Mitigation of Microcystis sp. with metallic peroxide granules: matrix effect on hydrogen peroxide release kinetics and toxicity study on invertebrates

An array of mitigation strategies has been applied over the years for toxic blue-green algae with the most recent one to be hydrogen peroxide (H2O2). Hydrogen peroxide has been widely used as an alternative to copper algaecides, and it is perceived as a more environmentally friendly option for treating surface waters. However, dense blooms demand high oxidant causing undesirable effects to the non-targeted organisms in the aquatic ecosystem. Slow releasing H2O2 metallic granules have been used in this study as an alternative approach to direct application of high-doses liquid H2O2 application. In this study, calcium peroxide (CaO2) granules were applied in surface water matrix (Kouris Dam, Cyprus) to examine: (a) their H2O2 releasing properties with varying pH values, (b) their mitigation efficiency on Microcystis sp. bloom in comparison with liquid H2O2, and (c) their toxicity on Gammarus sp. in a range of concentrations. Results showed that in acidified environments granules have higher H2O2 releasing capacity. Moreover, treatment of Microcystis sp. with 0.5 – 2.0 g/L CaO2 were efficient to eliminate the blooms and safe on zooplankton species. All of the above, are indicative towards the potential of CaO2 treatment, however its application necessitates further investigation prior taking it to the field.