How Does the Wastewater Treatment Process Work?

What is wastewater treatment?

It's cleaning used water and sewage so it can safely be returned to the environment. Clean water is the goal of wastewater treatment.

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Why are wastewater treatment plants important?

They protect public health from parasites, disease causing bacteria and harmful viruses. Treatment plants disinfect wastewater, eliminating the harmful organisms. Treatment plants also protect water quality so we can have clean oceans, lakes, streams and rivers.

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Where does wastewater come from?

Wastewater can come from human and household wastes from toilets, sinks baths and drains at home or from chemicals and other wastes from industrial factories, restaurants and shopping malls. Water that collects in street drains during a storm as well as groundwater that enters through cracks in the sewer is also considered wastewater.

 

altHow does a wastewater treatment plant work?

First, solids are removed. Bar screens let water pass, but not trash, such as rags or sticks. The trash is collected and disposed of. A large tank called a grit chamber slows down the flow of water. This allows grit, sand, and other solids to settle at the bottom of the tank. Later these solids are removed.

After this, organic matter is broken down and the water is disinfected. An aeration tank supplies large amounts of air to a mixture of wastewater, bacteria and other microorganisms. Oxygen in the air speeds the growth of helpful microorganisms, which consume harmful organic matter in the wastewater. Another tank, called a sedimentation tank, allow the microorganisms to form clumps and settle. A disinfectant such as ultraviolet light is generally used on wastewater before it leaves the treatment plant. This kills disease-causing organisms in the water.

Following treatment, the water can be safely returned to nearby creeks, rivers or streams. It can also be reused on land for irrigation or other agricultural processes.

 

altWhat are biosolids?

Raw sludge may be treated or thickened in a way that removes some of its water, then further processed to produce biosolids. To reduce the odor and disease-causing organisms, raw sludge decomposes in digester tanks. Removing most of the water from the mixture is called dewatering. This can occur in drying beds. The processed biosolids, called “cake” are then ready to be disposed.

Biosolids can be used to improve the soil for crops, lawns, fields and parks. During stabilization, biosolids may produce methane gas which can be burned to supply energy.