Effects of manganese dioxide on composting maturity, greenhouse gas and odor emission of multi-organic solid waste micro-aerobic composting

In the process of aerobic composting, a large amount of volatile gas will be produced, which will cause harm to the environment, lead to the serious loss of carbon, nitrogen and other nutrients, and affect the improvement of organic fertilizer quality. Studies have shown that by adjusting the ventilation rate and additive during composting, pollution gas emissions can be reduced, and carbon and nitrogen elements can be fixed to improve maturity. In order to explore the effects of manganese mineral addition on maturity, greenhouse gas and odor emissions during micro-aerobic composting, three treatments were set up in this experiment with the multi-component mixture composting composed of kitchen waste, rice straw, sheep manure and vegetable waste as the research object. During the whole composting period, all treatments were forced intermittent ventilation. The ventilation rate was set to 0.14 L/(kg·min) as the aerobic composting control(CK), the ventilation rate was 0.06 L/(kg·min) as the micro-aerobic treatment (T1), the ventilation rate was 0.06 L/(kg·min) and the addition of manganese dioxide (MnO₂) was T2 treatment, and each treatment was repeated twice. The ventilation cycle was one hour, and 10 minutes of air was ventilated every 50 minutes in the first 16 days. In order to make the compost material mature smoothly, the ventilation cycle was adjusted to 20 minutes of air every 40 minutes on the 17th day. The composting experiment was carried out in six 50 L closed fermentation tanks. Through the determination of maturity indexes such as germination index and electrical conductivity, it was shown that after 70 days of composting, all the treatment materials were basically transformed into mature compost. The results showed that aerobic or micro-aerobic composting of multiple wastes could transform the materials into compost, but the quality of final compost products in T2 treatment was significantly higher than that in T1 treatment. Both T1 and T2 treatments could reduce the emissions of NH₃ and N₂O to varying degrees. Compared with CK treatment, the emissions of NH₃ in T1 and T2 treatments decreased by 30.29% and 26.47%, respectively, and the emissions of N₂O decreased by 33.19% and 38.60%, respectively. However, the CH₄ emissions increased by 127.22% and 87.58%, respectively, and the total greenhouse effect T1 and T2 treatments decreased by 29.26% and 31.38%, respectively, compared with CK. The emission of H₂S and volatile organic compounds (VOCs) in odor(OC) was concentrated in the first 14 days, and the emission of H₂S and VOCs in T1 and T2 treatments under low ventilation rate increased significantly, and the emission of H₂S increased by 501.04% and 320.35% respectively compared with CK. VOCs increased by 39.82% and 53.63%, respectively. Therefore, microaerobic composting can achieve the purpose of emission reduction, but the reduction of ventilation rate will aggravate the emission of odor ; the addition of MnO₂ can improve the maturity of micro-aerobic composting to a certain extent and reduce the emission of greenhouse gases and odors, which can provide technical support for the efficient resource utilization of multi-organic wastes and the synergy of pollution reduction and carbon reduction.