application of hydrogen peroxide for the removal of toxic cyanobacteria and other phytoplankton from wastewater phytoplankton blooms containing elevated levels of cyanobacteria are common in wastewatertreatment plants microcystis aeruginosa the most common freshwater cyanobacterial species produces the hepatotoxin microcystin which is a threat to human and environmental health blooms also affect the viability of treating and reusing water and cause problems when detritus accumulates in pipe and pumping delivery infrastructure we proposed the application of hydrogen peroxide h2o2 to induce cyanobacterial cell death spectral fingerprinting of phytoplankton into four groups cyanobacteria chlorophyta diatoms and cryptophyta allowed for determination of equivalent chlorophylla chla concentrations contributed by photosynthetic pigments an indicative measure of the photosynthetic activity of each phytoplankton group this was used to establish the effect of h2o2 addition on phytoplankton in wastewater samples the lowest h2o2 dose that caused statistically significant exponential decay of phytoplankton groups was approximately 30 x 103 g h2o2microg phytoplankton chla at this dose cyanobacteria and total phytoplankton exhibited a halflife of 23 and 45 h respectively cyanobacteria decayed at a rate approximately twice that of chlorophyta and diatoms and the combined chla of all phytoplankton groups decreased to negligible levels within 48 h of h202 application