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Addressing Water Scarcity in Tamil Nadu- Novel Perspective
Tamil Nadu is facing a water insufficiency of more than 11 per cent at present and it is expected to upsurge in the coming years. As a matter of fact, due to lack of flowing rivers, Tamil Nadu is reliant on on its adjacent states. To improve the water stress, Tamil Nadu has taken steps to implement water reuse and sea water desalination system.
Thoothukudi District: Thoothukudi District is an administrative district of Tamil Nadu state and it is situated in the south eastern part of TamilNadu which is in arid and water scarce region. The city of Thoothukudi is the district headquarters.

Thoothukudi district spreads over an area of 4621 km². The District comprises of 1 Municipal Corporation, 2 Municipalities, 19 Town Panchayats and 1718 habitations in 12 blocks having 4,62,010 households and a population of 17,50,176 (Census,2011).


Ramanathapuram District:
Ramanathapuram District is an administrative district of Tamil Nadu state and it is situated in the south eastern part of the TamilNadu which is in arid and water scarce region. The city of Ramanathapuram is the district headquarters. Ramanathapuram District has an area of 4123 sq.km. It is bounded on the north by Sivaganga District, on the northeast by Pudukkottai District, on the east by the Palk Strait, on the south by the Gulf of Mannar, on the west by Thoothukudi District, and on the northwest by Virudhunagar District. The District Comprises of 4 Municipalities, 7 Town Panchayats and 2520 rural habitations in 11 blocks.

Need for Desalination Plant:
Considering the existing scenario of nonsustainable and drinking water quality of ground water in these Districts, the Hon’ble Chief Minister of Tamil Nadu has announced in the Floor of Assembly on 10.04.2013, under Rule 110 of Legislative Assembly, that Desalination Plants of 100 MLD Capacity each will be installed in Ramanathapuram and Tuticorin Districts, as a permanent measure to provide drinking water to the public for all seasons. In the above context, Tamilnadu Water Supply and Drainage Board (TWADB), Chennai entrusted the assignment to M/s Tamilnadu Water Investment Company Limited, Chennai for conducting planning study and preparation of pre-feasibility report including financial viability, for setting up of either one number of 100 MLD or more than one plant of various capacities, totaling 100 MLD sea water Reverse Osmosis Desalination plants in these districts.



Population and Water Requirements
Thoothukudi District: Details of Population & Water Demand




Field Study and Survey Work:
Field study and survey work was done to evaluate each site for:
  • Access to good quality sea water; Brine disposal and dispersion
  • Physical suitability for construction of desalination plant, eg soils and flooding
  • Acceptability from an environmental point of view and Access to electrical power And the following activity was performed.
  • Obtained Present population and Existing Water Supply Scheme & Infrastructure details. Identified candidate site by carrying out reconnaissance survey.
  • Obtained data/records of Government lands, for fixing up the site in and around to the probable locations
  • Obtained details from TNEB on the source and availability of electrical power to the site and preliminary assessment were made on the power requirement for each site.
  • Collected Sea Water Samples for analysis of Water Quality Parameters
  • Carryout Oceanographic survey covering, Bathymetry, Sea Bed Geology, Wind, Current, Tides, Waves & Marine Ecology and Biology
Ramanathapuram District:



Selection of Technology
Almost all the new stand-alone desalination plants, which have come up worldwide in the recent past, are based on reverse osmosis as this has a distinct edge over other desalination technologies in such applications. Chennai Metro Water have also selected seawater reverse osmosis technology for the Minjur & Nemmeli plant and the Pre-feasibility Report was prepared by TWIC


Site Selection & Sizing of Plant Capacity
Thoothukudi District: Initial Site Identification

Potential sites for a desalination plant were identified as a result of meetings with the TWAD board officials and

knowledge of local conditions. Sites were selected to leverage existing distribution infrastructure. The site selection process initially identified 10 sites that represent a wide range of potential locations. These sites are Manapadu, Tharuvaikulam, Veppalodai, Sippikulam and Vaippar/Vembar.

Initial Site Screening and Selection
Out of 10 sites initially identified, five sites were eliminated due to nonsuitability of engineering parameter like sea water depth, intake and outfall, land availability, potential environmental and social concerns or the potential lack of community acceptance. The site identified for further studies are Alanthalai, Kayalpattinam South, Kayalpattinam North, Tharuvaikulam, and Vaippar

Evaluation of Site and Selection Criteria
After initial screening further study was done for the selected site to assess the suitability for setting up the SWRO Plant based on the following criteria as present in the below table

Ramanathapuram District: Initial Site Identification
Potential sites for a desalination plant were identified as a result of meetings with the TWAD Board officials and knowledge of local conditions. Sites




were selected to leverage existing distribution infrastructure. The site selection process initially identified 10 sites that represent a wide range of potential locations. These sites are Kannirajapuram, Narippayur, Kuthiraimozhi, Valinokkam, Chinna Ervadi, Kilakarai, Uchipuli / Mandapam, Keelanagachi / Mandapam, Chithrakottai / Devipattinam, Karankadu/ Near Thondi

Evaluation of Site and Selection Criteria
After initial screening, further study was done for the selected site to assess the suitability for setting up the SWRO Plant based on the following criteria as present in the below table




Techno Economic Feasibility option
Thoothukudi District:

Based on the above, two options were shortlisted as detailed below:



Option -1 (Multiple Location): Grouping the beneficiaries considering the proximity for conveying product water from two supply centers, one at Alanthalai another at Vaippar

Option -2 (Single Location): Total beneficiaries conveyed product water from one supply center i.e. at Vaippar considered the best ranking.

Based on the above the grouping of beneficiaries, capacity of plant for multiple location and single location are estimated as detailed below

Ramanathapuram District:
Based on the above para, two options were shortlisted as detailed below: Option -1 (Multiple Location): Grouping the beneficiaries considering the proximity for conveying product water from two supply centers, one at Kuthiraimozhi another at Keelanagachi

Option -2 (Single Location): Total beneficiaries conveyed product water from one supply center i.e. at Keelanagachi considered the best ranking.



Based on the above the grouping of beneficiaries, capacity of plant for multiple location and single location are estimated as detailed below

Financial Analysis
Overview
  • Evaluation period: 3½ Years Development / Construction and 30 Years of Operation Construction Start date: 2016; Likely COD: 2018
  • Evaluation under three Financing Options
  • 100% Grant
  • 50% Grant and 50% Loan
  • Under PPP (with 70% Loan & 30% Equity)
Levelized Cost:
Based on the above the levelized cost was worked out for various funding pattern

Break Even Tariff:
Based on the above assumption the Break Even Tariff was worked

Conclusions
The TN Govt sanctioned the Prefeasibility and financial model and sanctioned 2 nos 60 MLD in phase one at Kuthiraimozhi and Alanthalai. It was decided to go for DBOT model with 25 years O&M. This was the initial model adopted by TN Govt based on prefeasibility study alike to the one followed by the states in Australian Coast. This distinctive experiment by TN Govt. would help to address the issue of water security in the two districts as well bring about major savings in cost and time.