How Desalination Plants Can Partially Meet Chennai’s Perennial Water Shortage

M R Subramani

Jun 24, 2019, 04:05 PM | Updated 04:05 PM IST

Minjur desalination plant near Chennai.
Minjur desalination plant near Chennai.
  • Tamil Nadu’s capital and one of India’s biggest metropolitan cities — Chennai — is facing one of its worst water shortages in recent memory.
  • According to the India Meteorological Department (IMD), rainfall deficiency in the metropolitan city last year was over 60 per cent.
  • With costs for supplying water from desalination plants being higher and the expenses to set up such plants rising, such a source can be seen only as a short-term solution.
  • Christ King Girls Higher Secondary School in East Tambaram, a Chennai suburb, gave a two-day break to its classes VI to VIII students last week. The reason was that the school, which has over 2,500 students on its rolls, was running short of water.

    Borewells in the school’s campus have run dry and it is being forced to buy two tankers of water (24,000 litres) every day. After a hue and cry was raised over its move, the school clarified that the students were given the break for safety reasons as a sump to store the water was being constructed.

    A few kilometres away from East Tambaram is Chrompet, where a Central Board of Secondary Education school functions only half a day due to water shortage.  Companies functioning in the Information Technology (IT) corridor along the Old Mahabalipuram Road (OMR) in the heart of Chennai have asked their staff to work from their homes since they don’t have adequate quantity of water to meet the needs of their staff.

    Offices and homes on OMR require 30 million litres of water and the IT firms consume 60 per cent of this. Some 4,000 water tankers supply water to meet the needs of those living or working in the OMR region. There are other firms on OMR like Cognizant that don’t allow employees to wash their lunch boxes.

    Tamil Nadu’s capital and one of India’s biggest metropolitan cities — Chennai — is facing one of its worst water shortages in recent memory. According to Chennai Metropolitan Water Supply and Sewerage Board (CMWSSB), the storage level in the four major reservoirs that supply water to the city was a meagre 22 million cubic feet (MCFT) on 21 June. This is less than 1 per cent of the level of 2,456 MCFT when compared with the water level at the same time a year ago.

    The city’s Sholavaram and Red Hills reservoirs have run dry, while Chembarambakkam reservoir’s storage level is at a pathetic 1 MCFT. The level in Poondi reservoir, which receives water from Krishna river as part of the Telugu Ganga project, is 22 MCFT. The metropolis’ problem has been compounded by lack of any rain since 5 December last year until 20 June, when some parts of the city received good showers.

    Chennai depends on the North-East Monsoon during October-December for its water supply needs but last year’s monsoon ended with a 59 per cent rainfall deficit. According to the India Meteorological Department (IMD), rainfall deficiency in the metropolitan city last year was over 60 per cent. The city has able to carry on thus far only because in August Chennai witnessed a 34 per cent surplus rainfall.

    Until 1870, Chennai was dependent on shallow wells for water, after which organised water supply began with inflows from Sholavaram and Red Hills reservoirs. In 1914, the city commenced with its protected water supply, and as the years rolled on, officials augmented the supply from various sources like Poondi and Chembarambakkam reservoirs and the Veeranam water-supply project.

    The city corporation also began tapping groundwater from aquifers identified at Tamaraipakkam, Minjur and Panjetty. The state government also commissioned two desalination plants to convert sea water into drinking water at Nemmeli in Kanchipuram district and Minjur in Thiruvallur district, with a capacity to supply 100 million litres a day (MLD).

    Chennai’s population has nearly trebled to over nine million people in the last five decades, The metro city’s land area has also increased from 176 sq km to 426 sq km now what with the Tamil Nadu government coming up with the Greater Chennai Corporation.

    According to a CMWSSB presentation, close to 831 million litres a day (MLD) of water is supplied through pipelines and tanker lorries for domestic and industrial purposes. This is done when the reservoir levels are 80 per cent full on 1 January every year. In case the reservoir levels are half full, then the period between end of March to end of October receives alternate days of water supply in the anticipation that the Telugu Ganga river water of 22 MCFT becomes available by June as expected every year.

    However, the water demand for the current population in the city is over 1,100 MLD, thus leaving the metropolitan city with a water shortage in excess of 200 MLD. CMWSSB supply already includes 200 MLD from the Minjur and Nemmeli desalination plants.

    “For a perennial supply of over 800 MLD of water a day, CMWSSB needs Chennai city’s reservoirs storage level to be at 80 per cent of total capacity in January. Such a storage level can ensure water supply until the North-East Monsoon sets in during October,” says R S Kumar, Managing Partner, Varaha Pipeline Engineering and Business Solutions.

    Moreover, CMWSSB water supply suffers from transmission and distribution (T&D) losses. A few years ago, the loss was at 40 per cent due to pipeline leakages and bursts; this has now come down to 19 per cent. Although global T&D losses are at 12 per cent, according to R S Kumar — an expert in seawater intake and outfall reverse osmosis projects — the losses can be brought down to 7 per cent.

    When the situation is such that Chennai faces constant water shortage, what can be the solution? Can desalination plants be a solution to Chennai’s unending water woes?

    This question crops up because the state government has set up two desalination plants that together provide 200 MLD a day, while two more are in the pipeline with a total capacity to supply another 550 MLD. In addition, the state government announced two weeks ago that it will set up five mini-desalination plants at a cost of Rs 120 crore to supply 1 MLD of water each.

    R S Kumar says that desalination water plants can help solve Chennai’s water shortage only to some extent. “Desalinated water can augment Chennai’s water supply by 30 to 35 per cent. It can be a solution for the next 30 years,” he says. This is assuming that the reservoirs are at 50 per cent of their capacity every year on 31 December, after the North-East Monsoon officially ends.

    Israel meets 70 per cent of its drinking water needs through desalination plants after decades of efforts.  This Middle-East nation segregates desalinated water for drinking and other purposes. It adds minerals to desalinated water for drinking, “...as after the reverse osmosis process the water needs to be remineralised to 300 parts per million, while inferior quality water is used for washing and industrial purposes,” says Kumar.

    Desalination plants can be set up using two kinds of technologies — thermal and membrane. For each technology, there are three methods that can be used for desalination purposes. Thermal desalination plants are not generally favoured since waste recovery is poor in them. On the other hand, when sea water has to be fetched a couple of kilometres away from the shore, the membrane type desalination plants with reverse osmosis process are considered.

    One of the problems of setting up desalination plants in the eastern coast of the country is the increased occurrence of biofouling — the spoiling of wetted surfaces due to growth of microorganisms — in the Bay of Bengal. Biofouling affects the desalination plants from being used to their maximum potential and this aspect has to be considered while conducting baseline studies before developing the plant itself.

    The effects of biofouling are removed through processes including chlorination, air-blasting and pigging.  These tend to push up costs. Overall, the cost of desalinated water is 15 paise per litre. These costs include supply and financing funds for setting up the desalination plant.

    With membrane technology improving each day, the costs of producing desalinated water can come down. But it is likely to rule around Rs 100 per kilolitre from the current Rs 120-150, according to Kumar.

    According to Frost and Sullivan — a growth consultation firm — the costs of treating desalinated water is higher than water from other sources. The higher costs leads to inflation of production costs for industrial users and thus, there are not many takers to use desalinated water.

    According to a CMWSSB estimate in 2013, the cost of desalinated water is Rs 48.63 a kilolitre for a build-own-operate-transfer plant. The cost is Rs 30 for an engineering-procurement-construction plant, including seven years of maintenance. (Sources say that CMSSB had to pay higher variable costs and finally it ended up paying Rs 80 a kilolitre for treatment.)

    The CMWSSB is considering supplying tertiary-treated water for industrial uses but has pegged the cost at Rs 45 a kilolitre. The costs are far higher compared to what the corporation spends for treating water from its reservoirs (Rs 2-4 a kilolitre) and well fields (Rs 12.94 a kilolitre.)

    Also, costs for setting up desalination plants seem to increase. The Minjur desalination plant was set up at a cost of Rs 550 crore, while the Nemmeli plant cost was Rs 914.42 crore. Both plants have a capacity to supply 100 MLD. In addition, the Tamil Nadu government has coastal zone clearance from the centre to set up an additional 150 MLD desalination plant at Nemmeli and a 400 MLD at Perur on the East Coast Road.

    The cost for setting up the new desalination plant at Nemmeli has been estimated at Rs 1650 crore, while the Perur plant cost has been projected at Rs 3,912 crore. Both these plants are a long way off as they have to go through various permission processes, including raising funds.

    With costs for supplying water from desalination plants being higher and the expenses to set up such plants rising, such a source can be seen only as a short-term solution.

    “These plants can help meet the needs for 30 years. After that, we have to see. The population would be rising sharply and water needs will increase. In such a situation, the share of water that will be met from desalination will come down,” says Kumar.

    Frost and Sullivan says that demand for water will rise with economic and population growth. Reduced desalination plant costs and government push can help reverse-osmosis-based plants to mushroom across coastal states like Tamil Nadu. Private-sector participation and joint ventures can help more desalination plants to come up, while the cost of production could drop with using new technologies.

    M.R. Subramani is Executive Editor, Swarajya. He tweets @mrsubramani

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