Cyanobacterial management in full-scale water treatment and recycling processes: reactive dosing following intensive monitoring

Abstract

The presence of cyanobacteria within full-scale treatment plants including spent filter backwash water and sludge treatment facilities is an increasing problem faced by water utilities. The fate of cyanobacterial associated taste and odour (T&O) compounds during these processes is unknown. This study aimed to better understand the occurrence of cyanobacteria and T&O compounds, 2-methylisoborneol (MIB) and geosmin, within a full-scale water treatment additional plant with recycling processes and investigate effectiveness of supplementary treatment processes applied within the plant following results of intensive and real time sampling. Samples were obtained from the source water and at key points within the treatment train, including the sludge thickener where MIB was noted to reach approximately 1500 ng L⁻¹. Potassium permanganate and powdered activated carbon were dosed into the sludge thickener and the concentration of MIB producing cyanobacterial cells and MIB in the sludge thickener was reduced by greater than 99%. However, MIB concentrations were still measured at approximately 20 ng L⁻¹ in the finished water, attributed to the addition of water recycled from the sludge thickener. A correlation between total MIB and the sample fluorescence was established and used to guide chemical dosing to maintain low levels. These results demonstrate that in situ fluorescence probes could be used to optimise the application of potassium permanganate and activated carbon when applied to reduce reducing cyanobacteria and MIB concentration during water treatment however further investigation would be required.