Microcystin-LR removal from drinking water supplies by chemical oxidation and activated carbon adsorption

Microcystin-LR (MC-L) is among the most toxic and frequent cyanotoxins found in surface water and a provisional value of 0.001 mg/L is indicated by World Health Organization guidelines for water for human consumption. Among the conventional processes used for surface water treatment, the most effective in microcystin removal are chemical oxidation and adsorption. This study investigated two processes for the treatment of raw water of lake of Garda, drawn from the drinking water treatment plant of Desenzano d/G (Brescia, Italy), spiked with pure MC-LR. The experimental tests on adsorption with activated carbon were performed using carbon from both a mineral (M21) and a plant source (C25). Determination of the adsorption isotherm show that the activated carbon M21 is more effective than C25 in MC-LR removal. During the continuous flow column test with the carbon M21, the limit concentration for MC-LR was reached after about 4,000 bed volumes. Finally, chemical oxidation with sodium hypoclorite, which is more effective than chlorine dioxide for MC-LR removal, shows a yield of 80% with a concentration of 3 mgCl₂/L with a consequent reduction of MC-LR concentration from 10 to 1.5–2 μg/L.