城市污泥堆肥温度动态变化过程及层次效应

Temperature Dynamic During the Sewage Sludge Composting Process

对城市污泥强制通风静态垛堆肥的温度变化规律进行了研究。结果表明 ,当调理剂比例较低时 ,堆体升温速率和降温速率都较为缓慢 ,堆肥处理时间长 ,堆体温度较低。当调理剂比例较高时 ,堆体升温速率较快 ,堆肥温度将在较短时间内达到灭菌稳定化所要求的高温。堆体温度在高温阶段持续的时间与调理剂比例有着密切的联系 ,当调理剂比例太高时 ,高温持续时间短 ,如加入适当比例的回流污泥 ,堆温可以在 5 0℃以上高温阶段持续足够的时间。当堆肥原料的起始温度高于 1 5℃ ,堆体一般要经历升温阶段、高温持续阶段和降温阶段 ,但是当堆肥原料的起始温度很低时 ,堆体温度还要经历一个起爆阶段。堆体内不同层次的温度有着不同的变化趋势 ,堆肥初始阶段 ,堆体下层温度高于上层温度 ,随后上层温度逐渐高于下层温度。

It was well recognized that many factors influenced the composting process and the resulting product. Temperature was the most important ecological determinant within composing material. Temperature increase was a function of starting points, metabolic heat evolution and heat conservation, with the achievement of minimum temperature levels being essential to an effective composting process and contributing substantially to the high rates of decomposition achieved during processing. Few studies had been undertaken to understand the processes of microbes, heat losses from the mass, and the ecological nature, including microbial succession. The temperature of a composting mass depended largely on airflow. The temperature between the center and the surface of the composting mass varied greatly in static piles largely because of airflow. Turning of stacks or forced aeration, as in environmentally controlled composting, could control temperature effectively. Termination of such practices resulted in the temperature soon returning to the range of 70℃ to 80℃. The forced aerating influenced the temperatures at different positions, so the temperature changes were different. To know the difference was important to control the composting process, improve the quality of the composting product. The study was carried out to investigate the temperature dynamic during the sewage sludge aerobic static composting. All experimented composting piles were placed in a building in 1.6 m × 1.0 m bays with cement floors and walls. Aeration boards were laid on the bottom of the bays. The piles contained sewage sludge (moisture content=83%～85%,Volatile Solid=49%～58%), recycled compost and bulking agent with five proportions. A bulking agent layer on the aeration boards dispersed air through the 1.0 m high mix layer. All piles were covered with a 20-cm insulating layer of recycled compost. Each bay had an aerator to supply ambient air. Sensors were inserted into the middle layer and upper layer of the piles' geometrical centers to detect the temperatures, and the detected values were fed back to the computerized control system. In order to study the difference among the different layers, six sensors were inserted into the piles in the treatment II from the bottom to the top. A three-stage control algorithm controlled the damper duty cycle of aerators. The control software logged temperatures every 15 minutes and generated reports. The temperature increasing and decreasing speed was slow, less than 4.7℃/d and 2.9℃/d respectively, and the composting duration was long and the composting temperature was lower when the proportion of bulking agent was lower. On the contrary, when the proportion of bulking agent was high, the temperature decreasing was faster, about 12～17.6℃/d, and the composting temperature was high enough to destroy the pathogenic microorganisms. The duration in high temperature period related to the proportion of bulking agent: the duration was shorter when the latter was higher, but long enough to destroy the pathogenic microorganisms when the recycled compost was added. The composting process suggested by earlier reports could be divided into three stages: temperature increasing stage, high temperature stage and temperature decreasing stage. However our experiment indicated that the composting process should be divided into four periods: besides the three periods previously stated, the period from the low temperature to the 15℃ should be noticed because it was important for the microorganisms to proliferate and the composting process to start. The temperature changing trends at the different places in the composting piles were different. The temperature of the upper-layer was lower than that of the under-layer in the early stage, and then the former was higher with the development of composting process. The temperature of middle-layer was higher at the high temperature stage, but the temeprature of under-layer was higher at starting stage and it should be studied in future.