Drinking Water Taste and Odor Studies - Chicago, Illinois
For the City of Chicago, Department of Water, Greeley and Hansen conducted a study to identify the causes of the highly unusual, both in intensity and duration, musty/earthy taste and odor problems experienced by the Jardine and South Water Purification Plants and to project the potential escalation and longevity of the problems. A survey was conducted of 110 water treatment plants in the United States and Canada, that use water from the Great Lakes, to determine if they were having similar taste and odor problems and if they had an y explanations for the cause(s). Also contacted were 35 personnel of organizations familiar with the water quality and ecology of the Great Lakes to identify any changes that had occurred in the lakes that might be related to the taste and odor incidents. A literature search was conducted to draw from the scientific and engineering knowledge pertaining to musty/earthy tastes and odors. Lake Michigan water quality data applicable to the Illinois shoreline were also analyzed.
The research efforts indicated that 2-methylisoborneol (MIB) and geosmin were causing musty/earthy tastes and odors in Chicago's drinking water. A pilot filter testing program was performed to evaluate the effectiveness of granular activated carbon (GAC) over sand dual media in removing MIB and geosmin from the water passing through Chicago's 700 mgd South Water Purification Plant. The testing consisted of 12 weeks of side-by-side evaluations of 6 pilot filters containing GAC over sand dual media.
Although the sand portions of the dual media tested were identical and the same GAC depth was used in each pilot filter, the characteristics of the GAC were different. The testing evaluated the performance of virgin GAC from two manufacturers; virgin GACs having two different gradations; and virgin GACs versus used GACs that had been in service for 1 and 2 years. All GAC over sand dual media were tested at filtration rates of 3, 4 and 5 gallons per minute per square foot to study the effects of empty bed contact time on the GACs' ability to remove MIB and geosmin. The performance of the GAC over sand dual media in removing particulates were also monitored and evaluated.