The effect of water treatment processes on the removal of hepatotoxins from Microcystis and Oscillatoria cyanobacteria: A laboratory study

Abstract

The behaviour of hepatotoxins from Microcystis and Oscillatoria cyanobacteria in some common water treatment processes was investigated on the laboratory scale in order to obtain data on their potential transfer to drinking water. Two toxins were separated from both of the freeze-dried cyanobacterial materials used in the experiments, a natural bloom consisting of M. wesenbergii and M. viridis and a laboratory-grown culture of O. agardhii. The concentrations of all four toxins before the treatments were between 30 and 60 μg/1. The investigated water treatment processes, selected from among methods applied in Finland, were: (1) Al 2(SO 4) 3 flocculation with sand filtration and chlorination; (2) FeCl 3 flocculation with sand filtration and chlorination; (3) addition of activated carbon powder with Al 2(SO 4) 3 flocculation, sand filtration and chlorination; (4) Al 2(SO 4) flocculation with sand filtration, activated carbon filtration and chlorination; and (5) ozonation with Al 2(SO 4) 3 flocculation, sand filtration and chlorination. The conventional flocculation-filtration-chlorination procedures resulted in a relatively small decrease in the toxin concentrations. Activated carbon powder in low doses did not improve the results, but activated carbon filtration as well as ozonation completely removed the toxins. The toxin concentrations were determined by HPLC. The proper functioning of the treatment processes was monitored by measurement of the KMnO 4 value, turbidity and flocculation chemical residues.