State Key Laboratory of Pollution Control and Resource Reuse, College of Environmental Science and Engineering, Tongji University, 1239 Siping Road, Shanghai, 200092, China; College of Engineering and Applied Science, Stony Brook University, 100 Nicolls Road, Stony Brook, NY, 11794, USA; Department of Civil and Environmental Engineering, Colorado School of Mines, 1500 Illinois Street, Golden, CO, 80401, USA.
College of Engineering and Applied Science, Stony Brook University, 100 Nicolls Road, Stony Brook, NY, 11794, USA.
Water Res. 2018 Nov 15;145:464-472. doi: 10.1016/j.watres.2018.08.057. Epub 2018 Aug 28.
The propane hydrate formation was proposed to have potentials in realizing free-conditioning dewatering of sewage sludge with implications to simultaneous clean water extraction and highly efficient volume reduction. Primarily, the investigation on phase equilibrium of propane hydrates found that the organic components of sewage sludge promoted the propane hydrate formation in terms of decreasing equilibrium pressure by up to 19.2%, compared with that in pure water. Further, the feasibility of hydrate-based dewatering was verified through the observation of propane hydrate formation in sewage sludge and also the quality analysis of water generated from decomposition of up-floated formed hydrates. The formation of up-floated propane hydrates extracted water molecules from sewage sludge into homogeneous crystal phase, which actually excluded sludge particles from hydrate phase and realized the reduction of water in sludge phase. The efficiency of water conversion into hydrates was determined by monitoring propane pressure, which indicated that 14 batch runs decreased the water content of sludge from 98.81wt.% to 44.3wt.% under free-conditioning conditions. The chemical oxygen demand, total nitrogen and total phosphorus of hydrate-extracted water were measured to be 21 ± 1 mg/L, 10.5 ± 0.2 mg/L and 0.4 ± 0 mg/L, respectively, which reflected the excellent separation performance and also indicated that the hydrate-extracted water can be directly discharged without further treatments. Finally, the unit energy consumption of hydrate-based dewatering process based on a continuous operation mode was calculated to be 2673.96 kW h/t dry solid of sewage sludge, which was nearly half of that in thermal drying process. Therefore, the propane hydrate-based process is believed to maximize the green operation of enhanced sludge dewatering while minimizing the energy and additional material consumption.
丙烷水合物的形成具有在污水污泥无调节条件下实现自由脱水的潜力，这意味着可以同时提取清洁水并实现高效的体积缩减。首先，通过对丙烷水合物相平衡的研究发现，与纯水中的相平衡压力相比，污水污泥中的有机成分通过降低平衡压力高达 19.2%，促进了丙烷水合物的形成。此外，通过观察污水污泥中丙烷水合物的形成以及对上浮形成的水合物分解产生的水的质量分析，验证了水合物脱水的可行性。上浮形成的丙烷水合物将水分子从污水污泥中提取到均相晶体相中，实际上将污泥颗粒从水合物相中排除，实现了污泥相中水分的减少。水转化为水合物的效率通过监测丙烷压力来确定，这表明在无调节条件下，14 批运行将污泥的含水量从 98.81wt.%降低至 44.3wt.%。测量水合物提取水中的化学需氧量、总氮和总磷分别为 21±1mg/L、10.5±0.2mg/L 和 0.4±0mg/L，这反映了出色的分离性能，也表明水合物提取水可以直接排放，无需进一步处理。最后，根据连续操作模式，计算基于水合物的脱水工艺的单位能耗为 2673.96kW·h/t 干固体的污水污泥，这接近热干燥工艺的一半。因此，丙烷水合物工艺被认为可以在最小化能源和额外材料消耗的同时，最大限度地实现增强污泥脱水的绿色操作。
