Columbus Water Works (CWW)

Wastewater Treatment Services


Treatment of wastewater is essential to prevent contamination of waterways, drinking water sources, and other natural water resources. Wastewater is 'used' water that goes down the drains of homes, businesses, and industries every day. Many of your typical activities contribute to wastewater, such as flushing your toilet, running your dishwasher and washing machine, and even taking a shower. From these drains, wastewater travels through a network of underground pipes known as the collection system. To make use of the natural force of gravity, sewer pipes are often built along the natural slope of the land so the wastewater will flow downhill in them toward a treatment facility. In low lying areas where gravity flow is not possible, pump stations are used to force wastewater uphill to the appropriate treatment facility.

It's interesting to note that 99.9 percent of wastewater is actually water. The treatment process to bring wastewater to within regulated levels before being discharged back into the environment is broken into several phases:

Preliminary treatment - wastewater coming to the treatment plant, also known as influent, enters through the head chamber where a device called the bar screen removes large solid pieces of debris. Sand and grit are also removed in this area. This helps to protect the mechanical units that house other processes during treatment. Debris from the grit tank and bar screen is collected and sent to the city landfill.

Primary treatment - during this step, wastewater is sent to a primary settling tank where the solids and greases physically separate from the liquid. The wastewater is held in the tank for several hours so solid particles can sink to the bottom and the oils and greases can float to the top.

Secondary treatment - this phase relies on a biological treatment from microorganisms or 'good bugs' that literally eat the organic material in the wastewater. The partially treated wastewater goes into an area of the plant called 'aeration basins' where the heavy liquid is mixed and air bubbles are added to help the good bugs multiply as they feed on the organic matter. This mixture is then sent to a tank known as the final clarifier where the remaining solids settle to the bottom. The material on the bottom is then sent to the solids handling facility.

Final treatment - a disinfectant, typically chlorine, is added to the remaining wastewater to kill any harmful microorganisms before it is discharged into the Chattahoochee River. The treated wastewater that is discharged is called effluent. Additionally CWW adds the extra step of removing the chlorine before it discharges ithe effluent into the river.

Solids processing - solids from the primary settling tank and the clarifier (discussed under Primary and Secondary Treatment above) are sent to an anaerobic digester, which means oxygen is not necessary for the process. Like secondary treatment, this process also uses 'good bugs' to eat organic material resulting in a significant (90 - 95%) reduction in pathogens. The resulting product is a wet soil-like material called 'biosolids' that contains 95-97% water. Mechanical equipment, such as filter presses or centrifuges, squeezes the water from the biosolids to reduce the volume. During part of the year, CWW applies the biosolids to 600 acres of fields it owns near the South Columbus Water Resources Facility. To learn more about this process.

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