08/03/2020 | Industrial Wastewater | 8 MINUTE READ

How Does a Wastewater Treatment Plant Work?

Among the more effective methods of controlling pollution is with a wastewater treatment plant, which is designed to clean water and sewage before the water is returned to the environment. Wastewater treatment plants are able to get rid all different kinds of pollutants and solids that can be found in sewage, which ensures that the majority of pollutants are removed from the water for good. Any organic matter that’s present in water or sewage when it goes through a wastewater treatment plant is broken down to make sure that the water is restored with oxygen.

The sewers that are connected to schools, homes, and commercial buildings are tasked with sending wastewater to the collection tanks at the treatment plant in question, which allows for a consistent flow. Once impurities have been removed from the sewage, this water is effectively purified before being sent out into the environment. These facilities are beneficial for the environment because they reduce suspended and organic solids, which limits the total amount of pollution that’s sent into the environment. Less water pollution helps to limit the spread of disease, keep fish healthy, and allow other types of aquatic life to avoid destruction.

Keep in mind that networks of sewers are responsible for delivering wastewater to treatment plants. Once the water and sewage has been delivered, it will be kept within basins and collection tanks until treated. While wastewater treatment plants are highly beneficial, they weren’t always necessary. Throughout the past centuries, the bacteria that was naturally present in waterways would automatically work to break down any solids and organic matter into byproducts that were relatively harmless. This was a natural purification process that kept the waterways relatively clean and free from impurities.

Today, wastewater treatment plants are necessary because the naturally occurring bacteria isn’t enough to account for the increases in sewage production and population. While the wastewater that’s sent through sewers is no longer able to be naturally purified, wastewater treatment plants use a similar purification method to get rid of pollution. There are, however, some materials that can cause issues for treatments plants, which mainly include heavier solids that are difficult to remove from the water. These solids include paper, plastic, rags, large food particles, money, wood, and eggshells. There are four sets of operations that are used in a wastewater treatment plant to help purify wastewater, which include the:

  • Pretreatment phase
  • Primary treatment phase
  • Secondary treatment phase
  • Sludge treatment phase

This article provides extensive details on how wastewater treatment plants work and the four phases that occur in the water purification process.

1. Pre-treatment Phase


The pre-treatment phase that occurs at a wastewater treatment plant is designed to get rid of the larger and easier to remove items from the water. These items can include everything from tree branches and cans to plastic bottles and rags. Some of the operations that can occur during this phase include collection of the wastewater, segregation, adjustment, and eventual decontamination. The primary objectives that are sought during the pre-treatment phase include:

  • Separating waste into non-active and active streams
  • Recovering certain products for recycling, which benefits the environment
  • Facilitating the conditioning, treatment, and transport of waste by separating the active streams into various components or by converting the waste into another form

While this phase is the initial and likely most straightforward aspect of the wastewater treatment process, there are a variety of factors that you will need to consider during this phase, which include:

  • Waste minimization
  • Impacts to the economy
  • Objectives and standards for radiological protection
  • Requirements for the treatment, storage, conditioning, transport, and eventual disposal of the waste

By treating the water before officially getting started with the main treatment process, you can reduce costs, bolster safety, and lower exposure to radiation in any future operations within the wastewater treatment facility. In the majority of plants, grit chambers and equalization basins are used for the regulation of water inflow, which allows any glass, stones, or sand to settle. The sewage will then remain in the basins until the primary treatment phase is ready to begin. While some treatment plants will skim off fats and grease from the water surface during the initial pre-treatment phase, other plants will take care of this process once primary treatment begins.

2. Primary Treatment Phase


Once the pre-treatment phase concludes, the primary treatment phase can begin. The wastewater will be collected in sedimentation tanks and large basins at this point, which is done to allow contaminants to sink to the bottom of the water. Once the smaller particles in the water have settled, scrapers are used to collect the solids and send them to hoppers, which are connected directly to the important sludge treatment equipment. In the event that oil and grease weren’t removed from the surface of the water during the pre-treatment phase, these substances will now be removed with surface skimmers.

At certain plants, specialized equipment will be used to combine the fats with lye, which allows for the creation of glycerol and soaps. Settling tanks or sedimentation tanks are highly important during the primary treatment phase if you want to get rid of some of the smaller contaminants in the water. While a grit chamber will have already been used to get rid of sand, eggshells, or other solid materials, these chambers are unable to remove smaller particles, which is what the settling tank is used for.

3. Secondary Treatment Phase


This is a very important phase of the wastewater treatment process that involves the agitation and aeration of the water within secondary basins. It’s at this point in the process that microorganisms are added to the water in order to break down any organic matter into sludge that can be more readily discarded. Certain plants will grow a substantial amount of microbes that are able to send any waste material over a biofilm.

On the other hand, it’s also possible for these treatment facilities to mix the waste material with the biomass for the purpose of developing activated sludge that’s able to be recycled. This process is great for the environment and will allow treatment plants to easily get rid of any waste materials that have been collected during the secondary treatment phase. The fine particles that are used in this process are able to remove nitrogen and carbon from any organic wastes.

Some facilities will go through the process of making weed beds and wetlands to decompose any organic materials. The other technologies that can be used in the secondary treatment phase include biological aerated filters and membrane bioreactors. The waste water that’s collected during this process will be distributed directly into an additional clarifier tank. The three main methods that can be used throughout the secondary treatment phase include:

All three methods have proven to be effective, which means that the method your wastewater treatment plant selects is largely based on preference.

4. Sludge Treatment Phase


The final phase of the wastewater treatment process is referred to as the sludge treatment phase. During the secondary treatment phase, the solids and organic matter that remain in the water are converted into sludge that can be treated and recycled. The sludge treatment phase involves the treatment of the remaining water as well as any sludge or bio-solids. Gravity will do its part in separating the heavier grit from the organic waste, the former of which can then be distributed to a landfill.

Any remaining sludge will be sent over to some kind of thickener, which is where the sludge will be centrifuged before being placed into digesting tanks that consist of anaerobic bacteria. The digesting tanks are responsible for the production of methane, which can itself be used to effectively power the entire plant. While the primary sludge is sent to a thickener, any stabilized sludge can be deodorized and sent into soil for the purpose of acting as fertilizer.

Any of the wastewater that remains will be treated to get rid of such nutrients as nitrogen and phosphorous. Once treated, the water can be properly disinfected with ozone, ultraviolet light, or chlorine. When the water is fully disinfected, it will be sent back to the waterways.

While wastewater treatment plants were once unnecessary for the treatment of wastewater, they are now critical towards ensuring that the water that passes through residential and commercial sewers is purified before reaching rivers, oceans, and other waterways. Some of the solid matter that’s collected during the wastewater treatment process can even be recycled into soap and other products. All of the discharge from wastewater treatment plants must adhere to standards that have been set by the Environmental Protection Agency in the U.S., which ensures that people can be confident about the water they drink and that the environment can benefit from the wastewater treatment process.

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Posted by Sensorex on August 3, 2020

Sensorex is a global leader in the design and manufacture of quality sensors for water quality and process applications. The company offers more than 2000 sensor packages for pH, ORP, conductivity, dissolved oxygen, free chlorine, chlorine dioxide, UV transmittance and other specialty measurements, as well as a full line of sensor accessories and transmitters. Its expert technical support engineers solve analytical sensor challenges with custom designs and off the shelf products.

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