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

Insight into N2O emission and denitrifier communities under different aeration intensities in composting of cattle manure from perspective of multi-factor interaction analysis

Nitrous oxide (N2O) emission from composting is a significant contributor to greenhouse effect and ozone depletion, which poses a threat to environment. To address the challenge of mitigating N2O emission during composting, this study investigated the response of N2O emission and denitrifier communities (detected by metagenome sequencing) to aeration intensities of 6 L/min (C6), 12 L/min (C12), and 18 L/min (C18) in cattle manure composting using multi-factor interaction analysis. Results showed that N2O emission occurred mainly at mesophilic phase. Cumulative N2O emission (QN2O, 9.79 mg·kg-1 DW) and total nitrogen loss (TN loss, 16.40 %) in C12 composting treatment were significantly lower than those in the other two treatments. The lower activity of denitrifying enzymes and the more complex and balanced network of denitrifiers and environmental factors might be responsible for the lower N2O emission. Denitrification was confirmed to be the major pathway for N2O production. Moisture content (MC) and Luteimonas were the key factors affecting N2O emission, and nosZ-carrying denitrifier played a significant role in reducing N2O emission. Although relative abundance of nirS was lower than that of nirK significantly (P < 0.05), nirS was the key gene influencing N2O emission. Community composition of denitrifier varied significantly with different aeration treatments (R2 = 0.931, P = 0.001), and Achromobacter was unique to C12 at mesophilic phase. Physicochemical factors had higher effect on QN2O, whereas denitrifying genes, enzymes and NOX- had lower effect on QN2O in C12. The complex relationship between N2O emission and the related factors could be explained by multi-factor interaction analysis more comprehensively. This study provided a novel understanding of mechanism of N2O emission regulated by aeration intensity in composting.

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.

Effects of C/N ratio on N2O emissions and nitrogen functional genes during vegetable waste composting

Nitrous oxide (N2O) generation during composting not only leads to losses of nitrogen (N) but also reduces the agronomic values and environmental benefits of composting. This study aimed to investigate the effect of the C/N ratio on N2O emissions and its underlying mechanisms at the genetic level during the composting of vegetable waste. The experiment was set up with three treatments, including low C/N treatment (LT, C/N = 18), middle C/N treatment (MT, C/N = 30), and high C/N treatment (HT, C/N = 50). The results showed that N2O emission was mainly concentrated in the cooling and maturation periods, and the cumulative N2O emissions decreased as the C/N ratio increased. Specifically, the cumulative N2O emission was 57,401 mg in LT, significantly higher than 2155 mg in MT and 1353 mg in HT. Lowering the C/N ratio led to increasing TN, NH4+-N, and NO3--N contents throughout the composting process. All detected nitrification-related gene abundances in LT continued to increase during composting, significantly surpassing those in MT during the cooling period. By contrast, in HT, there was a slight increase in the abundance of detected nitrification-related genes but a significant decrease in the abundance of narG, napA, and norB genes in the thermophilic and cooling periods. The structural equation model revealed that hao and nosZ genes were vital in N2O emissions. In conclusion, increasing the C/N ratio effectively contributed to N2O reduction during vegetable waste composting.

Microbial Sources and Sinks of Nitrous Oxide during Organic Waste Composting

Composting is widely used for organic waste management and is also a major source of nitrous oxide (N2O) emission. New insight into microbial sources and sinks is essential for process regulation to reduce N2O emission from composting. This study used genome-resolved metagenomics to decipher the genomic structures and physiological behaviors of individual bacteria for N2O sources and sinks during composting. Results showed that several nosZ-lacking denitrifiers in feedstocks drove N2O emission at the beginning of the composting. Such emission became negligible at the thermophilic stage, as high temperatures inhibited all denitrifiers for N2O production except for those containing nirK. The nosZ-lacking denitrifiers were notably enriched to increase N2O production at the cooling stage. Nevertheless, organic biodegradation limited energy availability for chemotaxis and flagellar assembly to restrain nirKS-containing denitrifiers for nitrate reduction toward N2O sources but insignificantly interrupt norBC- and nosZ-containing bacteria (particularly nosZ-containing nondenitrifiers) for N2O sinks by capturing N2O and nitric oxide (NO) for energy production, thereby reducing N2O emission at the mature stage. Furthermore, nosZII-type bacteria included all nosZ-containing nondenitrifiers and dominated N2O sinks. Thus, targeted strategies can be developed to restrict the physiological behaviors of nirKS-containing denitrifiers and expand the taxonomic distribution of nosZ for effective N2O mitigation in composting.

Greenhouse gas emission characteristics and influencing factors of agricultural waste composting process: A review

China, being a major agricultural nation, employs aerobic composting as an efficient approach to handle agricultural solid waste. Nevertheless, the composting process is often accompanied by greenhouse gas emissions, which are known contributors to global warming. Therefore, it is urgent to control the formation and emission of greenhouse gases from composting. This study provides a comprehensive analysis of the mechanisms underlying the production of nitrous oxide, methane, and carbon dioxide during the composting process of agricultural wastes. Additionally, it proposes an overview of the variables that affect greenhouse gas emissions, including the types of agricultural wastes (straw, livestock manure), the specifications for compost (pile size, aeration). The key factors of greenhouse gas emissions during composting process like physicochemical parameters, additives, and specific composting techniques (reuse of mature compost products, ultra-high-temperature composting, and electric-field-assisted composting) are summarized. Finally, it suggests directions and perspectives for future research. This study establishes a theoretical foundation for achieving carbon neutrality and promoting environmentally-friendly composting practices.

Synergistic effects of Fe-based nanomaterial catalyst on humic substances formation and microplastics mitigation during sewage sludge composting

In this study, a novel Fe-based nanomaterial catalyst (Fe0/FeS) was synthesized via a self-heating process and employed to explore its impact on the formation of humic substances and the mitigation of microplastics. The results reveal that Fe0/FeS exhibited a significant increase in humic acid content (71.01 mg kg-1). Similarly, the formation of humic substances resulted in a higher humification index (4.91). Moreover, the addition of Fe0/FeS accelerated the degradation of microplastics (MPs), resulting in a lower concentration of MPs (9487 particles/kg) compared to the control experiments (22792 particles/kg). Fe0/FeS significantly increased the abundance of medium-sized MPs (50-200 μm) and reduced the abundance of small-sized (10-50 μm) and large-sized MPs (>1000 μm). These results can be attributed to the Fe0/FeS regulating the ▪OH production and specific microorganisms to promote humic substance formation and the degradation of MPs. This study proposes a feasible strategy to improve composting characteristics and reduce contaminants.

Life cycle assessment of greenhouse gas emissions for various feedstocks-based biochars as soil amendment

Anthropogenic greenhouse gas (GHG) emissions are a major factor influencing climate change. The application of biochar as a soil amendment may be an effective way to reduce GHG emissions. Life cycle assessment (LCA) is widely used to assess the impact of biochar as a soil amendment on GHG emissions. The methodology is effective in assessing the impacts of the various stages of the biochar life cycle on GHG emissions. However, because of the diversity of biochar types, it is difficult to summarize the regularity of biochar life cycle impacts on GHG emissions. This paper summarizes the pathways of biochar's effect on GHG emissions and in-depth analyzes the mechanism of biochar's influence on GHG emissions from the perspective of biochar properties. Finally, the review comprehensively analyzes the effects of different types of biochar feedstock on GHG emissions at the stages of feedstock pretreatment, preparation, and application of the life cycle. The conclusions are as follows: (1) Biochar affects GHG emissions in three ways: feedstock supply, pyrolysis process, and application process. (2) The impact of biochar on GHG emissions is influenced by a combination of the physicochemical properties of biochar. (3) Biochar has a positive impact (feedstock pretreatment stage and preparation stage) or a negative impact (application stage) on life cycle GHG emissions. (4) The carbon sequestration capacity of biochar varies by feedstock type. The ranking of carbon sequestration capacity is waste wood biochar (WWB) > crop straw biochar (CSB) > livestock manure biochar (LMB) > sewage sludge biochar (SSB).

Urea addition as an enhanced strategy for degradation of petroleum contaminants during co-composting of straw and pig manure: Evidences from microbial community and enzyme activity evaluation

Alterations in microbial community succession patterns and enzyme activities by petroleum pollutants during co-composting of straw and swine manure with the supplementary nitrogen source are unclear. In this study, urea was added into co-composting systems, and the removal performance of petroleum, microbial enzyme activity and community changes were investigated. Results showed that the polyphenol oxidase and catalase activities which were both related to the degradation of petroleum contaminants were accordingly increased from 20.65 to 30.31 U/g and from 171.87 to 231.86 U/g due to urea addition. The removal efficiency of petroleum contaminants in composting with urea increased from 45.06% to 82.29%. The addition of urea increased the diversity and abundance of petroleum-degrading microorganisms, and enhanced microbial linkages. This study provides a novel strategy for the degradation of petroleum hydrocarbon as well as a new insight into the effect of urea on both microbial processes and composting phases.

Facilitating mitigation of agricultural non-point source pollution and improving soil nutrient conditions: The role of low temperature co-pyrolysis biochar in nitrogen and phosphorus distribution

The current study generated co-pyrolysis biochar by pyrolyzing rice straw and pig manure at 300 °C and subsequently applying it in a field. Co-pyrolysis biochar demonstrated superior efficiency in mitigating agricultural non-point source pollution compared to biochar derived from individual sources. Furthermore, it displayed notable capabilities in retaining and releasing nutrients, resulting in increased soil levels of total nitrogen, total phosphorus, and organic matter during the maturation stage of rice. Moreover, co-pyrolysis biochar influences soil microbial communities, potentially impacting nutrient cycling. During the rice maturation stage, the soil treated with co-pyrolysis biochar exhibited significant increases in available nutrients and rice yield compared to the control (p < 0.05). These findings emphasize the potential of co-pyrolysis biochar for in-situ nutrient retention and enhanced soil nutrient utilization. To summarize, the co-pyrolysis of agricultural waste materials presents a promising approach to waste management, contributing to controlling non-point source pollution, improving soil fertility, and promoting crop production.

Study on the effectiveness and mechanism of a sustainable dual slow-release model to improve N utilization efficiency and reduce N pollution in black soil

Long-term intensive cultivation has led to serious N loss and low N fertilizer utilization efficiency (NUE) in black soil areas. The lost N is not only a waste of resources but also a serious pollution threat to the environment, leading to the decline in water quality and food safety and the greenhouse effect. In the present study, a stable dual slow-release model, CPCS-Urea, was prepared by in situ polymerization using nitrapyrin, urea and melamine-formaldehyde resin as raw materials. The effect of the dual slow-release model was systematically evaluated using two consecutive years of field experiments. Five treatments were established in the field experiment: no N fertilizer (N0), urea (N180), 1 % CPEC-Urea, 0.5 % CPCS-Urea, and 1 % CPCS-Urea. The results showed that the new dual slow-release CPCS-Urea model outperformed both the use of urea and the traditional slow-release CPEC-Urea model in reducing N losses and improving NUE. The application of CPCS-Urea reduced nitrate (NO3-) leaching by 28.2 %-47.2 % and N2O emissions by 36.5 %-42.4 % and increased NUE by 20.7 %-28.5 % compared to urea application. The CPCS-Urea model modulated the activity of ammonia-oxidizing bacteria (AOB) and dissimilatory nitrate reduction to ammonium (DNRA) bacteria in soil, showing a significant decrease in AOB activity and an increase in DNRA activity. This results in a lower soil NO3--N yield and a 53.1 %-72.0 % increase in NH4+-N content, providing sufficient N for the entire growth and development cycle of maize. In short, the dual slow-release CPCS-Urea model has great application prospects for promoting agricultural development in black soil areas.

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.

Mechanism of magnetite-assisted aerobic composting on the nitrogen cycle in pig manure

Magnetite affects nitrogen cycle of pig manure (PM) biostabilisation was investigated. Various doses of magnetite (0 % (T1); 2.5 % (T2); 5 % (T3); 7.5 % (T4)) were homogeneously added into PM and wolfberry branch fillings (BF) mixture for a 50-day composting. Compared to T1, total nitrogen (TN) loss in gaseous form increased remarkably by 17.51 %, 56.31 %, and 24.91 %, respectively, in T2-T4. In particular, T3 dramatically increased the cumulative N2O emission but decreased NH3 emissions. However, T2 and T3 enhanced the total nitrogen contents by 7.24 % and 3.09 %. Structural equation models (SEM) analysis indicated that magnetite addition increased the direct and indirect pathways of N2O emission. Further analysis revealed that Ruminofilibacter and N2O emission were significantly correlated, and Pseudomonas played a vital role in nitrogen preservation. Although using 2 % magnetite as an additive could increase the TN content, the obvious increase of N2O emission should be considered in engineering practice.

Relative contribution of ammonia-oxidizing bacteria and denitrifying fungi to N2O production during rice straw composting with biochar and biogas residue amendments

Nitrous oxide (N2O) production is associated with ammonia-oxidizing bacteria (amoA-AOB) and denitrifying fungi (nirK-fungi) during the incorporation of biochar and biogas residue composting. This research examined the relative contribution of alterations in the abundance, diversity and structure of amoA-AOB and nirK-fungi communities on N2O emission by real-time PCR and sequence processing. Results showed that N2O emissions showed an extreme relation with the abundance of amoA-AOB (rs = 0.584) while giving credit to nirK-fungi (rs = 0.500). Nitrosomonas and Nitrosospira emerged as the dominant genera driving ammoxidation process. Biogas residue changed the community structure of AOB by altering Nitrosomonadaceae proportion and physiological capacity. The denitrification process, primarily governed by nirK-fungi, served as a crucial pathway for N2O production, unveiling the pivotal mechanism of biochar to suppress N2O emissions. C/N and NH4+-N were identified as significant parameters influencing the distribution of nirK-fungi, especially Micromonospora, Halomonas and Mesorhizobium.

Synergistic effects of biochar derived from different sources on greenhouse gas emissions and microplastics mitigation during sewage sludge composting

This study aimed to investigate the effects of biochar derived from different sources (wheat straw, sawdust and pig manure) on greenhouse gas and microplastics (MPs) mitigation during sewage sludge composting. Compared to the control, all biochar significantly reduced the N2O by 28.91-41.23%, while having no apparent effect on CH4. Sawdust biochar and pig manure biochar significantly reduced the NH3 by 12.53-23.53%. Adding biochar decreased the global warming potential during composting, especially pig manure biochar (177.48 g/kg CO2-eq.). The concentration of MPs significantly increased in the control (43736.86 particles/kg) compared to the initial mixtures, while the addition of biochar promoted the oxidation and degradation of MPs (15896.06-23225.11 particles/kg), with sawdust biochar and manure biochar were more effective. Additionally, biochar significantly reduced the abundance of small-sized (10-100 μm) MPs compared to the control. Moreover, biochar might regulate specific microbes (e.g., Thermobifida, Bacillus and Ureibacillus) to mitigate greenhouse gas emissions and MPs degradation.

Microbial dynamics and nitrogen retention during sheep manure composting employing peach shell biochar

In this study, the effects of peach shell biochar (PSB) and microbial agent (EM) amendment on nitrogen conservation and bacterial dynamics during sheep manure (SM) composting were examined. Six treatments were performed including T1 (control with no addition), T2 (EM), T3 (EM + 2.5 %PSB), T4 (EM + 5 %PSB), T5 (EM + 7.5 %PSB), and T6 (EM + 10 %PSB). The results showed that the additives amendment reduced NH3 emissions by 6.12%∼32.88% and N2O emissions by 10.96%∼19.76%, while increased total Kjeldahl nitrogen (TKN) content by 8.15-9.13 g/kg. Meanwhile, Firmicutes were the dominant flora in the thermophilic stages, while Proteobacteria, Actinobacteriota, and Bacteroidota were the dominant flora in the maturation stages. The abundance of Bacteroidota and Actinobacteriota were increased by 17.49%∼32.51% and 2.31%∼12.60%, respectively, which can accelerate the degradable organic materials decomposition. Additionally, redundancy analysis showed that Proteobacteria, Actinobacteriota, and Bacteroidota were positively correlated with NO3--N, TKN, and N2O, but a negative correlation with NH3 and NH4+-N. Finally, results confirmed that (EM + 10 %PSB) additives were more effective to reduce nitrogen loss and improve bacterial dynamics.

Improvement of soil acidification and ammonium nitrogen content in tea plantations by long-term use of organic fertilizer

Soil acidification is common in some Chinese tea plantations, which seriously affected growth of tea trees. Hence, it is essential to explore soil remediation in acidified tea plantations for sustainable development of the tea industry. We sought to determine how different fertilizers affect acidified soil and their N transformation in tea plantations. Different fertilizers were used on acidified tea plantation soils for 4 years (2017-2021), and changes in soil pH, indices related to soil N transformation and tea yield were analysed to construct interaction networks of these indices and find which had the largest influence on fertilization. Long-term use of sheep manure reduced soil acidification, increased soil pH, enhanced the number and intensity of N-fixing and ammonifying bacteria, urease, protease, asparaginase and N-acetamide glucose ribosidase activity and nifH gene expression. This treatment reduced the number and intensity of soil nitrifying and denitrifying bacteria, nitrate reductase and nitrite reductase activity, while the expression of amoA-AOA, nirK, nirS, narG and nosZ in turn increased ammonium N content of the soil, reduced nitrate N content, and enhanced tea yield. Topsis index weight analysis showed that ammonium N content in the soil had the largest impact among fertilization effects. Long-term use of sheep manure was beneficial in restoring the balance of the micro-ecosystem in acidified soil. This study provides an important practical basis for soil remediation and fertilizer management in acidified tea plantation soils.

Impacts of adding FeSO4 and biochar on nitrogen loss, bacterial community and related functional genes during cattle manure composting

This study investigated the impacts of adding FeSO₄ and biochar to cattle manure and rice straw composts on functional genes controlling nitrogen loss, bacterial community, nitrification, and denitrification. Four treatments were established, including a control group (CP), and CP mixtures that included 4% biochar (TG1), 4% FeSO₄ (TG2), or 2% FeSO₄ and 2% biochar (TG3). Compared to CP, TG1-3 had a lower total nitrogen loss rate, and TG3 resulted in reduced NH₃ (52.4%) and N₂O (35.6%) emissions to mitigate nitrogen loss. The abundance of amoA and narG gene in TG3 was higher than in the other groups, and TG3 was beneficial to the growth of Proteobacteria and Actinobacteria. According to redundancy and Pearson analysis, TG3 had a positive effect on the nitrification process by increasing the abundance of amoA and narG. Thus, biochar and FeSO₄ addition mitigate nitrogen loss by regulating the nitrification processes.

Reasonable deep application of sheep manure fertilizer to alleviate soil acidification to improve tea yield and quality

Soil acidification in Chinese tea plantations is widespread, and it has significantly affected the growth of tea trees; it was important to explore soil remediation of acidified tea plantations in depth for the sustainable development of tea industry. In this study, the effects of sheep manure fertilizer with different application depths on soil acidification, tea yield and quality, and soil nitrogen transformation in tea plantations were analyzed for five consecutive years from 2018 to 2022. The results showed that long-term use of sheep manure fertilizer significantly reduced soil acidification (P< 0.05) in tea plantations, improved soil pH and soil ammonium nitrogen content, enhanced root activity and root nitrogen uptake capacity of tea trees, and thus improved tea yield and quality. The effect of different application depths of sheep manure fertilizer on tea yield and quality was mainly reflected in the transformation ability of soil ammonium nitrogen and nitrate nitrogen, which showed that high transformation ability of soil ammonium nitrogen and high ammonium nitrogen content were beneficial to high tea yield and vice versa, and the best effect was achieved when sheep manure was applied at a depth of 50 cm and 70 cm. The topsis analysis confirmed that sheep manure fertilization had a greater effect on root activity, ammonium nitrogen, ammonia intensity, and nifH gene. This study provided an important practical basis for the restoration of acidified tea plantation soil through sheep manure fertilizer management.

Exploring gaseous emissions and pivotal enzymatic activity during co-composting of branch and pig manure: the effect of particle size of bulking agents

The purpose of current study was to probe the effect of various length of branch on gaseous emissions and vital enzymatic activity. Four lengths (<2 cm, 2 cm, 5 cm, and 10 cm) of clipped branch were mingled with collected pig manure for 100 days aerobic fermentation. The consequence demonstrated that the amendment of 2 cm of branch showed conducive to decline the greenhouse gas emissions, which the CH₄ emissions decreased by 1.62-40.10%, and the N₂O emissions decreased by 21.91-34.04% contrasted with other treatments. Furthermore, the peak degree of enzymatic activities was also observed in 2 cm of branch treatment by the optimizing living condition for microbes. In view of microbiological indicators, the most abundant and complex bacterial community could be monitor in 2 cm of branch composting pile, which verified the microbial facilitation. Summing up, the strategy of 2 cm branch amendment would be recommended.

Activated carbon enhanced traditional activated sludge process for chemical explosion accident wastewater treatment

With the development of industries, explosion accidents occur frequently during production, transportation, usage and storage of hazard chemicals. It remained challenging to efficiently treat the resultant wastewater. As an enhancement of traditional process, the activated carbon-activated sludge (AC-AS) process has a promising potential in treating wastewater with high concentrations of toxic compounds, chemical oxygen demand (COD) and ammonia nitrogen (NH₄⁺-N), etc. In this paper, activated carbon (AC), activated sludge (AS) and AC-AS were used to treat the wastewater produced from an explosion accident in the Xiangshui Chemical Industrial Park. The removal efficiency was assessed by the removal performances of COD, dissolved organic carbon (DOC), NH₄⁺-N, aniline and nitrobenzene. Increased removal efficiency and shortened treatment time were achieved in the AC-AS system. To achieve the same COD, DOC and aniline removal (90%), the AC-AS system saved 30, 38 and 58 h compared with the AS system, respectively. The enhancement mechanism of AC on the AS was explored by metagenomic analysis and three-dimensional excitation-emission-matrix spectra (3DEEMs). More organics, especially aromatic substances were removed in the AC-AS system. These results showed that the addition of AC promoted the microbial activity in pollutant degradation. Bacteria, such as Pyrinomonas, Acidobacteria and Nitrospira and genes, such as hao, pmoA-amoA, pmoB-amoB and pmoC-amoC, were found in the AC-AS reactor, which might have played important roles in the degradation of pollutants. To sum up, AC might have enhanced the growth of aerobic bacteria which further improved the removal efficiency via the combined effects of adsorption and biodegradation. The successful treatment of Xiangshui accident wastewater using the AC-AS demonstrated the potential universal characteristics of the process for the treatment of wastewater with high concentration of organic matter and toxicity. This study is expected to provide reference and guidance for the treatment of similar accident wastewaters.

Additive facilitated co-composting of lignocellulosic biomass waste, approach towards minimizing greenhouse gas emissions: An up to date review

Although the composting of lignocellulosic biomass is an emerging waste-to-wealth approach towards organic waste management and circular economy, it still has some environmental loopholes that must be addressed to make it more sustainable and reliable. The significant difficulties encountered when composting lignocellulosic waste biomass are consequently discussed in this study, as well as the advances in science that have been achieved throughout time to handle these problems in a sustainable manner. It discusses an important global concern, the emission of greenhouse gases during the composting process which limits its applicability on a broader scale. Furthermore, it discusses in detail, how different organic minerals and biological additives modify the physiochemical and biological characteristics of compost, aiming at developing eco-friendly compost with minimum odor, greenhouse gases emission and an optimum C/N ratio. It brings novel insights by demonstrating the effect of additives on the microbial enzymes and their pathways involved in the degradation of lignocellulosic biomass. This review also highlights the limitations of the application of additives in composting and suggests possible ways to overcome these limitations in the future for the sustainable and eco-friendly management of agricultural waste. The present review concludes that the use of additives in the co-composting of lignocellulosic biomass can be a viable remedy for the ongoing issues with the management of lignocellulosic waste.

A review of additives use in straw composting

Straw composting is not only a process of decomposition and re-synthesis of organic matter, but also a process of harmless treatment, avoiding air pollution caused by straw burning. Many factors, including raw materials, humidity, C/N, and microbial structure, may determine the composting process and the quality of final product. In recent years, many researches have focused on composting quality improvement by adding one or more exogenous substances, including inorganic additives, organic additives, and microbial agents. Although a few review publications have compiled the research on the use of additives in composting, none of them has specifically addressed the composting of crop straw. Additives used in straw composting can increase degradation of recalcitrant substances and provide ideal living surroundings for microorganism, and thus reduce nitrogen loss and promote humus formation, etc. This review's objective is to critically evaluate the impact of various additives on straw composting process, and analyze how these additives enhance final quality of composting. Furthermore, a vision for future perspectives is provided. This paper can serve as a reference for straw composting process optimization and composting end-product improvement.

Critical review of biochemical pathways to transformation of waste and biomass into bioenergy

In recent years, biofuel or biogas have become the primary source of bio-energy, providing an alternative to conventionally used energy that can meet the growing energy demand for people all over the world while reducing greenhouse gas emissions. Enzyme hydrolysis in bioethanol production is a critical step in obtaining sugars fermented during the final fermentation process. More efficient enzymes are being researched to provide a more cost-effective technique during enzymatic hydrolysis. The exploitation of microbial catabolic biochemical reactions to produce electric energy can be used for complex renewable biomasses and organic wastes in microbial fuel cells. In hydrolysis methods, a variety of diverse enzyme strategies are used to promote efficient bioethanol production from various lignocellulosic biomasses like agricultural wastes, wood feedstocks, and sea algae. This paper investigates the most recent enzyme hydrolysis pathways, microbial fermentation, microbial fuel cells, and anaerobic digestion in the manufacture of bioethanol/bioenergy from lignocellulose biomass.

Limited dissolved oxygen facilitated nitrogen removal at biocathode during the hydrogenotrophic denitrification process using bioelectrochemical system

Effects of limited dissolved oxygen (DO) on hydrogenotrophic denitrification at biocathode was investigated using bioelectrochemical system. It was found that total nitrogen removal increased by 5.9%, as DO reached about 0.24 mg/L with the cathodic chamber unplugged (group R_Exposure). With the presence of limited DO, not only the nitrogen metabolic pathway was influenced, but the composition of microbial communities of ammonia-oxidizing bacteria and nitrite-oxidizing bacteria were enriched accordingly. After metagenomic analysis, enriched genes in R_Exposure were found to be associated with nearly each of nitrogen removal steps as denitrification, nitrification, DNRA, nitrate assimilation and even nitrogen fixation. Moreover, genes encoding both Complexes III and IV constituted the electron transfer chain were significantly enriched, indicating that more electrons would be orientated to the reduction of NO₂^--N, NO-N and oxygen. Therefore, enhanced nitrogen removal could be attained through the co-respiration of nitrate and oxygen by means of NH₄⁺-N oxidation.

Mechanism of sulfur-oxidizing inoculants and nitrate on regulating sulfur functional genes and bacterial community at the thermophilic compost stage

The emission of H₂S odors predominantly occurred at the thermophilic phase of composting, which could cause odorous gas pollution and reduce the fertilizer value of composting products. And sulfur-oxidizing bacteria (SOB) possess oxidative capacities for inorganic sulfur compounds with nitrate applied as electron acceptors. Therefore, this study aimed to assess the effectiveness of combined additives (SOB inoculants and nitrate) on the bacterial community diversity, sulfur-oxidizing gene abundances, and metabolic function prediction at the thermophilic stage of sewage sludge composting. The highest sulfate contents were increased by 1.02-1.34 folds, and the abundances of the sulfur-oxidizing genes (sqr, pdo, sox, and sor) were also enhanced by adding the combined additives. Network patterns revealed a strengthened interaction of inoculants and sulfur functional genes. Microbial functional pathways predicted higher metabolic levels of carbohydrate and amino acid metabolisms with the addition of combined additives, and the predicted relative abundances of sulfur metabolism and nitrogen metabolism were increased by 19.3 ± 2.5% and 24.7 ± 4.1%, respectively. Heatmap analysis showed that the SOB might have a competitive advantage over the indigenous denitrifying bacteria in using nitrate for biochemical reactions. Correlation analyses suggested that sulfur-oxidizing efficacy could be indirectly affected by the environmental parameters through changing the structure of bacterial community. These findings provide new insights toward an optimized inoculation strategy of using SOB and nitrate to enhance sulfur preservation and modulate the bacterial communities at the thermophilic phase of sewage sludge composting.

Winter Green Manure Decreases Subsoil Nitrate Accumulation and Increases N Use Efficiencies of Maize Production in North China Plain

Planting a deep-rooted green manure (GM) (more than 1.0 m depth) greatly improves soil fertility and reduces the loss of nutrients. However, few studies have examined the response of soil nitrogen (N) distribution in the soil profile and subsoil N recovery to the long-term planting and incorporation of deep-rooted GM. Based on a 12-year (2009−2021) experiment of spring maize-winter GMs rotation in the North China Plain (NCP), this study investigated the effects of different GMs that were planted over the winter, including ryegrass (RrG, Lolium L.) (>1.0 m), Orychophragmus violaceus (OrV, Orychophragmus violaceus L.) (>0.8 m), and hairy vetch (VvR, Vicia villosa Roth.) (>1.0 m), on the spring maize yield, N distribution in the deep soil profile, N use efficiencies, functional gene abundances involving soil nitrification−denitrification processes and N2O production. Compared with the winter fallow, the maize yield significantly increased by 11.6% after 10 years of green manuring, and water storage in 0−200 cm soil profile significantly increased by 5.0−17.1% at maize seedling stage. The total N content in the soil layer at 0−90 cm increased by 15.8−19.7%, while the nitrate content in the deep soil layer (80−120 cm) decreased by 17.8−39.6%. Planting GM significantly increased the N recovery rate (10.4−32.7%) and fertilizer N partial productivity (4.6−13.3%). Additionally, the topsoil N functional genes (ammonia-oxidizing archaea amoA, ammonia-oxidizing bacterial amoA, nirS, nirK) significantly decreased without increasing N2O production potential. These results indicated that long-term planting of the deep-rooted GM effectively reduce the accumulation of nitrates in the deep soil and improve the crop yield and N use efficiencies, demonstrating a great value in green manuring to improve the fertility of the soil, increase the crop yield, and reduce the risk of N loss in NCP.

Recent advances in biowaste management towards sustainable environment

Bio-wastes and their utilization has been increasing enormously, due to its generation and management practices towards making the clearner environment. Bio-waste disposal that follow the emerging global human population has commended the hunt to certain methods sustainably for the bio-waste management to overwhelmed the ecological issues, prompted by means of the collection of such waste materials. The bio-conversion process of the various bio-wastes into high value added products seems to be practicable in various venues in terms of technological and financial supports. Thereby, this preface presentat about of bio-wastes management and new trends towards circular economy and challenges to acheive it by considering the Virtual Special Issue (VSI) dedicated in Bioresourse Technology Journal.

Characteristics of carbon, nitrogen, phosphorus and sulfur cycling genes, microbial community metabolism and key influencing factors during composting process supplemented with biochar and biogas residue

Carbon (C), nitrogen (N), phosphorus (P), and sulfur (S) cycling functional genes and bacterial and fungal communities during composting with biochar and biogas residue amendments were studied. Correlations between microbial community structure, functional genes and physicochemical properties were investigated by network analysis and redundancy analysis. It was shown that the gene of acsA abundance accounted for about 50% of the C-related genes. Biogas residue significantly decreased the abundance of denitrification gene nirK. Biogas residues can better promote the diversity of bacteria and fungi during composting. Biochar significantly increased the abundance of Humicola. Redundancy analysis indicated that pile temperature, pH, EC were the main physicochemical factors affecting the microbial community. WSC and NO₃^--N have significant correlation with C, N, P, S functional genes. The research provides a theoretical basis for clarifying the metabolic characteristics of microbial communities during composting and for the application of biochar and biogas residues in composting.

Evaluation of key microbial community succession and enzyme activities of nitrogen transformation in pig manure composting process through multi angle analysis

This experiment aimed to investigate changes in enzyme activity, microbial succession, and nitrogen conversion caused by different initial carbon-to-nitrogen ratios of 25:1, 35:1 and 20:1 (namely CK, T1 and T2) during pig manure composting. The results showed that the lower carbon-to-nitrogen ratio (T2) after composting retained 19.64 g/kg of TN which was more than 16.74 and 17.32 g/kg in treatments of CK and T1, respectively, but excessive conversion of ammonium nitrogen to ammonia gas resulted in nitrogen loss. Additional straw in T1 could play the role as a bulking agent. After composting, TN in T1 retained the most, and TN contents were 63.51 %, 67.34 % and 56.24 % in CK, T1 and T2, respectively. Network analysis indicated that many types of microorganisms functioned as a whole community at various stages of nitrogen cycle. This study suggests that microbial community structure modification might be a good strategy to reduce ammonium nitrogen loss.

Evaluation of the synergistic effects of biochar and biogas residue on CO2 and CH4 emission, functional genes, and enzyme activity during straw composting

This study examined the effects of biochar, biogas residue, and their combined amendments on CO₂ and CH₄ emission, enzyme activity, and related functional genes during rice straw composting. Results showed that the biogas residue increased CO₂ and CH₄ emissions by 13.07 % and 74.65 %, while biochar had more obvious inhibition. Biogas residue addition enhanced functional gene abundance more than biochar. Biogas residue raised the methanogens mcrA gene by 2.5 times. Biochar improved the Acetyl-CoA synthase and β-glucosidase activities related to carbon fixation and decreased coenzyme activities related to methanogens. Biochar and biogas residue combined amendments enhanced the acsB gene abundance for CO₂ assimilation process and decreased methyl-coenzyme M reductase α subunit activity. Pearson correlation analysis indicated that organic matter was the significant variable affecting CO₂ and CH₄ emissions (P < 0.01). These results indicated biochar played significant roles in carbon loss and greenhouse emissions caused by biogas residue incorporation during composting.

On-Farm Composting of Agricultural Waste Materials for Sustainable Agriculture in Pakistan

Agriculture is the economic backbone of Pakistan. 67% of country's population resides in rural areas and primarily depends on agriculture. Pakistan's soils are poor in OM and have a low C : N ratio, and the overall fertility status is insufficient to support increased crop yields. Compost is an excellent alternative solution for improving soil OM content. However, this excellent alternative supply in Pakistan has yet to be used. Mass volumes of leaves, grass clippings, plant stalks, vines, weeds, twigs, and branches are burned daily. In this study, different compost piles (P1, P2, and P3) of compost were made using different agricultural and animal waste combinations to assess temperature, pH, and NPK. Results revealed that P3 demonstrated the most successful composting procedure. The temperature and pH levels throughout the composting process were determined in a specified range of 42-45^oC and 6.1-8.3, respectively. Total nitrogen content ranged from 81.5 to 2175 ppm in farm compost. Total phosphorus concentrations range from 1.33 to 13.98 ppm, and potassium levels, on the other hand, range from 91.53 to 640 ppm in farm compost. The overall nitrogen concentration grew progressively between each pile at the end of a week. The varied concentrations revealed that adding various forms of agricultural waste would result in a variation in the quantity of NPK owing to microbial activity. On-farm composting has emerged as an effective technique for the sustainability of agricultural activities, capable of resolving crucial problems like crop residues and livestock waste disposal. Based on this study's results, the pile (P3) combination shows the best NPK value performance and is recommended for agricultural uses to overcome the OM deficiency.