The novel application of type II deep eutectic solvents (DES) for sludge dewatering

Abstract

Dewatering is a necessary step before the treatment and disposal of waste activated sludge, which also presents a huge challenge for the high-affinity binding between sludge and water. Hence, the aim of this paper is to introduce a new green and cheap deep eutectic solvent (DES) as a conditioner for waste activated sludge. A type II deep DES, which composed of choline chloride (ChCl) and CuCl2·2H2O, was creatively proposed to intensify the dewatering performance of sludge. We mainly focused on the effects of DES dosages and processing temperatures on the physicochemical properties of sludge. The results showed that DES has a considerable promotion on sludge dewaterability, and it also showed good correlations between DES dosage and capillary suction time (CST), zeta potential, soluble chemical oxygen demand (SCOD), and pH. The mechanisms of intensified dewatering performance can be explained by two aspects. One was that DES disrupted the extracellular polymeric substances (EPS) structures and disassociated the hydrophilic biopolymers (proteins and polysaccharides) from sludge. The other was that DES neutralized the surface negative charges of sludge and thus destabilized the flocs, which act as a coagulant. This study would broaden the application scope of DES, and may bring new insights to the field of sludge treatment.