Sewage Treatment Plant

What is sewage treatment plant? 

 A sewage treatment plant, also known as a wastewater treatment plant, is designed to treat and purify wastewater or sewage before it is released back into the environment or reused. The process typically involves several stages to remove impurities, solids, organic matter, and harmful substances from the wastewater. Here is a general overview of the sewage treatment plant process:

1. Collection and Screening: The wastewater is collected through a network of underground sewer pipes and directed to the treatment plant. Large debris such as sticks, rags, and plastics are removed using bar screens or mechanical screens.

2. Grit Removal: The wastewater then passes through a grit chamber where sand, gravel, and other heavy particles settle down by gravity. These materials are removed using mechanisms like grit classifiers or grit pumps.

3. Primary Treatment (Sedimentation): The wastewater flows into large settling tanks called primary clarifiers. The flow velocity is reduced, allowing suspended solids and heavier organic matter to settle at the bottom as sludge. The sludge is then removed for further treatment.

4. Secondary Treatment (Biological Process): The partially treated wastewater undergoes biological treatment to remove dissolved organic matter and nutrients. This process typically involves the following steps:

   a. Aeration: The wastewater is mixed with air and introduced into large tanks called aeration basins. Microorganisms, including bacteria and protozoa, consume the organic matter and convert it into biomass, carbon dioxide, and water.

   b. Clarification: The mixture of wastewater and biomass (activated sludge) is then passed into secondary clarifiers. Here, the activated sludge settles at the bottom, while the treated water moves to the next stage.

   c. Return of Activated Sludge: A portion of the settled activated sludge is recycled back to the aeration basins to maintain a healthy population of microorganisms for continuous treatment.

5. Tertiary Treatment (Advanced Treatment): In some cases, additional treatment processes are applied to further enhance the quality of the treated water. These processes can include:

   a. Filtration: The water passes through sand filters or other media filters to remove any remaining solids and microorganisms.

   b. Disinfection: Chemical disinfectants, such as chlorine or ultraviolet (UV) light, are used to kill or inactivate harmful bacteria, viruses, and other pathogens in the water.

   c. Nutrient Removal: Some wastewater treatment plants may also incorporate processes like biological nutrient removal (BNR) to reduce the levels of nitrogen and phosphorus in the treated water.

6. Sludge Treatment: The sludge collected from primary and secondary treatment processes undergoes further treatment. This treatment can involve processes such as thickening, digestion (anaerobic or aerobic), and dewatering to reduce its volume and stabilize it for proper disposal or reuse.

7. Effluent Discharge or Reuse: After undergoing the treatment processes, the wastewater, now known as effluent, is discharged into nearby water bodies or used for various purposes like irrigation, industrial processes, or groundwater recharge, depending on the plant's design and local regulations.

Why Sewage needs to be treated before being discharged into rivers or other bodies of water?

Sewage needs to be treated before being discharged into rivers or other bodies of water due to several important reasons:

1. Protection of Public Health: Untreated sewage contains harmful pathogens, including bacteria, viruses, and parasites, which can cause diseases such as cholera, typhoid fever, and hepatitis. Treating sewage helps remove or inactivate these pathogens, reducing the risk of waterborne illnesses and protecting public health.

2. Environmental Protection: Sewage contains various pollutants, such as suspended solids, nutrients (nitrogen and phosphorus), organic matter, heavy metals, and chemicals. Discharging untreated sewage directly into rivers can lead to significant environmental damage. It can deplete oxygen levels in the water, harm aquatic life, disrupt the balance of ecosystems, and contribute to water pollution.

3. Water Quality Preservation: Rivers and other water bodies are valuable resources for drinking water supply, recreation, and supporting diverse aquatic ecosystems. Treating sewage before discharge helps maintain the quality of these water sources, ensuring they remain safe and usable for various purposes.

4. Nutrient Control: Sewage contains nutrients like nitrogen and phosphorus, which can promote excessive algae and plant growth in receiving waters, a phenomenon known as eutrophication. This can lead to oxygen depletion in the water, negatively impacting fish and other aquatic organisms. Treatment processes can remove or reduce these nutrients, preventing eutrophication and preserving the ecological balance.

5. Regulatory Compliance: Most countries have regulations and environmental standards in place that mandate the treatment of sewage before its discharge into water bodies. These regulations aim to protect public health, maintain water quality, and ensure sustainable management of wastewater.

By treating sewage before discharge, the harmful components can be removed or significantly reduced, making the effluent safer and less harmful to the environment. This helps to protect both human health and the integrity of aquatic ecosystems, ensuring the sustainable use and management of water resources.