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

Methylotrophic substrates stimulated higher methane production than competitive substrates in mangrove sediments

Although mangrove forests can uptake atmospheric CO2 and store carbon as organic matter called "blue carbon", it is also an important natural source of greenhouse gas methane. Methanogens are major contributors to methane and play important roles in the global carbon cycle. However, our understanding of the key microbes and metabolic pathways responsible for methanogenesis under specific substrates in mangrove sediments is still very limited. Here, we set an anaerobic incubation to evaluate the responses of methanogens in mangrove sediments from South China to the addition of diverse methanogenic substrates (H2/CO2, acetate, trimethylamine (TMA), and methanethiol (MT)) and further investigated the dynamics of the whole microbial community. Our results showed that diverse substrates stimulated methanogenic activities at different times. The stimulation of methanogenesis was more pronounced at early and late periods by the addition of methylotrophic substrates TMA and MT, respectively. The amplicon sequencing analysis showed that genus Methanococcoides was mainly responsible for TMA-utilized methanogenesis in mangrove sediment, while the multitrophic Methanococcus was most abundant in H2/CO2 and MT treatments. Apart from that, the bacteria enrichments of Syntrophotalea, Clostridium_sensu_stricto_12, Fusibacter in MT treatments might also be associated with the stimulation of methane production. In addition, the metagenomic analysis suggested that Methanosarcinaceae was also one of the key methanogens in MT treatments with different genomic information compared to that in TMA treatments. Finally, the total relative abundances of methanogenesis-related genes were also highest in TMA and MT treatments. These results will help advance our understanding of the contributions of different methanogenesis pathways and methanogens to methane emissions in mangrove sediments.

Succession from acetoclastic to hydrogenotrophic microbial community during sewage sludge anaerobic digestion for bioenergy production

To assess microbial dynamics during anaerobic digestion (AD) of sewage sludge (SWS) from a municipal Wastewater Treatment Plant (WWTP), a Biochemical Methane Potential (BMP) assay at 37 °C under mono-digestion conditions was conducted. Utilizing the Illumina MiSeq platform, 16S ribosomal RNA (rRNA) gene sequencing unveiled a core bacterial community in the solid material, showcasing notable variations in profiles. The research investigates changes in microbial communities and metabolic pathways to understand their impact on the efficiency of the digestion process. Prior to AD, the relative abundance in SWS was as follows: Proteobacteria > Bacteroidota > Actinobacteriota. Post-AD, the relative abundance shifted to Firmicutes > Synergistota > Proteobacteria, with Sporanaerobacter and Clostridium emerging as dominant genera. Notably, the methanogenic community underwent a metabolic pathway shift from acetoclastic to hydrogenotrophic in the lab-scale reactors. At the genus level, Methanosaeta, Methanolinea, and Methanofastidiosum predominated initially, while post-AD, Methanobacterium, Methanosaeta, and Methanospirillum took precedence. This metabolic transition may be linked to the increased abundance of Firmicutes, particularly Clostridia, which harbor acetate-oxidizing bacteria facilitating the conversion of acetate to hydrogen.

Micro-positive pressure significantly decreases greenhouse gas emissions by regulating archaeal community during industrial-scale dairy manure composting

In this study, the effects of micro-positive pressure formed by covering with a semipermeable membrane in the heating phase of dairy manure composting on greenhouse gas emissions and the mechanism of reducing methane emissions by the archaeal community were investigated. A large-scale experiment was conducted with semipermeable membrane-covered composting (SMC), forced aeration composting (FAC), and traditional static composting (TSC) groups. The results showed that the oxygen concentration and methanogen abundance were key factors in regulating methane emissions. In the heating phase of SMC, the micro-positive pressure could enhance the O2 utilization rate and heating rate, resulting in Methanobrevibacter and Methanobacterium greatly decreasing, and the abundance of mcrA decreased by 90.03%, while that of pmoA did not increase. Compared with FAC and TSC, the cumulative methane emissions in SMC decreased by 51.75% and 96.04%, respectively. Therefore, the micro-positive pressure could effectively reduce greenhouse gas emissions by inhibiting the growth of methanogens.

Response of phosphorus fractions transformation and microbial community to carbon-to-phosphorus ratios during sludge composting

Phosphorus (P) is one of the essential nutrient elements for plant growth and development. Sludge compost products can be used as an important source of soil P to solve the shortage of soil P. The difference in the initial carbon-to-phosphorus ratio (C/P) will lead to difference in the bacterial community, which would affect the biological pathway of P conversion in composting. However, few studies have been reported on adjusting the initial C/P of composting to explore P conversion. Therefore, this study investigated the response of P component transformations, bacterial community and P availability to C/P during sludge composting by adjusting initial C/P. The results showed that increasing C/P promoted the mineralization of organic P and significantly increased the content of the labile P. High C/P also increased the relative content of available P, especially when the C/P was at 45 and 60, it reached 60.51% and 60.47%. High C/P caused differences in the community structure, and improved the binding ability of microbial network modules and the competitiveness of microbial communities. Additionally, high C/P strengthened the effect of microbial communities on the transformation of P components. Finally, the study showed that C/P was the main contributor to P content variation (64.7%) and indirectly affected P component conversion by affecting the microbial community. Therefore, adjusting the C/P is crucial to improve the P utilization rate of composting products.

Current status and future developments of assessing microbiome composition and dynamics in anaerobic digestion systems using metagenomic approaches

The metagenomic approach stands as a powerful technique for examining the composition of microbial communities and their involvement in various anaerobic digestion (AD) systems. Understanding the structure, function, and dynamics of microbial communities becomes pivotal for optimizing the biogas process, enhancing its stability and improving overall performance. Currently, taxonomic profiling of biogas-producing communities relies mainly on high-throughput 16S rRNA sequencing, offering insights into the bacterial and archaeal structures of AD assemblages and their correlations with fed substrates and process parameters. To delve even deeper, shotgun and genome-centric metagenomic approaches are employed to recover individual genomes from the metagenome. This provides a nuanced understanding of collective functionalities, interspecies interactions, and microbial associations with abiotic factors. The application of OMICs in AD systems holds the potential to revolutionize the field, leading to more efficient and sustainable waste management practices particularly through the implementation of precision anaerobic digestion systems. As ongoing research in this area progresses, anticipations are high for further exciting developments in the future. This review serves to explore the current landscape of metagenomic analyses, with focus on advancing our comprehension and critically evaluating biases and recommendations in the analysis of microbial communities in anaerobic digesters. Its objective is to explore how contemporary metagenomic approaches can be effectively applied to enhance our understanding and contribute to the refinement of the AD process. This marks a substantial stride towards achieving a more comprehensive understanding of anaerobic digestion systems.

Regulation of fungal communities during pig manure composting

The role of protein shell (PS) amendment in altering the fungal community during pig manure (PM) composting was investigated. Six different dosages of PS based on the dry weight of PM (0 %, 2.5 %, 5 %, 7.5 %, 10 %, and 12 %; T1-T6, respectively) were mixed with wheat straw to make the initial feedstock and composted for 42 days. The results showed that Ascomycota, Basidiomycota, and Giomeromycota were the most abundant phyla in all treatments. However, the relative abundance of Giomeromycota was the highest in the control treatment, although a substantially greater population was observed in all treatments. Genus abundance declined steadily from T1 to T6; however, T4 and T6 had smaller populations. Correlation analysis also suggested that T6 amendment increased the overall fungal dynamics and organic matter degradation. Thus, T6 was more efficient to enhance the overall fungal population and dynamics with considerable network connections among all the analyzed parameters.

Sulfur-aided aerobic biostabilization of swine manure and sawdust mixture: Humification and carbon loss

To investigate how sulfur addition affects humification and carbon loss during swine manure (SM) biostabilisation, various proportions of sulfur, i.e., 0 (CK), 0.2%-0.8% (S1-S4) were added to SM in a 70-day pilot-scale test. Compared to CK (16.07%), sulfur addition resulted in the mineralization of 17.05%-24.27% of the total organic carbon. Sulfur addition also reduced CH4 emissions, which were 3.7%-29.3% lower than that of CK. The total global warming potential values were in the range of 913.1-968.2 g CO2 eq kg-1 for all treatments. Although the sulfur-added treatments showed lower HA/FA ratios than CK after 70 days, no significant impact on the maturity of the final products was observed. Sulfur addition impacted the microbial community, CH4, CO2, N2O emissions, and affected the variation of temperature in biowaste biostabilization. These discoveries provided an important basis for understanding the function of sulfur in regulating the aerobic bio-decomposition of organic waste.

Metabolic responses and microbial community changes to long chain fatty acids: Ammonia synergetic co-inhibition effect during biomethanation

Anaerobic co-digestion is an established strategy for increasing methane production of substrates. However, substrates rich in proteins and lipids could cause a long chain fatty acids (LCFA)-ammonia synergetic co-inhibition effect. The microbial mechanisms of this co-inhibition are still unclear. The current study explored the effect of the synergetic co-inhibition on microbial community changes and prediction of metabolic enzymes to reveal the microbial mechanisms of the co-inhibition effect. The results indicated that during the synergetic co-inhibition, methanogens were mainly affected by ammonia. Decreased relative abundances of Petrimonas (82%) and Paraclostridium (67%) showed that ammonia inhibition contributed to the suppression of LCFA β-oxidation under the synergetic co-inhibition conditions. The accumulation of more LCFA could further suppress microorganisms' activities involved in several steps of anaerobic digestion. Finally, decrease of critical enzymes' abundances confirmed the synergetic co-inhibition effect. Overall, the current study provides novel insights for the alleviation of synergetic co-inhibition during anaerobic digestion.

The addition of nano zero-valent iron during compost maturation effectively removes intracellular and extracellular antibiotic resistance genes by reducing the abundance of potential host bacteria

Applying compost to soil may lead to the spread of antibiotic resistance genes (ARGs) in the environment. Therefore, removing ARGs from compost is critical. In this study, for the first time, nano zero-valent iron (nZVI) was added to compost during the maturation stage to remove ARGs. After adding 1 g/kg of nZVI, the abundance of total intracellular and total extracellular ARGs was decreased by 97.62% and 99.60%, and that of total intracellular and total extracellular mobile genetic elements (MGEs) was decreased by 92.39% and 99.31%, respectively. A Mantel test and network analysis indicated that the reduction in potential host bacteria and intI1 after nZVI treatment promoted the removal of intracellular and extracellular ARGs. The addition of nZVI during composting reduced the horizontal transfer of ARGs and improve the total nitrogen and germination index of compost, allowing it to meet the requirements for organic fertilizers.

Enhancing nitrate attenuation in groundwater via selectively applying surface agricultural practices: A novel and sustainable strategy for non-point source pollution mitigation

Non-point nitrate pollution in groundwater has been accelerated by agricultural development, but sustainable nitrogen removal is a challenge because of its wide distribution and negative side effects. Surface agricultural practices (SAPs), which are demonstrably effective in driving the downward infiltration of dissolved organic carbon (DOC), have not been well explored for their potential to enhance nitrate attenuation in groundwater. Therefore, a combination of soil column and groundwater incubation experiments was performed to investigate the carbon and nitrogen responses to different SAPs (manure fertilization, lucerne planting, and straw return). The soil column experiment showed that SAPs promoted DOC and reduced nitrate leaching into groundwater, and straw treatment witnessed the highest DOC leaching flux (252.71 g m^-2 yr^-1) and lowest nitrate leaching flux (9.51 g m^-2 yr^-1). The groundwater incubation experiment showed that leachates from the straw treatment displayed the best denitrification-enhancement performance, with the highest NO₃^--N reduction efficiency (92.93%) and rate (1.627 mg/day), N₂ selectivity (99.78%), and net nitrogen removal (0.09 mg). Furthermore, Fourier transform ion cyclotron resonance mass spectrometry confirmed that CHOS molecules with lower double bond equivalents (0-5) and larger carbon numbers (10-15) were more accessible to denitrifiers. This study provides a new path for the sustainable control of non-point source nitrate pollution.

Biochar enhanced organic matter transformation during pig manure composting: Roles of the cellulase activity and fungal community

Fungal degradation of cellulose is a key step in the conversion of organic matter in composting. This study investigated the effects of adding 10% biochar (including, prepared from corn stalk and rape stalk corresponding to CSB and RSB) on organic matter transformation in composting and determined the role of cellulase and fungal communities in the conversion of organic matter. The results showed that biochar could enhance the conversion of organic matter, especially in RSB treatment. Biochar could increase cellulase activity, and RSB could enhance 33.78% and 30.70% the average activity of cellulase compared with the control and CSB treatments in the mesophilic to thermophilic phase, respectively. The results of high throughput sequencing demonstrated that Basidiomycota dominant in mesophilic phase, and Ascomycota dominant in other phases of composting. The redundancy analysis showed that Alternaria, Thermomycees, Aspergillus, Wallemia, and Melanocarpus might be the key fungi for the degradation of organic matter, and Fusarium, Penicillium, and Scopulariopsis may promote the conversion of organic matter. Network showed that the addition of RSB changed the interactions between fungal communities and organic matter transformation, and RSB treatment enriched members of Ascomycota related to organic matter transformation and cellulase activity. These results indicated that RSB improved organic matter conversion by enhancing the role of cellulase and fungal communities.

The driving mechanism of passivator islands adsorbing and immobilizing heavy metals during chicken manure composting

The aim of this study was to assess the effectiveness of biochar and montmorillonite islands on heavy metal adsorptive immobilization and identify crucial driving factors and pathways during chicken manure composting. Compared to montmorillonite (6.74 and 89.25 mg/kg), biochar exhibited an obviously higher ability of Cu and Zn enrichment (41.79 and 167.77mg/kg), might be attributed to its abundant active functional groups. Network analysis showed that compared to Cu, core bacteria positively and negatively related to Zn was obviously more and less in passivator islands, respectively, which might explain significantly higher Zn concentration. Structural Equation Model displayed that dissolved organic carbon (DOC), pH and bacteria were critical driving factors. Pretreatment of passivator packages, such as soaking in the solution being rich in DOC and inoculating specific microbial agents accumulating heavy metals via extracellular adsorption /intracellular interception would significantly improve the effectiveness of adsorptive passivation on heavy metals.

Comparison and Evaluation of GHG Emissions during Simulated Thermophilic Composting of Different Municipal and Agricultural Feedstocks

Composting is widely used to recycle a variety of different organic wastes. In this study, dairy manure, chicken litter, biosolids, yard trimmings and food waste were selected as representative municipal and agricultural feedstocks and composted in simulated thermophilic composting reactors to compare and evaluate the GHG emissions. The results showed that the highest cumulative emissions of CO2, CH4 and N2O were observed during yard trimmings composting (659.14 g CO2 kg-1 DM), food waste composting (3308.85 mg CH4 kg-1 DM) and chicken litter composting (1203.92 mg N2O kg-1 DM), respectively. The majority of the carbon was lost in the form of CO2. The highest carbon loss by CO2 and CH4 emissions and the highest nitrogen loss by N2O emission occurred in dairy manure (41.41%), food waste (0.55%) and chicken litter composting (3.13%), respectively. The total GHG emission equivalent was highest during food waste composting (365.28 kg CO2-eq ton-1 DM) which generated the highest CH4 emission and second highest N2O emissions, followed by chicken litter composting (341.27 kg CO2-eq ton-1 DM), which had the highest N2O emissions. The results indicated that accounting for GHG emissions from composting processes when it is being considered as a sustainable waste management practice was of great importance.

Review of inventory data for the biological treatment of sewage sludge

The biological treatment of municipal sewage sludge, including anaerobic digestion and composting, was reviewed with the purpose of establishing inventory data to address all the inputs and outputs related to sludge treatment. We identified 193 scientific papers, resulting in 64 datasets on anaerobic digestion and 35 datasets on composting. For anaerobic digestion, biogas production varied significantly (up to a factor of four) depending on the sludge. A useful correlation was identified between the amount of methane produced and the degradation of volatile solids. According to statistical tests, no significant differences were found in biogas production for mesophilic and thermophilic digesters. In addition, methane content varied significantly, and very few data were available for digestate composition or for energy consumption and recovery. For composting, accurate estimates relating to the degradation of sewage sludge could not be made, since organic bulking materials were part of the final composted product. Data on emissions to air are currently scarce, which points to the need for more published information. The inventory data evaluated herein are useful in the feasibility assessment of the biological treatment of sewage sludge, for comparing technologies, for example in LCA studies and as a basis for evaluating the performance of a specific biological sludge treatment plant. However, a great deal of the reviewed data originated from laboratory and pilot-scale studies, and so there is a need for more complete datasets on the performance of full-scale technologies, in order to establish full inventories and identify differences in technologies and operational conditions.

Exploring the mechanism associated with methane emissions during composting: Inoculation with lignocellulose-degrading microorganisms

Inoculation with microorganisms is an effective strategy for improving traditional composting processes. This study explored the effects of inoculation with lignocellulose-degrading microorganisms (LDM) on the degradation of organic matter (OM), methane (CH₄) emissions, and the microbial community (bacteria and methanogens) during composting. The results showed that LDM accelerated the degradation of OM (including the lignocellulose fraction) and increased the CH₄ releases in the later thermophilic and cooling stages during composting. At the ending of composting, LDM increased the CH₄ emissions by 38.6% compared with the control. Moreover, LDM significantly increased the abundances of members of the bacterial and methanogenic community during the later thermophilic period (P < 0.05). In addition, LDM promoted the growth and activity of major bacterial genera (e.g., Ureibacillus) with the ability to degrade macromolecular OM, as well as affecting key methanogens (e.g., Methanocorpusculum) in the composting system. Network analysis and variance partitioning analysis indicated that OM and temperature were the main factors that affected the bacterial and methanogen community structures. Structural equation modeling demonstrated that the higher CH₄ emissions under LDM were related to the growth of methanogens, which was facilitated by the anaerobic environment produced by large amounts of CO₂. Thus, aerobic conditions should be improved during the end of the thermophilic and cooling composting period when inoculating with lignocellulose-degrading microorganisms in order to reduce CH₄ emissions.

Comprehensive evaluation of spent mushroom substrate-chicken manure co-composting by garden waste improvement: physicochemical properties, humification process, and the spectral characteristics of dissolved organic matter

The performance of garden waste on spent mushroom substrate (SMS) and chicken manure (CM) co-composting efficiency and humification is unclear. Therefore, this study investigated the impact of garden waste addition on SMS-CM co-composting physicochemical properties, humification process, and the spectral characteristics of dissolved organic matter (DOM). The results showed that garden waste improved the physicochemical properties of SMS-CM co-compost, the thermophilic period was advanced 2 days, the seed germination index increased by 30.2%, and the total organic carbon and total nitrogen content increased by 8.80% and 15.0%, respectively. In addition, garden waste increased humic substances (HS) and humic acid (HA) contents by 10.62% and 34.52%, respectively; the HI, PHA and DP increased by 31.53%, 43.19% and 55.53%, respectively; and the SUVA₂₅₄ and SUVA₂₈₀ of DOM also increased by 6.39% and 4.39%, respectively. In particular, HA content and DOM humification increase rapidly in the first 10 days. The increase of HA accounted for 52% of the total increase during composting. Fourier-transform infrared and two-dimensional correlation analysis further confirmed that garden waste could facilitate the degradation of organic molecules, including amino acids, polysaccharides, carboxyl groups, phenols, and alcohol, and contributed to the preferential utilization of carboxyl groups and polysaccharides and thus enhanced humification.

Effect of microbial agents on maturity, humification, and stability and the bacterial succession of spent mushroom substrate composting

Two composting experiments were conducted to investigate the effects of commercial microbial agents on microbial succession and nutrient flow such as humification, maturation, and stability during the aerobic composting of the spent mushroom substrate (SMS). The cellulose degradation rate of T (added microbial agents at the initial stage) reached 41.8%, which was much significantly (p < 0.05) higher than that of CK (14.9%). The seed germination index (GI) in T (82.38%) was significantly (p < 0.05) higher than that in CK (74.74%) in the maturation phase. Moreover, the total organic carbon/total nitrogen ratio (C/N) and electrical conductivity (EC) value of T decreased to 10.5 and 2.37 mS/cm, respectively. Chemical detection and fluorescence excitation-emission region integration method (EEM-FRI) analysis showed that the microbial agents significantly accelerated the organic matter (OM) decomposition and promoted the quality of mature compost using SMS as a single raw material. The bacterial abundance of T was significantly richer than the CK due to the addition of microbial agents. The results could provide a comprehensive understanding of adding microbial agents into composting SMS and a scientific feasibility strategy to rational utilization of resources in the edible fungi industry, which was conducive to the waste management and sustainable development of the edible fungi industry.

Simultaneous nitrate and phosphate removal based on thiosulfate-driven autotrophic denitrification biofilter filled with volcanic rock and sponge iron

This study constructed two thiosulfate-driven autotrophic denitrification biofilters filled with volcanic rock (VR-BF), sponge iron and volcanic rock (SIVR-BF), respectively. The nitrate removal load (3200 g/m³/d) and efficiency (98 %) of SIVR-BF were higher than those of VR-BF. The removal of phosphate in SIVR-BF was mainly through forming FePO₄ and Fe₃(PO₄)₂(OH)₂. Sulfur and iron cycles in SIVR-BF contributed to Fe (II)/Fe (III) electron shuttle, as well as S^2-, S⁰, Sn^2- electron buffer and energy storage, which improved nitrate removal and electron utilization. The formation of multi-path collaborative denitrification dominated by sulfur autotrophic denitrification (64.2 ∼ 89.6 %) in SIVR-BF. The other denitrification pathways, such as iron autotrophic denitrification, which buffered pH and reduced sulfate production. Thiobacillus (38.6 %) and Ferritrophicum (25.3 %) were the dominant genus of VR-BF and SIVR-BF, respectively, which played crucial roles in autotrophic denitrification of iron and sulfur. SIVR-BF was a promising process to realize iron-sulfur coupling autotrophic denitrification and phosphate removal.

Synergistic effect of yeast integrated with alkyl polyglucose for short-chain fatty acids production from sludge anaerobic fermentation

An efficient strategy for short-chain fatty acid (SCFA) production from sludge anaerobic fermentation was proposed with the combination of yeast and alkyl polyglucose (APG). It revealed that the synergetic effect of yeast and APG could boost the SCFA concentration to the maximum value of 2800.34 mg COD/L within 9 days at 0.20 g/g suspended solids (SS) yeast and 0.20 g/g SS APG, which was significantly higher than that of its counterparts. Interestingly, the sludge solubilization, the biodegradability of fermentation substrate, as well as the acidification of hydrolyzed products, was evidently improved in the coexistence of APG and yeast. The activities of hydrolytic enzymes and acetate kinase were also stimulated, whereas the coenzyme F420 was inhibited. The synergetic effect of yeast and APG used in this work enriches the study of carbon resource recovery from sludge anaerobic fermentation.

Oxygen dynamics, organic matter degradation and main gas emissions during pig manure composting: Effect of intermittent aeration

To investigate the effect of intermittent aeration on oxygen dynamics, organic matter degradation and main gas emissions, a lab-scale pig manure composting experiment was conducted with intermittent aeration (I_A, 30-min on and 30-min off) and continuous aeration (C_A). Although aeration volume and oxygen supply of I_A was only half of C_A, I_A could obviously enhance the oxygen utilization efficiency by 96.67 % and reduce energy dissipation for aeration by 50.87 %. Based on the comprehensive analysis of total organic matter, total carbon, total nitrogen, cellulose, hemicellulose and lignin contents, there was no significant difference in organic matter degradation between I_A and C_A (p > 0.05). Moreover, a reduction of 21.71 %, 38.93 %, 44.40 % and 62.19 % of CH₄, N₂O and the total GHG emission equivalent as well as NH₃ emissions was realized, respectively, in I_A compared with C_A. Therefore, adopting intermittent aeration was a useful strategy and choice for high-efficiency, high-quality and environment-friendly composting.

Optimization of vegetable waste composting and the exploration of microbial mechanisms related to fungal communities during composting

The application of additives to regulate the microbial functional composition during composting has attracted much research attention. However, little is known about the succession and role of the fungal community in the laboratory-scale composting of vegetable waste supplemented with pig manure and microbial agents. The purpose of this study was to identify effective additives for improving vegetable waste composting performance and product quality, and to analyze the microbial community succession during composting. The results showed that the combined addition of pig manure and microbial agents (T2 treatment) accelerated the pile temperature increase, enhanced total organic carbon degradation (23.36%), and promoted the maturation of the compost. Furthermore, the T2 treatment increased the activities of most enzymes, reshaped the microbial community, and reduced the relative abundance of potential animal (1.60%) and plant (0.095%) pathogens. The relative abundance of Firmicutes (71.23%) increased with the combined addition of pig manure and microbial agents in the thermophilic stage. In the middle and late stages, Saccharomonospora, Aspergillus, and Thermomyces, which were related to C/N and total phosphorus, were enriched in the T2 treatment. Network analysis demonstrated that the complexity and stability of the fungal network were more evidently increased in the T2 treatment, and Saccharomonospora, Aspergillus, and Microascus were identified as keystone taxa. The keystone taxa associated with extracellular enzymes contributed significantly to compost maturation. These results provide a reference for the application of additives to improve compost safety in pilot-scale composting.

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.

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.

Effects and microbial mechanisms of phosphogypsum and medical stone on organic matter degradation and methane emissions during swine manure composting

The degradation of organic matter (OM) and CH₄ emissions during composting greatly influence the composting efficiency and greenhouse effect. This study evaluated the effects of adding phosphogypsum (PPG) and medical stone (MS) on OM breakdown, CH₄ emissions, and their underlying mechanisms. MS accelerated the breakdown of OM in the early composting stage, whereas PPG increased it in the cooling and maturation periods. At the ending of composting, humification was also significantly promoted by PPG and MS (P < 0.05). Moreover, MS and PPG reduced CH₄ emissions by 27.64% and 23.12%, respectively, and significantly inhibited the activities of methanogens in terms of their abundance (mcrA) and composition (dominant genera such as Methanobrevibacter, Methanocorpusculum, and Methanothermus) (P < 0.05). Interestingly, MS enhanced the activity of enzymes and bacterial metabolism related to OM degradation in the early composting stage, whereas PPG promoted them during the cooling and maturity stages. MS and PPG inhibited the activities of enzymes related to CH₄ release during the cooling and maturity stages. Therefore, PPG and MS may have influenced OM degradation and CH₄ releases during composting via changes in bacterial metabolism and enzyme activity levels. PPG and MS could have altered the activities of methanogens to influence the transformation of carbon and CH₄ emissions according to network analysis and partial least-squares path modeling analysis. These findings provide insights at the molecular level into the effects of adding PPG and MS on OM degradation and CH₄ emissions during composting, thereby facilitating the application of PPG and MS in composting systems.

Metagenomic and HT-qPCR analysis reveal the microbiome and resistome in pig slurry under storage, composting, and anaerobic digestion

Direct application of pig slurry to agricultural land, as a means of nutrient recycling, introduces pathogens, antibiotic resistant bacteria, or genes, to the environment. With global environmental sustainability policies mandating a reduction in synthetic fertilisation and a commitment to a circular economy it is imperative to find effective on-farm treatments of slurry that maximises its fertilisation value and minimises risk to health and the environment. We assessed and compared the effect of storage, composting, and anaerobic digestion (AD) on pig slurry microbiome, resistome and nutrient content. Shotgun metagenomic sequencing and HT-qPCR arrays were implemented to understand the dynamics across the treatments. Our results identified that each treatment methods have advantages and disadvantages in removal pollutants or increasing nutrients. The data suggests that storage and composting are optimal for the removal of human pathogens and anaerobic digestion for the reduction in antibiotic resistance (AMR) genes and mobile genetic elements. The nitrogen content is increased in storage and AD, while reduced in composting. Thus, depending on the requirement for increased or reduced nitrogen the optimum treatment varies. Combining the results indicates that composting provides the greatest gain by reducing risk to human health and the environment. Network analysis revealed reducing Proteobacteria and Bacteroidetes while increasing Firmicutes will reduce the AMR content. KEGG analysis identified no significant change in the pathways across all treatments. This novel study provides a data driven decision tree to determine the optimal treatment for best practice to minimise pathogen, AMR and excess or increasing nutrient transfer from slurry to environment.

Microbial composition and nitrogen removal pathways in a novel sequencing batch reactor integrated with semi-fixed biofilm carrier: evidence from a pilot study for low- and high-strength sewage treatment

The sequencing batch reactor (SBR) activated sludge process is a well-established technology for sewage treatment. One of the drawbacks of SBRs, however, total nitrogen (TN) removals is insufficient. By means of introducing four improvements, including semi-fixed biofilm carrier, sludge elevation mixing and change for the mode of influent and effluent, compliant standard for TN discharge was obtained in this novel SBR configuration during low- and high-strength sewage load. To illustrate the microbial compositions and functions of the attached biofilm on semi-fixed carrier and the suspended aggregates, as well as the nitrogen removal pathway, high throughput 16S rRNA gene amplicon sequencing, PICRUSt2 algorithm, and KEGG database were applied. The results revealed that (i) the microbial communities from suspended aggregates and biofilm samples were significantly different from each other; (ii) during low-strength sewage loads, TN removal was mainly by nitrification-denitrification. The suspended aggregates was responsible for denitrification, while the biofilm was focused on ammonium oxidation; (iii) during high-strength sewage loads, function of nitrate reductase from suspended aggregates was faded, and anammox and N assimilation by biofilm became dominant. Meanwhile, TN removal referring to the formation of L-glutamine via assimilation was the main pathway.

Effects of different carbon sources on methane production and the methanogenic communities in iron rich flooded paddy soil

Various carbon sources as substrates and electron donors can produce methane via different metabolic pathways. In particular, the methane produced by rice cultivation has a severe impact on climate change. However, how Fe³⁺, the most abundant oxide in paddy soil, mediates the methanogenesis of different carbon sources is unknown. In this study, we investigated the effect of four carbon sources with different chain lengths (acetate, glucose, nonanoate, and starch) on CH₄ production and associated methanogens in iron-rich paddy soil over 90 days of anaerobic incubation. We found that glucose and starch were the more preferential substrates for liberating methane compared to acetate, and the rate was also faster. Nonanoate was unable to support methane production. Methanosarcinales and Methanobacteriales were the most predominant methanogenic archaea as shown by 16S rRNA gene sequencing, though their abundance changed over time. Additionally, a significantly higher content of iron-reducing bacteria was observed in the glucose and starch treatments, and it was significantly positively correlated with the copy number of the methanogenic mcrA gene. Together, we confirmed the methanogenic capacity of different carbon sources and their related microorganisms. We also showed that iron oxides play a central role in regulating methane emissions from paddy soils and need more attention to be paid to them.

Dynamic Microstructure Assembly Driven by Lysinibacillus sp. LF-N1 and Penicillium oxalicum DH-1 Inoculants Corresponds to Composting Performance

The effects of Lysinibacillus sp. LF-N1 and Penicillium oxalicum DH-1 inoculants (LFPO group) on compost succession and the microbial dynamic structure of co-composting wheat straw and cow manure composting were investigated. The inoculants contributed to longer thermophilic stages, higher temperatures (62.8 °C) and lower microbial diversity in the LFPO treatment compared to the control group (CK). Moreover, LFPO inoculation increased the germination index and accelerated organic matter and lignocellulose degradation in the compost. Microbial analysis confirmed that the inoculants effectively altered the microbial communities. The predominant biomarkers for bacteria and fungi in inoculated compost were members of Lysinibacillus and Penicillium, respectively. Functional prediction showed greater lignocellulose degradation and less pathogen accumulation in the LFPO group. The cooccurrence network analysis showed that the network structure in LFPO compost was greatly simplified compared to that in CK. Bacterial cluster A was dominated by Lysinibacillus, and fungal cluster B was represented by Penicillium, which were significantly correlated with temperature and lignocellulose degradation, respectively (p < 0.05). These results demonstrated that the LF-N1 and DH-1 inoculants drove the bacterial and fungal assemblies to induce physicochemical property changes during cocomposting.

Diversity and Potential Function of Prokaryotic and Eukaryotic Communities from Different Mangrove Sediments

Mangrove trees generally play important roles in protecting intertidal ecosystems. The mangrove root-associated sediments provide a repertoire of microbial communities that contribute to pivotal ecological functions in the system. In the present study, we used the high-throughput sequencing and PICRUSt-predicted functional information (based on 16S/18S rDNA profiles) to investigate the bacterial, archaeal, and fungal communities in two mangrove systems, located in the estuary of the Jiulong River (China), with different contaminated conditions and frequencies of human activity. Diverse distribution patterns for microbial communities were observed in six sediment samples collected from the two survey areas, which were found to be related mainly to the substrates in mangrove sediments. The sediments were predominated by relatively higher ratios of heterotrophic bacteria that participated in the degradation of organic matters, including phylum of Chloroflexi, Acidobacteriota, Desulfobacterota, and Proteobacteria. In addition, Crenarchaeota and Ascomycota presented the highest abundances of archaea and fungi, respectively. The relatively high concentrations of calcium, nitrogen, magnesium, and phosphorus in mangrove sediments correlated significantly with the microbial communities. In addition, although the potential functions were similar in the two sites based on COG and KEGG pathways, the abundances of enzymes involved in the degradation processes of cellulose and hemicellulose and the metabolism of nitrogen and sulfur presented distinctions. These results provide insights into the environmental conditions shaping microbial assemblies of the mangrove sediments under the impacts of human activities; for instance, a more abundant amount of calcium was found in urban areas in this study.

Dual roles of dissolved organic nitrogen in groundwater nitrogen cycling: Nitrate precursor and denitrification promoter

Dissolved organic nitrogen (DON) has been reported to be prevalent in groundwater worldwide. Owing to the diversity of physicochemical properties, DON plays complex roles in nitrogen cycling processes, which has further implications for nitrate (NO₃^--N) pollution control in groundwater. To characterize these crucial roles, we investigated the effects of three types of DON (amino acid, urea, and protein) on NO₃^--N accumulation in groundwater with a 60-day incubation experiment and established quantitative correlations between microbial indicators (bacterial communities and nitrogen functional genes) and nitrogen content. The results showed that NO₃^--N content increased by 30.3% and 38.8% and was strongly correlated with the presence of amino acid and urea; however, the addition of protein did not lead to an additional increase in NO₃^--N, possibly due to different extents of mineralization and denitrification caused by different types of DON. Molecular biological experiments demonstrated that Nitrospira (1.8-3.2%) contributed to nitrification in the urea treatment, whereas Arthrobacter (2.0-6.9%) and Thermomonas (11.9-13.1%) were key communities controlling denitrification in amino acid and protein treatments. amoA and nxrA were continuously enriched in the presence of urea; however, amino acid and protein were strongly correlated with napA-dominated and narG-dominated denitrification processes, with the path coefficient - 2.912 and - 2.450 respectively. Combined analyses showed that DON with distinct physicochemical properties played dual roles (NO₃^--N precursor and denitrification promoter) to varying degrees, which could have significant impacts on NO₃^--N accumulation in groundwater. This study may provide guidance for environmental risk evaluation and control strategies for NO₃^--N pollution in groundwater.

Optimising mixed aerobic and anaerobic composting process parameters for reducing bacterial pathogenicity in compost-derived products

Although composting techniques are continuously optimised and adjusted, the removal of bacterial pathogen based on the quality of composting products needs further to ensure safe of agricultural use. In this study, we combined aerobic composting and anaerobic process to determine the optimal combination (turning frequency of once a day, the proportion of swine manure to corn straw (3:1), and mixed 6-day anaerobic process) that benefits the reduction of bacterial pathogens, among which the maximum removal efficiency of up to 92.96% was observed for Clostridium_sensu_stricto_1 reached, thereby improving the quality of the compost products. The variation partition analysis and redundancy analysis indicated that physicochemical factors such as temperature, TOC, and pH significantly affected the removal of bacterial pathogens. Therefore, the additive effects of physicochemical factors on bacterial pathogen removal requires further process optimisation. These findings offer powerful technological support for improving agricultural waste recycling and enhancing the safety of fertiliser application.

Effect of distillery sewage sludge addition on performance and bacterial community dynamics during distilled grain waste composting

This study evaluated the dynamics of physicochemical characteristics and bacterial communities during the co-composting of distilled grain waste (DGW) and distillery sewage sludge (SS), with DGW mono-composting as a control. Results showed that co-composting with SS significantly improved DGW degradation efficiency (61.38% vs. 54.13%) and end-product quality (seed germination index: 129.82% vs. 113.61%; N + P₂O₅ + K₂O: 9.08% vs. 5.28%), compared to DGW mono-composting. Microbial community analysis revealed that co-composting accelerated the bacterial community succession rate and enhanced the abundance of the phyla Proteobacteria, Firmicutes, Chloroflexi, and Deinococcota by 45.86%, 4.38%, 37.49%, and 15.29%, respectively. Network analysis showed that DGW-SS co-composting altered the interactions among the bacterial genera and improved bacterial community stability. Spearman correlation analysis indicated that the correlation between bacterial genera and environmental factors was more significant in DGW-SS co-composting. Therefore, co-composting of DGW and SS is a suitable strategy for the treatment of solid byproducts from spirit distilleries.

Response of bacterial community to iron oxide nanoparticles during agricultural waste composting and driving factors analysis

The succession of bacterial communities and their function, and the core microorganisms for water soluble organic carbon (WSC) and organic matter (OM) changes during agricultural waste composting with addition of iron oxide nanomaterials (FeONPs, Fe₂O₃ NPs and Fe₃O₄ NPs) were investigated. Moreover, driving factors for bacterial composition and metabolism were analyzed. Results showed that FeONPs treatments increased the relative abundance of thermophilic microorganisms for OM degradation. Most of the core genera were responsible for decomposition of OM and synthesis of WSC. Additionally, FeONPs promoted the metabolism of amino acids. The most significant factors for dominant genera in control, Fe₂O₃ NPs and Fe₃O₄ NPs group were moisture (62.1%), moisture (62.0%) and OM (58.2%), respectively. For metabolism, the most significant factors in control, Fe₂O₃ NPs and Fe₃O₄ NPs group were temperature (57.2%), NO₃^--N (60.5%), NO₃^--N (62.6%), respectively. The relationships between compost properties, bacterial community and metabolism were changed by FeONPs.

Indigenous Microorganisms Offset Arbuscular Mycorrhizal Fungi-Induced Plant Growth and Nutrient Acquisition Through Negatively Modulating the Genes of Phosphorus Transport and Nitrogen Assimilation

Arbuscular mycorrhizal (AM) fungi that promote plant growth and nutrient acquisition are essential for nutrient-deficient karst areas, while they inevitably regulate host plants jointly with indigenous microorganisms in natural soil. However, how indigenous microorganisms regulate AM-induced benefits on plant growth and nutrient acquisition remains unclear. In this study, the Bidens tripartita as the common plant species in the karst region was cultivated into three soil substrates treated by AM fungi inoculation (AMF), AM fungi inoculation combining with indigenous microorganisms (AMI), and the control without AM fungi and indigenous microorganisms (CK). The plant biomass and concentration of nitrogen (N) and phosphorus (P) were measured, and the transcriptomic analysis was carried out using root tissues. The results showed that AM fungi significantly enhanced the plant biomass, N, and P accumulation with the reduction of plants' N/P ratio; however, the indigenous microorganisms offset the AM-induced benefits in biomass and N and P acquisition. In addition, there are 819 genes in differentially expressed genes (DEGs) of AMF vs. AMI ∩ AMF vs. CK, meaning that AM fungi induced these genes that were simultaneously regulated by indigenous microorganisms. Furthermore, the enrichment analysis suggested that these genes were significantly associated with the metabolic processes of organophosphate, P, sulfur, N, and arginine biosynthesis. Notably, 34 and 17 genes of DEGs were related to P and N metabolism, respectively. Moreover, the indigenous microorganisms significantly downregulated these DEGs, especially those encoding the PHO1 P transporters and the glnA, glutamate dehydrogenase 2 (GDH2), and urease as key enzymes in N assimilation; however, the indigenous microorganisms significantly upregulated genes encoding PHO84 inducing cellular response to phosphate (Pi) starvation. These regulations indicated that indigenous microorganisms restrained the N and P metabolism induced by AM fungi. In conclusion, we suggested that indigenous microorganisms offset nutrient benefits of AM fungi for host plants through regulating these genes related to P transport and N assimilation.

Enhancements of short-chain fatty acids production via anaerobic fermentation of waste activated sludge by the combined use of persulfate and micron-sized magnetite

The combination of persulfate (PDS) with micron-sized magnetite (Fe₃O₄) was introduced into the process of anaerobic fermentation (AF) to scrutinize the short chain fatty acid (SCFA) production from waste activated sludge for the first time. The synergetic effect of PDS and Fe₃O₄ results in the promotion of intracellular and extracellular substance liberation, augment in key hydrolases activities, and enrichment of hydrolytic and acidifying microbial population. Meanwhile, carbohydrate, amino acid, and energy metabolism as well as enzymes, are considerably accelerated. Consequently, the maximum SCFAs yield is significantly enhanced to 391.25 mg COD/L on day 8 of AF with the addition of 0.3 g Fe₃O₄/g SS and 0.5 g PDS/g SS, which was 2.39-folds than that of the control. The relative abundance of Actinobacteria were highly enriched and reached to 35.76% at the class level. This work affords an effective avenue to evidently boost the production of SCFAs from WAS via AF.

In situ biogas upgrading via cathodic biohydrogen using mitigated ammonia nitrogen during the anaerobic digestion of Taihu blue algae in an integrated bioelectrochemical system (BES)

Biohydrogen using migrated ammonia as nitrogen source, and biogas upgrading with hydrogen collected at biocathode in an integrated bioelectrochemical system (BES) were investigated, during the anaerobic digestion of Taihu blue algae. Under an applied voltage of 0.4 V, biohydrogen (202.87 mL) reached 2.34 and 2.90 times than groups with applied voltage of 0 V and 0.8 V, respectively. Moreover, biohydrogen of the group with 1000 mg/L initial ammonia addition (524.16 mL) reached 1.53 times than that the of the control. With 0.25 bar of H₂ injected at the beginning (R1), highest methane production (286.62) mL and content (75.73%) were obtained. Comparing to other groups, not only microbial genus responsible for both aceticlastic and hydrogenotrophic methanogens of the group R1 were apparently enriched, but key enzymes related to methane production also acquired better abundances. Therefore, it's promising to conduct the ammonia alleviating, hydrogen producing and biogas upgrading simultaneously using BES.

Microbial community and metabolic responses to electrical field intensity for alleviation of ammonia inhibition in an integrated bioelectrochemical system (BES)

Bioelectrochemical system (BES) is a promising solution for mitigation of ammonia inhibition in anaerobic digestion (AD) process. However, the effect of electric field intensity on microbial community changes and metabolic function prediction during the alleviation of ammonia inhibition are still missing. The results of the current study represented that the improvement of ammonia removal (20.6%) and methane production (14.6%) could both be achieved at 0.2 V while higher voltages led to reductions of methane production (more than 48.9%) compared with the control. Moreover, hydrogenotrophic methanogens (Methanobacterium) seemed to be more robust to high voltages compared with aceticlastic methanogens (Methanosaeta). Additionally, bacteria for hydrolysis and acidogenesis (Rikenellaceae and Soehngenia) were found vulnerable to external electric field intensity. Furthermore, abundances changes of metabolic pathways demonstrated that the degradation of carbohydrates, lipids and proteins during all steps (hydrolysis, acidogenesis, acetogenesis and methanogenesis) of AD process could be affected by different applied voltages.

New insights into restoring microbial communities by side-stream supersaturated oxygenation to improve the resilience of rivers affected by combined sewer overflows

Combined sewer overflows (CSOs) are a dominant contributor to urban river pollution. Therefore, reducing the environmental impacts of CSOs and improving the self-purification capacity of water bodies are essential. In this study, the side-stream supersaturation (SSS) oxygenation was applied to restore microbial function of rivers which are affected by CSOs to improve the self-purification capacity. The results showed that apart from the dissolved organic matter inputs from CSO event, the sediment had become an important contributor to pollution in the studied river. After the long-term (46 d) implementation of SSS oxygenation, dissolved oxygen and the oxidation-reduction potential of the river water increased by 98% and 238%, respectively, compared to emergency control measures implemented following individual CSO events. The NH₃-N concentrations and the chemical oxygen demand also decreased by 20% and 45%, respectively. In addition, the occurrence of microbial functions related to information storage and processing, and cellular process and signaling, increased by 1.87% and 0.82% in response to SSS oxygenation, respectively, and the Shannon index of the sediment microbial community increased by more than 15%. The frequencies of genes related to nitrification and sulfur oxidation also increased by 20-450% and >50%, respectively. This research provides new insights into the ecological restoration of rivers affected by CSOs.

Comparative evaluation of biochar, pelelith, and garbage enzyme on nitrogenase and nitrogen-fixing bacteria during the composting of sewage sludge

This study investigated the effects of garbage enzyme (GE), pelelith (PL), and biochar (BC) on nitrogen (N) conservation, nitrogenase (Nase) and N-fixing bacteria during the composting of sewage sludge. Results showed that the addition of GE, PL, and BC reduced NH₃ emissions by 40.9%, 29.3%, and 67.4%, and increased the NO₃-N contents of the end compost by 161.4, 88.2, and 105.8% relative to control, respectively, thus increasing the TN content. Three additives improved Nase, cellulase, and fluorescein diacetate hydrolase (FDA) activities and the abundances of nifH gene, and the largest increase was BC, followed by PL and GE. In addition, the additives also markedly influenced the succession of N-fixing bacteria, and significantly increased the abundance of Proteobacteria during the whole process. The BC and PL additions strengthened the sensitivity of N-fixing bacteria to environmental variables, and FDA, TN, moisture content, and NO₃-N significantly affected the N-fixing bacteria at genus level.

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.

Garbage enzymes effectively regulated the succession of enzymatic activities and the bacterial community during sewage sludge composting

This study evaluated nitrogen transformation, enzymatic activities and bacterial succession during sewage sludge composting with and without garbage enzymes (GE and CK, respectively). The results showed that GE addition significantly increased fluorescein diacetate hydrolase (FDA), cellulase, and nitrogenase activities during the composting process. GE addition reduced the cumulative NH₃ emissions by 66.5%, increased the peak NH₄-N content by 26.3% and increased the total nitrogen (TN) content of the end compost by 39.2% compared to CK. Microbiological analysis revealed that GE addition significantly increased the relative abundance of Firmicutes during the thermophilic and cooling phases relative to CK. The selected factors affected the bacterial community composition in the following order: NH₄-N > TOC > FDA > TN > C/N. Network analysis also showed that the enzymes were secreted mainly by Bacillus and norank_f_Caldilineaceae in GE, while they were secreted primarily by norank_f_Methylococcaceae in CK during the composting process.

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.

Degradation of Nitrogen, Phosphorus, and Organic Matter in Urban River Sediments by Adding Microorganisms

Reducing and remediating endogenous sediment pollution in urban rivers using appropriate microbiological remediation technology is regarded as a safe, effective, and environmentally sustainable mechanism. In this study, the pollutant removal efficiency of three microorganism types at different dosages was studied in the laboratory. To optimize the microbial restoration scheme, a comprehensive analysis of their effectiveness in removing total nitrogen (TN), total phosphorus (TP), total organic matter (OM), and polycyclic aromatic hydrocarbons (PAHs) was conducted, and associated structural changes in the sediment bacteria were analyzed. The results showed that using nitrifying bacteria and Bacillus as microbial agents resulted in superior removal efficiencies of TN and TP in sediments, whereas yeast was not as effective. The removal rates of TN reached 27.65% and 20.88% when 5 mg nitrifying bacteria and 10 mg Bacillus respectively, were used. A comparative analysis showed that nitrifying bacteria exhibited a better TN removal effect; however, Bacillus exhibited a better TP removal effect. The results of high-throughput sequencing revealed no significant changes to the microbial community structures when optimal microorganisms or beneficial microorganisms that thrive using OM as a source of C and energy were added. This study provides insights into the processes and mechanisms involved in the microorganism degradation of black and odorous sediment, and the results can be used as a basis for developing endogenous pollution control policies and methods for urban rivers.

Use of additives in composting informed by experience from agriculture: Effects of nitrogen fertilizer synergists on gaseous nitrogen emissions and corresponding genes (amoA and nirS)

The effects of two nitrogen fertilizer synergists (urease inhibitor, UI; nitrification inhibitor, NI) on NH₃ and N₂O emissions and the successions of the amoA and nirS genes during composting were assessed. Results showed that the UI and UI + NI treatments reduced NH₃ emissions by 26.3% and 24.3%, respectively, and N₂O emissions were reduced by 63.9% for UI + NI treatment but were not reduced by UI. The addition of UI and NI significantly reduced the abundance of the nirS gene during thermophilic stage, while significantly increased that of the amoA gene during maturation stage. Crenarchaeota was the principal nitrifying archaeal phylum and was significantly affected by pH. Proteobacteria was the main denitrifying bacterial phylum, whose relative abundance was higher for UI + NI treatment than the other treatments. PICRUSt analysis showed that the addition of UI and NI inhibited enzymatic activity related to N transformation during thermophilic stage while enriching enzymatic activity during maturation phase.

Greenhouse gas emissions from inorganic and organic fertilizer production and use: A review of emission factors and their variability

Fertilizers have become an essential part of our global food supply chain and are necessary to sustain our growing population. However, fertilizers can also contribute to greenhouse gas (GHG) emissions, along with other potential nutrient losses in the environment, e.g. through leaching. To reduce this environmental impact, tools such as life cycle assessments and decision support systems are being used to aid in selecting sustainable fertilization scenarios. These scenarios often include organic waste-derived amendments, such as manures, composts and digestates. To produce an accurate assessment and comparison of potential fertilization scenarios, these tools require emission factors (EFs) that are used to estimate GHG emissions and that are an integral part of these analyses. However, such EFs seem to be very variable in nature, thereby often resulting in high uncertainty on the outcomes of the analyses. This review aims to identify ranges and sources of variability in EFs to provide a better understanding of the potential uncertainty on the outcomes, as well as to provide recommendations for selecting EFs for future studies. As such, an extensive review of the literature on GHG emissions from production, storage, transportation and application of synthetic fertilizers (N, P, K), composts, digestates and manures was performed. This paper highlights the high variability that is present in emissions data and confirms the great impact of this uncertainty on the quality and validity of GHG predictions related to fertilizers. Variability in EFs stem from the energy source used for production, operating conditions, storage systems, crop and soil type, soil nutrient content, amount and method of fertilizer application, soil bacterial community, irrigation method, among others. Furthermore, a knowledge gap exists related to EFs for potassium fertilizers and waste valorization (anaerobic digestion/composting) processes. Overall, based on this review, it is recommended to determine EFs on a case by case basis when possible and to use uncertainty analyses as a tool to better understand the impact of EF variability.

Biofilms attached to Myriophyllum spicatum play a dominant role in nitrogen removal in constructed wetland mesocosms with submersed macrophytes: Evidence from 15N tracking, nitrogen budgets and metagenomics analyses

The mechanisms behind nitrogen removal by the submersed macrophyte-biofilm complex in wetlands remain to be fully elucidated. This study investigated the role of Myriophyllum spicatum and the biofilm on their leaves in nitrogen removal in mesocosm experiments. ¹⁵N tracking showed that 61.9% and 30% of the ¹⁵N, respectively, was removed from the system and assimilated by the macrophyte-biofilm complex after loading with 5.4 mg L^-115N labelled NH₄⁺ for 17 days. Nitrogen budget results showed that about 0.2%, 0.2% and 3.6% of the nitrogen were emitted as water-, HCl- and NaOH-soluble nitrogen-gas species, respectively. Bacteria (76.7-91.8%) were the predominant domain in all samples, followed by eukaryotes (8.0-23.0%), archaea and viruses. Network analyses showed that there were positive- and negative-correlative relationships among nitrogen-cycling genes and nitrifiers and denitrifiers. Our data highlight the important role of biofilm on submersed macrophytes for nitrogen removal.

Composting pig manure and sawdust with urease inhibitor: succession of nitrogen functional genes and bacterial community

Understanding the relationship between nitrogen (N) cycle and N transformation-related functional genes is crucial to reduce N loss during composting process. Urease inhibitor (UI) is widely used to reduce N loss in agriculture. However, the effects of UI on N transformation and related N functional genes during composting have not been well investigated. The goal of this study was to investigate the effects of a urease inhibitor (UI) on N functional genes and bacterial community succession during pig manure composting. Results showed that the addition of UI decreased the ammonium N content during the thermophilic stage and notably increased the total N and nitrite N contents of the final compost. The UI significantly decreased the abundances of amoA, nirS, nirK, and nosZ during the initial composting stage, while the opposite trend was observed at the maturation stage. Bacterial community richness and diversity were increased after the UI amendment, but the relative abundance of the phyla Firmicutes and Proteobacteria significantly decreased compared with control during the thermophilic stage. Redundancy analysis indicated that the evaluated environmental factors and bacterial community showed a cumulative 94.7% contribution to the total variation in N functional genes. In summary, UI addition is a recommended method for N conservation during composting, but the added forms of UI, such as delayed addition, combined with adsorbing materials, or microorganism inoculant, should be further evaluated.

Effects of microbial inoculation on enzyme activity, available nitrogen content, and bacterial succession during pig manure composting

This study evaluated enzyme activity, available nitrogen, and bacterial succession during pig manure composting with and without microbial inoculation (ABB and CK, respectively). ABB reached the thermophilic stage 2 days than CK. Cellulose, urease, phosphatase, and sucrase activities were higher in ABB than in CK on days 12-24 of composting, but catalase activity was lesser in ABB than in CK throughout composting. NH4+-N and NO3--N were significantly increased in ABB at the maturity stage. 16S rRNA sequencing revealed Nocardiopsaceae, Bacillaceae, Streptosporangiaceaec, Flavobacteriaceae, and Caldicoprobacteraceae as the dominant bacteria at the family level. Metabolism function analysis revealed that human diseases were reduced and carbohydrate metabolism was increased in ABB. Correlation analysis revealed that urease, sucrose, and phosphatase were significantly correlated with bacteria at the species level, whereas NH4+-N and NO3--N were not significantly correlated. These results indicated that microbial inoculation accelerated the composting process and significantly regulated microbial functions.

Coupled photocatalytic-bacterial degradation of pyrene: Removal enhancement and bacterial community responses

Polycyclic aromatic hydrocarbons (PAHs) are a class of pollutants that ubiquitously present in environment and hard to be degraded by microorganisms. Herein, we reported a novel photocatalytic-bacterial coupled removal system to treat PAH-polluted water. Using pyrene as the model pollutant, we demonstrated that the removal percentage of different groups was in order: 63.89% ± 1.03% (Vis-Biological) > 61.27% ± 1.08% (UV-Biological) > 59.58% ± 1.15% (UV) > 57.41% ± 1.13% (Vis) > 6.65% ± 0.72% (Biological) > 1.70% ± 0.34% (Control), showing the coupled system significantly improved the removal percentage of pyrene. Additionally, we observed that the coupled system driven by visible light showed higher removal percentage than UV light, exhibiting a good potential for future application. Sequencing analysis of 16S rRNA genes showed that alpha diversity (richness, evenness and diversity) got promoted and data of the relative abundance showed that Pseudomonadaceae was substituted as the dominant bacteria for Planococcaceae, with some other functional bacteria quickly acclimatizing in the bacterial community. Difference analysis indicated that over half of top fifteen genera were generally different significantly (p < 0.001) among two different samples, and UV light altered structure and composition of bacterial community more than visible light. Functional features' change suggested that the bacterial community not only protected itself but also participated in degrading pyrene. Overall, our study offered a new method for PAH degradation and contributed to further understanding of coupled catalytic-bacterial degradation processes.