Microwave-alkali treatment with water elutriation to enhance waste activated sludge solubilization for carbon sources and nutrients recovery

Abstract Effects of MW treatment, combined MW-alkali (MA) treatment, and combined MA-water elutriation (MAW) treatment on sludge solubilization were studied; this work aims at the recovery of carbon sources and nutrients. Effects of MW power input, MW heating time, NaOH dosages, alkali treatment durations, and sludge solids concentration on sludge solubilization were explored. These treatments produced good chemical oxygen demand (COD) dissolution degree outcomes, with optimal values of 12.38±0.20% (MW treatment), 54.68±0.28% (MA treatment), and 55.58±0.68% (MAW treatment), respectively. Besides, MW treatment could disrupt sludge flocs and biomass cell membranes, with a 120 mg/L volatile fatty acids (VFAs) release (280 W for 5 min). A reduction of VSS/TSS ratio was 10.50% by alkali treatment, and 22.60% by MA treatment. Compared with MA treatment only, water elutriation after MA resulted in outstanding nutrients release, with optimal dissolution degrees increasing from 67.87±0.52% to 81.87±0.60% (TP), and 56.08±0.94% to 73.73±1.04% (TN), respectively. MW power inputs, MW heating duration, alkali treatment time, and especially NaOH dosages had significant effects on sludge solubilization, but solids concentration had a minor effect on sludge solubilization. Moreover, higher MW power input, longer MW heating time, and greater sludge solids concentration could cause gelatinization and even carbonization.