Dewatering performance enhancement of waste activated sludge using FeCl3 and freeze-thaw synergistic co-conditioning method

Abstract

The dramatic increase in the production of waste activated sludge (WAS) presents new challenges for the development of advanced deep dewatering technologies. Conventional individual conditioning techniques, such as FeCl3 coagulation and freeze-thaw conditioning, often exhibit poor effectiveness and low efficiency. This study proposes a method to significantly improve the dewatering performance of WAS by co-conditioning with FeCl3 and freezing-thawing. The study reveals the improvement effects and mechanisms through comparative experiments. The results demonstrated a significant reduction in the Specific resistance to filtration (SRF) of WAS from 96.39 × 1012 m/kg to 0.91 × 1012 m/kg following co-conditioning. Moreover, the moisture content of the sludge cake following filter pressing exhibited a notable decline from 66.41 % to 49.19 %. The analysis of the mechanism indicates that the co-conditioning method initially initiates the neutralization of zeta potential and the compression of the EPS (extracellular polymeric substances) structure through the addition of FeCl3, thereby facilitating the release of a portion of the intracellular bound water. Subsequently, the freeze-thaw conditioning treatment results in the further destruction of the EPS structure, the release of additional bound water, and the re-agglomeration of flocs to form smooth drainage channels, thereby significantly improving the dewatering performance of WAS. A synergistic effect was found between the co-conditioning methods. The synergistic effect is specifically observed in the optimization of particle size distribution and the improvement of sludge cell lysis efficiency, which cannot be fully achieved by individual conditioning methods. Finally, an economic analysis was conducted on co-conditioning, revealing that this technology is economically advantageous and holds promising research prospects.