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冷热联用对市政脱水污泥低温干燥的影响
Effect of combined cooling and heating methods on low-temperature drying of municipal dewatered sludge
为探究冷热联用干燥市政脱水污泥的可行性，明确冷冻对市政脱水污泥低温干燥的影响，以市政脱水污泥为试验材料，利用扫描电镜（SEM）及流式细胞仪研究了冷冻对污泥的作用.考察了不同冷冻温度和冷冻时间对脱水污泥干燥特性的影响，并对不同含水率和厚度的脱水污泥冷热联用低温干燥效果进行了分析.结果表明：冷冻使污泥的内部微小孔隙增多.当冷冻温度降到-30℃时，细胞死亡率达到15.5%，是未冷冻时的9.7倍.当干燥温度为60℃，冷冻温度分别为-10℃、-20℃和-30℃时，脱水污泥完成干燥的时间分别缩短了25.0%、33.3%和29.2%.质量为5g±0.1g，厚度为3mm，直径为50mm的污泥样品冷冻6h后达到最大强化效果.污泥含水率的下降会导致强化效果减弱，当含水率降至45%时强化效果消失.增加泥饼厚度使强化效果小幅下降，5mm、10mm和15mm厚的泥饼强化效果分别为33.3%、31.3%和30.4%.
This work was to explore the feasibility of drying municipal dewatered sludge by combined cooling and heating methods, and to reveal the influence of the freezing operation on the drying of dewatered sludge at low temperatures. The experimental sludge samples were collected in a municipal wastewater treatment plant after mechanically dewatering. The influence of freezing operation was studied with scanning electron microscopy (SEM) and flow cytometry. In addition, the influence of different freezing temperatures and time on the characteristics of the drying process for the dewatered sludge were also investigated, as well as the effect of combined cooling and heating methods on the dewatered sludge with different moisture contents and cake thickness. It was found that the freezing operation could increase the micropores inside the sludge samples. When the temperature was reduced to -30℃, the death rate of cells exhibited 15.5%, which was 9.7 times higher than that under unfrozen condition. With the drying temperature set at 60℃, as well as freezing temperatures at -10℃, -20℃ and -30℃, respectively, the drying effect was strengthened and the drying rates were improved by 25.0%, 33.3% and 29.2%, correspondingly. Especially, after freezing for 6 hours, the drying rate of the sludge sample reached the highest value, which had the weight of 5g ±0.1g, the cake thickness of 3mm and the diameter of 50mm. It was also found that the decrease in moisture content might weaken the strengthening effect, which was even lost when the content reduced to 45%. The increase of sludge cake thickness might decline the drying rate as well, which exhibited the values of 33.3%, 31.3% and 30.4% at the thickness of 5mm, 10mm and 15mm, respectively. In a word, this work might provide a valuable reference for the development of the sludge drying process using a heat pump with the combined cooling and heating methods.
combined cooling and heating methods / dewatered sludge / low temperature drying / strengthening effect
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国家自然科学基金资助项目（51878539）；陕西省重点研发计划项目（2018ZDXM-SF-025）；陕西省水利科技项目（2017SLKJ-10）；西安市科技计划项目（2016063SF/SF09）
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