Steps taken during the water purification process ensure CWLP's ability to convert raw lake water into a safe, clean product that consistently meets state water quality standards. For more information about the water purification process, click the blue expandable panels below.
The water is then pumped to the Purification Plant, where it passes through a chemical dosing chamber to receive lime, which softens the water, and ferric sulfate (iron) and polymer, both of which coagulate the suspended particles in the water. From the dosing chamber, the water passes to one of five upflow clarifiers.
In the clarifiers, 90% of the suspended particles are removed from the water, which is then sent to the filter gallery for the final step in the purification process. On its way to the filter gallery, the clarified water receives a dose of carbon dioxide to lower the pH (which was raised during the lime softening process), chlorine to kill bacteria, and fluoride to prevent tooth decay.From the filter gallery, the clean water is sent to two clearwells on the plant grounds for temporary storage prior to distribution (via the utility's new high-service pump station that was completed in spring 2014). At this point, the purification process is complete. It has taken less than two hours to convert raw lake water into a safe, clean product that consistently meets state water quality standards.
CWLP has a total of five clarifiers, which over time have represented three different technologies. The oldest technology was the Spaulding Upflow Clarifer, which was designed by the utility's first Water Plant Superintendent, Charles Spaulding, and placed into operation when the lakeside Water Purification Plant was built in 1935. For many years, this type of clarifier was considered state-of-the-art. It is still used by purification plants around the world. In Spaulding Upflow Clarifiers, water flows downward, through a large inverted cone in the center of the clarifier. At the bottom of this cone, a series of revolving paddles mix the water and chemicals used in the treatment process—including ferric sulfate and polymer, which help dirt and other suspended particles coagulate (stick together). Then, flowing outward and upward into the main body of the clarifier, the water passes through a "blanket" of lime sludge formed from an accumulation of coagulated particles. Most of the suspended particles in the upflowing water are trapped there. The cleaned water then flows over the top of the clarifier and heads to the filter gallery. All three original Spaulding Upflow Clarifiers were rebuilt as Helical Flow Clarifiers (see below).
The second type of clarifier used by CWLP is a Permutit unit, which is simply a modified version of the Spaulding clarifier. CWLP currently has two Permutit-style clarifiers, which were built in the mid-1950s.
The third and newest model, is the Helical Flow Clarifier, designed by another former CWLP Water Plant Superintendent, Dave Wyness. In this type of clarifier, the water is introduced into the base of the clarifier where it moves upward in an ever expanding and slowing spiral motion, passing through the lime sludge blanket on its way. The Helical Flow Clarifier is superior to the Spaulding unit in two ways. First, it has no moving parts and requires no power to operate. Second, it is better at removing suspended particles and produces a better overall water quality. As in the Spaulding Clarifiers, water that has passed through the sludge blanket then overflows the top of the clarifier and heads to the filter gallery for the final stage of purification.
From the filter gallery, the clean water is sent to two underground clearwells for temporary storage prior to distribution.
Links to more information about water purification and related topics can be found in the left-hand column of this page.