What is Sewage System | Civil Engineering Optional Notes for UPSC PDF Download

Sources of Sewage

• Residential water use in kitchens and bathrooms.
• Commercial and industrial facilities.
• Rainwater runoff and groundwater infiltration through cracks in the sewer system.

Transportation of Sewage to Treatment Plants

1. Local Sewers: Owned by city and town sewer departments, these 5,100 miles of pipes transport wastewater to MWRA interceptor sewers.
2. Interceptor Sewers: These 227 miles of pipes, ranging from 8 inches to 11 feet in diameter, carry wastewater to MWRA treatment plants. Most flow by gravity, but pumping stations are used in low-lying areas.
3. Deep-Rock Tunnels: Sewage is pumped through deep-rock tunnels under Boston Harbor to Deer Island Treatment Plant.

Sewage Treatment Process

1. Collection and Pumping:

   • Screening: Large objects are screened out.
   • Pumping: Sewage is pumped through deep-rock tunnels to Deer Island.

2. Preliminary Treatment:

   • Grit Chambers: Mud and sand settle out as "grit," which is taken to a landfill.

3. Primary Treatment:

   • Settling Tanks: Up to 60% of solids settle out as sludge. This stage removes few toxic chemicals.

4. Secondary Treatment:

   • Aeration: Oxygen is added to encourage microbial growth.
   • Microbial Consumption: Microbes consume waste and settle in secondary tanks. This removes 80-90% of solids and a significant proportion of toxic chemicals.

Disposal of Treated Wastewater and Sludge

1. Treated Wastewater (Effluent):

   • Disinfection: The effluent is disinfected.
   • Discharge: It is discharged into Massachusetts Bay through a 9.5-mile outfall tunnel with 55 diffusers, ensuring high dilution rates.

2. Sludge Processing:

   • Digesters: Sludge is mixed and heated to reduce volume and kill bacteria.
   • Transport and Pelletizing: It is transported to Quincy, where it is dewatered, heat-dried, and converted into pellet fertilizer for agriculture, forestry, and land reclamation.

Management of Toxic Chemicals

Toxic chemicals pose significant risks, and the MWRA enforces regulations to manage their levels:

1. Industrial Control:

   • Regulations limit the amount of toxic chemicals industries can discharge.
   • The Toxic Reduction and Control Department monitors and enforces these regulations, imposing fines for non-compliance.
   • The MWRA collaborates with industries to reduce toxic chemical use.

2. Household Contributions:

   • Households are a major source of toxic chemicals through improper disposal of products like motor oil, pesticides, paints, solvents, and cleaners.
   • Alternatives with lower toxicity are available for many household tasks.

Conclusion