Advancement in Sewage Sludge Dewatering with Hydrate Crystal Phase Change: Unveiling the Micro-Moisture Migration and Dewaterability Mechanisms

Sludge dewatering plays a crucial role in reducing the sludge volume, facilitating transportation, and enhancing energy recovery. However, conventional mechanical dewatering methods often generate high-concentration organic wastewater containing toxic substances and decrease the caloric value of sludge. To address this challenge, a hydrate-based method was proposed as a solution for both sludge dewatering and simultaneous discharges of clean water. Our study investigates the mechanism and feasibility of gas hydrate in sludge dewatering using a visual Nuclear Magnetic Resonance system to observe the spatial and temporal distribution of liquid water during the sewage sludge dewatering process with a crystal hydrate phase change. Our findings indicate that hydrate formation drives directional water transport and transforms part of the bound water irreversibly into free water. The results reveal that the relative percentage of free water in sludge increased from 4.0% to 36.6% after hydrate dissociation, while the mechanically bound water and bound water decreased from 66.6% and 29.4% to 36.6% and 26.8%, respectively. These results demonstrate the effectiveness of the hydrate method in removing free water and improving the sludge dewatering performance. It is essential to realize the green operation of sludge dewatering while reducing energy and chemical consumption.