Rao Binqi, Su Jiangge, Xu Shengjun, Pang Hongru, Xu Peng, Zhang Yan, Zhu Jianwei, Tu Houde
College of Mechanical and Electrical Engineering, China Jiliang University, Hangzhou, 310018, PR China.
College of Mechanical and Electrical Engineering, China Jiliang University, Hangzhou, 310018, PR China.
Water Res. 2022 Nov 1;226:119231. doi: 10.1016/j.watres.2022.119231. Epub 2022 Oct 10.
Both huge volume and high moisture content of municipal sludge have brought great troubles and attracted extensive concerns in the world. The bound water of sludge and pore clogging in the process of pressure filtration dewatering are two key factors influencing the deep-dewatering effect of municipal sludge. The results of this study suggest that microwave irradiation (MI) can be used to synchronously evaporate water, reduce the bound water of sludge and solve the blockage of sludge pore channels during the process filtration dewatering, which can greatly reduce the moisture content of municipal sludge. Low-field nuclear magnetic resonance, carbon dioxide gas absorption and desorption, and scanning electron microscope were synthetically used to detect the pore structure of sludge cakes. Thermogravimetric differential scanning calorimetry was used to detect binding energy to calculate moisture distribution. Thermal mechanism was revealed by dielectric constant, thermal conductivity, fractal dimensions, water saturation and porosity in different layers of sludge cake. The results showed that the bound water in sludge samples after MI was reduced by 19.4%, the pore fractal dimension was reduced from 2.955 to 2.867, the surface fractal dimension increased from 2.099 to 2.362 with the conditions of microwave power (700 w) and treat time (5 min). When the water saturation was close to 1, the dielectric constant of middle and outer layers was the main factor of heating, while the water saturation was close to 0, the main factor became the difference of thermal conductivity in middle and outer layers. Moreover, after MI, moisture content of sludge was greatly reduced from 68.4% to 40.1% for its thermal effect, further reduced to 34.1% by the continuous mechanical dewatering for its non-thermal effect which change the pore structure and moisture distribution. These conclusions are helpful to understand microwave thermal and non-thermal mechanism and shed light on new dewatering-drying integrated techniques of municipal sludge.
城市污泥的巨大产量和高含水量给全世界带来了巨大困扰并引发了广泛关注。污泥中的结合水以及压力过滤脱水过程中的孔隙堵塞是影响城市污泥深度脱水效果的两个关键因素。本研究结果表明，微波辐射（MI）可用于同步蒸发水分、降低污泥的结合水，并解决过滤脱水过程中污泥孔隙通道的堵塞问题，这可以大幅降低城市污泥的含水量。综合运用低场核磁共振、二氧化碳气体吸附与解吸以及扫描电子显微镜来检测污泥饼的孔隙结构。采用热重差示扫描量热法检测结合能以计算水分分布。通过污泥饼不同层的介电常数、热导率、分形维数、水饱和度和孔隙率揭示热机制。结果表明，在微波功率（700瓦）和处理时间（5分钟）的条件下，微波辐射后污泥样品中的结合水减少了19.4%，孔隙分形维数从2.955降至2.867，表面分形维数从2.099增至2.362。当水饱和度接近1时，中层和外层的介电常数是加热的主要因素，而当水饱和度接近0时，主要因素变为中层和外层热导率的差异。此外，微波辐射后，由于热效应，污泥含水量从68.4%大幅降至40.1%，通过连续机械脱水，因其非热效应改变了孔隙结构和水分分布，含水量进一步降至34.1%。这些结论有助于理解微波热和非热机制，并为城市污泥脱水干燥一体化新技术提供启示。
