Impact of bentonite on greenhouse gas emissions during pig manure composting and its subsequent application

Nitrogen conversion and mechanisms related to reduced emissions by adding exogenous modified magnesium ore during aerobic composting

In this study, modified products with a higher specific surface area and pore volume were prepared by light burning magnesite (MS) to increase its magnesium content and surface activity. MS heated at 650 °C (MS650) was applied in aerobic composting to assess its effect on nitrogen transformation during composting and the possible related chemical and microbial mechanisms. Adding MS650 reduced the NH3 emissions (0.74-52.4%), N2O emissions (29.0-57.9%), and greenhouse gas emissions (41.8-60.3%), and its effect on reducing nitrogen emissions was negatively correlated with the amount added, where the optimum proportion of MS650 was 2.5%. Struvite precipitation and physical adsorption were the chemical mechanisms responsible for nitrogen retention. MS650 inhibited the growth of nitrifying, nitrate reducing, and denitrifying bacteria. The total organic carbon content, electrical conductivity, and N2O together explained most of the variation (52.7%) in nitrogen functional genes, followed by Proteobacteria (28.6%). These findings have important implications for reducing nitrogen and greenhouse gas emissions, and improving the quality of compost products.

Effects of selenate on greenhouse gas release and microbial community variations during swine manure composting

Co-composting of livestock manure and selenate is an effective means to produce selenium-rich organic fertilizer. However the effect of selenate on greenhouse gas emission during composting is still unknown. To probe the influences of selenate on greenhouse gas and microbial community changes during swine manure composting. Various dose of selenate were added to the fresh swine manure and wheat straw for 80 days aerobic composting, sequentially labeled as T1 (control) to T6 (0, 1, 2, 3, 4 and 5 mg kg-1). Results indicated that selenate generally increased the nitrous oxide (N2O) and ammonia (NH3) emissions while presented varying impacts on methane (CH4) emissions. Compared with the control, adding 2 and 5 mg kg-1 selenate reduced the CH4 emission by 39.60% and 13.75%, respectively, while other concentrations presented opposite results. Meanwhile, adding 2 mg kg-1 selenate could reduce the global warming potential and improve the compost maturity. According to the microbial results, adding 2 mg kg-1 selenate enhanced the richness and variety of the microbes and might influence Proteobacteria, Chloroflexi, Actinobacteria and Methylococcaceae_unclassified to decrease the global warming potential.

Co-composting of dewatered sludge and wheat straw with newly isolated Xenophilus azovorans: Carbon dynamics, humification, and driving pathways

Composting is a biological reaction caused by microorganisms. Composting efficiency can be adequately increased by adding biochar and/or by inoculating with exogenous microorganisms. In this study, we looked at four methods for dewatered sludge waste (DSW) and wheat straw (WS) aerobic co-composting: T1 (no additive), T2 (5% biochar), T3 (5% of a newly isolated strain, Xenophilus azovorans (XPA)), and T4 (5% of biochar-immobilized XPA (BCI-XPA)). Throughout the course of the 42-day composting period, we looked into the carbon dynamics, humification, microbial community succession, and modifications to the driving pathways. Compared to T1 and T2, the addition of XPA (T3) and BCI-XPA (T4) extended the thermophilic phase of composting without negatively affecting compost maturation. Notably, T4 exhibited a higher seed germination index (132.14%). Different from T1 and T2 treatments, T3 and T4 treatments increased CO2 and CH4 emissions in the composting process, in which the cumulative CO2 emissions increased by 18.61-47.16%, and T3 and T4 treatments also promoted the formation of humic acid. Moreover, T4 treatment with BCI-XPA addition showed relatively higher activities of urease, polyphenol oxidase, and laccase, as well as a higher diversity of microorganisms compared to other processes. The Functional Annotation of Prokaryotic Taxa (FAPROTAX) analysis showed that microorganisms involved in the carbon cycle dominated the entire composting process in all treatments, with chemoheterotrophy and aerobic chemoheterotrophy being the main pathways of organic materials degradation. Moreover, the presence of XPA accelerated the breakdown of organic materials by catabolism of aromatic compounds and intracellular parasite pathways. On the other hand, the xylanolysis pathway was aided in the conversion of organic materials to dissolved organics by the addition of BCI-XPA. These findings indicate that XPA and BCI-XPA have potential as additives to improve the efficiency of dewatered sludge and wheat straw co-composting.

Greenhouse gas emission characteristics and influencing factors of agricultural waste composting process: A review

China, being a major agricultural nation, employs aerobic composting as an efficient approach to handle agricultural solid waste. Nevertheless, the composting process is often accompanied by greenhouse gas emissions, which are known contributors to global warming. Therefore, it is urgent to control the formation and emission of greenhouse gases from composting. This study provides a comprehensive analysis of the mechanisms underlying the production of nitrous oxide, methane, and carbon dioxide during the composting process of agricultural wastes. Additionally, it proposes an overview of the variables that affect greenhouse gas emissions, including the types of agricultural wastes (straw, livestock manure), the specifications for compost (pile size, aeration). The key factors of greenhouse gas emissions during composting process like physicochemical parameters, additives, and specific composting techniques (reuse of mature compost products, ultra-high-temperature composting, and electric-field-assisted composting) are summarized. Finally, it suggests directions and perspectives for future research. This study establishes a theoretical foundation for achieving carbon neutrality and promoting environmentally-friendly composting practices.