By S. Sivathasan –
“If we could produce fresh water from salt water at a low cost, that would indeed be a great service to humanity, and would dwarf any other scientific accomplishment”. President John F Kennedy – 1962.
Water for domestic needs is among the indispensables of life. In this segment, potable use claims primacy. Fresh water was used direct for millennia past. It is no longer advisable to do so for reasons that are well known. Water from traditional sources – rivers, lakes and ground – has been subjected to sophisticated technologies for perfect purification. With population in a steadily increasing mode and supplies proving to be inadequate at places of population concentration, desalination has caught world attention.
A stock of 199 plants in 1962 when Kennedy made his call, growing to 16,000 in 2012 is a measure of progress. The year 1945 saw the first desalination plant in operation with a capacity of 326,000 liters per day (l/d). The largest to be delivered in 2014 at Ras Al Khair in Saudi Arabia will have a capacity of 1.025 billion l/d, using both membrane and thermal technology. As of now the cumulative capacity is over 70 billion l/d. In the first 50 years what was seen was an upward curve in the number of plants constructed. Cost reduction by half in 20 years accounted for the steep increase. The last few years witnessed a scaling down. Capital and operational costs require to be brought down for the next spurt. A dramatic reduction is called for though limitations to such efforts have to be realized. The challenge is before the scientist and the technologist. Promising signals are already on the radar.
Cost of energy has been a principal factor in water purification. The use of membrane technology for the Reverse Osmosis (RO) process was a path breaking innovation. Technological efficiency apart, it reduced costs substantially. However a continuously declining tempo in economies of installation and operation has not been maintained. This phenomenon explains the steady rise after 1980 of stock of plants and volumes delivered and a declining trend after year 2004. Together with innovative processes has to go development of cheaper sources of energy. Harnessing solar and wind energy in increasing magnitude and decreasing unit cost per liter is a striking phenomenon of this century. Processes other than RO too are being developed. It is said that the use of carbon nano – tube based membranes could reduce desalination cost by 75%. Scientists in US are in the forefront in developing better cost effective technologies. As recently as in 2013 it is reported that material scientists from MIT have designed a next generation water desalination membrane. Once perfected, commercial application will follow. When the world is poised on the threshold of cost effectiveness, water stressed areas can be in a mood of optimism.
Together with water purification is the concern with which brine disposal issues are addressed. Brine is a salt solution that comes off once pure water is extracted. It is about1.5 times the volume of water that is taken and is discharged into deep saline aquifers. From the turn of the century nearly 50 billion liters are so discharged daily and the volume is now 100 billion. Nearly 20% of global desalinated water and therefore a similar proportion of brine discharge is in the Middle East. No adverse impact is experienced or reported to the point of affecting the programme of desalination in any part of the world.
The world is moving on to a particular pattern in water use. The change is conditioned by three principal developments. A near quadrupling of population in the century ending by 2050, with a mandate to quadruple food supplies; industrialisation on an exponential scale and unstoppable urbanization. It is likely that an increasing demand on fresh water will be dominated by agriculture. Along with fresh water, increasing quantities of recycled water will relieve industrial needs. For domestic purposes fresh water for the inland and desalinated water in the littoral areas for a width of 50 miles along the sea may develop into the standard pattern. An ever burgeoning demand on sea water necessitates more viable technologies and cost effective energy sources to employ the technologies. In this pursuit the scientific community is actively engaged in both the developed and the developing world. Performance in the recent past would suggest promising results.
Among the countries that are well endowed with water resources, Sri Lanka is one. Yet there is an imbalance between the wet zone and the dry zone. In the latter segment river flows impounded in tanks change the availability structure thus abating water stress. They also provide the source for a portion to be siphoned off for domestic and industrial use. It is the coastal stretch from the North to East and South that remains impoverished. The next half a century is bound to see development, population movement, urban centres and population concentrations. Preceding them should be assured water availability and the ready sources are salt water and brakish water. Desalination will change the landscape drastically. In the eastern and southern coasts, the districts of Mullaiithivu, Trincomalee, Batticaloa, Amparai, Hambantota and even Matara would require studied consideration of salt water desalination.
“The problem of ground water in Jaffna is as complicated as the Jaffna man”. This was the perceptive comment of an Israeli expert who toured the peninsula 40 years back studying the ground water situation. The features are indeed distinctive. The furthest point from the sea is just 12 miles. The whole of the peninsula is underlain by limestone which is both porous and cavernous. It helps in storage of rain water, discharging excess to the sea through seepage and also promoting reverse seepage of sea water when wells are overdrawn. The frailties of nature are further compounded by certain compulsions. To maximize agricultural production there is a heavy use of inorganic fertilizers and agrochemicals. Added to them is the high density of soakage pits. Water contamination is at a calamitous level with ruinous effect on the health of the people. Wholesome potable water is of the highest priority in Jaffna.
There are assets as well. The deep natural Nilavarai well at Puththur has a water lens of 156 feet. Heavy draw off is possible though lower layers are brakish. A battery of other wells both dug and tube is also practicable though sustained pumping will cause brakishness. The remedy lies in desalination with Reverse Osmosis process. Globally 40% of desalination is with brakish water. The deficit can be met from sea water desalination. Drawing fresh water from Iranamadu above 40,000 acre feet has its constraints.
Water stressed countries and states have been in the forefront in adopting the desalination strategy to meet their water needs. In the last decade, global capacity reached 70.8 billion liters per day, signifying a doubling of what was achieved in the preceding half a century. Production of 120 billion liters per day is estimated to be reached by 2020. Annual growth rate is now 15%. It is also worthy of note that high capacity plants are more in vogue. The larger ones have a capacity range of 100 million to 1billion l/d. It is also good to look at some of the countries that have adopted them: Saudi Arabia, Emirates, Algeria, Israel, Singapore, some states in the US and some cities in Australia.
Tamil Nadu commissioned its first desalination plant in July 2010. It is situated north of Chennai and has a capacity of 100 million l/d. Close to it is the plant at Nemeli with a capacity of 100 million l/d. It is scheduled for opening next month. A third of 200 million l/d capacity at Pattipulam north of Chennai is being planned. A few more are needed to meet the requirements of Chennai. Singapore has already commissioned two of the largest plants. China is a phenomenon by itself planning to triple capacity to 2.2 billion l/d by 2015. It is projected to meet 15% of industrial needs in the eastern seaboard.
Climate change which was a bogey earlier is now understood as a fact of life. Coping with the emerging situation is the challenge. Warming continues to have its adverse impact on both rainfall and snowfall. Resulting depletion of water resources is what mankind is experiencing. Since multiple uses make their demands, augmenting supply is vital. Sea water being an inexhaustible source, it is readily selected for processing.
Unprecedented demographic changes in the last 70 years have placed a heavy demand on water for food production. The trend will move unabated for the next half a century. The first charge on water will continue to be for agriculture. It is well researched and noted that productivity and production are disproportionately enhanced more by water than by land resources. Countries well positioned for industrialization and FDI loose out when supply together with the highest standard of purity is not assured. Pharmaceuticals and wafers and chips for the electronic industry are cases in point. The cost factor of desalination recedes when matched against the imperatives of industrialization and growth challenges in employment.
Human ingenuity exploiting the endowments of nature and also triumphing over limitations is among the lessons of history. Concerns about water availability and assurance of continuity will dominate the current century. Desalination volumes, costs and geographical spread yet depict features of incipient development. Solar and wind energy economies together with desalination technologies are sure to make their demands on the intellectual resources of scientists. Going apace will be the siphoning off of larger financial resources. The upshot of it all is a climate of optimism.