Goal: Measure and equalize flow, remove large particles
Raw sewage from domestic and commercial sources enters the treatment plant at the Headworks. Large inorganic solids in the waste stream (rags, garbage, etc.) are filtered out through large bar screens. Debris go into a dumpster and are taken to WPWMA (Western Placer Waste Management Association) for landfill.
The screened wastewater is then ready for its first biological treatment in the Oxidation Ditch.
Goal: storage and flow equalization
Ponds are used for storing wastewater when plant inflow (called influent) is greater than the plant capacity. The ponds also play a role in managing the amount of wastewater in the oxidation ditch. Typical inflow in dry weather is 1.3 million gallons per day (MGD). The peak inflow of up to about 4 (MG) typically occurs in winter.
Pond 2a includes surface aerators which minimize odor generation until the water is directed into secondary treatment
Goal: Remove organics and nutrients
Wastewater goes through its first biological process in the Oxidation Ditch. Brushes circulate through the wastewater which provides oxygen for a huge population of microorganisms (bacteria and protozoa) that feed on organic materials in sewage . These bacteria eat and breakdown the nonsettleable organic material—a process that occurs naturally in the environment but is enhanced in wastewater treatment. Microorganisms need oxygen to grow and reproduce.
Auburn’s wastewater plant has multiple ponds which can be used to regulate the amount of flow in the Oxidation Ditch. Wastewater is moved between ponds as needed to ensure a consistent amount of flow is available to sustain a healthy population of microorganisms.
Auburn’s Oxidation Ditch also removes nitrogen from the wastewater thru biological processes called “nitrification” where organic nitrogen is converted into nitrate and then “denitrification” where nitrate is converted into nitrogen gas, which is then emitted into the atmosphere.
Goal: remove organic nutrients
Wastewater from the Oxidation Ditch is routed to the three Clarifiers which separate the wastewater from the existing solids and microorganisms. The material which settles at the bottom of the tanks is called sludge. The sludge (containing all those microorganisms and a small amount of solid organic waste) are then recirculated back to the Oxidation Ditch where they start the process all over again -- the ultimate form of recycling. Excess sludge is further concentratedand dewatered so that it can be trucked away and used as landfill.
The wastewater produced here (now called secondary-treated water or effluent) is ready for final treatment and filtering.
Goal: remove smallest particles of organic waste
The treated effluent might still contain tiny particles of organic waste which are too small to be filtered out by sand filters. Special coagulants are added at this stage so that those tiny particles will stick together in larger and larger clumps. Then they are filtered out as they pass through several feet of sand. What remains is a clear and clean effluent. But, one final process remains to kill pathogens and bacteria, Ultraviolet (UV) Disinfection.
Goal: inactivate pathogens and bacteria
Ultraviolet light inactivates pathogens and viruses in the final stage of wastewater treatment. The now clear effluent passes through channels where numerous UV lights neutralize any bacteria or virus within the water. UV Disinfection is a common process used in food and water purification. It is also used to sterilize medical implements and work facilities.
The remaining effluent is now tertiary treated effluent suitable and completely safe for discharge into the environment.
An electrical control room manages the UV system which uses large amounts of energy, most of which is offset by power generated by the Solar Array.
Goal: ensure effluent meets permit requirements, test microorganism population
The Auburn Wastewater Treatment Plant, like most wastewater treatment plants, has a state of the art laboratory to test the plant’s performance at various stages. It tests effluent before discharge to Auburn Ravine to confirm the plant is providing full treatment prior to discharge. One critical function is to regularly test the wastewater for amount of BOD (biochemical oxygen demand), which is a measure of the wastewater’s waste strength and number of microorganisms. It is important to maintain a healthy population of microorganisms. A population too large without enough organic waste solids to support it will start to feed upon itself. Too small of a population cannot keep up with the load of biological waste. The lab technicians test the effluent in the Oxidation Ditch and Clarifiers and continually adjust flow and remove sludge as necessary to keep the population at its optimal level.
Goal: produce power for the wastewater treatment plant
There are 4,056 modules generating about 1.2 million kWh (kilowatt hours) of clean solar energy for the Auburn Wastewater Treatment Plant, particularly the UV Disinfection system which is a significant power draw. Over 20 years, the system will generate more than 24 million kWh of energy. The array built and operated by Pacific Power Renewables, puts an unusable flood plain to good use. Each panel is capable of tracking the sun, which further maximizes the amount of power generated.
The treated effluent is then discharged into the Auburn Ravine Creek which is an “effluent dominated” stream. This means that at certain times of the year, the water body is comprised mostly of the discharged treated effluent. The treated effluent is clean and healthy for the plant, animal and aquatic life.