AWWA WQTC65935

Cyanobacteria are a concern for water authorities worldwide as their persistence in water supplies causes numerous problems for water treatment plants. These include exertion of an additional demand on coagulants and clogging of filters which results in reduced filter run-times and increasing backwash frequencies. However, the major problem of cyanobacteria is the metabolites they produce; in particular, cyanotoxins and taste and odor (T&O) compounds. These metabolites not only account for a large number of consumer complaints due to aesthetic problems, but they also have the potential to compromise human health. Furthermore, these metabolites have been shown to be somewhat recalcitrant to conventional water treatment processes. One of the major species of cyanobacteria which plague Australian water authorities is Anabaena circinalis, which can produce geosmin (a T&O compound) and a range of saxitoxins (potent neurotoxins). Recent surveys of A. circinalis blooms in South Australian water sources have shown these metabolites are present at significant concentrations. This study evaluated the treatment processes at two existing South Australian water treatment plants for the removal of A. circinalis cells and the associated metabolites, geosmin and saxitoxins. In particular, the coagulation process, powdered activated carbon (PAC) dosing and biological sand filtration were assessed for their ability to remove these contaminants. The results so far have shown that if optimized, coagulation can remove most of the cyanobacterial cells and a significant proportion of the metabolites as they are largely contained within the cells (intracellular). Under favorable conditions, biological rapid sand filtration can remove the remainder of the geosmin, representing the dissolved form (extracellular) whereas PAC is not quite as effective, and still allows a fraction of the geosmin to enter the distribution system. Includes 7 references, figures.