Desalination Explained

By Paddy Padmanathan
(Edited by Alison M.  Jones, NWNL Director)
Pictures and graphics provided by Paddy Padmanathan

Mr. Padmanathan, a professional civil engineer for over 35 years, is President and CEO of ACWA Power, a company that delivers desalinated water in 11 countries. His goal today is to promote localization of technology and industrialization of emerging economies.

NWNL:  While we can’t squeeze water out of thin air, we can squeeze potable water out of salt water. The high cost of desalination and ecosystem degradation by its brine waste are now being studied and corrected.  Thus, as our planet seeks more freshwater, NWNL asked this author, whom we recently met, to share his assessment of desalination and to describe recent adjustments to former desalination processes in this blog.

Picture5.pngShuqaiq 2 IWPP, RO desalination plant

Desalination’s Recent Global Development

Desalination is the process by which unpotable water such as seawater, brackish water and wastewater is purified into freshwater for human consumption and use. Desalination is no longer some far-fetched technology we will eventually need in a distant future to secure global water supply.

Desalination technology has been used for centuries, if not longer, largely as a means to convert seawater to drinking water aboard ships and carriers. Advances in the technology’s development in the last 40 years has allowed desalination to provide potable fresh water at large scale.

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Desalination Capacity (Source: Pacific Institute, The World’s Water, 2009)

In the Arabian Gulf, desalination plays a particularly crucial role in sustaining life and economy. Some countries in the Gulf rely on desalination to produce 90%, or more, of their drinking water.  The overall capacity in this region amounts to about 40% of the world’s desalinated water capacity. Much of this is in Kuwait, the United Arab Emirates, Saudi Arabia, Qatar and Bahrain. The remaining global capacity is mainly in North America, Europe, Asia and North Africa. Australia‘s capacity is also increasing substantially.

Global desalination capacity has increased dramatically since 1990 to a 2018 value of producing 105 million cubic meters of water daily (m3/day). Of this cumulative capacity, approximately 95 million m3/day is in use.

Picture2.pngQuadrupling of worldwide desalination capacity (1998-2018) continues.

Proponents and Critics of Desalination

Estimates indicate that by 2025, 1.8 billion people will live in regions with absolute water scarcity; and two-thirds of the world population could be under stress conditions. Desalinated water is possibly one of the only water resources not dependant on climate patterns. Desalination appears especially promising and suitable for dry coastal regions.

Proponents of desalination claim it creates jobs; stops dependence on long-distance water sources; and prevents local traditional water sources from being over-exploited.  It even supports development of energy industries, such as the oil and gas industries in the Middle East. As well, research and development are making desalination plants increasingly energy efficient and cost-effective.

It is valid that the environmental impacts of desalination plants include emission of large amounts of greenhouse gas emissions, because even with all the advances in technology to reduce energy intensity, desalination is still an energy-intensive process. While the industry continues to work on reducing energy intensity, the solution to reducing greenhouse gas emissions is to link desalination with renewable energy.

Energy is also the most expensive component of cost of produced water, contributing up to one-third to more than half of the cost. Renewable energy costs are now becoming competitive with fossil-fuel-generated energy in many locations where desalination is the only option available for providing potable water. As a result, more attention is turning towards de-carbonization of desalination.

Desalination also degrades marine environments through both its intake and discharge processes. After separating impurities from the water, the plant discharges the waste, known as brine, back into the sea. Because brine contains much higher concentrations of salt, it causes harm to surrounding marine habitats. Considerable attention and investment are going towards minimizing the damage with more appropriate design of intake and discharge facilities. In the case of discharge, temperature and salt concentrations are reduced though blending prior to discharge. Ensuring this discharge only at sufficient depths of sea water and spreading discharge across a very wide mixing zone will ensure sufficient and quick dilution.

Desalination Technologies

Main water sources for desalination are seawater and brackish water. Key elements of a desalination system are largely the same for both sources:

  1. Intake — getting water from its source to the processing facility;
  2. Pretreatment — removing suspended solids to prepare the water for further processing;
  3. Desalination — removing dissolved solids, primarily salts and other inorganic matter from a water source;
  4. Post-treatment — adding chemicals to desalinated water to prevent corrosion of downstream infrastructure pipes; and
  5. Concentrate management and freshwater storage — handling and disposing or reusing the waste from the desalination; and storing this new freshwater before it’s provided to consumers.

The majority of advancements in technology has happened at Stage 3, the desalination process itself.

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The 5 Stages of Desalination (with Stage 3 details in the blue circle) .

There are two main categories of desalination methods: thermal (or distillation) and membrane. Until 1998, most desalination plants used the thermal process. Thereafter, the reverse osmosis (RO) desalination process via a membrane-based filtration method took hold.  As more and more technological advancements were developed, the number of plants using membrane technology surpassed that of thermal. As of 2008, membrane processes accounted for 55% of desalination capacity worldwide, while thermal processes accounted for only 45%.

Thermal Methods

There are three thermal processes; multistage flash (MSF), multiple effect distillation (MED), and mechanical vapor compression (MVC), which all use the same basic principle of applying heat to create water vapor. The vapor then condenses into pure water, while separating it from most of the salts and impurities.  All three thermal processes use and reuse the energy required to evaporate water.

Thermal distillation was the earliest method used in the Middle East to commercially desalinate seawater for several reasons:

  1. The very saline and hot Arabian Gulf and Red Sea periodically have high concentrations of organics. Until recent advances in pre-treatment technologies, these organics presented challenging conditions for RO desalination technology.
  2. Only in recent times, with advances in membrane science, have RO plants been reliably utilized for the large production capacities required in this region.
  3. Dual-purpose, co-generation facilities in the Middle East combine water production with electric power to take advantage of shared intake and discharge structures.This usually improves energy efficiencies by 10% to 15% as thermal desalination processes utilize low-temperature waste steam from power-generation turbines.

In the past, these three reasons, combined with highly-subsidized costs of energy available in the Middle East, made thermal processes the dominant desalination technology in this region.  Amongst the three thermal processes, MSF is the most robust and is capable of very large production capacities. The number of stages used in the MSF process directly relate to how efficiently the system will use and reuse the heat that it is provided.

Picture4.pngShuaibah 3 IWPP:  An MSF [thermal] desalination plant.

Membrane Methods

Commercially-available membrane processes include Reverse Osmosis (RO), nanofiltration (NF), electrodialysis (ED) and electrodialysis reversal (EDR). Typically, 35-45% of seawater fed into a membrane process is recovered as product water. For brackish water desalination, water recovery can range from 50% to 90%.

Reverse Osmosis (RO), as the name implies, is the opposite of what happens in osmosis. A pressure greater than osmotic pressure is applied to saline water.  This causes freshwater to flow through the membrane while holding back the solutes, or salts. The water that comes out of this process is so pure that they add back salts and minerals to make it taste like drinking water.

Today, the Reverse Osmosis (RO) process uses significantly less energy than thermal distillation processes due to advances in membranes and energy-recovery devices. Thus, RO is the more environmentally-sustainable solution; and it has reduced overall desalination costs over the past decade.

Picture6.pngShuaibah Expansion IWP, RO membrane racks & energy recovery, RO desalination plant

Desalination Technology Today: Comparisons and Areas for Improvements

While all the desalination technologies in use today are generally more efficient and reliable than before, the cost and energy requirements are still high. Ongoing research efforts are aimed at reducing cost (by powering plants with less-expensive energy sources, such as low-grade heat) and overcoming operational limits of a process (by increasing energy efficiency).

Since the current technologies are relatively mature, improvements will be incremental. Emerging technologies such as Forward Osmosis or Membrane Distillation will further reduce electric power consumption and will use solar heat. To approach the maximum benefit of desalination, it will take disruptive technologies such Graphene membranes. They are in very early stage of development.  Ultimately, no desalination process can overcome its thermodynamic limits. However, desalination is a valuable contribution to today’s increasing needs for fresh water supplies.

Day Zero – A Water Warning

By Stephanie Sheng for No Water No Life (NWNL)
Edited by NWNL Director, Alison Jones

Stephanie Sheng is a passionate strategist for environmental and cultural conservation. Having worked in private and commercial sectors, she now uses her branding and communications expertise to drive behavior change that will help protect our natural resources. Inspired by conservation photographers, The Part We Play is her current project.  Her goal is to find how best to engage people and encourage them to take action. 

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I was horrified when I first heard the news from South Africa of Cape Town’s water crisis and impending ‘Day Zero’ – the day their taps would run dry. Originally forecasted for April 16, then pushed out to May, the apocalyptic-sounding day has now successfully been pushed out to next year. Had Day Zero remained slated for April or May, Cape Town would have been the first major city to run out of water. Although postponed, the threat still remains, and thus restrictions on water usage to 13.2 gallons (50 liters) per day for residents and visitors. Water rationing and a newly-heightened awareness around water use is now the new, legally-enforced normal in Cape Town.

Two things struck me as I read about this situation. First, the seemingly unthinkable felt very close. My visit to Cape Town a few years ago reminded me of San Francisco, my home before New York. Suddenly I was reading that this seemingly-similar city was on the brink of having no water coming out of their taps. As that hit me, I considered what modern, urban life would be like when water is scarce.

ClimateChange-ColumbiaBC.jpgCape Town’s restriction of 13.2 gal (50 L) per day is miniscule in comparison to the 39.6 gal (150 L) per day used by the average UK consumer[1] and the 79.3 to 99 gal (300 to 375 L) per day used by the average US consumer.[2] Unsurprisingly, Cape Town had to undergo drastic changes. It is now illegal to wash a car or fill a swimming pool. Hotel televisions blare messages to guests to take short 90-second showers. Washroom taps are shut off in restaurants and bars. Signs around bathroom stalls say, “If it’s yellow, let it mellow.” Hand sanitizer is now the normal method of hand cleaning.WASH-Tanzania.jpgShocked by the harsh realities of what water shortage could look like here at home, I was inspired to walk through my day comparing my water habits to the new realities being faced by those in the Cape Town facing a severe crisis. I wanted to discover opportunities where I could cut back, even though I consider myself on the more conscious end of the usage spectrum.

Here is a breakdown of my average water usage per day while living and working in NY, based on faucets spewing 2.6 gal (10 L) per minute[3], and a toilet flush using 2.3 gal (9L).[4]

  • Faucet use for brushing teeth and washing face for 4 min/day: 6 gal (40L)
  • Faucet use for dish washing and rinsing food for 7 min/day:5 gal (70L)
  • Toilet flushes, 4/day: 5 gal (36 L)
  • Drinking water: 4 gal (1.5 L)
  • Showering for 9 min/day — 8 gal (90 L)

My water usage totaled roughly 62.8 gal (237.5 L) per day. That is lower than the average American’s usage, but still more than four times the new water rations for Capetonians!

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Living in an urban city that isn’t facing an impending water shortage, it may be more difficult to control certain uses than others (e.g. not flushing the toilet at work). However, there are some simple, yet significant ways to lower our daily water use:

  • Turn off the faucet while you brush your teeth and wash your face.
  • Use the dishwasher instead of washing dishes by hand. Only run it when full.
  • Only run the laundry with full loads.
  • When showering, shut off the water while you soap up and shave. Put a time in your shower to remind you not to linger.
  • Recycle water when possible. If you need to wait for hot water from the faucet, capture the cold water and use it for pets, plants, hand washing clothes, and such.

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Water use discussed thus far includes obvious personal contributors to our water footprint. But the biggest contributor is actually our diet. Agriculture accounts for roughly 80% of the world’s freshwater consumption[5]. Different foods vary greatly in the amount of water consumed in their growth and production. Meat, especially from livestock with long life cycles, contains a high “virtural water” content per serving. For example, 792.5 gal (3,000 L) of water are required for a ⅓ lb. beef burger[6] – representing four times as much water as required for the same amount of chicken. That virtual water content ratio is even greater when red meat is compared to vegetables.

We don’t have to become vegetarians, but we can cut down on meat and choose meats other than beef and lamb. That change alone would save hundreds of thousands of gallons (or liters) consumed in a year, which is much greater than the 18,069.4 gal (68,400 L) I’d save by reducing my current water usage to that of a Capetonian. Consideration of virtual water content offers some food for thought!

Sources

[1] BBC News
[2] United States Geological Survey
[3] US Green Building Council: Water Reduction Use
[4] US Green Building Council: Water Reduction Use
[5] Food Matters Environment Reports
[6] National Geographic
All images/”hydrographics” are © Alison Jones, No Water No Life®.
For more “hydrographics” visit our
website.

Serpentine Curves and Manufactured Angles of the Mississippi

Aerial photos of the Atchafalaya Basin.

USA:  Louisiana, Aerial photo of Atchafalaya Basin area,

USA:  Louisiana, Aerial photo of Atchafalaya Basin area, Wax Lake Outlet area

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USA:  Louisiana, Aerial photo of Atchafalaya Basin area, Wax Lake Outlet area

USA:  Louisiana, Aerial photo of Atchafalaya Basin area,

– Posted by Jasmine Graf, NWNL Associate Director

Oysters for the Raritan and Hudson Bays

oysters

NWNL focuses on solutions to watershed degradation as much as it does on watershed threats. This spring, NWNL guest writer Carly Shields is investigating an exciting innovative approach to reducing pollution and stabilizing shorelines in the New Jersey-New York Raritan and Hudson Bays. Her first report begins:

“Oysters are more than something you’re served at a restaurant with Tabasco or Worcestershire sauce and a glass of white wine. Oysters are actually a keystone species in North America – and especially in areas like the New York Harbor. In two watersheds that were once the main source for the oyster business, concerned scientists and stewards are now trying to re-seed, and eventually re-harvest, a billion oysters in the waters of New York City.  New York Harbor School students are making it possible for these pollution-filtering mollusks to make a comeback.

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The marine-science focus of the high school on Governors Island is teaching its own students and middle school students in all five boroughs about the importance of oysters in their local waters and how to be the caretakers for these shellfish. This public high school is spawning oyster larvae:  something not done by any other school in the state of New York or anywhere – outside of California.

With the help of NYC students, the school has already grown seven million oysters, which are now back in the New York Harbor. Aquaculture teachers from the school are helping students take New York harbor water, and then spiking the water temperatures. This allows the larvae to think it’s time to spawn. The larvae then metamorphose into full-sized adult oysters.“

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Further investigations and interviews by Carly Shields for NWNL will explain the ecological importance of re-establishing oyster beds to improve water quality and strengthen shorelines. The latter is increasingly necessary due to wave erosion and higher water levels from severe storms like Sandy and further climate disruption.

Is the California Drought here to stay?

The short answer is an emphatic, “YES!” It is real. Even if El Niño arrives next year, as some climatologists have hinted, California currently uses too much water to allow replenishment of its reservoirs and ground water – now at historic low levels. It is predicted that precipitation levels will fluctuate wildly, as they have historically, while water demand increases. The California Data Exchange Center reports that California reservoirs are at 62.39% of average. Some are as low as 7 and 9%. The Sierra snowpack in the northern part of the state has reached 21% of average, up from 12% before the early March storms. Nowhere in the state is the snowpack above 34% and very little rain is forecast for the rest of this year’s rainy season. San Francisco residents depend on snow melt for their water. Some towns in California are predicted to have no water within 60 days. Irresponsible water use should not drain our precious resource.

One answer is conservation and planning. According to Barton H. “Buzz” Thompson, an expert in environmental and natural resources law and policy at Stanford University, there are many ways that Californians can use less water. At a symposium presented by the Bill Lane Center for the American West and the Water in the West Project at Stanford University, Thompson proposed that the state protect ground water, protect the environment, avoid building new reservoirs and desalinization plants, set up water exchanges where even fish have water rights, and encourage water utilities to tier water rates.

Many of us who were here in the big droughts of 1976-77 and 1985-86 have already tightened our belts, so trying to reach the voluntary 20% reduction, as requested by Governor Brown, is going to mean even more careful planning. California has more people and less water. The state produces nearly half of US-grown fruits, nuts and vegetables and has the highest per-state cash farm receipts in the nation, per CA Dept of Food and Agriculture. This farmland has international importance as well. It grows 70% of the world’s almonds.

The state needs to put serious water conservation measures in place before any rains that El Nino might bring next year could lull everyone back into complacency.

Related links for more information:

http://west.stanford.edu/publications/video/california-drought-causes-context-and-responses

http://www.aquafornia.com

http://www.cdfa.ca.gov/statistics/

*Posted from San Francisco by Barbara Folger, NWNL Project Coordinator

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Columbia River is one of the most hydro-dammed rivers in the world

The Columbia is one of the most hydro-dammed river basins in the world with some dams now over 70 years old. These dams change downstream water flows, and stop fish migrations. They are also buckling under decades of accumulated polluted sediment. The pressure is on for decommissioning many of these older dams, and 2 large ones on the Columbia have been removed recently – keeping the decades of that polluted sediment behind them from rushing downstream.

The Columbia is typical of many rivers that are heavily polluted by agriculture, industry, nuclear plants, livestock farms, and human waste. And now many of those pollutants are too deeply embedded for us to remove.

Nature could have done that clean-up job, but we’ve destroyed too many of the natural filters that would freely purify our dirty water: forest, wetlands, oysters…

New pix shared

Check out NWNL’s new photo gallery – Mara River Basin: Use and abuse of its water resources.