Optimization of process parameters for reducing gas emission from kitchen waste compost

The implementation of garbage sorting policy resulted in an explosion of food waste amount in community, which makes the existing facilities of treating wastes face great challenges. Aerobic compost has the advantages of flexible treatment scale, easy adjustment of parameters and high process adaptability, and is an important technology for food waste treatment and resource utilization. However, the aerobic composting of food waste has some problems such as long fermentation period and easy to produce polluted gas, which seriously limits the promotion of local treatment and utilization. Pollution gas generation is directly related to oxygen supply and utilization in the reactor. In order to improve the fermentation rate, reduce the emission of polluted gas, and optimize the process parameters of food waste composting, a total of 9 treatments were set up in this study, and the three-factor and three-level orthogonal composting experiment L₉ (3⁴) was adopted. The food waste and maize stover were mixed according to the wet-weight ratio of 3:1, and the maize stover was crushed to 0.5-10, 10-20, 20-40 mm by the crusher, respectively. The moisture content of all the initial mixed materials was adjusted to 55%, 60% and 65% respectively, and the oxygen supply method of continuous ventilation was adopted. The ventilation intensity was 0.1, 0.2 and 0.3 L/(min·kg), respectively, and the composting test was carried out in an 8 L closed fermenter for 21 days. The influence of particle size, moisture content and ventilation rate on reactor temperature, oxygen concentration, pH value, EC value, GI value and pollution gases (H₂S, NH₃, N₂O and CH₄) were investigated. The results showed that the initial particle size, moisture content and ventilation rate had significant effects on the fermentation process and pollutant gas emission during the composting process of food waste. Adjusting the process parameters could accelerate the temperature rise of the pile, improve the rot degree of the pile, and shorten the composting cycle to about 11 days. The optimal treatment group increased to 60 ℃ 12 hours after the reaction began which effectively accelerated the composting process. All the physical and chemical indicators reached the NYT525-2021 organic fertilizer standards. In the pollution gases, H₂S and N₂O are mainly emitted during the heating and high temperature periods of compost, while NH₃ and CH₄ are mainly emitted during the high and low temperature periods of compost. According to the variance analysis of orthogonal test, the particle size of the material has a significant influence on H₂S emission, and the moisture content and ventilation rate have a significant influence on H₂S and N₂O emission. The emission reduction rates of H₂S, NH₃, N₂O and CH₄ in the optimal treatment group were 63.8%, 95.8%, 20.9% and 84.9%. In terms of total greenhouse effect reduction, the reduction rate of the best treatment group was 22.3%. Considering the composting cycle and emission reduction effect of pollution gas, the optimal process parameter combination of food waste composting is as follows: initial material particle size 0.5-10 mm, initial water content 60%, ventilation rate 0.2 L/(min·kg).