Nesapakkam STPs Co-treatment in Chennai

Scale of service

City scale

Area of installation (Sq. Ft.)



Faecal Sludge and Septage


Treated water, dried Sludge and methane

Year of Installation

Co-treatment begun in July 2006

Capital investment (INR)


No. of Users

130,000 to 200,000 dependent on OSS

Treatment time

Not known

C.O.D. (inlet for Septage)

1070 mg/l

B.O.D. (inlet for septage)

250 mg/l

Location of the technology:

This STP is located in south western Chennai at 13°02'10.0"N 80°11'37.4"E.

Need for technology

The main motivation that drove co-treatment was the need to end unauthorised and unregulated dumping of faecal sludge and septage into the environment. This was done by private operators who desludged septic tanks from areas uncovered by the sewerage system.  

Initially, combined waste water flow ranged from 95 to 100 MLD, and there was scope for spare treatment of up to 17-22 MLD. This enabled co-treatment of septage at Nesapakkam STP.


System description

The treatment technology used in the STP is Activated Sludge Process. When co-treatment was introduced in 2006, a decanting station was created at the Nesapakkam STP to allow desludging trucks to discharge septage loads. This station has a provision for up to four desludging trucks to decant simultaneously along with parking area for additional three to four trucks. The decanting station consists of a covered receiving tank followed by grit removal chamber and screens. This receiving tank further connected to an odour control air scrubbing unit. Septage from the receiving tank moves into the trunk sewer line passing outside the decanting facility and consequently flows into the terminal SPS that feeds into the STP.

52 private desludging trucks are registered with Nesapakkam STP. They have a capacity of 9,000 Litres (9kL) each. Each truck makes several trips daily and the STP receives around 200 truckloads of septage is are discharged at Nesapakkam every day.

Operation and maintenance:

Maintenance of the installation

Some modifications were needed in the plant’s operation and maintenance with the introduction of Co-treatment.

  1. Increase in aeration was required, thus aeration tanks have four aerators (plus two standbys) to ensure proper treatment. Total aeration capacity of the plant is 12,000 m3 /hr and each aerator has a capacity of 3,000 m3 / hr.
  2. Energy cost of the plant has increased.

Annual O&M cost of the plant along with Co-Treatment (INR)