Sewage Treatment Plants (STP)

The sewage treatment process involves a series of physical, biological, and chemical steps designed to remove contaminants from domestic, commercial, and industrial wastewater before it is discharged to the environment.

Preliminary Treatment

This stage removes large solids and debris using:

• Screens – to capture rags, plastics, and other coarse materials.
• Grit chambers – to settle sand, gravel, and heavy inorganic particles.

Primary Treatment

Wastewater flows into primary sedimentation tanks, where suspended solids settle at the bottom as sludge, and oils and grease rise to the surface for removal. This reduces the organic load entering the next stage.

Secondary (Biological) Treatment

Microorganisms break down dissolved and suspended organic matter. Common biological methods include:

• Activated Sludge Process
• Aeration Tanks
• Trickling Filters
• Sequencing Batch Reactors (SBR)

The treated water then enters secondary clarifiers where biological flocs settle out.

Tertiary (Advanced) Treatment

Further purification is performed to meet higher discharge or reuse standards. This may include:

• Filtration- (sand or membrane filters)
• Nutrient removal (nitrogen and phosphorus reduction)
• Activated carbon treatment

Disinfection

Final disinfection eliminates pathogens. Common methods include:

• Chlorination
• Ultraviolet (UV) disinfection
• Ozonation

Sludge Treatment and Disposal

Sludge removed from primary and secondary stages is processed through:

• Thickening
• Anaerobic digestion
• Dewatering

Finally, it is sent for safe disposal or beneficial reuse.