Simultaneous removal of cyanobacteria and algal organic matter (AOM) by CaCO3 precipitation combined with Polyaluminum chloride (PACl) flocculation

Abstract

Simultaneous removal of cyanobacteria and algal organic matter (AOM) is still a difficult task for drinking water treatment plants (DWTPs) during cyanobacteria blooms. CaCO3 precipitation, an environment-friendly drinking water treatment technique, has been recommended to removal cyanobacteria or AOM from drinking water. However, knowledge of simultaneous removal performance by CaCO3 precipitation is limited. Here, the simultaneous removal performance to cells and AOM of CaCO3 precipitation, combined with polyaluminum chloride (PACl) flocculation, was investigated, as well as the underlying mechanisms. The results showed that CaCO3 precipitation strategy significantly improved the simultaneous removal performance of PACl, with removal efficiency up to 98 % for cells and 48 % for AOM. CaCO3 precipitation exhibited reliable simultaneous removal effects at various initial cells densities and AOM concentrations. Scanning electron microscope (SEM), transmission electron microscope (TEM) and zeta potential results suggested that mutual flocculation between positively charged CaCO3 crystalline particles and negatively charged cells is the main responsible mechanism for cells removal. Despite that the adsorption of AOM on CaCO3 nuclei surface delays its precipitation, co-precipitation removal mechanism of AOM is realized during CaCO3 nucleation. Moreover, further AOM removal can be obtained by CaCO3 crystalline particles via chemisorption between organic molecules and the particles surface.