Wastewater Process

The Wastewater Treatment process consists of preliminary treatment, primary treatment, secondary treatment, tertiary treatment, disinfection, and solids processing. Keeping all of these steps functioning effectively is an intricate balance of physical, biological, and chemical processes.

Preliminary Treatment:

Wastewater entering the treatment plant is also known as influent. Screening removes large objects, such as sticks, rags, leaves, plastics, sanitary products, rocks, toys, or trash. This Andritz screen system has 6 mm openings to prevent large debris from passing through. Collected debris falls into a hopper where it is later disposed of at a certified landfill.  

Sand and grit that make it through the screens are processed in the next step, grit removal. Flows are slowed through a Smith and Loveless Pista Grit system. Grit that falls to the bottom of the chamber is removed and placed into a hopper for proper disposal.

Primary Treatment:

Two 70’ diameter Envirodyne clarifiers slow down the wastewater to allow time for additional solids to settle to the bottom and lighter grease and oil to float to the top. Wastewater will remain in these tanks for approximately 2-3 hours. The solids (sludge) that settle to the bottom are pumped to an anaerobic digester for further processing while the solids that float to the top are removed with a skimmer arm and disposed of at a certified landfill.  

Secondary Treatment:

After primary treatment, wastewater flows into four aeration tank trains that contain a Biological Nutrient Removal (BNR) system and activated sludge. The BNR is an anoxic zone that assists with the removal of Phosphorus from the wastewater. The activated sludge is an aerobic zone full of microbiology that removes nutrients further. This microbiology requires dissolved air which is forced into the tanks with a Neuros Turbo blower. Sodium aluminate is also added to assist with the nutrient removal. 

After the wastewater is mixed with air, it flows to two 84’ Envriodyne final clarifiers for final settling. Once again the solids (sludge) will settle to the bottom and removed for further processing in the anaerobic digester. The floatable solids will be removed with a skimmer arm and transferred to the head of the plant to be reprocessed.

Tertiary Treatment:

Tertiary treatment is an advanced treatment process that removes smaller suspended solids that is not possible through primary and final settling. The wastewater is filtered through a sand-like media called anthracite in three tertiary filter tanks.  As the media becomes clogged with all the small solids it is cleaned or backwashed on a regular basis by a US Filter Traveling Bridge.


Disinfection significantly reduces any remaining bacteria and viruses. Ohio EPA requires that the plant disinfect the wastewater from May 1st to October 31st every year. The City has a Wedeco ultraviolet (UV) unit that accomplishes this task. Wastewater flows over submerged bulbs that generate UV light. This light kills the pathogenic bacteria, disinfecting the wastewater quickly.

After the wastewater completes its journey through the treatment processes, it is discharged into River Styx.

Solids Handling:

All of the solids that are removed from the wastewater are processed through an anaerobic digester. The solids (sludge) are heated to a mesophilic range (±95°F). The heating of the sludge allows it to become more stable and reduce pathogen levels. Another advantage of anaerobic digestion is the creation of methane gas. This gas is used to fuel a boiler that heats the sludge for the process to be sped up.

After heating and processing, the solids are now known as biosolids. These Class B biosolids are pressed on an Ashbrook belt filter press into a cake sludge (18-20% solids) that is stored until ready for beneficial use on farm fields.

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