Wastewater Treatment

WRRF employees 2022

Treatment Processes


Treatment is accomplished by physical (settling), biological (micro-organisms), and disinfection(alteration) processes to remove the oxygen demand, total solids, ammonia, and bacteria from the water before it enters the receiving stream. Physical treatment is taking place at the plant head works and final clarifiers. Biological treatment takes place in the Oxidation Ditch System and in our three Aerobic digesters. Disinfection is the final process that takes place at with our Ultra Violet System. The U.V system uses Ultra Violet light to alter the bacteria so it cannot reproduce and soon after seizes to exist.


The plant has its own laboratory that has a certified inspection every other year. 24-hour composite influent and final effluent samples are collected twice per week and analyzed for Carbonaceous Biochemical Oxygen Demand, Total Suspended Solids, and Ammonia Nitrogen. A broad amount of other tests are done on a daily bases on influent, effluent, and digested sludge. The U.S. Environmental Protection Agency dictates how much B.O.D., Suspended Solids, NH3,  Nutrients, and bacteria that can be discharged from the treatment plant to the Cedar River. The city is issued a permit by the agency; which sets parameters on influent / effluent water quality and sludge program.


Solids removed from the treated water are stabilized in Aerobic Digesters for an average of 52 days to reduce Pathogens (disease causing organisms). These treated solids are discharged to the Reed Beds for drying and storage purposes and in time will be applied to farm land around Charles City. Regulations need to be followed and each year a sludge report is sent to IDNR and EPA.


When Environmental Protection Agency regulations are followed and met, water discharged by the Charles City Water Resource Recovery Facility  does not cause any environmental damage to the Cedar River.


Design Capacity


  • 4.66 MGD AWW flow
  • 6716 lbs/day BOD
  • 5379 lbs/day TSS
  • 1023 lbs/day TKN


To learn more about treating wastewater visit http://www.epa.gov/npdes/pubs/bastre.pdf