Wastewater Treatment

This course will walk you through a typical sewage treatment facility deployed at a local municipality. We will highlight the typical stages of waste water treatment and one of the many important technologies of chemical and biological treatment.

Introduction to Waste Water Treatment. Learn about how a local Municipality works towards developing a sustainable water treatment facility

Colaba Waste Water Treatment Facility

MSDP-II  and Colaba WWTF

The MSDP-II is a strategic action plan of MCGM aiming to improve the environment and sanitation in the city.

The Colaba Wastewater Treatment Facility is one of the major plants undergoing upgradation under the MSDP-II works. The Colaba WWTF will be developed on a design-build-operation-maintenance basis. The capacity of Colaba WWTF is designed for 37 Million Litres per day and the operational life is projected to be 30 years.

Waste water treatment - Overview

An Overview of water treatment

The sewage generated by the residential, commercial and industrial establishments is conveyed to the Wastewater Treatment Facility through  network of pipes and pumping stations. The incoming sewage undergoes following phases of treatment:

  •  Preliminary TreatmentWith Mechanical Fine Screens and Vortex Type Grit Removal System
  • Secondary Treatment: With fine bubble diffuser aeration system in Sequential Batch Reactors
  • Tertiary Treatment: With Disc Filters and Chlorine disinfection.
  • The Sludge is treated first by  Sludge Thickening followed by the Sludge dewatering Units and disinfection.

Select the components that constitute sewage water

  • Water
  • Chemicals
  • Solid debris
  • Organic matter
  • Dry leaves
  • Plastic films
  • Wet wipes
  • Toxic waste

Sources of sewage water

  • Residential areas
  • Commercial buildings
  • Industrial zones

Capabilities of Colaba WWTF

  • Treatment of sewage to Re-use quality
  • Treatment of sludge
  • Treatment of sewage to environmentally safe standards of disposal

Preliminary Treatment

First step in waste water treatment

Inlet Chamber & Medium Screens 

The influent raw sewage will be first screened to remove debris. The technical specifications for the Inlet Chamber and the Medium Screens (20mm bar spacing) are as displayed. The pumps are submersible type with variable frequency drives and with adequate standby arrangement.

What is the First step of treating waste water

  • Segregating Solid matter from water
  • Chemically treating entire sewage water
  • Collect waste water and dispose it into the ocean

Emergency Flow

Emergency Flow

The Influent Pumping Station incorporates an Emergency Overflow System. The Emergency Overflow system will be automatically activated in event of power supply failure or an inflow of sewage in excess of maximum flow.

Events when use of emergency flow line can expected

  • High tide
  • Monsoon
  • Festivals
  • Power failure

Grit Removal

Fine Screen and Grit removal system

The raw sewage pumped from the IPS flows by gravity through the Mechanically Raked Fine Screens (with 6mm of clear opening) into a set of Grit Chambers. The Hydrodynamic Vortex type Grit Removal system is an effective and low maintenance design.

The detailed technical specifications for the Fine Screen and the Vortex Type Grit Chambers can be seen here.

What is separated in Second screen

  • Finer solid particles
  • chemicals

About the incoming sewage in the fine screen chamber?

  • The incoming sewage is raw
  • The incoming sewage is treated with chemicals before being processed in the fine screen chamber

Benefits of Hydrodynamic Vortex type Grit Removal system

  • Effective method of circulating liquid-solid suspension
  • Low maintenance
  • Looks good

Secondary Treatment

Secondary treatment

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The incoming pre-treated sewage flows  into the Secondary Sewage Treatment Unit. The Sequential Batch Reactor (i.e SBR)  comprise of a battery of 4 basins. From the Distribution chamber the sewage flows into the Selector basin. The Selector serves the purpose of denitrification.


These are the components of a SBR basin

  • Process air blower

  • Return Activated Sludge (RAS) Pump and the Surplus Activated Sludge (SAS) Pump

  • Decanter

  • Fine bubble diffuser

  • Level transmitter and PLC screen

From the selector tanks the mixture of wastewater and sludge flows to the main Reactor basin of the SBR.  In the Reactor basin a network of fine bubble diffusers provide air for the main biological process of wastewater purification. The diffusers are fed with compressed air from the air blowers. The aeration also keeps the sludge in suspension and no further mechanical mixing equipment is required.

A Fully Automatic SBR process with four basins will work in the following sequence:

  • Filling

  • Reacting i.e the Aerobic Biological Treatment

  • Settling of biomass for clarification

  • Decanting of treated and clarified effluent.

  • Idling (getting ready to repeat the cycle)

Primary function of SBR

  • Biological reaction
  • Chemical reaction

Component changing the composition of waste water

  • Compressed air as fine bubbles
  • Nitrogen
  • Oxygen

Tertiary Treatment for treatment upto Re-use quality

Tertiary Disc Filters

Tertiary filters

The treated water outflow from the SBR flows into the Tertiary Disc Filter. This is a fully submerged filter with vacuum suction for cleaning the filter disc. The Polyester Fibre Disc Filters proposed provide the benefits such as –

  • Low Power Consumption

  • Continuous Filtration. No stoppage for backwash or during media replacement

  • Completely Automated with PLC and SCADA

  • This filter media gives better performance and can be applied with chemical dosing such as PAC, Polymer.

What do tertiary disc filters treat?

  • Secondary treated sewage
  • Sludge
  • Primary treated sewage

Disinfection Tank

Disinfection using Chlorine

The disinfection process is carried out in the Chlorine Contact Tank (CCT) having longitudinal baffles to lengthen the water travel length within the tank. The Technical Specification for the Chlorination Process is as shown

Longitudinal shape of baffles facilitate

  • Increased contact time with chlorine
  • Time for solids to settle

Congratulations!! You are now up to date with waste water treatment process. Stay Tuned to learn more about treatment of sludge extracted from WWTF in 'Waste Management' course