Wastewater Treatment Process: Definition, Procedure & Steps

Wastewater treatment is the procedure used for the purpose of removing contaminants from wastewater. It further involves the process of converting water into an effluent that can be recycled into the water cycle. Once returned to the water cycle, the effluent is in an acceptable environmental impact or is reused for a variety of purposes.

Wastewater treatment procedure involves the process of treating wastewater appropriately. There are different ways to treat wastewater in a wastewater treatment plant. The treatment plant for domestic wastewater is referred to as a sewage treatment plant. The industrial wastewater treatment process takes place either in a separate industrial wastewater treatment plant or in a sewage treatment plant. Agricultural wastewater treatment plants and leachate treatment plants are two other types of wastewater treatment plants. To know more about the wastewater treatment plant process, read the article below.

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Wastewater Treatment: Details

A wastewater treatment plant is a facility that treats wastewater, making it considerably cleaner and safer to be released into water bodies. A wastewater treatment plant is a place where wastewater from homes and other buildings is collected and processed. WWTP is an abbreviation for Waste-Water Treatment Plant. A wastewater treatment plant is also referred to as a sewage treatment plant. A modern wastewater treatment plant treats wastewater or sewage through a series of physical, chemical, and biological processes until it becomes fit to be discharged into the environment. 

Wastewater Treatment: Process

Treatment of wastewater involves physical, chemical, and biological processes, which remove physical, chemical and biological matter that contaminates the wastewater. The sewage treatment plant treats all of the collected sewage water. Before wastewater is discharged into water reservoirs, it goes through the following processes.

Wastewater Treatment: Design / Diagram

I. Screening

The wastewater that enters the sewage treatment plant is first filtered through bar screens, a process known as screening. The bar screen separates large trash objects from the wastewater, such as rags, sticks, cans, plastic bags, napkins, sanitary towels, and so on. As a result, screening removes large pieces of trash from the wastewater. These large pieces of rubbish that are caught by the bar screen are removed from time to time. 

II. Grit and Sand Removal

The wastewater (or sewage) that passes through the bar screen is forced to flow slowly through a tank known as the ‘grit and sand removal tank.’ Because wastewater flows slowly, grit and sand settle to the bottom of the tank. This grit and sand is periodically removed from the tank.

III. First Sedimentation tank

The wastewater (or sewage) is then pumped into a sedimentation tank and allowed to settle for a while. The majority of the solid organic matter (faeces, for example) settles as sludge on the sloping bottom of the sedimentation tank. As a result, the solid component of sewage is known as sludge. In this manner, the first sedimentation tank separates the solid organic sludge from the rest of the wastewater.

a. The sludge is removed from the bottom of the first sedimentation tank and placed in a large, closed tank known as the digester tank. Many different types of anaerobic bacteria decompose the organic matter in sludge in the digester tank to produce biogas. The biogas produced here can be used directly as a fuel or to generate electricity. The digested sludge that remains after the removal of biogas is collected, dried, and used as manure.

As a result, wastewater treatment (or sewage treatment) yields two useful products: (i) biogas and (ii) sludge. Biogas is used as a fuel, and sludge is used as manure (or fertiliser). The use of dried sludge as manure restores the nutrients to the soil.

b. The wastewater remaining in the first sedimentation tank contains some organic waste in the form of tiny suspended particles as well as soluble organic matter. Some oil and grease may also be floating on the surface of the wastewater in the sedimentation tank. A skimmer collects these floating materials. As a result, the first sedimentation tank contains mostly watery waste. It is also known as clarified water. 

IV. Aeration Tank

The primarily clarified water from the first sedimentation tank is pumped into the aeration tank (The tank in which air is put into water is called aeration tank). Aerobic bacteria already exist in the watery waste. Compressed air is bubbled through the watery waste in the aeration tank to provide oxygen for aerobic bacteria to activate and grow rapidly in this water.

The large number of aerobic bacteria produced in this manner digest any remaining human waste, food waste, soaps, and other unwanted and harmful matter in the wastewater, resulting in relatively pure water. Aerobic bacteria clean the clarified watery waste and render it almost harmless in this way.

V. Second Sedimentation Tank

The treated watery waste from the aeration tank is pumped into the second sedimentation tank and allowed to settle. The microorganisms used in the aeration tank settle at the bottom of the tank, forming a fine sludge known as ‘activated sludge.’ It is known as activated sludge because it contains active microorganisms such as aerobic bacteria and oxygen.

Some of the activated sludge is returned to the aeration tank to boost the population of aerobic bacteria and accelerate the cleaning of watery waste. The digester tank receives the remaining activated sludge. The water in the second sedimentation tank contains very little organic material and suspended matter.

Because there aren’t many harmful substances in this water, it’s perfectly safe. This water is then either discharged into a river (or sea) or allowed to percolate into the ground. Natural processes clean the water even more. Please keep in mind that the water in a river is naturally cleaned through processes similar to those used in a wastewater treatment plant.

VI. Disinfecting

Before releasing treated water into the distribution system, it may be necessary to disinfect it with chemicals such as chlorine or ozone. The goal of disinfection in wastewater treatment is to completely remove any harmful microorganisms from the water before it is discharged back into the environment. The treated wastewater can also be filtered through sand layers. The majority of the remaining suspended matter in the treated wastewater is removed by sand filtration.

Wastewater Treatment: Flow Chart

Wastewater Treatment Plant in India

The number of sewage treatment plants has grown over time. According to a \(1992\) World Health Organization study, only \(209\) of India’s \(3,119\) towns and cities had partial wastewater treatment facilities, only eight had full facilities, and \(114\) cities dumped untreated sewage and partially cremated bodies directly into the Ganges River.

The CPCB announced \(816\) plants with a total capacity of \(23,277\) mld in \(2014/15\). In November \(2016\), Shri Anil Madhav Dave, Minister of State for Environment, Forests, and Climate Change revealed newer CPCB figures: the country has \(193\) common effluent treatment plants with a combined capacity of \(1,474\) mld. In various states, including Tamil Nadu and West Bengal, there are 920 sewage treatment plants (STPs), of which \(615\) are operational, \(80\) are non-operational, \(154\) are under construction, and \(71\) are in the planning stage.

In \(2015\), the estimated sewage generation in the country was \(61,948\) mld, with a treatment capacity of \(23,277\) mld. This effectively means that \(38,671\) mld, or \(62\) percent, are not treated. Figures from the Centre for Science and Environment for \(2009\) revealed regional differences in India: While the treatment capacity of \(35\) metropolitan cities with populations greater than one million people totalled \(51\) percent, Class I cities commanded only \(32.5\) percent of the equipment, and Class II cities reached \(1\) percent.

Summary

A wastewater treatment plant is a place where wastewater from homes and other buildings is collected and processed. The sewage treatment plant treats all of the collected sewage water. There are four stages of wastewater treatment, including screen, sedimentation, and discharging into water reservoirs. It can take up to two years to treat a large amount of wastewater.

FAQs on Wastewater Treatment

Frequently asked questions related to wastewater treatment process is listed as follows:

Q. What are the three stages of wastewater treatment?
Ans: There are three main stages of the wastewater treatment process; they are primary, secondary and tertiary process.

Q. What is the process of a wastewater treatment plant?
Ans: The process of wastewater treatment plant is as follows:
1. Primary treatment: It is the initial stage. Waste water is passed through rotating screens called bar screens at this stage to remove large objects such as plastic, cans, rags, and sticks. After that, the water is filtered through a grit and sand tank to remove small stones and pebbles. The liquid is then pumped through a sedimentation tank, where solid waste settles to the bottom.
2. Secondary treatment: At this stage, the treatment involves pumping air into the clarified water to encourage the growth of aerobic bacteria. Bacteria decompose the suspended waste. The water on top is removed and passed through sand and drying beds to separate the solid waste from it.
3. Tertiary treatment: The treated water is chemically treated at this stage. To kill disease-causing organisms, the water is disinfected with chemicals such as chlorine or may be exposed to ultraviolet rays. Ozone gas can also be used to treat it. After that, the water is discharged into the distribution system.

Q. What are the four stages of wastewater treatment?
Ans: The four stages of wastewater treatment are;
1. Physical water treatment
2. Biological water treatment
3. Chemical treatment
4. Sludge treatment

Q. What are the two types of wastewater treatment?
Ans: There are two wastewater treatment plants,
(i) chemical or physical treatment plants,  
(ii) biological wastewater treatment plants.

Q. What are the types of wastewater treatment?
Ans: Types of wastewater treatment system are;
A. Effluent treatment plants
B. Sewage treatment plants
C. Common and combined effluent treatment plant
D. Activated sludge plant

Q. What are the main sources of wastewater?
Ans: The main sources of wastewater are Domestic wastewater, agricultural wastewater, industrial wastewater, petroleum.

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