Influence of Additives on Solar-Controlled Anaerobic and Aerobic Processes of Cow Manure and Tomato Waste

As a type of high-water-content agricultural waste, vegetable waste (VW) is extremely prone to spoilage and environmental pollution. Anaerobic digestion (AD) technology can accelerate the degradation of VW; however, its direct reaction might encounter the risk of termination due to excessive acidification. How to effectively prevent excessive acidification and further accelerate the degradation and maturity of VW remains a significant challenge at present. This paper employed the methods of AD of biogas and aerobic treatment (AT) of biogas slurry (BS) to develop a set of three groups of coupled devices for thermostatic anaerobic and aerobic processes with temperature control by solar collectors. The reaction process was further facilitated by adopting a mixture of raw materials and exogenous additives. In Lanzhou, a comparative experiment was carried out to examine the impacts of a blank group (BG) (additive-free), a 1 g/L urea group (UG), and a 1 g/L plant ash group (PG) on the decomposition process of the mixture of cow dung and tomato stems and leaves. The thermostatic batch wet AD stage of the mixed raw materials at (26 ± 2 °C) lasted for 49 days. The substrate after digestion underwent aerobic aeration treatment for 8 h at different temperatures and different aeration rates. The results show that the system could be initiated smoothly and maintain stable operation in winter under the temperature control of the solar collector; adding additives during AD significantly boosted biogas and methane production during the first 28 days, with urea being the most effective. During the subsequent aerobic phase, UG demonstrated the highest bio-effectiveness under optimized conditions of (30 ± 1 °C) and an aeration rate of 12 L/min. Comprehensive analysis revealed that the optimal operation strategy was identified as the use of UG with a 29-day reaction cycle. The research results have significant referential value for the rapid decomposition of high-water-content agricultural and livestock waste in cold regions.