Effect of different struvite crystallization methods on gaseous emission and the comprehensive comparison during the composting

A comprehensive review on agricultural waste utilization through sustainable conversion techniques, with a focus on the additives effect on the fate of phosphorus and toxic elements during composting process

The increasing trend of using agricultural wastes follows the concept of "waste to wealth" and is closely related to the themes of sustainable development goals (SDGs). Carbon-neutral technologies for waste management have not been critically reviewed yet. This paper reviews the technological trend of agricultural waste utilization, including composting, thermal conversion, and anaerobic digestion. Specifically, the effects of exogenous additives on the contents, fractionation, and fate of phosphorus (P) and potentially toxic elements (PTEs) during the composting process have been comprehensively reviewed in this article. The composting process can transform biomass-P and additive-born P into plant available forms. PTEs can be passivated during the composting process. Biochar can accelerate the passivation of PTEs in the composting process through different physiochemical interactions such as surface adsorption, precipitation, and cation exchange reactions. The addition of exogenous calcium, magnesium and phosphate in the compost can reduce the mobility of PTEs such as copper, cadmium, and zinc. Based on critical analysis, this paper recommends an eco-innovative perspective for the improvement and practical application of composting technology for the utilization of agricultural biowastes to meet the circular economy approach and achieve the SDGs.

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.

Effects of thermophilic bacteria inoculation on maturity, gaseous emission and bacterial community succession in hyperthermophilic composting

Hyperthermophilic composting, characterized by temperatures equal to or exceeding 75 °C, offers superior compost maturity and performance. Inoculation with thermophilic bacteria presents a viable approach to achieving hyperthermophilic composting. This study investigates the effects of inoculating thermophilic bacteria, isolated at different temperatures (50 °C, 60 °C, and 70 °C) into compost on maturity, gaseous emissions, and microbial community dynamics during co-composting. Results indicate that the thermophilic bacteria inoculation treatments exhibited peak temperature on Day 3, with the maximum temperature of 75 °C reached two days earlier than the control treatment. Furthermore, these treatments demonstrated increased bacterial richness and diversity, along with elevated relative abundances of Firmicutes and Proteobacteria. They also fostered mutualistic correlations among microbial species, enhancing network connectivity and complexity, thereby facilitating lignocellulose degradation. Specifically, inoculation with thermophilic bacteria at 60 °C increased the relative abundance of Thermobifida and unclassified-f-Thermomonosporaceae (Actinobacteriota), whereas Bacillus, a thermophilic bacterium, was enriched in the 70 °C inoculation treatment. Consequently, the thermophilic bacteria at 60 °C and 70 °C enhanced maturity by 36 %-50 % and reduced NH3 emissions by 1.08 %-27.50 % through the proliferation of thermophilic heterotrophic ammonia-oxidizing bacteria (Corynebacterium). Moreover, all inoculation treatments decreased CH4 emissions by 6 %-27 % through the enrichment of methanotrophic bacteria (Methylococcaceae) and reduced H2S, Me2S, and Me2SS emissions by 1 %-25 %, 47 %-63 %, and 15 %-53 %, respectively. However, the inoculation treatments led to increased N2O emissions through enhanced denitrification, as evidenced by the enrichment of Truepera and Pusillimonas. Overall, thermophilic bacteria inoculation promoted bacteria associated with compost maturity while attenuating the relationship between core bacteria and gaseous emissions during composting.

Ca(H2PO4)2 and MgSO4 activated nitrogen-related bacteria and genes in thermophilic stage of compost

This study was conducted to investigate the effects of Ca(H2PO4)2 and MgSO4 on the bacterial community and nitrogen metabolism genes in the aerobic composting of pig manure. The experimental treatments were set up as control (C), 1% Ca(H2PO4)2 + 2% MgSO4 (CaPM1), and 1.5% Ca(H2PO4)2 + 3% MgSO4 (CaPM2), which were used at the end of composting for potting trials. The results showed that Ca(H2PO4)2 and MgSO4 played an excellent role in retaining nitrogen and increasing the alkali-hydrolyzed nitrogen (AN), available phosphorus (AP), and available potassium (AK) contents of the composts. Adding Ca(H2PO4)2 and MgSO4 changed the microbial community structure of the compost. The microorganisms associated with nitrogen retention were activated. The complexity of the microbial network was enhanced. Genetic prediction analysis showed that the addition of Ca(H2PO4)2 and MgSO4 reduced the accumulation of nitroso-nitrogen and the process of denitrification. At the same time, despite the reduction of genes related to nitrogen fixation, the conversion of ammonia to nitrogenous organic compounds was promoted and the stability of nitrogen was increased. Mantel test analysis showed that Ca(H2PO4)2 and MgSO4 can affect nitrogen transformation-related bacteria and thus indirectly affect nitrogen metabolism genes by influencing the temperature, pH, and organic matter (OM) of the compost and also directly affected nitrogen metabolism genes through PO43- and Mg2+. The pot experiment showed that composting with 1.5% Ca(H2PO4)2 + 3% MgSO4 produced the compost product that improved the growth yield and nutrient content of cilantro and increased the fertility of the soil. In conclusion, Ca(H2PO4)2 and MgSO4 reduces the loss of nitrogen from compost, activates nitrogen-related bacteria and genes in the thermophilic phase of composting, and improves the fertilizer efficiency of compost products. KEY POINTS: • Ca(H2PO4)2 and MgSO4 reduced the nitrogen loss and improved the compost effect • Activated nitrogen-related bacteria and altered nitrogen metabolism genes • Improved the yield and quality of cilantro and fertility of soil.

Phosphate additives promote humic acid carbon and nitrogen skeleton formation by regulating precursors and composting bacterial communities

This study aimed to compare the effect of different phosphate additives including superphosphate (CP) and MP [Mg(OH)2 + H3PO4] on nitrogen conversion, humus fractions formation and bacterial community in food waste compost. The results showed the ratio of humic acid nitrogen in total nitrogen (HA-N/TN) in CP increased by 49 %. Ammonium nitrogen accumulation was increased by 75 % (CP) and 44 % (MP). Spectroscopic techniques proved that phosphate addition facilitated the formation of complex structures in HA. CP enhanced the dominance of Saccharomonospora, while Thermobifida and Bacillus were improved in MP. Structural equation modeling and network analysis demonstrated that ammonium nitrogen can be converted to HA-N and has positive effects on bacterial composition, reducing sugars and amino acids, especially in CP with more clustered network and synergic bacterial interactions. Therefore, the addition of phosphate provides a new idea to regulate the retained nitrogen toward humification in composting.

Contribution of zeolite to nitrogen retention in chicken manure and straw compost: Reduction of NH3 and N2O emissions and increase of nitrate

Co-composting of chicken manure, straw and zeolite was investigated in a water bath heating system to estimate the effect of zeolite on physicochemical properties and metabolic functions related to nitrogen conversion. The results indicated that NH3 catches by zeolite was concentrated in the early stage and zeolite with 10 % addition reduced 28 % NH3 and 55 % N2O emissions as compost ended. The nitrate content in 10 % zeolite group was 17 % higher than that in control group. There was no significant increase of NO2- in zeolite group. More NO2- formed NH3, rather than being converted to NOx through denitrification. The abundance of nitrification genes amoA and hao increased except nxrA in zeolite groups. Denitrification was the most obvious at 20 d and zeolite decreased the abundance of denitrification genes narG, nirK and nosZ at this time.

Effects of biochar combined with MgO desulfurization waste residue on nitrogen conversion and odor emission in chicken manure composting

Aim: Chicken manure is known to produce strong odors during aerobic composting, which not only pollutes the surrounding environment but also leads to the loss of valuable nutrients like nitrogen and sulfur, thus reducing the quality of the fertilizer. Methods: In this study, we explored the use of biochar combined with MgO desulfurization waste residue (MDWR) as a novel composting additive. Our approach involved conducting composting tests, characterizing the compost samples, conducting pot experiments, and examining the impact of the additives on nitrogen retention, deodorization, and compost quality. Results: Our findings revealed that the addition of biochar and MDWR significantly reduced ammonia volatilization in chicken manure compost, demonstrating a reduction rate of up to 60.12%. Additionally, the emission of volatile organic compounds (VOCs) from chicken manure compost treated with biochar and MDWR decreased by 44.63% compared to the control group. Conclusions: The composting product treated with both biochar and MDWR (CMB) exhibited a 67.7% increase in total nitrogen (TN) compared to the blank control group, surpassing the other treatment groups and showcasing the synergistic effect of these two additives on nitrogen retention. Moreover, the CMB treatment facilitated the formation of struvite crystals. Furthermore, our pot experiment results demonstrated that the CMB treatment enhanced vegetable yield and quality while reducing nitrate content. These findings highlight the significant impact of MDWR on nitrogen retention, deodorization, and compost quality enhancement, thereby indicating its promising application prospects.

Determining the extraction conditions and phytotoxicity threshold for compost maturity evaluation using the seed germination index method

The phytotoxicity of the compost aqueous extracts determines the maturity. To improve the accuracy of compost maturity evaluation using the seed germination index (GI) method, different extraction methods (different moisture content and extraction ratio) were designed to obtain samples with various phytotoxic level. This study analyzed the effects of different extraction condition of compost samples on GI, and established the relationship between phytotoxicity and GI. The results showed that the moisture content and extraction ratio of the compost significantly affected the GI. The extraction ratio for the compost with 60-70 % moisture content was 1:10 (ratio of compost mass to extract volume). However, commercial compost, which must have a moisture content of 30-45 %, had an extraction ratio of 1:30 (w:v). More importantly, compost extraction based on dry weight, with a moisture content of 10-15 %, more effectively reflected the phytotoxicity variations during composting. In such cases, the extraction ratio should be at least 1:30 (w:v) but not exceed 1:50 (w:v). The relationship between phytotoxicity and GI showed that dissolved organic carbon and dissolved nitrogen were the most important factors influencing GI, followed by NH4+, electrical conductivity, K, volatile fatty acids, Zn, and Cu. For composts with a GI greater than 70 %, the dissolved organic carbon, dissolved nitrogen, and NH4+ concentrations were below 257, 164, and 73 mg/L, respectively. These findings provide an optimized standard method for compost maturity evaluation using GI and a concentration threshold of key phytotoxicity is proposed to achieve accurate control of compost maturity.

A novel composting system for mitigating ammonia emissions and producing nitrogen-rich organic fertilizer

Ammonia emissions not only lead to environmental pollution but also reduce the quality of compost products. Here, a novel composting system (condensation return composting system, CRCS) was designed for mitigating ammonia emissions. The results showed that the CRCS reduced ammonia emissions by 59.3% and increased the total nitrogen content by 19.4% compared with the control. By integrating the results of nitrogen fraction conversion, ammonia-assimilating enzyme activity, and structural equation modeling, it was found that the CRCS facilitated the conversion of ammonia to organic nitrogen by stimulating ammonia-assimilating enzyme activity and ultimately retained nitrogen in the compost product. Moreover, the pot experiment confirmed that nitrogen-rich organic fertilizer produced by the CRCS significantly increased the fresh weight (45.0%), root length (49.2%), and chlorophyll content (11.7%) of pakchoi. This study provides a promising strategy for mitigating ammonia emissions and producing nitrogen-rich organic fertilizer with high agronomic value.

Transmission and regulation insights into antibiotic resistance genes in straw-sludge composting system amended with calcium peroxide

This study developed a Fenton-like system by adding calcium peroxide (CaO2) to a composting system containing straw and sludge. The objective was to examine the influence of antibiotic resistance genes (ARGs) and the structure of the bacterial community. The findings indicated that the inclusion of CaO2 facilitated the reduction of ARGs. ARGs abundance in the test group (T) with CaO2 was 19.02% lower than that in the control check group (CK) without CaO2, and the abundance of ARGs in both groups after composting was lower than the initial abundance. Additionally, the structure of bacterial community in both groups underwent significant changes. Redundancy analysis (RDA) revealed that the CaO2-induced Fenton-like reaction predominantly affected temperature, pH, and the bacterial community by means of reactive oxygen species (ROS). In conclusion, the addition of CaO2 enhanced the removal of ARGs from sewage-sludge and improved compost quality in the composting.

Effect of aeration/micro-aeration on lignocellulosic decomposition, maturity and seedling phytotoxicity during full-scale biogas residues composting

With the accelerated construction of biogas plants, the amount of biogas residues are expanding. Composting has been widely implemented to deal with biogas residues. Aeration regulation is the main factor affecting the post-composting treatment of biogas residues as high-quality fertilizer or soil amendment. Therefore, this study aimed to investigate the impact of different aeration regulations on full-scale biogas residues compost maturity by controlling oxygen concentration under micro-aeration and aeration conditions. Results showed that micro-aerobic extended the thermophilic stage of 17 days at above 55 ℃ and facilitated the mineralization process of organic nitrogen into nitrate nitrogen to retain higher N nutrition levels compared to aerobic treatment. For biogas residues with high moisture, aeration should be regulated at different full-scale composting stages. Total organic carbon (TOC), NH4+-N, NO3--N, total potassium (TK), total phosphorus (TP) and the germination index (GI) could be used to evaluate stabilization, fertilizer efficiency and phytotoxicity of compost with frequent monitoring times. However, seedling growth trials were still necessary in full-scale composting plants when changing of composting process or biogas residues feedstock.

Reducing nitrogen loss during kitchen waste composting using a bioaugmented mechanical process with low pH and enhanced ammonia assimilation

Exploring the regulation of nitrogen transformation in bioaugmented mechanical composting (BMC) process for rural kitchen waste (KW) is essential to avoid the "not-in-my-backyard" phenomenon caused by nitrogen loss. Herein, nitrogen transformation and loss in BMC versus conventional pile composting (CPC) of KW were compared. The results showed that the total nitrogen loss in the BMC was 6.87-39.32 % lower than that in the CPC. The main pathways to prevent nitrogen loss in the BMC were reducing NH₃ by avoiding a sharp increase in pH followed by transforming the preserved NH₄⁺-N into recalcitrant nitrogen reservoir via enhanced ammonia assimilation. The enriched thermophilic bacteria with mineralization capacities (e.g., Bacillus and Corynebacterium) during rapid dehydration and heating in the BMC accumulated organic acids and easy-to-use carbon sources, which could lead to lower pH and ammonia assimilation enhancement, respectively. This study provides new ideas for formulating low-cost nitrogen conservation strategies in decentralized KW composting.

Measures for Controlling Gaseous Emissions during Composting: A Review

Composting is a promising technology for treating organic solid waste. However, greenhouse gases (methane and nitrous oxide) and odor emissions (ammonia, hydrogen sulfide, etc.) during composting are practically unavoidable, leading to severe environmental problems and poor final compost products. The optimization of composting conditions and the application of additives have been considered to mitigate these problems, but a comprehensive analysis of the influence of these methods on gaseous emissions during composting is lacking. Thus, this review summarizes the influence of composting conditions and different additives on gaseous emissions, and the cost of each measure is approximately evaluated. Aerobic conditions can be achieved by appropriate process conditions, so the contents of CH4 and N2O can subsequently be effectively reduced. Physical additives are effective regulators to control anaerobic gaseous emissions, having a large specific surface area and great adsorption performance. Chemical additives significantly reduce gaseous emissions, but their side effects on compost application must be eliminated. The auxiliary effect of microbial agents is not absolute, but is closely related to the dosage and environmental conditions of compost. Compound additives can reduce gaseous emissions more efficiently than single additives. However, further study is required to assess the economic viability of additives to promote their large-scale utilization during composting.

Effects of dicyandiamide, phosphogypsum and superphosphate on greenhouse gas emissions during pig manure composting

This study investigated the effects of dicyandiamide, phosphogypsum and superphosphate on greenhouse gas emissions and compost maturity during pig manure composting. The results indicated that the addition of dicyandiamide and phosphorus additives had no negative effect on organic matter degradation, and could improve the compost maturity. Adding dicyandiamide alone reduced the emissions of ammonia (NH₃), methane (CH₄) and nitrous oxide (N₂O) by 9.37 %, 9.60 % and 31.79 %, respectively, which was attributed that dicyandiamide effectively inhibited nitrification to reduce the formation of N₂O. Dicyandiamide combined with phosphogypsum or superphosphate could enhance mitigation of the total greenhouse gas (29.55 %-37.46 %) and NH₃ emission (18.28 %-21.48 %), which was mainly due to lower pH value and phosphoric acid composition. The combination of dicyandiamide and phosphogypsum exhibited the most pronounced emission reduction effect, simultaneously decreasing the NH₃, CH₄ and N₂O emissions by 18.28 %, 38.58 % and 36.14 %, respectively. The temperature and C/N content of the compost were significantly positively correlated with greenhouse gas emissions.

An Alternative to Vermiculite: Composting on Tropical Islands Using Coral Sand to Enhance Nitrogen Retention during Ventilation

Reducing nitrogen loss during composting with forced ventilation was comprehensively investigated in this study. Coral sand was tailored in the co-composting in the co-composting of sludge and litters. The physicochemical results revealed that forced ventilation prolonged the thermophilic phase and accelerated the substrate decomposition. With the addition of 10% native coral sand, the amount of nitrogen loss decreased by 9.2% compared with the original group. The microbial community evaluation revealed that the effect of forced ventilation on colony abundance was significantly greater than that of adding coral sand. This study demonstrated that when composting on a tropical island, adding coral sand under forced ventilation was a viable solution for realizing sustainable development.

Feasibility of Biochar Derived from Sewage Sludge to Promote Sustainable Agriculture and Mitigate GHG Emissions-A Review

Sewage sludge (SS) has been connected to a variety of global environmental problems. Assessing the risk of various disposal techniques can be quite useful in recommending appropriate management. The preparation of sewage sludge biochar (SSB) and its impacts on soil characteristics, plant health, nutrient leaching, and greenhouse gas emissions (GHGs) are critically reviewed in this study. Comparing the features of SSB obtained at various pyrolysis temperatures revealed changes in its elemental content. Lower hydrogen/carbon ratios in SSB generated at higher pyrolysis temperatures point to the existence of more aromatic carbon molecules. Additionally, the preparation of SSB has an increased ash content, a lower yield, and a higher surface area as a result of the rise in pyrolysis temperature. The worldwide potential of SS output and CO₂-equivalent emissions in 2050 were predicted as factors of global population and common disposal management in order to create a futuristic strategy and cope with the quantity of abundant global SS. According to estimations, the worldwide SS output and associated CO₂-eq emissions were around 115 million tons dry solid (Mt DS) and 14,139 teragrams (Tg), respectively, in 2020. This quantity will rise to about 138 Mt DS sewage sludge and 16985 Tg CO₂-eq emissions in 2050, a 20% increase. In this regard, developing and populous countries may support economic growth by utilizing low-cost methods for producing biochar and employing it in local agriculture. To completely comprehend the benefits and drawbacks of SSB as a soil supplement, further study on long-term field applications of SSB is required.

Mitigating gas emissions from poultry litter composting with waste vinegar residue

The composting process is important in the recycling of organic wastes produced in agriculture, food, and municipal waste management. This study explored the suitability of using waste vinegar residue (WVR) as an amendment in poultry litter (PL) composting. Four treatments, including poultry litter (CK), poultry litter+vinegar residue (VR), poultry litter+vinegar residue+lime (VR_Ca) and poultry litter+vinegar residue+biochar (VR_B), were conducted. During a 42-day composting period, the dynamics of carbon dioxide (CO₂), ammonia (NH₃), nitrous oxide (N₂O) and methane (CH₄) emissions, as well as the physicochemical properties and abundances of the bacteria and fungi of the feedstock were tracked to examine the potential barriers in the co-composting of WVR and PL. Compared to those of the CK, using a WVR amendment lowered the pH, increased the electrical conductivity significantly at the early stage, resulted in a strong inhibition of bacterial and fungal growth and delayed the thermophilic period of poultry litter composting while significantly reducing NH₃ and N₂O and GHG (CO₂-e) emissions. A preadjustment of the WVR with alkaline biochar or lime lengthened the thermophilic period and increased the germination index (GI) by alleviating the inhibitory effect of the WVR on bacterial and fungal growth during composting. However, such preadjustment might reduce the mitigation effect on NH₃. In conclusion, WVR can be recycled through co-composting with poultry litter, and the additional mitigation of N losses and N conservation can be achieved without halting compost quality.

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 a cascade artificial neural network for modeling and optimization of process parameters in co-composting of cattle manure and municipal solid waste

The present study was carried out to improve, test, and validate the Cascade Forward Neural Network (CFNN) for co-composting of municipal solid waste (MSW) and cattle manure (CM). Composting was performed in vessel pilot-scale reactors with different CM rates for 105 days. The CFNN used 5 input variables containing CM and MSW mixture combinations, and 1 output for each of the compost quality parameters. The CFNN results were compared with Response Surface Methodology (RSM) and Feed Forward Neural Network (FFNN) results. Multi-objective optimization process using Genetic Algorithm (GA), the total desirability, which has a much better value than the RSM, was obtained as 0.4455 and the CM ratio and processing time were determined as approximately 23.39% and 104.86 days, respectively. It is concluded that CFNN is a unique modeling tool, exhibiting superior modeling and prediction performance in MSW and compost modeling for CM.

In-situ generation of H2O2 by zero valent iron to control depolymerization of lignocellulose in composting niche

Lignocellulosic degradation is a bottleneck of bioconversion during the composting process. In-situ generation of H₂O₂ in the composting system was an ideal method for efficiently promoting lignocellulase degradation, and zero valent iron (ZVI) was concerned because it can generate H₂O₂ by reducing dissolved oxygen. This study focused on the effects of ZVI treatment on lignocellulose degradation, microbial communities, and carbohydrate-active enzymes (CAZymes) genes during composting. Its results indicated that ZVI increased H₂O₂ content during composting, accompanied by the formation of •OH. The degradation rates of lignin, cellulose and hemicellulose in ZVI group (20.77%, 30.35% and 44.7%) were significantly higher than in CK group (17.01%, 26.12% and 38.5%). Metagenomic analysis showed that ZVI induced microbial growth that favored lignocellulose degradation, which increased the abundance of Actinobacteria and Firmicutes but reduced Proteobacteria. At the genus level, the abundance of Thermomonospora, Streptomyces, and Bacillus significantly increased. In addition, glycoside hydrolases and auxiliary activities were important CAZymes families of lignocellulose degradation, and their abundance was higher in the ZVI group. Redundancy analysis showed that the increased H₂O₂ and •OH content was a critical factor in improving lignocellulose degradation. Overall, H₂O₂ as a co-substrate enhanced the enzymatic efficiency, •OH unspecifically attacked lignocellulose, and the increase in functional microbial abundance was the main reason for promoting lignocellulose degradation in composting.

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.

Co-composting of kitchen waste with agriculture and forestry residues and characteristics of compost with different particle size: An industrial scale case study

Since the implementation of domestic waste classification in China, the kitchen waste production has increased rapidly. The unique physical and chemical properties of kitchen waste make it impossible for direct composting for composting alone. This study investigated the co-composting of kitchen waste with agriculture and forest residues at an industrial scale at the Nangong Composting Plant (Located in Beijing). Cornstalks, garden waste, and watermelon seedlings were composted with kitchen waste, with the added agriculture and forestry residues comprising 5%, 10% and 20% of the weight. Industrial composting was performed 30 days at a scale of 165-180 tone. The mixed compost products were screened to different particle sizes, and the maturity, humification, and calorific value were analyzed. The kitchen waste mixed with 20% agricultural complementary materials reached hyperthermophilic temperature (82 °C), had reduced moisture content (45%), and resulted in better composting performance at an industrial scale. By adding 20% complementary materials to kitchen waste produced mature compost with a higher germination index (GI) (91%) by adjusting the pH, electrical conductivity (EC), carbon to nitrogen ratio (C/N), and moisture content. The compost in the 5% and 10% complementary materials treatments did not fully mature and had a GI of<10%, influenced by the higher EC and NH₄⁺-N content. The property of final compost with different particle size vary greatly. The small particle size compost (≤45 mm) had higher uniformity, maturity, and humification degree, and it was suitable to use as a fertilizer; the larger particle size (>45 mm) had more material with lower calorific value (8000-10,000 kJ·kg^-1), and could be used as refuse-derived fuel. To make better use of kitchen waste compost, 45-mm particle size screening is suggested at an industrial-scale composting plant. These results support industrial-scale kitchen waste composting in China.

Superphosphate, biochar, and a microbial inoculum regulate phytotoxicity and humification during chicken manure composting

The germination index (GI) is the best index for evaluating compost phytotoxicity and maturity. In order to improve GI and reduce phytotoxicity of chicken manure compost, superphosphate, biochar, and a microbial inoculum were added in this study. Maturity indices (pH, electrical conductivity, and GI), water-soluble ion, organic matter, humic acid, humic precursor contents, and the bacteria community were analyzed during the experiment. NH₄⁺, volatile fatty acids, and humic acid strongly affected the GI, which increased as the humic acid content increased and the volatile fatty acid and NH₄⁺ contents decreased. The three additives affected compost maturity differently. Adding biochar decreased microbial diversity and complexity, but improved the GI mainly by affecting abiotic factors. Adding the microbial inoculum increased biotic activity and promoted humus and precursor formation. Superphosphate activated core functional bacteria and increased bacterial diversity and complexity, and 16 genera and 2 phyla (Gemmatimonadota and Chloroflexi) were found only in this composting pile. Superphosphate markedly accelerated humification and decreased the salt (NH₄⁺ and NO₃^-) and heavy metal ion (Cu²⁺, Cd²⁺, Cr³⁺) contents, forming stable substances to reduce the key phytotoxic matters, which in turn decreased the compost phytotoxicity and improved the GI. These results provide a new sight for promoting maturity by functional material regulation in composting.

Impact of biochar, calcium magnesium phosphate fertilizer and spent mushroom substrate on humification and heavy metal passivation during composting

The effects of exogenous additives (biochar, calcium magnesium phosphate fertilizer, and spent mushroom substrate) on humification process and heavy metal passivation during pig manure composting were investigated. The aerobic composting trial were carried out in 60 L reactors for 49 d. The calcium magnesium phosphate fertilizer, biochar, and spent mushroom substrate amendment treatments all accelerated the organic matter degradation and increased the temperature, decreased the volatile fatty acid content by 45%-49.0% and promoted humification of the compost (increasing the humic acid content and humus index). The biochar passivated Cu best, calcium magnesium phosphate fertilizer passivated Zn best (passivation rate 13.85%), and spent mushroom substrate passivated Cd, Cr, and Pb best (passivation rates 25.47%-47.91%). The additives amendment improved Cu, Zn, Cd, Cr, and Pb passivation performance by promoting composting humification process.

Influence of microbial inoculants on co-composting of lignocellulosic crop residues with farm animal manure: A review

The rapidly developing agro-industry generates huge amounts of lignocellulosic crop residues and animal manure worldwide. Although co-composting represents a promising and cost-effective method to treat various agricultural wastes simultaneously, poor composting efficiency prolongs total completion time and deteriorates the quality of the final product. However, supplementation of the feedstock with beneficial microorganisms can mitigate these negative effects by facilitating the decomposition of recalcitrant materials, enhancing microbial enzyme activity, and promoting maturation and humus formation during the composting process. Nevertheless, the influence of microbial inoculation may vary greatly depending on certain factors, such as start-up parameters, structure of the feedstock, time of inoculation, and composition of the microbial cultures used. The purpose of this contribution is to review recent developments in co-composting procedures involving different lignocellulosic crop residues and farm animal manure combined with microbial inoculation strategies. To evaluate the effectiveness of microbial additives, the results reported in a large number of peer-reviewed articles were compared in terms of composting process parameters (i.e., temperature, microbial activity, total organic carbon and nitrogen contents, decomposition rate of lignocellulose fractions, etc.) and compost characteristics (humification, C/N ratio, macronutrient content, and germination index). Most studies confirmed that the use of microbial amendments in the co-composting process is an efficient way to facilitate biodegradation and improve the sustainable management of agricultural wastes. Overall, this review paper provides insights into various inoculation techniques, identifies the limitations and current challenges of co-composting, especially with microbial inoculation, and recommends areas for further research in this field.

Co-composting of food waste and swine manure augmenting biochar and salts: Nutrient dynamics, gaseous emissions and microbial activity

The prominent characteristics of the biochar, high porosity, sorption capacity with low density improve the aeration, making it a desirable amendment material for composting process. The composting efficiency was analysed by the impact of rice husk biochar amendment (0, 2, 4, 6, 8 and 10%) in the presence of salts for the co-composting of food waste and swine manure, in composting reactors for 50 days. Results revealed that biochar amendment had improved the degradation rates by microbial activities in comparison with control. The final compost quality was improved by reducing the bulk density (29-53%), C/N ratio (29-57%), gaseous emissions (CO₂, CH₄, and NH₃) and microbial pathogens (Escherichia coli and Salmonella sp.). However, 6% biochar amendment had significant improvement in compost quality, degradation rates and nutritional value which is recommended as the ideal ratio for obtaining mature compost from the feedstock, food waste and swine manure.

Current status of global warming potential reduction by cleaner composting

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

Role of phosphorous additives on nitrogen conservation and maturity during pig manure composting

This study compared different types and addition amounts of phosphorous additives on nitrogen conservation and maturity during pig manure composting. Phosphogypsum and superphosphate were applied with the same amount of phosphorus (5% of the initial total nitrogen, molar basis) or weight (10% of initial dry matter) and compared to a control treatment without additives. Results show that phosphorous additives could effectively conserve nitrogen. Adding phosphogypsum could significantly reduce NH₃ emission and total nitrogen loss, but increase N₂O emission. Application of 10% superphosphate mitigated NH₃ emissions and total nitrogen loss but inhibited the organic matter degradation and compost maturity. More importantly, with the addition of 5% initial total nitrogen (i.e., 2.5% dry matter), superphosphate could synchronously reduce NH₃ and N₂O emissions and improve compost quality by introducing additional nutrients into the compost. In comprehensive evolution of gaseous emissions, nitrogen loss, and compost maturity, superphosphate addition with 2.5% of initial dry matter was suggested to be used in practice.

Effects of lactic acid on modulating the ammonia emissions in co-composts of poultry litter with slaughter sludge

The aim of this work was to study the feasibility of lactic acid addition during poultry litter and slaughter sludge composting for controlling NH₃ emissions. The results indicated that lactic acid addition reduced NH₃ emissions and promoted the maturity of the composting product. Compared to the blank, nitrogen loss in the form of NH₃ emissions in the 0.4%, 0.7%, and 1.0% lactic acid treatments decreased by 3.36%, 8.29%, and 14.65%, respectively. Moreover, lactic acid addition promoted the relative abundance of Lactobacillales, while the microbial community of the blank was dominated by Bacillales. The mechanism behind the control of NH₃ emissions via the addition of lactic acid involved the secretion of large amounts of lactic acid by Lactobacillales, which lowers the pH of the initial compost pile. This study suggests that lactic acid is a suitable additive for composting.

Effect of microplastics on greenhouse gas and ammonia emissions during aerobic composting

The aim of this study was to investigate the effect of polyethylene (PE), polyvinyl chloride (PVC) and polyhydroxyalkanoate (PHA) microplastics on greenhouse gas and ammonia emissions during 60 days composting. PE, PVC and PHA microplastics were respectively mixed with the cow manure; and a treatment without microplastics was used as the control. Compared to the control, PE and PVC inhibited organic matter degradation. Conversely, PHA accelerated temperature increases and organic matter degradation. Meanwhile, PE and PHA aggravated CH₄ and NH₃ emissions by 7.9-9.1% and 20.9-33.9%, respectively. PVC decreased CH₄ and NH₃ emissions by 6.6% and 30.4%, respectively. Additionally, the N₂O emissions of the PE and PVC treatments were higher than those of the control while PHA decreased N₂O emissions by 11.8%. Furthermore, PE, PVC and PHA microplastics reduced the NO₃^--N contents and compost maturity. The results indicated that microplastics reduced compost quality while the effects of microplastics on greenhouse gases and ammonia emissions were related to their sources.

Exploring the microbial mechanisms of organic matter transformation during pig manure composting amended with bean dregs and biochar

This study researched the impacts of biochar (B) and bean dregs (BD) on organic matter degradation and humification, as well as the bacterial community and functional characteristics during pig manure (PM) composting. The temperature, pH, and dissolved organic carbon (DOC) were reached the maturity of compost. Results indicated that BD + B treatment promoted organic matter degradation and increased humic acid content by 19.5-25.1% from the control (CK). Additionally, the bacterial communities were determined by high-throughput sequencing, and their metabolic functions were evaluated through the phylogenetic investigation of communities by reconstructing unobserved states (PICRUSt). BD + B influenced the microbial community structure of compost, and the PICRUSt results indicated that BD + B strengthened the metabolism of carbohydrates and amino acids. Redundancy analysis (RDA) was conducted, and a positive correlation was observed between organic matter transformation and temperature, pH, DOC, and community structure. Therefore, regulating these compost properties can effectively promote organic matter transformation during composting.

Evolution of phytotoxicity during the active phase of co-composting of chicken manure, tobacco powder and mushroom substrate

This study systematically investigated the phytotoxicity of chicken manure co-composted with tobacco powder and mushroom substrate on seed germination during active phase of composting. All compost products met the sanitation requirements specified in the Chinese national standard; however, only the mushroom substrate compost satisfied the maturity standard. From day 28, the composting entered the end of active phase and the concentrations of K+, Zn2+, Na+, Cu2+ and Fe3+ decreased gradually. Redundancy analysis indicated that the germination index, catalase and peroxidase activities was positively correlated with K+, Zn2+, Na+, Cu2+, Fe3+ and NO3--N, and negatively correlated with NH4+-N, Mg2+ and Ca2+, among which the most significant ions were Fe3+, Mg2+ and Zn2+ for all treatments. The malondialdehyde concentration of germinated seeds had adverse correlation with the above ions parameters.

Effects of calcium magnesium phosphate fertilizer, biochar and spent mushroom substrate on compost maturity and gaseous emissions during pig manure composting

This study used a laboratory-scale system to investigate the effects of calcium magnesium phosphate fertilizer (CaMgP), biochar, and spent mushroom substrate (SMS) on compost maturity and gasous emissions during pig manure composting. The results showed that the addition of CaMgP, Biochar or SMS had no negative effect on the quality and maturity of compost, and all three additives could reduce the emissions of ammonia (NH₃), hydrogen sulfide (H₂S), dimethyl sulfide (Me₂S) and dimethyl disulfide (Me₂SS). Among them, the effect of adding CaMgP on NH₃ emission reduction was the most obvious, reduced 42.90%. The emission reduction of CaMgP to H₂S was similar to that of SMS, which decreased by 34.91% and 32.88% respectively. The emission reduction effects of the three additives on Me₂S and Me₂SS were obvious, all of which were over 50%. However, only adding SMS reduced the N₂O emission by 37.08%.

Effects of external additives: Biochar, bentonite, phosphate, on co-composting for swine manure and corn straw

Composting is an acceptable and economically feasible process for recycling agricultural biomass waste. The addition of external additives to adjust the process of composting has been attracted lots of research attention. To investigate the effects of external additives on nutrients transformation process of composting, a laboratory reactors scale co-composting based on swine manure and corn straw (CK) with the additives of phosphate (MP), calcium bentonite (CB) and biochar (BC) were performed for 30 days. The results showed the addition of phosphate and biochar could contribute to accelerating temperature rise and shorten the thermophilic phase. The germination index (GI) of MP and BC achieved 180% and 150%, respectively. The excitation-emission matrix (EEM) demonstrated the intensities of the peak C (humic acids) of the MP treatment was 829.5, and the P_V,n/P_III,n value (9.59) of MP treatment was particularly higher compared to other three treatments according to the fluorescence regional integration (FRI) analysis. The Fourier Transform Infrared spectroscopy (FTIR) indicated the rate of decomposition of aliphatic C substances was higher than that of aromatic C substances. According to the X-ray diffraction (XRD) spectra results, characteristic peaks at both 16° and 22° were decreased, indicating cellulose and amorphous components were degraded. It further proved the formation of struvite component in MP treatment. Therefore, based on the maturity indicators, EEM and XRD results, phosphate is an efficient additive and recommended for swine manure and corn straw co-composting.

Effects of microbial culture and chicken manure biochar on compost maturity and greenhouse gas emissions during chicken manure composting

The effects of chicken manure biochar (CMB) and chicken manure integrated microbial consortium (CMMC) as co-amendments were assessed on compost maturity and reduction of greenhouse gases and ammonia (NH₃) emissions during chicken manure composting. Composting was conducted using six combinations of CMB and CMCC (0 % CMB + 0 % CMMC, 0 % CMB + 10 % CMMC, 2 % CMB + 10 % CMMC, 4 % CMB + 10 % CMMC, 6 % CMB + 10 % CMMC, 10 % CMB + 10 % CMMC added on a dry weight basis) in six polyvinyl chloride composting reactors for 42 days under an aerobic environment. Co-amendment of CMB and CMMC extended the thermophilic stage and promoted compost maturity. The release of greenhouse gases [nitrous oxide (N₂O) and methane (CH₄)] and NH₃ from treatments co-amended by CMB and CMMC were reduced by 19.0-27.4 %, 9.3-55.9 % and 24.2-56.9 %, respectively, compared with the control. In addition, a redundancy analysis showed that the C/N ratio and temperature had a significant relationship with greenhouse gases and NH₃ emissions among all physiochemical characteristics.

Effects of moisture and carbon/nitrogen ratio on gaseous emissions and maturity during direct composting of cornstalks used for filtration of anaerobically digested manure centrate

This study investigated the maturity and gaseous emission during direct composting of cornstalks used as organic media for filtration of anaerobically digested manure centrate. Effects of moisture and carbon/nitrogen (C/N) ratio on composting performance were evaluated. Results show that cornstalks could effectively retain suspended solids and organic matter in digested manure centrate to lower their C/N ratio and attain microbial inoculation. Filtered cornstalks became more compostable when their moisture decreased from 76% to 60% or C/N ratio increased from 12 to 24. Nevertheless, such adjustment aggravated the emission of greenhouse and odours gases during composting. Regardless of composting conditions, the phylum Firmicutes was the most dominant with reduced abundance during composting. Similar reduction also occurred to several abundant phyla, including Atribacteria, Synergistetes and Euryarchaeota. By contrast, the phylum Bacteroidetes, Chloroflexi, Proteobacteria and Actinobacteria enriched as composting progressed. In addition, compost maturity was insignificantly affected by matrix moisture and C/N ratio.

Compost supplementation with nitrogen loss and greenhouse gas emissions during pig manure composting

This research investigated the influence of biochar (B) and bean dregs (BD) amendments on carbon and nitrogen losses through greenhouse gas (GHG) emissions during pig manure (PM) composting. The treatments included 15% BD, 10% B and 15% BD+10% B (w/w dry basis of PM) amendments in the compost, whereas the CK (control) lacked any additives. The NH₄⁺-N, C/N and germination index (GI) of the end products ensured compost maturity. Compared with the CK, the 15% BD amendment increased the total nitrogen content (TKN) of the final product by 8.05% but also increased NH₃ (54.98%) and GHG emissions (40.35%) as well as nitrogen loss (25.62%). Furthermore, the combined treatment of 15% BD+10% B improved the TKN (2.83%) of the end product and controlled NH₃ emissions (33.71%), GHG emissions (29.56%) and nitrogen loss (24.26%) while increasing CO₂ only with the 15% BD amendment. Therefore, the combination of BD+B was recommended.

The Characteristics of Carbon, Nitrogen and Sulfur Transformation During Cattle Manure Composting-Based on Different Aeration Strategies

This study aimed to investigate the characteristics of gaseous emission (methane-CH₄, carbon dioxide-CO₂, nitrous oxide-N₂O, nitric oxide-NO, hydrogen sulfide-H₂S and sulfur dioxide-SO₂) and the conservation of carbon (C), nitrogen (N), and sulfur (S) during cattle manure composting under different aeration strategies. Three aeration strategies were set as C60, C100, and I60, representing the different combinations of aeration method (continuous-C or intermittent-I) and aeration rate (60 or 100 L·min^-1·m^-3). Results showed that C, N, S mass was reduced by 48.8-53.1%, 29.8-35.9% and 19.6-21.9%, respectively, after the composing process. Among the three strategies, the intermittent aeration treatment I60 obtained the highest N₂O emissions, resulting in the highest N loss and greenhouse gas (GHG) emissions when the GHG emissions from power consumption were not considered. Within two continuous aeration treatments, lower aeration rates in C60 caused lower CO₂, N₂O, NO, and SO₂ emissions but higher CH₄ emissions than those from C100. Meanwhile, C and N losses were also lowest in the C60 treatment. H₂S emission was not detected because of the more alkaline pH of the compost material. Thus, C60 can be recommended for cattle manure composting because of its nutrient conservation and mitigation of major gas and GHG emissions.

Influence of FeONPs amendment on nitrogen conservation and microbial community succession during composting of agricultural waste: Relative contributions of ammonia-oxidizing bacteria and archaea to nitrogen conservation

Composting amended with iron oxide nanoparticles (FeONPs, α-Fe₂O₃ and Fe₃O₄ NPs) were conducted to study the impacts of FeONPs on nitrogen conservation and microbial community. It was found that amendment of FeONPs, especially α-Fe₂O₃ NPs, reduced total nitrogen (TN) loss, and reserved more NH₄⁺-N and mineral N. Pearson correlation analysis revealed that decrease of ammonia-oxidizing bacteria (AOB) in FeONPs treatments played more important role than ammonia-oxidizing archaea (AOA) in reserving more NH₄⁺-N and mineral N, and reducing TN loss. Bacterial community composition at phylum level did not shift with addition of FeONPs. Firmicutes, Actinobacteria, and Proteobacteria were the three most dominant phyla in all treatments. Overall, this study provides a method to reduce TN loss and improve mineral N reservation during composting, and gives a deep insight into the role of AOB and AOA in nitrogen transformation.

Effects of inoculation amount and application method on the biodrying performance of municipal solid waste and the odor emissions produced

The effects of inoculation amount and application method on the biodrying of municipal solid waste (MSW) was investigated in this study. Results showed that a low level (5%) of inoculation with mature compost significantly improved the biodrying index (4.96), while adding greater amounts decreased the biodrying performance by increasing the volatile solid degradation rate. Covering the pile with inoculation material resulted in the highest water removal (72.7%) and greatest water content reduction (from 60.2% to 17.7%). Meanwhile, first covering and then incorporating the inoculation material into the biodrying pile did not improve biodrying performance. Clearly, addition of varying amounts of inoculation material via different application methods enhanced cellulose degradation rates by 2.3-14.2%. Using 10% inoculation material reduced the NH₃ emissions by 39.1-54.3% regardless of inoculation method, inoculation amount had a greater effect on NH₃ emissions than that of inoculation method. The covering inoculation material could reduce 65.08% H₂S emission, the inoculation method had a greater effect on H₂S emissions than that of inoculation amount. Given the comprehensive considerations of emission reduction and biodrying performance, a covering of 10% inoculating material is a suitable approach to improve biodrying performance and mitigate odorous gases emissions.

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

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

Use of mature compost as filter media and the effect of packing depth on hydrogen sulfide removal from composting exhaust gases by biofiltration

A study was conducted to investigate the utilization of mature compost as a biofilter medium for the removal of hydrogen sulfide (H₂S) from the exhaust gases of the composting process. Source-selected kitchen waste from municipal solid waste was composted in a reactor, and the exhaust gas was passed through a biofilter packed with a 1:4 (wet weight) mixture of mature compost and sand. Two treatments were applied under sterilized and unsterilized conditions to quantify the contribution of microbial activity. The effect of packing depth on H₂S removal efficiency was also studied. A global H₂S removal efficiency of 51% was obtained in the biofilter for loading rates in the range of 0-429 mg H₂S m^-3 h^-1. The adsorption capacity was the main factor affecting H₂S removal efficiency, contributing 64.2% to the total removal efficiency, with microbial activity contributing 35.8%. The relationship between the cumulative amount of H₂S removed and the packing height was well-described by a linear equation. The equation indicated that 99% H₂S removal efficiency could be achieved using a packing height of 96 cm for unsterilized packing material or 158 cm for sterilized packing material.

Comparing the effects of three in situ methods on nitrogen loss control, temperature dynamics and maturity during composting of agricultural wastes with a stage of temperatures over 70 °C

The study investigated the effects of three in situ methods for controlling nitrogen loss and maturity with different mechanisms: struvite-based addition (K₂HPO₄ and MgO, MP), woody peat addition (WP) and intermittent aeration (IA), during composting of vegetable waste (cucumber vine) with temperature over 70 °C to inactivate potential viral pathogens. The experiment was conducted in a 200 L pilot-scale composting system, with which temperature and ammonia emission were recorded in real time, and solid samples were collected and analyzed during the process. The results indicated that the methods of MP and IA reduced the total nitrogen loss by 27.5% and 16.1%, respectively, without inhibitory effects on the temperature, nutrient availability and maturity. The WP method significantly decreased the nitrogen loss but could not maintain the thermophilic stage over 70 °C, because of its influence on the material physio-chemical characteristics caused by woody peat addition. In conclusion, all three methods could promote the maturity process, and 20 days should be adequate for vegetable waste composting with a good nutrient availability. Considering the two factors of reducing nitrogen loss and achieving high temperatures together, we recommended the struvite-based controlling method with the mechanism of chemisorption to reduce nitrogen loss during vegetable waste composting that requires temperatures over 70 °C.

Effects of phosphogypsum, superphosphate, and dicyandiamide on gaseous emission and compost quality during sewage sludge composting

This study investigated the effects of phosphogypsum, superphosphate, and dicyandiamide on gaseous emission and compost quality during sewage sludge composting. Results showed that phosphogypsum reduced ammonia (NH₃) and methane (CH₄) emissions but increased nitrous oxide (N₂O) emission. Superphosphate simultaneously reduced NH₃, N₂O and CH₄ emissions. Dicyandiamide markedly reduced N₂O emission during composting. Combination of phosphogypsum and dicyandiamide reduced CH₄ and N₂O emissions by 75.6% and 86.4%, while NH₃ emission was increased by 22.0%. Combination of superphosphate and dicyandiamide reduced NH₃, CH₄ and N₂O emissions by 12.3%, 81.0% and 88.2%, respectively. More importantly, with the addition of 10% initial raw materials, phosphogypsum and superphosphate conserved nitrogen and improved compost quality by introducing additional nutrients.

Comparative evaluation of the use of acidic additives on sewage sludge composting quality improvement, nitrogen conservation, and greenhouse gas reduction

The aim of this study was investigated the effects of acidic additives apple pomace (AP), citric acid (CA), elemental sulphur (ES), phosphoric acid (PA), magnesium hydrogen phosphate (PM), and calcium superphosphate (CP)) on N conservation and greenhouse gas (GHG) emissions during sewage sludge composting. Results showed that adding the additives have no negative effects on compost hygienisation, but could improve the N conservation. Treatments with additives showed 2.56-5.48% N loss of initial N, which is lower than the control (9.73%). Compared to other compost products, ES- and PA-treatments had the lower NH₃ volatilizations (0.80% and 0.98% of initial N, respectively) and germination index values (0.52 and 0.74, respectively), while the higher N₂O emissions (2.48% and 2.29% of initial N, respectively) and salinities. Comprehensive evolution of N loss, GHG emissions and compost maturity in this study, the feasibility of using AP, CA, and PM in high-quality compost production is promising.

Performance evaluation of gaseous emissions and Zn speciation during Zn-rich antibiotic manufacturing wastes and pig manure composting

In this study, the co-composting performance of Zn-rich antibiotic manufacturing wastes (AMW) and pig manure (PM) was evaluated. Four treatments, representing 2.5%, 5%, 10% and 20% of AMW (of PM dry weight) and control without AMW, were established during composting. Results suggested that the temperature, pH, electrical conductivity, NH₄⁺-N and germination index in end product met the maturity and sanitation requirement. More than 99% of residual antibiotic was removed. Compared with PM composting alone, the cumulative CH₄ and N₂O emissions in AMW composting increased by 13.46-79.00% and 10.78-65.12%, respectively. While the higher mixing ratios of AMW (10% and 20%) presented a negative impact on composing by inhibiting organic matter (OM) degradation and higher NH₃ emissions. The AMW had highly bioavailable Zn, but the exchangeable faction of Zn significantly decreased with the composting progress.

Effects of C/N ratio and earthworms on greenhouse gas emissions during vermicomposting of sewage sludge

The emissions of greenhouse gases (CO₂, CH₄, and N₂O) during bio-stabilization of sewage sludge under different C/N ratios with/without Eisenia fetida were evaluated in this study. Vermicomposting led to the more significant reductions of pH, TOC and C/N ratio compared to the control treatment without earthworms. C/N ratio had a significant effect on the emission of N₂O, whereas its influences on CO₂ or CH₄ emission were not obvious. Earthworms reduced the CH₄ emission greatly, although the CO₂ emission was not affected by earthworms. Furthermore, a higher emission of N₂O was observed in vermicomposting compared to the control. Both the C/N ratios and earthworms exerted statistically significant effects on the total GHG emission. Vermicomposting could enhance the degradation of organics and accelerate the mineralization process of nitrogen, whereas the increase in the C/N ratio could reduce GHG emission during vermicomposting of sewage sludge.

Impact of vermiculite on ammonia emissions and organic matter decomposition of food waste during composting

This study investigated the effects of adding vermiculite to the food waste composting process. Four treatments with varying vermiculite percent compositions, 0%, 5%, 10% and 15% (w/w, wet weight of food waste basis) mixed with initial food waste were designed and then composted for 42 days. Results show that adding vermiculite prolongs the thermophilic phase, speeds up the organic matter loss, reduces the NH₃ emissions and electrical conductivity values. Compared to the control, the amount of nitrogen loss through NH₃ emissions in the treatments of 5%, 10% and 15% vermiculite decreased by 9.89%, 26.39% and 18.65%, respectively. Finally this work suggests that vermiculite is a suitable additive for food waste composting, especially when the makeup of the compost is 10% vermiculite.

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.