Evaluation of total greenhouse gas emissions during sewage sludge composting by the different dicyandiamide added forms: Mixing, surface broadcasting, and their combination

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.

Elucidating carbon conversion and bacterial succession by amending Fenon-like systems during co-composting of pig manure and branch

The essential point of current study was to investigate the effect of a Fenton-like system established by oxalic acid and Fe(II) on gas emission, organic matter decomposition and humification during composting. Branches were pretreated with Fenton reagents (0.02 M FeCl2·4H2O + 1.5 M H2O2) and then adding 10 % oxalic acid (OA). The treatments were marked as B1 (control), B2 (Fenton reagent), B3 (10% OA) and B4 (Fenton-like reagent). The results collected from 80 d of composting showed that adding Fenton-like reagent benefited the degradation of organic substances, as reflected by the total organic carbon and dissolved organic carbon, and the maximum decomposition rate was observed in B4. In addition, the Fenton-like reagent could improve the synthesis of humus characterized by complex and stable compounds, which was consistent with the spectral parameters (SUVA254, SUVA280, E253/E203 and Fourier transform-infrared indicators) of DOC. Furthermore, the functional microbial succession performance and linear discriminant effect size analyses provided microbial evidence of humification improvement. Notably, compared with the control, the minimum value of CH4 cumulation was reported in B4, which decreased by 30.44 %. Concluded together, the addition of a Fenton-like reagent composed by OA and Fe(II) is a practical way to improve the humification. Furthermore, the mechanisms related to the promotion of humification should be investigated from free radicals, functional genes, and metabolic pathways.

Different crystalline manganese dioxide and biochar co-conditioning aerobic composting: Reduced ammonia volatilization and improved organic fertilizer quality

Aerobic composting is a sustainable and effective waste disposal method. However, it can generate massive amounts of ammonia (NH3) via volatilization. Effectively reducing NH3 volatilization is vital for advancing aerobic composting and protecting the ecological environment. Herein, two crystal types of MnO2 (α-MnO2 and δ-MnO2) are combined with biochar (hydrochar (WHC) and pyrochar (WPC), respectively) and used as conditioners for the aerobic composting of chicken manure. Results reveal that α-MnO2 (34.6%) can more effectively reduce NH3 accumulation than δ-MnO2 (27.1%). Moreover, the combination of WHC and MnO2 better reduces NH3 volatilization (48.5-58.9%) than the combination of WPC and MnO2 (15.8-40.1%). The highest NH3 volatilization reduction effect (58.9%) is achieved using the combination of WHC and δ-MnO2. Because the added WHC and δ-MnO2 promote the humification of the compost, the humic acid to fulvic acid ratio (HA/FA ratio) dramatically increases. The combination of WHC and δ-MnO2 doubled the HA/FA ratio and resulted in a net economic benefit of 130.0 RMB/t. Therefore, WHC and δ-MnO2 co-conditioning can promote compost decomposition, improving the quality of organic fertilizers and substantially reducing NH3 volatilization.

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.

Appraising co-composting efficiency of biodegradable plastic bags and food wastes: Assessment microplastics morphology, greenhouse gas emissions, and changes in microbial community

Biodegradable plastic bags (BPBs) to collect food waste and microplastics (MPs) produced from their biodegradation have received considerable scientific attention recently. Therefore, the current study was carried out to assess the co-composting efficiency of biodegradable plastic bags (polylactic acid (PLA) + polybutylene terephthalate (PBAT) + ST20 and PLA + PBAT+MD25) and food waste. The variations in greenhouse gas (GHG) emissions, microbial community and compost fertility were likewise assessed. Compared with the control, PLA + PBAT+ST20 and PLA + PBAT+MD25 both accelerated organic matter degradation and increased temperature. Moreover, PLA + PBAT+ST20 aggravated CH₄ and CO₂ emissions by 12.10 % and 11.01 %, respectively. PLA + PBAT+MD25 decreased CH₄ and CO₂ emissions by 5.50 % and 9.12 %, respectively. Meanwhile, compared with PLA + PBAT+ST20, the combined effect of plasticizer and inorganic additive in PLA + PBAT+MD25, reduced the NO₃^--N contents, seed germination index (GI) and compost maturity. Furthermore, adding BPBs changed the richness and diversity of the bacterial community (Firmicutes, Proteobacteria and Bacteroidetes). Likewise, redundancy analysis (RDA) showed that the co-compost system of BPBs and food waste accelerated significantly bacterial community succession from Firmicutes and Bacteroidetes at the initial stage to Proteobacteria and Actinobacteria at the mature stage, increased co-compost temperature to over 64 °C and extended thermophilic composting phase, and promoted the degradation of MPs. Additionally, according to structural equation model quantification results, the inorganic additive of PLA + PBAT+MD25 had more serious toxicity to microorganisms and had significantly adverse effects on GI through CO₂-C (λ = -0.415, p < 0.05) and NO₃^--N (λ = -0.558, p < 0.001), thus reduced compost fertility and quality. The results also indicated that the BPBs with ST20 as an additive could be more suitable for industrial composting than the BPBs with MD25 as an additive. This study provided a vital basis for understanding the potential environmental and human health risks of the MPs' generated by the degradation of BPBs in compost.

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.

Exploring gaseous emissions and pivotal enzymatic activity during co-composting of branch and pig manure: the effect of particle size of bulking agents

The purpose of current study was to probe the effect of various length of branch on gaseous emissions and vital enzymatic activity. Four lengths (<2 cm, 2 cm, 5 cm, and 10 cm) of clipped branch were mingled with collected pig manure for 100 days aerobic fermentation. The consequence demonstrated that the amendment of 2 cm of branch showed conducive to decline the greenhouse gas emissions, which the CH₄ emissions decreased by 1.62-40.10%, and the N₂O emissions decreased by 21.91-34.04% contrasted with other treatments. Furthermore, the peak degree of enzymatic activities was also observed in 2 cm of branch treatment by the optimizing living condition for microbes. In view of microbiological indicators, the most abundant and complex bacterial community could be monitor in 2 cm of branch composting pile, which verified the microbial facilitation. Summing up, the strategy of 2 cm branch amendment would be recommended.

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.

Role of selenite on the nitrogen conservation and greenhouse gases mitigation during the goat manure composting process

This study aimed to explore the roles of selenite (Se) on nitrogen conservation and greenhouse gases (GHGs) mitigation during the composting process. Six levels of Se(IV) dosages (i.e. 0, 2, 4, 6, 8 and 10 mg/kg) were examined for 80-day composting of goat manure and wheat straw mixtures, where the different blending proportions were marked as T1 (Control), T2, T3, T4, T5 and T6, respectively. The results showed that adding Se(IV) was beneficial for reducing NH₃ by 3.50-42.41% by buffering pH and promoting nitrification. For N₂O, it showed different responses to different Se(IV) dosages, and it was increased by 29.62-71.29% in T2-T4 but reduced by 30.45-69.54% in T5-T6. Methane (CH₄), another main component of GHGs, was increased by 1.35-107.42% by adding 2-10 mg/kg Se(IV). To further evaluate the effect of Se(IV) on GHGs, global warming potential value was calculated, which was 103.32-499.80 and minimum value was in T5. Furthermore, the physicochemical indexes, especially temperature and OM, had vital effects on microbial community. Overall, the results obtained from this study demonstrated that the application of Se (IV) in composting was reasonable to generate Se-rich organic fertilizer, and the 8 mg/kg was suggested from perspectives of nitrogen conservation and GHGs reduction.

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.

Combined addition of biochar and garbage enzyme improving the humification and succession of fungal community during sewage sludge composting

The influences of combination of garbage enzyme and biochar on total organic carbon (TOC) degradation, humification and the fungal succession during sewage sludge (SS) composting were established. Results showed that the GE and BC + GE treatments significantly increased the enzyme activity of fluorescein diacetate hydrolase (FDA) and increased the TOC degradation rate by 9.8% and 21.9% relative to control. The excitation-emission matrix (EEM) combined with the percentage fluorescence response (Pi, n) also proved that the combination of BC and GE promoted fulvic acid-like and humic-like substances production, and thus increased humification. Furthermore, the combination of BC and GE effectively decreased the relative abundance of Unclassified_k_Fugni, while increased the abundance of Ascomycota and Basidiomycota compared with control. The four genera, Pseudeurotium, Talaromyces, Trichoderma, and Penicillium, were the main fungi for the humification. Comparatively, the combined of BC and GE showed the optimal performance for TOC degradation and humification during SS composting.

Pollution control in biochar-driven clean composting: Emphasize on heavy metal passivation and gaseous emissions mitigation

Present study was focus on the pollution control aspect of gaseous mitigation and heavy metal passivation as well as their associated bacterial communities driven by apple tree branch biochar (BB) during sheep manure composting. Six treatment was performed with distinct concentration of BB from 0%, 2.5%, 5%, 7.5%, 10%, and 12.5% as T1 to T6. Compared with compost without additive, biochar-based composting recorded faster thermophilic process (4thd) and longer duration (12-14d), lower gaseous emission in terms of ammonia (5.37-10.29 g), nitrous oxide (0.12-0.47 g) and methane (4.38-30.29 g). Notably highest temperature (65.3 ℃) and active thermophilic duration (14d), minimized gaseous volatilization were detected in 10%BB composting. Aspect of non-degradability and enrichment-concentration properties of heavy metals, the total copper (Cu) and zinc (Zn) were increased (from initial 12.71-17.91 to final 16.36-29.36 mg/kg and 107.39-146.58-161.48-211.91 mg/kg). In view of available diethylene triamine pentacetic acid (DTPA) extractable form, DTPA-Cu and DTPA-Zn from 4.29 to 6.57 and 31.66-39.32 mg/kg decreased to 3.75-4.82 and 23.43-40.54 mg/kg, especially the maximized passivation rate of 46.95% and 56.27% were present in 10%BB composting. Additionally, bacterial diversity of biochar-based composting was increased (1817-2310 OTUs) than control (1686 OTUs) and dominant by Firmicutes (52.75%), Bacteroidetes (28.41%) and Actinobacteriota (13.98%). Validated 10% biochar-based composting is the optimal option for effectively control environmental pollution to obtain hygienic composting.

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.

Influence of reusable polypropylene packing on ammonia and greenhouse gas emissions during sewage sludge composting-a lab-scale investigation

Bulking agents are particularly important for sewage sludge composting. In this study, reusable polypropylene packing (RPP) was mixed with sawdust to improve composting. The effect of the mix ratio of sawdust and RPP on the physicochemical characteristics, nitrogen transformation, and emissions of greenhouse gas (GHG) as well as differences in the germination index values was detected in a lab-scale composting experiment. The results showed that the unique use of RPP as a bulking agent increased the moisture content over 70%, which resulted in poorer porosity and a less efficient O₂ utilization environment and thus suppressed the degradation of organic matter. The highest CH₄ 9275.8 mg and lowest CO₂ 202.6 g emissions were detected after 25 days of composting in the treatment with RPP used as a bulking agent. When the mixing ratio of sawdust and RPP was 1:1, the temperature, oxygen supply, and dissolved organic carbon degradation were improved. The NH₃, N₂O, and CH₄ emissions were reduced by 32.2, 18.3, and 90.7% compared with a treatment with RPP as a unique bulking agent. The RPP had no effect on conserving nitrogen during sludge composting; the total nitrogen loss was reduced from 29.3 to 18.2% when sawdust was mixed with RPP in a ratio of 1:1. Therefore, mixing RPP and sawdust in the dry weight ratio of 1:1 (sawdust: RPP) can be potentially used for reducing composting cost and improving the sewage sludge composting by reducing the amount of sawdust mixed and mitigating GHG and NH₃ emissions.

Alternating magnetic field mitigates N2O emission during the aerobic composting of chicken manure

Nitrous oxide (N₂O) emission is an environmental problem related to composting. Recently, the electric field-assisted aerobic composting process has been found to be effective for enhancing compost maturity and mitigating N₂O emission. However, the insertion of electrodes into the compost pile causes electrode erosion and inconvenience in practical operation. In this study, a novel alternating magnetic field-assisted aerobic composting (AMFAC) process was tested by applying an alternating magnetic field (AMF) to a conventional aerobic composting (CAC) process. The total N₂O emission of the AMFAC process was reduced by 39.8% as compared with that of the CAC process. Furthermore, the results demonstrate that the AMF weakened the expressions of the amoA, narG, and nirS functional genes (the maximum reductions were 96%, 83.7%, and 95.5%, respectively), whereas it enhanced the expression of the nosZ functional gene by a maximum factor of 36.5 as compared with that in CAC. A correlation analysis revealed that the nitrification and denitrification processes for N₂O emission were suppressed in AMFAC, the main source of N₂O emission of which was denitrification. The findings imply that AMFAC is an effective strategy for the reduction of N₂O emission during aerobic composting.

Improving sewage sludge compost process and quality by carbon sources addition

In present study, the effects of carbon sources on compost process and quality were evaluated in the lab-scale sewage sludge (SS) composting. The composting experiments were performed for 32 days in 5 L reactors. The results showed that carbon sources could change the nitrogen conversion and improve the compost quality. Especially, the readily degradable carbon source could promote organic matter degradation, improve nitrogen conversion process and accelerate compost maturation. The addition of glucose and sucrose could increase dissolved organic carbon, CO₂ emission, dehydrogenase activity, nitrification and germination index during the SS composting. That's because glucose and sucrose could be quickly used by microbes as energy and carbon source substance to increase activity of microbes and ammonia assimilation. What's more, the NH₃ emission was reduced by 26.9% and 32.1% in glucose and sucrose treatments, respectively. Therefore, the addition of readily degradable carbon source could reduce NH₃ emission and improve compost maturity in the SS composting.

Effects of urease inhibitors on enzymatic activities and fungal communities during the biosolids composting

This study evaluated the influences of urease inhibitors (UIs) on nitrogen conversion, enzyme activities, and fungal communities during aerobic composting. Results showed that UI addition reduced NH₃ emissions by 22.2% and 21.5% and increased the total nitrogen (TN) content by 9.7% and 14.3% for the U1 (0.5% UI of the dry weight of the mixture) and U2 (1% UI of the dry weight of the mixture) treatments, respectively. The addition of UI inhibited the enzyme activity during thermophilic stage while increased enzyme activity during the cool and maturity stages. Ascomycota, Basidiomycota and unclassified fungi were the main phyla, and Ascomycota increased significantly during the maturity period. Network analysis showed that Aspergillus, Penicillium, Trichoderma, Talaromyces, Peseudeurotium, and Exophiala were the main “connecting” genera. The redundancy analysis (RDA) showed that the fungal community was mainly influenced by temperature, DOC, pH, and urease. The results suggested that UI was an effective additive for nitrogen conservation and the increase of enzyme activity reduce nitrogen loss and promote enzyme activity during biosolids composting.

Adding UI was effective for nitrogen conservation and the increase of enzyme activity during biosolid composting.

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

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

Influence of spent mushroom substrate and molasses amendment on nitrogen loss and humification in sewage sludge composting

The present study included lab-scale sewage sludge (SS) composting amended by molasses and spent mushroom substrate (SMS) in 5 L composting reactor system. The influence of molasses and SMS amendment on nitrogen loss and humification of SS composting was evaluated. The results showed that SMS amendment, especially combination with molasses raised composting temperature, increased CO₂ volatilization, promoted organic matter degradation, improve germination index and humification process. The addition of SMS and molasses contain carbohydrates used as carbon source and energy substance by microorganisms could increase microbial activity and ammonia assimilation. In the SMS + molasses treatments, NH₃ volatilization was reduced by 33.1%–37.3% and N₂O volatilization was only 17.8%–25.4% of that in the control treatment, furthermore, the nitrogen loss rate was reduced by 27.2%–32.2%. Consequently, the addition of SMS and molasses improved the compost maturity and reduced nitrogen loss in the SS composting process.

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.

Effects of dicyandiamide and Mg/P on the global warming potential of swine slurry and sawdust cocomposting

Composting is an emerging strategy for swine slurry treatment; nonetheless, significant greenhouse gases (GHG) emissions may occur during this process. We carried out two separate assays with increasing doses of dicyandiamide (DCD; up to 1.1% w/w) as a nitrification inhibitor and solutions of MgCl₂ and H₃PO₄ (Mg/P; up to 0.09/0.06 mol kg^-1) to promote struvite crystallization in order to assess their efficiencies as additives to decrease GHG emission during swine slurry cocomposting with sawdust (1:1v/v). We monitored the nitrous oxide (N₂O-N), methane (CH₄-C), and carbon dioxide (CO₂-C) emissions and the ammonia (NH₄⁺-N) and nitrate/nitrite (NOx-N) concentrations in compost reactors (35 L) during the first 4-5 weeks of composting. DCD had no effect on CH₄-C and CO₂-C emissions but decreased N₂O-N losses by up to 56% compared with control. However, DCD inactivation was favored by thermophilic conditions and N₂O-N emissions increased to same levels of control after 13 days. Mg/P was effective to decrease N₂O-N losses only at the highest dose, which also sustained higher [NH₄⁺-N] in the compost by the end of the assessment. Nonetheless, the use of 0.09/0.06 mol kg^-1 of Mg/P also decreased CH₄-C and CO₂-C emissions compared with lower doses of Mg/P and unamended treatments. Overall, DCD and Mg/P amendments decreased the global warming potential (GWP) of swine slurry composting by up to 46 and 28%, respectively. The Mg/P application may be also interesting to increase the compost quality by increasing its NH₄⁺-N availability. Graphical abstract.

Different characteristics of greenhouse gases and ammonia emissions from conventional stored dairy cattle and swine manure in China

Livestock manure emits considerable amounts of greenhouse gases (GHGs) and ammonia (NH₃), inducing climate change and air pollution. However, there remains a lack of knowledge in the literature related to GHGs and NH₃ emissions from the manure of various livestock species. This study reports on a field observation we conducted to analyze GHGs and NH₃ emissions of solid stored manure from dairy cattle and swine, which represent the two main livestock species raised in China. Results showed that although dairy cattle manure emitted 521.9% more methane (CH₄) than swine manure, they separately emitted 50.8% and 40.9% less nitrous oxide (N₂O) and carbon dioxide (CO₂) emissions, respectively. With respect to their global warming potential, the GHGs emission from dairy cattle manure was similar to that from swine manure. NH₃ emissions from swine manure were significantly higher, namely, greater by a factor of 2.4 compared to dairy cattle manure. Differences in gas emissions between dairy cattle and swine manure can be explained by differences in the physicochemical characteristics of their manure and their associated microbiological, chemical, and physical processes that produce gas during storage periods. Based on our results, this study highlights the necessity for prospective mitigation strategies to simultaneously decrease GHGs and NH₃ emissions from livestock manure. Our findings provide useful implications for understanding GHGs and NH₃ emissions, which can be used to develop corresponding mitigation strategies for livestock manure management in China.

Exploring the mechanisms of organic matter degradation and methane emission during sewage sludge composting with added vesuvianite: Insights into the prediction of microbial metabolic function and enzymatic activity

Effect mechanisms of organic matter (OM) degradation and methane (CH₄) emission during sewage sludge (SS) composting with added vesuvianite (V) were studied by high-throughput sequencing (HTS) and phylogenetic investigation of communities by reconstruction of unobserved states (PICRUSt). Results show that the addition of V accelerated the OM degradation and decreased the cumulative CH₄ emissions by 33.6% relative to the control. In addition, V significantly decreased the mcrA gene abundance and the methanogen community richness at the genus level. PICRUSt also indicated that V strengthens the microbial metabolic function and enzymatic activity related to OM degradation, and reduced the enzymatic activity related to CH₄ production. Methanogens community variation analysis proved the ratio of carbon and nitrogen and moisture content are the significant variables affecting CH₄ emissions. Thus, optimizing the ratio of carbon and nitrogen and moisture content will decrease CH₄ emission during SS composting.

Beneficial influences of pelelith and dicyandiamide on gaseous emissions and the fungal community during sewage sludge composting

Reducing the emissions of NH₃ and greenhouse gases (GHGs) during composting is essential for improving compost quality and controlling environmental pollution. This paper investigates the effects of pelelith (P) combined with dicyandiamide (DCD) on gaseous emissions and the fungal community diversity during sewage sludge (SS) composting. Results showed that the P and P + DCD treatments decreased the cumulative gaseous emissions by 41% and 22% for NH₃, 21% and 34% for N₂O, and 31.5% and 33.0% for CH₄, respectively. The evolution of the fungal community analysis showed that Ascomycota and unclassified fungi dominated during the thermophilic stage, while only Ascomycota was the dominant fungal phylum during the maturity stage, composing 62%, 66%, and 73% of the total fungal community in the control, P, and P + DCD, respectively. The P and P + DCD significantly increased the fungal community richness at the genus level. Fungal community abundance was found to be significantly related to temperature, pH, organic matter, and total Kjeldahl nitrogen, which also influence the gaseous emissions during SS composting. It suggested that the combined addition of pelelith and dicyandiamide (DCD) was an effective method for reducing the emissions of NH₃ and greenhouse gases during SS composting.