Adsorption of microcystin-LR by activated carbon and removal in full scale water treatment

Removal of microcystin toxins from drinking water was evaluated at two full scale treatment plants that employed coagulation-sedimentation, dual media filtration and chlorination combined with either granular activated carbon filtration or powdered activated carbon. The influence of natural organic matter on the adsorption of the cyanobacterial toxin, microcystin-LR, by activatedcarbon was also evaluated in laboratory studies over a range of toxin concentrations similar to those typically observed in raw water at these plants. The sensitive protein phosphatase inhibition bioassay was used to quantify microcystin. Conventional treatment processes combined with activated carbon generally removed more than 80% of microcystin from raw water, but a residual concentration of 0.1-0.5 μg equivalents of microcystin-LR per liter was observed considering both (GAC and PAC) treatment facilities. Most values of residual microcystin-LR were at the low end of this range, but the upper end approaches the guidance level being considered by Health Canada for these toxins in drinking water