Ultrasound-enhanced coagulation for Microcystis aeruginosa removal and disinfection by-product control during subsequent chlorination

Abstract Ultrasound techniques have gained increased interest in environmental remediation because of their promising performance and reagent-free nature. This study investigated the effects of ultrasound-coagulation on Microcystis aeruginosa removal, disinfection by-product (DBP) formation during subsequent chlorination, and acute toxicity and DBP-associated toxicity variations in chlorinated effluents. Compared with coagulation using polymeric aluminum chloride (5 mg-Al/L) alone, ultrasound-coagulation showed significantly enhanced turbidity removal, with the removal ratio increasing from 51% to 87%–96%. Although the addition of ultrasound may not substantially improve and even deteriorate the coagulation removal of DOC following the leakage of intracellular organic matter, the significantly improved DBP control was achieved as the cells dominated DBP formation. With the addition of ultrasound, the chlorine demand, aggregate DBP concentration and total organic halogen concentration reductions in the chlorinated M. aeruginosa solution increased from 15%, 47% and 52% (coagulation alone), respectively, to 56%–78%, 56%–80% and 68%–89%. The enhanced DBP mitigation was mainly attributed to the enhanced algal removal. Similarly, the acute toxicity and DBP-associated toxicity of chlorinated effluents further decreased from 100% and 0.0092 (coagulation alone) to 30%–88% and 0.0029–0.0060. Therefore, ultrasound-enhanced coagulation is a promising strategy for urgent algal removal, DBP mitigation and toxicity abatement.