What is a Sewage Treatment Plant & How does it work? Explain it with via diagram

Working Principle of an STP:

The working principle of a Sewage Treatment Plant revolves around several stages designed to remove physical, biological, and chemical contaminants from wastewater. Here’s an outline of the process:

Physical Treatment (Preliminary and Primary)

• Screening and Grit Removal: Large debris and grit are physically removed to protect equipment and prevent clogging.
• Sedimentation: In primary treatment, sewage is allowed to settle in large tanks, separating solid waste (sludge) from the liquid effluent.

Biological Treatment (Secondary Treatment)

• Aeration: The wastewater is exposed to air (oxygen), encouraging the growth of bacteria and other microorganisms that break down organic matter (such as food, waste, and other pollutants).
• Activated Sludge Process: Wastewater is mixed with bacteria that feed on organic pollutants, converting them into harmless substances like carbon dioxide and water.
• Secondary Sedimentation: After aeration, the treated water moves to secondary clarifiers, where the excess microbial sludge is allowed to settle out.

Chemical Treatment (Tertiary Treatment)

• Filtration: Further filtering removes fine solids and particles that remain after biological treatment.
• Disinfection: Chemical disinfectants like chlorine or advanced methods like UV radiation are used to kill any remaining harmful microorganisms.
• Advanced Purification: Additional treatment technologies like reverse osmosis may be applied if the treated water needs to meet higher quality standards, such as for reuse in irrigation or industrial applications.

Sludge Treatment and Disposal

• Thickening: The sludge, which contains organic matter and contaminants, is thickened to reduce its volume.
• Digestion: In anaerobic or aerobic digesters, microorganisms break down the organic matter in the sludge.
• Dewatering: After digestion, the remaining sludge is dewatered, making it easier to handle, dispose of, or sometimes recycle into useful products like compost or biofuels.

Effluent Disposal or Reuse

• The final treated effluent (cleaned water) can be discharged into natural water bodies (like rivers or lakes) or reused for non-potable purposes like agricultural irrigation, cooling in industrial processes, or even for landscaping.

Diagram of STP Plant

1. Preliminary Treatment

• Screening: Large debris like plastics, leaves, and other solid objects are removed using large mesh screens.
• Grit Removal: Heavy particles like sand and gravel are settled out in a grit chamber to prevent damage to machinery.

2. Primary Treatment

• Sedimentation: The wastewater is allowed to sit in large tanks where heavy solids (sludge) settle at the bottom, and lighter materials like grease and oils float to the top.
• Skimming: The floating grease is skimmed off the surface and the settled sludge is removed.

3. Secondary Treatment (Biological Treatment)

• Aeration: The partially treated water is introduced to aeration tanks, where air is bubbled through the water to encourage the growth of bacteria and other microorganisms that break down organic matter.
• Activated Sludge Process: Microorganisms feed on the organic pollutants, converting them into simpler compounds, thus reducing the biological oxygen demand (BOD) of the water.

4. Tertiary Treatment (Advanced Treatment)

• Filtration: The water passes through sand or carbon filters to remove remaining solids and particles.
• Chemical Treatment: Chemicals may be added to remove phosphates or disinfect the water (e.g., chlorine or UV light to kill bacteria and pathogens).
• Advanced Filtration: Techniques such as membrane filtration or reverse osmosis may be used for further purification, especially if the water is to be reused.

5. Sludge Treatment

• Thickening: The sludge from the primary and secondary treatments is thickened to remove excess water.
• Digestion: The sludge is treated biologically to reduce its volume and pathogens.
• Dewatering: The remaining sludge is dewatered to a solid form, making it easier to handle or dispose of.

6. Discharge or Reuse
The treated water is now safe for discharge into natural water bodies like rivers or lakes or can be reused for non-potable purposes like irrigation, industrial processes, or cooling water in power plants.

If necessary, the sludge can be used for composting, as fertilizer, or safely disposed of in landfills.

In summary, STPs are designed to reduce contaminants in wastewater through physical, biological, and chemical processes to ensure that the water is safe for the environment and human use.

About Unistar Aquatech Private Limited:

Unistar Aquatech Private Limited, located in Ghaziabad, Uttar Pradesh, is a leading manufacturer of water and wastewater treatment plants. Renowned for our exceptional quality and client satisfaction, we specialize in Commercial RO Plant and Industrial RO Plant, Sewage Treatment Plant, Water Softener Plant, and Effluent Treatment Plant. Our standout feature is our 24/7 customer support, ensuring you always have assistance when needed. For inquiries or support, call us at +91-9811701883, +91-8588881234 or email india@unistaraquatech.com