Pictures of the Plant

Interceptor – Wastewater flows to the plant either by gravity or pumped by various lift stations in town to a siphon structure that runs underneath the Cass River. This siphon structure consists of one 10" and two 16" diameter interceptor sewers. This structure was built during the summer of 1998. The interceptor sewer flows into a wetwell in the basement of the Main pump station.

Incoming Wastewater
Incoming Wastewater

Screening – Preliminary treatment begins with screening. A mechanical bar screen removes rags, sticks, plastics, and similar materials for the wastewater. These items could damage or plug up the wastewater pumps and must be removed before the flow can be pumped into the plant. Wastewater passes through a series of parallel bars, while larger objects are retained. A rake mechanism periodically removes the materials, which are then collected and stored for eventual disposal to a landfill.



Raw Wastewater Pumps

Raw wastewater Pumping – Following screening, the flow enters a wetwell where vertical submersible pumps deliver the wastewater to the treatment units. There are four pumps in the drywell side of the main pump station, each with a capacity of over 2,200 gallons per minute (gpm). The facility can treat wastewater at a maximum rate of 7,000,000 million gallons per day (mgd). When flows to the treatment plant exceed this rate, the excess wastewater is pumped to the equalization basin for storage. After the high flows have subsided, this stored wastewater is returned to the treatment units.
Grit removal – The raw wastewater pumps deliver the flow to a grit removal unit. This unit uses centrifugal action to remove sand, coffee grounds, eggshells, bone chips, and similar materials that comprise grit. This material is also disposed of at a landfill.


Grit Removal Unit


Primary Tank

Primary Treatment – After grit removal, the wastewater flows by gravity to the primary tanks. These tanks provide a quiescent condition where heavier solids can settle out. The settled sludge is pumped to the digesters for treatment. The primary tanks also remove any floating grease or oil present.




Aeration Tank



Organisms At Work


Aeration Tank – Effluent from the primary tanks flows by gravity to the aeration basins. A complex community consisting of microorganisms is cultivated to remove phosphorous, ammonia, and suspended & dissolved solids. This is called biological treatment. Three centrifugal blowers and fine bubble diffusion aerators provide mixing and the needed oxygen supply. The WWTP is specifically designed for biological removal of phosphorous in the aeration basins.



Final Clarifier


Return Sludge Pumps


Final Clarifiers – The wastewater leaving the aeration basins is known as mixed liquor and flows by gravity to up to four 50-foot diameter final clarifiers. The solids in the mixed liquor settles to the bottom of the tank and is returned by pumps to the aeration basin as activated sludge (microorganisms).


Polishing Tank – The effluent from the final clarifiers flows into this tank to capture any remaining solids that may have escaped the clarifiers. This tank can also be used for disinfection with Sodium Hyperchlorite (strong bleach) if wastewater flows are high.


Polishing Tank





Outfall at Cass River


Disinfection – The final treatment step before discharge is disinfection with ultraviolet radiation. From there, the clear treated effluent is aerated as it flows down an 18" effluent line to the Cass River. Aeration enhances the dissolved oxygen content that is essential to aquatic life in the River.


Digesters – Solids that have been settled out in the primary tanks, along with activated sludge that has been wasted, are pumped to the digesters. Sludge digestion is a biological stabilization process that proceeds under a controlled temperature of 95 to 100 degrees F. With adequate heat and mixing, anaerobic (without oxygen) digestion is largely completed in the digesters within 15 to 20 days.


Digester Complex



Storage Tank

Biosolids Storage Tank – Digested sludge (biosolids) is transferred to 500,000 gallon storage tank during periods of the year when the sludge cannot be applied to surrounding farmland. Land application of the biosolids is done by liquid injection of the biosolids in the spring before planting and in the summer & fall after harvests. The stabilized sludge is an excellent soil conditioner as well as a useful fertilizer. With proper treatment and recycling to the land, biosolids becomes a valuable resource that is not a threat to the environment.


Operational Control – The WWTP is equipped with programmable logic controllers that monitor the entire treatment process. This system allows the operating staff to check conditions throughout the Plant. The staff also use computers to track inventory & maintenance needs. A laboratory facility provides space to perform all required testing. Wastewater is tested daily following each stage of treatment, and the results are reported to the State to demonstrate compliance with the City’s discharge permit.