500 and CB800 resulted in contrasting effects on the Proteobacteria diversity. The CB50010 favored the Pseudomonas abundance (up to 793%), Saccharibacteria (583%), Parcubacteria (138%), Actinobacteria (65%), and Firmicutes (48%) microbial communities, while CB80010 favored the Saccharibacteria (386%), Proteobacteria (12%) and Acidobacteria (11%), as compared to the control. These results imply that CB500 and CB800 have a remarkable impact on microbial biomass and bacterial diversity in smelter contaminated soils. Particularly, CB500 was found to be suitable for enhancing microbial biomass, bacterial growth of specific phylum, and diversity, which can be useful for bioremediation of mining soils.

Design and characterization of a biomass template/SnO2 nanocomposite for enhanced adsorption of 2,4-dichlorophenol.

2,4-Dichlorophenol (2,4-DCP) is a hazardous chlorinated organic chemical derived from phenol that exerts serious effects on living organisms. In the present study, SnO2 templated with grapefruit peel carbon as a nanocomposite (SnO2@GPC) was designed via ball-milling, and its mechanism of 2,4-DCP adsorption in aqueous solution was determined. Batch adsorption experiments revealed that the maximum adsorption efficiency of SnO2@GPC occurred at 6.0 pH, 3 mg L-1 initial adsorbate concentration, 2 h contact time, and 293 K temperature. The SnO2@GPC nanocomposite and its non-tin-bearing counterpart, grapefruit derived char (@GPC), showed maximum adsorption capacities (QL) of 45.95 and 22.09 mg g-1 and partition coefficients of 41.77 and 10.83 mg g-1 µM-1, respectively. The adsorption of 2,4-DCP was best described by the Redlich-Peterson model followed by the Langmuir model with high correlation coefficients (R2 ≥ 0.96), and the adsorption kinetic data best fitted the pseudo-second-order model (R2 ≥ 0.98). The thermodynamic parameters indicated that the reaction was spontaneous, exothermic, and involved high affinity between SnO2@GPC and 2,4-DCP. The high desorption efficiency obtained (>80%) demonstrated the recyclability of the adsorbent. The enhanced QL of SnO2@GPC was due to the effective combination of GPC and SnO2. A thin porous layer of GPC on SnO2 nanoparticles provided effective channels, a large surface area, and an abundance of active sites for 2,4-DCP adsorption. Thus, the SnO2@GPC nanocomposite could potentially be used as a low-cost adsorbent to remove 2,4-DCP from water.

Performance of dry water- and porous carbon-based sorbents for carbon dioxide capture.

Carbon dioxide is the primary greenhouse gas that has a strong impact on global warming. Several technologies have been developed for capturing CO2 to mitigate the greenhouse effect. The objective of this research was to investigate the performance of several sorbents based on dry water and porous carbon materials for capturing CO2. Seven sorbents were prepared and comparatively evaluated for their CO2 capture capabilities: (i) Conocarpus biochar (CBC); (ii) commercial activated carbon (CAC); (iii) normal dry water (NDW); (iv) K2CO3-treated CBC (TCBC); (v) K2CO3-modified dry water (MDW); (vi) MDW and 2% TCBC (MDWTCBC); and (vii) MDW and 2% activated carbon (MDWCAC). The sorption process was carried out with initial CO2 concentration of 5.7%, temperature of 25 °C, feed gas flow rate of 0.5 l min-1 and a pressure of 1.0 bar. The pure CO2 was mixed with O2 or N2 to achieve the desired inlet concentration of CO2. The CO2 adsorption capacity and partition coefficient (PC) of the tested sorbents were evaluated at 5% and 100% breakthrough (BT). The results showed a longer breakthrough and equilibrium adsorption times for CO2 when mixed with N2 than with O2. Among all sorbents, both CAC and CBC showed enhanced CO2 capture performance with equilibrium (100% BT) adsorption capacities of 239 and 197 mg g-1, respectively (in terms of PC: 1.0 × 10-3 and 7.9 × 10-4 mol kg-1 Pa-1, respectively). In contrast, the performance of TCBC and the dry water-based sorbents was far lower than CAC or CBC. The CO2 adsorption data fitted well to the non-linearized form of the pseudo-first-order kinetic model. The Fourier-transform infrared spectral patterns indicated that the reaction of CO2 molecules with the hydroxyl groups of sorbents is possible through the formation of chemisorbed CO2 species. It could be concluded that the activation process did not play a role in increasing the CO2 capture performance in order to form new active sorption sites. However, Conocarpus biochar can be used as efficient sorbent for CO2 capture with a better performance than other materials tested previously (e.g., activated carbon).

Manure storage operations mitigate nutrient losses and their products can sustain soil fertility and enhance wheat productivity.

Livestock manure is a valuable source of nutrients for plants. However, poor handling practices during storage resulted in nutrient losses from the manure and decrement in its nitrogen (N) fertilizer value. We explored the influence of divergent storage methods on manure chemical composition, carbon (C) and N losses to the environment as well as fertilizer value of storage products after their application to the wheat. Fresh buffalo manure (FM) was subjected to different storage operations for a period of ∼6 months, (i) fermentation by covering with a plastic sheet (CM) (ii) placed under the roof (RM) (iii) heap was unturned (SM) to remain stacked at an open space and (iv) manure heap turned monthly (TM) to make compost. During storage, 8, 24, 45 and 46% of the initial Ntotal was lost from CM, RM, SM, and TM, respectively. The respective C losses from these treatments were 16, 34, 47 and 44% of the initial C content. After stored manures application to the wheat crop, mineral N in the soil remained 27% higher in CM (14.1 vs. 11.1 kg ha-1) and 3% (10.8 vs. 11.1 kg ha-1) lower in SM compared to FM treatment. In contrast, microbial biomass C and N was 35 (509 vs.782 mg C kg-1 soil) and 25% (278 vs.370 mg N kg-1 soil) lower in CM than FM treatment, respectively indicating lower N immobilization of CM in the soil. These findings could result in the highest grain yield (5166 kg ha-1) and N uptake (117 kg ha-1) in CM and the lowest in SM treatments (3105 and 61 kg ha-1, respectively). Similarly, wheat crop recovered 44, 15 and 13% N from CM, TM and SM, respectively. Hence, management operations play a critical role in conserving N during storage phase and after stored manure application to the field. Among the studied operations, storing animal manure under an impermeable plastic sheet is a much better and cheaper option for decreasing N losses during storage and improving wheat yield when incorporated into the soil. Therefore, by adopting this manure storage technique, farmers can improve the agro-environmental value of animal manure in Pakistan.

Lignite Scaffolding as Slow-Release N-Fertilizer Extended the SN Retention and Inhibited N Losses in Alkaline Calcareous Soils.

Conventional nitrogen (N) fertilizers particularly urea mineralized quickly in soil. Without sufficient plant uptake, this rapid mineralization favors the heavy N losses. Lignite is a naturally abundant and cost-effective adsorbent capable of extending multiple benefits as a soil amendment. Therefore, it was hypothesized that lignite as an N carrier for the synthesis of lignite-based slow-release N fertilizer (LSRNF) could offer an eco-friendly and affordable option to resolve the limitations of existing N fertilizer formulations. The LSRNF was developed by impregnating urea on deashed lignite and pelletized by a mixture of polyvinyl alcohol and starch as a binder. The results indicated that LSRNF significantly delayed the N mineralization and extended its release to >70 days. The surface morphology and physicochemical properties of LSRNF confirmed the sorption of urea on lignite. The study demonstrated that LSRNF also significantly decreased the NH3-volatilization up to 44.55%, NO3-leaching up to 57.01%, and N2O-emission up to 52.18% compared to conventional urea. So, this study proved that lignite is a suitable material to formulate new slow-release fertilizers, suiting to alkaline calcareous soils favorably where N losses are further higher compared to non-calcareous soils.

Comparative biotic and abiotic effects on greenhouse gas emissions from agricultural ecosystems: application of straw or biochar?

Farmland has become a significant contributor to greenhouse gas (GHG) emissions, and research has shown that the addition of straw or biochar may be a viable method for mitigating these emissions. However, there is a lack of understanding regarding the comparative biotic and abiotic effects of straw and biochar amendments on GHG emissions. To address this knowledge gap, we conducted a meta-analysis of 100 published papers to quantify the impact of straw and biochar application on GHG emissions. Our findings indicate that straw application significantly increased CO2 and CH4 emissions from agricultural ecosystems by 46.2% and 113.5%, respectively, but did not have a significant effect on N2O emissions. Conversely, biochar amendment significantly reduced CO2, CH4, and N2O emissions by an average of 11.0%, 31.7%, and 22.8%, respectively. We also found that straw and biochar amendments increased soil pH, soil organic carbon (SOC), and C/N ratio, and there were significant differences between them. Moreover, straw application significantly increased the microbial biomass carbon (MBC) content and microbial quotient by 37.1% and 20.1%, respectively, while biochar application increased the MBC content by 25.0% without a significant effect on the microbial quotient. Furthermore, both straw and biochar applications promoted the nitrification process and increased the abundance of ammonia-oxidizing bacteria (AOB) by 50.7% with straw and by 57.5% and 75.1% with biochar for ammonia-oxidizing archaea (AOA) and AOB, respectively. The denitrification process was also stimulated by straw or biochar amendment, resulting in an increase in the abundance of nirK by 22.9% and 16.8%, respectively. Biochar amendment additionally increased the abundance of nosZ by 29.4%, indicating that the main reason for reducing N2O emissions through biochar application is the conversion of NO3--N to N2. Thus, compared to straw application, biochar application is a more effective method for reducing greenhouse gas emissions.

Biochar promotes soil organic carbon sequestration and reduces net global warming potential in apple orchard: A two-year study in the Loess Plateau of China.

The Loess Plateau is China's primary apple-growing area, and the orchard is a significant source of greenhouse gases (GHGs) emissions due to high nitrogen fertilizer input. Thus, a two-year field study was carried out to investigate the effects of apple wood derived biochar on GHGs emissions during apple orchard production, including soil organic carbon sequestration (SOCSR) and net global warming potential (NGWP) assessments. There are four treatments in this study: 20 t ha-1 biochar in a non-fertilized plot (B); no biochar in a fertilized plot (F); 20 t ha-1 biochar in a fertilized plot (FB); no biochar in a non-fertilized plot (CK). Results showed that the combined application of biochar and fertilizer stimulated CO2 emissions by 9.25% and 8.39% than either biochar or fertilizer alone. Meanwhile, biochar in fertilized plot increased annual N2O emissions by 32.6% as compared to fertilized plot without biochar amendment. Compared with CK, biochar had no significant effect on GHG emissions in unfertilized plot. The N2O emission factor of FB and F were 0.91% and 0.45% respectively in 2017-2018 and they were both 0.34% in 2018-2019. Moreover, compared with CK, the FB and B treatments increased the SOCSR by 316.52% and 354.78%, while, decreased the NGWP by 368.93% and 480.91%, respectively. Thus, biochar application may help reduce the impact of apple production on climate change by sequestering more soil organic carbon and decreasing the NGWP.

Changes in surface characteristics and adsorption properties of 2,4,6-trichlorophenol following Fenton-like aging of biochar.

Fenton-like system formed in a natural soil environment deemed to be significant in the aging process of biochar. Aged biochars have distinct physico-chemical and surface properties compared to non-aged biochar. The aged biochar proved to be useful soil amendment due to its improved elements contents and surface properties. The biochar aging process resulted in increased surface area and pore volume, as well as carbon and oxygen-containing functional groups (such as C=O, -COOH, O-C=O etc.) on its surface, which were also associated with the adsorption behavior of 2,4,6-trichlorophenol (2,4,6-TCP). The biochar aging increased the adsorption capacity of 2,4,6-TCP, which was maximum at pH 3.0. The 2,4,6-TCP adsorption capacity of aged-bush biochar (ABB) and aged-peanut shell biochar (APB) was increased by 1.0-11.0% and 7.4-38.8%, respectively compared with bush biochar (BB) and peanut shell biochar (PB) at the same initial concentration of 2,4,6-TCP. All biochars had similar 2,4,6-TCP desorption rates ranging from 33.2 to 73.3% at different sorption temperatures and times. The desorbed components were mainly 2,4,6-TCP and other degraded components, which were low in concentration with small molecule substance. The results indicated that the aged-biochar could be effective for the long-term remediation of naturally organic polluted soils.

Effects of sheep bone biochar on soil quality, maize growth, and fractionation and phytoavailability of Cd and Zn in a mining-contaminated soil.

Biochar prepared from various feedstock materials has been utilized in recent years as a potential stabilizing agent for heavy metals in smelter-contaminated soils. However, the effectiveness of animal bone-derived biochar and its potential for the stabilization of contaminants remains unclear. In the present study, sheep bone-derived biochar (SB) was prepared at low (500 °C; SBL) and high temperatures (800 °C; SBH) and amended a smelter-contaminated soil at 2, 5, and 10% (w/w). The effects of SB on soil properties, bioavailable Zn and Cd and their geochemical fractions, bacterial community composition and activity, and the response of plant attributes (pigments and antioxidant activity) were assessed. Results showed that the SBH added at 10% (SBH10) increased soil organic carbon, total nitrogen, and phosphorus, and also increased the oxidizable and residual Zn and Cd fractions at the expense of the bioavailable fractions. The SBH10 lowered the Zn and Cd contents in maize roots (by 57 and 60%) and shoot (by 42 and 61%), respectively, compared to unamended control. Additionally, SBH10 enhanced urease (98%) and phosphates (107%) activities, but reduced dehydrogenase (58%) and ß-glucosidase (30%) activities. Regarding the effect of the pyrolysis temperature, SBH enhanced the activity of Acidobacteria, Bacteroidetes, Firmicutes, Nitrospirae, Verrucomicrobia, Chlorobi, and Microgenomates, but reduced Actinobacteria and Parcubacteria in comparison to SBL. However, only the SBL10 reduced the Proteobacteria community (by 9%). In conclusion, SB immobilized Zn and Cd in smelter-affected soils, enhanced the bacterial abundance and microbial function (urease, phosphates), and improved plant growth. However, validation of the results, obtained from the pot experiment, under field conditions is suggested.

Stable isotopes reveal the formation diversity of humic substances derived from different cotton straw-based materials.

Humic substances (HS) are essential in environment processes and carbon (C) sequestration in soils. In this study, organic materials such as cotton straw and its derived compost and biochar were added to the soil on a C-equivalent basis and incubated for 30 and 180 days in order to investigate the different forms of plant biomass derived C sequestration in HS. The C distribution in humic acid (HA), fulvic acid (FA), and humin (Hu) derived from organic materials was investigated using the 13C isotope method, while the catalase, sucrose, and ß-glucosidase activities were also determined. The results showed that C3 distribution of Hu derived from straw, compost and biochar increased from 40.94% to 67.12%, 74.47% and 80.75%, respectively. In addition, the increase of C3 distribution of HA or FA derived from straw, compost and biochar were 4.69%, 10.09% and 1.49%, respectively. There were significantly positive correlations between catalase, sucrase and ß-glucosidase activities and C3 derived HA and FA. The principal component analysis showed that catalase, sucrase and ß-glucosidase were explained mainly by the first principal component indicating a significant correlation. These findings suggest that straw, compost and biochar are mainly sequestrated in Hu. Comparatively, the straw and compost are more likely to contribute to the formation of HA and FA in soil, but biochar favors the Hu, which helps in soil C sequestration. The formation of HA and FA derived from organic materials was supported by catalase, sucrase and ß-glucosidase activities.

Fabrication and evaluation of silica embedded and zerovalent iron composited biochars for arsenate removal from water.

Waste date palm-derived biochar (DPBC) was modified with nano-zerovalent iron (BC-ZVI) and silica (BC-SiO2) through mechanochemical treatments and evaluated for arsenate (As(V)) removal from water. The feedstock and synthesized adsorbents were characterized through proximate, ultimate, and chemical analyses for structural, surface, and mineralogical compositions. BC-ZVI demonstrated the highest surface area and contents of C, N, and H. A pH range of 2-6 was optimum for BC-ZVI (100% removal), 3-6 for DPBC (89% removal), and 4-6 for BC-SiO2 (18% removal). Co-occurring PO43- and SO42- ions showed up to 100% reduction, while NO3- and Cl- ions resulted in up to 26% reduction in As(V) removal. Fitness of the Langmuir, Freundlich and Redlich-Peterson isotherms to As(V) adsorption data suggested that both mono- and multi-layer adsorption processes occurred. BC-ZVI showed superior performance by demonstrating the highest Langmuir maximum adsorption capacity (26.52 mg g-1), followed by DPBC, BC-SiO2, and commercial activated carbon (AC) (7.33, 5.22, and 3.28 mg g-1, respectively). Blockage of pores with silica particles in BC-SiO2 resulted in lower As(V) removal than that of DPBC. Pseudo-second-order kinetic model fitted well with the As(V) adsorption data (R2 = 0.99), while the Elovich, intraparticle diffusion, and power function models showed a moderate fitness (R2 = 0.53-0.93). The dynamics of As(V) adsorption onto the tested adsorbents exhibited the highest adsorption rates for BC-ZVI. As(V) adsorption onto the tested adsorbents was confirmed through post-adsorption FTIR, SEM-EDS, and XRD analyses. Adsorption of As(V) onto DPBC, BC-SiO2, and AC followed electrostatic interactions, surface complexation, and intraparticle diffusion, whereas, these mechanisms were further abetted by the higher surface area, nano-sized structure, and redox reactions of BC-ZVI.

Crop types have stronger effects on soil microbial communities and functionalities than biochar or fertilizer during two cycles of legume-cereal rotations of dry land.

The addition of biochar to agricultural fields has been widely studied, but most of these studies have emphasized its effects by growing a single type of crop over short- to long-term time spans. Additionally, a limited number of studies have focused on the soil microbial community composition with respect to biochar addition in legume-cereal crop rotation. In this study, we examined soil microbial community structures by adding biochar (0, 5, and 10 t ha-1) and fertilizer (nitrogen-N, phosphorous-P and potassium-K) during 2 cycles of mash bean and wheat rotations. The results showed that the bacterial (16S rRNA) gene abundance was often increased by biochar addition in the presence of mash bean (Vigna mungo L.) but not wheat. When the soil received fertilizer, the bacterial gene abundance was less responsive to biochar addition. Fungal (ITS rRNA) copy numbers were enhanced by biochar and fertilizer in presence of wheat but were decreased in the presence of mash bean. Fertilizer addition also resulted in less change in ITS genes after biochar addition. Microbial functional groups including Gram+, Gram- and Pseudomonas bacteria were stimulated by biochar or fertilizer only in mash bean soils, while mycorrhizae were significantly increased by biochar in wheat soils. Although biochar addition affected soil properties, microbial community assays were not greatly altered by these physicochemical properties. In conclusion, the crop type played a decisive role, rather than biochar or fertilizer addition, in shaping microbial community structures (16S and ITS phyla) during crop rotation.

Evaluating the efficiency of different natural clay sediments for the removal of chlortetracycline from aqueous solutions.

Natural clay sediments were collected from ten different localities in Saudi Arabia (S-1 from eastern, S-2 to S-4 from middle and S-5 to S-10 from western regions), characterized and evaluated for their efficiency towards chlortetracycline (CTC) removal from aqueous solutions. Sediment S-4 exhibited highest surface area (288.5 m2 g-1), followed by S-5, S-9, and S-1 (252.1, 249.6, and 110.4 m2 g-1, respectively). Sediments S-5, S-9, S-2, and S-4 showed the highest cation exchange capacities (CEC) (62.33, 56.54, 52.72, and 46.85 cmol kg-1, respectively). The pH range of 3.5-5.5 was optimum for the highest CTC removal. Freundlich model was best fitted to CTC sorption data (R2 = 0.96-0.99), followed by Dubinin-Radushkevich model (R2 = 0.89-0.97). The sediments S-4, S-5, and S-9 exhibited the highest CTC removal efficiency (98.80-99.05%), which could be due to higher smectite and kaolinite contents, CEC, surface area and layered structure. Post-sorption XRD patterns shown new peaks and peak shifts confirming the sorption of CTC. Electrostatic interactions, interlayer sorption and H-π bonding were the potential CTC sorption mechanisms. Therefore, natural clay sediments with high sorption capacities could efficiently remove CTC from contaminated aqueous media.

Effect of cotton straw-derived materials on native soil organic carbon.

Different types of crop straw and their derived biochars and compost treatments have huge potential for carbon sequestration to sustain crop productivity. In this study, cotton straw (straw), cotton straw-derived compost (compost) and cotton straw-derived biochar (biochar) with equivalent carbon (C) content were added to soil and incubated for 30 and 180 days. The C sequestration potential of these organic materials was determined by 13C isotope trace method. The structural characteristic of soil organic carbon (SOC) was analyzed by solid-state 13C NMR spectroscopy. The SOC concentration was measured by wet oxidation and dry combustion methods. The results showed that 50.84%, 41.03% and 38.55% of native SOC were replaced by biochar, compost, and straw, respectively. The carbohydrate C and methoxyl C contents were significantly higher in straw and biochar amendments respectively, while phenolic C and alkyl C were high in compost amendment and a higher proportion of aryl C occurred in biochar treatment. These findings revealed that straw material was easier to be decomposed, but compost and biochar showing better stability.

Biochar Immobilizes and Degrades 2,4,6-Trichlorophenol in Soils.

Soil contamination by chlorophenol compounds, such as 2,4,6-trichlorophenol (2,4,6-TCP), is of great concern because they are environmentally persistent, are difficult to degrade, and can lead to cancer. Thus, means of degrading these compounds in situ are desperately needed. Biochar was investigated as a material to sequester, reduce downward transport, and aid in soil 2,4,6-TCP degradation. In 2 column studies, wheat straw (Triticum aestivum L.)-derived biochar (pyrolyzed at 450 °C) application to soil (up to 5% by wt) improved soil water and soil organic carbon content. Biochar reduced 2,4,6-TCP downward transport, likely attributable to improved soil water mobility and retention, allowing 2,4,6-TCP to be more easily transported and sorbed to organic functional groups on biochar, leading to enhanced degradation. The 2,4,6-TCP was rapidly degraded into a combination of benzene derivatives and low-molecular weight organic compounds in the first 2 mo following biochar application. The present study provides evidence that biochars can be used to improve environmental quality by lessening the downward transport and enhancing the degradation of organochlorine compounds such as 2,4,6-TCP. Environ Toxicol Chem 2019;38:1364-1371. © 2019 SETAC.

Efficiency and surface characterization of different plant derived biochar for cadmium (Cd) mobility, bioaccessibility and bioavailability to Chinese cabbage in highly contaminated soil.

Cadmium (Cd) contamination in red soil has become a serious environmental concern due to its toxic effects on organisms and the food chain. Possible eco-friendly solutions for Cd immobilization were required to reduce its mobility through biochar. This study evaluated the comparative efficiency of rice straw (RSB), rice hull (RHB) and maize stover (MSB) derived biochar (BC) on Cd mobility and its accumulation in Chinese cabbage (Brassica chinensis L.), which is highly Cd accumulating crop. Results showed that the soil chemical properties (pH, organic carbon and nutrients) significantly increased with increasing the biochar application rate from 1.5% to 3%. Concentration of Cd decreased in CaCl2 extract by 58.6, 39.7 and 46.49% and in toxicity characteristics leaching test (TCLP) by 42.9, 32.7 and 36.7% for RSB, RHB and MSB, respectively at 3% application rate. The simple bioaccessibility extraction test (SBET) techniques showed a significant decrease in Cd by 30.5, 20.6 and 27.5% for RSB, RHB and MSB, respectively at the 3% application rate. Moreover, the Cd contents in the cabbage shoots decreased by 25, 21.3 and 23.1% for RSB, RHB and MSB at a 3% application rate and in the roots by 31.3, 23.9 and 26.5% for RSB, RHB and MSB at a 3% application rate, respectively. Bioaccumulation (BCF) and translocation factors (TF) were significantly decreased upto 26.5% and 11%, respectively among all biochar types. Overall, RSB demonstrated positive results as soil amendments for Cd immobilization and thereby, reducing its bioavailability in the Cd contaminated soil to mitigate food security risks.

Effects of chemical oxidation on surface oxygen-containing functional groups and adsorption behavior of biochar.

Biochar is a beneficial soil amendment but the changes in its surface properties during the aging process, especially the oxygen-containing functional groups and the associated adsorption behaviors, are not well documented. In this paper, the aged wheat straw biochar was simulated by chemical oxidation with HNO3-H2SO4 and NaOH-H2O2 systems. Characterization results showed that carbon loss and oxygen incorporation ran throughout the aging process. Surface oxygen-containing functional groups were found to be increased in all treated biochars, especially for carboxyl. Much more developed mesopores were observed in aging biochar, specific surface area was increased by 126% for biochar treated with NaOH-H2O2, and 226% for biochar treated with 40% of HNO3-H2SO4. Thermogravimetric analysis showed that the increasing oxygen-containing functional groups led to 14% and 30% mass loss by treating biochar with alkali and acid, respectively. The improved biochar surface through the increase of oxygen-containing functional groups enhanced the cadmium sorption capacity, and the sorption capacity increased by 21.2% in maximum. Roughed surface from oxidation was another reason for increasing cadmium adsorption. Results indicated that the adsorption performance of biochar on pollutant would be changed during aging process along with the changing surface properties.

An efficient phosphorus scavenging from aqueous solution using magnesiothermally modified bio-calcite.

Bio-calcite (BC) derived from waste hen eggshell was subjected to thermal treatments (calcined bio-calcite (CBC)). The BC and CBC were further modified via magnesiothermal treatments to produce modified bio-calcite (MBC) and modified calcined bio-calcite (MCBC), respectively, and evaluated as a novel green sorbent for P removal from aqueous solutions in the batch experiments. Modified BC exhibited improved structural and chemical properties, such as porosity, surface area, thermal stability, mineralogy and functional groups, than pristine material. Langmuir and Freundlich models well described the P sorption onto both thermally and magnesiothermally sorbents, respectively, suggesting mono- and multi-layer sorption. Langmuir predicted highest P sorption capacities were in the order of: MCBC (43.33 mg g-1) > MBC (35.63 mg g-1) > CBC (34.38 mg g-1) > BC (30.68 mg g-1). The MBC and MCBC removed 100% P up to 50 mg P L-1, which reduced to 35.43 and 39.96%, respectively, when P concentration was increased up to 1000 mg L-1. Dynamics of P sorption was well explained by the pseudo-second-order rate equation, with the highest sorption rate of 4.32 mg g-1 min-1 for the MCBC. Hydroxylapatite [Ca10(PO4)6(OH)2] and brushite [CaH(PO4)·2H2O] were detected after P sorption onto the modified sorbents by X-ray diffraction analysis, suggesting chemisorption as the operating sorption mechanism.

Enhanced rice production but greatly reduced carbon emission following biochar amendment in a metal-polluted rice paddy.

Soil amendment of biochar (BSA) had been shown effective for mitigating greenhouse gas (GHG) emission and alleviating metal stress to plants and microbes in soil. It has not yet been addressed if biochar exerts synergy effects on crop production, GHG emission, and microbial activity in metal-polluted soils. In a field experiment, biochar was amended at sequential rates at 0, 10, 20, and 40 t ha(-1), respectively, in a cadmium- and lead-contaminated rice paddy from the Tai lake Plain, China, before rice cropping in 2010. Fluxes of soil carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) were monitored using a static chamber method during the whole rice growing season (WRGS) of 2011. BSA significantly reduced soil CaCl2 extractable pool of Cd, and DTPA extractable pool of Cd and Pb. As compared to control, soil CO2 emission under BSA was observed to have no change at 10 t ha(-1) but decreased by 16-24% at 20 and 40 t ha(-1). In a similar trend, BSA at 20 and 40 t ha(-1) increased rice yield by 25-26% and thus enhanced ecosystem CO2 sequestration by 47-55% over the control. Seasonal total N2O emission was reduced by 7.1, 30.7, and 48.6% under BSA at 10, 20, and 40 t ha(-1), respectively. Overall, a net reduction in greenhouse gas balance (NGHGB) by 53.9-62.8% and in greenhouse gas intensity (GHGI) by 14.3-28.6% was observed following BSA at 20 and 40 t ha(-1). The present study suggested a great potential of biochar to enhancing grain yield while reducing carbon emission in metal-polluted rice paddies.

Does metal pollution matter with C retention by rice soil?

Soil respiration, resulting in decomposition of soil organic carbon (SOC), emits CO2 to the atmosphere and increases under climate warming. However, the impact of heavy metal pollution on soil respiration in croplands is not well understood. Here we show significantly increased soil respiration and efflux of both CO2 and CH4 with a concomitant reduction in SOC storage from a metal polluted rice soil in China. This change is linked to a decline in soil aggregation, in microbial abundance and in fungal dominance. The carbon release is presumably driven by changes in carbon cycling occurring in the stressed soil microbial community with heavy metal pollution in the soil. The pollution-induced increase in soil respiration and loss of SOC storage will likely counteract efforts to increase SOC sequestration in rice paddies for climate change mitigation.