Unraveling impacts of inoculating novel microbial agents on nitrogen conversion during cattle manure composting: Core microorganisms and functional genes

Extreme thermophilic microbial inoculation for reducing NH3 and N2O emissions in hyperthermophilic aerobic composting of refinery waste activated sludge

Ammonia (NH3) and nitrous oxide (N2O) release are the main causes of nitrogen loss during aerobic composting. In this study, hyperthermophilic aerobic composting of refinery waste activated sludge (RWAS) was performed by adding extreme thermophilic bacteria, and the effects of inoculation on NH3 and N2O emissions were systematically studied. The results revealed that inoculation achieved hyperthermophilic aerobic composting (T group), increased maturity, and reduced NH3 and N2O emissions by 32.36% and 10.17%, respectively. The results of microbial network analysis and structural equation modeling revealed that inoculation altered the mechanisms influencing NH3 and N2O release. Nitrogen genes and dominant bacteria were positively correlated with NH3 and N2O release during conventional composting (CK group), whereas dominant bacteria and physicochemical factors were the main factors affecting NH3 and N2O release during hyperthermophilic composting(T group). The correlation between the dominant bacteria and the release of NH3 and N2O was weakened in the hyperthermophilic aerobic composting system, resulting in a decrease in the release of the above gases.

Insights into nitrogen metabolism and humification process in aerobic composting facilitated by microbial inoculation

To enhance the retention of compost nutrients, specifically in nitrogen metabolism and humification, compound microbial agents were added during the aerobic composting of bagasse pith and buffalo manure. The introduction of the microbial agent successfully colonized the mixture, boosted the degradation capacity of organic matter, and facilitated the formation of nitrogenous substances and humic substances (HSs). The incorporation of a composite microbial inoculum led to a substantial rise in total Kjeldahl nitrogen (TKN) by 62.04%, nitrate nitrogen (NO- 3-N) by 291.65%, and amino acid (AA) by 78.77%. Furthermore, this intervention resulted in achieving a humic acid (HA) to fulvic acid (FA) ratio of 1.64. Metagenomic sequencing revealed enhanced synergistic interactions among microorganisms through inoculation, increasing the abundance of functional genes related to nitrification and nitrogen fixation compared to the uninoculated control. Spearman correlation analysis identified unclassified_c__Deltaproteobacteria, unclassified_f__Planctomycetaceae, Chryseosolibacter, unclassified_f__Hyphomicrobiaceae as the principal producers of HA. This research provides insights into the interactions between nitrogen metabolism and humification in composting, aiming to effectively retain compost nutrients and support the long-term sustainability of agriculture.

Mechanism of nitrogen conversion and microbial communities controlling the acidification and storage of pig farm fecal water

The effect of acidifiers on nitrogen transformation during manure wastewater storage remains unclear. In this study, we investigate the effects of two types of acidifiers on nitrogen transformation, bacterial structure, and functional genes during manure wastewater storage. The results indicate that the internal reactions in manure wastewater storage could be divided into three stages, i.e., nitrification (first 35 days), denitrification (mainly from days 36-84), and the final stage during which the internal environment of the manure wastewater stabilized. The addition of acidifiers effectively reduced nitrogen loss, with the total nitrogen content increasing from 12.8 to 25.83 %, and ammonia emissions decreasing from 31.67 to 43.81 %. The optimal nitrogen retention effect was observed for sulfuric acid. Furthermore, acidifiers primarily inhibited microbial activity and the abundance of functional genes, without altering the dominant bacterial community structure or nitrogen transformation pathways. These results provide a foundation for the use of acidifiers to reduce nitrogen loss during manure wastewater storage.

Impact of C/N/P dietary nutrient on manure characteristics: Pollutant fractions and microbial community

Regulation of labile fraction of excreted manure represents a promising advance for environmental pollution mitigation. However, investigation of the properties of various pollutant fractions within manure and potential influence of dietary nutrient fractions on the release of labile manure remains unclear. Feeding trials involving pigs at three distinct growth stages fed by diets with nine different energy levels were conducted and the characteristics of labile manure generated under various treatments based on nutrient profiles were analyzed. The impact of dietary nutrient fractions on variables such as labile manure pollutants, pig performance, manure weight and dominant microorganisms were evaluated via theoretical modeling and correlation analysis. The results indicated that critical dietary nutrient factors such as dietary C fraction, protein N-materials and dietary P fraction varied respectively with pig growth stages. The labile manure composition and proportion were influenced by dietary C/N/P fractions and indigestible components, through regulation of the structure of the gut microbiota and the relative abundance of gut microbes. This study finds that initiating dietary regulatory measures could effectively control the release of labile manure and reduce its proportion in the overall manure and thus, provides a novel approach to achieve manure source pollution control, ensure environmental-friendly diet formula and mitigate manure-related environmental pollution.

Promoting effect of ammonia oxidation on sulfur oxidation during composting: Nitrate as a bridge

Ammonia (NH3) and hydrogen sulfide (H2S) are the main odor components in the composting process. Controlling their emissions is very important to reduce environmental pollution and improve the quality of composting products. This study explored the effects of functional bacteria on nitrogen and sulfur metabolism in the composting process of food waste (FW) by adding ammonia-oxidizing bacteria (AOB, A treatment), sulfur-oxidizing bacteria (SOB, S treatment), and combined AOB and SOB (AS treatment), respectively. The key bacterial species involved in nitrogen and sulfur transformation were identified, and the intrinsic mechanisms by which ammonia oxidation drove sulfur oxidation during composting were deciphered. Compared with control treatment (CK), the combined addition of functional microorganisms increased the maximum of soxB gene abundance by 1.72 times, thus resulting in the increase in the SO42- content by 44.00 %. AS treatment decreased the cumulative H2S emission and total sulfur (TS) loss by 40.24 % and 34.69 %, respectively, meanwhile lowering NH3 emission. Correlation network analysis showed that the simultaneous addition of AOB and SOB enhanced the correlation between microorganisms and sulfur oxidation genes, and Acinetobacter, Aeribacillus, Brevibacterium and Ureibacillus might be involved in the ammonia oxidation-promoted sulfur oxidation process. In summary, the optimized inoculation strategy of AOB and SOB could drive biological transformation of nitrogen and sulfur by regulating microbial community, ultimately reducing odor emissions and improving sulfur conservation.

Performance evaluation and microbial community succession analysis of co-composting treatment of refinery waste activated sludge

Refinery waste activated sludge (RWAS) is riched in organic matter with energy recovery value, while unique petroleum components in RWAS may pose challenges to the recycling process. Aerobic composting technology is an effective means of organic solid waste resource treatment, which can convert organic solid waste into fertilizer for agriculture. This study explores the effect of petroleum components on the performance of RWAS composting by co-composting it with chicken manure. The results showed that more than 65% of petroleum was removed by aerobic composting. After composting, germination index (GI) exceeded 80%, and a humic acid to fulvic acid ratio (HA/FA) was greater than 1. These results signified that the petroleum components slightly affect the harmless and recycling of RWAS. The microbial community succession found that Firmicutes (54.11-91.96%) and Ascomycota (82.35-97.21%) emerged as the dominant phyla during the thermophilic phase of composting. Thermobifida, norank_f__Limnochordaceae and Kernia were the key microorganism in the degradation of petroleum and the humification of composting, and reduced the phytotoxicity of composting products. Redundancy analysis found that the degradation of petroleum was conducive to the formation of humic acid. These findings indicate that aerobic composting technology can remove petroleum components in RWAS and convert them into composted fertilizers, providing key technical support for managing RWAS in a sustainable and environmentally friendly manner.

Effects of crayfish shell powder and bamboo-derived biochar on nitrogen conversion, bacterial community and nitrogen functional genes during pig manure composting

This study investigated the effects of crayfish shell powder (CSP) and bamboo-derived biochar (BDB) on nitrogen metabolism, bacterial community and nitrogen functional genes during pig manure composting. Four treatments were established: CP (with no additives), TP1 (5 % BDB), TP2 (5 % CSP) and TP3 (2.5 % BDB + 2.5 % CSP). Compared to CP, the germination index (GI) of TP reached > 85 % 10 days earlier. Meanwhile, TP3 reduced NH3 and N2O emissions by 42.90 % and 65.9 %, respectively, while increased TN (total nitrogen) concentration by 5.43 g/kg. Furthermore, additives changed the bacterial structure and formed a beneficial symbiotic relationship with essential N-preserving bacteria, thereby enhancing nitrogen retention throughout the composting process. Metagenomic analysis revealed that additives upregulated nitrification genes and downregulated denitrification and nitrate reduction genes, ultimately improving nitrogen cycling and mitigating NH3 and N2O emissions. In conclusion, the results confirmed that TP3 was the most effective treatment in reducing nitrogen loss.

Effects of two strains of thermophilic nitrogen-fixing bacteria on nitrogen loss mitigation in cow dung compost

Excavating nitrogen-fixing bacteria with high-temperature tolerance is essential for the efficient composting of animal dung. In this study, two strains of thermophilic nitrogen-fixing bacteria, NF1 (Bacillus subtilis) and NF2 (Azotobacter chroococcum), were added to cow dung compost both individually (NF1, NF2) and mixed together (NF3; mixing NF1 and NF2 at a ratio of 1:1). The results showed that NF1, NF2, and NF3 inoculants increased the total Kjeldahl nitrogen level by 38.43%-55.35%, prolonged the thermophilic period by 1-13 d, increased the seed germination index by 17.81%, and the emissions of NH3 and N2O were reduced by 25.11% and 42.75%, respectively. Microbial analysis showed that Firmicutes were the predominant bacteria at the thermophilic stage, whereas Chloroflexi, Proteobacteria, and Bacteroidetes were the predominant bacteria at the mature stage. These results confirmed that the addition of the isolated strains to cow dung composting improved the bacterial community structure and benefited nitrogen retention.

Performance of microbial inoculation and tricalcium phosphate on nitrogen retention and conversion: Core microorganisms and enzyme activity during kitchen waste composting

The substantial release of NH3 during composting leads to nitrogen (N) losses and poses environmental hazards. Additives can mitigate nitrogen loss by adsorbing NH3/NH4, adjusting pH, and enhancing nitrification, thereby improving compost quality. Herein, we assessed the effects of combining bacterial inoculants (BI) (1.5%) with tricalcium phosphate (CA) (2.5%) on N retention, organic N conversion, bacterial biomass, functional genes, network patterns, and enzyme activity during kitchen waste (KW) composting. Results revealed that adding of 1.5%/2.5% (BI + CA) significantly (p < 0.05) improved ecological parameters, including pH (7.82), electrical conductivity (3.49 mS/cm), and N retention during composting. The bacterial network properties of CA (265 node) and BI + CA (341 node) exhibited a substantial niche overlap compared to CK (210 node). Additionally, treatments increased organic N and total N (TN) content while reducing NH4+-N by 65.42% (CA) and 77.56% (BI + CA) compared to the control (33%). The treatments, particularly BI + CA, significantly (p < 0.05) increased amino acid N, hydrolyzable unknown N (HUN), and amide N, while amino sugar N decreased due to bacterial consumption. Network analysis revealed that the combination expanded the core bacterial nodes and edges involved in organic N transformation. Key genes facilitating nitrogen mediation included nitrate reductase (nasC and nirA), nitrogenase (nifK and nifD), and hydroxylamine oxidase (hao). The structural equation model suggested that combined application (CA) and microbial inoculants enhance enzyme activity and bacterial interactions during composting, thereby improving nitrogen conversion and increasing the nutrient content of compost products.

Sustainable management and valorization of biomass wastes using synthetic microbial consortia

In response to the persistent expansion of global resource demands, considerable attention has been directed toward the synthetic microbial consortia (SMC) within the domain of microbial engineering, aiming to address the sustainable management and valorization of biomass wastes. This comprehensive review systematically encapsulates the most recent advancements in research and technological applications concerning the utilization of SMC for biomass waste treatment. The construction strategies of SMC are briefly outlined, and the diverse applications of SMC in biomass wastes treatment are explored, with particular emphasis on its potential advantages in waste degradation, hazardous substances control, and high value-added products conversion. Finally, recommendations for the future development of SMC technology are proposed, and prospects for its sustainable application are discussed.