Development of sludge-derived mesoporous material with loaded nano CaO2 and doped Fe for re-utilization of dewatered waste-activated sludge as dewatering aids

Abstract

A novel approach to converting dewatered waste-activated sludge (WAS) into conditioning reagents for enhanced dewatering of raw WAS is proposed in this study. Primarily, WAS pretreated by K2FeO4 was dewatered and converted into Fe-doped sludge-derived mesoporous material (SDMM) through thermal cracking methods. Subsequently, half of the resulting SDMM were modified by H2SO4-HNO3 coupled with thermal reflux to realize the carboxylation, and the remaining SDMM was used as the template for nano CaO2 loading. As a result, nano CaO2-loaded Fe-doped SDMM and carboxylic SDMM were successfully synthesized and jointly used to improve the dewaterability of raw WAS. The carboxylic material created the beneficial acidic condition for the solubilization of nano CaO2; nano CaO2 eliminated the negative impacts of EPS on WAS dewaterability by OH formation with the catalysis of ferrous substances (Fe2O3/FeOOH) in situ doped in SDMM; and the porous structure of SDMM acted as a filtration aid. As a result, a 64.1% specific resistance of filtration (SRF) reduction was achieved with the total addition of 1 g/g dry solid (DS) SDMM without pH pre-adjustment. The synergistic effects of the filtration aid, peroxidation and dewatered WAS utilization were simultaneously realized by the novel development of SDMM.