Knowledge Bank

Based on climate change projections, the occurrence and intensity of cyanobacterial blooms is expected to increase; also it is more likely that these blooms will produce multiple cyanotoxins in drinking water supplies. Therefore, the drinking water industry needs to understand how to most effectively remove a range of cyanotoxins from the water column. The most common cyanotoxin found in the United States is microcystin, and the most common isoform of microcystin is microcystin-LR (MCLR). Microcystin-LR can be found in both intracellular and extracellular forms in drinking water. Typical water treatment processes, such as coagulation/flocculation, filtration, and sedimentation, are ineffective against extracellular toxins. Powdered activated carbon (PAC) has been shown to be effective against extracellular toxins. In this study, the effectiveness of PAC application under typical coagulation/flocculation processes and conditions was tested. Batch tests were performed to determine how adsorbent dose and presence of coagulant (specifically, aluminum sulfate) impact the adsorption process, and therefore, MCLR removal. It was decided that the coagulant and PAC should be added simultaneously to reduce the effect of natural organic matter adsorption competition. As expected, the addition of the alum resulted in a decrease in the amount of MCLR adsorbed to the PAC; however, overall MCLR removal increased when alum was added. It is hypothesized that this increase is due to adsorption to aluminum hydroxide particle, but more research is needed to confirm this. Results of this test will be used to develop guidelines and best practices to be used by utilities to optimize cyanotoxin removal.