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Wastewater Treatment Process
The wastewater treatment plant receives its flow mainly from the western and southern parts of the city.  There is one combined sewer overflow at the intersection of Market St. and Columbia St.  The plant is permitted at four MGD.  There are two basic processes, the liquid and solid handling. 

Liquid Process Flow
  • The flow enters the plant through a 16 inch main.  The flow is divided into two channels and passes through a comminuter in each channel.  Then the wastewater is pumped to the aerated grit channel. 
  • The grit settles into hoppers at the bottom of the tank.  The grit is then pumped to a grit removal system where the grit is separated from the water and sent to the landfill.
  • After the grit channel the flow is split into two channels and passes through a manual bar screen.  The screens are then cleaned and the screenings are sent to the landfill. 
  • Next the flow is directed into one of four primary settling tanks.  The raw sludge is scraped into hoppers at the head of the tanks and the floatable material is taken to the end of the tanks.  The floatable material is manually skimmed off of the tanks and is sent to the landfill. 
  • The primary effluent flows to one of four aeration tanks.  The aeration basins provide the biological treatment of the wastewater.  The aeration basins are the plug flow type. 
  • The return activated sludge (RAS) and the wastewater enter at the beginning of the tank.  The aerators provide mixing as well as the oxygen needed for the biological mass.  The mixed liquor travels through a channel into one of four rectangular secondary clarifiers.  The solids settle to the bottom of the tank and scrappers pull the solids to hoppers at the head of the tank. 
  • Hydraulic pressure pushes the solids out of the tank and two RAS pumps return it to the head of the aeration basins.  Overflow from the secondary clarifiers travels through the chlorine contact tank to the post aeration tank. 
  • In post aeration, sulfur dioxide is added to remove any remaining chlorine and oxygen is added to meet the dissolved oxygen requirements.  The flow then travels through a parshall flume and out the discharge main to Walnut Creek.

Solids Process Flow
  • Solids handling includes thickening, digestion, dewatering, and storage. 
  • The waste activated sludge (WAS) is diverted from the return activated sludge (RAS) line.  The WAS enters into the aerated grit chamber and is transferred to the primary settling tanks.  The WAS and the raw sludge is removed from the hoppers at the head of the tanks by hydraulic pressure and transferred to a holding tank. 
  • The sludge is then pumped to a gravity belt thickener.  The thickened sludge is then pumped into a digester where it is heated and circulated. 
  • After digestion it is pumped to a holding tank where it is mixed and stored.  Tanker trucks then transfer the digested sludge to an in ground holding tank at Warsaw’s wastewater treatment facility number two. 
  • There the sludge is pumped to a belt press thickener and the pressed material is conveyed to the biosolids storage building.  The sludge is then disposed of by land application.


City Hall  |  102 S. Buffalo Street  |  Warsaw, IN 46580
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