堆肥废气余热回用对寒区好氧堆肥的影响

黑龙江地处高寒地区，好氧堆肥存在自然升温、高温维持困难、增温设备能耗高、堆肥周期长等问题。该研究在传统好氧堆肥设备中增设板翅余热换热系统，利用堆肥废气热能预热通风空气，系统研究不同环境温度时堆肥废气余热回用对好氧堆肥增温效果及堆肥品质的影响。结果表明：通风量、通风频率分别为16 L/min、每间隔2 h 通风20 min时更有利于堆体升温；回收堆体排出废气的余热预热通风空气能够显著提升好氧堆肥堆体的温度（P<0.05），环境温度分别为11.4～13.4 ℃和7.1～8.6 ℃时，堆体最高温度可分别达到63.8和62.4 ℃，50 ℃以上可分别维持7.15和5.61 d，而且在含水率、有机质、C/N、pH值、电导率（Electrical Conductivity，EC）等堆肥效果方面也更具优势，有机质含量可分别降到53.28%和55.06%。该余热回收系统实际可行，且当环境温度为7.1～8.6 ℃及以下时，好氧堆肥必须采取余热回用措施才能维持正常的堆体温度，达到无害化标准要求。研究结果可为北方高寒地区好氧堆肥技术的应用及推广提供支撑。

Effects of preheating ventilation air using exhaust gas on aerobic composting in cold regions

Heilongjiang Province is the main grain-producing area and the major animal husbandry in China. It is a high demand to efficiently utilize the agricultural straw and livestock/poultry manure at present, particularly for the reduced and harmless treatments. The current comprehensive treatment can often include anaerobic digestion and aerobic composting. Among them, aerobic composting has been widely used in recent years, due to the short reaction cycle and favorable harmlessness effect. Furthermore, the organic fertilizer produced by aerobic composting can be used to effectively improve the soil in the fields. However, Heilongjiang Province is located in the northeast of China, where winter is cold and long. It is difficult for the composting temperature to maintain high temperature. Consequently, excessive energy can often be consumed by the composting equipment during the long composting cycle. Alternatively, aerobic composting is one type of biochemical reaction process that produces heat. The average heat production of different composting materials can reach 1.91 kJ/kg of dry material so the maximum temperature can reach 65 ℃ or more. It can be feasible to utilize the heat energy recycling of exhaust gas for the heating air passing into the pile. The impact of ventilation on the temperature of the composting pile can be reduced to improve the efficiency and quality of composting. The heating energy consumption and composting cost can also be reduced for the further purification of the exhaust gas during composting. However, it still remained unclear about the influence of the preheating ventilation air using exhaust gas from composting on the composting process and compost quality. In this study, the plate-fin afterheat exchange system was designed and introduced into the aerobic composting system via preheating the ventilation air with the heat energy of exhaust gas during composting to reduce the restriction of low temperature in cold areas during aerobic composting. A systematic investigation was conducted to explore the effect of the heat energy reuse of exhaust gas on composting temperature and composting effect under different ambient temperatures. The results showed that the ventilation rate of 16 L/min and the ventilation lasted for 20 min every 2 h were more conducive to the temperature rise during aerobic composting. The maximum temperature of aerobic composting with an effective volume of 75 L reached 61 ℃ when the ambient temperature of 12.8-14.8 ℃, and the duration was maintained for 1.75 d above 60 ℃. The temperatures of the pile during aerobic composting increased significantly by preheating the ventilation air with composting exhaust gas. When the ambient temperatures were 11.4-13.4 ℃ and 7.1-8.6 ℃, the maximum temperatures of composting reached 63.8 ℃ and 62.4 ℃, respectively, and the duration was maintained for 7.15 d and 5.61 d above 50 ℃, respectively. Meanwhile, the composting effects presented the absolutely superior moisture content, organic matter, C/N, pH value, and Electrical Conductivity (EC). The organic matter content of composting was reduced from 71.33% to 53.28% and 55.06%, respectively, at the ambient temperatures of 11.4-13.4 ℃ and 7.1-8.6 ℃. Once the ambient temperature was reduced to 7.1-8.6 ℃ and below, the afterheat recycling and utilization must be taken for the aerobic composting to maintain the normal composting temperatures for the requirements of harmlessness standards. The afterheat recycling system of aerobic composting was practically feasible. The findings can provide favorable support for the application and promotion of aerobic composting technology in northern cold regions.