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SEWER SERVICE CHARGES

BASE RATE SCHEDULE

Billing Handled by the Greenwood Commissioners Of Public Works

The Greenwood Metropolitan District operates two Wastewater Treatment Facilities (WWTF). The West Alexander WWTF has a permitted capacity of 2.2 million gallons per day (MGD) and is located at 225 Joe Bernat Drive. The Wilson Creek WWTF has a permitted capacity of 12 MGD and is located at 482 Wilson Creek Road.

On an average day both facilities together treat approximately 8.3 MGD of wastewater from domestic, commercial, and industrial sources to a pollutant removal level of greater than 98%. This treated wastewater is then returned to the environment.

These facilities employ the same treatment processes that occur in a natural aquatic environment. The WWTF maintains these natural biological processes in a controlled environment.

How A Wastewater Treatment Facility Works

After traveling through miles of the collection and trunk system the raw wastewater begins the reclamation process at the WWTF Headworks.

Headworks

The Headworks consists of these major components:

Bar screen – The bar screen removes debris such as sticks and rags.

Grit Chamber – The grit chamber removes sand and silt from the waste stream. These two components protect downstream equipment such as pumps from excessive wear and damage.

Equalization Basin – The equalization basin protect downstream process from incoming flow surges during periods of high flows.

Primary Treatment Top of Page

After the headworks the flow enters the primary treatment process. This process consists of settling tanks called Clarifiers. These clarifiers remove large settleable solids from the waste stream.

Secondary Treatment

Next the flow stream enters the secondary treatment process. This process is made up of the following components:

Attached Growth Biological reactors – commonly called trickling filters these reactors contain a media on which biological growth (algae) attaches. The algae and the organisms living in it consume the organic matter and convert the nutrients in the waste stream.

Suspended Growth Biological reactors – commonly called aeration basins or oxidation ditches these reactors contain a suspension of biological organisms that also consume the organic matter and convert the nutrients in the waste stream.

Secondary Clarifiers – these large settling tanks separate the biological growth in the waste stream from the treated wastewater. Most of the captured biological growth is returned to the bioreactor for more work while a small portion is taken out of the system.

Tertiary Treatment Top of Page

The Secondary treatment process is followed by the tertiary, or third, treatment process. This process consists of sand filters. The sand filters remove fine suspended solids from the waste stream creating a high quality effluent.

Disinfection / Dechlorination / Post Aeration

After tertiary treatment the wastewater goes through the disinfection and dechlorination process. A chlorine solution is injected into the waste stream to kill any remaining organisms that may spread disease or infections. After the chlorine has done its job a small chlorine residual remains. This residual must be eliminated to protect he aquatic life in the receiving stream. The Decholrination process performs this task. A solution of sulfur dioxide is injected into the waste stream to neutralize the residual chlorine.

Prior to discharge to the receiving stream the treated wastewater is aerated to maintain a dissolved oxygen content suitable for aquatic life.

Solids Process Top of Page

The solids captured and produced during the treatment process must receive treatment before being returned to the environment.

When the solids are removed from the treatment process they first go through a thickening process to remove as much free water as possible. After thickening the solids are injected with a polymer to aid in solids/ water separation and pumped to a machine called a Belt Filter Press. This machine consists of a series of rollers and two continuous fabric belts between which the solids are subjected to sheering forces to remove excess water. The material produced by this process is called a solids “cake”.

The solids cake material is now conveyed to a solids pasteurization process in which lime is first added to the solids to raise the pH of the material to reduce the number of pathogens. Then the lime/solids blend is conveyed through a heat vessel to further reduce the number of pathogens. This process produces a material called Class “A” Biosolids. These Class “A” Biosolids are safe to distribute to the general public for pH adjustment and amendment of the soil.

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