Impact of hydroxyl aluminum speciation on dewaterability and pollutants release of dredged sludge using polymeric aluminum chloride

Abstract

Flocculation conditioning is a common pretreatment step for dredged sludge dewatering, while various pollutants in sludge might release into the residual water during flocculation conditioning and dewatering process, leading to secondary pollution. In this study, polymeric aluminum chloride (PAC) with different alkalinity was used as conditioners to enhance the dewaterability of dredged sludge in Baiyangdian Lake, and effects of hydroxyl aluminum speciation on dewatering performance and release of pollutants of dredged sludge were investigated. The results showed that the surface positive charge density of the mediumly polymeric hydroxyl aluminum (Alb) and highly polymeric hydroxyl aluminum (Alc) was higher, and the produced flocs were more compact, the abundant pore structure in flocs enhanced the water transport capacity and dewatering performance. Correlation analysis results showed that the release of heavy metals in residual water was mainly related to Ala, and the release of high molecular weight organic matter (aromatic protein), nitrogen and phosphorus was related to Alb, while Alc helped reduce pollutions in residual water. Alc showed better performance in improving dredged sludge dewaterability, and reduce the release of pollutants. This study provides an optimized strategy of flocculants for dredged sludge treatment based on aluminum speciation control.