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Methods of Waste Water Treatment

Removing wastewater from urban areas has been in practice since London, England created the first sewer system in the early 1800s. But when disease broke out in 1850 due to water pollution, it was learned that in order to ensure public health and sanitation, wastewater must not only be removed but also treated. Today, every major city in the developed world has some form of standardized wastewater treatment. The most common form of wastewater treatment occurs at wastewater treatment plants and can consist of physical, chemical and biological processes.

  1. Pre-Treatment

    • Before wastewater can be treated, all solids must be removed from the wastewater through a pretreatment process. Solids such as leaves, branches, trash, dirt and sand are removed to prevent treatment system damage and clogging. Solid removal is normally done by a mechanical screen that sifts out unwanted solid waste. Some modern treatment plants also conduct grit removal and fat and grease removal phases prior to treatment; but these processes are not always conducted because they require more specialized equipment. A standard wastewater treatment plant's pre-treatment process typically removes 40 to 50 percent of water contaminants.

    Primary Clarifiers

    • Once all solid waste is removed, the biological process known as "primary treatment" begins as the water passes through the plant's primary clarifiers. Here, the wastewater is injected with air, normally done by an aerated tank or by spinning the water. The air encourages the growth of natural microorganisms, often called "activated sludged," that clean the wastewater by digesting pollutants and other organic material.

    Secondary Clarifiers

    • Next, the wastewater enters secondary clarifiers where the activated sludge settles to the bottom of the water and is reused. Normally, some of the activated sludge is kept at the treatment site to be reused and the remaining sludge is disposed of at a landfill. Once the activated sludge is removed, the water is filtered one last time to ensure no solid particles remain.

    Sodium Hypochlorite

    • The next step in wastewater treatment is adding the chemical component, sodium hypochlorite. Sodium hypochlorite is a chemical compound more commonly known as "bleach." Because sodium hypochlorite is a very strong chemical compound, very little is used when disinfecting water. An average of 1 liter of sodium hypochlorite is used to clean every 4,000 liters of water. Once the treatment process is done, wastewater is said to be 90 percent free of contaminants.

    Water Return

    • Once waste water if fully processed and clean, it is returned to the environment. Most treatment plants have a natural source of water close-by, whether it be a stream, river, lake or pond. Typically, water is distributed back into the natural source via a series of underground pipes or viaducts.

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