A regulating method for reducing nitrogen loss based on enriched ammonia-oxidizing bacteria during composting

A critical review on characterization, human health risk assessment and mitigation of malodorous gaseous emission during the composting process

Composting has emerged as a suitable method to convert or transform organic waste including manure, green waste, and food waste into valuable products with several advantages, such as high efficiency, cost feasibility, and being environmentally friendly. However, volatile organic compounds (VOCs), mainly malodorous gases, are the major concern and challenges to overcome in facilitating composting. Ammonia (NH3) and volatile sulfur compounds (VSCs), including hydrogen sulfide (H2S), and methyl mercaptan (CH4S), primarily contributed to the malodorous gases emission during the entire composting process due to their low olfactory threshold. These compounds are mainly emitted at the thermophilic phase, accounting for over 70% of total gas emissions during the whole process, whereas methane (CH4) and nitrous oxide (N2O) are commonly detected during the mesophilic and cooling phases. Therefore, the human health risk assessment of malodorous gases using various indexes such as ECi (maximum exposure concentration for an individual volatile compound EC), HR (non-carcinogenic risk), and CR (carcinogenic risk) has been evaluated and discussed. Also, several strategies such as maintaining optimal operating conditions, and adding bulking agents and additives (e.g., biochar and zeolite) to reduce malodorous emissions have been pointed out and highlighted. Biochar has specific adsorption properties such as high surface area and high porosity and contains various functional groups that can adsorb up to 60%-70% of malodorous gases emitted from composting. Notably, biofiltration emerged as a resilient and cost-effective technique, achieving up to 90% reduction in malodorous gases at the end-of-pipe. This study offers a comprehensive insight into the characterization of malodorous emissions during composting. Additionally, it emphasizes the need to address these issues on a larger scale and provides a promising outlook for future research.

Incorporating microbial inoculants to reduce nitrogen loss during sludge composting by suppressing denitrification and promoting ammonia assimilation

To address the challenge of increasing nitrogen retention in compost, this study investigated the effects of microbial communities on denitrification and ammonia assimilation during sludge composting by inoculating microbial inoculants. The results showed that the retention rates of total Kjeldahl nitrogen (TKN) and humic acid (HA) in MIs group (with microbial inoculants) were 4.94 % and 18.52 % higher than those in the control group (CK), respectively. Metagenomic analysis showed that Actinobacteria and Proteobacteria were identified as main microorganisms contributing to denitrification and ammonia assimilation. The addition of microbial agents altered the structure of the microbial community, which in turn stimulated the expression of functional genes. During cooling period, the ammonia assimilation genes glnA, gltB and gltD in MIs were 15.98 %, 24.84 % and 32.88 % higher than those in CK, respectively. Canonical correspondence analysis revealed a positive correlation between the dominant bacterial genera from the cooling stage to the maturity stage and the levels of NO3--N, NH4+-N, HA, and TKN contents. NH4+-N was positively correlated with HA, indicating NH4+-N might be incorporated into HA. Heat map and network analyses revealed NH4+-N as a key factor affecting functional genes of denitrification and ammonia assimilation, with Nitrospira identified as the core bacteria in the microbial network. Therefore, the addition of microbial agents could increase nitrogen retention and improve compost product quality.

Effects of Bacillus-based inoculum on odor emissions co-regulation, nutrient element transformations and microbial community tropological structures during chicken manure and sawdust composting

This study aims to evaluate whether different doses of Bacillus-based inoculum inoculated in chicken manure and sawdust composting will provide distinct effects on the co-regulation of ammonia (NH3) and hydrogen sulfide (H2S), nutrient conversions and microbial topological structures. Results indicate that the Bacillus-based inoculum inhibits NH3 emissions mainly by regulating bacterial communities, while promotes H2S emissions by regulating both bacterial and fungal communities. The inoculum only has a little effect on total organic carbon (TOC) and inhibits total sulfur (TS) and total phosphorus (TP) accumulations. Low dose inoculation inhibits total potassium (TK) accumulation, while high dose inoculation promotes TK accumulation and the opposite is true for total nitrogen (TN). The inoculation slightly affects the bacterial compositions, significantly alters the fungal compositions and increases the microbial cooperation, thus influencing the compost substances transformations. The microbial communities promote ammonium nitrogen (NH4+-N), TN, available phosphorus (AP), total potassium (TK) and TS, but inhibit nitrate nitrogen (NO3--N), TP and TK. Additionally, the bacterial communities promote, while the fungal communities inhibit the nitrite nitrogen (NO2--N) production. The core bacterial and fungal genera regulate NH3 and H2S emissions through the secretions of metabolic enzymes and the promoting or inhibiting effects on NH3 and H2S emissions are always opposite. Hence, Bacillus-based inoculum cannot regulate the NH3 and H2S emissions simultaneously.

Change of core microorganisms and nitrogen conversion pathways in chicken manure composts by different substrates to reduce nitrogen losses

Due to the rapid development of animal husbandry, the associated environmental problems cannot be ignored, with the management of livestock and poultry manure emerging as the most prominent issue. Composting technology has been widely used in livestock and poultry manure management. A deeper understanding of the nitrogen conversion process during composting offers a theoretical foundation for selecting compost substrates. In this study, the effects of sawdust (CK) and spent mushroom compost (T1) as auxiliary materials on nitrogen as well as microbial structure in the composting process when composted with chicken manure were investigated. At the end of composting, the nitrogen loss of T1 was reduced by 17.18% relative to CK. When used as a compost substrate, spent mushroom compost accelerates the succession of microbial communities within the compost pile and alters the core microbial communities within the microbial community. Bacterial genera capable of cellulose degradation (Fibrobacter, Herbinix) are new core microorganisms that influence the assimilation of nitrate reduction during compost maturation. Using spent mushroom compost as a composting substrate increased the enzyme activity of nitrogen assimilation while decreasing the enzyme activity of the denitrification pathway.

Unraveling the effect of added microbial inoculants on ammonia emissions during co-composting of kitchen waste and sawdust: Core microorganisms and functional genes

Despite the role of microorganisms in nitrogen biotransformation has been extensively explored, how microorganisms mitigate NH₃ emissions in the transformation of nitrogen throughout the composting system is rarely addressed. The present study explored the effect of microbial inoculants (MIs) and the contribution of different composted phases (solid, leachate, and gas) on NH₃ emissions by constructing a co-composting system of kitchen waste and sawdust with and without the addition of MI. The results showed that NH₃ emissions increased markedly after adding MIs, in which the contribution of leachate ammonia volatilization to NH₃ emissions was most prominent. The core microorganisms of NH₃ emission had a clear proliferation owing to the MIs reshaping community stochastic process. Also, MIs can strengthen the co-occurrence between microorganisms and functional genes of nitrogen to promote nitrogen metabolism. In particular, the abundances of nrfA, nrfH, and nirB genes, which could augment the dissimilatory nitrate reduction process, were increased, thus enhancing NH₃ emissions. This study bolsters the fundamental, community-level understanding of nitrogen reduction treatments for agricultural.

Biochar Can Improve Absorption of Nitrogen in Chicken Manure by Black Soldier Fly

(1) Background: There is growing interest in using insects to treat nutrient-rich organic wastes, such as the black soldier fly (BSF), one of the most efficient organic waste recyclers for upcycling nutrients into the food system. Although biochar (BC) was shown to enhance nutrient retention and the final product quality during the composting of livestock and poultry manure in many previous studies, little information is available on the effect of BC on livestock manure bioconversion by black soldier fly larvae (BSFL). (2) Methods: This study investigated the effect of adding a small amount of BC to chicken manure (CM) on the bioconversion system of the black soldier fly (including N2O and NH3 emissions and the final distribution of nitrogen during the treatment process). (3) Results: The lowest N2O and NH3 emission and highest residual nitrogen in the substrate were observed in the 15% BC treatment. The highest bioconversion rate of CM (8.31%) and the peak of larval biomass was obtained in the 5% BC treatment. (4) Conclusions: The results demonstrate the feasibility of adding 5% BC to reduce pollution and achieve a satisfactory BSFL-based CM bioconversion efficiency.

Artificial intelligence and machine learning approaches in composting process: A review

Studies on developing strategies to predict the stability and performance of the composting process have increased in recent years. Machine learning (ML) has focused on process optimization, prediction of missing data, detection of non-conformities, and managing complex variables. This review investigates the perspectives and challenges of ML and its important algorithms such as Artificial Neural Networks (ANNs), Random Forest (RF), Adaptive-network-based fuzzy inference systems (ANFIS), Support Vector Machines (SVMs), and Deep Neural Networks (DNNs) used in the composting process. In addition, the individual shortcomings and inadequacies of the metrics, which were used as error or performance criteria in the studies, were emphasized. Except for a few studies, it was concluded that Artificial Intelligence (AI) algorithms such as Genetic algorithm (GA), Differential Evaluation Algorithm (DEA), and Particle Swarm Optimization (PSO) were not used in the optimization of the model parameters, but in the optimization of the parameters of the ML algorithms.

Preparation, biocontrol activity and growth promotion of biofertilizer containing Streptomyces aureoverticillatus HN6

Nowadays, due to the excessive dependence on chemical fertilizers and pesticides in agricultural production, many problems, such as soil hardening and soil-borne diseases, have become increasingly prominent, which seriously restrict the sustainable development of agriculture. The application of microbial fertilizer prepared by biocontrol microorganisms can not only improve soil structure and increase fertility but also have the function of controlling diseases. Streptomyces aureoverticillatus HN6 has obvious disease prevention and growth promotive effect, which can improve the rhizosphere fertility of plants and even regulate the rhizosphere microbial community of plants. Based on the comparison of frame composting and natural composting, we used the response surface method to optimize the preparation conditions of Streptomyces HN6 bacterial fertilizer. The results showed that natural composting not only produced higher composting temperatures and maintained long high temperature periods in accordance with local conditions, but was also more suitable for composting in the field according to local conditions. Therefore, the substrate's conductivity changed more, the ash accumulation increased, and the substrate decomposed more thoroughly. Thus, this composting method is highly recommended. Additionally, Streptomyces HN6 microbial fertilizer EC20 can reduce cowpea fusarium wilt and promote cowpea growth. The number of plant leaves, plant height and fresh weight, increased significantly in the microbial fertilizer EC20. Moreover, Streptomyces HN6 fertilizer EC20 could significantly induce soil invertase, urease and catalase activities. Our study highlights the potential use of Streptomyces HN6 as a biofertilizer to improve plant productivity and biological control of plant pathogenic fungi.

Phytotoxicity of farm livestock manures in facultative heap composting using the seed germination index as indicator

Static facultative heap composting of animal manure is widely used in China, but there is almost no systematic research on the phytotoxicity of the produced compost. Here, we evaluated the phytotoxic variation in compost produced by facultative heap composting of four types of animal manure (chicken manure, pig manure, sheep manure, and cattle manure) using different plant seeds (cucumber, radish, Chinese cabbage, and oilseed rape) to determine germination index (GI). The key factors that affected GI values were identified, including the dynamics of the phytotoxicity and microbial community during heap composting. Sensitivity to toxicity differed depending on the type of plant seed used. Phytotoxicity during facultative heap composting, evaluated by the GI, was in the order: chicken manure (0-6.6 %) < pig manure (14.4-90.5 %) < sheep manure (46.0-93.0 %) < cattle manure (50.2-105.8 %). Network analysis showed that the volatile fatty acid (VFA) concentration was positively correlated with Firmicutes abundance, and NH₄⁺-N was correlated with Actinobacteria, Proteobacteria, and Bacteroidetes. More bacteria were stimulated to participate in conversions of dissolved organic carbon, dissolved nitrogen, VFA, and ammonia-nitrogen (NH₄⁺-N) in sheep manure heap composting than that in other manure. The GI was most affected by VFA in chicken manure and cattle manure heap composting, while NH₄⁺-N was the main factor affecting the GI in pig manure and sheep manure compost. The dissolved carbon and nitrogen content and composition, as well as the core and proprietary microbial communities, were the primary factors that affected the succession of phytotoxic substances in facultative heap composting, which in turn affected GI values. In this study, the key pathways of livestock manure composting that affected GI and phytotoxicity were found and evaluated, which provided new insights and theoretical support for the safe use of organic fertilizer.

Isolation and application of a thermotolerant nitrifying bacterium Gordonia paraffinivorans N52 in sewage sludge composting for reducing nitrogen loss

A thermotolerant strain with heterotrophic nitrification capability obtained from sludge composting was identified as Gordonia paraffinivorans N52. Strain N52 utilized 51.8% of ammonium nitrogen (NH₄⁺-N) at 60℃, and the nitrogen balance results indicated that 25.5% of the consumed NH₄⁺-N was changed into nitrification intermediates, 53.0% to intracellular nitrogen, and only 5.2% was lost. The successful detection of enzymes related to nitrification and PCR amplification of functional genes further demonstrated nitrification ability of the isolated strain. Moreover, orthogonal test indicated that conditions for the optimal nitrification performance were C/N 15, 50℃, 150 rpm and pH 8. Compared with the control group, the addition of Gordonia paraffinivorans N52 to sewage sludge composting reduced 27.6% of ammonia emissions, accelerated the conversion from NH₄⁺-N to nitrate nitrogen and decreased the total nitrogen loss. These results suggested that inoculation of Gordonia paraffinivorans N52 effectively controlled ammonia emissions and reduced nitrogen loss in composting.

Characterization of heterotrophic nitrification by a thermotolerant Brevibacillus Agri N2 isolated from sewage sludge composting

A thermotolerant strain isolated from sewage sludge (SS) composting was identified as Brevibacillus Agri N2, which showed the efficient capability for heterotrophic nitrification under high-temperature conditions. Incubation at 60 °C, strain N2 could utilize 45.47% of ammonium nitrogen (99.64 mg/L), 68.89% of hydroxylamine nitrogen (51.14 mg/L) and 76.77% of nitrite nitrogen (55.20 mg/L), with a minor part of nitrogen loss for 1.64%, 2.82% and 5.01%, respectively. The successful detection of ammonia monooxygenase, hydroxylamine oxidase, and nitrate oxidoreductase and PCR amplification of amoA, hao and nxrA genes provided evidence of nitrification ability by strain N2. Furthermore, single-factor experiments indicated that the optimal conditions for efficient nitrification performance by strain N2 were succinate as carbon source, 50 °C, C/N 12, pH 8 and 200 r/min. Strain N2 could perform the complete nitrification process, with minimal nitrogen loss at high temperature conditions, which indicated it had the potential for practical application for reducing nitrogen loss of SS composting.

Influence of carbon-to-phosphorus ratios on phosphorus fractions transformation and bacterial community succession in phosphorus-enriched composting

This study aims to assess the effect of different carbon-to-phosphorus (C:P) ratios on phosphorus (P) fractions transformation, bacterial community succession and microbial P-solubilizing function in kitchen waste composting with rock phosphate (RP) amendment and phosphate-solubilizing bacteria (PSB) inoculation. Results indicated that initial C:P ratio at 50 enhanced organic carbon degradation, available P (AP) accumulation, the amount of PSB and pqqC gene abundance in composting but higher C:P ratio increased microbial biomass phosphorus (MBP) content. Redundancy analysis showed C:P ratios, PSB amount and pqqC gene abundance greatly affected bacterial community diversity and composition. Network analysis indicated that lower C:P ratio enhanced the interaction frequency in core bacterial network for AP transformation. Variance partitioning analysis abiotic factors contributed more to MBP and AP conversion. The study revealed that C:P ratio could directly drive PSB to regulate P fractions and the accumulation of MBP or AP in P-enriched 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.

Effect of inoculation with newly isolated thermotolerant ammonia-oxidizing bacteria on nitrogen conversion and microbial community during cattle manure composting

Nitrogen loss during composting is closely related to NH₄⁺-N conversion, and ammonia-oxidizing bacteria (AOB) are important microorganisms that promote NH₄⁺-N conversion. Since the biological activity of conventional AOB agents used for compost inoculation declines rapidly during the thermophilic phase of composting, new compound inoculants should be developed that are active during that phase. In the current study, the effects of inoculating cattle manure compost with newly isolated AOB (5%, v/w) [thermotolerant AOB X-2 strain (T-AOB-2), mesophilic AOB X-4 strain (M-AOB-4), and AOB X-2 combined with AOB X-4 (MT-AOB-2-4)] on the conversion of nitrogen, compost maturity, and the resident microbial community were studied. During 35 days of composting, compared with the control, AOB inoculation reduced NH₃ emissions by 29.98-46.94%, accelerated the conversion of NH₄⁺-N to NO₂^--N, increased seed germination values by 13.00-25.90%, and increased the abundance of the microbial community at the thermophilic phase (16.38-68.81%). Network analysis revealed that Bacillaceae play a crucial role in the composting process, with the correlation coefficients: 0.83 (p < 0.05) with NH₃, 0.64 (p < 0.05) with NH₄⁺-N, and 0.81 (p < 0.05) with NO₂^--N. In addition, inoculation with MT-AOB-2-4 notably increased the total nitrogen content of compost, prolonged the sanitation stage, and promoted compost maturity. Hence, MT-AOB-2-4 may be used to increase the microbial community abundance and improve the efficiency of cattle manure composting.

Mechanism associated with the positive effect of nanocellulose on nitrogen retention in a manure composting system

Additives can play important roles in effectively inhibiting nitrogen losses during livestock manure composting due to the activities of microbes. This study investigated the effects of adding nanocellulose at 300 mg/kg, 600 mg/kg, and 900 mg/kg (NC900) on nitrogen conversion, nitrogen conversion functional genes, and related microorganisms during composting. The results showed that compared with the control, nanocellulose hindered the ammoniation reaction. In addition, NC900 promoted nitrification, interfered with the denitrification process, and reduced the abundance of the nirK gene, thereby increasing the nitrate nitrogen content and decreasing ammonia spillover. NC900 promoted nitrogen fixation by increasing the abundance of members of Rhizobiales, which play important roles in nitrogen fixation. In general, compared with the control, NC900 improved the retention of nitrogen by controlling ammonia emissions. The results obtained in this study demonstrate that nanocellulose can be applied in the treatment of organic solid waste and agricultural production.

The nitrogen cycle and mitigation strategies for nitrogen loss during organic waste composting: A review

Composting is a promising technology to decompose organic waste into humus-like high-quality compost, which can be used as organic fertilizer. However, greenhouse gases (N₂O, CO₂, CH₄) and odorous emissions (H₂S, NH₃) are major concerns as secondary pollutants, which may pose adverse environmental and health effects. During the composting process, nitrogen cycle plays an important role to the compost quality. This review aimed to (1) summarizes the nitrogen cycle of the composting, (2) examine the operational parameters, microbial activities, functions of enzymes and genes affecting the nitrogen cycle, and (3) discuss mitigation strategies for nitrogen loss. Operational parameters such as moisture, oxygen content, temperature, C/N ratio and pH play an essential role in the nitrogen cycle, and adjusting them is the most straightforward method to reduce nitrogen loss. Also, nitrification and denitrification are the most crucial processes of the nitrogen cycle, which strongly affect microbial community dynamics. The ammonia-oxidizing bacteria or archaea (AOB/AOA) and the nitrite-oxidizing bacteria (NOB), and heterotrophic and autotrophic denitrifiers play a vital role in nitrification and denitrification with the involvement of ammonia monooxygenase (amoA) gene, nitrate reductase genes (narG), and nitrous oxide reductase (nosZ). Furthermore, adding additives such as struvite salts (MgNH₄PO₄·6H₂O), biochar, and zeolites (clinoptilolite), and microbial inoculation, namely Bacillus cereus (ammonium strain), Pseudomonas donghuensis (nitrite strain), and Bacillus licheniformis (nitrogen fixer) can help control nitrogen loss. This review summarized critical issues of the nitrogen cycle and nitrogen loss in order to help future composting research with regard to compost quality and air pollution/odor control.

Microhabitat drive microbial anabolism to promote carbon sequestration during composting

Transforming organic waste into stable carbon by composting is an eco-friendly way. However, the complex environment, huge microbial community and complicated metabolic of composting have limited the directional transformation of organic carbon, which is also not conducive to the fixation of organic carbon. Therefore, this review is based on the formation of humus, a stable by-product of composting, to expound how to promote carbon fixation by increasing the yield of humus. Firstly, we have clarified the transformation regularity of organic matter during composting. Meanwhile, the microhabitat factors affecting microbial catabolism and anabolism were deeply analyzed, in order to provide a theoretical basis for the micro habitat regulation of directional transformation of organic matter during composting. Given that, a method to adjust the directional humification and stabilization of organic carbon has been proposed. Hoping the rapid reduction and efficient stabilization of organic waste can be realized according to this method.

Industrial Composting of Sewage Sludge: Study of the Bacteriome, Sanitation, and Antibiotic-Resistant Strains

Wastewater treatment generates a huge amount of sewage sludge, which is a source of environmental pollution. Among the alternatives for the management of this waste, industrial composting stands out as one of the most relevant. The objective of this study was to analyze the bacterial population linked to this process and to determine its effectiveness for the reduction, and even elimination, of microorganisms and pathogens present in these organic wastes. For this purpose, the bacteriome and the fecal bacteria contamination of samples from different sewage sludge industrial composting facilities were evaluated. In addition, fecal bacteria indicators and pathogens, such as Salmonella, were isolated from samples collected at key stages of the process and characterized for antibiotic resistance to macrolide, β-lactam, quinolone, and aminoglycoside families. 16S rRNA phylogeny data revealed that the process clearly evolved toward a prevalence of Firmicutes and Actinobacteria phyla, removing the fecal load. Moreover, antibiotic-resistant microorganisms present in the raw materials were reduced, since these were isolated only in the bio-oxidative phase. Therefore, industrial composting of sewage sludge results in a bio-safe final product suitable for use in a variety of applications.

Planifilum fulgidum Is the Dominant Functional Microorganism in Compost Containing Spent Mushroom Substrate

The extensive accumulation of spent mushroom substrate (SMS) owing to the large-scale production of edible fungi is causing environmental problems that cannot be ignored. Co-composting is a promising method for agricultural and animal husbandry waste disposal. In this study, the composition and function of microbial communities in the process of cattle manure–maize straw composting with SMS addition were compared through an integrated meta-omics approach. The results showed that irrespective of SMS addition, the predominant fungi were Ascomycota, while the dominant bacteria were Firmicutes, Proteobacteria, Actinobacteria, and Bacteroidetes. High temperature promoted the evolution from Gram-negative bacteria (Bacteroides, Proteobacteria) to Gram-positive bacteria (Firmicutes, Actinomycetes). The composting process was accelerated by SMS addition, and the substrate was effectively degraded in 14 days. Metaproteomics results showed that the dominant microorganism, Planifilum fulgidum, secreted large amounts of S8, M17, and M32 proteases that could degrade macromolecular protein substrates in the presence of SMS. Planifilum fulgidum, along with Thermobifida fusca and Melanocarpus albomyces, synergistically degraded hemicellulose, cellulose, and protein. In addition, the dominant microorganisms related to the initial raw materials such as Pichia, Lactobacillus in the microbial agent and Hypsizygus in SMS could not adapt to the high-temperature environment (>60 °C) and were replaced by thermophilic bacteria after 5 days of composting.

A review on nitrogen dynamics and mitigation strategies of food waste digestate composting

Food waste digestate is a by-product of the anaerobic digestion of food waste. Presence of high ammonium nitrogen content significantly increase the nitrogen loss upon direct application on soil or by conventional composting. In this review, a comprehensive discussion regarding the effective management of food waste digestate is outlined, in which global food waste digestate production, characteristics, and composting are discussed. The nitrogen dynamics cycle considering high ammonium nitrogen content in the digestate is also evaluated, including ammonification, nitrification, denitrification, and other possible mechanisms based on the current literature. Mitigation strategies for reducing nitrogen loss via C/N ratio adjustment and the addition of physical, chemical, and microbial amendments were evaluated and estimated for 15 countries based on the available data on food waste anaerobic digestion plants. Reduced nitrogen loss and high quality compost could be produced from food waste digestate by adapting mitigation strategies.

Two types nitrogen source supply adjusted interaction patterns of bacterial community to affect humifaction process of rice straw composting

This study investigated effects of high-nitrogen source (urea) (R_UR) and protein-like nitrogen source (chicken manure) (R_CM) on humification process during lignocellulose biomass composting. It demonstrated that decreasing ratio of crude fiber (CF), polysaccharide (PS) and amino acids (AAs) in R_CM (29.75%, 53.93% and 73.73%, respectively) was higher than that in R_UR (14.73%, 28.74% and 51.92%, respectively). Humic substance (HS) concentration increased by 7.51% and 73.05% during R_UR and R_CM composting, respectively. The lower total links, more independent modularization and higher proportion of positive correlations between functional bacteria and organic components was observed with R_CM network than R_UR, indicating that protein-like nitrogen source supply may alleviate competition within bacterial community. Moreover, chicken manure supply favorably selects greater special functional bacterial taxa (Pusillimonas, Pedomicrobium, Romboustia and other 24 genus) related to AAs and stimulates the collaborative division of bacterial community. This is significance for strengthening effective transformation of organic components.

Pathways and mechanisms of nitrogen transformation during co-composting of pig manure and diatomite

The aim of this study was to investigate the pathways and mechanisms of nitrogen transformation during the composting process, by adding diatomite (0%, 2.5%, 5%, 10%, 15% and 20%) into initial mixtures of pig manure and sawdust. The results revealed that diatomite facilitated the conversion from NH₄⁺-N to amino acid nitrogen and hydrolysis undefined nitrogen, then reduced NH₃ and N₂O emission by 8.63-35.29% and 14.34-73.21%, respectively. Moreover, the structure and abundance of nitrogen functional genes provided evidence for nitrogen loss. Furthermore, compared with the control (0.03), the treatment blended with 10% diatomite (T3) had the highest value in composting score (-1.27). Additionally, the ratio of carbon and nitrogen (57.30%) was vital for reducing nitrogen loss among all physio-chemical parameters in this study. In conclusion, adding diatomite was a practical way to enhance nitrogen conservation and increase quality of end products, and the optimum added dosage was at 10%.

Insight to nitrification during cattle manure-maize straw and biochar composting in terms of multi-variable interaction

This study investigated nitrification process during cattle manure-maize straw (CM) and biochar (CMB) composting in terms of multi-variable interaction (MVI) among environmental parameters, ammonia-oxidizing archaea (AOA) and bacteria (AOB) community structure, nitrogen-related enzymes as well as substrates using structural equation model (SEM). Results showed that adding biochar significantly reduced potential ammonia oxidation rates. SEM analysis revealed that AOB was affected by temperature and pH, which stimulated the release of urease, increased NH₄⁺-N concentration and finally exerted influence on nitrification in CM. Temperature (0.755) and NO₂^--N (-0.994) were identified as the main factors mediating nitrification in CM and CMB, respectively. Moreover, MVI analysis indicated that nitrification and denitrification occurred simultaneously. Mutual verification of SEM and quantitative analyses (RNA level) confirmed that AOB predominated nitrification. The above results indicated that nitrification could be better explained by MVI using SEM during composting.

Challenges and Control Strategies of Odor Emission from Composting Operation

Composting is a biological decomposition process that occurs from microbial progression, which brings about the degradation and stabilization of various organic waste into compost. During composting, the emission of undesirable odor adversely affects compost quality and causes environmental deterioration. Also, odor emission from composting adversely affects human health and well-being. Ammonia (NH₃), volatile organic compounds (VOCs), and hydrogen sulfide (H₂S) are major components of odorous gases responsible for unpleasant odor. Physiological parameters such as pH, temperature, and aeration affect the pattern of odor emission during the composting process. The lack of techniques for the accurate identification and estimation of odor and control are some major challenges associated with composting. Therefore, the present review article concentrates on challenges and solutions to odor control. Biotrickling filter, optimization of process parameters, usage of additives, microbial inoculation, and pre-treatment techniques are practiced to lower odor emission during the process. The application of metagenomics may provide insight into the various biogeochemical pathways that can be explored in the future for odor control.

Influence of moisture content on chicken manure stabilization during microbial agent-enhanced composting

Moisture content (MC) influences substance transformation during composting and the function of exogenous microbial agents. Unsuitable MC could cause leaching, nutrient loss, and secondary contamination. In this study, chicken manure composting with varied MC (45-61%) was conducted under functional microbial agent inoculation to explore the optimum condition for composting and the potential mechanism. Due to the enhanced decomposing, nitrosation, and nitrification effect lead by the functional microorganism, treatment with the optimal MC (53%) exhibited the highest composting temperature (61 °C) and longest high-temperature period (15 days), achieving a final carbon-nitrogen ratio (C/N), humic acids and fulvic acids ratio (HA/FA), and NH₄⁺-N/NO₃^--N at 19.20, 2.00, and 0.93, respectively. After composting, the total nitrogen (TN) increased by 13.01-22.10% in the treatments with microbial agent inoculation compared with original stack, while it decreased by 7.76% in control. The highest nutrient (5.63%, 5.63-14.20% higher than the other composts) and better product safety (11.43-23.58% higher seed germination than others) were observed in treatment with MC at 53%, exceeding the Chinese national standard for organic fertilizer. Obviously, under optimum MC, microbial agent augmentation lead to high quality and safe compost products after a short composting period (25 days) without any leaching, which suggested an efficient way to promote the recycling and recovery of husbandry waste.

Composting of anaerobic sludge from the co-digestion of used disposable nappies and expired food products

Anaerobic sludge originating from the co-digestion of used disposable nappies and expired food products treated in a pilot two-stage system was examined as feed material for a continuous pilot-scale composter (capacity: 300 L feed per week). The feed materials and final compost products were analyzed and evaluated for their suitability as compost materials. Ιn terms of stability, the compost products were identified as stable through static respiratory index measurement (0.11-0.24 g O₂/(kg Volatile Solids h)), heavy metals concentrations were within acceptable limits (i.e. concentration of Cu, Cd, Zn, Pb, Cr, As lower than 1 mg/kg dry mass) as well as polycyclic aromatic hydrocarbons (0.06-0.34 mg/kg dry mass lower than 6 mg/kg dry mass). During composting, significant losses of nitrogen from the digestate and the urea added for C/N correction were observed (51-75%), indicating that the adjustment of C/N ratio through the addition of chemicals is not efficient in composting processes with forced aeration and the pre-existing nitrogen in digestate was susceptible to air-stripping. The continuous composting process implemented proved capable of producing mature compost with a retention time of 14 d. The final products were within acceptable limits for all the parameters examined, except for the presence of pathogens (Salmonella and Enterococcus) which were not eliminated, even though the composter reached 56 °C for 3-4 days at the thermophilic stage. The characteristics of the anaerobic sludge samples examined indicate that direct land application of the anaerobic effluent should be considered as an option.

Ammonia volatilization from composting with oxidized biochar

Animal manure, agricultural residues, and other sources of biomass can be diverted from the waste stream and composted into valuable fertilizer. However, composting often results in substantial N loss through NH₃ gas volatilization. We investigated biochar's capacity to improve NH₃ -N retention during composting of poultry manure and straw. After 7 wk, total N loss from composting with unoxidized biochar was twofold and sixfold higher than N loss from composting with oxidized biochar and without biochar (307, 142, and 51 mg N g^-1 N in the initial compost feedstocks, respectively). When cumulative NH₃ -N loss was calculated relative to CO₂ -C loss to account for differences in microbial activity, NH₃ -N/CO₂ -C loss from compost with oxidized biochar was 55% lower than from compost with unoxidized biochar (82% lower based on mass balance). Oxidized biochar particles removed from compost after 7 wk retained 16.0 mg N g^-1 biochar, compared with only 6.1 mg N g^-1 retained by unoxidized biochar, suggesting that N retention by biochar particles provides a mechanism for reduced NH₃ -N loss. These data show that oxidized biochar enhanced microbial activity, doubled composting rate, and reduced NH₃ -N loss compared with unoxidized biochar and that biochar's physiochemical characteristics modulate its performance in compost. In particular, the presence of oxidized surface functional groups, which can be increased artificially or through environmental weathering, appear to play an important role in key compost processes. This has implications for other natural and managed systems where pyrogenic organic matter may mediate biological activity and nutrient cycles.

Influence of Aerobic Pretreatment of Poultry Manure on the Biogas Production Process

Anaerobic digestion of poultry manure is a potentially-sustainable means of stabilizing this waste while generating biogas. However, technical, and environmental protection challenges remain, including high concentrations of ammonia, low C/N ratios, limited digestibility of bedding, and questions about transformation of nutrients during digestion. This study evaluated the effect of primary biological treatment of poultry manure on the biogas production process and reduction of ammonia emissions. Biogas yield from organic matter content in the aerobic pretreatment groups was 13.96% higher than that of the control group. Biogas production analysis showed that aerobic pretreatment of poultry manure has a positive effect on biogas composition; methane concentration increases by 6.94–7.97% after pretreatment. In comparison with the control group, NH3 emissions after aerobic pretreatment decreased from 3.37% (aerobic pretreatment without biological additives) to 33.89% (aerobic pretreatment with biological additives), depending on treatment method.

Sulfur-aided composting facilitates ammonia release mitigation, endocrine disrupting chemicals degradation and biosolids stabilization

In order to investigate the potential effect of sulfur (S) aided composting on NH₃ volatilization mitigation, bisphenol A (PBA) and estrogens (estrone, 17β-estradiol, estriol, and 17a-ethinylestradiol) degradation and biosolids stabilization, five treatments of S (i.e., 0, 0.25%, 0.50%, 1.0%, and 2.0%, dry weight basis) were applied to the mixtures of biosolids and wheat straw during the 50 days of composting stabilization process. Results implicated addition of S decreased alkalinity of compost system, mitigated NH₃ volatilization, facilitated degradation of bisphenol A and estrogen in biosolids, and improved biosolids stabilization. Compared to control, the S-added treatments reduced nitrogen loss by 29.39%-97.22%, and degraded PBA and estrogens in biosolids by 25.42-72.63% and 21.11-68.14%, respectively, with S additions in range of 0.25-2.0%. In terms of economic efficiency and ecological risk, S addition at ≤0.50% is suggested for composting stabilization of biosolids.

Effect of enriched thermotolerant nitrifying bacteria inoculation on reducing nitrogen loss during sewage sludge composting

In the study, enriched thermotolerant nitrifying bacteria (TNB) was acquired from compost samples by domesticated cultivation under high temperature, and was inoculated into sewage sludge composting. The effect of inoculation on physical-chemical parameters, nitrogen loss and bacterial population involved in nitrogen transformation were determined. The results revealed that inoculation with enriched TNB improved the compost quality in terms of temperature, pH, organic matter degradation, C/N ratio and germination index. Compared to the control treatment, inoculation also decreased 29.7% of ammonia emission and reduced nitrogen loss by converting more NH₄⁺-N into NO₃^--N in composting. In addition, inoculation increased the population of nitrifying bacteria and was not capable of inhibiting the growth of indigenous ammonifying bacteria as well. The results suggested that inoculation with enriched TNB was a feasible way to reduce nitrogen loss and promote maturity in sewage sludge composting.

Humus formation driven by ammonia-oxidizing bacteria during mixed materials composting

The aim of this study was to identify the effects of ammonia-oxidizing bacteria (AOB) inoculation on humus formation. Both nitrogen conversion and humus formation were considered as the main processes, because NH₄⁺-N-like compounds not only substrates of nitrification, but also precursors of humus. During composting, the inoculation of AOB indeed increased humus concentration by fixing NH₃ emission as NH₄⁺-N, but it has also promoted nitrogen transformation. While the main reason was the changed bacteria community structure caused by inoculating AOB. Moreover, the relationship between bacteria and nitrogen transformation and humus formation has become closer. And bacteria were more likely to synthesize humus. Therefore, it is conjectured that AOB inoculation could not only provide NH₄⁺-N for humus formation, but also enhance the anabolism of microorganisms. This suppose has been confirmed by structural equation model in this study. Therefore, AOB inoculation has a driving effect on promoting humus formation.

Effects of Zeolite and Biochar Addition on Ammonia-Oxidizing Bacteria and Ammonia-Oxidizing Archaea Communities during Agricultural Waste Composting

The effects of zeolite and biochar addition on ammonia-oxidizing bacteria (AOB) and archaea (AOA) communities during agricultural waste composting were determined in this study. Four treatments were conducted as follows: Treatment A as the control with no additive, Treatment B with 5% of zeolite, Treatment C with 5% of biochar, and Treatment D with 5% of zeolite and 5% biochar, respectively. The AOB and AOA amoA gene abundance as well as the ammonia monooxygenase (AMO) activity were estimated by quantitative PCR and enzyme-linked immunosorbent assay, respectively. The relationship between gene abundance and AMO enzyme activity was determined by regression analysis. Results indicated that the AOB was more abundant than that of AOA throughout the composting process. Addition of biochar and its integrated application with zeolite promoted the AOB community abundance and AMO enzyme activity. Significant positive relationships were obtained between AMO enzyme activity and AOB community abundance (r2 = 0.792; P < 0.01) and AOA community abundance (r2 = 0.772; P < 0.01), indicating that both bacteria and archaea played significant roles in microbial ammonia oxidation during composting. Using biochar and zeolite might promote the nitrification activity by altering the sample properties during agricultural waste composting.

Using the modified pine wood as a novel recyclable bulking agent for sewage sludge composting: Effect on nitrogen conversion and microbial community structures

This study investigated the effect of a recoverable sulphuric acid and sodium hydroxide-modified pinewood (MOP) as a bulking agent during sewage sludge and sawdust composting (MOPC), with a control experiment using unpretreated pinewood (UNP; UNPC) as the bulking agent. Results show that addition of MOP effectively promoted the degradation of organic matter during composting. The maximum temperature increased by 1.50 °C and the high temperature period (T > 50 °C) of composting was extended 4 days longer than the control experiment. Furthermore, MOP addition reduced the loss of nitrogen by 9.40%. High-throughput sequencing analysis showed that the bacterial communities in the UNPC and MOPC treatments were significantly different. Pseudoxanthomonas was the dominant bacteria during the thermophilic and cooling phases of the MOPC treatment. In addition, the recycling efficiency of the UNP and MOP was 99.18% and 99.37%, respectively.

Identifying the action ways of function materials in catalyzing organic waste transformation into humus during chicken manure composting

The aim of this study is to detect the action properties of functional materials (FM) in transforming waste into resource products with high humus content. FM (MnO₂ and reducing sugar) were added in different periods of chicken manure composting. During composting, concentration of humic acids (HA) as aromatic fraction of humus, was increased by FM. The promotive effects of adding FM in later period was the most obvious. While adding FM in the beginning period could accelerate organic matter degradation, but it did not promote HA formation. Meanwhile, the microbial diversity was higher in groups by adding FM in the beginning and thermophilic periods. Therefore, it was speculated that FM might improve HA formation by promoting the abiotic polymerization of precursors. Eventually, structural equation model showed that FM was beneficial to abiotic pathway of HA formation. But the formation efficiency was reduced by interfering with biotic pathway.

Biological nutrient removal and recovery from solid and liquid livestock manure: Recent advance and perspective

Rapid development of livestock industry produces large amount of livestock manure rich in nutrients, organic matters, antibiotics, and heavy metals, thus imposes great harms to human and environment, if the manure is not suitably treated. Biological removal and recovery of nutrients from manure as agriculture fertilizer is attractive due to low cost and simple operation. This review offers an overview of recent development in biological nutrient removal and recovery from livestock manure. Livestock manure is divided into solid manure and liquid manure. Composting and anaerobic digestion of solid manure are fully discussed and important parameters are investigated. Then various processes of nutrient removal and recovery from liquid manure are summarized. Brief economic sustainability and eco-environmental effects are carried out. Finally, current challenges and future prospects in this field are analyzed.

Effect of inoculating microorganisms in chicken manure composting with maize straw

The effects of inoculating with microorganisms on chicken manure compost with maize straw were investigated in a self-built aerated static box (0.6 m³) by assessing the influences of temperature, moisture, pH, C/N ratio, transformation of nitrogen, humification levels and composting maturity. Results showed that inoculation with microorganisms prolonged the thermophilic stage in composting compared to control groups, increasing the temperature, pH and germination index as the composting period progressed. This suggests that inoculation with microorganisms were helpful in facilitating the process of composting, as it significantly reduced NH₄⁺ content during the cooling stage. Additionally, NO₃^- increased after the first pile turning on day 10, continuing until the end of thermophilic stage. Improvements across transformation of nitrogen, humification levels and composting maturity were also seen in inoculation piles. Conclusively, we suggested inoculating using cocktails of microorganisms to increase efficiency and promote maturity in chicken manure composting.

Effect of Cornstalk Biochar Immobilized Bacteria on Ammonia Reduction in Laying Hen Manure Composting

NH₃ emission has become one of the key factors for aerobic composting of animal manure. It has been reported that adding microbial agents during aerobic composting can reduce NH₃ emissions. However, environmental factors have a considerable influence on the activity and stability of the microbial agent. Therefore, this study used cornstalk biochar as carriers to find out the better biological immobilization method to examine the mitigation ability and mechanism of NH₃ production from laying hen manure composting. The results from different immobilized methods showed that NH₃ was reduced by 12.43%, 5.53%, 14.57%, and 22.61% in the cornstalk biochar group, free load bacteria group, mixed load bacteria group, and separate load bacteria group, respectively. Under the simulated composting condition, NH₃ production was 46.52, 38.14, 39.08, and 30.81 g in the treatment of the control, mixed bacteria, cornstalk biochar, and cornstalk biochar separate load immobilized mixed bacteria, respectively. The cornstalk biochar separate load immobilized mixed bacteria treatment significantly reduced NH₃ emission compared with the other treatments (p < 0.05). Compared with the control, adding cornstalk biochar immobilized mixed bacteria significantly decreased the electrical conductivity, water-soluble carbon, total nitrogen loss, and concentration of ammonium nitrogen (p < 0.05), and significantly increased the seed germination rate, total number of microorganisms, and relative abundance of lactic acid bacteria throughout the composting process (p < 0.05). Therefore, the reason for the low NH₃ emission might be due not only to the adsorption of the cornstalk biochar but also because of the role of complex bacteria, which increases the relative abundance of lactic acid bacteria and promotes the acid production of lactic acid bacteria to reduce NH₃ emissions. This result revealed the potential of using biological immobilization technology to reduce NH₃ emissions during laying hen manure composting.

Driving effects of minerals on humic acid formation during chicken manure composting: Emphasis on the carrier role of bacterial community

This work was aimed to determine the effects of different minerals on humic acid (HA) formation. Minerals can stimulate the formation of complex compounds, however, whether they can promote the conversion of complex compounds to HA has not been verified. Four treatments were setup from chicken manure mixed with rice hull and then added biochar (BC), montmorillonite (MMT) and biochar combined with montmorillonite (BC-MMT) for composting, while the control check (CK) was composted without minerals. The results showed that HA concentration was increased by 28.09%, 40.79%, 45.39% and 38.96% during CK, BC, BC-MMT and MMT composting. However, the bacterial community was the main reason for affecting HA concentration. Network analysis showed that obligate and facultative core microbes drove HA formation, and these driving effects were affected by minerals. Therefore, the core bacterial community promoted HA formation, which provided an insightful method to improve HA production.

Biochar combined with montmorillonite amendments increase bioavailable organic nitrogen and reduce nitrogen loss during composting

This study aimed to compare the effects of biochar, montmorillonite and their mixture on nitrogen availability and nitrogen loss during chicken manure composting. Four lab-scale composting experiments, the control (CK), 5% biochar addition (BC), 5% montmorillonite addition (M) and 2.5% biochar + 2.5% montmorillonite addition (BCM), were established. Results showed that the addition of BC, M and BCM significantly improved the contents of bioavailable organic nitrogen and NH₄⁺-N in composts. In addition, BC and BCM reduced N loss by 19.2% and 12.2%, respectively, in comparison with CK. Significant shift of key bacterial communities associated with N transformation were also found in four treatments. Redundancy analysis and structural equation models indicated different additives changed the correlation among bacterial communities, environmental factors and organic N fractions. Comparison of N availability and N loss indicated that the combination of biochar and montmorillonite are more effective than that of separate application during composting.

Recognition of the neutral sugars conversion induced by bacterial community during lignocellulose wastes composting

The aim of this study was to explore the conversion characteristics of neutral sugars during different lignocellulose wastes composting from rice straw (RS), leaf (L) and mushroom dreg (MD). The results showed that the changes of neutral sugars were different during different wastes composting, but the changes of various hexose or pentose were similar during composting of the same material. The diversity of bacterial community led to different conversion characteristics of neutral sugars. During RS composting, each neutral sugar was transformed by a specific group of bacteria. However, a group of bacteria could transform multiple neutral sugars during MD and L composting. Furthermore, GM/AX value was first applied to composting, which could be used to characterize the conversion of neutral sugars during composting. This will help to provide more efficient recommendations for lignocellulose wastes treatment and accelerating humic substances synthesis during composting.

Hyperthermophilic composting reduces nitrogen loss via inhibiting ammonifiers and enhancing nitrogenous humic substance formation

Composting is an efficient and economic approach used to convert organic waste into organic fertilizers. However, the substantial nitrogen loss during the composting process is one of the major disadvantages of conventional thermophilic composting (cTC). Here, we demonstrated for the first time that hyperthermophilic composting (hTC) was able to mitigate nitrogen loss by 40.9% compared to cTC after 44 days of composting in a full-scale plant. Results demonstrate a decrease in NH₃ volatilization (52.4%), together with an inhibitory effect on protease (19.4-87.5%) and urease (9.1-75.2%) enzyme activities and the ammonification rate (5.2-80.1%) for hTC. Additionally, this study found that hTC could accelerate the humification process, thereby enhancing the formation of the recalcitrant nitrogen reservoir (mainly in the form of nitrogenous humic substances) and reducing the substrate for ammonification reactions. These findings suggest that hTC can significantly reduce nitrogen loss and provide insights into the role of humic substances in nitrogen retention in composting systems.

Composting swine carcasses with nitrogen transformation microbial strains: Succession of microbial community and nitrogen functional genes

In this study, nitrogen transformation strains, including three ammonium transformation strains, one nitrite strain and one nitrogen fixer, were inoculated at different swine carcass composting stages to regulate the nitrogen transformation and control the nitrogen loss. The final total nitrogen content was significantly increased (p < 0.01). The bacterial communities were assessed by amplicon sequencing and association analysis. Proteobacteria, Actinobacteria, Bacteroidetes and Firmicutes were the four most dominant phyla.,Brevibacterium, Streptomyces and Ochrobactrum had a significant (p < 0.05) and positive correlation with total nitrogen and ammonium nitrogen content in both groups. The quantitative results of nitrogen transformation genes showed that ammonification, nitrification, denitrification and nitrogen fixation were simultaneously present in the composting process of swine carcasses, with the latter two accounting for a higher proportion. The ammonium transformation strains significantly (p < 0.05) strengthened nitrogen fixation and remarkably (p < 0.01) weakened nitrification and denitrification, which, however, were notably (p < 0.05) enhanced by the nitrite strain and nitrogen fixer. In this research, the inoculated strains changed the bacterial structure by regulating the abundance and activity of the highly connected taxa, which facilitated the growth of nitrogen transformation bacteria and regulated the balance/symbiosis of nitrogen transformation processes to accelerate the accumulation of nitrogen.

Improvement of cleaner composting production by adding Diatomite: From the nitrogen conservation and greenhouse gas emission

In order to investigate the improvement of Diatomite (DM) on the production of cleaner composting, reflected by emission of NH₃ and greenhouse gases (GHGs), three dosages of DM (0%, 5% and 10%) were added into mixture of pig manure and sawdust for 42 days composting. Addition of DM promoted the transformation of organic matter and improved the quality of end product. Meanwhile, it was confirmed by the increase of NO₃^--N formation and nitrogen conservation. Besides, adding DM aided on reducing emission of CH₄, N₂O and NH₃ by 18.27%-30.41%, 26.89%-84.16% and 10.41%-23.70%, respectively. Furthermore, the DM had a positive effect on the maturity of compost products, reflecting by GI value and HA/FA. Consequently, through the factor analysis, 10% was suggested to improve the quality of end product and reduce nitrogen loss as well as GHGs emission.

Effect of phosphate amendments on improving the fertilizer efficiency and reducing the mobility of heavy metals during sewage sludge composting

Composting has been globally applied as an effective and cost-efficient process to manage and reuse sewage sludge. In the present study, four different phosphates as well as a mixture of ferrous sulfate and monopotassium phosphate were used in sewage sludge composting. The results showed that these phosphate amendments promoted an increase in temperature and the degradation of organic matter as well as reduction on nitrogen loss during 18 days of composting. In addition, ferrous sulfate and phosphate had a synergistic effect on reducing nitrogen loss. The contents of total phosphorus and available phosphorus in the compost with addition of 1% phosphate were 40.9% and 66.1% higher than the compost with control treatment. Using the BCR (Community Bureau of Reference) sequential extraction procedure, the addition of calcium magnesium phosphate significantly reduced the mobility factor of Cd, Zn and Cu by 24.2%, 1.7% and 18.8%, respectively. The mobility factors of Pb were increased in all samples, but the monopotassium phosphate treated sample exhibited the greatest Pb passivation ability with the lowest mobility factor increase (1.8%) among all treatments. The X-ray diffraction patterns of compost samples indicated that the passivation mechanism of Cu and Zn may be the forming CuFeS₂ and ZnCu(P₂O₇) crystals during sewage sludge composting. The germination index showed that the compost of all treatments was safe for agricultural application; the germination index of the calcium magnesium phosphate treatment was 99.9 ± 11.8%, which was the highest among all treatments.

Effect of different components of single superphosphate on organic matter degradation and maturity during pig manure composting

Single superphosphate (SSP) as an additive could improve phosphorus availability and reduce nitrogen loss for composts, but few studies have explored the influence of SSP on the transformation of carbon fractions in composting. The aim of this work was to assess the effect of different components of SSP, including calcium dihydrogen phosphate (CDP), calcium sulfate (CS) and free acid (FA) on organic matter degradation and maturity during pig manure composting. The results showed that CDP had significantly negative effects on the duration of thermophilic phase and organic matter degradation, but lengthened the curing phase for the transformation of organic matter. FA could intensify the inhibiting effect of CDP and postpone the biodegradation process of composting, but CS could buffer the effect of CDP on the degradation of organic carbon fractions by controlling pH. The study reveals the roles of different components of SSP to the transformation of organic carbon fractions, which lays a foundation for regulating the effects of chemical additives during composting. Regulating the content of CDP in SSP or applying SSP with other chemical additives to control the biotoxicity of excess phosphate on microbial activity should be concerned for complete and efficient composting in further study.

Effects of exogenous microbial inoculum on the structure and dynamics of bacterial communities in swine carcass composting

Composting is a widely accepted method for the disposal of deceased livestock. It is a biological self-heating process during which animal carcasses are converted to fertilizer products. Additional inoculants can facilitate the composting progress. This study investigated how the addition of microbial inoculants could improve the composting effectiveness and could change the structure and dynamics of bacterial communities in the carcass composting process. Four strains of Bacillus were inoculated into the swine carcass composting piles. The groups with the additional inoculants showed a higher temperature in the thermophilic phase and higher germination indices in the composted products. The sequencing results showed that the dominant phyla were Proteobacteria, Firmicutes, and Actinobacteria, and the dominant classified genera were Brevibacterium and Bacillus. Canonical correlation analysis showed that temperature and moisture exerted a stronger influence on the bacterial community diversity. The interaction network of dominant genera and the abundance variation of the bacterial community demonstrated that the inoculated bacterial agent changed the structure of bacterial communities and enriched the diversity of the species due to antagonism and symbiosis among the dominant bacterial communities.

How does manganese dioxide affect humus formation during bio-composting of chicken manure and corn straw?

The aim of this study is to reveal the roles of MnO₂ in Maillard reaction of biotic composting, and to identify its effectiveness in promoting humus formation. Corn straw (CS) and chicken manure (CM) have been chosen to be composted. During CS composting, addition of MnO₂ rapidly reduced reducing sugars concentration (decreased by 84.0%) in 5 days and significantly improved humus production by 38.7% compared with treatment without MnO₂. Whereas in CM composting, the promoting effect of MnO₂ on humus formation was relatively weak by comparing with the treatment group of CS. Additionally, the presence of MnO₂ has reshaped bacteria community, which might be the reason of MnO₂ stimulated bacteria to utilize organic matter during CM composting. Therefore, the structural equation modeling has confirmed that MnO₂ mainly performed as chemical catalyst to promote humus formation during CS composting. Besides catalyst, MnO₂ also played as a bioactive activator in CM composting.

Effect of inoculation with a microbial consortium that degrades organic acids on the composting efficiency of food waste

In order to overcome the excessive acidification problem, a microbial consortium for the degradation of organic acids (MCDOA), which acts synergistically in degrading organic acids, was developed and used as an inoculum to improve the efficiency of food waste composting. MCDOA could eliminate the initial lag phase of the pile temperature rise because of excessive acidification and effectively shorten the composting period. Fluorescence regional integration analysis of the excitation-emission matrix spectra of dissolved organic matter showed that compared with raw material, in compost with MCDOA inoculation, the percent fluorescence response (Pi,n ) values of Regions I, II and IV decreased by 95.11%, 94.19% and 87.41%, respectively, and Pi,n of Region V increased by 172.57%. The decreased and increased levels were markedly higher than in the two control groups (MgO and K2 HPO4 treatment, and uninoculated compost). These findings revealed that MCDOA accelerated the degradation of proteinaceous compounds and the formation of complicated humic-like materials. Bacterial profiles implied that MCDOA could improve the indigenous bacterial community structure and diversities of acetic and propionic acid-degrading and lignin-degrading bacteria, which might account for the high composting efficiency and degree of humification of the inoculated compost.

Nitrogen loss reduction by adding KH2PO4-K2HPO4 buffer solution during composting of sewage sludge

Nitrogen loss through gaseous emission, mainly ammonia emission, was an inevitable problem during sewage sludge composting. In this study, MgSO₄ + K₃PO₄ (Run A), K₂SO₄ + KH₂PO₄-K₂HPO₄ (Run B) and MgSO₄ + KH₂PO₄-K₂HPO₄ (Run C) were mixed with mixtures before composting, aiming at researching the effects of buffer solution on reducing nitrogen loss during composting. Ammonia loss of Run C was reduced by 53.8% and 45.5%, and nitrogen loss of Run C was decreased by 61.2% and 67.1%, compared to that of Run A and Run B, respectively. Besides, organic matter degradation of Run C was 36.8%. Among the three amended treatments, nitrogen loss in Run C was effectively reduced and organic matter degradation was slightly improved. The addition of MgSO₄ and KH₂PO₄-K₂HPO₄ was confirmed to be effective to maintain a desired pH range for struvite precipitation as well as to reserve more ammonia in the compost to promote the formation of struvite.

Transformation of organic nitrogen fractions with different molecular weights during different organic wastes composting

This study aimed to investigate different transformation mechanisms of organic nitrogen (N) fractions during composting with different raw materials, and the contributions of bacterial communities and environmental factors to organic N fractions transformation. The results showed that high molecular weight organic N was first degraded to low molecular weight organic N and then turned into NH₄⁺ during chicken manure composting. In comparison, organic N fractions were stored in composts rather than mineralization during garden waste and municipal solid waste composting. Meanwhile, bacterial communities, environmental factors and the combination of them were the main drivers of N transformation during chicken manure, municipal solid waste and garden waste composting, respectively. In conclusion, the proposed organic N transformation mechanisms in this study provided a theoretical basis for improving the quality of compost products.