Performance and mechanism of antibiotic resistance removal by biochar-enhanced sediment microbial fuel cell.

This study is the first to explore the performance and mechanism of biochar-impacted sediment microbial fuel cell for removing antibiotic resistance genes (ARGs), and examines the effects of different biochar contents. The addition of 5% biochar produced the highest output voltage and power density, which increased by 100% and 219%, respectively, while simultaneously reducing the abundance and risk of ARGs. Comparatively, the addition of moderate amount of biochar (1-5%) promoted the removal of ARGs, while the opposite was true for excessive (10%) biochar. Biochar affected ARGs through prophages, insertion sequence, and transposons. Biological factors and voltage jointly influenced ARGs variation, with the former accounting for 56%. Further analysis of functional genes indicated that biochar controlled ARGs by regulating the synthesis of genetic material and amino acids to influence metabolism. Overall, findings of this study shed light on the potential removal of ARGs in microbial electrochemical systems.

Enhancing simultaneous nitrogen and phosphorus availability through biochar addition during Chinese medicinal herbal residues composting: Synergism of microbes and humus.

The disposal of Chinese medicinal herbal residues (CMHRs) derived from Chinese medicine extraction poses a significant environmental challenge. Aerobic composting presents a sustainable treatment method, yet optimizing nutrient conversion remains a critical concern. This study investigated the effect and mechanism of biochar addition on nitrogen and phosphorus transformation to enhance the efficacy and quality of compost products. The findings reveal that incorporating biochar considerably enhanced the process of nutrient conversion. Specifically, biochar addition promoted the retention of bioavailable organic nitrogen and reduced nitrogen loss by 28.1 %. Meanwhile, adding biochar inhibited the conversion of available phosphorus to non-available phosphorus while enhancing its conversion to moderately available phosphorus, thereby preserving phosphorus availability post-composting. Furthermore, the inclusion of biochar altered microbial community structure and fostered organic matter retention and humus formation, ultimately affecting the modification of nitrogen and phosphorus forms. Structural equation modeling revealed that microbial community had a more pronounced impact on bioavailable organic nitrogen, while humic acid exerted a more significant effect on phosphorus availability. This research provides a viable approach and foundation for regulating the levels of nitrogen and phosphorus nutrients during composting, serving as a valuable reference for the development of sustainable utilization technologies pertaining to CMHRs.

Biochar dose-dependent impacts on soil bacterial and fungal diversity across the globe.

Biochar, a widely used material for soil amendment, has been found to offer numerous advantages in improving soil properties and the habitats for soil microorganisms. However, there is still a lack of global perspectives on the influence of various levels of biochar addition on soil microbial diversity and primary components. Thus, in our study, we performed a global meta-analysis of studies to determine how different doses of biochar affect soil total carbon (C), nitrogen (N), pH, alpha- and beta-diversity, and the major phyla of both bacterial and fungal communities. Our results revealed that biochar significantly increased soil pH by 4 %, soil total C and N by 68 % and 22 %, respectively, in which the positive effects increased with biochar doses. Moreover, biochar promoted soil bacterial richness and evenness by 3-8 % at the biochar concentrations of 1-5 % (w/w), while dramatically shifting bacterial beta-diversity at the doses of >2 % (w/w). Specifically, biochar exhibited significantly positive effects on bacterial phyla of Acidobacteria, Bacteroidetes, Gemmatimonadetes, and Proteobacteria, especially Deltaproteobacteria and Gammaproteobacteria, by 4-10 % depending on the concentrations. On the contrary, the bacterial phylum of Verrucomicrobia and fungal phylum of Basidiomycota showed significant negative responses to biochar by -8 % and -24 %, respectively. Therefore, our meta-analysis provides theoretical support for the development of optimized agricultural management practices by emphasizing biochar application dosing.

Zea mays cultivation, biochar, and arbuscular mycorrhizal fungal inoculation influenced lead immobilization.

Plant cultivation can influence the immobilization of heavy metals in soil. However, the roles of soil amendments and microorganisms in crop-based phytoremediation require further exploration. In this study, we evaluated the impact of Zea mays L. cultivation, biochar application, and arbuscular mycorrhizal fungi (AMF) inoculation on soil lead (Pb) immobilization. Our results indicated that biochar addition resulted in a significant, 42.00%, reduction in AMF colonization. Plant cultivation, AMF inoculation, and biochar addition all contributed to enhanced Pb immobilization, as evidenced by decreased levels of diethylenetriaminepentaacetic acid- and CaCl2-extractable Pb in the soil. Furthermore, soil subjected to plant cultivation with AMF and biochar displayed reduced concentrations of bioavailable Pb. Biochar addition altered the distribution of Pb fractions in the soil, transforming the acid-soluble form into the relatively inert reducible and oxidizable forms. Additionally, biochar, AMF, and their combined use promoted maize growth parameters, including height, stem diameter, shoot and root biomass, and phosphorus uptake, while simultaneously reducing the shoot Pb concentration. These findings suggest a synergistic effect in Pb phytostabilization. In summary, despite the adverse impact of biochar on mycorrhizal growth, cultivating maize with the concurrent use of biochar and AMF emerges as a recommended and effective strategy for Pb phytoremediation.IMPORTANCEHeavy metal contamination in soil is a pressing environmental issue, and phytoremediation has emerged as a sustainable approach for mitigating this problem. This study sheds light on the potential of maize cultivation, biochar application, and arbuscular mycorrhizal fungi (AMF) inoculation to enhance the immobilization of Pb in contaminated soil. The findings demonstrate that the combined use of biochar and AMF during maize cultivation can significantly improve Pb immobilization and simultaneously enhance maize growth, offering a promising strategy for sustainable and effective Pb phytoremediation practices. This research contributes valuable insights into the field of phytoremediation and its potential to address heavy metal pollution in agricultural soils.

Synergistic effects of arbuscular mycorrhizal fungi and biochar are highly beneficial to Ligustrum lucidum seedlings in Cd-contaminated soil.

Cadmium (Cd) contamination is a widespread environmental issue. There is a lack of knowledge about the impacts of applying arbuscular mycorrhizal fungi (AMF) and biochar, either alone or in their combination, on alleviating Cd phytotoxicity in Ligustrum lucidum. Therefore, a pot experiment was conducted in a greenhouse, where L. lucidum seedlings were randomly subjected to four regimes of AMF treatments (inoculation with sterilized AMF, with Rhizophagus irregularis, Diversispora versiformis, alone or a mixture of these two fungi), and two regimes of biochar treatments (with or without rice-husk biochar), as well as three regimes of Cd treatments (0, 15, and 150 mg kg-1), to examine the responses of growth, photosynthetic capabilities, soil enzymatic activities, nutritional concentrations, and Cd absorption of L. lucidum plants to the interactive effects of AMF, biochar, and Cd. The results demonstrated that under Cd contaminations, AMF alone significantly increased plant total dry weight, soil pH, and plant nitrogen (N) concentration by 84%, 3.2%, and 13.2%, respectively, and inhibited soil Cd transferring to plant shoot by 42.2%; biochar alone significantly enhanced net photosynthetic rate, soil pH, and soil catalase of non-mycorrhizal plants by 16.4%, 9%, and 11.9%, respectively, and reduced the soil Cd transferring to plant shoot by 44.7%; the additive effect between AMF and biochar greatly enhanced plant total dry weight by 101.9%, and reduced the soil Cd transferring to plant shoot by 51.6%. Furthermore, dual inoculation with D. versiformis and R. irregularis conferred more benefits on plants than the single fungal species did. Accordingly, amending Cd-contaminated soil with the combination of mixed-fungi inoculation and biochar application performed the best than either AMF or biochar alone. These responses may have been attributed to higher mycorrhizal colonization, soil pH, biomass accumulation, and biomass allocation to the roots, as well as photosynthetic capabilities. In conclusion, the combined use of mixed-fungi involving D. versiformis and R. irregularis and biochar addition had significant synergistic effects on enhancing plant performance and reducing Cd uptake of L. lucidum plants in Cd-contaminated soil.

Effects of Common Biochar and Acid-Modified Biochar on Growth and Quality of Spinach in Coastal Saline Soils.

The rational development and efficient utilization of saline soils can alleviate the problem of insufficient arable land faced by agricultural production in China. A prominent problem is improving soil salt and water conditions for promoting land resources' productivity in coastal areas. Biochar is widely used for soil improvement, as it has remarkable properties. A pot experiment was conducted to study the effects of two kinds of biochar (common biochar and acid-modified biochar) with three addition rates (2%, 4%, and 8%) on the growth, yield, photosynthetic characteristics, and quality of spinach. The results revealed that 2% and 4% common biochar increased the plant height, stem diameter, and leaf area index, effectively improving the yield of spinach and water productivity, while 8% common biochar was detrimental to the growth of spinach to some extent. Acid-modified biochar significantly benefited the growth and increased the water productivity of spinach, ensuring high yields, while also improved quality. Similarly, acid-modified biochar was less effective at high additions than at low-to-medium additions. The integrated biological response version 2 (IBRV2) values under acid-modified biochar treatments were all significantly higher than those under common biochar, but there is no significant difference among three treatments in the same biochar group, which suggested a pronounced amelioration in spinach growth within saline-alkali soil upon the incorporation of acid-modified biochar. Overall, applying acid-modified biochar at the rate of 4% exhibited enormous potential for increasing the yield and quality of spinach in saline soils.

Trade-offs in carbon-degrading enzyme activities limit long-term soil carbon sequestration with biochar addition.

Biochar amendment is one of the most promising agricultural approaches to tackle climate change by enhancing soil carbon (C) sequestration. Microbial-mediated decomposition processes are fundamental for the fate and persistence of sequestered C in soil, but the underlying mechanisms are uncertain. Here, we synthesise 923 observations regarding the effects of biochar addition (over periods ranging from several weeks to several years) on soil C-degrading enzyme activities from 130 articles across five continents worldwide. Our results showed that biochar addition increased soil ligninase activity targeting complex phenolic macromolecules by 7.1%, but suppressed cellulase activity degrading simpler polysaccharides by 8.3%. These shifts in enzyme activities explained the most variation of changes in soil C sequestration across a wide range of climatic, edaphic and experimental conditions, with biochar-induced shift in ligninase:cellulase ratio correlating negatively with soil C sequestration. Specifically, short-term (<1 year) biochar addition significantly reduced cellulase activity by 4.6% and enhanced soil organic C sequestration by 87.5%, whereas no significant responses were observed for ligninase activity and ligninase:cellulase ratio. However, long-term (≥1 year) biochar addition significantly enhanced ligninase activity by 5.2% and ligninase:cellulase ratio by 36.1%, leading to a smaller increase in soil organic C sequestration (25.1%). These results suggest that shifts in enzyme activities increased ligninase:cellulase ratio with time after biochar addition, limiting long-term soil C sequestration with biochar addition. Our work provides novel evidence to explain the diminished soil C sequestration with long-term biochar addition and suggests that earlier studies may have overestimated soil C sequestration with biochar addition by failing to consider the physiological acclimation of soil microorganisms over time.

Biochar improved the composting quality of seaweeds and cow manure mixture and altered the microbial community.

The beneficial effects of biochar addition during composting have been proved for many feedstocks, like manures and crop straws. However, the effect of biochar on the quality of composting product with seaweed as the feedstock and the bacterial response has not been investigated. In this study, the wheat straw biochar addition on the quality of the composting product and the bacterial response was explored at the rate of 0-10%. The results showed that biochar addition at the optimal rate (5%, w/w) could increase the germination index and the ratio of the optical density of humic acid at 460 nm to that at 660 nm (E4/E6) of the composting product, which indicated the decreased biotoxicity and enhanced compost maturity. The significant increase of the nitrate nitrogen (NO3 --N) content of the composting product proved the improvement of N cycling during composting process with biochar addition. The bacterial community of composting product was shifted and the relative abundance of some beneficial taxa (e.g., Muricauda and Woeseia) was significantly increased with biochar addition. Furthermore, the relative abundance of some bacterial genes related to amino acid metabolism and carbohydrate metabolism was also increased with biochar addition. The results of our study provided the positive effect of biochar addition on the composting of seaweed and could help to produce high quality seaweed fertilizer by composting with biochar addition.

Effects of Arbuscular Mycorrhizal Fungi and Biochar on Growth, Nutrient Absorption, and Physiological Properties of Maize (Zea mays L.).

Arbuscular mycorrhizal fungi (AMFs) and biochar are two common alternatives to chemical fertilizers applied to soil to improve crop growth. However, their interactive effects on maize (Zea mays L.) growth, nutrient absorption, and physiological properties remain poorly understood. In this study, maize plants were grown in pots treated with biochar and AMFs Diversispora eburnea, alone or in combination. The results showed that the individual application of AMFs or biochar increased maize growth and mineral contents in shoots and roots (including P, K, Ca, Na, Mg, Fe, Mn, and Zn). The chlorophyll a, chlorophyll b, and total chlorophyll contents in AMF-treated leaves were significantly higher than those in the control treatment group. However, AMFs had no synergistic effects with biochar on maize growth, nutrient absorption, nor photosynthetic pigments. The application of biochar to the soil significantly reduced mycorrhizal colonization by 40.58% in the root tissues, accompanied by a significant decline in mycorrhizal dependency from 80.57% to -28.67%. We conclude that the application of biochar and AMFs can affect maize growth, nutrient uptake, and physiological properties. Our study can provide vital information for further resource use optimization in agroecosystems.

Small biochar addition enhanced anammox granular sludge system for practical wastewater treatment: Performance and microbial community.

Anaerobic ammonium oxidation (Anammox) granular sludge (AnGS) has poor strength and is prone to disintegration under complex environmental conditions, especially in the presence of complex organic carbon, which renders the Anammox process instable. Herein, with a mixture of landfill leachate and domestic sewage as wastewater, the effect on the properties of AnGS with two small particle size (0.1-0.2 mm) biochars (coconut and peach biochars) addition were investigated at different COD concentrations (150 mg·L-1, 200 mg·L-1, and 250 mg·L-1), as well as at different BOD/TN (B/N) (0.3 and 0.5). Results showed that the nitrogen removal efficiencies decreased from 89 % to 72 % as the COD concentration increased by 100 mg·L-1, while peach biochar reactor had better nitrogen removal performance. Excessive organic carbon supply inhibits AnAOB proliferation and B/N had the most significant effect on AnAOB (p < 0.05). The Polymerase Chain Reaction (PCR) indicated peach biochar reactor get higher activity of anammox-related functional genes (hzsA, hdh).

Banana, pineapple, cassava and sugarcane residue biochars cannot mitigate ammonia volatilization from latosols in tropical farmland.

Ammonia (NH3) volatilization is a major pathway of soil nitrogen loss in tropical farmland, causing many environmental issues. Biochar can improve soil quality and affect soil NH3 volatilization. However, little is known about the effects of tropical crop residue biochar on soil NH3 volatilization in tropical farmland. Therefore, a laboratory incubation study was conducted using four kinds of tropical crop residue biochar (pineapple straw (stem and leaves), banana straw, cassava straw and sugarcane bagasse pyrolyzed at 500 °C) with five addition rates (0.5%, 1%, 2%, 4%, and 6%) to evaluate their impact on NH3 volatilization from tropical latosols. The results showed that NH3 volatilization peaked twice under biochar application, once at 1-5 days and again at 12-16 days. The cumulative NH3 volatilization (0.14-0.47 mg kg-1) of the 20 biochar treatments was higher than that of the control (0.12 mg kg-1). With the increase in the biochar addition rate, the soil pH, soil organic matter (SOM), urease activity, nitrate nitrogen content (NO3--N), nitrification rate and cumulative NH3 volatilization increased gradually, and the 6% biochar treatment resulted in the highest NH3 volatilization loss (0.19-0.47 mg kg-1). The type of biochar is also a main factor affecting soil NH3 volatilization. The cumulative NH3 volatilization was the highest under pineapple straw biochar, as it was 19-43% higher than when the other three biochars were applied. However, sugarcane bagasse biochar had the lowest cumulative NH3 volatilization due to its low quartz, sylvite and calcite contents, lack of -OH hydroxyl groups and high adsorbability. NH3 volatilization was positively correlated with the soil pH, SOM, urease activity, NO3--N and nitrification rate. In conclusion, four tropical crop residue biochars can increase NH3 volatilization in tropical latosols, so reducing NH3 volatilization needs to be further considered in tropical crop residue biochar applications.

Biochar Addition Altered Bacterial Community and Improved Photosynthetic Rate of Seagrass: A Mesocosm Study of Seagrass Thalassia hemprichii.

Seagrass meadows, as typical "blue carbon" ecosystems, play critical ecological roles in the marine ecosystem and decline every year. The application of biochar in soil has been proposed as a potential soil amendment to improve soil quality and mitigate global climate change. The effects of biochar on soil bacterial activities are integrally linked to the potential of biochar in achieving these benefits. However, biochar has been rarely applied in marine ecosystems. Whether the application of biochar could work on the seagrass ecosystem remained unknown. In this study, we investigated the responses of sediment and rhizosphere bacterial communities of seagrass Thalassia hemprichii to the biochar addition derived from maize at ratios of 5% by dry weight in the soil during a one-month incubation. Results indicated that the biochar addition significantly changed the sedimental environment with increasing pH, total phosphorus, and total kalium while total nitrogen decreased. Biochar addition significantly altered both the rhizosphere and sediment bacterial community compositions. The significant changes in rhizosphere bacterial community composition occurred after 30days of incubation, while the significant variations in sediment bacterial community composition distinctly delayed than in sediment occurred on the 14th day. Biochar application improved nitrification and denitrification, which may accelerate nitrogen cycling. As a stabilizer to communities, biochar addition decreased the importance of deterministic selection in sediment and changed the bacterial co-occurrence pattern. The biochar addition may promote seagrass photosynthesis and growth by altering the bacterial community compositions and improving nutrient circulation in the seagrass ecosystem, contributing to the seagrass health improvement. This study provided a theoretical basis for applying biochar to the seagrass ecosystem and shed light on the feasible application of biochar in the marine ecosystem. Graphical Abstract.

Evaluation of biochar addition and circulation control strengthening measures on efficiency and microecology of food waste treatment in anaerobic reactor.

The process of strengthening an expanded granular sludge blanket (EGSB) reactor under ammonia nitrogen stress conditions and by adopting three strengthening measures, namely, opening the circulation (OC), adding modified biochar (MB), adding modified biochar along with opening the circulation (MBOC), to treat food waste was studied. When the ammonia nitrogen concentration of influent increased to 1200 mg/L, the removal rate of COD reduced to about 75%, while the removal rate of ammonia nitrogen was about 6%. The average COD removal rate of the anaerobic reactor in the last 5 days of each operating cycle i.e. OC, MB and MBOC, was 85.51%, 84.11% and 90.03%, respectively. At the 30th day of each treatment-OC, MB and MBOC, the protease content in the sludge was 44.61, 42.47, 46.24 NH2-N (mg)/mg, respectively. and the content of coenzyme F420 was 0.244, 0.217 and 0.267 mmol/g, respectively. Proteobacteria was the most abundant phylum in the stage I (OC), reaching 34.36%. It was accounted for 16.68% and 21.38%, respectively, in the stage II (MB) and stage III (MBOC). The dominant archaea in the three stages were Methanosaeta, whose abundance was 38.98% in stage I, which increased to 64.94% and 64.01% in stage II and III, respectively. Among the active carbohydrate enzymes, the gene abundance of Glycoside transferases in the MBOC stage was the largest among the three stages.

Comparative effect of biochar and activated carbon addition on the mesophilic anaerobic digestion of piggery waste in batch mode.

A comparative study of the batch mesophilic anaerobic digestion of piggery waste was carried out with the addition of 5% biochar and 5% activated carbon. The results obtained showed that the bioreactors amended with biochar increased cumulative methane production, the kinetic constant for methane production and the COD removal efficiency compared to the control reactors and reactors with activated carbon addition. The maximum methane production and the kinetic constant were 6.9% higher in the reactors with biochar addition compared to the controls; while the COD removal efficiency was 3% higher in the case of biochar addition. In the case of activated carbon, only a slight improvement in anaerobic digestion performance was observed compared to the control.

Advanced pre-treatment of stripped biogas slurry by polyaluminum chloride coagulation and biochar adsorption coupled with ceramic membrane filtration.

Biogas slurry retention is a critical problem that cannot be solved by using the reuse method. Therefore, a new approach was taken to compensate for the shortcomings in the reuse method. In this study, after ammonia stripping, the ammonia nitrogen concentration in the stripped biogas slurry (SBS) still cannot reach the effluent standard (80 mg/L), so a variety of processes were needed to treat the SBS. Polyaluminum chloride (PAC) and rice husk biochar (B) were used to pretreat SBS. The effect of different pre-treatments on the COD value, ammonia nitrogen concentration, turbidity, total phosphorus (TP), and other indicators was investigated. After different pre-treatments by PAC and biochar, the pretreated SBS was filtered by a ceramic membrane, and the indicators of SBS were removed in the next step. After adding PAC and biochar together, ammonia nitrogen concentration was decreased to 68.09 mg/L, with a removal rate of 63%. The total phosphorus (TP) was also decreased, and its removal rate reached 92.5%. When the SBS was pretreated with PAC and biochar and then filtered through a ceramic membrane under different operating pressures, the removal rates of COD, total nitrogen (TN), turbidity, and suspended solids (SS) reached 81%, 88%, 96%, and 99% respectively. Moreover, by increasing the pressure from 0.1 to 0.3 MPa, the membrane flux was improved from 45 to 100.6 L/m2·h. This study proves that the combined pre-treatments of PAC and biochar can comprehensively remove various indicators from SBS while ensuring membrane flux during the membrane filtration process.

Biochar rhizosphere addition promoted Phragmites australis growth and changed soil properties in the Yellow River Delta.

Biochar addition can enhance plant growth and change soil physicochemical properties in saline soil. However, it is unclear whether the positioning of biochar additions (e.g., rhizosphere addition and surface addition) alters such impacts and whether such positioning effects interact with salinity levels. In the Yellow River Delta, China, we carried out a field experiment in which biochar was not added (control) or was added to the soil surface (surface addition) or to the soil at the rhizosphere position (rhizosphere addition) of Phragmites australis in three sites with different salt levels (1‰ - low, 5‰ - medium and 10‰ - high). Rhizosphere addition of biochar significantly improved the growth of P. australis, especially its fine root mass. Both rhizosphere addition and surface addition of biochar significantly decreased nitrate nitrogen content and electrical conductivity, and the inhibitory effects were more effective at the sites with medium and high salt levels in 2018. Structural equation modeling showed that biochar addition could directly increase the fine root mass of P. australis by decreasing the soil electrical conductivity, further improving the total mass of P. australis. Overall, rhizosphere addition of biochar is a better choice for improving the productivity of P. australis in saline soil and is beneficial to P. australis wetland restoration in the Yellow River Delta. Long-term field research is needed to better understand the effect and mechanism of biochar application.

Microbial community composition, co-occurrence network pattern and nitrogen transformation genera response to biochar addition in cattle manure-maize straw composting.

A better understanding of the microbial group influencing nitrogen (N) dynamics and cycling in composting matrix is critical in achieving good management to alleviate N loss and improve final compost quality. This study investigated the bacterial composition, structure, co-occurrence network patterns and topological roles of N transformation in cattle manure-maize straw composting using high-throughput sequencing. The two treatments used in this experiment were cattle manure and maize straw mixture (CM) and CM with 10% biochar addition (CMB). In both treatments, the bacterial community composition varied during composting and the major phyla included Actinobacteria, Firmicutes, Proteobacteria, Bacteroidetes and Chloroflexi. The phyla Actinobacteria and Proteobacteria were more abundant in CMB treatment while Firmicutes was abundant in CM piles. The metabolic functional profiles of bacteria was predicted using the "phylogenetic investigation of communities by reconstruction of unobserved states" (PICRUSt) which revealed that except for cellular processes pathway, CMB had slight higher abundance in metabolism, genetic information processing and environmental information processing than the CM. Pearson correlation revealed more significant relationship between the important bacteria communities and N transformation in CMB piles compared with CM. Furthermore, network pattern analysis revealed that the bacterial networks in biochar amended piles are more complex and harbored more positive links than that of no biochar piles. Corresponding agreement of multivariate analyses (correlation heatmap, stepwise regression, Path and network analyses) revealed that Psychrobacter, Thermopolyspora and Thermobifida in CM while Corynebacterium_1, Thermomonospora and Streptomyces in CMB were key bacterial genera affecting NH4+-N, NO3--N and total nitrogen (TN) transformation respectively during composting process. These results provide insight into nitrogen transformation and co-occurrence patterns mediating microbes and bacterial metabolism which could be useful in enhancing compost quality and mitigating N loss during composting.

Simultaneous effects of biochar and nitrogen fertilization on nitrous oxide and methane emissions from paddy rice.

Synthetic fertilizers are major agents of gaseous emissions including nitrous oxide (N2O), and rice cultivation is a primary source of methane (CH4) emission. Biochar (BC) addition to agricultural soils is a potential approach to mitigate N2O and CH4 emissions. This greenhouse study was conducted to assess the simultaneous effects of BC and nitrogen (N) fertilization to reduce N2O and CH4 emissions along with higher biomass accumulation in rice under controlled conditions. Nine treatment combinations of BC amendments at 0, 2 and 4% by weight (weight of BC/weight of soil) mixed into 3500 g of unsterile soil with 0, 70 and 140 kg N ha-1 were used in growing rice. Results show that BC-only treatments enhanced the volumetric water contents (VWC) by 9-14% and soil pH by 5-7% coupled with higher daily and cumulative seasonal CH4-C fluxes by 85-95% and 48-51%, respectively, compared with control treatment. Under 2% and 4% BC amendments, N at 140 kg ha-1 lowered the daily and cumulative seasonal CH4-C fluxes by 24-42% and 20-30%, respectively as compared to 70 kg N ha-1. Furthermore, BC amendments in N-treated soils reduced the daily and total seasonal N2O-N emissions by 27-67% and 49-61%, respectively, relative to N-only treatments. However, N addition in BC-amended soils showed 10-16% decreased VWC compared with the BC-only treated soils. In terms of rice growth, BC-only reduced the above- and below-ground biomass accumulation, delayed the tillering phase, and resulted in fewer vegetative tillers except for BC-treated pots with 140 kg N ha-1. Thus, this study suggests that the use of BC amendment at 2% with 140 kg N ha-1 may be a beneficial strategy to reduce the net GHG emissions from paddy rice in an Alfisol.

Enhanced nitrogen removal in biochar-added surface flow constructed wetlands: dealing with seasonal variation in the north China.

In the present study, the performance of surface flow constructed wetlands (SFCWs) added with different dosage of biochar (group A 0%, group B 10%, group C 20%; v/v) was investigated, to evaluate the effect of biochar on nitrogen removal of a constructed wetland. No significant difference was observed in NH4+-N removal among three groups even during different seasons. Labile organic carbon released from biochar distinctly enhanced denitrification process, which improved NO3--N removal efficiency by 4.58% in group B and 10.33% in group C. More importantly, compared with group A, biochar addition increased plant N removal by 82.24% and 192.11% in groups B and C, respectively. This result indicated that biochar could increase the accumulation of plant net biomass. In addition, TN removal of group A was much lower at low temperature (4.9 °C). However, no obvious influence of temperature on TN removal was observed in groups B and C with biochar addition. Microbial community analysis showed that, compared with that in group A, the total relative abundance of the main denitrification bacteria (Proteobacteria, Firmicutes, and Bacteroidetes) increased by 0.81% in group B and 13.63% in group C. These results provide a reasonable strategy for improving the performance of SFCWs under cold climate.

Reducing nitrogen loss and phytotoxicity during beer vinasse composting with biochar addition.

The aim of this study was to investigate the feasibility of composting of beer vinasse generated from brewing industry, the effect of biochar amendment on beer vinasse composting was also evaluated based on the changes of different physicochemical parameters, phytotoxicity and final compost quality. Four different treatments were performed of beer vinasse with biochar addition at 0, 5%, 10%, 15% (w/w dry basis). The final product obtained from beer vinasse composting was phytotoxicity-free (GI: 120.8%), mature (C/N: 19.88, NH4+-N: 295.0mg/kg, DOC: 9.76g/kg) and nutrient-rich (especially for P: 1.92%) compost except high N loss (60.76%), which had the potential to be as soil amendment or fertilizer. Biochar addition contributed to decomposition of DOC indicating higher microbial activity and attain phytotoxicity-free standard rapidly. N loss significantly reduced by 27% with biochar at 15% addition. And 15% biochar addition ensured all parameters, which was involved in composts quality, to attain the mature standard. Therefore, it was suggested that biochar addition at 15% was optimal.