The Process Used To Treat Wastewater In Water Treatment Plants

By Author: Rohan Mehra
Total Articles: 23
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Wastewater is defined as water that has already been used to some extent. The water from homes, businesses, or industries is considered wastewater. Runoff water from outdoor activities and melted snow is also wastewater.

The purpose of wastewater treatment is to process human and industrial waste so that it is not toxic for humans or the environment. Wastewater may contain chemical, biological, or physical pollutants that can make it unsafe for human use. If untreated wastewater gets into the public drinking supply, it can potentially cause severe illness. Most of the time, wastewater is usually released back into the environment or is used by industries after treatment.

Wastewater treatment is divided into five distinct stages: Preliminary, Primary, Secondary, Disinfection and Sludge treatment. The earlier treatment stages remove the coarser solids and as the stages progress, specific solute contaminants get removed in the latter stages.

1. Preliminary Treatment or Pre-treatment

During the initial treatment stage, that is the preliminary stage, large objects and debris are ...
... removed by screening, sedimentation, and skimming. Wastewater pretreatment removes everything from twigs and rocks to diapers and bottles. This stage also eliminates most of the grit. The sewage flow and velocity are kept high in this stage to prevent the settling of solids.

2. Primary Treatment

After the Preliminary stage, the wastewater enters the Primary stage. During this stage, the flow is reduced in order to encourage sedimentation. The settled solids are scraped from the bottom and the floating material is skimmed. This stage removes a significant amount of oil, grease, and soap.

3. Secondary Treatment

The secondary treatment stage uses aerobic biological processes to remove the remaining organic matter, this includes human waste, food, oils, and soap. Some of the remaining solid matter is processed using microorganisms to form a coagulated mass that can be removed easily. Along with coagulation, flocculation is also used. This too causes particles to stick together so they can be filtered out more easily. Aluminum sulfate is often used in this process. After these insoluble solids settle at the bottom, the purified water is filtered out.

4. Disinfection

This stage is also known as the tertiary treatment phase. Chemicals like chlorine and chloramines are used in the water treatment disinfection process to raise the quality of the effluent. Ozone or ultraviolet light and other methods such as sand filtration, putting effluent in highly aerobic lagoons or constructed wetlands are also utilized.

Chlorine is cheap and effective as well but it can create carcinogenic compounds that are toxic for aquatic species. On the other hand, ultraviolet light creates water that is healthier for the environment as it is deadly to bacteria and viruses because it alters their genetic structure rendering them incapable of reproducing. However, it is not effective if the water is cloudy. Therefore, sometimes a combination of tertiary treatments is used.

5. Sludge Treatment

The final stage in the water treatment process includes removing sludge or biosolids. The sewage sludge is composed of both organic and inorganic materials as well as pathogens. Gravity separates the organic waste from the heavier grit, which can be deposited in a landfill. The remaining sludge passes to a thickener where it is centrifuged. Then it is fed to digesting tanks containing anaerobic bacteria. These tanks produce methane that can be used to power the plant. The final product can be partially deodorized and used as a fertilizer.

The remaining wastewater is treated to remove the other nutrients like phosphorous and nitrogen then returned to the water supply.

There are three main methods through which wastewater is treated:

1. Biological: When the water will be used for drinking purposes, biological methods like aerobic treatment and fermentation are utilized to treat it.

2. Physical: Physical methods include processes like sedimentation, filtration, and aeration. Sometimes, sand filters are used in the separation of oil and water to remove oil and grease particles.

3. Chemical: Chlorine is most often used to treat sewage and other types of wastewater. The process is called chlorination and is the most effective means of destroying several types of viruses and bacteria.

Conclusion

Water treatment is a critical foundation of society. Water treatment improves the quality of life and security of humans by providing access to clean drinking water, safe water for home use and water for agricultural purposes. As technology has become more and more advanced, several unique and promising water treatment plant accessories are being supplied by water treatment components manufacturers.

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