Optimization of composting technology for vertical silo reactor

Reactor composting technology is a new and quick composting method. The reactor quickly degrades the material and kills pathogens; however, the reactor product is still unable to reach full maturity and requires further curing. The influence of process parameters, such as composting time, reactor discharge aeration mode, maturing treatment, and costs, on the reactor technology is still unclear. To investigate how the composting time and aeration mode affect the reactor efficiency, a pilot composting experiment was performed in a 12 m³ vertical composting reactor with chicken manure and sawdust using continuous and intermittent aeration modes (i.e., gas supply). The composting process was divided into two stages:reactor composting and curing. Five composting times (2, 4, 6, 8, and 10 days) were used in the reactor composting stage, and a static pile turned once per week was used for curing. Samples were taken every 2 days during the reactor composting stage and every 3 days during the curing stage. The temperature, moisture content, total nitrogen, organic matter, and germination index were measured, and the organic matter degradation rate, product moisture content, nitrogen loss, and operating costs were assessed. The results showed that the organic matter degradation rate in the 10-day compost increased by 60.7% (intermittent aeration) and 66.2% (continuous aeration) compared to the 2-day compost, and the product moisture content reduced by 41.2% (intermittent aeration) and 40.7% (continuous aeration). Most of the material degradation occurred during the reactor composting stage, and more time taken during this stage meant that less maturing time was required. However, the cost increased because of high energy consumption and a reduction in the composting reactor capacity. Increasing the reactor composting time also increased nitrogen loss. The 10-day composted material with a continuous gas supply lost 17.5% more nitrogen than the 2-day composted material. Compared with an intermittent gas supply, a continuous gas supply improved the composting efficiency, shortened the composting cycle by 32.1%, and increased the product total nitrogen content by 7.4% on average. The daily energy consumption during the reactor composting stage was 20.2% higher with the continuous gas supply, compared with the intermittent gas supply, but a shorter composting cycle reduced the average operating costs by 16.5%. Based on these results, the "continuous gas supply mode + 8-d in-reactor composting (R8-C)" is recommended to improve the reactor composting efficiency and costs.