Application of Various Oxidants for Cyanobacteria Control and Cyanotoxin Removal in Wastewater Treatment

Cyanobacteria blooms are an increasing issue in wastewater-treatment systems as the associated toxins could induce health risks due to potential passage through irrigation practices using recycled water. The impacts of hydrogen peroxide (H2O2), chlorine, potassium permanganate (KMnO4), and ozone on Microcystis aeruginosa cell viability, and the concomitant toxin release and degradation in wastewater, were investigated. All of these treatments could inactivate M. aeruginosa cells to varying degrees in wastewater due to its chemically challenging matrix. In this paper chlorine was shown to be a feasible option to be used as the last barrier in wastewater-treatment plants due to its strong oxidizing potential resulting incomplete cell inactivation and subsequent degradation of the majority of cyanotoxins in 30 min. However, this was dose dependent as although the release of extracellular toxins was oxidized using 5 mg L-1 chlorine, lower doses of 3 and 4 mg L-1 chlorine were unable to effectively degrade the resultant extracellular toxins. KMnO4 was also effective when a high dose (10 mg L-1) was applied as a postoxidation step to reduce the negative impacts caused by cyanobacteria in wastewater and unlike chlorine does not form any toxic disinfection byproducts. H2O2 was also an effective oxidant as it degraded the majority of intracellular and extracellular toxins after a 2-day treatment. Although 4 and 6 mg L-1 ozone could reduce the total toxins, apparent increase of extracellular microcystins were observed for both ozone treatments. (C) 2014 American Society of Civil Engineers.