Preparation, characterization and sludge conditioning performance of modified coal fly ash

Abstract

Filtration aids have been widely used in improving sludge dewatering performance, while the previous filtration aids have relatively lower efficiency in adsorption and bridging ability. In this study, a modified coal fly ash (MCFA) was prepared by soaking raw coal fly ash (RCFA) with sulfuric acid. Scanning electron microscopy (SEM), X-ray powder diffraction (XRD), Specific Surface Area and Pore Size Analyzer (BET) and X-ray photoelectron spectroscopy (XPS) were utilized to characterize its structure and morphology. The sludge conditioning performance and dewatering performance on secondary sludge was carried out based on the specific resistance to filtration, capillary suction time and LB-EPS protein content analysis. It showed that the optimum conditions for preparing MCFA from RCFA was a soaking time of 2h, the acid concentration of 5.0mol/L and the ratio of acid to RCFA 5:1, under which MCFA exhibited a higher efficiency in sludge conditioning. XRD analysis revealed a high proportion of silicon in MCFA at ca. 26.80%, whereas XPS implied that more silicon was grafted onto the Si–O structure. SEM and BET measurements indicated that the surface of MCFA had underwent a strong corrosion, exhibiting a larger surface area, high pore volume and small average particle size, which had promoted its adsorption capacity and permeability in aiding sludge dewatering.