Co-treatment at Tonca STP, Panaji

Location: Tonca, Panaji, Goa

Designed Capacity of the STP : 12.5MLD (Design)
9-10 MLD (Actual, dependent on season)

Scale: Zonal

STP operational since: 2005

Implementing Organisation: City corporation of Panaji

Co-treatment operational since: N/A

Area of the plant: N/A

Capital Cost for co-treatment : INR 0.14 million(only for addition of decanting chamber)

Project Background

Co-treatment of septage at STP is being undertaken at only one location in Panaji, namely Tonca.
The STP is located in the south eastern part and serves most of Panaji (area under CCP). The installed capacity of 12.5MLD and the other which is yet to be commissioned (and for which trial runs are ongoing) with aninstalled capacity of 15 MLD. The former serves approximately 12,000 households (throughapproximately 2,800 connections) while the latter will treat the waste water flows from the city’s outgrowth’s. Co-treatment of septage at the 12.5 MLD plant was initiated soon after the plant was commissioned in 2005.

Treatment technology

The STP is based on Cyclic Activated Sludge Technology.For co-treatment the following element was added:

  • Decanting Station: A decanting station has been created at the Tonca STP to allow desludging trucksto discharge septage. The decanting station is located just outside the plant and has a high boundarywall. The decanting station was created at a cost of approximately INR 0.14 million. The area insidethe decanting station is paved.
  • The facility is a very basic set up comprising of a manhole into which the trucks discharge septage.
  • The manhole is just upstream of the STP preliminary treatment works and the septage added to sewage at the manhole enters the STP through the main inlet and passes to the inlet chamber, prior to the preliminary treatment process and subsequently undergoes the entire treatment cycle. There is no equalization / storage tank for receiving septage, and septage discharge occurs based on the frequency of trucks visiting the STP. The decanting station also has a small rudimentary cabin for a supervisor who monitors the entry and exit of trucks and maintains a register in which a record ofthe trucks using the facility is maintained.
  • The trucks are permitted entry between 9 am and 5 pm every day except on Sundays andgovernment holidays. The decanting station can accommodate only two trucks at a time and onlyone truck can decant at a time. There is no parking available within the decanting station and thiscauses long queues of desludging tanks which park on both sides of the road close to the STP waitingfor their turn to decant. Also the trucks use the space within the PHE office / STP complex to park.

Change in Bye-laws encouraging co-treatment

The Goa Public Health (Amendment) Rules, 2010 made provisions for protecting and advancing public health. Under the Act, some of the measures related to sanitation include closure of cesspools; prohibiting discharge of injurious refuse and solid waste into drains; providing sufficient number of public sanitary conveniences; prohibiting discharge of sewage, poisonous and polluting liquid into water bodies19; safe disposal of sullage and sewage, etc. This Act has ensured that the activity of septage disposal across the state has been regulated and the practice of indiscriminate discharge of septage into the sea, creeks, etc. has stopped.

Business model

Co-treatment of septage at Tonca STP was initiated soon after the plant was commissioned in  2005.Septage from areas not covered by UGSS in Panaji, OGs and CTs in PUA and also other parts in NorthGoa is received and treated at this plant. Typical fees levied by private operators for desludging septic tanks ranges from INR 3,000 to 3,500 per septic tank.

Approximately 120 truckloads of septage are discharged at the plant on a daily basis, with desludging trucks (capacity of 4-8 kL) making multiple trips. The septage discharge is permitted only at the decanting facility located at the STP and not at any SPS in the city.

Tipping fee of INR 500 is charged per trip by PHE towards the cost of treatment and safe disposal of septage. The truck owners deposit this amount with PHE usually in advance as alump sum (for 10, 20 or 40 trips). The payment can be made either in cash or online and theoperators are issued a receipt which they have to show to the supervisor for entry into thedecanting facility. The tipping fee collections are approximately INR 18 million per annum.

Type of charge


Rate (in INR)

Annual Collections


Per trip

INR 500 per trip

Daily: INR 60,000

User Fee

Payment made inadvance


Monthly: INR 1.5 million
Yearly: INR 18 million


Contact person:
Mr. Dilip Dhavilakar
Executive Engineer, WD III, PHE North, PWD St. Inez, Panaji

*This study has been adapted from a study conducted by Mr. Sanjay Gupta, Independent consultant,