Synergistic effect of innovative bentonite and poly aluminum chloride (PAC) combination for excess and digested sludge thickening and dewatering

Abstract

Urban wastewater sludge dewatering is one of the challenging issues that wastewater treatment plants face today and needs sustainable solutions. This study aimed to evaluate the effectiveness of the bentonite and poly aluminum chloride (PAC) combination as physical and chemical conditioners for sludge conditioning. This research has shown that the optimal dose for conditioning untreated excess and anaerobically digested sludge is a 0.3% PAC-to-bentonite ratio (1.8 g/g PAC + 6 g/g bentonite for anaerobically digested sludge and 0.324 g/g PAC + 1.08 g/g bentonite for biological excess sludge). Additional tests on extracellular polymeric substances proved that this method can significantly affect parameters such as total organic carbon, protein, and polysaccharides in sludge samples. It was found that time to filtration and specific resistance to filtration parameters were also reduced by 78% and 72% in anaerobically digested sludge and by 90% and 66% in untreated excess sludge respectively when this combination was used. Significant changes in other parameters such as sludge particle size, zeta potential, and others demonstrate the effect of PAC and bentonite combination on sludge types. In addition, the cost for preparing the solutions of both polymers at the considered optimal concentrations was calculated. For each ton of conditioned sludge, the cost ranges between 77$ and 94$. It has been demonstrated that the combination of bentonite and PAC, along with other conventional materials such as acidic modified bentonite, facilitates the dewatering process effectively despite the smaller clots in the sludge after conditioning, which reduces the porosity of the sludge and prevents dewatering.