Learn About How We Safely Treat Wastewater
The Central Marin Sanitation Agency (CMSA) subregional wastewater treatment plant is part of an environmentally sensitive system designed to collect wastewater pump, treat and dispose of wastewater from much of Central Marin County.
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Chemical Injection. Chemicals are injected into the sewer pipeline system occurs about one mile before the treatment plant to reduce corrosion and odors.
The Headworks uses mechanical screens to remove large items, grit and sand. Bar Screens capture and remove large items.
Aerated Grit Chambers remove grit, dirt and sand, which is hauled away to a landfill.
Special clarifier tanks allow heavy solids to sink out by gravity. Lighter solids, such as oil and grease are skimmed from the surface.
Primary Clarifiers. Wastewater moves slowly through these long tanks where grease rises and is scrapped off, while heavier materials settle to the bottom and are scraped out. to decrease odors and corrosion.
Several Stages of treatment further clean the wastewater.
Biotowers are the first stage of biological treatment. Effluent from primary treatment is pumped up the biotower and then trickles down through a dense grid of plastic. Natural bacteria grows on the media and consumes the solids in wastewater as it trickles down.
Aeration Tanks. Tiny air bubbles released from the bottom of the tank provide air for the microorganisms that consume remaining organic matter. The organisms clump together and sink where they are removed.
The wastewater is disinfected with chlorine and then dechlorinated before being discharged safely into the bay.
Chlorine Contact tanks release a computer controlled dose of sodium hypochlorite (bleach) to kill pathogens. The water is then tested for chlorine levels, dechlorinated and pumped to the outfall pipe.
Outfall. A 1-1/2 mile long pipeline into the Bay.
The solids, called sludge, are sent into a heated digester where they break down further.
Digesters heat the solids collected from primary and secondary treatment allowing anaerobic bacteria to consume more organic matter. This step reduces pathogens and odors, resulting in high quality bio-solids.
Centrifuges remove excess water from the collected solids. In summer the solids are used as a soil amendment on pasture land. In winter the solids are used to replace soil cover in a landfill.
Energy Recovery and Recyling
Energy Recovery. Methane Gas and excess heat are collected from the wastewater treatment process. Both the gas and the heat are used to provide the plant with electricity and to power the treatment plant.
Recycling. Mimicking nature's own processes, gas, heat, solids and water are all pulled from the wastewater and recycled as part of the wastewater treatment system.