Wastewater Treatment Plant: Anaerobic Decomposition and Cleaning of Water

Poor sanitation and contaminated drinking water are the cause of a large number of diseases. If we look at our own country. A vast number of our people are still without sewerage facilities. In this blog, we will learn about wastewater treatment.

Where do they relieve themselves?

A very large fraction of our people defecate in the open, on dry riverbeds, on railway tracks, nearfields, and many a time directly in water. Untreated human excreta is a health hazard. It may cause water pollution and soil
pollution.

Both the surface water and groundwater get polluted. Groundwater is a source of water for wells, tube wells, springs, and many rivers as you learned in an earlier chapter. Thus, it becomes the most common route for water-borne diseases. They include cholera, typhoid, polio, meningitis, hepatitis, and dysentery.

In a home or building clean water often comes through GI pipes of ½ inches or ¾ inches or 1inch diameter. There is also another set of pipes of nearly 4-inch diameter that take away wastewater from kitchens, toilets, and bathrooms.

This wastewater, small and big pipes, open in a manhole near the entrance of a building. If you could see through the ground you would see a network of big and small pipes.

The network of all the pipes that carry wastewater is called sewers and all sewers together form sewerage.

Wastewater is carried from home to a point of disposal called the sewage treatment plant. After treatment of wastewater, the clean water is released into a nearby water body or into the ground.

Sewerage has manholes that are used to clean the sewerage and clear the blockage. Manholes are also provided at points where there is a change in direction of the sewer line. Manholes are located every 50 to 60m in the sewerage.

Wastewater Treatment Plant

When wastewater is transported through sewers to the treatment plant, it passes through several stages before it is released into a nearby water body or into the ground.

Treatment of wastewater involves physical, chemical, and biological processes which remove physical, chemical, and biological matter that contaminate the water.

In the first stage, wastewater is passed through bar screens. Large objects like plastics, rags, plastic packets, toilet papers, cans, and napkins are removed by mechanical screens (bar screens).

Now a day’s fine screens (6mm mesh) are commonly employed to remove small inert solids.

In the next stage, wastewater goes to the grit and sand removal tank. Here the speed of the water is kept low to allow sand and grit to settle down in the tank. Grit, sand, and solids retained by bar screens are usually sent to landfills for disposal.

The wastewater passes into a large sedimentation tank, which is sloped towards the middle. Solids like feces settle at the bottom of the tank and form a watery sludge. The sludge is removed from the bottom with a scraper. Floating solids like grease and oils are removed by a skimmer. Water so cleared is called clarified water.

Anaerobic decomposition

The sludge removed from the sedimentation tank is transferred to a separate tank, where it is decomposed by anaerobic bacteria.

Biogas produced during decomposition is used as a fuel or can be used to generate electricity.

Clarified water is passed into the aerator. Air is pumped into the clarified water to help aerobic bacteria to grow. Bacteria consume human waste, food waste, soaps, and other wastes still remaining in the clarified water.

After many hours the bacteria settle at the bottom of the tank as activated sludge. The activated sludge is 97% water. The water in the top is 95% clean. It has a very low level of organic matter. It is discharged into a water body or into the ground.

Sometimes this water, before releasing into the ground or water body, is treated with chemicals like chlorine and ozone. Activated sludge is dried in a sand bed. Dried sludge is used as manure.

Cleaning of water

Wastewater produced in homes, industries, hospitals, educational and commercial organizations should be cleaned before it is released into a water body such as rivers or lakes or is reused.

Cleaning of water is a process of removing pollutants from the water before it enters a water body or is reused. The process of wastewater treatment is known as sewage treatment.

Read More:
What is Sewage: Types Of Sewage and Sewage Disposal – Class 7

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