Wastewater Treatment

Scientists and engineers have developed methods to treat wastewater and make it reusable or safe for release to the environment. The processes the biological, physical and chemical pollutants from the water.

Wastewater can be first treated close in its primary storage area like septic tanks and aerobic treatment systems. The water can be collected there and then transported to various water treatment plants through water pipes.
There are basically six different methods through which wastewater is cleaned and turned into reusable water. These methods used various techniques to clean water and their results vary according to the quality of water.

The process:

  1. Preliminary Treatment
    Preliminary treatment of water is done to protect the pumping equipment from getting jammed by all the slime and dirt in the water. This method removes and reduces the large floating particles, inorganic solids and pollutants like oil and grease from the water. This is the first step of wastewater treatment and facilitates further decontamination of the water.

    In this stage, solid waste particles are removed from the water with the help of devices like Screens, grinders, cutters, grit chambers and pre-aeration tanks. All of these devices are very carefully designed and applied on wastewater from different resources.
  2. Primary Treatment
    In the second method, all the heavy solids are from the wastewater through the process of sedimentation. Sedimentation is the process in which waste water goes through big tanks called primary sedimentation tanks. All the sludge in the water gets can settled on the bottom of this tank and all greasy substance like oil rises to the surface. The oil on surfaces is skimmed off and sludge is removed and sent to be processed separately, through special scrapers fitted inside the tanks. The purpose of this treatment is to decrease the speed of wastewater to allow the solids to settle down and light particles to surface. The water treated through this process is like the water gone through stream.

  3. Secondary Treatment
    This kind of treatment depends on aerobic organisms which biochemically rot organic solids to inorganic particles. In this treatment, water is passed through four different types of devices. At first, it goes through trickling filters to secondary settling tanks. Then, the water is accumulated in final settling tanks to remove additional sludge. The treated water then goes through intermittent sand filters. The water is then, finally filled in a stabilization pond where it goes through the process of chlorination. Even though, this process is performed at every step of wastewater purification, but it becomes much more important in the later stages.

    Chlorination helps in disinfecting the water, prevents wastewater decomposition and controls the odour. Even though chlorination is most commonly used methods of wastewater disinfection, there are some other methods used also which can be used for this purpose, for example, the ozone method. This method is much safer for fish and other living forms. It also doesn’t add any peculiar smell or taste to the water like chlorine does.

  4. Tertiary Wastewater Treatment
    Tertiary treatment has been added to wastewater treatment process since 1970's. Tertiary treatment involves additional treatment rendered to wastewater after the secondary treatment. Many times, this only involves extra sand filters to remove increased suspended solids. Sometimes, tertiary treatment may also include removing plant nutrients, nitrogen and phosphorous from the water to improve its purity.

    Tertiary treatment has come into practice because of improvement in wastewater treatment units and awareness about environmental effects of the purified wastewater. Tertiary wastewater treatment is also sometimes known as the advanced water treatment. This is the highest degree of water treatment and may include chemical and physical methods to produce high quality of water.

  5. Sludge Treatment
    Even though sludge treatment is not directly connected to the process of procurement of fresh water to consumers through wastewater treatment, it is an important step. Sludge is solid waste removed from the wastewater in treatment units. It is essential to treat this sludge to some to prepare it for final disposal. The main objective of sludge treatment is to remove all the water from it and decompose the organic solids into mineral solids or at least in more stable organic ones. Sludge treatment process can be done by the following methods: This is accomplished by a combination of two or more of the following methods:

water treatment

1. Conditioning with chemicals
2. Centrifuging
3. Digestion with or without heat
4. Elutriation
5. Heat drying
6. Incineration
7. Thickening
8. Drying on sand bed -- open or covered
9. Vacuum filtration and
10. Wet oxidation

After purification, treated wastewater becomes almost as pure as potable water and is ready to be reused for various purposes. Even though, most countries don’t provide this water for drinking purposes, but it has become a major source for irrigation and commercial purposes. Treated wastewater has also helped cities in restoring the depleting underground water levels.

The National Association of Clean Water Agencies
Texas Water Resources Institute
World Health Organization
Canadian Water & Wastewater Association


Human feces contain on the order of 10 billion bacteria per gram. This is part of Nature’s design, of course, as the microorganisms play a symbiotic part in the digestive system. Once outside the body, feces pose a disease risk to others, especially if they get in the water supply. Outbreaks of the disease cholera are attributed to human fecal waste in drinking water and routine disinfection of municipal water supplies is driven by the fear of disease.

Industrial disinfection and sterilization commonly is divided into food and non-food applications. Food applications require stricter microbial and bacterial control and according to EPA sterilization in those applications should achieve at least 99.999% efficiency in harmful microorganism removal. For comparison, non-food applications require 99.9% removal. ‘Food applications’ requirements are also applied in other segments of services and industry such as health care, pharmaceuticals, biomedical applications, artificial transplants and other similar ones.

Summary of Clean Water Act

Dissolved Oxygen

Dissolved oxygen is an important part of water quality. Fish and other aquatic organisms do better when there is enough oxygen in the water. Runoff with a high concentration of organic matter can lower the amount of dissolved oxygen. The parameter biochemical oxygen demand (BOD) load is often measured. If it is too high, that is a problem.

Ion Exchange

Physically, an ion exchange contactor has components similar to a sandfilter, with resin used instead of sand, and with all the components required for media support, influent distribution, effective bed use, and treated water collection. The big difference being that inplace regeneration is required.

Basically, an ion exchange unit must include

  1. Influent inlets and a distribution system
  2. A treated water outlet and collection system
  3. Inlet and outlet back wash nozzles
  4. Regenerate inlet and outlet nozzles
  5. Resin media
  6. Media support system
  7. Under drainage system
  8. Flow rate controls
  9. Sampling nozzles

As with sand filters, exchangers can be gravity or pressure fed, although pressure systems are commonly employed. They can also be operated as an upflow or downflow process, with downflow systems acting as a filter and exchanger. Ion exchanger vessels are commonly pressurized vertical steel vessels, lined to provide corrosion protection from the regeneration chemicals. Stainless steel and reinforced plastic can be used for some processes.

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