IntroductionThe DuPage Water Commission and its member utilities typically receives an increase in taste and odor complaints during the late summer and early fall months when water temperatures increase. The number of taste and odor complaints has increased dramatically during the last few years. Most complaints generally are that the water has a musty/earthy taste and odor.
CauseThe increase in musty/earthy tastes-and-odors is considered to be related to the zebra mussel colonization of the Great Lakes. The zebra mussel is a freshwater bivalve that invaded the Great Lakes about 1986. Zebra mussels appear to have been introduced into the Great Lakes in 1985 or 1986 when one or more transoceanic ships discharged their ballast water into Lake St. Clair.
The increase in musty/earthy tastes-and-odors is considered to be a result of a complicated lake ecology. Simply put, the zebra mussels consume planktonic (floating) algae and, thus, have decreased the quantities of planktonic algae in the Great Lakes. Decreases in planktonic algae have caused increased water clarity. Increases in water clarity has allowed sunlight to penetrate deeper, stimulating the growth of aquatic plants and benthic (bottom dwelling) green algae. Additionally, nutrients in the zebra mussel feces on the lake bottom can stimulate benthic green algae growth, especially in the immediate vicinity of zebra mussel beds. The benthic green algae die off around July. The die-off of the green algae returns high concentrations of nutrients to the water for the growth of benthic blue-green algae and actinomycetes, a filamentous bacterium.
Both blue-green algae and actinomycetes are capable of producing 2-methylisoborneol (2-MIB) and geosmin. 2-MIB and geosmin are two compounds known to produce musty/earthy tastes-and-odors in drinking water.
Current Operational ProceduresThe Chicago Water Department adds powdered activated carbon (PAC) to the water at the Jardine Water Purification Plant. The application rate of PAC is based upon the concentration of 2-MIB and geosmin. The Commission and its member utilities constantly raise and lower the water elevations within their storage tanks to keep the water in the tanks fresh. Water customers are urged to contact their water utility with any taste and odor complaints. These complaints will be forwarded to the Commission, who in turn logs them with the Chicago Water Department.
Taste and Odor ResearchTaste-and-odor treatment options include potassium permanganate, activated carbon, biological filtration and ozonation. Some of these options were eliminated because the Commission's type of operation. The Commission purchases treated water from Chicago and re-pumps the water to its customer utilities. There is no space available to construct some of these treatment facilities. The only option that could be considered was oxidation using ozone or advanced oxidation processes using ozone-hydrogen peroxide.