曝气量与辅料粒径对餐厨废弃物辅热生物干化的影响

为解决餐厨废弃物生物干化处理周期长、脱水效率低的问题，该研究分别设置3个不同曝气量（0.4、0.6和0.8 L/(min·kg)）和不同辅料粒径（粗粒径>15.0 mm、细粒径<5.0 mm和混合粒径5.0～15.0 mm）进行析因试验，探究其对餐厨废弃物生物干化效果的影响。研究结果表明，相较于粒径而言，曝气量对于辅热生物干化温度变化和除水影响更大。0.6 L/(min·kg)曝气下升温速度较快，高温期持续时间更长，有效积温更高。除0.4 L/(min·kg)和细粒径处理，其他处理辅热生物干化过程高温期均超过7 d；0.8 L/(min·kg)和细粒径处理的除水效果最好，生物干化指数最高为4.0，最终含水率为17.0%，水分去除率为95.8%。能量和水分平衡计算表明：辅热生物干化过程中，主要的除水方式为蒸发除水，占总除水量40%～80%；主要能量来源为生物产热（63.0%～76.0%），能量损失主要有蒸发潜热（26.0%～46.5%）和反应器热损失（28.3%～49.4%），0.8 L/(min·kg)和细粒径处理的能量利用效率最高为65.1%。经过16 d辅热生物干化，除0.4 L/(min·kg)和细粒径处理pH值与发芽指数不能满足腐熟标准，其他处理均能完全腐熟，可满足有机肥标准。

Effects of aeration rate and particle size of bulking agents on the thermally assisted bio-drying of kitchen waste

Abstract: Much more Kitchen Wastes (KW) have been generated and collected separately, as the proposals for the practice of waste separation in China. Among them, bio drying is an emerging technique to remove water from biodegradable wastes. However, the KW bio drying is also confined to the application in practice, due to the long treatment cycle, low temperature and dehydration efficiency. In this study, a thermally assisted bio-drying system was established and developed to fully meet the market demand for better performance and high efficiency of water removal. The air-flow rate and bulking agent were the most important factor for the traditional bio drying process. But there were few reports about the sole and synergetic effect on the thermally assisted bio-drying process. Therefore, a comparison was then made to clarify the influence of aeration volume and particle size on the auxiliary heat biological drying, particularly for the low consumption of energy efficiency and high bio drying efficiency. Three aerations (0.4, 0.6, and 0.8 L/(min·kg)) and different particle sizes of auxiliary material (coarse particle size > 15.0 mm, fine particle size < 5.0 mm, and mixed particle size 5.0-15.0 mm) were set for the factorial experiments, in order to explore the biological drying efficiency for the kitchen wastes. Some bio drying parameters were determined to assess the bio drying performance. The flow balance of energy and water in the system was calculated to further assess the water removal and energy utilization rate. The results show that the aeration rate posed a greater effect on the bio drying temperature and water removal, compared with the particle size. A better performance was achieved, particularly for the higher heating rate and the longer duration at the high-temperature stage, and the higher effective accumulated temperature under the 0.6 L/(min·kg) aeration. The high-temperature stage of auxiliary heat bio drying was more than seven days, except for the treatment with the 0.4 L/(min·kg) and fine particle size. The treatment of 0.8 L/(min·kg) and fine particle size performed the best for the water removal. Specifically, the highest bio drying index was 4.0, the final water content was 17.0%, and the water removal rate was 95.8%. The energy and water balance show that evaporation was the main way of water removal in the bio-drying process, accounting for 40%-80% of the total water removal. The main input energy was the heat production of biomass (63.0%-73.0%), whereas, the main output energy was the latent heat of evaporation (26.0%-46.5%) and reactor heat loss (28.3%-49.4%). The highest energy utilization efficiency was achieved in the treatment with the 0.8 L/(min·kg) and fine particle size, up to 65.1%. The latent heat of evaporation accounted for 48% of the output energy in the treatment with the 0.8 L/(min·kg) and fine particle size. However, the pH value and germination index in the treatment with the 0.4 L/(min·kg) and fine particle size failed to meet the compost safety and maturity standards after 16 days of bio drying by auxiliary heat. Therefore, the fine particle size of bulking agents with a higher aeration rate (≥0.6 L/(min·kg)) can be expected for the bio drying process with the auxiliary heat for KW for better bio drying and energy utilization efficiency.