Taste and odor problems in source waters and water treatment facilities

Over the past decade, consumer complaints regarding off-flavors and off-odors in metropolitan Phoenix area drinking water has increased substantially. Unpleasant tastes and odors from the volatile organic compounds, 2 methylisoborneol (MIB) and Geosmin, in drinking water have not been linked to health risks, but create a negative impression of drinking water quality. Blue-green algae (Cyanobacteria) and Actinomycetes are considered the primary causal agents of taste and odor problems. Sampling of reservoirs, rivers and canals supplying the Phoenix metropolitan area water treatment plants (WTPs) was conducted for over three years to identify biological, physical and chemical parameters that may serve as predictors of taste and odor episodes. MIB was the primary taste and odor compound observed in most reservoirs and canals, but Geosmin was frequently encountered in the Consolidated Canal, which supplies the City of Chandler, Arizona. Water temperature, specific conductance, nitrogen concentrations and cyanobacteria abundance were correlated with MIB and Geosmin concentrations, but did not yield reliable predictive information. Although over 1,300 strains of algae, cyanobacteria and Actinomycetes were isolated from source waters, MIB and Geosmin production was restricted to a limited number of organisms. Four cyanobacteria species, Phormidium sp. and three Pseudanabaena species, were confirmed as MIB producers. Two cyanobacteria species, Oscillatoria splendida and Oscillatoria agardhii, and two actinomycete strains of Streptomyces sp. were confirmed as Geosmin producers. A web-based interactive taxonomic guide with over 200 photomicrographs was constructed to assist WTP personnel in identifying MIB and Geosmin producers, and other dominant taxa found in local source waters. Data from real-time monitoring of MIB and Geosmin at the Chandler WTP enabled personnel to respond to elevated concentrations of these compounds. Adjusting powdered activated carbon (PAC) doses in response to these results improved treatment practices and water quality. A comparative study of thirteen PAC brands determined the relative cost effectiveness of each product for removal of MIB and Geosmin from source waters. Study results will assist both researchers and potable water treatment facility personnel in understanding and mitigating taste and odor problems in drinking water supply sources and treatment facilities.