Looking at the sea for water: Are desalination plants worth their salt?

Desalination of seawater is emerging as a solution to global water crisis. India, too can benefit from it.

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SC Lahiry

In India, fresh water is depleting fast with the rise in consumption for economic activities. Poor management of water resources has led to overexploitation of groundwater. The World Resources Institute’s March 2016 report said 54 percent of India was water stressed, with scarcity affecting every part of the country except the Himalayan region and the ghats. “Almost 600 million people are at higher risk of surface water supply disruptions,” the report said, attributing water stress to climate change and poor water management.

We are fortunate that our country is endowed with vast seawater resources covering large parts of over a dozen of states and union territories. Ensuring purified seawater supply through dedicated networks would help people immensely. The process would eliminate the paradoxical situation faced by the people in the coastal region--having access to an inexhaustible supply of saline water but no way to use it.

Some sporadic efforts have already been made by establishing desalination plants near Chennai, Puducherry, Andhra Pradesh, Gujarat, etc. Some more such plants are being contemplated in places like Thane and Cuddalore.

Status of freshwater supply

NASA pointed out that India's water tables are declining at a rate of 0.3 metres per year. Between 2002 to 2008, the country consumed more than 109 cubic kilometres of groundwater, which is double the capacity of India's largest surface water reservoir, the upper Wainganga (Economic Survey,2015-16 p 74).

The Global Runoff Data Centre, University of Hampshire and International Earth Science Information Networks have projected that around 30 percent area of India falls in the extreme water scarce zone having less than 500 cubic metre per person per year of renewable freshwater supply. Moreover, 50 percent of groundwater sources in the country are not “completely safe”. Of the 660 districts, groundwater in 276 districts has high levels of fluoride, 387 districts have nitrate over the safe level and 87 districts have arsenic as per the Central Ground Water Board report. It is revealed from the above facts that the freshwater supply is declining quite rapidly. Finding new sources of water for our living has become a priority.

Is seawater desalination a solution?

The water received after the desalination process is water with less than 500mg/lit dissolved solids which is suitable for most domestic, industrial and agricultural uses. All desalination processes involve three liquid streams--the saline feed water, low salinity product, and a very saline concentrate. The saline feed water is drawn from oceanic or underground sources. It is separated by the desalination process into the two output streams--the low salinity product water and very saline concentrate streams (O.K.Buros et al.the USAID desalination, Englewood, Mannual).

The seawater desalination is increasingly becoming a vital option for alleviating severe water shortage around the world. Israel now gets 55 percent of its domestic water from desalination and that has helped to turn one of the driest countries into the unlikeliest of water giants (Scientific American:"Israel proves the desalination era is here" by Rowan Jacobsen July 29,2016).

Australia, Caribbean Islands, the Middle East, South Africa, USA, etc are some other countries that have established large desalination plants for domestic use. According to the UN World Water Development Report, 2014, more than 17,000 desalination plants are now operating in 150 countries worldwide, a capacity that could nearly be doubled by 2020. According to International Desalination Association, desalination produces 21 billion gallons of water per day, providing a crucial water source in arid places. It claims that 300 million people get water from desalination and their numbers are quickly rising. In the coastal region of India, a few seawater desalination plants are in operation using reverse osmosis. As per the Desalination Association of India, there are more than 1000 membrane-based desalination plants of various capacities ranging from 20 m3/day to 10,000 m3/day.

Reverse Osmosis (RO) desalination process

A view across a reverse osmosis desalination plant. Image by James Grellier, Wikimedia Commons*

A reverse osmosis (RO) system consists of four major components or processes--pretreatment, pressurisation, membrane separation and post treatments stabilisation. Water from pressurised saline solution is separated from the dissolved salts by flowing it through a water permeable membrane. The permeate (liquid flowing through a water-permeable membrane) is encouraged to flow through the membrane by the pressure differential created between pressurised feed water and the product water, which is at near atmospheric pressure. The remaining feed water continues through the pressurised size of the rector as brine. No heating or phase change takes place.The major energy requirement is for the initial pressurisation of the feed water. The operating pressure for seawater desalination ranges from 800-1000 PSI (O.K.Buros et al.the USAID desalination, Englewood, Mannual).

Rapid development of technology

Desalination technologies are advancing rapidly, and seawater can now be reclaimed with a single pass through an RO membrane. Nanotechnology-based solutions, especially nano metal catalysts, are gaining prominence in providing solutions to alleviate water quality problems, especially in Indian markets. While there are many technologies available today, the appropriateness of the technology is a very important question.

Israel, the world leader in the process, has come out with several state-of-the-art technologies. Desalination plants using the RO system is currently the only workable solution as proven by the most advanced and energy-efficient $500 million plant at Sorek, Israel. The new Sorek desalination plant, the largest RO desal facility (150 million cubic metre capacity) in the world works by pushing salt water into a membrane containing microscopic pores. The water gets through while the larger salt molecules are left behind. But microorganisms in seawater quickly colonise the membranes and block the pores, and controlling them requires periodic costly and chemical-intensive cleaning.

Researchers of Israel’s Zuckerberg Institute for Water Research have developed a chemical-free system using porous lava stone to capture the microorganisms before they reach the membranes. It’s just one of the many breakthroughs in membrane technology that have made desalination much more efficient (Scientific American: ibid). The largest plant in the Western Hemisphere, a $1 billion state-of-the-art RO facility being built near San Diego, USA, is set to begin producing 54 million gallons of water a day, supplying water to three lakh residents in early 2016. At least 15 other plants using RO in the West Coast are currently in some stages of implementation.

The Department of Atomic Energy (DAE), GOI has done pioneering work in developing indigenous desalination and water purification technologies. At DAE, a seawater desalination plant operating on the RO process with a capacity of 18 lakh litres per day has been set up. A Multi-Stage Flash (MSF) Seawater Desalination Plant with a capacity of 45 lakh litres per day has also been set up at Kalpakkam. The desalination plant is intended primarily for meeting the industrial and potable drinking water requirements of the DAE unit. For the foreseeable future, reverse osmosis will likely remain the top desalination choice.

How financially viable is the process?

The capital and operating cost for desalination have tended to decrease over the years though energy prices have increased. The water produced by desalination cost just a third of what it did in the 1990s. Sorek plant can produce a thousand litres of drinking water for 58 cents. Israeli households pay $30 a month for their water similar to households in most of US cities and far less than Las Vegas ($47) or Los Angeles ($58) (Scientific American: ibid).

According to Desalination Association of India, the production cost of a brackish water desalination plant could be Rs 10 to 15 per m3 while the production cost for a seawater desalination plant varies between Rs 40 to 50 per m3 (The production cost of desalted water from effluent varies from Rs 15 to 50 per m3 depending upon the TDS load in the effluent stream). According to DAE, on an average, the cost of conversion of seawater into desalinated water is about 10 paise per litre of water produced. When large-scale plants are built, the economy of scale will provide a further reduction in the conversion cost of seawater into desalinated water. It is essential for the technology to be appropriate in terms of energy efficiency, environmental soundness, etc. In addition to the suitability of the technology, it is also important to look into the appropriateness of the product for a particular geographical location. Some of the critical factors which a product should consider are ease of use, service support, the rate of filtration, efficiency in removing taste and smell, etc (Safe water for the Last Mile-Technology Solutions, Development Alternatives, Delhi,2013).

Purification of seawater holds the key to the holistic development of a country's water resources. The solar and wind energy available in abundance in the region should form as alternative sources of fuel for this purpose and falling prices (of renewable energy) will considerably reduce the production cost. A development strategy utilising seawater in the coastal region of the country would need to be formulated quickly. The finances of setting up desalination plants in the region may be shared by the central government, the state government, the local bodies and private companies. National Water Policy, 2016 (under finalisation) should articulate policy framework for the utilisation of seawater. Under the ambitious Sagarmala project, where setting up of a no of major development projects have been contemplated in coastal States, groundwater-based development should be discouraged as far as possible and treated seawater should be used.

(This article was first published on The India Water Portal. You can read the original article here. The author is former Adviser, Planning Commission, and has voluntarily contributed this article to India Water Portal. The views and opinions expressed in this article are those of the author/s.)