Wastewater Treatment

Wastewater Treatment Plant

The result of fifteen years of engineering studies and design, EPA negotiations, and planning by St. Marys Council, the Administration, and plant operators, a new wastewater treatment plant began operation in 2009. The new facility increases daily plant capacity to 3,000,000 gallons and allows for the treatment of wet weather flows up to 9,000,000 gallons each day. Total construction cost amounted to $11,012,020. View the related documents to the construction of the new wastewater treatment plant:

Flow Equalization

Equipment at the beginning of the treatment plant controls the volume of wastewater that can be processed for treatment. During high flow conditions (>9,000,000 gallons per day) when the plant cannot treat all of the flow, an electric gate can divert a portion of the flow to a 2,700,000 gallon equalization basin for storage. The captured wastewater in the equalization basin is automatically returned to the treatment plant for treatment when system flows return to normal. A computerized process monitoring and control system controls all aspects of flow equalization

Wastewater Treatment

Polluted wastewater pumped into the Wastewater Treatment Plant goes through a complex, multi-stage treatment process that takes about 22 hours. The treatment plant uses physical, biological, and chemical processes to removed contaminants, producing a high-quality discharge.

Wastewater Treatment Stages

  • Influent Screening and Vortex De-gritting: large and heavy inorganic material are removed.
  • Orbal® Oxidation Ditch: wastewater is biologically treated to reduce biological oxygen demand and to oxidize ammonia. The ditch is sized to accommodate the design loading without the need for separate primary settling. A chemical is added to remove phosphorus.
  • Final Clarifiers: two peripheral feed clarifiers separate sludge from treated wastewater. Clear wastewater flows to the disinfection process. Sludge is returned to the oxidation ditch or wasted to the solids reduction process.
  • UV Disinfection: the energy from ultraviolet lights is utilized to reduce the pathogen content of the wastewater.
  • Plant Effluent: treated wastewater is discharged to the St. Marys River through a 36" outfall structure.
  • Cannibal® Solids Reduction Process: solids removed or generated during treatment undergo further treatment through a cannibal solids reduction process. The process consists of a solids separation module, which screens small material from the solids, and an interchange module. In the interchange module, the solids are subjected to alternating periods of oxygen-available (aerobic) and oxygen-deficient (facultative) environments, which encourages cannibalization of the microorganisms, reducing the volume of the solids.
  • Sludge Storage: solids ultimately are wasted from the cannibal process to one of two digesters for thickening and storage. Sludge is either applied to agricultural land as a soil conditioner (biosolids) or dewatered and disposed of in a landfill.


The Wastewater Treatment Plant Laboratory contains all the various equipment and chemicals needed to monitor the wastewater. Thoroughly trained Lab Technicians check water quality during all stages of the treatment process to ensure optimum treatment and to protect the water quality of the St. Marys River. Tests include pH, phosphorus, ammonia, nitrate, alkalinity, dissolved oxygen, biological oxygen demand (BOD), carbonaceous biological oxygen demand (CBOD), chlorine residual, total, fixed, and volatile solids, and bacteriological.


Regular maintenance is a very important part of operating a public wastewater utility. Personnel are charged with many tasks and projects in order to keep the treatment plant operating at peak levels. Examples include: preventative maintenance of treatment plant and lift station equipment, regular inspections of the plant and lift stations, and many other activities.


Two full-time operators staff the St. Marys Wastewater Treatment Plant eight hours per day, seven days per week. Two supervisors, a laboratory technician, and two maintenance men split time between the plant and other duties. All employees are Ohio EPA, certified operators. The increasingly technical nature of Federal and State regulations requires continuing training on the part of all employees.