All wastewater enters the plant site through the 72 inch diameter interceptor sewer pipe  A coarse rack removes any large objects.  The water continues to flow by gravity to a bar screen where leaves, paper products, etc. are removed and taken to a landfill.  The water is then pumped to a second bar screen where it flows by gravity through the rest of the plant.  The flow continues into an aerated grit tank where inert solids settle before being discharged to a grit washer.  Primary treatment removed the "settle-able solids".  Sludge settles to the bottom where it is removed for further processing before it also goes to the landfill.

The primary effluent overflows the weirs and enters two of the four aeration tanks where it mixes with return activated sludge (called mixed liquor) and is aerated.  Ferric chloride is added for phosphorus removal.  The mixed liquor overflows the final settling tank weirs into one of the two chlorine contact tanks where sodium hypochlorite is added to destroy harmful bacteria that may still be present.  The effluent from this tank is then treated with sodium bisulfite to remove any hypochlorite residual remaining.  The flow is then discharged into the St. Joseph River.

The storm water retention system handles excess wet weather flows.  Three screw pumps pump the raw sewage into the two-compartment, 3.5 million gallon retention basin.  The retention basin looks like a giant underground swimming pool.  Here the flow is disinfected with sodium hypochlorite.  The sewage in the retention basin can then be bled back into the incoming wastewater where it flows through the treatment process.

In addition to wastewater from sewers, the Niles WWTP also accepts a significant amount of septic tank discharge. The trucks that clean septic tanks come to the WWTP to discharge their load.  This septic wastewater gets treated just like other sewage from the sewer system.  The Niles WWTP is the one major plant in this area that still accepts septic tank discharge.

Aerial Photo of the Wastewater Treatment Plant