Microcystin release following the chlorination of hydrogen peroxide treated microcystis-laden waters

Abstract

Freshwater systems worldwide are facing increased risks of impairment as a result of the proliferation of harmful algal blooms. Moreover, many cyanobacterial blooms release toxic compounds that are referred to as cyanotoxins. One of the most problematic bloom forming cyanobacteria resulting from anthropogenic-induced eutrophication is Microcystis aeruginosa, which is capable of releasing Microcystin. While most of its cyanotoxins are intracellular, they can become available to the environment when the cells lyse. Conventional water treatment processes are unable to remove these toxins that have been found in finished water. In an effort to control these blooms, chemical algaecides are typically applied. In this study, the efficacy of two algaecides, namely hydrogen peroxide (H2O2) and copper sulphate (CuSO4), was first assessed with regards to their abilities to reduce Microcystis levels and minimizing intra-cellular toxin leakage. The results showed that while applying high dosages of the two algaecides inhibited Microcystis, the total toxin levels tended to exceed the 1 µg/L World Health Organization (WHO) recommended standard. The impacts of chlorinating algaecide treated water were then quantified. The results showed that the use of CuSO4 followed by a subsequent filtration and chlorination step proved to be the most effective approach towards inhibiting the cyanobacteria and reducing toxin levels. Yet, toxin and trihalomethane levels were found to be high when chlorination occurred within the first 48 hrs of algaecide application. Filtrating and chlorinating water that had been treated with H2O2, showed a significant drop in toxin levels; yet the WHO standard was not met irrespective of the H2O2 dose or when the chlorination was implemented.