Removing solids

At our Rinconada Water Treatment Plant, we remove the suspended solids in large tanks called clarifiers, the largest feature at the plant. Each tank is approximately 20 feet deep and 117 feet square. Clarifiers at Rinconada Water Treatment Plant

We add special chemicals--such as aluminum sulfate--to the

water that enters the clarifier. These chemicals, called coagulants, cause the solid particles to clump together. This process is called flocculation.

Eventually, the clumps form a "sludge blanket." The solid clumps are far heavier than the water, so the blanket sinks to the bottom. As it does, the blanket works like a finely-meshed net to catch other smaller particles.

The water at the top of the tank, now free of solids, overflows to the gutter-like spokes you see radiating from the center of the tanks in the picture above.

Rakes slowly rotate along the bottom of the clarifier. They scrape the settled sludge at the bottom of the tank into the center where it is removed periodically through pipes that run under the clarifiers.