Comparison and modeling of the adsorption of two microcystin analogues onto powdered activated carbon.

The presence of cyanobacterial toxins, such as microcystins, in drinking water supplies is a major concern for water authorities worldwide due to possible adverse health effects associated with exposure to these compounds. Adsorption onto powdered activated carbon in the water treatment process offers an effective treatment option for the removal of these compounds. However, for the efficient use of powdered activated carbon, knowledge of the appropriate dose to apply is required. In this study the adsorption of two microcystin analogues, microcystin-LR and microcystin-LA, onto powdered activated carbon was studied for two waters. Analysis of batch kinetic and equilibrium adsorption data showed that the homogeneous surface diffusion model could successfully predict the adsorption kinetics of the two toxins. The application of the homogeneous surface diffusion model is extremely useful to water treatment plant operators as it can be used to predict the powdered activated carbon dose for the removal of algal toxins based on the analogue(s) present, influent toxin concentration and powdered activated carbon contact time. Adsorption was also found to be different for the two toxin analogues, and dependent on the water character. Microcystin-LR was much more easily removed than microcystin-LA in both waters, and adsorption of both analogues was lower in the water with a higher dissolved organic carbon concentration.