How Does A Sewage Treatment Plant Function?

Posted by Linda Hudson on February 24th, 2017

The operation of sewage treatment plant is similar to that of a Septic tank. However, in sewage treatment plants mechanical components facilitates in breaking down solids in order to generate a cleaner and more environment-friendly effluent.

Let us understand how they work?

Primary Treatment

In the first step, sewage is passed through a screen where large floating objects are removed. After it, sewage is passed through a grit chamber where small stones, sand, etc. are made to settle down to the bottom. After screening, the grit has been removed. Still, sewage contains organic and inorganic matter along with several suspended solids. The wastewater is moved to sedimentation tank. When the flow speed of the tank is reduced, the suspended solids gradually settle at the bottom which collectively forms sludge. Biosolids are usually removed by pumping in the tanks.

Secondary Treatment

Around 85% of organic matter is removed by secondary treatment by use of bacteria. The major techniques used in this process are trickling filter and activated sludge process. A trickling filter is a bed of stones through which sewage is passed from three to six feet deep. In recent years, at some places, for example, Traverse City sewage treatment plant use advanced membrane filtration technology to generate high-quality effluent. Bacterial gather and decompose a large portion of organic matter, and the treated water flows through the pipes to aeration tank where it is mixed with air and sludge and kept still for several hours. This water that contains the excess of bacteria is then shifted to another tank to remove.

The secondary treatment is completed by disinfecting the effluent with chlorine. Chlorine kills not only pathogenic bacteria but also remove nasty odor. At many places, the excess chlorine is also treated by a process called dechlorination. Alternatives to chlorination, for example, UV rays or ozone is also used where the treated sewage effluent may cause risk to aquatic life.

At present, several additional pollutants like heavy metals, chemicals, and toxic substance have made the sewage treatment difficult. In such conditions, advanced water treatment techniques like filtration, carbon absorption, and reverse osmosis are being introduced. Waste effluents after treatment can be used for industrial and agricultural purposes.