Critical review of oxidant application and scalability for managing toxic Microcystis blooms in wastewater stabilisation ponds

Wastewater stabilisation ponds (WSPs) provide favourable conditions for cyanobacterial proliferation. Cyanobacterial toxins (cyanotoxins) pose a risk to human health, environmental flows, and recycled water schemes if not managed appropriately. Cyanotoxins are released predominantly during cyanobacterial cell lysis and under cell stress, but also during normal cell death. A variety of algaecides and oxidants are proven to be effective against cyanobacteria, yet each has a range of limitations, which include low effectiveness towards cyanotoxins, increased cyanotoxin gene synthesis, impact on non-target microorganisms and the microbiological assemblage composition, toxic residuals that can accumulate in sediment, high cost, and impracticality to implement at a large scale. This paper critically reviews the options for chemical control of microcystin-producing bloom-forming cyanobacteria, covering published literature describing laboratory, field experiments, and full-scale trials. This is the first study to assess the scalability of chemical treatment options in WSPs against toxic cyanobacterial blooms. Based on the reviewed case studies, multiple-criteria decision analysis (MCDM) of chemical remediation options was developed and showed that hydrogen peroxide and ozone nanobubbles are the most feasible and scalable treatment methods for future implementation in large-scale WSPs.