Additional Treatment Facilities

Treatment Ponds

The water-cleaning processes in the wastewater treatment plant are essentially the same as what occurs naturally in a lake or stream. A treatment plant simply speeds up the natural water purification process. During big storms, the amount of wastewater entering the treatment plant can exceed the plant’s capacity. When that happens, the District sends some of the wastewater directly to the treatment ponds. In the ponds, the water undergoes natural purification processes, resulting in clean water after about a month. The same water processed through the treatment plant would be cleaned in one day!

Process

There are four ponds linked together by gate valves, with a total area of 342 acres and a capacity of about 665 million gallons. Water enters at Pond 1 and leaves after slowly meandering through all four ponds. In the ponds, bacteria use the oxygen to metabolize the solids and chemicals in the water and release carbon dioxide. Algae use the carbon dioxide released by the bacteria as well as nutrients in the water to grow, releasing oxygen back into the water. 

The water in the first pond is a greenish gray, turning greener with algae in each following pond. By the time the water gets to the fourth pond it looks a lot like green pea soup. Hundreds of ducks and geese nest here in the spring and thousands of them, including pelicans, seagulls, and other migrating birds stay here in the winter. Water and algae from Pond 4 is pumped to the flocculating clarifiers for further treatment.

Flocculating Clarifiers: Physical / Chemical

Water that has been treated in the ponds is sent to the Flocculating Clarifiers to remove algae from the water. Flocculation is a physical/chemical process whereby chemicals called polymers are mixed with the algae and water from Pond 4, causing the algae to clump together and form what is called floc. The algae floc is heavier than water and settles to the bottom of the clarifier. A slowly rotating paddle on the bottom collects the solids that settled, which is known as sludge. This algae sludge is pumped back into Pond 1.

The clean water that leaves the Flocculating Clarifiers is piped either to the sand filters or directly to chlorination, depending on the water quality.