Photo Tour of El Estero
Wastewater Treatment Plant

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Wet Well & Auger
City sewers collect and deliver wastewater to the plant influent wet well.  Large debris is removed by augers for disposal.  It is important to remove these materials because they could cause damage to the plant equipment.  The captured material is then removed and properly disposed.

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Grit Chamber
Inorganic materials like sand and gravel are allowed to settle to bottom of tank while organics are kept in suspension.  The sand or grit is then separated from the water and hauled to a landfill for disposal.

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Primary Treatment – Primary Clarifiers
Primary clarifiers separate waste from the water by slowing the flow.  The heavy solids fall to the bottom of the tank, where they become a thick slurry known as primary sludge.  The material that floats is also skimmed from the surface of the tanks.  Both the primary sludge and skimmed material are pumped to the solids treatment process.

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Secondary Treatment – Aeration Basin (Liquids)
Wastewater flowing out of the clarifiers still contains some solids and dissolved materials. A secondary treatment process uses microorganisms to consume the remaining organic material and nutrients.  Aeration tanks use air bubbles to provide the mixing and oxygen that are needed by the microorganisms.

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Secondary Treatment – Secondary Clarifiers (Liquids)
The microorganisms that grow in the aeration tank settle to the bottom of the secondary clarifiers. Most of them are recycled back to the aeration basin where they continue to remove organics and nutrients from the wastewater. Excess microorganisms that grow in the system are removed from and pumped to a solids treatment process.

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Secondary Treatment - Chlorine Disinfection (Liquids)
The final treatment process is disinfection.  Chlorine is added to the water to kill disease-causing bacteria and virus.  The treated water is held in tanks to allow sufficient time for disinfection to occur.  Following disinfection the chlorine is neutrualized with sodium bisulfate and slowly discharged 1.5 miles off shore.

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Tertiary Treatment – Filtration (Liquids)
The secondary effluent is filtered through sand and crushed activated charcoal to remove small solid particles.  Treated wastewater can be reused for industrial processes and for landscape irrigation, such as on golf courses.

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Recycled Water – (Liquids)
Water that has gone through advanced treatment is stored and used for irrigation to decrease the amount of drinking water used to water landscaping.  Recycled water that is used for irrigation can provide valuable nutrients, such as nitrogen and phosphorus, to the plants being grown while conserving our drinking water.
More on using recycled water

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Dissolved Air Flotation Thickener (DAF) (Solids)
Scum from primary and secondary clarifiers are concentrated and separated from liquid by using air bubbles to float particles to the surface.  The thickened solids are then skimmed off the surface and pumped to the Anaerobic Digesters for further decomposition.

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Gravity Thickener (Solids)
Sludge from primary and secondary clarifiers are concentrated and separated from liquid by using gravity.  The thickened solids are then skimmed off the surface and pumped to the Anaerobic Digesters for further decomposition.

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Anaerobic Digesters (Solids)
The solids collected and removed from each thickener are digested by anaerobic microorganisms.  Usable byproducts are produced during this process. Methane gas is used to create heat and produce energy.

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Belt Filter Press -
Biosolids (Solids)
These units process the fully digested sludge by removing entrained water to produce a material that can be used as a soil amendment for agriculture.

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Biosolids (Solids)
Biosolids contain nutrients and minerals.  Using highly monitored biosolids as a soil amendment and composting feedstock provides a way of reintroducing these elements back into the soil.

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Fuel Cell – Anaerobic Digester Gas
Gas produced during anaerobic decomposition is converted into electricity using fuel cell technology.  The fuel cells produce enough electricity to meet about half of El Estero’s needs.

El Estero Co-generation Project