Desalination: Tapping The Remaining 97%

Desalination has, in the past, been viewed as an expensive means of solving growing water supply problems. Research projects being conducted in water-scarce countries like those in the Middle East are, however, starting to overcome many of these obstacles. Rowan Watt-Pringle reports on new desalination methods with revolutionary potential.

Most industry experts agree that desalination will play an increasingly vital role in meeting the growing demand for fresh water over the coming decades. With fears over water supply growing year on year it's somewhat remarkable to consider that around 97% of the water on earth is salty, while only 1% is available as fresh water in lakes and rivers.

Mutaz Ghandour, CEO of leading desalination industry analysts Metito Overseas places the issue in clear contrast, "the demand for fresh water is increasing twice as fast as population growth".

Meanwhile, a 2009 desalination report from Lux Research analyst Michael LoCascio, entitled "Desalination's Future Champions", has predicted that desalination use will triple by 2020. 

In light of this, its clear that what is needed are new methods and technologies with which to review desalination costs and find a way to tap into the remaining 97%.

Current desalination technology and trends

There are two schools of desalination: thermal and membrane. The major thermal technologies are multi-stage flash, multi-effect distillation and vapour compression distillation, while reverse osmosis (RO), electrodialysis and electrodialysis reversal technologies desalinate water using membranes.

"Tianjin itself hopes to double its output within four years."

The Lux report states that RO, which currently dominates the desalination industry, will continue to be the principal technology used. Despite this, the report sees a host of other technologies taking a more central role, with forward osmosis (FO) technology taking a growing share of the desalination market.

RO should continue to dominate small-scale water production in conjunction with hybrid systems incorporating FO technology, which have come to the fore since the turn of the millennium.

According to the report, this will eventually lead to FO becoming the central technology for seawater desalination plants, once firms have become more comfortable with its intricacies, while there are also many ways in which industry players are attempting to drive down the costs involved with the current technology.

Genesys International – maintaining membranes

Genesys International's product range looks to minimise the negative aspects of using membranes, such as fouling and scaling.

Bruce Schroder of Genesys' South African agency Sud-Chemie – the largest water treatment supplier in Africa – cites the importance of its products: "Genesys is known internationally as the Rolls Royce of RO chemical supply. I have personal experience of the effectiveness of Genesys' chemicals, having worked with them in various industries; the products are huge in the Middle East."

Genesys International's David Golding expands: "Our products and services are applied in some of the biggest membrane plants in the world, including the large, Two Pass, SWRO/BWRO units at Ashkelon in Israel, Shuqaiq in Saudi Arabia (200,000m³/day) and Barka II in Oman, (128,000m³/day)," adds Golding.

Genesys' Membrane Master III computer program, meanwhile, is used to calculate scaling and fouling potentials in membrane system concentrates.

"Based on a chemical water analysis, membrane type and plant operating conditions, the multilingual Membrane Master program calculates scaling and fouling potentials for membrane system designers and operators," relates Golding, continuing, "The program selects the most suitable anti-scalant or anti-foulant product, derives the dosage rate and calculates consumptions."

According to Golding, this means that plant designers can identify critical scaling species and select the correct specialist anti-scalant: "In this way, efficiency is maximised and costs minimised," he says, adding, "The new version of the program, coming soon, will incorporate cleaning recommendations and a ready-reckoner for dose pump settings vs dilution."

MEDRC: leading the push for desalination

As much as 50% of the world's total desalination occurs in the Middle East and the Lux Research report claims that despite the region being traditionally reticent in adopting new technology, it is well-placed to lead desalination technology development and manufacturing: "As the demand for water in the region ratchets upward, domestic desalination systems integrators, engineering firms and even homegrown equipment and membranes could flourish."

"The report claims that DSE technology provides a very low temperature, membrane-free method of desalination."

The Middle East Desalination Research Centre (MEDRC) is central to this process, having coordinated and sponsored more than 34 desalination training programs in countries across the region.

The MEDRC also works towards fostering cooperation between countries and has awarded grants for 74 multinational research projects valued at more than $10m, involving 137 institutional research partners in 34 countries.

Research projects have ranged from studies on solar-powered desalting, to the design and development of a small packaged RO system, driven by a hybrid power supply system.

One completed study focused on a novel method to permanently improve the rejection of RO desalination modules. The result? A significant reduction in the cost of desalination.

China looks to stave off shortages

Chinese news agency Xinhua recently reported claims made by a senior official at the Tianjin Municipal Commission of Science and Technology, that as of March this year the country boasts seawater desalination facilities with a combined daily production capacity of 524,000t of fresh water.

Deputy director Li Baochun said that Tianjin itself hopes to double its output within four years, despite already accounting for 41% of China's total desalination capacity.

Tianjin has just finished hosting the 2011 International Desalination and Water Reuse Forum and has also put in a proposal to host the International Desalination Association World Congress in 2013.

As one of China's cities facing the threat of severe water shortages, Tianjin is backing desalination to get water to its people, with Li telling Xinhua that seawater desalination has become one of the key solutions to addressing the city and the country's water shortages.

Directional solvent extraction (DSE) technology

Researchers at the Massachusetts Institute of Technology (MIT) Department of Mechanical Engineering believe they have found the next big thing in desalination technology.

In a report published in February, Anurag Bajpayee, Tengfei Luo, Andrew Muto and Gang Chen put forward a new desalination method they call directional solvent extraction (DSE).

"97% of the water on earth is salty, while only 1% is available as fresh water."

According to the report, "Thermal energy based multi-stage flash distillation requires heating to temperatures above 90°C, which is expensive and accounts for 50% of its cost," while "Membrane-based reverse osmosis uses high grade electrical energy input, which accounts for 44% of its cost."

The report claims that DSE technology "provides a very low temperature, membrane-free method of desalination that could potentially reduce desalination costs and complexity and open up a new field of desalination research."

The researchers believe that because the process can function at much lower temperatures, their research opens up a way to use low temperatures in a cheaper manner – from terrestrial or solar energy, or by scavenging waste heat: "Sources that could provide such temperatures are abundant and inexpensive. Although the absolute energy consumption is high, the exergy of this energy is extremely low and thus we are utilising energy that would otherwise be wasted."

The technology uses directional solvents like decanoic acid to dissolve water but not salt and, while it is still very much in the research phase, there could be exciting times ahead, with the authors concluding: "It is anticipated that in large systems, heat recuperation will be used to improve the system efficiency. Commercialisation of such processes could lead to a drastic reduction in fuel and operating costs for desalination, which is critical to ensuring an affordable fresh water supply in the future. Further research into the identification of other suitable directional solvents, understanding the physics of the process, and the development of industrial processes offers tremendous opportunity."