Sewage Treatment and Water Quality

Sewage Treatment

Sewage treatment is the process of removing contaminants from wastewater, which includes both domestic sewage and industrial wastewater. Sewage Treatment Plants employ various physical, chemical, and biological processes to clean wastewater and make it suitable for discharge back into the environment.

Physical Treatment

• Screening: Removing large objects like rags and plastics.
• Sedimentation: Settling of solids from the wastewater.
• Floatation: Removing lighter materials that float, such as oils and greases.

Chemical Treatment

• Coagulation: Adding chemicals to cause suspended solids to clump together.
• Flocculation: Promoting coagulation by slowly stirring the wastewater.
• Disinfection: Using chemicals like chlorine or UV light to kill harmful microorganisms.

Biological Treatment

• Primary Treatment: Using bacteria to break down organic matter.
• Secondary Treatment: Further breaking down of organic matter by bacteria in clarifiers.
• Tertiary Treatment: Additional treatment processes, such as filtration or advanced oxidation, to achieve higher water quality.

How Clean is Water After Sewage Treatment?

Treated wastewater is generally safe for discharge back into the environment. However, the cleanliness of the water varies depending on the type and efficiency of the treatment plant. Modern plants typically achieve high removal rates of contaminants, including:

• Over 99% of suspended solids
• Over 95% of organic matter
• Almost all harmful microorganisms

However, some contaminants may still remain in treated wastewater, such as:

• Trace amounts of heavy metals
• Organic chemicals
• Nutrients (nitrogen and phosphorus)

These residual contaminants are often regulated by environmental authorities to minimize potential impacts on aquatic ecosystems and human health.

In summary, sewage treatment is crucial for protecting public health and the environment by removing contaminants from wastewater. Treated wastewater is generally safe for discharge back into the environment, although it may still contain some residual contaminants.