The addition of biochar and the use of membrane coverings are two methods used in aerobic composting of agricultural waste. The effectiveness of each of these two methods on compost quality and reduction of greenhouse gas emissions was tested in the laboratory. The results showed that both methods increased the maximum composting temperature and extended the thermophilic period. The germination index of biochar-treated compost and membrane-covered compost reached 70% on the 18th day, which was 12 days earlier than the corresponding value in the control group. The products from the biochar-treated compost had higher pH and lower electrical conductivity, compared with the product of the control group, indicating that these products are more suitable for acidic soils. In terms of greenhouse gas reduction, both methods were found to reduce the emissions of CH4 and N2O from composting. The addition of biochar had a better emission reduction effect on N2O, whereas the membrane covering technique yielded a better effect on CH4 emission reduction. The results of this study provide technical support for managed aerobic composting to reduce greenhouse gas emissions.

The effects of covering technology and the combined membrane covering with biochar on nutritional elements content during the aerobic composting process of agricultural waste were studied. The results showed that the concentration effect of organic matter degradation during composting increased the nitrogen, phosphorus, and potassium contents in all treatment groups. The proportion of available phosphorus and available potassium also increased to varying degrees. Compared with composting without an expanded poly(tetrafluoroethylene) (PTFE) covering with 0.2 to 0.4 µm pores, the covered composting increased the total nitrogen, total phosphorus, total potassium, available phosphorus, and available potassium contents by 13.1%, 12.6%, 7.4%, 21.5%, and 16.6%, respectively, while the addition of biochar to polymer membrane-covered composting increased the total nitrogen, total phosphorus, total potassium, available phosphorus, and available potassium contents by 19.7%, 13.7%, 8.3%, 18.0%, and 20.2%, respectively. This study indicated that membrane covering technology can effectively increase the nutrient element contents in compost products and the availability of phosphorus and potassium and that the addition of biochar enhances these effects.

In the process of anaerobic dry fermentation to produce biogas, maintaining a suitable pH in the environment is more conducive to the degradation of crop straw. When the pH in the fermentation environment is too low, the process of anaerobic digestion by anaerobic bacteria is inhibited. Therefore, it is necessary to quickly adjust the pH. In this work, we studied the control technology of a pH regulation system and then constructed a T-S fuzzy controller. Upon simplifying the T-S fuzzy controller, the system delay time was reduced, and two genetic algorithms with different fitness performance indicators were used to optimize the T-S fuzzy control. The simulation experiment in this study was designed through simulation software, and the results show that the improved control method has a fast regulation ability. Finally, on-site experiments were conducted using the four control methods under the acidification conditions set in the experimental device. The results show that the control method used in this study to improve performance by integrating the error sum of squares has a short control time and small oscillation and overshoot, and it can better regulate the environmental pH to achieve appropriate conditions when acidification occurs during anaerobic dry fermentation.

The production of huge amounts of biogas slurry during livestock breeding has resulted in pressing environmental issues. Although paddy fields can be potential sinks for the disposal of biogas slurry, the impacts of biogas slurry on rice production, grain quality, and relevant environmental risks in the Yangtze Delta region remain unclear. Herein, we conducted a field trial from 2021 to 2023 which involved different gradients of biogas slurry utilization, including CK (no fertilizer), CN (100% chemical nitrogen (N) of 240 kg ha⁻¹), NBS (biogas slurry replacing 50% chemical N), BS1 (replacing 100% chemical N), BS1.5 (replacing 150% chemical N), and BS2 (replacing 200% chemical N). The results showed that there were no significant differences in average rice yields between CN, NBS, BS1.5, and BS2 over the three-year study period, with an average yield of 8283 kg ha⁻¹, and the average yields of BS1 and CK were 7815 kg ha⁻¹ and 6236 kg ha⁻¹, respectively. However, heavy utilization of biogas slurry (BS1.5 and BS2) not only significantly reduced the rice seed-setting rate, the 1000-grain weight, and the processing quality, but also significantly increased the protein, amylose, Cu, and Zn content in rice grains; additionally, higher N losses occurred via surface water and increased NH₃ volatilization was observed, finally resulting in lower nitrogen-use efficiency. Meanwhile, moderate utilization of biogas slurry (NBS and BS1) led to better rice quality and nitrogen-use efficiency, lower potential food safety risk, and N loss. Further, compared to BS1, NBS showed higher yield, harvest index, processing quality, gel consistency, palatability scores, and nitrogen-use efficiency, but lower N losses were present. Overall, the NBS treatment balanced the agronomic benefits and environmental risks in the Yangtze River Delta region. In the future, more attention should be paid to food safety and environmental risks when using biogas slurry.

Trough composting is a highly efficient technology for treating livestock manure and converting it into valuable resources. The flow field in the aeration pipes and the flow field within the compost pile are critical factors affecting trough composting. Due to the large size of compost piles and the harsh internal environment, it is difficult to quantify the flow field distribution within the pipes and the compost piles. This study established a three-dimensional fluid model of the bottom pipeline and the compost pile within a 90 m³ trough composting system. The perforation spacing of the bottom pipe was optimized by gradually reducing the spaces between openings. Effect of optimized perforation spacing on flow velocity within the pipe and the compost pile were optimized. The results indicated that a gradually changed perforation structure can enhance both the magnitude and uniformity of flow velocity distribution within the pipeline and the compost pile. Field trials of trough composting at an engineering scale revealed that the average relative error between actual measured wind speeds over the compost pile and simulated values remained within 10%. This study provides a theoretical basis and data support for the engineering construction of aeration systems in trough composting.

Rural organic wastes are spatially dispersed across agricultural production areas and settlements, creating challenges for collection, treatment, nutrient recovery, and return to agricultural land. This study developed a township-scale spatial planning framework integrating waste quantification, centralized and decentralized composting, nutrient recovery, and techno-economic assessment in Beiyang Township, eastern China. Agricultural residues were allocated to five centralized composting reactors, whereas household kitchen waste was treated using decentralized bins. Machine-learning models estimated total carbon (TC) and total nitrogen (TN) retention under three composting-adoption scenarios. The defined study area was estimated to generate approximately 8745 t yr⁻¹ of rural organic waste, 82.8% of which originated from agricultural production. Under the high-adoption scenario, with 70% of agricultural waste and 75% of kitchen waste composted, retained TN was equivalent to approximately 27.9% of annual local crop N fertilizer demand on a total-N basis. Economic performance improved with increasing waste participation. Under the baseline scenario, four centralized reactors and the decentralized system were financially viable, whereas one reactor was non-viable. Under the moderate- and high-adoption scenarios, all configurations achieved positive NPVs and IRRs above the 10% benchmark rate. The framework supports coordination of rural organic-waste treatment, nutrient recycling, and sustainable agricultural land management at the township scale.