AWWA WQTC57032

Algae in drinking water supplies can cause a number of problems, including tastes and odors, filter clogging, interference with coagulation processes, and the production of toxins. Phytoplankton monitoring for the city of Columbus, Ohio began in 1938, in response to taste and odor problems. Since that time, monitoring has expanded as additional water supply reservoirs were constructed. Phytoplankton at each of the three reservoirs respond independently and reflect differences in watershed conditions and source water chemistry. Historically, the monitoring focus has been on taste and odor causing organisms and other organisms in the reservoirs that may cause treatment problems. However, phytoplankton monitoring within the treatment plant can also be very beneficial. Phytoplankton analysis has been used to evaluate treatment process efficiency in two full-scale surface water treatment plants. The effects of chemical dosage and other treatment changes on individual treatment processes or the entire water treatment plant can be evaluated using phytoplankton. Phytoplankton analysis has also been used to evaluate filter performance, jar tests, and to determine the source of high particle counts and turbidity increases. Phytoplankton monitoring is also used in conjunction with limnological monitoring of the water supply reservoirs. During summer stratification this monitoring is used to determine the optimum outlet elevation. The objective is to minimize algae related treatment problems as well as taste and odors associated with low dissolved oxygen water from below the thermocline. In the past, copper sulfate was occasionally used in the water supply reservoirs and river to eliminate plankton blooms. However, phytoplankton control strategies have changed to prevent the release of cyanobacteria (blue-green algae) toxins. Now more than ever, phytoplankton monitoring is important to identify and enumerate toxic algae. Elevated numbers of potentially toxic cyanobacteria (blue-green algae) are used as a trigger for increasing the frequency of sampling in the watershed and initiating microcystin ELISA toxin screening. Phytoplankton monitoring in the watershed has been a useful tool that gives advanced warning of potential treatment problems and increases the number of available options when dealing with a phytoplankton bloom. Monitoring phytoplankton through the treatment process is an additional tool to aid the treatment plant staff and assist in optimizing treatment.