Simultaneous removal of dissolved organic matter, Microcystis aeruginosa, and microcystin-lr by pre-oxidation and coagulation-flocculation processes

The purpose of this study was to evaluate the impact of the presence of Microcystis aeruginosa (MA) and microcystin-LR (MC-LR) on the removal of dissolved organic matter (DOM) by coagulation-flocculation in optimal conditions. Additionally, we determined the effect of pre-oxidation with NaOCl on the simultaneous removal of MA, MC-LR, and DOM, using the same processes and conditions. The water used in experimental tests was prepared with distilled water, strains of MA, microcystin-LR standards, and model compounds of DOM. Once the water was prepared, the proves were carried out in jar test equipment. We used a fractional factorial design to obtain the variables of significant influence and a response surface design to attain the optimal operation conditions of each process. The DOM removal decreased 32.25% when MA and MC-LR were in the process because they were competitors for the coagulant, but the main effect was caused by MA due its high concentration and physicochemical characteristics. The dose of pre-oxidant had no significant influence in the removal of three contaminants since the contact time in tests was very short.

Keywords: cyanobacteria, cyanotoxins, clarification, sodium hypochlorite, dissolved organic carbon, drinking water.