Abstract
Abstract. Cyanobacteria and cyanotoxins are a risk to human and ecological health, and a hindrance to biological wastewater treatment. This study investigated the use of hydrogen peroxide (H2O2) for the removal of cyanobacteria and cyanotoxins from within waste stabilization ponds (WSPs). The daily dynamics of cyanobacteria and microcystins (commonly occurring cyanotoxins) were examined following the addition of H2O2 to wastewater within both the laboratory and at the full scale within a maturation WSP, the final pond in a wastewater treatment plant. Hydrogen peroxide treatment at concentrations ≥ 0.1 mg H2O2 μg−1 total phytoplankton chlorophyll a led to the lysis of cyanobacteria, in turn releasing intracellular microcystins to the dissolved state. In the full-scale trial, dissolved microcystins were then degraded to negligible concentrations by H2O2 and environmental processes within five days. A shift in the phytoplankton assemblage towards beneficial Chlorophyta species was also observed within days of H2O2 addition. However, within weeks, the Chlorophyta population was significantly reduced by the re-establishment of toxic cyanobacterial species. This re-establishment was likely due to the inflow of cyanobacteria from ponds earlier in the treatment train, suggesting that whilst H2O2 may be a suitable short-term management technique, it must be coupled with control over inflows if it is to improve WSP performance in the longer term.
Highlights
Cyanobacteria are a common occurrence in waste stabilisation ponds (WSPs), a suspended growth biological treatment technology used in outdoor municipal wastewater treatment plants (WWTPs) (Furtado et al, 2009; Ho et al, 2010; Martins et al, 2011; Vasconcelos and Pereira, 2001)
The presence of cyanotoxins in drinking and recreational waters is often of greater concern to water management authorities than their presence in waste stabilization ponds (WSPs). As well as their inherent risk to human and ecological health, cyanobacteria are a hindrance to the wastewater treatment processes (Martins et al, 2011)
Laboratory trials were performed to determine the dynamics of cyanobacteria and microcystins removal by various H2O2 concentrations at the microcosm scale, followed by H2O2 application to a full-scale WSP
Summary
Cyanobacteria are a common occurrence in waste stabilisation ponds (WSPs), a suspended growth biological treatment technology used in outdoor municipal wastewater treatment plants (WWTPs) (Furtado et al, 2009; Ho et al, 2010; Martins et al, 2011; Vasconcelos and Pereira, 2001). Several genera produce toxins, including microcystins, which pose a significant health risk to humans and animals. Both cyanobacteria and their toxins (cyanotoxins) are a substantial threat to ecological systems (Christoffersen, 1996; de Figueiredo et al, 2004). The presence of cyanotoxins in drinking and recreational waters is often of greater concern to water management authorities than their presence in WSPs. as well as their inherent risk to human and ecological health, cyanobacteria are a hindrance to the wastewater treatment processes (Martins et al, 2011). Cyanobacteria and cyanotoxins inhibit the biological, physical, and chemical treatment of wastewater. The presence of cyanobacterial blooms increases the possibility that inadequately treated effluent will be discharged, possibly containing harmful cyanotoxins
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