Optimization of composting technology for vertical silo reactor

Reactor composting technology has gradually been recognized as a new type of fast composting method. Quick degradation and pathogen killing could be achieved in reactor, but the product from the reactor still cannot reach full maturity, which needs further curing stage. However, the influence of process parameters such as reactor composting time and aeration strategies on reactor discharge quality, subsequent maturing treatment and economic cost are still unclear. Therefore, in order to comprehensive investigate the reactor composting time and aeration mode on the efficiency and benefit of reactor composting technology making it more efficient, a pilot composting experiment was carried by a 12 m³ vertical composting reactor with chicken manure and sawdust as raw materials, under continuous and intermittent aeration modes in reactor, respectively. Composting process was divided to two stage, reactor composting and curing stage. Five different composting time (2 d, 4 d, 6 d, 8 d and 10 d) were setup in reactor composting stage, and subsequent curing was conducted as static pile with turning once per week. Fresh composting sample was taken every two days in reactor composting stage and each 3 days during curing stage. Temperature, moisture content, total nitrogen, organic matter and germination index were measured focusing on the degradation rate of compost organic matter, product moisture content, nitrogen loss and operating costs. The results of this study showed that the degradation rate of organic matter in the treated materials for 10 days in reactor composting was increased by 60.7% (intermittent) and 66.2% (continuous) than the materials remain in reactor for 2 days, and the moisture content of the product was reduced by 41.2% (intermittent) and 40.7% (continuous), respectively. The reactor composting stage is the main stage of material degradation happened, and the longer the reactor composting time, the shorter the required aging time. However, the cost of compost product would be increase since the higher energy consumption and reduced treated capacity of composting reactor. In addition, the increase of the reactor composting time would also increase the nitrogen loss of the compost material. The material composted for 10 days in the continuous gas supply reactor lost 17.5% more nitrogen than the material composted for 2 days. Continuous gas supply could improve composting efficiency, shorten the composting cycle by 32.1% compared with intermittent gas supply, and increase the total nitrogen content of the product by an average of 7.4%. Although the daily energy consumption of the reactor composting stage is 20.2% higher than that of intermittent gas supply, the shortening of the composting cycle reduces the average operating cost of the entire continuous gas supply by an average of 16.5%. Based on the experimental results, it is recommended to select the “continuous gas supply mode + 8 d in-reactor composting (R8-C)” treatment in this experiment, which can improve the efficiency of reactor composting, and has more economic potential in actual production.