Riding on Technology: New advancements in the water desalination process

New advancements in the water desalination process

The country’s industrial water requirement is significant, next only to the municipal and irrigation requirements. Heavy in­dus­tries such as power, oil, iron and steel, sugar, and paper and pulp are the major consumers of industrial water. With a steady growth in these industries, the demand for industrial water has also increased subsequently. In this respect, some notable developments have been witnes­s­ed on the technology front. Industries are moving towards membrane-based technologies to reduce their dependence on freshwater sour­ces, increase treatment capabilities and reduce operational costs as well.

In the coming years, the increasing awareness among industrial units regarding the need to re­duce their water footprint and the declining freshwater availability are expected to augment the demand for advanced technologies. In addition, the National Water Mission proposes the adoption of new and appropriate technologies for water supply to coastal cities such as low temperature desalination technologies that allow the use of ocean water, creating significant opportunities for global as well as domestic technology providers and equipment suppliers.

Smart Utilities provides a snapshot of the new advancements in desalination technologies, upcoming technologies in light of the Covid-19 pandemic and future opportunities for techno­logy providers…

New techniques

Hybrid technology

Hybrid technology, a combination of reverse osmosis (RO) and multistage flash (MSF) desalination, is being adopted in various projects ac­ro­ss the country. It has the provision for redundancy, utilisation of streams and production of two types of water for best utilisation. RO operates with the help of electricity and MSF uses low grade steam. Two types of desalinated water are produced. The desalinated water produced from MSF is pure and fit for industrial use, and that produced from RO is of potable quality. The desalination plant at Kalpakkam deploys the MSF-RO hybrid technology. It has a capacity of 6.3 million litres per day (mld) (4.5 mld MSF and 1.8 mld RO), and sources the required en­ergy from the Madras Atomic Power Station. The plant operates at a relatively lower pressure and employs fewer pretreatment chemicals because of relatively clean feed seawater.

Solar-powered desalination technology

Another technology that is slowly gaining mo­mentum is solar energy desalination, which produces clean water from seawater using solar energy. The country’s first solar-powered desalination plant was set up at the Viveka­nanda Me­morial, Kanyakumari, Tamil Nadu. The plant was created by a group of students from the Indian Institute of Technology Madras and was financed by the Ministry of Earth Scien­ces with an amount of Rs 12.2 million. It uses MSF technology and has the capacity to generate 10,000 litres of water per day. It requires 15 kV of power per day to function and since the plant is solar powered, it can be operated only during the daytime. Mean­while, the generated power is stored in 14 batteries to provide 30-minute power backup.

Another solar-powered desalination plant is situated in Narippaiyur village, Ramanathapuram. The plant uses a solar-thermal desalination pro­cess with a multiple-effect distillation system, wherein low-cost expanded steam is available from a steam turbine just ahead of the condenser. The plant has thermal storage and ensu­res solar desalination round the clock. Since no fossil fuel is used, the solar desalination technology will typically save 2,500 tonnes of carbon dioxide emissions annually in comparison to conventional coal-fired boilers producing 140,000 litres in a 24-hour period.

Wave-powered desalination

Wave-powered desalination is a sustainable, eco­nomical, scalable and eco-friendly solution to supply drinking water. The technology is now ga­the­ring momentum, targeting off-grid, coastal com­munities in developing countries that are facing water shortages, by harnessing the free and renewable energy source of ocean waves. For energy generation, the oscillating water column drive is partly submerged, with an opening to the sea below the waterline. Waves cause the water column to rise and fall, which alternately compresses and depressurises the air column. The air flows through a turbine, which drives the electrical generator. The next phase is to shift the cassion to a floating platform to make use of the 7 metre high monsoon season waves.

The country’s first ever ocean wave-powered de­salination plant is located in Vizhinjam, Tri­van­drum. It has the capacity to generate 7,000-8,000 litres per day, using tidal waves as its so­urce of energy. The plant was set up by the Na­tio­nal Institute of Oceanography. It uses 14 batteries to store power converted from direct current to alternating current using an inverter.

Low temperature evaporation desalination using waste heat

The utilisation of waste heat as energy input for seawater desalination is being perceived as an­other attractive option. The process involves eco-friendly ways to produce desalinated water and does not require chemical pretreatment of feed seawater. Ocean thermal energy can also be utilised for seawater desalination.

The unit essentially consists of three components – heater, separator and condenser. In the heater shell, vertical tubes are used. The feed seawater enters the unit at the bottom of the tubes and partly evaporates by the time it comes out from the top. After the water and vapour mixture come out of the tubes, the vapour rises th­rough the vertical shell, enters the horizontal tube bundle kept at the top of the vertical shell and condenses around the tubes (which are cooled by the sea water flowing inside), thus producing desalinated water.

The Chennai-based National Institute of Ocean Technology has set up low temperature evaporation-based desalination plants on the Minicoy, Agatti and Kavaratti islands in Lakshadweep. The plants use waste heat as their principal source of energy and have the capacity to generate 100,000 litres of water per day.

Emerging technologies in light of Covid-19

Since the outbreak of the Covid-19 pandemic, various industries have become cash-strapped. To deal with this, they are planning to deploy technologies that significantly reduce the cost of desalination. Several government policies are also mandating desalination as a primary source of water for industries. Thus, industries are planning to invest in new technologies that can make the desalination process more efficient.

However, desalination proves to be costlier than other alternatives for producing potable water like rainwater harvesting, recycling and reuse hampering its widespread implementation. Thus, indigenous development of membranes and water reco­very/reuse from effluents need to be pursued.

Technology providers need to demonstrate futuristic technologies on test beds before offering one single solution. This will enable authorities, industries and urban local bodies to take the right decision based on their requirements.

Te­ch­nologies need to be optimised for energy conservation as power is a major cost component for a desalination plant. New technologies like nano-engineered membranes, carbon nanotube membranes and acquapor in membranes need to be deployed and developed.

Opportunities and outlook

The desalination sector is ripe with opportunities for various technology providers. The segment offers huge opportunities for technology provi­ders as desalination technologies are advancing rapidly, and seawater can now be reclaimed with a single pass through an RO membrane. Accord­ing to India Infrastructure Research, of the 19 key up­coming industrial desalination plants in India, six will be deploying RO technology for water treatment. Meanwhile, two plants will be based on sea­water RO technology. Of the 22 key up­coming municipal desalination plants tracked, six will be deploying RO technology for water treatment and four will be based on seawater RO technology. These projects offer tremendous opportunities to desalination technology provi­ders as well as other stakeholders.

Going forward, technologies need to be optimised for energy conservation as power is a major cost component for a desalination plant. New techno­lo­gies like nano-engineered membranes, carbon nanotube membranes and ac­qua­por in membra­nes need to be deployed and developed.