Desalination, a modern technological process as it may sound, has its roots embedded in history. The origin of the discovery of this process dates back to the time of Aristotle (384 BC-322 BC) who is credited with its innovation as he spoke about his evaporator and desalination of sea water. But it was only after World War-II when desalination plants began to build.
Desalination across the globe
Potable water shortages are felt in many countries overseas. Therefore, desalination is favoured as a very useful process to alleviate water scarcity and create water availability for domestic purpose. Countries like Israel, which were once among the driest of all countries have become water giants. Australia, North Africa, Caribbean Islands, Middle East, South Africa and USA are some of the other countries that have established desalination plans for domestic use. According to UN World Water Development Report, 2014 more than 17,000 desalination plants are now operating in 150 countries worldwide, and capacity can double by 2020. International Desalination Association claims that desalination produces 21 billion gallons of water per day supplying water in arid regions.
Desalination in India
Natural and social causes have brought India-once an extremely rich and abundant source of all resources especially water-under the threat of becoming a water scarce country by 2025. Severe erosion of water table, increasing extraction of ground water, monsoon failure and water pollution by all means has been some of the major causes behind the situation. At the juncture that we are in at present, desalination seems to be a very effective solution for our water troubles. Desalination plants have been established in Tamil Nadu, Puducherry, Andhra Pradesh and Gujarat.
Innovative technologies used for desalination
Reverse Osmosis- The most dominant technology used for desalination today is Reverse Osmosis (RO). In RO systems, water from a pressurised saline solution is separated from the dissolved salts by flowing through a water-permeable membrane. The permeate — liquid flowing through a water-permeable membrane — is encouraged to flow through by the pressure differential created between pressurised feed water and the product water. The major energy requirement is for the initial pressurisation of the feed water. The RO plant in Chennai, believed to be the largest in India, generates around 100 million litres of fresh water. Although this process is viable and sufficient, the energy consumption and environmental impact of this process is somewhat not very impressive.
Forward Osmosis- The birth and growth of the desalination industry have always depended on technological advances to overcome physical and economic challenges. Thus, another process called Forward Osmosis (FO) came into being which is an osmotic process that uses a semi-permeable membrane to separate salts from water. FO uses an osmotic pressure gradient instead of hydraulic pressure, which is used in RO, to create the driving force for water transport through the membrane. No energy is needed to drive the water flux of an FO process, as the water flux is the natural tendency of the system. FO is an innovative membrane-based technology that has the potential to reduce the costs and environmental impacts of desalination.
Innovation on the global platform
ReFlex technology from Desalitech (USA)- This technology is based on a system comparable to a conventional reverse osmosis system but in batch operations. The average pressure in this operation is less than the constant pressure of a conventional system. In addition, the purge pressure is minimal, unlike the conventional system. Through this type of operation, energy consumption compared to the conventional system is reduced by 20-35%.
Technology used by IDE Technologies (Israel)- IDE Technologies has developed a process with 16″membranes arranged vertically which reduces the amount of pressure vessels, collectors, control equipment and plant size. The company has designed and built the largest and most advanced desalination plant in the world to date with this advanced technology.
The Massachusetts Institute of Technology and Jain Irrigation Systems- Together they have designed a photovoltaic-powered electrodialysis reversal system that desalinates water by using electricity to pull charged particles out of the water and further disinfect the potable water using ultraviolet rays. MIT and Jain Irrigation Systems specifically designed their system for low energy consumption, adapting traditional electrodialysis to limit costs, especially in off-grid areas.
Other innovative and proven technologies tested in various places across the world includes ion-exchange, nanofliteration, remineralization and disinfection. The primary focus today is to build a technology using hybrid renewable energy power comprising both solar and wind power.
The energy consumed in the treatment of saline water depends totally on the salinity of the water and therefore the source from which it has been made available is important. Seawater desalinisation should be the last resort according to this information. Moreover, a major deterrent is fouling that affects energy consumption, membrane life and water production ratio. Fouling prevention can help in saving energy.
The freshwater supplies are bound to reduce with the current rate of consumption and the growing population. This points to the direction towards proliferation of desalination of water for domestic, industrial and agricultural purposes. Moreover, Ministry of Urban Development plans to develop 100 smart cities in the country. This scheme requires an uninterrupted supply of treated water in the cities all the year round which necessitates the instalment of desalination plants at a rapid pace.
While discussing the future of desalination one thing that warrants mention is digitalisation. Use of digital technology to detect, anticipate and manage upsets and ongoing operations is required to enhance improvement in its functioning and making it more sustainable and affordable, a goal that the International Desalination Association (IDA) supports and promotes around the world.