Membrane desalination utilising RO was introduced in the 1960s.
Membrane desalination utilising RO was introduced in the 1960s.

Desalination is currently growing at a significant combined annual growth rate (CAGR) of 7.4%, according to data obtained for the IDA’s 27th desalination Inventory, compiled by Global Water Intelligence. This is at a time when process efficiencies have improved and costs have come down, with the energy consumption of seawater reverse osmosis (SWRO) desalination having decreased by more than 50 % in the last two decades.


The Al Khafji City desalination plant will be powered by solar PV energy.


Municipal and industrial wastewater reuse using membrane and thermal processes is part of this overall growth, with desalination technology now being utilised in all regions of the world. Water management strategies including conservation, water reuse and desalination are allowing stakeholders to optimise their water supply resources.

Desalination data

Development in the desalination and water reuse sector is being supported and monitored by the IDA. Established 42 years ago, the IDA is an NGO of the United Nations with over 2,600 core members and a network of affiliates who represent another 4,000 members within the public and private sectors, including end users, suppliers, researchers and service providers. Their services include organising global events (including the World Congress and other technical conferences), promoting research and development, providing education and disseminating information.

The growth in desalination over recent years has been recognised by the IDA as being due to an increase in global population, urbanisation, a ‘middle-class’ lifestyle in developing nations and depleted groundwater, which has put pressure on available water resources in terms of consumption and pollution of water sources. Recognition has grown that quality of life is greatly enhanced when there is an abundant clean water supply and desalination has made a valuable contribution by providing a reliable drinking water supply as well as an effective tool for wastewater treatment and water reuse.

According to Bluefield Research, the US currently reuses approximately 4.2 trillion m3 of water annually, making it the largest potential market for reuse by volume. However, this equates to 3 % of total supplies. The US is well behind the Singapore ‘NEWater’ reclaimed water rate; Singapore's four NEWater plants can meet up to 30 % of the nation’s current water needs. By 2060, Singapore’s Public Utilities Board plans to expand the current NEWater capacity so that NEWater can meet up to 55 % of their future water demand.

Israel leads the world in the proportion of water it recycles, treating 80 % of its sewage. 100 % of the sewage from the Tel Aviv metropolitan area is treated and reused as irrigation water for agriculture and public works.

Bluefield Research points towards real momentum in the GCC (Gulf Cooperation Council) region with US$ 22.4 billion of wastewater treatment spending in the region forecast in the period 2015-2020, representing a significant step toward bridging the region’s wastewater infrastructure gap, and offering significant new opportunities to complement a more established desalination sector.

In the USA, installed wastewater reuse capacity in Florida has grown 52 % since 2000, reaching 6.6 million m3/day in 2014. Analysis of a number of facilities, totalling spending of more than US$ 6 billion, signals opportunities for water solution providers aiming to address the region’s forecasted water challenges.

Municipalities are the main managers of desalination capacity, currently accounting for 60 % of the total global capacity. But advanced water treatment solutions are also quickly being adopted across industrial sectors. Established in regions of high water-scarcity or because of environmental regulations, the mining and energy sectors have been at the forefront of this shift. Industry accounts for 28 % of the capacity, electric power generation, 6 %, irrigation, 2%, tourism, 2 % and the military, 1%.

The various types of usage in the industrial sector are shown in Table 1. Figure 1 shows how the various types of feed water are utilised by desalination systems, with seawater and brackish water accounting for 59 % and 22 % respectively.

According to data supplied by Global Water Intelligence and the IDA, in 1980, the installed capacity of desalination worldwide was 5 million m3/day but in 2013 the total capacity had grown to over 80 million m3/day. The value of all desalination equipment sold in 2014 will be US$ 12 billion increasing by 61 % to over US$ 21 billion by 2019.

If we investigate the growth of new desalination systems the figures are even more significant. In 1980, one million m3/day of new desalination capacity was installed. In 2013 this had climbed to 6.2 million m3/day of new desalination capacity. In 2019 it is estimated that over 11 million m3/day of new capacity will be installed.

The top 10 desalination markets currently, measured by total installed capacity are Saudi Arabia, USA,
UAE, Spain, China, Kuwait, Australia, Algeria, Israel and Qatar. The top 10 plants are depicted in Table 2, with the largest installed and operating plant still being the Ras Al-Khair project in Saudi Arabia, projected to soon be producing 1,035,000 m3/day.

In the USA, the desalination capacity online and under construction is currently 11.1 million m3/day from more than 2,800 plants, primarily utilising brackish water. In California, the capacity is 1.7 million m3/day from more than 441 plants. The top two systems in the USA are Carlsbad in California (189,250 m3/day) and Boca Raton in Florida (151,400 m3/day).

New ideas for utilising renewable energy are being actively developed.

 

Technology

Thermal desalination systems utilising evaporators are widely exploited in the Arabian Gulf where the technology is often employed along with electric power generation to take advantage of readily available power supplies and the benefits of energy/water process synergies. Advances in thermal process design has resulted in new installations, largely in the GCC region.

Seawater is the dominant application but thermal technology is also used in food and pharmaceutical applications or for wastewater dewatering.

Thermal desalination plant costs are very site specific in terms of both capital and operating costs. Because of the relatively high energy requirement, locations are favoured where the energy is less expensive or the design is for dual purpose power/desalination plants. Hence, the GCC countries have the majority of thermal installations worldwide and these plants are installed as dual plants producing both electricity and water.

In the late 19th Century, the first major technical advance in desalination technology was the development of the multiple effect distillation (MED) process. Here, preheated feed water flowing over tubes in the first effect is heated by prime steam, resulting in evaporation of a fraction of the feed water content.

The water vapour generated by brine evaporation in each effect flows to the next effect, where heat is supplied for additional evaporation at a lower temperature. There the vapour condenses, giving up its latent heat to evaporate an additional fraction of water from the brine. The process of evaporation-plus-condensation is repeated from effect to effect, hence the term ‘multiple effect.’ Each effect operates at successively lower pressure and temperature.

In the mid-1960s multistage flash (MSF) distillation became popular. In MSF, seawater (after mixing with the recycle stream) is pressurised and heated to the maximum top brine temperature (TBT). When the heated brine flows into a stage maintained at slightly below the saturation vapour pressure of the water, a fraction of its water content flashes into steam. The flashed vapour passes through a mist eliminator and condenses on the exterior surface of heat transfer tubing.

The condensed liquid drips into trays as a product water. The unflashed brine enters a second stage, where it flashes again to vapour at a lower temperature, producing a further quantity of product water. The flashing-cooling process is repeated from stage to stage until both the cooled brine and the cooled distillate are finally discharged from the plant as blow-down brine and product water.

Membrane desalination utilising RO was introduced in the 1960’s (see Figure 2). Brackish water applications arose first with seawater treatment emerging on a large commercial scale in the 1990’s. The utilisation of membrane desalination has grown as costs have been reduced and system designs refined to optimise efficiencies. SWRO is now the largest segment of the desalination market.

In RO, treated water termed ‘permeate’ passes from the feed to the product side of the membrane when a pressure exceeding the osmotic pressure of the feed water is applied. This ‘reverses’ the natural osmotic flow and concentrates salt ions into a waste concentrate stream.

Improved efficiency

In the early years of desalination, positive displacement and centrifugal pumps provided 100 % of the energy to power a SWRO plant, but innovations in the field of energy recovery have improved energy efficiency. Waste energy from RO systems can currently be recovered, and can account for 25-30 % of the energy required to overcome the osmotic pressure of seawater. This lowers the total energy requirement of desalination plants dramatically.

Innovations in membrane performance, both in terms of impurity removal and permeate flow, have improved process efficiencies. For example, in 1978 RO membrane salt rejection was typically 98.6% and overall system recovery was 30 %. In 2014 salt rejection was typically 99.8% and recovery can be up as high as 50 %.

Improvements in pump and energy recovery technology have lowered energy consumption. The first SWRO system in the USA in 1978 consumed 9 kWh/m3 of permeate. In 2014, the energy requirements of SWRO is often 3.5 kWh/m3 or less.

Water from the Carlsbad desalination system in Southern California, which is due to be commissioned later this year, is expected to cost between US$ 1.50 to 1.67 per m3, depending on how much is purchased. The total cost, including the new pipeline to deliver the desalinated water, is projected at US$ 1.63 to 1.83 per m3.

The cost of the SWRO system alone is approximately 70 % of the total with the remainder being construction, infrastructure, and other costs not necessarily specific to the technology.

Municipalities around the world are reusing their wastewater to conserve and stretch their water supplies. Typically these reuse facilities take secondary municipal effluent and apply a series of steps often including membranes to remove impurities. This reclaimed water can be used for irrigation or industrial applications or direct or indirect potable water reuse.

Municipalities report that the cost of these reuse plants is between US$ 1.5 and $ 1.8 per m3 of water produced. This is typically less than SWRO installations due to the lower total dissolved solids content of secondary treated effluent.

Around the world municipalities and large industrial zones are adopting overall water management strategies that include conservation, leak prevention, wastewater reuse, and brackish water or seawater desalination, all to varying degrees.


Innovations

In thermal desalination, the expansion to the Shoaiba 2 plant in Saudi Arabia announced in January this year will result in the largest MED plant in the world. A single train of 10 MED effects operating at 16 bar with thermal vapour compression will produce 91,200 m3/day with a very high performance ratio of 14.6 kg of distillate per 2326 kJ or energy requirement of 159.3 kJ per kg of product. The project will take 20 months to complete.

Leon Awerbuch, dean at the IDA Academy of Desalination and Water Reuse explained: “This really is a fantastic development for MED, with a jump in the very short term from 5 to 20 MIGD. Now this is the same capacity as the largest MSF unit installed alongside RO at Ras Al-Khair. This is a very impressive push of MED to the forefront of thermal technology.”

“I am working on some of the ideas on how to improve the MED process, for example by hybridisation with nanofiltration to raise the TBT and improve efficiency.” Nanofiltration (NF) is a membrane process with a selective ability to reject certain ions. It is used in this application as a softening membrane able to reject 98-99 % of sulphates, calcium, magnesium and barium. Hence, applications exist where there is a need to improve the efficiency of existing thermal processes. If the TBT is increased, then so is the scaling potential so softening with NF potentially allows a higher TBT and increased thermal efficiency.

“On the other hand,” Awerbuch added, “we can soften the reject brine from the desalination plant using NF.” Reject from RO, MSF or MED could all be softened, potentially allowing system recoveries to be increased.

“There are a whole gamut of new ideas that are being applied to desalination, from forward osmosis to membrane distillation, not to mention the very new graphene membranes. Graphene is an extremely fashionable material with its single layer of carbon atoms supposed to be stronger than steel but also with unique properties,” Awerbuch explained.

According to Awerbuch, Dr David Cohen-Tanugi, in his doctorate thesis from the Massachusetts Institute of Technology, has shown that graphene, an atom-thick layer of carbon with exceptional physical and mechanical properties, could allow for water passage while rejecting salt ions if it contained nanometre-sized pores. Overall, this thesis reveals that graphene can act as an RO membrane with 103 times higher water permeability than commercial polymer membranes. This is as long as the nanopores are in the 0.6-0.8 nm range, that graphene is strong enough to withstand RO pressures, and it is supported by a substrate material with adequate porosity. A nanoporous graphene membrane could ultimately reduce either the energy footprint or the capital requirements of RO desalination.

The theoretical limit of separation typically for 50 % recovery is about 1.5 KWh per tonne but for seawater desalination the empirical optimum is 3.0 KWh per tonne depending on the salinity of water.

“Hence,” Awerbuch added, “graphene has the promise of energy reduction and better fluxes but it will take time to see commercial membranes. A lot of research is going on as we talk.”

Renewables

Advanced Water Technology (AWT) and Abengoa are currently building the world's first large-scale desalination plant powered by solar energy, in Saudi Arabia. The plant will produce 60,000 m3/day to supply Al Khafji City in North Eastern Saudi Arabia. Intentions are to build a zero-carbon footprint installation that contributes surplus electricity to the grid in the daylight hours in order to draw from the grid in the evening hours.

This pioneering project incorporates a solar PV (photovoltaic) (see Figure 3) plant that will be capable of supplying the power required by the desalination process, significantly reducing operational costs. It will also have an advanced control system to optimise power consumption and a pre-treatment system to reduce the high level of salinity and the fats, oils and greases that are present in the region's seawater.

The president of the IDA, Abdullah Al-Alshaikh is currently CEO of AWT and deputy governor for Planning and Development of Saline Water Conversion Corporation (SWCC) in Saudi Arabia.

“This project is already the largest scale up in the world,” explained Al-Alshaikh, “but stage two will be much larger.” The second phase will be designed to produce 300,000 m3/day utilising seawater from the Red Sea.

Phase 1 capacity was originally envisaged at 30,000 m3/day, but when the project was initiated two months ago it was decided to double the capacity. “We will use the latest high rejection RO membranes,” Al-Alshaikh explained, to obtain a system recovery of 40-45 %, “and a DAF will be included as part of the pre-treatment. The challenge is that the feed water is very shallow so we will be forced to design a special intake from the sea,” This will be approximately 5-6 km long rather than the standard 400-500 m. The plant will be in operation end of March 2017.

“We are using PV which is manufactured here in in Saudi Arabia by the King Abdulaziz City for Science and Technology, but in the future I think there will be a big chance to use thermal solar technology as it might be cost effective but nobody has applied it on a very big scale so far.”

In addition, the Masdar Institute of Science and Technology is currently collaborating with the manufacturers of four desalination pilot plants. Abengoa (Spain), Degrémont, Sidem/Veolia and Trevi Systems (USA), are trailing various desalination solutions. “This includes a unique solution incorporating forward osmosis with a modified process of polymer separation using thermal energy,” Awerbuch explained.

The project is designed to develop and demonstrate energy-efficient seawater desalination technologies efficient enough to be powered by renewable energy. The pilot test facility is located in Ghantoot, 90 km northwest of Abu Dhabi. During the course of the project, the test plants will provide 1500 m3/day of potable water to Abu Dhabi’s water infrastructure.

“There is a tremendous amount of news on renewable energy,” Awerbuch added. “ACWA Power International has won 200 MW solar power plants based on an incredible price.” This is US$ 0.06 per kWh. The projects are set to revolutionise solar energy by itself, regardless of whether the energy is subsequently used as a source of energy for desalination.

“Tons of new ideas are coming up in renewables,” Awerbuch said, “including wave, tidal, geothermal, wind, thermal solar and solar PV. There are some fascinating new solutions for coupling thermal solar with desalination, most of them using MED.” Figure 4 shows a wind power installation at sea.

According to Al-Alshaikh, “There are a tremendous number of new projects due to come online in Saudi Arabia mostly on the West Coast.” The largest desalination plant so far has been installed on the Eastern Coast. This will produce 1.5 million m3/day and will beat the 1,035,000 m3/day Ras Al-Khair plant, the largest current plant.

“You can see developments all over the world, with increasing use in China and India,” Awerbuch added. “Because of drought in California, fifteen desalination projects are proposed along the coast from Los Angeles to San Francisco Bay. Everybody is waiting for the inauguration of the Poseidon Carlsbad project; its success will encourage others and new regulation will possibly reduce the extended time required for approvals.”

Major projects are due to get underway in Qatar too with a large hybrid plant for ‘Facility D.’ Mitsubishi Corporation (MC) and Tokyo Electric Power Company (TEPCO) have just announced (May 25. 2015) that a 25-year power and water purchase agreement has been reached between Qatar General Electricity and Water Corporation and K1 Energy, a joint venture established by MC and TEPCO, This will be a hybrid 318,226 m3/day MSF and 272,765 m3/day RO project. The special purpose company will construct, own and operate a power generation plant (2.4 GW) and the water desalination plant, located 20 km south of Doha. Operations at the site are scheduled to commence in 2017.

In Egypt a number of projects have been awarded for an industrial zone in Sharm el Sheikh involving RWL with local Egyptian company Orascom. “There are lots of opportunities here including planned nuclear desalination,” Awerbuch explained, “because of a shortage of water and the tremendous growth of population and industrial development zones. The Nile cannot supply sufficient amounts of water.”

“The big challenge facing everybody is how to be sustainable,” said Al-Alshaikh. “Using fossil fuels in a country like Saudi Arabia is suicide because you are burning the source of the main income you have in order to produce power. If we really get into renewable energy that’s a plus to the rest of the world with the reduced carbon emissions and environmental impact.”

Renewable projects are increasing partly because of the reducing cost of the components and technology used. “In PV for example, “Al-Alshaikh explained, “there has been a drastic reduction in the price from 2003 to 2012 and, if this trend continues, PV will be head to head against conventional ways of generating power. By using renewables we are killing two birds with one stone. You don’t harm the environment and you can rely on a sustainable resource – the sun – especially in our region.”

Networking and education

The IDA has been addressing population and industrial growth at its first conference in Latin America, with host-city Rio de Janeiro, Brazil, having struggled in the recent past with droughts. According to Al-Alshaikh, not only was the conference timely considering the recent water challenges in the region, but it presented an opportunity to increase IDA’s outreach efforts in a region that has in the past not been as active.

“This puts desalination on the agenda in the region,” Awerbuch said. “We had quite a bit of involvement from Chile, Argentina and Brazil, with a lot of people talking about successful projects and potential solutions.

“The next IDA World Congress on desalination and water reuse will be held this year: August 30 to September 4 in San Diego USA. We have a record breaking number of papers being presented. The IDA World Congress happens every ‘odd’ year, the next one in 2017 in São Paulo, Brazil

“We are introducing regular IDA international water reuse conferences too, and these will take place in the ‘even’ years. Next year’s will be in September in Nice, France and we will focus on industrial and municipal water reuse. The topics will cover advanced techniques like membrane bioreactors, industrial water reuse in the oil-gas sector, petrochemicals, food and beverage, mining, power, and environmental water reuse.” Zero liquid discharge (ZLD) solutions will also be discussed at this 2016 conference.

The development of the IDA Academy remains a strong focus for the association. The first MSc course in conjunction with Herriot Watt University started this January, with a substantial increase in students expected from this coming September. The two-year course in water technology and desalination involves studies mainly online, but regular visits to campuses in Scotland, Dubai and Malaysia are required as part of the syllabus.

The IDA also designs and delivers tailored academy programs for major utilities like Dubai Electricity and Water, and courses also take place at the beginning and end of the World Congress and other conferences.

The future

Thinking about the future for desalination, Awerbuch told us that renewable energy will be a continuous focus of many regions. “We will see some unique developments in coupling thermal and hybrid projects happening more often. RO is currently dominating the whole field of conventional seawater but not renewables because RO depends on PV for electricity, and storage for the time being is very expensive.

“So thermal, will have a unique potential to further expand. I see a lot of work going into advanced MED. In the environmental area we will see a lot of progress. I would expect quite a lot of interest in China in the utilisation of salts and minerals from concentrated brine solutions.

“Nuclear energy is starting to become more serious too with numerous projects under construction, in Egypt specifically, and all these provide opportunities for water processes to be included alongside.”

“RO is continually evolving, with new membranes and new process configurations. In ten years from now we will see more forward osmosis and more membrane distillation,” said Corrado Sommariva, past president of IDA and a current director.

Regulation of the marketplace will be a big factor over the next few years. Sommariva explained that policy makers are not directly encouraging sustainable development because of subsidies. “People making policies are often not properly informed about the technologies that can be used and what future scenarios will be,” Sommariva explained.

“If people specify MSF or MED technology based on subsidised energy costs now, the costs won’t be the same in the future. Clearly there is lot of work that needs to be done by the policy makers to ensure sustainable generation of water. The more the energy consumption, the lower the tariff, so it works the other way round.”

“Sustainability as narrowly measured in terms of energy supply,” explained Al-Alshaikh, “is just beginning to happen. The best example of that is the Al Khafji Project in Saudi Arabia.

“But more importantly, sustainability is measured more broadly than just energy supply. Sustainability includes energy efficiencies, carbon emissions, water and brine discharge, smart technology applied to production and transmission, etc. These are actively coming online, and have been for the past few years, and they are creating huge impact in sustainability.”

“There are niche markets where maybe up to five percent of the water produced is generated sustainably,” Sommariva added “Twenty years ago nobody believed fossil fuels could be replaced in the power industry by renewables but incentives that have gradually reduced over time have generated an interest and this approach is what is required in the water sector at the moment. “

“I believe we have to shift from the idea of producing water at any cost to producing water more efficiently and more cleverly and I think we are gradually realising this.”