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City of Departments

Public Works & Utility Department

Wastewater Treatment Division

Wastewater Division

All influent flow into the treatment plants comes through the main lift building. This building houses equipment for preliminary treatment and pumps for transferring the wastewater for further treatment.

Barscreens

Evenly spaced bars in the channel then remove large solids and trash such as rags, wood, and rocks. This material is cleaned from the barscreens with a mechanical rake and disposed of in a landfill. Removal of these materials helps prevent clogging of pipes and protects mechanical equipment from excessive wear.

Grit Collector

Wastewater is then slowed using baffles whereupon the grit collector removes materials such as rocks, sand, cinders, and other large heavy materials. This process removes materials from the wastewater which would otherwise settle in tanks and digesters or clog pipes and cause wear on machinery.

Pumps

The wastewater treatment plant utilizes pumps of various sizes to lift water to the top of a hill to begin treatment.  Since this is the highest point the wastewater will reach in the treatmant process, it will be pulled down through the rest of the plant by gravity.

Primary Clarifiers

Next, wastewater reaches a pair of primary clarifiers where it will be detained for two to three hours, allowing for solids to settle or float so that they can be removed by mechanical rakes. These collected materials are then sent to digesters for treatment.

Aeration Basins

The Aeration Basins are the major component of wastewater treatment process, where we rely on microorganisms to consume, convert, and/or breakdown pollutants. Air supplied by blowers is used by operations staff to keep the preferred organisms alive to achieve the necessary treatment.

Secondary Clarifiers

The Secondary Clarifiers are designed to remove the solids just like the primary clarifiers. Once collected by the mechanical rakes, the sludge is either sent to the digesters for treatment or returned to the aeration basins to maintain microorganism populations.

Polishing Ponds

These large holding ponds helps to further reduce suspended solids and BOD concentrations in wastewater treated through the plant. These ponds hold a capacity of 6 million gallons and provide a detention time of 24 hours.

Dissolved Air Floatation

Solids removed in Secondary Clarifiers are pumped to a Dissolved Air Floatation Tank for thickening. Fine particles of air are used to force sludge to float, where the thickened sludge is removed using mechanical rakes. The thickened sludge is then pumped to digesters for treatment, while the water that was removed is sent back to the head of the plant for treatment.

Digester Building

The digester building consists of four large tanks designed to treat the solids that are removed through the wastewater treatment processes. In the digesters, the solids are heated for minimum of 15 days at a temperature greater than 95° F by pumping sludge through tubes that are heated with hot water (a heat exchanger). We then again rely on microorganisms to break down organic matter, providing solids reduction and killing pathogens. The biosolids are then handled as a liquid at a range of 2-4% solids. An average of 30,000,000 gallons of biosolids are treated each year and then used as fertilizer through our land application program.

Prior to the land application, the biosolids are analyzed to determine nutrient and metals content. Tanker trucks are then used to transport liquid sludge to permitted sites for land application to crop and pasture land. The City maintains around 2,000 acres of private farmland and the City’s 600+ acre Resource Recovery Farm for land application.

Resource Recovery Farm

The City’s Resource Recovery Farm (RRF) was established in 1994 on 600+ Acres of City owned land located between Dallas and Cherryville. The Farm was established to provide a place where a biosolids storage facility could be constructed and where land could be utilized for the land application of Biosolids from the City’s treatment facilities. The RRF is a public-private partnership between the City and EMA Resources, Inc., a biosolids management company. The City is responsible for the infrastructure and maintenance improvements to the RRF and Otter Creek is responsible for the day-to-day operation and management of the RRF. Otter Creek subcontracts the actual farming on the RRF to a local Gaston County Farmer.

In 1997, the City was awarded the United States Environmental Protection Agency (“USEPA”) Region IV First Place Award for Beneficial Use of Biosolids for its Biosolids Program, which included the Resource Recovery Farm. In addition the City was awarded Honorable Mention at the National level. These awards recognized the City’s activities for demonstrating biosolids management practices, which are environmentally safe, economically attractive and acceptable to the public.

The Resource Recovery Farm is equipped with two lined biosolids storage basins with a combined capacity of 8 million gallons and the equipment to mix and load the solids onto application vehicles for land application on the 200 acres of permitted crop and pasture land located on site or the other 1800+ acres located throughout Gaston County. These basins are primarily used for storage when when weather restricts land application.

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