How do they purify water in sewage plants?

Sewage plants, also known as wastewater treatment plants, play a critical role in ensuring that the water we use is safe for consumption and adequate for the ecosystem. The process of purifying water in sewage plants involves a series of mechanical, biological, and chemical processes that eliminate hazardous substances and bacteria from the water.

Primary Treatment

Primary treatment is the first stage of wastewater treatment after the sewage enters the plant. In this stage, the solid particles in the water are removed through a process called screening. The sewage is passed over a series of screens, which traps solid waste, such as leaves, paper, and sticks, that might block the processing equipment. After screening, the sewage is passed through a sedimentation tank, where the heavier solid particles, such as gravel and sand, settle at the bottom, forming sludge. The sludge is removed from the sedimentation tank, and the rest of the water is sent to the secondary treatment.

Secondary Treatment

The secondary treatment process focuses on biological processes that clean the wastewater. The water is circulated in large tanks called aeration basins, where air is pumped into the water to encourage the growth of microorganisms that break down organic matter. Aerobic bacteria consume the organic matter and convert it into carbon dioxide and water. Afterward, the water that contains the microorganisms and organic matter is channeled into a sedimentation tank where the organic particles easily settle to form sludge. The water then flows over a series of weirs and into the next stage of treatment.

Tertiary Treatment

The final stage of wastewater treatment is known as the tertiary treatment stage. Tertiary treatment is a physical and chemical process that filters out any remaining impurities from the water. The water that flows from the secondary treatment to these tertiary tanks has been cleaned, but it still contains dissolved impurities such as phosphorus, nitrogen, and dissolved metals. In the tertiary treatment stage, a range of technologies are used, including sand filters, activated carbon filters, ultra-filtration membranes, and reverse osmosis. These methods remove remaining contaminants, harmful chemical substances like bacteria, and viruses that are not easily eliminated any other way.

Disinfection and Distribution

After the tertiary treatment process, the water is almost ready for distribution. However, before it can be used, the water needs to be disinfected. Disinfecting the water reduces the number of bacteria, viruses, and other microorganisms that may remain in the water after the tertiary treatment process. Chlorine is one of the most commonly used disinfectants in sewage treatment plants. The water is chlorinated in contact basins, which is the last step for disinfection. Once chlorine is added into the water, it is then sent to the storage tank, ready for distribution to consumers.

Conclusion

Sewage plants play an important role in ensuring that humans and the ecosystem receive clean water. Although the process may vary slightly depending on the plant, the stages remain the same with primary treatment, secondary treatment, tertiary treatment, and disinfection. By understanding these critical processes, we can all take steps to reduce the amount of pollution we're causing in our environment and work to ensure that future generations have a sustainable source of clean water.