Wastewater Is Treated Through Three-Phase Process

Wastewater chemical treatment is used water from homes, businesses, industry and rainwater runoff that contains pollutants that must be removed before the water can be safely reintroduced to the environment. This is done to prevent pollution of other water sources. Pollutants in wastewater include human waste, washing detergents, grease, grit, oils, heavy metals and other organic material. Many municipalities require all commercial, industrial and residential users of their sewer system to treat their wastewater before it is discharged into a public water supply source.

Most wastewater is treated through a three-phase process known as tertiary treatment. This process consists of chemical, biological and physical processes to remove all contaminants from the water. After the tertiary treatment phase, reclaimed wastewater is usually returned to the environment in an environmentally sound manner.

The first step in treating wastewater is to remove the solids that are suspended in it. This is often done with screens and settling tanks. The wastewater is pumped through the tanks and the velocity is slowed, allowing the solids to settle. A scum forms on the top and is skimmed off, while a thick sludge forms on the bottom of the tank. The partially treated wastewater then goes on to the second phase of treatment.

During the biological treatment phase, microorganisms decompose the organic materials in the wastewater. The bacteria in the microorganisms use the organic materials as food and convert them into carbon dioxide, water and energy. This helps to eliminate odors from the wastewater and reduce the level of nutrients in it. Nutrients such as nitrogen and phosphorus can disrupt the dissolved oxygen balance of aquatic ecosystems and cause excessive growth of algae or weeds in lakes, rivers and streams.

After the biological treatment phase, the wastewater is usually sent to a sand filter where it is cleaned by passing it through sand. The sand filters help to further reduce the amount of nitrogen and phosphorus in the wastewater. The filtered wastewater is sometimes returned to the environment in a water treatment plant where it is spread on fields or in other natural areas as a form of groundwater recharge and evapotranspiration.

Chemical treatments in wastewater treatment include the addition of coagulants and flocculants to remove particles from the water. Coagulants are aluminum or iron-based chemicals that change the magnetic charges of waste materials in the water, causing them to stick together and become larger bodies that can be skimmed or filtered out of the water. Chemical coagulants are often used to remove pathogens, arsenic, organic matter and fluoride from wastewater.

Other chemicals may be added to the wastewater to control the pH of the water, or to make it more acidic or basic. This is done to protect the pipes that carry the treated wastewater and to ensure that the resulting water meets health standards for its intended use. The federal government delegates responsibility for treating wastewater to the states and cities through the Environmental Protection Agency’s National Infrastructure Protection Plan.