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

The bifunctional impact of polylactic acid microplastics on composting processes and soil-plant systems: Dynamics of microbial communities and ecological niche competition

Although extensive research has been conducted on the environmental impact of microplastics (MPs), their effects on microorganisms during the composting process and on the compost-soil system remain unclear. Our research investigates the microbial response to polylactic acid microplastics (PLAMPs) during aerobic composting and examines how compost enriched with PLAMPs affects plants. Our findings reveal that PLAMPs play a dual role in the composting process, influencing microorganisms differently depending on the composting phase. PLAMPs reduce the relative abundance of sensitive bacterial ASVs, specifically those belonging to Limnochordaceae and Enterobacteriaceae, during composting, while increasing the relative abundance of ASVs belonging to Steroidobacteriaceae and Bacillaceae. The impact of PLAMPs on microbial community assembly and niche width was found to be phase-dependent. In the stabilization phase (S5), the presence of PLAMPs caused a shift in the core microbial network from bacterial dominance to fungal dominance, accompanied by heightened microbial antagonism. Additionally, these intricate microbial interactions can be transferred to the soil ecosystem. Our study indicates that composting, as a method of managing PLAMPs, is also influenced by PLAMPs. This influence is transferred to the soil through the use of compost, resulting in severe oxidative stress in plants. Our research is pivotal for devising future strategies for PLAMPs management and predicting the subsequent changes in compost quality and environmental equilibrium.

Contributions of the bacterial communities to the microcystin degradation and nutrient transformations during aerobic composting of algal sludge

Aerobic composting is a useful method for managing and disposing of salvaged algal sludge. To optimize the composting process and improve compost quality, it is necessary to understand the functions and responses of microbial communities therein. This work studied the degradation process of organic matter and the assemblage of bacterial communities in algal sludge composting via 16S rRNA amplicon sequencing. The results showed that 77.08% of the microcystin was degraded during the thermophilic stage of composting, which was the main period for microcystin degradation. Bacterial community composition and diversity changed significantly during the composting, and gradually stabilized as the compost matured. Different composting stages may be dominated by different module groups separately, as shown in the co-occurrence networks of composting bacterial communities. In the networks, all bacteria associated with microcystin degradation were identified as connectors between different module groups. The algal sludge composting process was driven primarily by deterministic processes, and the main driving forces for bacterial community assembly were temperature, dissolved organic carbon, ammonium, and microcystin. At last, by applying the structural equation modeling method, the bacterial communities under influences of physiochemical properties were proved as the main mediators for the microcystin degradation. This study provides valuable insights into the optimization of bacterial communities in composting to improve the efficiency of microcystin degradation and the quality of the compost product.

Enhancing nitrogen transformation and humification in cow manure composting through psychrophilic and thermophilic nitrifying bacterial consortium inoculation

Excessive nitrogen release during composting poses significant challenges to both the environment and compost quality. Biological enhancement of humification and nitrogen conservation is an environmentally friendly and cost-effective approach to composting. The aim of this study was to develop a psychrophilic and thermophilic nitrifying bacterial consortium (CNB) and investigate its role in nitrogen transformation and humification during cow manure composting. Analysis revealed that CNB inoculation promoted microbial proliferation and metabolism, significantly increased the number of nitrifying bacteria (p < 0.05), and elevated the activity of nitrite oxidoreductase and nxrA gene abundance. Compared to the control, CNB inoculation promoted the formation of NO3--N (77.87-82.35 %), while reducing NH3 (48.89 %) and N2O (20.05 %) emissions and increased humus content (16.22 %). Mantel analysis showed that the higher abundance of nitrifying bacteria and nxrA facilitated the nitrification of NH4+-N. The improvement in nitrite oxidoreductase activity promoted NO3--N formation, leading to increased humus content and enhanced compost safety.

Plastic particles in urban compost and their grain size distribution

Gathering information on plastic particles in composts and the processes they undergo is important in terms of potentially limiting their further entry into the environment, for example, in improving the fertilising properties of soils. Microplastics (MPs) were determined in composts produced from urban greenery. They are present in decreasing order: polyethylene terephthalate, polystyrene, polyethylene, and polypropylene. The determination of polymers and additives used to improve their properties was performed by pyrolysis and gas chromatography with mass spectrometric detection (Py-GC/MS). Additives and microplastics are most concentrated in composts in the 0.315-0.63 and 0.63-1.25 mm grain size class, together with the carbon contained in the compost dry matter. Additives form 0.11-0.13% of MPs in dry matter of compost. The average concentration of microplastics in the particle size class from 0.63 to 1.25 mm is 2434 ± 224 mg/kg; in the total sample of composts, it is 1368 ± 286 mg/kg of P-MPs. For composts with particle size <2.5 mm, a relationship between the C/N ratio and the plastic particle concentration was statistically significant. It documents a similar behaviour of lignocellulose and plastic particles during the degradation processes. A relationship between the concentration of polymer markers and additives in the compost dry matter and their concentrations in the leachate has been demonstrated. The leachability from compost is higher for additives than for chemical compounds originating from the decomposition of the main components of MPs. The suitability of the use of the compost for agricultural purposes was monitored by the germination index (GI) for watercress. The lowest value of the GI was determined in the particle size class from 0.63 to 1.25 mm. The leachability of polymer markers and additives alone cannot explain the low GI value in this grain size class. The GI value is also influenced by the leachability of chemical compounds characterised by the value of dissolved organic carbon (DOC) and water-leachable nitrogen (Nw). A statistically significant dependence between DOC/Nw and the germination index value was found.

Novel perspective on qualitative assessment of swine manure compost maturity using organic carbon density fractions

Mature compost is safe and stable, yet quality assessments are challenging owing to current maturity indicators' limitations. This study employed density fractionation to separate organic carbon into light and heavy fractions, offering a new perspective for assessing maturity. Results showed that light fraction organic carbon progressively transitioned into heavy fraction during composting, reducing the proportion of total organic carbon from 82.82% to 44.03%, while heavy fraction organic carbon increased to 48.58%. During the first seven days, the reduction rate of light fraction organic carbon decreased slowly, while the increase rate of heavy fraction declined sharply, levelling off thereafter. Light/heavy fraction organic carbon ratio was significantly correlated with existing maturity indicators (carbon/nitrogen ratio, humic acid/fulvic acid ratio, biological growth-related indicators), with the ratio below 1.33 serving as a potential compost maturity marker. Thus, given its simplicity and reliability, organic carbon density fractions is an innovative indicator for compost maturity assessments.

Humification and fungal community succession during pig manure composting: Membrane covering and mature compost addition

The objective of this study was to elucidate the combined effect of a semi-permeable membrane (M) and mature compost (MC) on humification and fungal community succession in pig manure composting. Compared with the control, the concentrations of humic substances (HSs) increased by 44.54 % (M + 15 % MC) and 43.90 % (M). During the thermophilic phase, Aspergillus (67.26 %) was the dominant genus in the M + 15 % MC treatment. Membrane covering increased the relative abundance (RA) of other phyla (except for Ascomycetes and Basidiomycetes) on the 14th day and Basidiomycetes on the 80th day in M treatment. Humic acid, HSs were positively correlated with the RA of genera Myceliophthora, Kernia, and Mycothermus. Myceliophthora was the key genus in the M + 15 % MC treatment on the 80th day. The results showed that 15 % MC addition under membrane covering optimizes the quality of composting products.

Enhancing the transformation of carbon and nitrogen organics to humus in composting: Biotic and abiotic synergy mediated by mineral material

To investigate the conversion of carbon and nitrogen organic matter to humus mediated by mineral material additives through biotic and abiotic pathways, three chicken manure composting experiments were conducted using calcium superphosphate (CS) and fly ash (FA). Results showed that CS and FA promoted carbon and nitrogen organic degradation and improved compost maturity. The ratio of humic acid-like to fulvic acid-like substances for FA (30) was significantly higher than for control (18) and CS (13). Excitation-emission-matrix spectra and parallel factor analysis identified a higher transformation of protein-like components into humic-like components in FA. Network analysis showed that CS improved compost maturity by promoting the rapid conversion of humus precursors to humus, while FA increased the richness and diversity of the microbial community, such as Chloroflexi, the unique phylum in FA. Overall, CS and FA facilitated the humification process through abiotic and biotic pathways, and FA had better humification performance.

Optimization of organic solid waste composting process through iron-related additives: A systematic review

Composting is an environmentally friendly method that facilitates the biodegradation of organic solid waste, ultimately transforming it into stable end-products suitable for various applications. The element iron (Fe) exhibits flexibility in form and valence. The typical Fe-related additives include zero-valent-iron, iron oxides, ferric and ferrous ion salts, which can be targeted to drive composting process through different mechanisms and are of keen interest to academics. Therefore, this review integrated relevant literature from recent years to provide more comprehensive overview about the influence and mechanisms of various Fe-related additives on composting process, including organic components conversion, humus formation and sequestration, changes in biological factors, stability and safety of composting end-products. Meanwhile, it was recommended that further research be conducted on the deep action mechanisms, biochemical pathways, budget balance analysis, products stability and application during organic solid waste composting with Fe-related additives. This review provided guidance for the subsequent targeted application of Fe-related additives in compost, thereby facilitating cost reduction and promoting circular economy objectives.

Brown sugar as a carbon source can make agricultural organic waste compost enter the secondary thermophilic stage and promote compost decomposition

To enhance the efficiency of composting agricultural organic waste (AOW), this study aimed to examine the impact of inoculating tomato straw compost with two distinct microbial agents: ZymoZone (ZZ), a composite microbial agent derived from the straw compost and Effective Microorganisms (EM), a commercial microbial agent. Furthermore, in order to reactivate the microorganisms within the compost during the initial high temperature phase, 10% brown sugar was introduced as a carbon source. The objective of this addition was to assess its influence on the composting process. The findings revealed that compared to the control (CK) group, the ZZ and EM treatments extended the first high-temperature phase by 2 and 1 day, respectively. Furthermore, with the addition of 10% brown sugar, the ZZ and EM treatments remained in the second high-temperature phase for 8 and 7 days, respectively, while the CK treatment had already entered the cooling stage by then. Notably, the inoculation of microbial agents and the addition of brown sugar substantially augmented the activity of lignocellulose-related hydrolases, thereby promoting the degradation of lignocellulose in the ZZ and EM treatment groups. This was confirmed by FTIR analysis, which demonstrated that the addition of microbial agents facilitated the degradation of specific substances, leading to reduced absorbance in the corresponding spectra. XRD analysis further indicated a notable reduction in cellulose crystallinity for both the ZZ (8.00%) and EM (7.73%) treatments. Hence, the incorporation of microbial agents and brown sugar in tomato straw compost effectively enhances the composting process and improves the quality of compost products.

Effects of oyster shells on maturity and calcium activation in organic solid waste compost

With the rapid development of aquaculture, the production of oyster shells has surged, posing a potential threat to the environment. While oyster shell powder is widely recognized for its inherent alkalinity and rich calcium carbonate content, making it a superior soil conditioner, its role in organic solid waste composting remains underexplored. To investigate the effects of varying concentrations of oyster shell powder on compost maturation and calcium activation, this study employed thermophilic co-composting with acidic sugar residue and bean pulp, incorporating 0% (control), 10% (T1), 20% (T2), 30% (T3), and 40% (T4) oyster shell powder. Findings revealed that appropriate proportions of oyster shell powder significantly enhance temperature stability during composting and elevate maturation levels, notably reducing ammonia emissions between 62.5% and 76.7%. Intriguingly, the calcium in the oyster shell powder was significantly activated during composting, with the 40% addition group achieving the highest calcium activation rate of 48.5%. In summation, the inclusion of oyster shell powder not only optimizes the composting process but also efficiently activates the calcium, resulting in an alkaline organic-inorganic composite soil conditioner with high exchangeable calcium content. This research holds significant implications for promoting the high-value utilization of oyster shells.

The efficient solution to decline the greenhouses emission and enrich the bacterial community during pig manure composting: Regulating the particle size of cornstalk

In present study, four lengths of chopped cornstalks were amended with pig manure respectively for 100 days aerobic fermentation, which aimed to evaluate the impact of different length of agricultural solid wastes on gaseous emission and dominating bacterial community succession and connection. The result revealed that the maximum ammonia volatilization was observed in 5 cm of straw samples attributed to the prominent mineralization, which was opposite to the emission of CH4 and N2O. As for global warming potential, the minimum value was detected in 5 cm of straw samples, which decreased by 5.03-24.75% compared with other samples. Additionally, the strongest correlation and complexity of bacterial community could be detected in 5 cm of straw treatment, representing the most vigorous bacterial metabolic ability could be recorded by optimizing the microbial habitat. Therefore, in order to decline the greenhouse effect in livestock manure composting, the 5 cm of corn straw was recommended.

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

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

Biochar as functional amendment for antibiotic resistant microbial community survival during hen manure composting

The study aim was to reveal the mechanism of impact of two type biochar on composting of hen manure (HM) and wheat straw (WS). Biochar derived from coconut shell and bamboo used as additives to reduce antibiotic resistant bacteria (ARB) in HM compost. The results manifested that effect of biochar amendment was significant to reduce ARB in HM composting. Compared with control, the microbial activity and abundance were increased in both biochar applied treatment, and bacterial community was changed. Additionally, network analysis revealed that biochar amendment increased the quantity of microorganisms related to organic matter degrading. Among them, coconut shell biochar (CSB) played a pioneering role to mitigate ARB to better exert its effects. Structural correlation analysis showed that CSB reduce ARB mobility and promote organic matter degradation via improving beneficial bacterial community structure. Overall, composting with participation of biochar amendment stimulated antibiotic resistance bacterial dynamics. These results evidence practical value for scientific research and lay the foundation for agricultural promotion of composting.

Mechanisms and effects of novel ammonifying microorganisms on nitrogen ammonification in cow manure waste composting

It is essential to reduce nitrogen losses and to improve nitrogen conversion during organic waste composting because of environmental protection and sustainable development. To reveal newly domesticated ammonifying microorganisms (AM) cultures on the ammonification and nitrogen conversion during the composting, the screened microbial agents were inoculated at 5 % concentration (in weight basis) into cow manure compost under five different treatments: sterilized distilled water (Control), Amm-1 (mesophilic fungus-F1), Amm-2 (mesophilic bacterium-Z1), Amm-3 (thermotolerant bacterium-Z2), and Amm-4 (consortium: F1, Z1, and Z2), and composted for 42 days. Compared to control, AM inoculation prolonged the thermophilic phases to 9-19 days, increased the content of NH4+-N to 1.60-1.96 g/kg in the thermophilic phase, reduced N2O and NH3 emissions by 22.85-61.13 % and 8.45-23.29 %, increased total Kjeldahl nitrogen, and improved cell count and viability by 12.09-71.33 % and 66.71-72.91 %. AM was significantly associated with different nitrogen and microbial compositions. The structural equation model (SEM) reveals NH4+-N is the preferable nitrogen for the majority of bacterial and fungal growth and that AM is closely associated with the conversion between NH3 and NH4+-N. Among the treatments, inoculation with Amm-4 was more effective, as it significantly enhanced the driving effect of the critical microbial composition on nitrogen conversion and accelerated nitrogen ammonification and sequestration. This study provided new concepts for the dynamics of microbial in the ammonification process of new AM bacterial agents in cow manure compost, and an understanding of the ecological mechanism underlying the ammonification process and its contribution to nitrogen (N) cycling from the perspective of microbial communities.

Synergetic effect and mechanism of elementary sulphur, MgSO4 and KH2PO4 progressive reinforcement on pig manure composting nitrogen retention

The potential of sulphur (S), MgSO₄ (Mg), and KH₂PO₄ (P) in nitrogen retention, ammonia emission decrease, and microbial community succession during composting needs to be investigated. To achieve this, different levels of S (0, 0.2, 0.4, 0.6, and 0.8% in dry weight) plus Mg and P (S + Mg + P) were progressively added in 70 days pig manure aerobic composting. The results revealed that the amendment increased salinity and lowered pH and dephytotoxication of the product with the increase of S amount. However, no significant inhibition effects were observed on the evolution of the thermophilic phase and product maturity. In addition, the amendment significantly reduced the total NH₃ and N₂O emissions by 29.66%-58.83% and 20.89%-56.53%, increased NH₄⁺ level by 17.31%-73.27% in thermophilic phase and NO₃^- content by 37.12%-54.84% in a mature phase, and elevated the total Kjeldahl nitrogen content by 15.49%-37.35% during the composting. In addition, compared to the control, the supplement markedly encouraged the formation of guanite in the compost product. The S addition stimulated the growth of Anseongella, Actinomadura, Chelativorans, Castellaniella, Luteimonas, and Steroidobacter microbial communities which functioned well in the degradation of nitrogen-containing compounds and organic matter. Evidence from Redundancy Analysis, Firmicutes, Myxococcus, Chloroflexi, Gemmatimonadota, and Deinococcota showed positive correlations with pH. These results imply that adding S-Mg-P amendment encourages the population and activity of specific functional microorganisms, and facilitated the ammonia emission reduction by lowering pH and thus reserved nitrogen through the formation of guanite during composting. The investigation of bacterial community abundance and environmental variables at the phylum and genus levels over time revealed that adding of 0.6% S in conjunction with P and Mg minerals was suitable for nitrogen loss mitigation in composting. The findings suggest using S + Mg + P supplement to conserve nitrogen in pig dung aerobic composting.

Composting pig manure with nano-zero-valent iron amendment: Insights into the carbon cycle and balance

The effectiveness of nano-zero-valent-iron (NZVI) addition during composting of pig manure (PM) was investigated. Different dosages of NZVI were mixed with PM substrate during a 50 days composting process. The results revealed that the higher share of NZVI addition, the higher OM degradation rate is. On contrary, it was observed that the higher share of NZVI addition, the lower the fulvic acid and the humin degradation rate is. Meanwhile, NZVI amendment increased the CO₂ and CH₄ emissions by 29-47 % and 53-57 %, respectively. The in-depth analysis showed that NZVI addition increased the activity of Sphaerobacter and Luteimonas, which eventually led to the degradation of hard-to-degrade OM faster. Additionally, NZVI was found to increase the filtration of microorganisms, reducing the toxicity and hygiene of compost products. No significant improvement in humic substance enhancement was observed during composting with NZVI addition but improved OM degradation.

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.

A full-scale black soldier fly larvae (Hermetia illucens) bioconversion system for domestic biodegradable wastes to resource

Domestic biodegradable wastes (DBW) pose a threat to environmental quality and human health. Bioconversion via black soldier fly larvae (BSFL; Hermitia illucens L.) is an expedient way for converting 'waste to resource' (insect protein and biofertilizer). Although researches abounded in laboratory-reared experiments and bioconversion mechanisms were pertinent, the void of data from actual and full-scale operation restricts the intensification of BSFL technology and its global adoption. Hence, a full-scale BSFL bioconversion system lasting 4 years in Hangzhou (China) was investigated, and the feasibility and efficiency of 15 tonnes of DBW per day were studied. Through continuous technical optimization, the average production of fresh larvae was increased from 8.5% in 2017 to 15.3% in 2020, along with bioconversion rate of final vermicompost decreased from 35.4% to 14.5%. The total biomass reduction rate in 2020 was 68.7 ± 17.4 kg/(m³ d), equivalent to 0.735 ± 0.215 kg/(kg d) in the form of fresh larvae. Crude fat in fresh larvae accounted for 13.4%, and crude protein accounted for 16.2% in which the determined amino acid profile bore a strong resemblance to fish meal only except histidine and tyrosine. Its economic benefits proved the feasibility of this technology, and the profit reached up to 35.9 US$ per tonne of DBW in 2019. In conclusion, BSFL bioconversion system under current 'insect-farm' operation was a promising solution for DBW treatment with value-added waste recycling.

Biochar-amended composting of lincomycin fermentation dregs promoted microbial metabolism and reduced antibiotic resistance genes

Improper disposal of antibiotic fermentation dregs poses a risk of releasing antibiotics and antibiotic resistant bacteria to the environment. Therefore, this study evaluated the effects of biochar addition to lincomycin fermentation dregs (LFDs) composting. Biochar increased compost temperature and enhanced organic matter decomposition and residual antibiotics removal. Moreover, a 1.5- to 17.0-fold reduction in antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs) was observed. Adding biochar also reduced the abundances of persistent ARGs hosts (e.g., Streptomyces, Pseudomonas) and ARG-related metabolic pathways and genes (e.g., ATP-binding cassette type-2 transport, signal transduction and multidrug efflux pump genes). By contrast, compost decomposition improved due to enhanced metabolism of carbohydrates and amino acids. Overall, adding biochar into LFDs compost reduced the proliferation of ARGs and enhanced microbial community metabolism. These results demonstrate that adding biochar to LFDs compost is a simple and efficient way to decrease risks associated with LFDs composting.

Humification improvement by optimizing particle size of bulking agent and relevant mechanisms during swine manure composting

For purpose of clarifying the impact on particle size of bulking agents on humification and relevant mechanisms, different length (<2 cm, 2 cm, 5 cm, 10 cm) of branch and straw were blended with swine manure individually for 100 days aerobic composting. Results demonstrated that, 2 cm and 5 cm of branch and straw promoted the highest degradation of DOC by 41.49 % and 58.42 %, and increased the humic substances by 23.81 % and 55.82 % in maturity stage, respectively, compared with other treatments. As shown in microbial consequence, the maximum relative abundance of humus funguses increased by 99.55 % and 99.92 % at phylum, and 98.95 % and 99.24 % at genus in 2 cm and 5 cm of branch and straw treatment, thus verifying the result in variation of humus content. In a word, particle size could result in obvious impact on humification, and the optimized size were about 2 cm and 5 cm of branch and straw.

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.

Potential of biochar integrated manganese sulfate for promoting pig manure compost humification and its biological mechanism

This study aimed to clarify the effect of the integrated addition of different proportions of biochar (0 and 5%) and MnSO₄ (0, 0.25%, and 0.50%) to pig manure compost. The results indicated the integrated use of biochar (BC) and Mn²⁺ advanced the compost humification. In particular, the integrated use of 0.50% Mn²⁺ and 5% BC showed higher total organic carbon degradation (20.67%) and humic acid production (81.26 g kg^-1) than other treatments. Microbial community analysis showed the integrated use of BC and Mn²⁺ regulated the diversity and community structure of organic matter-mineralizing microbes by maintaining the relative abundance of bacteria Firmicutes (54.62%) and Proteobacteria (38.05%) at high levels during the thermophilic period and boosting those of the fungi of Ascomycota (58.91%) and Actinobacteria (15.60%) during the maturity period of composting. This study illustrated the potential and biological mechanisms of integrating BC and Mn²⁺ as additives in compost humification.

Roles of organic matter transformation in the bioavailability of Cu and Zn during sepiolite-amended pig manure composting

The application of clay minerals facilitates the bioavailability of heavy metals and the humification in livestock manure composting. However, whether the humification plays a critical role in the bioavailability of heavy metals is still unclear. Here, with the addition of sepiolite (SEP), the fractions of Cu and Zn, and the spectral characteristics of humic acids (HAs) during aerobic pig manure composting were investigated. The SEP-amended composting had a decreased peak temperature and an increased electrical conductivity, regardless of the SEP dosage. The seed germination index increased by 15.9 ± 0.5% (p < 0.05) with the appropriate dosage of SEP (6%), indicating a higher maturity and a lower phytotoxicity of the SEP-amended compost. The addition of SEP reduced the water-extractable organic matter (WEOM) content and increased the percentage of HAs by 2.8-10.7%. More interestingly, during SEP-amended composting, the reducible fraction of heavy metals was transformed into the oxidizable fraction, and the bioavailability of Cu and Zn decreased by 11.0-15.9% and 15.4-26.5%, respectively. Ultraviolet-visible (UV-vis) spectra and fluorescence spectra analyses showed that the SUVA₂₅₄ and complex fluorescent components of HAs in the SEP-amended composting increased by 4.4-15.8% and 1.2-9.0%, respectively. Nuclear magnetic resonance (NMR) further confirmed that the addition of SEP increased the aromatic index and percentage of carbonyl-carboxyl C of HAs by 3.4-8.3% and 4.6-5.7%, respectively. The redundancy analyses (RDA) described the SUVA₂₅₄, aromatic index and carbonyl-carboxyl C of HAs had a strong positive correlation with the oxidizable fraction of heavy metals, which was further confirmed by variance partitioning analysis (VPA). Overall, this work suggested that the HAs structure play an important role in the bioavailability of Cu and Zn during SEP-amended composting, potentially providing safe organic fertilizer.

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.

Elucidating the beneficial effects of diatomite for reducing abundances of antibiotic resistance genes during swine manure composting

Diatomite (DE) has been used for nitrogen conservation during the composting of feces but its effects on antibiotic resistance genes (ARGs) and the associated mechanisms are still unclear. In this study, DE was added at three different proportions (0%, 4%, and 8%) to swine manure during composting. The results showed that adding DE helped to reduce the abundances of ARGs and the maximum decrease (88.99%) occurred with the highest dose. DE amendment promoted the transformation of reducible copper into a more stable form, i.e., the residual fraction, which reduced the selective pressure imposed by copper and further decreased the abundances of ARGs. Tn916/1545 and intI1 were critical genetic components related to ARGs, and thus the reductions in the abundances of ARGs may be attributed to the suppression of horizontal transfer due to the decreased abundances of mobile genetic elements (MGEs). The microbial community structure (bacterial abundance and diversity) played key role in the evolution of ARGs. DE could enhance the competition between hosts and non-hosts of ARGs by increasing the bacterial community diversity. Compared with CK, DE amendment optimized the bacterial community by reducing the abundances of the potential hosts of ARGs and pathogens such as Corynebacterium, thereby improving the safety of the compost product. In addition, KEGG function predictions revealed that adding DE inhibited the metabolic pathway and genes related to ARGs. Thus, composting with 8% DE can reduce the risk of ARG transmission and improve the practical value for agronomic applications.

Effect of micronutrient selenium on greenhouse gas emissions and related functional genes during goat manure composting

To explore the effect of microelement selenium on greenhouse gas emission, nitrogen loss and related functional genes during the composting. Selenite and selenate were respectively mixed with goat manure and wheat straw and then composted the mixture without selenium regarded as control. The results indicated adding selenite prolonged the thermophilic phase and improved the organic matter degradation, while the selenate presented the opposite results. Selenite and selenate influenced ammonium transformation while prompting the formation of nitrate. Compared to the control, adding selenite and selenate both decreased NH₃ emissions (by 26.7%-53.1%) and increased the total nitrogen content of compost. The addition of selenium increased mcrA in the early phase of composting, thereby promoting CH₄ emission (by 3.5-18.4%). Meanwhile, adding selenate significantly reduced nirK abundance and consequently reduced N₂O emission. Moreover, selenate added treatment presented the highest compost maturity (88.77%) and the lowest global warm potential (117.46 g/kg CO₂-eq.) among all treatments.

Effects of mineral additives on antibiotic resistance genes and related mechanisms during chicken manure composting

In this study, two typical minerals (diatomite and bentonite) were applied during composting, and their influences on antibiotics, antibiotic resistance genes (ARGs), intI1 and the bacterial communities were investigated. The relative abundance of total ARGs decreased by 53.72% and 59.54% in diatomite and bentonite addition compared with control on day 42. The minerals addition also reduced the relative abundance of intI1, as much as 41.41% and 59.81% in diatomite and bentonite treatments. Proteobacteria and Firmicutes were the dominant candidate hosts of the major ARGs. There was a significant correlation between total ARGs and intI1 during the composting. Structural equation models further demonstrated that intI1 and antibiotics were the predominant direct factors responsible for ARG variations, and composting properties and bacterial community composition also shifted the variation of ARG profiles by influencing intI1. Overall, these findings suggest that diatomite and bentonite could decrease the potential proliferation of ARGs in chicken manure.

Carbon dioxide emission control of a vermicompost process using fly ash

Composting and vermicomposting generate a valuable product rich in plant nutrients and at the same time, reduce environmental pollution. However, along with these processes and in relation to the metabolism of the microorganism and the worms present in the vermicomposting, CO₂ is emitted to the atmosphere, contributing to the greenhouse effect. Taking these issues into account, different masses of fly ash were used to study the control of the CO₂ of the gas coming from a vermicomposting process and to evaluate the possibility of using the adsorbent as fertilizer in the culture of lettuce Lactuca sativa. Along the vermicomposting process, an increase in the concentration of CO₂ emissions was observed, with a maximum level of emission at the day 20 of the process and an average of 770 mg/L in air. After the adsorption process, the CO₂ concentration was lower due to the effect of the fly ash that was able to trap the emitted gas. The percentage of CO₂ adsorption shows maximum values of 55.5, 58.1 and 63.8% with 0.5, 1 and 1.5 kg of fly ash, respectively. The CO₂ uptake capacities of the different loads of fly ash used were 3.39, 7.03 and 6.84 mmol CO₂/g sorbent with 0.5, 1 and 1.5 kg of fly ash, respectively. After five weeks of sowing L. sativa, it was observed that when no fly ash was used in the soil, the length of the stem was 10.2 cm. Then, the length of the stem was 22 cm, and 16 cm when 10% of fly ash was applied and not applied in the adsorption process, getting a significant correlation between the load of fly ash and the length of the stem. The r when fly ash was used in the adsorption process was 0.9817 and 0.9811 when no ash fly was used in the process.

Key factors affecting seed germination in phytotoxicity tests during sheep manure composting with carbon additives

The germination index (GI) was widely applied to evaluate the phytotoxicity of compost. This study investigated the key phytotoxicity factors affecting seed germination in compost by using aqueous extracts in seed germination tests. The relationship between water-soluble substances in compost and seed germination, and their association with the microbial community were identified. In this study, sheep manure (SM) composted along or with three carbon additives (mushroom substrate, MS; cornstalks, CS; garden substrate, GS) for 49 days and, during this time, changes in multiple physical-chemical parameters, carbon and nitrogen matters, germination indexes (GI) and the compost microbiome were monitored. The results showed that all additives decreased water-soluble total nitrogen (TN), ammonium nitrogen (NH₄⁺-N) and low molecular weight organic acids, and significantly improved the seed germination indexes (seed germination rate, radical length and GI). The GI was correlated with water-soluble carbon degradation products (TOC, butyric acid, humic acid) and certain bacteria (Planifilum, Oceanobacillus, Ruminococcaceae_UCG_005 and Saccharomonospora). A structural equation model revealed that the main factors affecting seed germination were TOC (SM compost), acetic acid (SM+MS compost), humic acid (SM+CS compost), and pH (SM+GS compost). Low TOC and low molecular weight organic acids contents and higher humic acid content promoted GI. The research results could provide theoretical basis and measures for directional regulation of compost maturity.

Cattle manure compost humification process by inoculation ammonia-oxidizing bacteria

The effectiveness of newly isolated ammonia-oxidizing bacteria (AOBs; T-AOB-2, M-AOB-4 and MT-AOB-2-4) in promoting organic matter degradation and humification of cattle manure compost was explored. The results show that, compared with the control, the inoculation of AOBs (5%, v/w) promoted the humification process, particularly in the MT-AOB-2-4, which showed the lowest total organic carbon (19.13%) and dissolved organic carbon (2.61%), whereby humic substances (C_EX) and humic acid (C_HA) increased to 89.84 g/kg and 85.20 g/kg, and fulvic acid (C_FA) decreased to 4.63 g/kg. The high-throughput sequencing and quantitative PCR showed that the abundance of Bacillaceae, amoA and nirS had a significant correlation with humification factors. Among the treatments, the inoculation of MT-AOB-2-4 provided the driving force for the composting process by enhancing the bacterial activity and had the most significant effect on the formation of humic substances and the efficiency of organic matter decomposition.

Composting-a solution of eliminating a nitrite-rich wastewater by reusing it as a moisture conditioning agent

Composting could be applied to dispose various organic solid wastes and liquid wastes. Literature suggested that reusing a nitrogen-rich wastewater as a composting moisture conditioning agent could promote the maturity and nitrogen content of compost. However, it's unclear whether a nitrite-rich wastewater could be eliminated by composting because of the toxicity of nitrite. In this study, a nitrite-rich wastewater (STL, pH = 7.9) was reused as a composting moisture conditioning agent. The influence of STL reusing period (i.e., adding STL from the first day of mesophilic, thermophilic, and cooling period, and the addition lasted for 10 days) on composting performance was also discussed. Results revealed that organic matter decomposition was strongly suppressed by high concentration of free nitrous acid when STL was added in mesophilic period, whereas the organic matter hydrolysis was prompted when STL was added in thermophilic and cooling period. STL addition enhanced nitrification at high temperatures during composting, thus increasing the nitrate content of compost by 2-10 times compared with that of the control group (using tap water as a moisture conditioning agent). Nitrite addition also stimulated nitrous oxide emissions yielded by biotic or chemical processes during STL addition, especially under the transient condition at 50°C-55 °C, and resulted in a 28%-39% increase in greenhouse gas emissions compared with that of the control group. Therefore, the composting could be a solution of eliminating a nitrite-rich wastewater by reusing it as a moisture conditioning agent when nitrous oxide emission issue was properly addressed.

Evaluation of cornstalk as bulking agent on greenhouse gases emission and bacterial community during further composting

The aim of current work was to explore the impact of Cornstalk (CS) on greenhouse gaseous emission and maturation during further composting and analyzed its impact on bacterial diversity. Three kinds of immature fertilizers were collected from chicken, pig and dairy manure namely T1, T2 and T3 as control, T4, T5 and T6 were added CS into T1 to T3 and adjusted C/N to 25 namely treatment. The results illustrated that gases (N₂O, CH₄ and NH₃) emission of CS added treatments decreased by 6.39%-24.68%, 10.60%-23.23% and 13.00%-19.58%, respectively. But the CS amendment increased CO₂ emission by 15.53%-30.81%. The mineralization of carbon and nitrogen was mainly correlated to Firmicutes, Actinobacteria, Proteobacteria and Bacteroidota, CS amendment increased abundance by 22.28%, 17.79%, 1.48% and 35.90%, respectively. The strategy of employing CS would be the most feasible approach for recycling of immature manure, considering its compost quality and environmental from farm.

Moisture-Induced Pattern of Gases and Physicochemical Indices in Corn Straw and Cow Manure Composting

This study investigated the altering effect of moisture on the emission pattern of gases and the evolutionary dynamics of physicochemical indices in corn straw and cow manure composting. Exploring this effect was reasonable to unravel the use of moisture as a cheap alternative to control gaseous emissions and improve the final properties of compost. The nutrient dynamics of the compost showed 21.6% losses in total organic carbon content, with a 33.3% increase in total nitrogen content at the end of composting. All the gases (CH4, CO2, N2O and NH3) yielded a common emission pattern despite the differences in moisture content. Except for CH4, the peak and stable emission periods of all the gases were observed on the 5th day (thermophilic phase) and after the 27th day (late mesophilic phase) of composting, respectively. Emission reductions of 89%, 91%, 95% and 100% were recorded for CH4, CO2, N2O and NH3, respectively, during the late mesophilic phase of composting. From the study, the 65% moisture content was efficient in reducing the loss rate of the gasses and nutrient contents of the compost. This study would enable farmers to channel organic residues generated into compost while minimizing pollution and nutrient losses associated with the composting process.

Current status of global warming potential reduction by cleaner composting

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

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

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

Gases emission during the continuous thermophilic composting of dairy manure amended with activated oil shale semicoke

NH₃ and greenhouse gases emission are big problems during composting, which can cause great nitrogen nutrient loss and environmental pollution. This study investigated effects of the porous bulking agent of oil shale semicoke and its activated material on the gases emission during the continuous thermophilic composting. Results showed addition of semicoke could significantly reduce the NH₃ emission by 74.65% due to its great adsorption capacity to NH₄⁺-N and NH₃, further the effect could be enhanced to 85.92% when utilizing the activated semicoke with larger pore volume and specific surface area. In addition, the CH₄ emission in the semicoke and activated semicoke group was also greatly mitigated, with a reduction of 67.23% and 87.62% respectively, while the N₂O emission was significantly increased by 93.14% and 100.82%. Quantification analysis of the functional genes found the abundance of mcrA was high at the massive CH₄-producing stage and the archaeal amoA was dominant at the N₂O-producing stage in all the composting groups. Correlation and redundancy analysis suggested there was a positive correlation between the CH₄ emission and mcrA. Addition of semicoke especially activated semicoke could reduce the CH₄ production by inhibiting the methanogens. For the NH₃ and N₂O, it was closely related with the nitrification process conducted by archaeal amoA. Addition of semicoke especially activated semicoke was beneficial for the growth of ammonia-oxidizing archaea, causing the less NH₄⁺-N transformation to NH₃ but more N₂O emission.

Elucidating the optimum added dosage of Diatomite during co-composting of pig manure and sawdust: Carbon dynamics and microbial community

Six dosages of DM (0%, 2.5%, 5.0%, 10%, 15% and 20%) were added into initial mixtures for 42 days of aerobic composting to investigate the optimum added dosage of Diatomite (DM) during co-composting of pig manure and sawdust. The results showed that adding DM was beneficial for reducing CH₄ emissions and greenhouse gas emission equivalent (GHGE) values by 15.63-24.25% and 14.33-69.08%, respectively. Meanwhile, the main contributor to the GHGE value was N₂O (58.76-75.98%), followed by CH₄ (17.22-29.16%) and NH₃ (6.38-13.36%). Moreover, the maximum values in the degradation of total organic matter and the formation rate of humic acid were 20.46% and 82.19% in 10% DM added treatment (T3), respectively. Furthermore, the increase in spectral parameters, including the specific UV absorbance at 254 nm (SUVA₂₅₄), the specific UV absorbance at 280 nm (SUVA₂₈₀) and Fourier transform - infrared parameters were facilitated by DM amendment. Additionally, the higher values of the relative abundances of Proteobacteria (50.98%) and Bacteroidetes (12.73%), and related metabolisms such as carbohydrate metabolism and amino acid metabolism, as well as the lower value of methane metabolism reported in T3, supported the difference in CH₄ and humification of the two treatments. In conclusion, DM was determined to be an eco-practical additive to improve the quality of end products and reduce potential risks, and the best treatment in this study was 10% added treatment based on dry weight.

Re-using ammonium-rich wastewater as a moisture conditioning agent during composting thermophilic period improves composting performance

A weakly acidic ammonium-rich wastewater (STL) was intended to reuse as a moisture conditioning agent for composting to increase nitrogen content of compost. The influence of adding STL in the mesophilic period (MP), thermophilic period (TP), and cooling period (CP) on composting performance was investigated. Results revealed that organic degradation was strongly suppressed in MP, whereas no difference (p > 0.05) was observed between CP and control group (using tap water as moisture conditioning agent). The hydrolysis and mineralization of organic matter in TP were partly stimulated because reusing STL reduced free ammonia concentrations (<400 mg/L) of windrows. Additionally, the ammonium and nitrate nitrogen content of compost in TP increased by 71% and 425% without additional greenhouse gas emissions compared with control group. Therefore, ammonium-rich wastewater like STL could substitute tap water to condition compost moisture content and increase the nitrogen content of compost during the thermophilic composting period.

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%.

Material flow analysis and life cycle assessment of food waste bioconversion by black soldier fly larvae (Hermetia illucens L.)

This study provided a systematic analysis on material flow and environmental impacts of a food waste (FW) bioconversion plant using black soldier fly larvae (BSFL), with a daily capacity of 15 tons of FW (wet weight). Food waste feed (FWF) used for BSFL bioconversion consisted of 80% FW (collected from households, restaurants, and canteens) and 20% rice hull powder. Material flow analysis conducted on a dry weight basis showed that 6% of FWF was transformed into BSF pre-pupae, 51% was stored in matured compost, and 43% was emitted to the air. Emissions of high environmental concern such as methane, nitrous oxide and ammonia (NH₃) were sampled and quantified by laboratory analysis. The life cycle assessment revealed that the overall impact was 17.36 kg CO₂-eq/t FW for global warming potential, 5.54 kg SO₂-eq/t FW for acidification, 24.05 mol N-eq/t FW for terrestrial eutrophication, 0.54 kg N-eq NH₃/t FW for marine eutrophication, and 0.18 kg PM_2.5-eq/t FW of particulate matter up to 2.5 μm diameter. Moreover, emissions from post-composting, energy consumptions of drying and chemical fertilizer substitution ratio were detected by contribution analysis as the main contributors to those impacts. Finally, sensitivity analysis indicated that the substitution ratio of mineral fertilizer and protein feed as well as energy consumption were the most influential parameters, therefore control of the post-composting process of residual material should be closely monitored because it was responsible for significant environmental load caused by N-related emissions.

Improvement of two-stage composting of green waste by addition of eggshell waste and rice husks

With the development of urban greening and increases in the human population, the production of green waste (GW) has been increasing in China. Although GW is biodegradable, its composting is difficult because of its low degradation rate. This study focuses on how addition of eggshell waste (ESW; at 0, 10, and 20%) and/or rice husks (RH; at 0, 15, and 25%) affects the two-stage composting of GW on the basis of temperature, bulk density, particle-size distribution, pH, nitrogen changes, carbon dioxide emission, organic matter degradation, humic substances, the activities of microorganisms and enzymes, and the phytotoxicity to germinating seeds. The combined addition of 10% ESW and 25% RH produced the highest quality compost in the shortest time. To produce a stable and mature product, two-stage composting of GW required 30 days without additives but only 20 days with the combined addition of 10% ESW and 25% RH.

Gasification filter cake reduces the emissions of ammonia and enriches the concentration of phosphorous in Caragana microphylla residue compost

Nutrient loss is a major problem during agricultural waste composting. This study investigated the impact of gasification filter cake (GFC) addition on gaseous emissions and nutrient loss during composting of chicken manure mixed with Caraganna microphylla straw. The GFC was added to the composting mix at dry weight rates of 0% (GFC₀), 6.25% (GFC_6.25), 12.5% (GFC_12.5), 25% (GFC₂₅) and 50% (GFC₅₀). Overall, GFC_12.5 and GFC₂₅ efficiently enhanced organic matter decomposition, reduced N loss and enriched P and K concentrations during composting, as compared to GFC₀. However, GFC_6.25 did not show a significant effect on organic matter decomposition, while GF_C50 had no effect on N loss. As a result, an overall enhancement of nutrient contents was observed in the final composts of GFC_12.5 and GFC₂₅. These results suggest that the addition of GFC at moderate-rates (i.e. 12.5% and 25%) can enhance nutrient retention and thereby result in a nutrient-rich compost.

Influence of fine coal gasification slag on greenhouse gases emission and volatile fatty acids during pig manure composting

This study was evaluated industrial waste fine coal gasification slag (FCGS) as an additive on pig manure composting by parameters of greenhouse gases, NH₃, volatile fatty acids (VFAs) and maturity. Six treatments of FCGS (0%, 2%, 4%, 6%, 8% and 10%) were added into the mixture raw material and composted 42 days. Results illustrated that the FCGS amendment could prolong sanitation stage and promote the degree of maturity, germination index and C/N ratio during composting. With the increasing amendment of FCGS, GI was increased from 9.97 to 28.45%. Compared with control, increasing of FCGS proportion could reduce the mitigation of global warming potential (N₂O and CH₄), NH₃ and cumulative of VFAs from 8.89-77.04%, 3.81-71.65%, 5.18-28.02% and 8.79-83.33%. Finally, present study results revealed that 10%FCGS could improve composting and reduced the maturity period as well as compost quality, thus recommended as effective dosage for efficient pig manure 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.

Effect of clay on greenhouse gas emissions and humification during pig manure composting as supported by spectroscopic evidence

To evaluate the effect of clay on greenhouse gas (GHGs) emissions and humification during pig manure (PM) composting, two lab-scale composting experiments, a control and a 10% clay treatment, were established. The results showed that adding clay reduced the emissions of CH₄ and N₂O by 45.88% and 86.79%, respectively, promoted the degradation of organic matter (OM) and facilitated the synthesis of humic acid (HA). The spectrum of dissolved organic matter (DOM) indicated that adding clay promoted the formation of aromatic carbon compounds and the degradation of aliphatic carbon. Furthermore, compared with the control, the spectral parameters including the specific UV absorbance at 254 nm (SUVA₂₅₄), the specific UV absorbance at 280 nm (SUVA₂₈₀) and the ration of the area at 435-480 nm and at 300-345 nm (A₄/A₁) of DOM were increased by 5.45%, 3.66% and 29.26%, respectively. Combined with the excitation - emission matrix (EEM) and the percentage fluorescence response (Pi,n), the clay amendment promoted the decomposition of tyrosine and Tryptophan and the formation of humic-like substances, and thus increased humification. The variation in the HA/fulvic acid and the humification index confirmed these results. Therefore, clay amendment is beneficial for reducing GHG emissions, promoting humification and aromatization during pig manure composting.

Enhancing the production of biogas through anaerobic co-digestion of agricultural waste and chemical pre-treatments

Large amounts of agricultural solid wastes (ASWs) and animal dung are produced annually causing serious environmental problem that requires proper treatment. The present study proposes a strategy for optimizing the anaerobic co-digestion of ASWs and cow dung (CD), identifies the key factors governing the co-digestion performance and evaluates the effect of NaHCO₃ alkalinity treatment on improving the economy and performance of anaerobic digestion (AD). The results revealed that the highest cumulative methane production (CMP) of 297.99 NL/kgVS can be generated by co-digestion of ASWs and CD at a ratio of 60:40. Further improvement was achieved via alkalinity treatment with 1.0 g of NaHCO₃/gVS leading to decrease in lignin, cellulose, and hemicellulose contents of feedstock by 3.5%, 10.5% and 15.9%, respectively, converting them to soluble fractions and improving the CMP by 11.2-29.7% based on substrate quality. The improved CMP in the chemically treated substrates reflects a 19% increase in the generated revenue. The kinetics of the AD process was successfully fitted to modified Gompertz model with very low standard deviation residuals (SDR) ≤ 5.21 and R² ≥ 0.979. Results confirm that the proposed strategy is an effective method for producing biogas from co-digestion of ASWs and CD.

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.