Wastewater
Lift/Pump Stations
The City maintains and operates 14 lift stations that are strategically placed within the collection system and throughout the City. These lift stations convey the wastewater from the gravity collection system to the wastewater treatment facility for solids removal.
Primary Treatment
Primary Clarification
The first step of wastewater treatment consists of primary clarification utilizing four 60-foot diameter basins. Designed for a two-hour detention time, these clarifiers serve to settle out the larger solids. The settled solids are called primary sludge (bio-solids) which is pumped from the bottom of the clarifiers for further processing.
Secondary Treatment
Aeration Basins
The primary clarifier effluent flows to four 150 x 50 foot square aeration basins. This stage is the complete mix activated sludge process that mixes and provides oxygen to the wastewater to optimize the growth of bacteria and other organisms for the biological treatment of the waste. The basins are designed to provide four to six hours detention time.
The activated sludge then flows to four 65-foot diameter secondary clarifiers. These clarifiers are designed for a two- to three-hour detention time and provide the final settling of activated sludge solids in order to achieve liquids - solids separation.
Secondary Clarification
A portion of these settled solids (activated sludge) is returned to the aeration basins to maintain optimum biological growth and conditions. Excess activated sludge is pumped to additional solids processes.
Secondary clarifier effluent has now achieved over 90% removal of suspended solids and biochemical oxygen demand, and is then discharged to Rock Creek, a tributary to the Missouri River.
Solids Processing and Disposal
The sludges (bio-solids) removed from the wastewater must now be de-watered and conditioned for final disposal. Sludges from the primary clarifiers are sent through a degritter and a gravity thickener. The primary sludge is delivered at .5% solid slurry after degritting and primary thickening which converts the solids to 8 to 12% settled thickened sludge.
The secondary sludges (waste activated sludge) are sent to dissolved air flotation units of process. This waste activated sludge of .8 to 1.5% solids is now injected with air and polymer which thickens the sludge to 4%.
The gravity thickened (primary sludge) and flotation thickened waste activated sludge are delivered to a mixing/blending tank. Mixing and blending are accomplished with air diffusers.
Gravity Belt Filter Press
Thickened, and blended sludge is pumped to gravity belt presses where the slurried sludge is spread between woven cloth belts that travel through a series of large rollers that successively squeeze the remaining water from the sludge. The resulting sludge "cake" rolls off the press in a sheet of solid sludge that is dry enough to easily treat further with a lime stabilization process.
Lime Stabilization Process
The dewatered cake is then treated with quicklime in a post-dewatering alkaline stabilization process (pH ≥ 12 for ≥ 2 hours, temperature > 70 degrees Celsius), which consistently meets class A Exceptional Quality Biosolids standard per the Missouri Department of Natural Resources 40 CFR part 503 requirements. This robust treatment process ensures a stable, odor-controlled, pathogen-free biosolid ideally suited for beneficial agricultural use.