How Does a Wastewater Treatment Plant Work?

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One of the most form of waste is water waste. Think about all the water we use in our household for showering, cleaning utensils, doing laundry, flushing the toilet and many other water functions in our homes and work places.

Water is also an essential resource in most industries and companies, and the amount of water waste collected thereafter is thousands of gallons of water.

Most of these wastewater contains harmful chemicals that are a danger to both people and marine life.

Wastewater Treatment Plant

Water waste that originates from homes is also dirty, channelled through the sewerage system and if mishandled, can cause many diseases to human beings or lead to death and destruction of sea life.

In the olden days, sewerage systems and companies could channel their waste into water bodies and a natural process of purification would happen.

The large volume of clean water would dilute the waste, while living creatures and bacteria in the water would consume sewage and other organic matter converting it into carbon dioxide, new bacteria cells and other products.

However, with the increased population today, the amount of waste from domestic and industrial use has accumulated to great volumes limiting the process of natural purification, as a result waste water treatment plants were invented.

Waste water treatment plants were built to give nature a helping hand in purifying water.

The waste water is treated to ensure it is environmental friendly before being released into the society through rivers, oceans, seas, streams, dams or into the ground. Waste water treatment plants also helps to treat the water for recycling and reuse.

Treatment Stages for Wastewater

The most common use of waste water treatment plants is to speed up the process of water purification. This is achieved through two basic stages, primary and secondary. These stages are mostly combined into one in most waste water treatment plants.

Primary Stage of Waste Water Treatment

wastewater-treatment-primary-sludgeThe primary stage mainly involves removal of large floating objects in the waste water. As sewer or water from other sources such as rivers enters into a treatment plant, it passes through a screen.

The screen removes large objects such as rags, sticks and plastic bottles that can lead to clogging and damaging of the plant’s equipment.

After the large objects has been removed, the effluent then passes into the grit chamber. In this chamber, sand particles, small stones and cider that may be washed into the sewer system during a storm or present in the water offered for treatment, are allowed to settle at the bottom.

After screening and grit chamber, the effluent now contains organic and inorganic matter as well as minute suspended solid particles.

The minute solid particles the next components to be removed in the primary stage. This happens in a sedimentation tank. As the effluent flows from the grit chamber into the sedimentation tank, the flow of the effluent is slowed down allowing the minute solids to settle at the bottom of the tank.

Over time the solids form a thick heavy mass of solids known as raw primary bio solids. The bio solids are pumped out of the sedimentation tanks. They can be treated further to form fertilizers, incinerated or disposed into landfills.

In the past years, the remaining water waste, with organic and inorganic matter would then be released into water bodies. However, over the years, primary treatment alone has not been sufficient to meet water quality standards that is safe to be released into the environment.

Therefore, the water waste is then taken through secondary water treatment process.

Second Stage of Water Treatment

The secondary stage is an intense process of water treatment. In this stage, through the use of the bacteria present in the effluent, over 85% of organic matter are removed. After the sewage leaves the sedimentation process in the primary stage, it is pumped or flowed through one of the following processes;

Trickling Filter

A trickling filter is made up of 3 to 6 feet deep bed of stones, synthetic media or meshing pieces of wavy plastic. Bacteria gather and multiply on the trickling filter beds. As the effluent is passed through the trickling filter beds, these bacteria consume most of the organic matter in the sewer.

The partially clean water from the trickling filter then flows through a pipe into another sedimentation tank where excess bacteria are removed and for further treatment.

Activated Sludge Process

Wastewater Aeration

This is the most common trend in most waste water treatment plants today. Instead of trickling filter beds, this method uses activated sludge process which speeds up the rate at which bacteria act on the organic matter.

After the sewer moves from sedimentation tank in the primary stage, it is flowed into an aeration tank that contains air and sludge heavily laden with bacteria.

The solution is allowed to settle for several hours. During this time, the air and sludge, which is heavily loaded with bacteria, come into close contact with the effluent causing the bacteria to break down the organic matter into mild by-products.

The partially treated sewer is pumped into another sedimentation tank, where excess bacteria is removed.

The sludge is not disposed. After the process, it is now activated with many more bacteria and millions of tiny organisms. It can be pumped back to the aeration tank to mix with air and new effluent from the primary stage.

The secondary stage is completed by disinfecting the sewer using chlorine. After the sewer leaves the sedimentation tank and before it is released into receiving water, chlorine is added into the water to reduce odour and destroy pathogenic bacteria.

If the waste water treatment plant is careful enough, chlorination can lead to 99% destruction of harmful bacteria in the sewer.

However, before the now clean water is released into the environment, excess chlorine is removed through a process known as dechlorination. Alternative solutions for using chlorine as a disinfectant are the use of ozone or ultraviolet light.

These are commonly efficient in water waste treatment plants that release the sewer into the ocean where fish and other marine life are affected by the chlorine.

Waste water treatment plants are now faced with new challenges. Today’s waste water is made of heavy metallic components, chemical compounds and other toxic matter that are hard to remove through the primary and secondary stages of water treatment process.

With the rising demand for water supply due to increased population, water treatment plants are called to improve waste water treatment so that the water can be clean and safe enough to be reused even for domestic purposes. To achieve this, new advanced methods of water treatment are now used in most waste water treatment plants.

These advanced techniques include biological treatment that helps to remove multitude of chemicals such nitrogen and phosphorus.

Other techniques adopted by waste water treatment plants are reverse osmosis process, distillation, filtration and carbon adsorption.

These four methods, whether combined or used independently in a treatment plant, are capable of physically separating chemicals from the waste water.

The water collected from these waste water treatment processes is safe to be recycled in industries, agriculture, domestic use, recreational purposes or even for drinking.

Waste water treatment plants are also encouraging people to be environmental friendly and prevent pollution in the best capacity they can.

For instance, industries are urged to pre-treat their industrial waste in order to remove the excess or cumbersome pollutants in their waste water before releasing it into the sewerage system for further treatment.

This helps to remove the pollutants at the beginning of the process, instead of it waiting to be removed at the end in the pipeline of the waste water treatment plants.

If the waste water treatment plant is treating water for distribution into homesteads, there is a final stage that involves storage and distribution.

After treatment and disinfection, the water is stored in large underground and elevated storage tanks. The plants ensures there is ample water stored in these tanks for distribution even in cases of emergencies.

Clean Water Comes Back Into Your Home

The final process is the distribution process. This is the process that allows you to have water running in your taps.

The water is channelled through underground pipes through a distribution system. The distribution system consists of water pumps at the treatment plant, underground and overhead storage tanks, large and small pipelines, fire hydrants, valves and water meters.

End Note

Water is a basic resource for daily operations for human beings. It is also a home to millions of aquatic creatures. Water pollution can lead to diseases and death to animals, human beings and aquatic life.

Waste water treatment plants work by treating water from the sewerage system and industrial waste for discharge into the receiving waters such as rivers and oceans and for reuse in industries, domestic use, recreational purposes, agriculture and many other sectors that require water.

Although water waste is treatable, it is important to prevent water pollution.

This can be achieved by properly disposing waste and treating industrial water waste before releasing it into the society.


This is George, the Aquaman, editor at AquaMantra. I'm a water quality analyst by profession, and used to work at one of the largest water bottler company.
  1. It is interesting that 3 to 6 feed of stones and synthetic media make a trickling filter. My son told me yesterday that he watched a video about workers at a treatment plant and now he wants to work there when he grows up. If he does end up working at a wastewater plant, I imagine he would have specific work wear or something like that.

  2. Thanks for mentioning that water waste is one of the most forms of waste we have. I think it’s a good idea that a facility has a biological nutrient removal process to make the water cleaner. It also seems like a good investment that homes are connected to a reputable facility to ensure their utilities are safe to use.

  3. It’s amazing that 85% of organic matter is removed in just the second stage of the treatment. I remember I went on a field trip to a wastewater plant but I forgot what I learned. Thanks for breaking it down so that I can understand!

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