Effect of different particle-size biochar on methane emissions during pig manure/wheat straw aerobic composting: Insights into pore characterization and microbial mechanisms

A novel micro-CT approach for in situ visualization of the spatial dynamics of mesovoids in aerobic composting piles

The spatial configuration of mesovoids profoundly affects the aerobic composting microenvironment, which governs vital processes such as greenhouse gas production and emission, thermal conduction, and overall composting efficiency. Nondestructive in-situ characterization of the composting spatial structure is crucial to better understand its interaction mechanism with the microenvironment. In this study, a valuable contribution to the field of composting research was made by introducing micro-computed tomography (micro-CT) tool for in situ three-dimensional (3D) visual characterizing the void structure dynamics of straw and manure compost pile units at the mesoscale. Representative samples at different composting stages derived from wheat straw and cow manure were procured by pre-embedding samplers in laboratory-based aerobic composting reactor systems. Based on an advanced Skyscan 1275 micro-CT system, scanning conditions and image processing algorithms were determined, and the void structure and their dynamic changes in the pile unit during composting were in-situ 3D visualized for the first time. The micro-CT images effectively reveal well-developed void structures exhibiting spatiotemporal dynamics during composting, and they exhibit excellent consistency with conventional macrophysical effects and wet chemical analyses. Micro-CT quantification results of the void structure parameters changes in pile unit during composting were as follows: percentage of the total voidage and the connected voidage in pile unit were in the range of 52.34%-58.56%, indicating a very suitable composting spatial structural microenvironment. This new micro-CT method provides a valuable perspective for analyzing and understanding the complex aerobic composting process.

Enhancing C and N turnover, functional bacteria abundance, and the efficiency of biowaste conversion using Streptomyces-Bacillus inoculation

Microbial inoculation plays a significant role in promoting the efficiency of biowaste conversion. This study investigates the function of Streptomyces-Bacillus Inoculants (SBI) on carbon (C) and nitrogen (N) conversion, and microbial dynamics, during cow manure (10% and 20% addition) and corn straw co-composting. Compared to inoculant-free controls, inoculant application accelerated the compost's thermophilic stage (8 vs 15 days), and significantly increased compost total N contents (+47%) and N-reductase activities (nitrate reductase: +60%; nitrite reductase: +219%). Both bacterial and fungal community succession were significantly affected by DOC, urease, and NH4+-N, while the fungal community was also significantly affected by cellulase. The contribution rate of Cupriavidus to the physicochemical factors of compost was as high as 83.40%, but by contrast there were no significantly different contributions (∼60%) among the top 20 fungal genera. Application of SBI induced significant correlations between bacteria, compost C/N ratio, and catalase enzymes, indicative of compost maturation. We recommend SBI as a promising bio-composting additive to accelerate C and N turnover and high-quality biowaste maturation. SBI boosts organic cycling by transforming biowastes into bio-fertilizers efficiently. This highlights the potential for SBI application to improve plant growth and soil quality in multiple contexts.

Mitigating methane emissions and global warming potential while increasing rice yield using biochar derived from leftover rice straw in a tropical paddy soil

The sustainable management of leftover rice straw through biochar production to mitigate CH4 emissions and enhance rice yield remains uncertain and undefined. Therefore, we evaluated the effects of using biochar derived from rice straw left on fields after harvest on greenhouse gas emissions, global warming potential (GWP), and rice yield in the paddy field. The experiment included three treatments: chemical fertilizer (CF), rice straw (RS, 10 t ha-1) + CF, and rice straw-derived biochar (BC, 3 t ha-1 based on the amount of product remaining after pyrolysis) + CF. Compared with CF, BC + CF significantly reduced cumulative CH4 and CO2 emissions, net GWP, and greenhouse gas emission intensity by 42.9%, 37.4%, 39.5%, and 67.8%, respectively. In contrast, RS + CF significantly increased cumulative CH4 emissions and net GWP by 119.3% and 13.8%, respectively. The reduced CH4 emissions were mainly caused by the addition of BC + CF, which did not increase the levels of dissolved organic carbon and microbial biomass carbon, consequently resulting in reduced archaeal abundance, unlike those observed in RS + CF. The BC + CF also enhanced soil total organic carbon content and rice grain yield. This study indicated that using biochar derived from leftover rice straw mitigates greenhouse gas emissions and improves rice productivity in tropical paddy soil.

Wheat straw biochar as an additive in swine manure Composting: An in-depth analysis of mixed material particle characteristics and interface interactions

In recent research, biochar has been proven to reduce the greenhouse gases and promote organic matter during the composting. However, gas degradation may be related to the microstructure of compost. To investigate the mechanism of biochar additive, composting was performed using swine manure, wheat straw and biochar and representative solid compost samples were analyzed to characterize the mixed biochar and compost particles. We focused on the microscale, such as the particle size distributions, surface morphologies, aerobic layer thicknesses and the functional groups. The biochar and compost particle agglomerations gradually became weaker and the predominant particle size in the experiment group was < 200 μm. The aerobic layer thickness (Lp) was determined by infrared spectroscopy using the wavenumbers 2856 and 1568 cm-1, which was 0-50 μm increased as composting proceeded in both groups. The biochar increased Lp and facilitated oxygen penetrating the compost particle cores. Besides, in the biochar-swine manure particle interface, the aliphatic compound in the organic components degraded and the content of aromaticity increased with the composting process, which was indicated by the absorption intensity at 2856 cm-1 decreasing trend and the absorption intensity at 1568 cm-1 increasing trend. In summary, biochar performed well in the microscale of compost pile.

Contribution of zeolite to nitrogen retention in chicken manure and straw compost: Reduction of NH3 and N2O emissions and increase of nitrate

Co-composting of chicken manure, straw and zeolite was investigated in a water bath heating system to estimate the effect of zeolite on physicochemical properties and metabolic functions related to nitrogen conversion. The results indicated that NH3 catches by zeolite was concentrated in the early stage and zeolite with 10 % addition reduced 28 % NH3 and 55 % N2O emissions as compost ended. The nitrate content in 10 % zeolite group was 17 % higher than that in control group. There was no significant increase of NO2- in zeolite group. More NO2- formed NH3, rather than being converted to NOx through denitrification. The abundance of nitrification genes amoA and hao increased except nxrA in zeolite groups. Denitrification was the most obvious at 20 d and zeolite decreased the abundance of denitrification genes narG, nirK and nosZ at this time.

Biochar preparation and evaluation of its effect in composting mechanism: A review

This article provides an overview of biochar application for organic waste co-composting and its biochemical transformation mechanism. As a composting amendment, biochar work in the adsorption of nutrients, the retention of oxygen and water, and the promotion of electron transfer. These functions serve the micro-organisms (physical support of niche) and determine changes in community structure beyond the succession of composing primary microorganisms. Biochar mediates resistance genes, mobile gene elements, and biochemical metabolic activities of organic matter degrading. The participation of biochar enriched the α-diversity of microbial communities at all stages of composting, and ultimately reflects the high γ-diversity. Finally, easy and convincing biochar preparation methods and characteristic need to be explored, in turn, the mechanism of biochar on composting microbes at the microscopic level can be studied in depth.

Time-dependent impact of co-matured manure with elemental sulfur and biochar on the soil agro-ecological properties and plant biomass

Farmyard manure is the most common type of organic fertilizer, and its properties depend mainly on the type of livestock, bedding material and the conditions of fermentation. Co-maturing of manure with other amendments to modify its final properties has been seen as a win-win strategy recently. This study aimed to evaluate the differences in the effect of unenriched manure and manures co-matured with biochar, elemental sulfur or both amendments on the soil physico-chemical and biological properties, and plant (barley, maize) biomass production. For this purpose a pot experiment was carried out in a time-dependent way. Samples were taken from 12 week-lasting (test crop barley) and 24 week-lasting (test crop maize) pot cultivation carried out in a growth chamber. Co-matured manure with biochar showed the highest rate of maturation expressed as humic to fulvic acid ratio, its amendment to soil significantly increased the dry aboveground biomass weight in the half-time (12 weeks) of experiment. However, the effect vanished after 24 weeks. We received for this variant highest long-term (24 weeks) contents of total carbon and nitrogen in soil. Contrarily, co-matured manure with biochar and elemental sulfur led to short-term carbon sequestration (the highest total carbon in 12 weeks) due to presumed retardation of microbial-mediated transformation of nutrients. We conclude that the prolonged pot experiment with biochar or elemental sulfur enriched manure led to the increased recalcitrancy of soil organic matter and retardation of soil nutrient transformation to the plant-available form.

Effects of 3D-printed bulking agent on microbial community succession and carbohydrate-active enzymes genes during swine manure composting

The bulking agent plays an important role in aerobic composting, but their shape, porosity, and homogeneity need to be optimized. In the present work, a bulking agent with a uniform shape was prepared by 3D printing to explore its influence on physicochemical parameters, microbial community succession, and gene abundance of carbohydrate-active enzymes (CAZymes) in swine manure aerobic composting. The results showed that adding 3D-printed bulking agents can increase maximum temperature, prolong the thermophilic period, and improve the degradation rate of volatile solids, which was attributed to ameliorative air permeability by the porous 3D-printed bulking agent. The abundances of some pathogenic bacteria decreased and CAZymes genes increased respectively in response to the addition of the 3D-printed bulking agent, implying it has a certain positive effect on improving the safety of compost products and promoting the degradation of organic matter. In summary, the 3D-printed bulking agent has good application potential in laboratory-scale aerobic composting.

Synergistic metabolism of carbon and nitrogen: Cyanate drives nitrogen cycle to conserve nitrogen in composting system

In this study, HCO₃^- was used as a co-substrate for cyanate metabolism to investigate its effect on nitrogen cycle in composting. The results showed that the carbamate content in experimental group (T) with HCO₃^- added was higher than that in control group (CP) during cooling period. Actinobacteria and Proteobacteria were the dominant phyla for cyanate metabolism, and the process was mediated by cyanase gene (cynS). The cynS abundance was 16.6% higher in T than CP. In cooling period, the nitrification gene hao in T was 8.125% higher than CP. Denitrification genes narG, narH, nirK, norB, and nosZ were 25.64%, 35.33%, 45.93%, 36.62%, and 36.12% less than CP, respectively. The nitrogen fixation gene nifH in T was consistently higher than CP in the late composting period. Conclusively, cyanate metabolism drove the nitrogen cycle by promoting nitrification, nitrogen fixation, and inhibiting denitrification, which improved nitrogen retention and compost quality.

Co-composting of cattle manure with biochar and elemental sulphur and its effects on manure quality, plant biomass and microbiological characteristics of post-harvest soil

Improvement of manure by co-composting with other materials is beneficial to the quality of the amended soil. Therefore, the manure was supplied with either biochar, elemental sulphur or both prior to fermentation in 50 L barrels for a period of eight weeks. The manure products were subsequently analyzed and used as fertilizers in a short-term pot experiment with barley fodder (Hordeum vulgare L.). The experiment was carried out under controlled conditions in a growth chamber for 12 weeks. The sulphur-enriched manure showed the lowest manure pH and highest ammonium content. The co-fermentation of biochar and sulphur led to the highest sulphur content and an abundance of ammonium-oxidizing bacteria in manure. The biochar+sulphur-enriched manure led to the highest dry aboveground plant biomass in the amended soil, whose value was 98% higher compared to the unamended control, 38% higher compared to the variant with biochar-enriched manure and 23% higher compared to the manure-amended variant. Amendment of the sulphur-enriched manure types led to the highest enzyme activities and soil respirations (basal, substrate-induced). This innovative approach to improve the quality of organic fertilizers utilizes treated agricultural waste (biochar) and a biotechnological residual product (elementary sulphur from biogas desulphurization) and hence contributes to the circular economy.

Carbon and N conservation during composting: A review

Composting, as a conventional solid waste treatment method, plays an essential role in carbon and nitrogen conservation, thereby reducing the loss of nutrients and energy. However, some carbon- and nitrogen-containing gases are inevitably released during the process of composting due to the different operating conditions, resulting in carbon and nitrogen losses. To overcome this obstacle, many researchers have been trying to optimize the adjustment parameters and add some amendments (i.e., pHysical amendments, chemical amendments and microbial amendments) to reduce the losses and enhance carbon and nitrogen conservation. However, investigation regarding mechanisms for the conservation of carbon and nitrogen are limited. Therefore, this review summarizes the studies on physical amendments, chemical amendments and microbial amendments and proposes underlying mechanisms for the enhancement of carbon and nitrogen conservation: adsorption or conversion, and also evaluates their contribution to the mitigation of the greenhouse effect, providing a theoretical basis for subsequent composting-related researchers to better improve carbon and nitrogen conservation measures. This paper also suggests that: assessing the contribution of composting as a process to global greenhouse gas mitigation requires a complete life cycle evaluation of composting. The current lack of compost clinker impact on carbon and nitrogen sequestration capacity of the application site needs to be explored by more research workers.

Three-dimensional printed bulking agents reduce antibiotic resistance genes in swine manure aerobic composting by regulating oxygen concentration to alter host microorganisms and mobile genetic elements

Antibiotic resistance genes (ARGs) in manure aerobic composting are a potential environmental pollutant. Therefore, reducing the abundance of ARGs is crucial. The effects of adding three-dimensional printed bulking agents (3DBAs) on ARGs in aerobic composting of swine manure were investigated in this study. Compared with the control group, 3DBAs with different addition dosages can greatest reduce the total ARGs by 5.98%, tetracycline resistance genes by 14.02%, macrolide resistance genes by 9.65%, and sulfonamide resistance genes by 20.59%. By further combining physicochemical parameters, host microorganisms, and mobile genetic elements (MGEs) for analysis, it was found that oxygen concentration was vital for ARGs reduction, and 3DBAs with regular porosity and uniform size indirectly regulate the activity of host microorganisms and MGEs abundance by changing the oxygen consumption, finally reducing vertical or horizontal ARGs transfer risks. Overall, 3DBAs addition is an effective strategy to reduce the abundance of ARGs in aerobic composting.

Effects of biochar and biogas residue amendments on N2O emission, enzyme activities and functional genes related with nitrification and denitrification during rice straw composting

This study was carried out to determine the response characteristics of N₂O emission, enzyme activities, and functional gene abundances involved in nitrification/denitirification process with biochar and biogas residue amendments during rice straw composting. The results revealed that N₂O release mainly occurred during the second fermentation phase. Biogas residue amendment promoted N₂O emission, while biochar addition decreased its emission by 33.6%. The nirK gene was abundant through composting process. Biogas residues increased the abundance of denitrification genes, resulting in further release of N₂O. Biochar enhanced nosZ gene abundance and accelerated the reduction of N₂O. Nitrate reductase (NR), nitrite reductase (NiR), N₂O reductase (N₂OR), and ammonia monooxygenase (AMO) activities were greatly stimulated by biochar or biogas residue rather than their combined addition. Pearson regression analysis indicated that N₂O emission negatively correlated with ammonium and positively correlated with nosZ, nirK, 18S rDNA, total nitrogen, and nitrate (P < 0.05).

Methane Emission Reduction and Biological Characteristics of Landfill Cover Soil Amended With Hydrophobic Biochar

Biochar-amended landfill cover soil (BLCS) can promote CH₄ and O₂ diffusion, but it increases rainwater entry in the rainy season, which is not conducive to CH₄ emission reduction. Hydrophobic biochar–amended landfill cover soil (HLCS) was prepared to investigate the changes in CH₄ emission reduction and biological characteristics, and BLCS was prepared as control. Results showed that rainwater retention time in HLCS was reduced by half. HLCS had a higher CH₄ reduction potential, achieving 100% CH₄ removal at 25% CH₄ content of landfill gas, and its main contributors to CH₄ reduction were found to be at depths of 10–30 cm (upper layer) and 50–60 cm (lower layer). The relative abundances of methane-oxidizing bacteria (MOB) in the upper and lower layers of HLCS were 55.93% and 46.93%, respectively, higher than those of BLCS (50.80% and 31.40%, respectively). Hydrophobic biochar amended to the landfill cover soil can realize waterproofing, ventilation, MOB growth promotion, and efficient CH₄ reduction.

Comparative study on the characteristics and environmental risk of potentially toxic elements in biochar obtained via pyrolysis of swine manure at lab and pilot scales

Pyrolysis is considered as a promising method to immobilize potentially toxic elements (PTEs) in animal manures. However, comparative study on characteristics and environmental risk of PTEs in biochar obtained by pyrolysis of animal manure at different reactors are lacking. In this study, swine manure was pyrolyzed at 300-600 °C in a lab-scale or pilot-scale reactor with the aim to investigate their effects on characteristics and environmental risk of As, Cd, Cu, Ni, Pb, and Zn in swine manure biochar. Results showed that biochars produced from pilot scale had lower pH and carbon (C) content but higher oxygen (O) content than those from lab scale. Biochars from pilot scale had higher total PTEs (except Cd) concentrations and releasable PTEs (except Pb) but lower CaCl₂-extractable PTEs and phytotoxicity germination index (GI) to radish seedings than those from lab scale. Chemical speciation analysis indicated that PTEs in biochar produced from pilot-scale fast pyrolysis at 400 °C had higher percentage of more stable fraction (F5 fraction) and lower potential ecological risk index (RI) than those from lab-scale slow pyrolysis. These findings demonstrated that bioavailability and potential ecological risk of PTE in swine manure biochar were greatly decrease in the pilot-scale pyrolysis reactor and the optimum temperature was 400 °C considering the lowest potential ecological risk index.

Effects of Pig Manure and Its Organic Fertilizer Application on Archaea and Methane Emission in Paddy Fields

Paddy fields account for 10% of global CH4 emissions, and the application of manure may increase CH4 emissions. In this study, high-throughput sequencing technology was used to investigate the effects of manure application on CH4 emissions and methanogens in paddy soil. Three treatments were studied: a controlled treatment (CK), pig manure (PM), and organic fertilizer (OF). The results showed that the contents of Zn, Cr and Ni in paddy soil increased with the application of manure, but the contents of heavy metals gradually decreased with the growth of rice. The Shannon index and Ace index showed that the application of pig manure and organic fertilizer less affected the diversity and richness of soil Archaea. The results of community composition analysis showed that Methanobacterium, Methanobrevibacter, Methanosphaera, Methanosarcina and Rice_Cluster_I were the main methanogens in paddy soil after manure and organic fertilizer application. Soil environmental factors were changed after applied manure, among which total potassium (TK) and total nitrogen (TN) were the main environmental factors affecting methanogens in paddy soil. The changes of soil environmental factors affected the community composition of methanogens, and the increase of the relative abundance of methanogens maybe the main reason for the increase of CH4 emission flux. The relative abundance of methanogens and CH4 emission flux in paddy soil were increased by both pig manure and organic fertilizer application, and pig manure had a bigger impact than organic manure.

Effects of feeding a pine-based biochar to beef cattle on subsequent manure nutrients, organic matter composition and greenhouse gas emissions

Biochar in ruminant diets is being assessed as a method for simultaneously improving animal production and reducing enteric CH₄ emissions, but little is known about subsequent biochar-manure interactions post-excretion. We examined chemical properties, greenhouse gas (GHG) emissions and organic matter (OM) composition during farm scale stockpiling (SP) or composting (CP) of manure from cattle that either received a pine-based biochar in their diet (BM) or did not (RM). Manure piles were monitored hourly for temperature and weekly for top surface CO₂, N₂O and CH₄ fluxes over 90 d in a semiarid location near Lethbridge, AB, Canada. Results indicate that cumulative CO₂, N₂O and CH₄ emissions were not affected by biochar, implying that BM was as labile as RM. The pH, total C (TC), NO₃-N and Olsen P were also not influenced by biochar, although it was observed that NH₄-N and OM extractability were both 13% lower in BM than RM. Solid-state ¹³C nuclear magnetic resonance (NMR) showed that biochar increased stockpile/compost aromaticity, yet it did not alter the bulk C speciation of manure OM. Further analysis by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) revealed that dissolved OM was enriched by strongly reduced chemical constituents, with BM providing more humic-like OM precursors than RM. Inclusion of a pine-based biochar in cattle diets to generate BM is consistent with current trends in the circular economy, "closing the loop" in agricultural supply chains by returning C-rich organic amendments to croplands. Stockpiling/composting the resulting BM, however, may not provide a clear advantage over directly mixing low levels of biochar with manure. Further research is required to validate BM as a tool to reduce the C footprint of livestock waste management.

Biochar - An effective additive for improving quality and reducing ecological risk of compost: A global meta-analysis

Biochar is considered as a promising additive with multi-benefits to compost production. However, how the biochar properties and composting conditions affect the composting process and quality and ecological risk of compost is still unclear. In the present study, we conducted a global meta-analysis based on 876 observations from 84 studies. Overall, regardless of biochar properties and composting conditions, biochar addition could significantly increase the pH (5.90%), germination index (26.6%), contents of nitrate nitrogen (56.6%), total nitrogen (9.50%), and total potassium (10.1%), and degree of polymerization (29.4%) while decrease the electrical conductivity (-5.70%), contents of ammonium nitrogen (-33.7%), bioavailable zinc (-22.9%), and bioavailable copper (-38.6%), and emissions of ammonia (-44.2%), nitrous oxide (-68.4%), and methane (-61.7%). Other compost indicators, including the carbon to nitrogen ratio and total phosphorus content, were found to be insignificantly affected by biochar addition. The responses of tested compost indicators affected by the biochar properties and composting conditions were further explored, based on which the addition of straw biochars at a rate of 10-15% was recommended due to its greater potential to improve quality of compost and reduce its ecological risk. Combining the results of linear regression analysis and structural equation model, the increase in compost pH caused by biochar addition was identified as the key mechanism for the increased nutrient content and decreased heavy metal bioavailability. These results could guide us to choose suitable kinds of biochar or develop engineered biochars with specific functionality to realize an optimal compost production mode.

Valorization of food waste and poultry manure through co-composting amending saw dust, biochar and mineral salts for value-added compost production

The present study proposes a system for co-composting food waste and poultry manure amended with rice husk biochar at different doses (0, 3, 5, 10%, w/w), saw dust, and salts. The effect of rice husk biochar on the characteristics of final compost was evaluated through stabilization indices such as electrical conductivity, bulk density, total porosity, gaseous emissions and nitrogen conservation. Results indicated that when compared to control, the biochar amendment extended the thermophilic stage of the composting, accelerated the biodegradation and mineralization of substrate mixture and helped in the maturation of the end product. Carbon dioxide, methane and ammonia emissions were reduced and the nitrogen conservation was achieved at a greater level in the 10% (w/w) biochar amended treatments. This study implies that the biochar and salts addition for co-composting food waste and poultry manure is beneficial to enhance the property of the compost.

Composting and its application in bioremediation of organic contaminants

This review investigates the findings of the most up-to-date literature on bioremediation via composting technology. Studies on bioremediation via composting began during the 1990s and have exponentially increased over the years. A total of 655 articles have been published since then, with 40% published in the last six years. The robustness, low cost, and easy operation of composting technology make it an attractive bioremediation strategy for organic contaminants prevalent in soils and sediment. Successful pilot-and large-scale bioremediation of organic contaminants, e.g., total petroleum hydrocarbons, plasticizers, and persistent organic pollutants (POPs) by composting, has been documented in the literature. For example, composting could remediate >90% diesel with concentrations as high as 26,315 mg kg^−a of initial composting material after 24 days. Composting has unique advantages over traditional single- and multi-strain bioaugmentation approaches, including a diverse microbial community, ease of operation, and the ability to handle higher concentrations. Bioremediation via composting depends on the diverse microbial community; thus, key parameters, including nutrients (C/N ratio = 25–30), moisture (55–65%), and oxygen content (O₂ > 10%) should be optimized for successful bioremediation. This review will provide bioremediation and composting researchers with the most recent finding in the field and stimulate new research ideas.

Effects of bulking agents on greenhouse gases and related genes in sludge composting

The effect of organic bulking agents on CO₂, NH₃, N₂O and CH₄ emission and related genes was evaluated in 40 days sludge composting with wood chip, wheat straw and rice husk, respectively. The results showed wood chip had the highest C/N of 111.3, total porosity of 93.13% and aeration porosity of 78.98% among three bulking agents. Wheat straw had the highest water-holding porosity of 25.62%, which could be critical factor increasing CH₄ production and reducing NH₃ emission. Moreover, there was no significant difference in N₂O emission rates in three composting systems with three bulking agents. RDA analysis showed a negative correlation between mcrA and NH + 4-N. Nitrate content in raw feedstock was dominant factor limiting N₂O yield due to low amoA. The continuous increase of oxidation-reduction potential was significantly positive correlated with pmoA and negative correlation with nirK and norB, which reduced N₂O and CH₄ production in the curing period.

Biochar for agronomy, animal farming, anaerobic digestion, composting, water treatment, soil remediation, construction, energy storage, and carbon sequestration: a review

In the context of climate change and the circular economy, biochar has recently found many applications in various sectors as a versatile and recycled material. Here, we review application of biochar-based for carbon sink, covering agronomy, animal farming, anaerobic digestion, composting, environmental remediation, construction, and energy storage. The ultimate storage reservoirs for biochar are soils, civil infrastructure, and landfills. Biochar-based fertilisers, which combine traditional fertilisers with biochar as a nutrient carrier, are promising in agronomy. The use of biochar as a feed additive for animals shows benefits in terms of animal growth, gut microbiota, reduced enteric methane production, egg yield, and endo-toxicant mitigation. Biochar enhances anaerobic digestion operations, primarily for biogas generation and upgrading, performance and sustainability, and the mitigation of inhibitory impurities. In composts, biochar controls the release of greenhouse gases and enhances microbial activity. Co-composted biochar improves soil properties and enhances crop productivity. Pristine and engineered biochar can also be employed for water and soil remediation to remove pollutants. In construction, biochar can be added to cement or asphalt, thus conferring structural and functional advantages. Incorporating biochar in biocomposites improves insulation, electromagnetic radiation protection and moisture control. Finally, synthesising biochar-based materials for energy storage applications requires additional functionalisation.

Research progress and prospects for using biochar to mitigate greenhouse gas emissions during composting: A review

Biochar possesses a unique porous structure and abundant surface functional groups, which can potentially help mitigate greenhouse gas (GHG) emissions from compost. This review summarizes the properties and functions of biochar, and the effects of biochar on common GHGs (methane (CH₄), carbon dioxide (CO₂), and nitrous oxide (N₂O)) and ammonia (NH₃, an indirect GHG) during composting. Studies have shown that it is possible to improve the mitigation of GHG emissions during composting by adjusting the biochar amount, type of raw material, pyrolysis temperature, and particle size. Biochar produced from crop residues and woody biomass has a greater effect on mitigating CH₄, N₂O, and NH₃ emissions during composting, and GHG emissions can be reduced significantly by adding about 10% (w/w) biochar. Biochar produced by high temperature pyrolysis (500-900 °C) has a greater effect on mitigating CH₄ and N₂O emissions, whereas biochar generated by low temperature pyrolysis (200-500 °C) is more effective at reducing NH₃ emissions. Interestingly, adding granular biochar is more beneficial for mitigating CH₄ emissions, whereas adding powdered biochar is better at reducing NH₃ emissions. According to the current research status, developing new methods for producing and using biochar (e.g., modified or combined with other additives) should be the focus of future research into mitigating GHG emissions during composting. The findings summarized in this review may provide a reference to allow the establishment of standards for using biochar to mitigate GHG emissions from compost.

Effects of the functional membrane covering on the gas emissions and bacterial community during aerobic composting

The effects of the functional membrane covering on the gas emissions and bacterial community during dairy cow manure aerobic composting were investigated. A lab-scale aerobic composting experiment was conducted with the control group (CK), Gore group (Gore), and ZT group (ZT), namely, without and with two functional membranes. Covering the functional membrane retained heat and improved the seed germination index in Gore and ZT groups. Compared with the CK group, the Gore membrane decreased NH₃ and N₂O emissions by 11.77% and 26.40%, respectively. The ZT membrane decreased N₂O and CO₂ emissions by 68.44% and 1.56%, respectively. The Gore and ZT membranes decreased the global warming potential by 16.97% and 53.41%, respectively. Moreover, Covering the two functional membranes improved the Actinobacteria relative abundance and were conducive to the degradation of volatile solid. Altogether, membrane-covered aerobic composting is an important technology for the resource utilization of organic waste.

Hyperthermophilic composting significantly decreases methane emissions: Insights into the microbial mechanism

Methane (CH₄) emissions from thermophilic composting (TC) are a substantial contributor to climate change. Hyperthermophilic composting (HTC) can influence CH₄-related microbial communities at temperatures up to 80 °C, and thus impact the CH₄ emissions during composting. This work investigated CH₄ emissions in sludge-derived HTC, and explored microbial community succession with quantitative PCR and high-throughput sequencing. Results demonstrated that HTC decreased CH₄ emissions by 52.5% compared with TC. In HTC, the CH₄ production potential and CH₄ oxidation potential were nearly 40% and 64.1% lower than that of TC, respectively. There was a reduction in the quantity of mcrA (3.7 × 10⁸ to 0 g^-1 TS) in HTC, which was more significant than the reduction in pmoA (2.0 × 10⁵ to 2.1 × 10⁴ g^-1 TS), and thus lead to reduce CH₄ emissions. It was found that the abundance of most methanogens and methanotrophs was inhibited in the hyperthermal environment, with a decline in Methanosarcina, Methanosaeta and Methanobrevibacter potentially being responsible for reducing the CH₄ emissions in HTC. This work provides important insight into mitigating CH₄ emissions in composting.

Gases emission during the continuous thermophilic composting of dairy manure amended with activated oil shale semicoke

NH₃ and greenhouse gases emission are big problems during composting, which can cause great nitrogen nutrient loss and environmental pollution. This study investigated effects of the porous bulking agent of oil shale semicoke and its activated material on the gases emission during the continuous thermophilic composting. Results showed addition of semicoke could significantly reduce the NH₃ emission by 74.65% due to its great adsorption capacity to NH₄⁺-N and NH₃, further the effect could be enhanced to 85.92% when utilizing the activated semicoke with larger pore volume and specific surface area. In addition, the CH₄ emission in the semicoke and activated semicoke group was also greatly mitigated, with a reduction of 67.23% and 87.62% respectively, while the N₂O emission was significantly increased by 93.14% and 100.82%. Quantification analysis of the functional genes found the abundance of mcrA was high at the massive CH₄-producing stage and the archaeal amoA was dominant at the N₂O-producing stage in all the composting groups. Correlation and redundancy analysis suggested there was a positive correlation between the CH₄ emission and mcrA. Addition of semicoke especially activated semicoke could reduce the CH₄ production by inhibiting the methanogens. For the NH₃ and N₂O, it was closely related with the nitrification process conducted by archaeal amoA. Addition of semicoke especially activated semicoke was beneficial for the growth of ammonia-oxidizing archaea, causing the less NH₄⁺-N transformation to NH₃ but more N₂O emission.

Microbial lipid biosynthesis from lignocellulosic biomass pyrolysis products

Lipids are a biorefinery platform to prepare fuel, food and health products. They are traditionally obtained from plants, but those of microbial origin allow for a better use of land and C resources, among other benefits. Several (thermo)chemical and biochemical strategies are used for the conversion of C contained in lignocellulosic biomass into lipids. In particular, pyrolysis can process virtually any biomass and is easy to scale up. Products offer cost-effective, renewable C in the form of readily fermentable molecules and other upgradable intermediates. Although the production of microbial lipids has been studied for 30 years, their incorporation into biorefineries was only described a few years ago. As pyrolysis becomes a profitable technology to depolymerize lignocellulosic biomass into assimilable C, the number of investigations on it raises significantly. This article describes the challenges and opportunities resulting from the combination of lignocellulosic biomass pyrolysis and lipid biosynthesis with oleaginous microorganisms. First, this work presents the basics of the individual processes, and then it shows state-of-the-art processes for the preparation of microbial lipids from biomass pyrolysis products. Advanced knowledge on separation techniques, structure analysis, and fermentability is detailed for each biomass pyrolysis fraction. Finally, the microbial fatty acid platform comprising biofuel, human food and animal feed products, and others, is presented. Literature shows that the microbial lipid production from anhydrosugars, like levoglucosan, and short-chain organic acids, like acetic acid, is straightforward. Indeed, processes achieving nearly theoretical yields form the latter have been described. Some authors have shown that lipid biosynthesis from different lignin sources is biochemically feasible. However, it still imposes major challenges regarding strain performance. No report on the fermentation of pyrolytic lignin is yet available. Research on the microbial uptake of pyrolytic humins remains vacant. Microorganisms that make use of methane show promising results at the proof-of-concept level. Overall, despite some issues need to be tackled, it is now possible to conceive new versatile biorefinery models by combining lignocellulosic biomass pyrolysis products and robust oleaginous microbial cell factories.

Impact of biochar application on gas emissions from liquid pig manure storage

Biochars have been used to reduce gas emissions from manure composting practices and to recover nutrients from wastewater because of their effective sorption capacity. However, relatively less is known about the impacts of different alkaline biochars on the gas emissions from liquid manure. Materials including two commercial biochars prepared from walnut shell (WA) and coconut shell (CC), respectively, and coal (CO) were applied (with manure/biochar ratio of 20:1 in weight) to examine their influence on NH₃, CH₄, and N₂O emissions from liquid pig manure during a 68-d period in comparison with a control (CK, without biochars), and to investigate the evolution of the manure N mass balances and the changes in biochar properties during liquid manure storage to understand the characteristics of biochar. Compared with the CK, the application of WA, CC, and CO biochars increased the NH₃ emissions by 4.00, 3.87, and 1.23 times, respectively, the absorbed N content of the biochars was markedly lower than the enhanced gaseous losses through NH₃ emissions. Similarly, the total greenhouse gas (GHG) emissions from the manure with WA, CC, and CO biochar application were 6.28, 5.55, and 0.83 times greater than those observed with the CK, respectively, and were mainly attributed to the enhanced CH₄ emissions. The significant contribution (5%-12%) of indirect GHG emissions from the enhanced NH₃-N losses was also identified. The hypothesis for the enhanced gas emissions from liquid manure with biochar addition has been discussed in the present study; however, further investigation in the future is warranted.

Biochar reinforced the populations of cbbL-containing autotrophic microbes and humic substance formation via sequestrating CO2 in composting process

The quality of compost is drastically reduced due to the loss of carbon, which negatively impacts the environment. Carbon emission reduction and carbon dioxide (CO₂) fixation have attracted much attention in composting research. In this study, the relationship between CO₂ emission, humic substances (HS) formation and cbbL-containing autotrophic microbes (CCAM) was analyzed by adding biochar during cow manure composting. The results showed that biochar can facilitate the degradation of organic matter (OM) and formation of HS, as well as reinforce the diversity and abundance of CCAM community, thereby promoting CO₂ fixation and reducing carbon loss during composting. High-throughput sequencing analysis revealed significant increase in Actinobacteriota and Proteobacteria abundance by 30.97 % and 10.48 %, respectively, thus increasing carbon fixation by 32.07 %. Additionally, Alpha diversity index increased significantly during thermophilic phase, while Shannon index increased by 143.12 % and Sobs index increased by 51.62 %. Redundancy analysis (RDA) indicated that CO₂ was positively correlated with C/N, temperature, HS and dissolved organic matter (DOM), while the abundance of Paeniclostridium, Corynebacterium, Bifidobacterium, Clostridium, Turicibacter and Romboutsia were positively correlated with temperature, CO₂, C/N and E₂/E₄ (p <  0.01).

Microbial mechanisms related to the effects of bamboo charcoal and bamboo vinegar on the degradation of organic matter and methane emissions during composting

In this study, functional microbial sequencing, quantitative PCR, and phylogenetic investigation of communities by reconstruction of unobserved states (PICRUSt) were employed to understand the microbial mechanisms related to the effects of bamboo charcoal (BC) and bamboo vinegar (BV) on the degradation of organic matter (OM) and methane (CH₄) emissions during composting. BC + BV resulted in the highest degradation of OM. BV was most effective treatment in controlling CH₄ emissions and it significantly reduced the abundance of the mcrA gene. Methanobrevibacter, Methanosarcina, and Methanocorpusculum were closely related to CH₄ emissions during the thermophilic composting period. PICRUSt analysis showed that BC and/or BV enhanced the metabolism associated with OM degradation and reduced CH₄ metabolism. Structural equation modeling indicated that BC + BV strongly promoted the metabolic activity of microorganisms, which had a positive effect on CH₄ emissions. Together these results suggest that BC + BV may be a suitable composting strategy if the aerobic conditions can be effectively improved during the thermophilic composting period.

Feedstock particle size and pyrolysis temperature regulate effects of biochar on soil nitrous oxide and carbon dioxide emissions

Atmospheric greenhouse gas (GHG) concentration increases are a serious problem impacting global climate. Mitigation of agricultural GHG production is crucial as fertilized soils contribute substantially to changes in GHG atmospheric composition. Biochar derived from agricultural or forestry biowaste has been widely used in agriculture and may help mitigate GHG emissions. While different kinds of biochar and their effects on GHG emissions have been studied, feedstock particle size may interact with pyrolysis temperature to impact biochar effects on GHG emissions, but this has not been investigated. Here, feedstock particle size effects on biochar characteristics and soil nitrous oxide (N₂O) and carbon dioxide (CO₂) emissions were studied using Camellia oleifera fruit shell feedstock with three particle size fractions (0.5-2, 2-5, and 5-10 mm) each pyrolyzed at 300, 450, and 600 °C. Results showed that dissolved organic carbon in biochar increased with particle size when pyrolyzed at 300 °C, but decreased with pyrolysis temperature. The 0.5-2 mm shell-derived biochar was associated with the lowest N₂O and CO₂ emission rates but the highest net nitrogen mineralization rates compared to 2-5 mm and 5-10 mm shell-derived biochar when pyrolyzed at 300 °C. Overall, shell particle size was more important for soil processes at lower pyrolysis temperatures with less variation among particle sizes at higher pyrolysis temperatures. The results indicated that feedstock particle size may interact with pyrolysis temperature and impact mitigation of soil N₂O and CO₂ emissions.

Evolution of phytotoxicity during the active phase of co-composting of chicken manure, tobacco powder and mushroom substrate

This study systematically investigated the phytotoxicity of chicken manure co-composted with tobacco powder and mushroom substrate on seed germination during active phase of composting. All compost products met the sanitation requirements specified in the Chinese national standard; however, only the mushroom substrate compost satisfied the maturity standard. From day 28, the composting entered the end of active phase and the concentrations of K+, Zn2+, Na+, Cu2+ and Fe3+ decreased gradually. Redundancy analysis indicated that the germination index, catalase and peroxidase activities was positively correlated with K+, Zn2+, Na+, Cu2+, Fe3+ and NO3--N, and negatively correlated with NH4+-N, Mg2+ and Ca2+, among which the most significant ions were Fe3+, Mg2+ and Zn2+ for all treatments. The malondialdehyde concentration of germinated seeds had adverse correlation with the above ions parameters.

Effects of microbial culture and chicken manure biochar on compost maturity and greenhouse gas emissions during chicken manure composting

The effects of chicken manure biochar (CMB) and chicken manure integrated microbial consortium (CMMC) as co-amendments were assessed on compost maturity and reduction of greenhouse gases and ammonia (NH₃) emissions during chicken manure composting. Composting was conducted using six combinations of CMB and CMCC (0 % CMB + 0 % CMMC, 0 % CMB + 10 % CMMC, 2 % CMB + 10 % CMMC, 4 % CMB + 10 % CMMC, 6 % CMB + 10 % CMMC, 10 % CMB + 10 % CMMC added on a dry weight basis) in six polyvinyl chloride composting reactors for 42 days under an aerobic environment. Co-amendment of CMB and CMMC extended the thermophilic stage and promoted compost maturity. The release of greenhouse gases [nitrous oxide (N₂O) and methane (CH₄)] and NH₃ from treatments co-amended by CMB and CMMC were reduced by 19.0-27.4 %, 9.3-55.9 % and 24.2-56.9 %, respectively, compared with the control. In addition, a redundancy analysis showed that the C/N ratio and temperature had a significant relationship with greenhouse gases and NH₃ emissions among all physiochemical characteristics.

Effects of multiple antibiotics on greenhouse gas and ammonia emissions during swine manure composting

Antibiotics are commonly used in intensive farming, leading to multiple antibiotic residue in livestock waste. However, the effects of multiple antibiotics on the emissions of greenhouse gas and ammonia remain indistinct. This paper selects sulfamethoxazole and norfloxacin to represent two different types of antibiotics to explore their effects on gaseous emissions. Four treatments including CK (control), SMZ (spiked with 5 mg kg^-1 DW sulfamethoxazole), NOR (spiked with 5 mg kg^-1 DW norfloxacin), and SN (spiked with 5 mg kg^-1 DW sulfamethoxazole and 5 mg kg^-1 DW norfloxacin) were composted for 65 days. Coexistence of sulfamethoxazole and norfloxacin facilitated the biodegradation of organic carbon, and significantly (p < 0.05) increased the cumulative CO₂ emission by 31.9%. The cumulative CH₄ emissions were decreased by 6.19%, 23.7%, and 27.6% for SMZ, NOR, and SN, respectively. The total NH₃ volatilization in SMZ and NOR rose to 1020 and 1190 mg kg^-1 DW, respectively. The individual existence of sulfamethoxazole significantly (p < 0.05) ascended the N₂O emission rate in the first 7 days due to the increase of NO₂^--N content. In addition, coexistence of sulfamethoxazole and norfloxacin notably dropped the total greenhouse gas emission (subtracting CO₂) by 15.5%.

Particle size reduction of rice straw enhances methane production under anaerobic digestion

The objective of this study was to investigate the effects of particle size reduction (20, 1, 0.15, and 0.075 mm) on biogas production from rice straw waste through batch anaerobic digestion experiments. To clarify the digestion mechanisms, the microbial community and rice straw properties including fractal dimension, dissolution abilities and the bio-liquefaction degree were determined. Particle size reduction of rice straw improved methane yield from 107 mL g^-1 VS to 197 mL g^-1 VS. The elevated digestion efficiency was attributed to the cellulose degradation (degradation rate from 27% to 93%) rather than hemicellulose or lignin. The comminution pretreatment improved the basic morphology, dissolution abilities and bio-liquefaction degree, which associated with the shifts in the bacterial community and the decreased bacterial diversity. These results suggested that particle size reduction of the rice straw in conjunction with optimized microbial growth could improve the methane yield in anaerobic digestion processes.

Evaluation of integrated biochar with bacterial consortium on gaseous emissions mitigation and nutrients sequestration during pig manure composting

This study focused on evaluate the effectiveness of biochar alone compare integrated with bacterial consortium amendment on the gaseous emissions mitigation as well as carbon and nitrogen sequestration during pig manure composting. Six additive treatments were performed based on uniform mixing pig manure with wheat straw [bacterial consortium (T2), 12%wood biochar (T3), 12%wood biochar + bacterial consortium (T4), 12%wheat straw biochar (T5), 12%wheat straw biochar + bacterial consortium (T6), while T1 without any additive]. The results obviously indicated that integrated use of biochar and bacterial consortium could remarkably relieved gaseous emissions, improved carbon and nitrogen conservation as well as accelerated maturity of composting. Notably the optimum combination was existed in T6 owing to lowest nutrient losses (nitrogen and carbon losses were 9.91 g/kg and 189.54 g/kg) and gas emissions (30.16 g/kg) as well as supreme maturity (germination index > 100%); it's an economic-practical and environmental protection novel disposal approach for solid waste.

Exploring the mechanisms of organic matter degradation and methane emission during sewage sludge composting with added vesuvianite: Insights into the prediction of microbial metabolic function and enzymatic activity

Effect mechanisms of organic matter (OM) degradation and methane (CH₄) emission during sewage sludge (SS) composting with added vesuvianite (V) were studied by high-throughput sequencing (HTS) and phylogenetic investigation of communities by reconstruction of unobserved states (PICRUSt). Results show that the addition of V accelerated the OM degradation and decreased the cumulative CH₄ emissions by 33.6% relative to the control. In addition, V significantly decreased the mcrA gene abundance and the methanogen community richness at the genus level. PICRUSt also indicated that V strengthens the microbial metabolic function and enzymatic activity related to OM degradation, and reduced the enzymatic activity related to CH₄ production. Methanogens community variation analysis proved the ratio of carbon and nitrogen and moisture content are the significant variables affecting CH₄ emissions. Thus, optimizing the ratio of carbon and nitrogen and moisture content will decrease CH₄ emission during SS composting.

Variation of Greenhouse Gases Fluxes and Soil Properties with Addition of Biochar from Farm-Wastes in Volcanic and Non-Volcanic Soils

The decomposition of organic wastes contributes to greenhouse gas (GHG) emissions and global warming. This study evaluated the effect of biochar (BC) produced from different farm wastes (chicken, pig and cow manures) on greenhouse gas emissions and soil chemical and biological properties in different grassland soils (volcanic and non-volcanic soils). A 288-day laboratory experiment was carried out, monitoring CO2, N2O and CH4 emissions and evaluating total C, soil pH, microbial biomass and enzymatic activity in three grassland soils. The results varied depending on the soil type and feedstock of BC produced. BC-cow decreased emissions of CO2 and CH4 fluxes for volcanic and non-volcanic soils, probably due to decreases in β-glucosidase activity. Biochars from cow and pig manures increased soil C content, favouring the persistence of C into the soil at 288-days of incubation. Soil pH increased with the application of BC in the soils.

Effects of biochar size and type on gaseous emissions during pig manure/wheat straw aerobic composting: Insights into multivariate-microscale characterization and microbial mechanism

Greenhouse gas and ammonia emissions during composting with different biochar types and particle sizes were investigated. Compared with powder-biochar, granular-biochar improved pore connectivity and was benefit to methanotrophs activities, like Methylococcaceae, reducing CH₄ emissions. At the same particle size, bamboo biochar (BB) had a higher pore volume and more aerobic microenvironment within the compost than rice straw biochar (RSB), reducing GHG emissions. Bamboo biochar had high aromatic compound and NO₃^- concentrations and therefore surface π-π electron donor/acceptor interactions, causing low N₂O emissions and inhibiting denitrifying bacteria (e.g., Bacteroidales). More CO and CO bonds in rice straw biochar than bamboo biochar caused lower NH₃ emissions using rice straw than bamboo biochar. Powdered biochar had more exposed reactive functional groups and decreased NH₃ production better than granular biochar. Powdered bamboo biochar controls gaseous emissions better than other biochars during aerobic pig manure/wheat straw composting.