Cyanocidal Effect of H2O2 on the Bloom-Forming Microcystis aeruginosa and Sphaerospermopsis aphanizomenoides

Cyanobacterial blooms are a global concern causing water quality problems that have serious effects on recreational activities, irrigation, and drinking water usage. Various approaches are available to control cyanobacterial blooms in which Hydrogen Peroxide (H 2 O 2 ) emerges as a noteworthy environmentally safe oxidizing agent selectively inhibiting the growth of cyanobacteria and leaving no residue. The objective of this study was to assess how different concentrations of H 2 O 2 (1, 2, and 4 mg L -1 ) affect the growth of unicellular Microcystis aeruginosa and filamentous Sphaero-spermopsis aphanizomenoides cultures obtained from inland waters in Türkiye and to compare the effectiveness of H 2 O 2 application in monocultures and mixed cultures. For this purpose, the experimental setups were conducted in 96-well microtiter plates with eight replicates, and the growth of cultures during the experiment was monitored by measuring cell optical density at 665 nm (OD 665 ). The results showed that 1 mg L -1 H 2 O 2 had a significant effect on the growth of monocultures of Microcystis with cell densities of 100x10 3 cell mL -1 (p<0.05) and Sphaerospermopsis with 50x103 cell mL -1 . The cell growth of Microcystis cultures with higher densities declined at 4 mg L -1 H 2 O 2 addition, significantly. However, 4 mg L -1 H 2 O 2 dosage was effective up to 200x10 3 cell mL -1 Sphaeros-permopsis . In the mixtures of these species, 2 mg L -1 H 2 O 2 application was effective to suppress the tested cell densities in the case of Microcystis dominance.