Response of the denitrifier community and its relationship with multiple N2O emission peaks after mature compost addition into dairy manure compost with forced aeration

Control of nitrogen and odor emissions during chicken manure composting with a carbon-based microbial inoculant and a biotrickling filter

Although aerobic composting is usually utilized in livestock manure disposal, the emission of odorous gases from compost not only induces harm to the human body and the environment, but also causes loss of nitrogen, sulfur, and other essential elements, resulting in a decline in product quality. The impact of biotrickling filter (BTF) and insertion of carbon-based microbial agent (CBMA) on compost maturation, odor emissions, and microbial population during the chicken manure composting were assessed in the current experiment. Compared with the CK group, CBMA addition accelerated the increase in pile temperature (EG group reached maximum temperature 10 days earlier than CK group), increased compost maturation (GI showed the highest increase of 41.3% on day 14 in EG group), resulted in 36.59% and 14.60% increase in NO3--N content and the total nitrogen retention preservation rate after composting. The deodorization effect of biotrickling filter was stable, and the removal rates of NH3, H2S, and TVOCs reached more than 90%, 96%, and 56%, respectively. Furthermore, microbial sequencing showed that CBMA effectively changed the microbial community in compost, protected the ammonia-oxidizing microorganisms, and strengthened the nitrification of the compost. In addition, the nitrifying and denitrifying bacteria were more active in the cooling period than they were in the thermophilic period. Moreover, the abundance of denitrification genes containing nirS, nirK, and nosZ in EG group was lower than that in CK group. Thus, a large amount of nitrogen was retained under the combined drive of BTF and CBMA during composting. This study made significant contributions to our understanding of how to compost livestock manure while reducing releases of odors and raising compost quality.

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.

Relationships between different types of biochar and N2O emissions during composting based on roles of nosZ-carrying denitrifying bacterial communities enriched on compost and biochar particles

Biochar has demonstrated the potential in mitigating N2O emissions during composting. However, little is known about how microbial communities on biochar particles interact with N2O emissions. This study selected three types of biochar (corn stalk biochar (CSB), rape straw biochar (RSB), and bamboo charcoal (BC)) to investigate the relationship between N2O emissions and denitrifying bacterial communities on compost and biochar particles. The results showed that N2O emissions rate were higher in the thermophilic phase, and the average emissions rate of BC treatment were lower 40% and 26% than CSB and RSB, respectively. The nosZ-carrying denitrifying bacterial community played a key role in reducing N2O emissions, and the network indicated that Rhizobium and Paracoccus on compost particles may have played major roles in reducing N2O emissions, but only Paracoccus on biochar particles. Notably, BC enhanced the efficiency of N2O emission reduction by enhancing the abundance of these key genera.

Competition and interaction between DNRA and denitrification in composting ecosystems: insights from metagenomic analysis

This study investigated denitrification and dissimilatory nitrate reduction to ammonium (DNRA) competition for nitrite in composting of sugarcane pith and cow manure. Metagenomic analysis showed that Actinobacteria was the main DNRA microorganism. During heating phase and thermophilic phase, the abundances of denitrification functional genes (nirK and nirS decreased by 40.22% and 98.60%, respectively) and DNRA functional genes (nirB, nirD increased by 195.24% and 176.61%, and nrfA decreased by 45%, respectively) showed different trends. Interestingly, the abundance of nrfA increased by 250% during cooling and maturity phases. Mantel test revealed that competition between denitrification and DNRA microorganisms for NO₂^--N limited the succession of their respective communities (P < 0.01). Network analysis showed that unclassified Solirubrobacterales, Altererythrobacter and Microbacterium were the key microorganisms in DNRA microbial communities. The results provided new insights into the key microorganisms and their driving factors affecting DNRA and nitrogen management in the composting ecosystems.

Effects of chemical additives and mature compost on reducing nitrogen loss during food waste composting

This study is aimed at adding different types of mature compost and sulfur powder, as additives into food waste composting to investigate the effect on nitrogen loss and compost maturity. The composting experiment used the in-vessel composting method and was conducted continuously for 15 days. High-throughput sequencing was used to analyze the bacterial community during composting. Results showed that the secondary fermentation mature compost mixed with sulfur powder group had the most reduction of ammonia emission (56%) and the primary fermentation mature compost amendments were the most effective for nitrous oxide emission reduction (37%). The temperature, pH, and nitrogen forms of transformation of the pile significantly affect the nitrogen loss during composting. Firmicutes helped to promote the rapid warming of the pile, and Actinobacteria and Proteobacteria played an important role in decomposition of organic matter. Thermobifida and Ureibacillus had a main contribution to the rapid degradation of organic matter in the process of composting. The relative abundance of nitrogen-fixing bacteria was higher, and the relative abundance of predominantly ammonifying and denitrifying bacteria was lower than the control group, with the addition of different additives.

Effect of biochar combined with a biotrickling filter on deodorization, nitrogen retention, and microbial community succession during chicken manure composting

The high-nitrogen content and dense structure of poultry manure compost cause volatilization of N to ammonia (NH₃). This study evaluated the combined application of biochar and biotrickling filtration (BTF) to remove of odor in chicken manure mixed straw compost (w/w, 2.5:1). Adding of 10% biochar reduced NH₃, hydrogen sulfide (H₂S), and total volatile organic compounds (TVOCs) contents by 20.04%, 16.18%, and 17.55% respectively, and decreased the N loss rate by 8.27%, compared with those observed in control. The organic matter content decreased by 28.11% and germination index reached 97.36% in the experimental group. Meanwhile, the N-cycling microorganisms such as Pusillimonas and Pseudomonas became more active, and the relative abundance of sulfur-cycling microorganisms Hydrogenispora decreased in the experimental group. Following BTF application, the NH₃, H₂S, and TVOCs removal rates reached 95%, 97%, and 53%, respectively.

The addition of sawdust reduced the emission of nitrous oxide in pig manure composting by altering the bacterial community structure and functions

Although composting, a measure to dispose agricultural waste, is widely accepted and applied, specific knowledge of microbially driven effects on nitrous oxide (N₂O) emissions during composting remains limited. Here, we monitored the impact of sawdust on N₂O emissions during pig manure composting. The results suggested that adding sawdust to the compost improved the compost temperature and reduced N₂O emissions. The addition of sawdust significantly altered the bacterial community structure and enhanced community turnover during the composting process. The addition of sawdust significantly reduced the relative abundance of denitrification and ureolysis, while increasing the relative abundance of nitrogen fixation. Specifically, adding sawdust may reduce N₂O emissions by reducing the relative abundance of Salinithrix, Truepera, Azomonas, Iamia, Silanimonas, Phycisphaera, and Gp21 during the thermophilic and mature phases of the composting period.

Regulating bacterial dynamics by lime addition to enhance kitchen waste composting

This study examined bacterial dynamics in response to lime addition to enhance kitchen waste composting using modular network analysis. Bacterial communities could be separated into three meta-modules corresponding to the mesophilic, thermophilic, and mature stage of composting. Lime addition at 1% (wet weight) suppressed acidogens and denitrifiers (e.g. Lactobacillus and Acinetobacter) at the mesophilic stage to reduce greenhouse gas emissions. The matrix pH and temperature were also increased by lime addition via hydrogen reaction to favor bacterial growth and activity. Thus, thermophilic bacteria (e.g. Thermoactinomycetaceae and Planifilum) were enriched with lime addition to facilitate lignocellulose biodegradation for humus formation at the thermophilic stage. Further lime addition to 1.5% reduced ammonia emission at the thermophilic stage via chemical fixation. Moreover, lime inhibited denitrifiers but proliferated nitrifiers at the mature stage to decrease nitrous oxide emission and enhance nitrate content, respectively. As such, lime addition improved both biotic and abiotic composting performance.

Current status of global warming potential reduction by cleaner composting

The global living standards are currently undergoing a stage of growth; however, such improvement also brings some challenges. Global warming is the greatest threat to all living things and attracts more and more attention on a global scale due to the rapid development of economy. Carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) are the common components of greenhouse gases, which contribute to the global warming. Mitigation technologies for these gas emissions are urgently needed in every industry for the aim of cleaner production. Traditional agriculture also contributes significantly to enhance the greenhouse gases emission. Composting is a novel and economic greenhouse gases mitigation strategy compared to other technologies in terms of the organic waste disposal. Some of the European countries showed an increase of more than 50% in the composting rate. The microbial respiration, nitrification and denitrification processes, and the generation of anaerobic condition makes the emission of greenhouse gases inevitable during composting. However, although there have been a lot of papers that focused on the reduction of greenhouse gases emission in composting, none of these has summarized the methods of reducing the emission of greenhouse gases during the composting. This review discusses the benefit of composting in greenhouse gases mitigation in the organic waste management and the current methods to improve mitigation efficiency during cleaner composting. Key physical, chemical, and biological parameters related to greenhouse gases mitigation strategies were precisely studied to give a deep understanding about the emission of greenhouse gases during cleaner composting. Furthermore, the mechanism of greenhouse gases emission mitigation strategies for cleaner composting based on various external measures would be helpful for the exploration of novel and effective mitigation strategies.

Insights into influences of sucrose amendment on nitrification and denitrification in sewage sludge composting

Sucrose amendment could promote ammonia assimilation and reduce nitrogen loss in sewage sludge (SS) composting, but the effects of sucrose amendment on nitrification and denitrification are still unknown that were firstly researched in present paper. Result showed that sucrose amendment reduced 33.0% of N₂O emission by changing the physicochemical indexes, nitrogen forms, related bacteria and functional genes. In the sucrose treatment, the higher nitrifying bacteria community, amoA and nxrA genes abundance were, the lower hao, narG、nirS、nirK and norB genes abundance were. Based on the correlation analysis, the number of nitrifying bacteria was significantly positively correlated with NO₃^- and nxrA abundance, indicating that sucrose amendment promoted the growth of nitrifying bacteria, the contents of NO₃^- and the activity of nitrite oxidation. Moreover, contents of NO₂^- were positively correlated with N₂O emission, narG, nirS and norB abundance, indicating that denitrification was the main path of N₂O generated.

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.

Incorporation of solar-heated aeration and greenhouse in grass composting

Composting is an environment-friendly method for recycling organic waste, and incorporation of heat and aeration can enhance favorable conditions for microbial growth in the process. This research aimed to evaluate the influence of the introduction of solar heat and aeration to the waste grass exposed to the composting process. The compost piles studied were subjected to different processes: application of solar-heated aeration, only-aeration, solar heating with a greenhouse, and control. Solar-heated air was introduced to a compost pile of grass clippings and compared with a greenhouse compost system. The composting process of 70 days was monitored for temperature, oxygen, moisture, organic matter loss, and humification rate. Germination index has been used to evaluate the maturation of the composts produced. The highest temperature was obtained at the compost pile with the greenhouse. This system reached the highest temperature (68.2 °C) on day 15; the ambient temperature on that day was 20.6 °C. The decreases in the C/N ratios after day 70 of composting were 20% and 15% for the greenhouse and the system where solar-heated air was introduced, respectively. Although the temperature of the solar-heated air was higher than that of the greenhouse, thermophilic temperature levels could not be reached in the aerated compost pile, which indicated a cooling effect of excessive aeration even with the heated air. Composting of grass clippings resulted in a decrease in organic matter content and enhancement in seed germination and root growth, obtaining high GI levels, inferring no phytotoxicity. This study showed that composting of grass clippings with low C/N ratios and high humidity can still be possible by using solar energy.

The addition of bean curd dreg improved the quality of mixed cow manure and corn stalk composting: enhancing the maturity and improving the micro-ecological environment

Bean curd dreg (BCD) is a by-product of bean products, which can be used as a great ingredient for composting, but it combined with cow manure and corn stalk composting was rarely reported. In this study, the effect of BCD on the maturity and the micro-ecological environment was investigated under a lab-scale composting experiment and found that BCD was conducive to improve the maturity of compost during the BCD application. The excitation-emission matrix (EEM) showed that the final humus content in BCD treatments was richer than that in CK treatment. High-throughput sequencing results showed that BCD-applied better ameliorated the bacteria community structure with higher Actinomycetes abundance and lower denitrifying bacteria abundance in the late stage of composting. PICRUSt results showed that BCD-added decreased the abundance of microbial metabolic genes in the high temperature period (> 70 °C), but the metabolic abundance increased rapidly as the temperature cooled down. Compared with CK, the metabolic abundance decreased significantly on day 24, which was consistent with the conclusion of composting maturity. Redundancy analysis (RDA) results indicated that there were significant discrepancies in the microbial community structure of samples at different composting periods and the change of the dominant population in the BCD-treated compost samples were more outstanding than that in the CK treatment. Hence, BCD is a very good composting modifier that compensates for the disadvantages of composting and enhances the fertility of the compost product.

Effects of sulfoxaflor on greenhouse vegetable soil N2O emissions and its microbial driving mechanism

The wide application of pesticides ensures the safety of food production, but it also has a serious impact on soil ecosystem. Although sulfoxaflor as a pesticide has great potential for application due to its excellent insecticidal activity and low crossresistance, little is known about its soil environmental safety risks. In this study, the effects of sulfoxaflor on N₂O emissions and microorganisms in greenhouse vegetable soils were studied by indoor simulation culture experiments. Dynamic changes of soil main inorganic N and N₂O emission rate were tested, and the abundance and community of total bacteria and microorganisms related to N cycle were analyzed. The results indicated that soil microorganisms rapidly degraded sulfoxaflor, and the N₂O emissions rate and ammonium nitrogen (NH₄⁺-N) content significantly increased, while nitrate nitrogen (NO₃^--N) content was significantly decreased. Sulfoxaflor significantly changed the abundance and community of total bacteria, nitrite reducing and nitrous oxide reducing bacteria, but had no significant effect on ammoxidation microorganisms. The N₂O emission rate was positively correlated with gene abundance of denitrifying microorganisms. Under 65% soil maximum water holding capacity, sulfoxaflor may broke the dynamic balance of N₂O production and consumption in the denitrification process, which caused a significant increase in N₂O emission. Therefore, the application of sulfoxaflor had a certain effect on N cycling and utilization in greenhouse vegetable soil.

Elucidating the role of earthworms in N2O emission and production pathway during vermicomposting of sewage sludge and rice straw

Vermicomposting is a sustainable option for the recycling of biodegradable organic waste. However, it also produces nitrous oxide (N₂O), which is a highly potent greenhouse gas. In this study, the N₂O stable isotope and functional genes for nitrogen cycling were determined to investigate the sources of N₂O during vermicomposting. The results showed that vermicomposting promoted the organic degradation and nitrogen nitrification, and the presence of earthworms increased the emission of N₂O during vermicomposting compared to that during the control treatment with no earthworms. The site preference analysis of N₂O stable isotope showed that both nitrification and denitrification were present during the early stages of vermicomposting, while nitrification was the dominant contributor to N₂O production in the later stages. Moreover, earthworms increased the gene copies of amoA, and stimulated the nitrifying bacteria, and hence, increased the N₂O emission via nitrification. In addition, the activity of earthworms reduced the gene number of nosZ during vermicomposting, while the denitrification was the main source of N₂O in the earthworm gut, as the conditions inside the gut inhibited nosZ. Overall, nitrification was the major pathway (55.8-88.7 %) for N₂O production, which was promoted by the introduction of earthworms through nitrification.

Use of corn stover as bulking agent in dairy manure composting toward Japanese circular dairy farming

In response to the recent development of ear corn feeding systems and the shortage of bulking agents for manure composting in the Hokkaido region, the plausibility of using corn stover (a residue of ear corn harvesting) as an alternative bulking agent for dairy manure composting was tested. The temperature profile, quality of the final product, and greenhouse gas emissions were evaluated and compared with the values obtained from manure that used wheat straw, a typical bulking agent. A sufficiently high temperature profile (>70°C) and active organic matter degradation were achieved by mixing in corn stover. After active organic matter degradation for 8 weeks, CO₂ production was significantly lower and the stable final products were obtained. The total solids level increased significantly, to 48.8–50.4%, while the C/N ratio dropped significantly, from 19.9–21.8 to 11.2–12.8. Methane emission from the corn-stover-based pile was 0.36% of initial volatile solids, while nitrous oxide emission was 0.58% of initial N, proving that the use of corn stover can mitigate greenhouse gas emission and that its mitigating effect was comparable to those of other bulking agents. Together, the results showed that the use of corn stover can be a suitable alternative bulking agent for dairy manure composting and can serve as part of an ecologically friendly and “circular” method of dairy farming.

Influence of spent mushroom substrate and molasses amendment on nitrogen loss and humification in sewage sludge composting

The present study included lab-scale sewage sludge (SS) composting amended by molasses and spent mushroom substrate (SMS) in 5 L composting reactor system. The influence of molasses and SMS amendment on nitrogen loss and humification of SS composting was evaluated. The results showed that SMS amendment, especially combination with molasses raised composting temperature, increased CO₂ volatilization, promoted organic matter degradation, improve germination index and humification process. The addition of SMS and molasses contain carbohydrates used as carbon source and energy substance by microorganisms could increase microbial activity and ammonia assimilation. In the SMS + molasses treatments, NH₃ volatilization was reduced by 33.1%–37.3% and N₂O volatilization was only 17.8%–25.4% of that in the control treatment, furthermore, the nitrogen loss rate was reduced by 27.2%–32.2%. Consequently, the addition of SMS and molasses improved the compost maturity and reduced nitrogen loss in the SS composting process.

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

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

Passivation of lead and cadmium and increase of the nutrient content during sewage sludge composting by phosphate amendments

As an efficient and cost-effective biological treatment method for sewage sludge, composting has been widely used worldwide. To passivate heavy metals and enhance the nutrient content in compost, in the present study, phosphate rock, calcium magnesium phosphate, and monopotassium phosphate were added to the composting substrate. According to the Community Bureau of Reference sequential extraction procedure, phosphate rock and monopotassium phosphate amendments exhibit a good passivation effect on Cd and Pb. The X-ray diffraction patterns proved the formation of Pb₃(PO₄)₂ and Cd₅(PO₄)₂SiO₄ crystals, and X-ray absorption near-edge structure spectroscopy illustrated the change in P speciation after phosphate amendment. Furthermore, phosphate amendment increased the contents of total P and available P, and it reduced the loss of N during sewage sludge composting. The germination index showed that the target phosphate amendments in sewage sludge compost had no negative effects on seed germination, and this method has great potential to be used as a soil amendment.

Nitrous oxide emission and the related denitrifier community: A short-term response to organic manure substituting chemical fertilizer

Partially substituting chemical fertilizer with organic manure can aid in the disposal of agricultural wastes via recycling into agricultural land, reduce chemical fertilizer application, and influence nitrogen (N) transformation. However, relatively few studies have investigated the association between soil physicochemical properties, denitrifier communities and N₂O emission after short-term substitution of organic manure in vegetable fields. We conducted a short-term vegetable field experiment which included one control treatment (CT, no fertilizer) and three fertilization treatments containing equal amount of total N, phosphorus and potassium (CF, chemical fertilizer only; CMR, chemical fertilizer plus mushroom residue; COM, chemical fertilizer plus cattle manure). The results showed that partial substitution of chemical fertilizer with organic manure greatly increased cumulative N₂O emissions, N₂O emission factors and yield-scaled N₂O emissions by 122-203%, 238-600% and 128-181%, respectively. Compared with the CF treatment, short-term substitution with organic manure reduced the abundance of nirS- and nosZ-type denitrifiers, and increased that of nirK-type denitrifiers. Modeling indicated that nirS abundance, together with soil available N, NIR activity, nirK abundance, SOC, NH₄⁺, and NO₃^- were the primary factors associated with cumulative N₂O emissions. The denitrifier community composition of the CF- treated soil was separated from that of soils treated with CMR and COM, and was primarily influenced by soil NH₄⁺ concentration. NIR activity showed a significant correlation with denitrifier community composition. Overall, short-term substitution of chemical fertilizer with cattle manure (lower C/N ratio) reduced the abundance of nirS- and nosZ-type denitrifiers, but stimulated N₂O emission.

Roles of nxrA-like oxidizers and nirS-like reducers in nitrite conversion during swine manure composting

Nitrite has a key role in nitrogen conversion during composting. In this study, the dynamic changes in the NO₂^- contents, abundances of nirS and nxrA, and the bacteria that harbored these genes were determined during composting. NO₂^- accumulated during the initial composting stage. The nirS gene was abundant throughout composting, whereas the nxrA gene was only abundant in the late composting phases. Ralstonia sp. and Thauera sp. were the dominant denitrifiers that harbored nirS, and Nitrobacter winogradskyi Nb-255 was the dominant nitrifier that harbored nxrA. Structural equation modeling showed that NO₂^- was mainly reduced by nirS in the early phases, and oxidized by nxrA in the late phases, but especially in the maturity phase. Network analysis showed that the dominant bacteria harboring nirS and nxrA were hubs in the modules related to the reduction and oxidation of NO₂^-, and they had competitive relationships during the cooling and maturity phases.

Nitrogen removal from food waste digestate using partial nitritation-anammox process: Effect of different aeration strategies on performance and microbial community dynamics

The feasibility of employing anammox and partial nitritation-anammox (PN/A) processes for nitrogen removal from food waste (FW) digestate was investigated in this study. The effects of different aeration strategies on the microbial community were also investigated. To achieve this, after anammox enrichment (Phase 1), the reactor was fed with digestate supplemented with nitrite (Phase 2), and subsequently different aeration strategies were evaluated to establish PN/A. Aeration strategies with high anoxic periods (30 and 45 min) in relation to aerobic periods (15 min) coupled with low air flow rates (0.026 L  min^-1. L_reator^-1) were found to be better for establishing PN/A, as coefficients of produced nitrate/removed ammonium were closer to those reported previously (0.17 and 0.21). Aeration conditions considerably altered the microbial community. Candidatus Brocadia was replaced by Candidatus Jettenia, after the first aeration strategies. These results support the feasibility of FW digestate treatment using anammox and PN/A processes and provide a better understanding of the effect of aeration on microbial dynamics in PN/A reactors.

Influence of matured compost inoculation on sewage sludge composting: Enzyme activity, bacterial and fungal community succession

The influence of matured compost inoculation during sewage sludge with sawdust composting was assessed. Mature compost reduced the heating rate, thermophilic phase, peak temperature, and volatile solid degradation rate, with no significant effect on pH and germination index. Matured compost addition also increased the cellulase, peroxidase, arylsulfatase, and urease contents during the mesophilic phase, and increased the urease content but decreased the cellulase, peroxidase, protease, and arylsulfatase contents during the cooling phase, with no significant effect on enzyme activities at the thermophilic phase. Matured compost increased the diversity of bacteria during the mesophilic and thermophilic phases, but reduced the fungal diversity throughout composting. Matured compost significantly improved uniformity of the bacterial community and affected the structure of the bacterial and fungal communities, while changing the correlation between some functional microorganisms and enzyme activities. These results provide guidance for optimizing the composting process when matured compost as bulking agent.

Performance of mature compost to control gaseous emissions in kitchen waste composting

This study investigated the performance of mature compost to mitigate gaseous emissions during kitchen waste composting. Cornstalk was mixed with kitchen waste at a ratio of 3:17 (wet weight) as the bulking agent. Mature compost (10% of raw composting materials on the wet weight basis) was mixed into or covered on the composting pile. A control treatment without any addition of mature compost was conducted for comparison. Results show that mature compost did not significantly affect the composting process. Nevertheless, gaseous emissions during kitchen waste composting were considerably reduced with the addition of mature compost. In particular, mixing mature compost with raw composting materials reduced ammonia, methane, and nitrous oxide emissions by 58.0%, 44.8%, and 73.6%, respectively. As a result, nitrogen could be conserved to increase nutrient contents and germination index of the compost product. Furthermore, the total greenhouse gas emissions during kitchen waste composting were reduced by 69.2% with the mixture of mature composting. By contrast, a lower reduction in gaseous emissions was observed when the same amount of mature compost was covered on the composting pile.

Application of ceramsite and activated alumina balls as recyclable bulking agents for sludge composting

Composting is a major sludge-treatment method and bulking agents are very important in sludge composting. In this study, ceramsite and activated alumina balls were chosen as recyclable bulking agents for sludge composting. Variations in the temperature, pH, electrical conductivity, organic matter, dissolved organic carbon, moisture content, and heavy metals were detected during composting with different bulking-agent treatments as well as differences in the germination index values. The results showed that both bulking agents could ensure the maturity of the compost; further, ceramsite treatment resulted in the best water removal efficiency. According to the sequential extraction procedure, both ceramsite and activated alumina balls could stabilize Cd but they also increased the mobility of Zn. After comparing the effects of different particle sizes of ceramsite on composting, 20 mm was determined to be the most optimal value. Additionally, the recovery rates of ceramsite and activated alumina balls were 96.9% and 99.9%, respectively.

Hyperthermophilic composting significantly decreases N2O emissions by regulating N2O-related functional genes

This study reported for the first time that hyperthermophilic composting (HTC) could mitigate 90% of the cumulative amount of N₂O emissions compared to traditional composting (TC) in a full-scale experiment. The concentrations of NO₂^--N and NO₃^--N in HTC were significantly lower than those in TC, which may be the main reason for the reduced N₂O emissions. Furthermore, this study found that the decrease in N₂O emissions in HTC compared to TC was mainly due to the inhibition of the abundance of the bacterial amoA and norB genes, which could decrease the nitrification rate and control N₂O formation, respectively. Partial least squares path modeling revealed that a high temperature was the key factor in lowering N₂O emissions in HTC, while physicochemical properties were the dominant factor in enhancing N₂O emissions in TC. These results suggested that HTC is a promising technique for reducing N₂O emissions in manure composting.