Harvesting of microcells from cyanobacteria-laden water by energy-efficient electro-flocculation-flotation with aluminum hydrates

Abstract

Electrocoagulation-flotation (ECF) is able to effectively harvest microcells from eutrophicated drinking water reservoirs to reduce algogenic organic matter (AOM) during cyanobacteria blooming. However, ECF needs high current density (CD) and prolonged reaction time with inevitable high-energy consumption. This study aimed to investigate a novel electrocoagulation-flocculation-flotation (EFF) process, with 10 min EC reaction and 15 min flocculation followed by 10 min flotation, for Microcystis aeruginosa (MA) cell harvesting from water as well as AOM reduction with Al hydrates at various CD and pH conditions. The results have shown that significant MA cell separation and dissolved organic carbon (DOC) reduction by EFF occurred at pH 8 with 5 mA/cm2, accounting for 95 % and 56 %, respectively. At such a condition, the formation of dominant colloidal Al species (Alc) governed the EFF to promote cells and AOM destabilization by strong sweep flocculation along with weak charge neutralization by polymeric Al species (Alb). Moreover, the pronounced reduction in soluble microbial product-like (SMPL) substances could be further improved by up to 60 % with EFF. It was also found that EFF required only 2.07 × 10−2 kWh/kg in energy input and served energy saving ~63 % less than that by prolonged ECF at similar MA cell separations. It concluded that EFF was an energy-efficient technique to fast separate and harvest microcells from MA-laden water and AOM reduction with low energy input for practical application in drinking water treatment.