Wastewater Treatment Process

Public Works

The following is an overview of the wastewater treatment process at the WRRF.

WRRF SITE LAYOUT
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STEP 1 | PRELIMINARY TREATEMENT
Removes large solids and grit from wastewater that can interfere with treatment processes. This process consists of influent pumping, screening, grit removal, septage handling, and flow splitting control.

STEP 2 | OXIDATION DITCHES
The heart of the treatment facility. Reduces the Biochemical Oxygen Demand (BOD), Total Suspended Solids (TSS), ammonia, and nutrients leaving the treatment facility.

STEP 3 | FINAL CLARIFIERS
Solids are removed through settling. Concentrated impurities, called sludge, are discharged from the bottom of the tank while the particles that float to the surface of the liquid are removed into a scrum trough using pumps.

STEP 4 | TERTIARY TREATMENT
Final cleaning process to remove any organic matter, suspended solids, and nutrients, as well as destroy pathogens. Includes tertiary filtration, ultraviolet (UV) disinfection, effluent aeration, effluent pumping, and effluent water systems for in-house reuse.

STEP 5 | RETURN SLUDGE
Solids that settle in the clarifiers are collected to the center, where they are removed by means of pumps located in the basement of the Return Sludge Building. Collected solids are either returned to the oxidation ditches (RAS) or removed from the process (WAS).

STEP 6 | SLUDGE DIGESTION
Decomposition of organic solids into stable substances. Digestion of sludge reduces the total mass of solids, destroys pathogens, and makes it easier to dewater or dry the sludge.

STEP 7 | DEWATERING
A conditioning of chemical and polymer are mixed with the sludge and the tapered shaft on the screw press "squeezes" more and more water out of the solids. As the solids move to the end of the screw press, a "cake" product is produced that can either be spread on crop land for fertilization or used as a beneficial topsoil amendment for the City Landfill.

STEP 8 | CAKE STORAGE
Cake is "slung" in a thin layer over the entire area of the storage pad to promote further drying of the material. The large covered concrete pad provides long-term biosolids storage.