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Wastewater Treatment Plant How It Works

Barry Zerkle– Wastewater Treatment Plant Superintendent
Phone: (937) 498-8721
Fax: (937) 498-8169
bzerkle@sidneyoh.com

The City of Sidney’s Wastewater Treatment Plant is rated as a Class IV facility by the Ohio Environmental Protection Agency (OEPA) and is a “Conventional” Activated Sludge Facility. The treatment, or removal of pollutants is carried out in a number of separate processes. Each process can be discussed independently but it is important to understand that each process is dependant on the others to work effectively as a system of treatment.

Sewage enters the Wastewater Plant through the sanitary sewer system that provides service to the City of Sidney, the Village of Port Jefferson, and other business outside of the City of Sidney limits.

-Preliminary Treatment Process-

The incoming sewage (Influent) flows through either the channel grinder or a pair of manually cleaned bar screens. Normally all flow passes through the channel grinder where cutting teeth shred incoming objects such as rags and sticks. This is done to prevent larger objects from damaging equipment later in the treatment process.

The Sewage is then pumped through a meter to measure volume to the Screen Building. When the sewage enters the screen building a sample can be collected with an automatic sampler and the pH is measured by an on-line pH meter. The sewage then passes through a mechanical fine screen that removes any material larger than 1/4" size. The material removed (screenings) is disposed of in a sanitary landfill. At this point the sewage flows by gravity through the rest of the treatment plant.

After the sewage has been screened it flows through a grit tank. The grit tank allows the velocity of the sewage to slow to about 0.7 to 1.4 feet per second. This allows grit (sand, silt, and other inorganic material) to settle out while keeping organic material in suspension. It is important to remove grit because it can cause excessive wear on the equipment if it were to continue through the treatment process.  The grit is removed, dried, and hauled to a sanitary landfill as needed.

After the grit has been removed, ferric sulfate is added to remove hydrogen sulfide and to prevent its formation in other treatment processes.

-Primary Treatment Process-

Once the sewage (Influent) has undergone Preliminary Treatment it flows through an aerated channel to one of two Primary Clarifiers. Each Primary Clarifier holds approximately 500, 000 gallons. The Primary Clarifiers allow the sewage to slow down to allow organic solids to settle to the bottom. The solids that settle to the bottom are collected and pumped to the Anaerobic Digesters for further treatment. Sewage flows through weirs near the surface of the Primary Clarifier and into another aerated channel. The sewage is now called Primary Effluent. The majority of the pollutants in the Primary Effluent consist of dissolved and suspended solids. It takes approximately 1 to 2 hours for the sewage to pass through the Primary Clarifiers.

-Secondary Treatment Process-

The Primary Effluent enters one of six aeration basins. Each aeration basin holds approximately 316,000 gallons. The aeration basins have diffusers located near the bottom of the tank. When compressed air is passed through the diffusers, they generate bubbles. The bubbles perform two essential functions; they keep the contents of the tank mixed and they maintain the dissolved oxygen concentration in the basins. The basins contain microorganisms that use the remaining pollutants in the Primary Effluent for food. The aeration basins are responsible for the removal of the dissolved solids, suspended solids, and ammonia. As the microorganisms convert the pollutants to food they multiply in number. It is essential for the Operational staff at the WWTP to maintain the proper balance of microorganisms to the available food (pollutants). If an imbalance occurs the treatment process will become upset and the plant will no longer operate efficiently. It takes approximately 9 hours for the flow to pass through the aeration basins.

After the Aeration Basins the flow enters the Secondary Clarifiers. The Secondary Clarifiers operate in the same way as the Primary Clarifiers in that they allow material to settle to the bottom. All of the microorganisms are still present in the flow that enters the Secondary Clarifiers. The microorganisms cannot be released to the receiving stream because they would have a negative affect on the water quality and they provide an essential function in the wastewater treatment plant. The microorganisms naturally clump together to form what is called a “floc” particle. The floc particles settle to the bottom of the secondary clarifier where they are collected and pumped back into the aeration basins. A portion of this flow is pumped back to the head of the plant where it can be removed in the Primary Clarifiers with the sludge. The clean treated water flows through weirs near the surface of the final clarifier. The Effluent then flows through a series of pipes to the Disinfection Process.

  -Disinfection Process-

The flow (Effluent) from the Secondary Treatment Process flows into a chamber where chlorine is added. Chlorine is a powerful oxidizer and it kills any remaining microorganisms. A small amount of ammonium hydroxide is added with the chlorine to make this process more efficient. Once the chlorine is added the Effluent flows through the Chlorine Contact Tank to allow sufficient time for the chlorine to disinfect the Effluent. After approximately 30 minutes the Effluent flows through a channel where Sulfur Dioxide is added to remove any remaining Chlorine. It is important to remove any residual Chlorine before the flow enters the Great Miami River. If the Chlorine was not removed it could have a negative impact on the aquatic life located in the river. Once the chlorine is removed the Effluent flows through another meter to measure volume and then flows through a series of channels called cascade aeration that allows the effluent to fall approximately 3’. This turbulence naturally increases the dissolved oxygen content of the effluent similar to water flowing over a rock or going over a waterfall in a river or creek. After the Effluent passes through the cascade aeration it is called Final Effluent.  The Final Effluent flows through a pipe where a sample can be collected by the automatic sampler and where on-line monitors provide continuous monitoring of the pH and dissolved oxygen concentration. The Final Effluent is then discharged into the Great Miami River.

  -Solids Handling Process-

The Solids Handling Process is designed to provide treatment to the sludge that is generated in the treatment of sewage. The sludge that is removed from the Primary Clarifier is pumped to the Anaerobic Digester. The Anaerobic Digester also relies on microorganisms to treat the sludge by breaking down the organic solids for food. The Anaerobic Digester is sealed off from the atmosphere to prevent air from entering the tank. The tank is also heated to approximately 98 o F to maintain a favorable environment for the microorganisms. The sludge is held in the digester for approximately 15 days for treatment to occur. A byproduct of this type of treatment process is the production of methane gas. Methane gas is the main component of natural gas and has a BTU value of 650 or 65% of the BTU value of natural gas. The gas produced in the digester is used as fuel in a heat exchanger that provides the heat necessary to maintain the Anaerobic Digester temperature.

After the sludge has undergone treatment in the Anaerobic Digester it flows by gravity into the Secondary Digesters. The Secondary Digesters provides storage. The sludge that has undergone treatment and is now in storage is called Biosolids. The Biosolids are held in storage until it is dewatered in a centrifuge. The centrifuge removes the water and concentrates the solids. The Biosolids enter the centrifuge with a solids concentration of approximately 1.5% to 2%. After the Biosolids are processed in the centrifuge the solids concentrations is 18% to 20% and the Biosolids require about 10 times less storage area.

Biosolids contain nitrogen, phosphorous, and material that makes it an excellent fertilizer and soils amendment. The City of Sidney Wastewater Treatment Plant operates a Biosolids Recycling Program that includes the land application of Biosolids on area farm grounds to replace the need of fertilizer for crop growth. For more information on the Biosolids Recycling Program click on the Biosolids Recycling Program link.

  -Summary-

The information presented above is a brief overview of the treatment processes used at the City of Sidney’s Wastewater Treatment Plant. The City of Sidney WWTP relies on a highly skilled staff, automation, and continuous monitoring to provide the highest level of treatment cost effectively.  If you would like more information on the City of Sidney’s WWTP or would like to take a tour please contact the WWTP Superintendent’s office at 937-498-8721 or BZerkle@sidneyoh.com.

 

 

 

 

 

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