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.

Picture1.png

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.

Picture3.png

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.

Wild and Scenic River: Niobrara River

All photos © Alison M. Jones

On May 24, 1991, sections of Nebraska’s Niobrara River were added to the Wild and Scenic River System. A total of 104 miles of the Niobrara River are designated under the Wild and Scenic River System. 76 miles are designated as Scenic, and 28 miles are Recreational. The designated sections include:

  • Borman Bridge to State Highway 137
  • Knox County’s western boundary to the Niobrara-Missouri River confluence, and
  • Verdigre Creek-Niobrara River confluence to the north boundary of Verdigre Town.

NWNL visited braided sections between Nebraska and S. Dakota of the Niobrara River during a 2017 Mississippi River Basin expedition documenting Nebraska’s Missouri River tributaries. Our Missouri River Basin/ Niobrara Expedition Statement of Purpose describes the values and vulnerabilities of these watersheds, as well as our Methodology for this expedition. For more information about the Wild and Scenic Rivers Act read the first part of this blog series. The following pictures of the Niobrara River were taken by NWNL Director Alison Jones during her 2017 expedition.

From The National Wild and Scenic Rivers System: “Perhaps the epitome of a prairie river, the Niobrara is known as a biological crossroads. Although passing primarily through private land, it also flows through the Fort Niobrara National Wildlife Refuge and the largest single holding of The Nature Conservancy where bison have been reintroduced. The upper portion provides excellent canoeing.”

Jones_170612_NE_3776The Niobrara River Bridge connecting South Dakota and Nebraska
Jones_170612_NE_4405-2Braided patterns at the Missouri-Niobrara Rivers Confluence
Jones_170612_NE_4406-2Nebraska’s Niobrara State Park view of the Niobrara River
Jones_170613_NE_3795-2Niobrara River before entering Nebraska’s Mormon Canal
Jones_170613_NE_4468-2A new Niobrara River channel flowing under Mormon Canal bridge
Jones_170613_NE_4536-2The Niobrara River cutting through sandy soils of Verdel, Nebraska

 

The Clean Water Act: Its Beginnings in the Columbia and Raritan Rivers

By Isabelle Bienen, NWNL Research Intern
(Edited by Alison M.  Jones, NWNL Director)
All photos © Alison M. Jones unless otherwise noted

Isabelle Bienen is Northwestern University junior studying Social and Environmental Policy & Culture and Legal Studies. As NWNL Summer Intern, she wrote a 5-blog series on the history, purpose and current status of the U.S. Clean Water Act [CWA] in NWNL’s three US case-study watersheds. Her 1st blog was CWA Beginnings in the Mississippi River Basin.

Jones_070708_OR_6995.jpgColumbia River, Astoria OR

Columbia River Basin

The Pacific North West’s Columbia River Basin empties more water into the Pacific Ocean than any other river in the Americas. Starting at its Canadian Rocky Mountains source, it runs for 1,243, collecting water from the U.S. states of Washington, Oregon, Idaho, Montana, Wyoming, Nevada, and Utah.1 The Columbia River is one of the most hydroelectric river systems in the world, with over 400 dams that provide power, irrigation and flood control.1 This river basin has positively impacted urban development, agriculture, transportation, fisheries and energy supplies across a significant swath of the western United States.

Jones_070628_OR_5171_M.jpgJuvenile fish bypass at the McNary Dam in Oregon

However large, unregulated industry in this watershed caused the Columbia River system to become severely polluted. Salmon populations were heavily affected by this pollution, especially when combined with the dams presenting migratory barriers to salmon going upstream from the ocean to cool, freshwater tributaries for spawning.  Before such the pollution and dam impacts Columbia Basin provided spawning habitat for one of the largest salmon runs in the world.1

The many indigenous Native Americans in this basin, including Colville, Wanapum, Yakama, Nez Perce, Chinook and other tribes, had relied on plentiful and healthy salmon populations as their primary source for food, trade, and general cultural use. The depletion of the salmon, below 10% of the population numbers before the hydro-dams, today severely impacts their cultural traditions and livelihoods.

Jones_110924_WA_6020-2.jpgMembers of the Chinook Nation at a Canoe Reparation Ceremony in Washington 

Additionally, pollutants in today’s remaining salmon are very dangerous to human health. It is estimated that members of Columbia Basin tribes eat about 2.2 pounds of fish daily. However, based on water quality issues, the Department of Health’s recommended limit for fish consumption is just one 7-ounce serving per month – ⅓ of their usual per day consumption .7

Jones_070627_WA_4800.jpgIrrigation wasteway carrying polluted water to Columbia River

Hanford Nuclear Site on the Columbia River in Eastern Washington poses another water quality concern for Columbia River Basin stakeholders. Hanford’s nine nuclear reactors “have produced 60% of the plutonium that fueled the US’s nuclear weapons arsenal, including plutonium used in the bomb dropped on Nagasaki on August 9, 1945.”2 These reactors are no longer operating; but their nuclear waste is stored here in leaking, single-cell tanks right on the Columbia River Basin.2 Groundwater containing remnants of radioactive waste from Hanford Nuclear Site still flows into the Columbia River, per an EPA project manager at a Hanford Advisory Board 2017 meeting.3

Jones_070625_WA_4429_M.jpgHanford Nuclear Site: Laboratory and Chemical Waste Storage Unit

Industrial pollution from the Portland Harbor Superfund Site was added to the EPA’s National Priorities List in December 2000, after years of contamination from industries in the Willamette River, a major tributary to the Lower Columbia River Basin and critical salmon and steelhead migratory corridor and nursery.4 The Portland Harbor Superfund Site is rife with PCB’s, PAH’s, dioxins, pesticides and heavy metals that are a health risk to humans and the environment. In January 2017 the EPA accepted a remedy for cleaning up Portland Harbor. By the end of the year, Dec. 2017, the EPA agreed to a Portland Harbor Baseline Sampling Plan.4

This 2017 cleanup is an example of usage of the Superfund Law, “a U. S. federally funded program used to clean up sites contaminated by hazardous pollutants.4  Cleanup of this harbor is beneficial to the international commerce on the Willamette River, which provides economic stability to many global communities. The river is also a migratory corridor and breeding habitat for salmon and steelhead trout, especially important for local tribes for natural and cultural purposes.4

Jones_070620_WA_0708.jpgMidnight Mine,WA: old uranium mine on Spokane River, now Superfund Site 

Being a transboundary river starting in Canada, the US reaches of the Columbia have been threatened by Canada’s Teck Cominco zinc smelting plant in Trail, Canada, right on the banks of the Columbia, just 12 miles upstream of the US-Canada border. Since 1896, Teck Cominco has dumped zinc slag and remnants of copper, gold, and other pollutants into the Columbia River and spewed toxins into the air that killed acres of upstream forests.

This Canadian Teck Cominco plant has polluted 12 miles of the Columbia River in Canada and many miles further downstream in the U.S.  Due to elevated lead counts in the blood of children eating salmon in Washington State, U.S. Native American tribes took Teck Cominco to the U.S. Supreme Court and won their case with a decision that demanded Teck Cominco reduce its large groundwater plume of toxins.5 Ultimately, a Washington state judge ruled that Teck Cominco is liable for contaminating the Columbia River and  responsible for funding its clean up.

Raritan River Basin

Jones_150511_NJ_0933.jpgColonial Era mill on South Fork of Raritan River, Clinton NJ

On the East Coast, the Raritan River Basin drains water from 6 New Jersey counties and 49 New Jersey municipalities, making it the largest watershed in the state, covering approximately 1,100 square miles.5 With approximately 1.5 million people living in the Raritan River Basin, New Jersey is the most densely populated state in the nation. This places intense pressure on the need to maintain both healthy and adequate supplies of fresh water.6  

In the mostly-rural Upper Raritan Basin, its North Branch and South Branch continue to provide a clean, fresh water habitat for endangered wild brook trout. However, this location now faces issues of nonpoint-source pollution from agricultural runoff via rainfall or snowmelt. The most common pollutants found in such runoffs include excess fertilizers, herbicides, insecticides, fecal matter, oil, grease and other toxic chemicals.8 Due to the many dairy farms in the Upper Raritan, runoff of pollutants – and especially fecal matter – flow downstream and impact the Lower Raritan River.  

Jones_090621_NJ_0979.jpgFish head washed onto bank of Raritan River in Perth Amboy NJ

Lower Raritan Basin polluting sources are different from Upper Raritan nonpoint sources. For centuries, high amounts of industrial waste have polluted the Raritan Bay and the Lower Raritan River, which forms at the confluence of the North Branch and South Branch of the Raritan. Since the Colonial Era, mills and factories lined this New York-Philadelphia water corridor, using the river for dumping their waste.

Additionally, today’s Lower Raritan River Basin is also heavily polluted by sewer discharge and more impermeable surfaces in increasingly-high densities of urban and suburban areas. In these highly built-up centers, sewn together with surfaces of concrete and cement, pollution is exacerbated by frequent flood-runoff and rainfall that is not absorbed into the soil. The increasing intensity of storms, attributed to climate change, worsens this problem.

Jones_090515_NJ_4550.jpgSpillway for runoff into Raritan River, New Brunswick, NJ

Lack of control in Combined Sewer Overflow points (CSO’s) is especially prevalent in Perth Amboy. Director of the Clean Water Division in EPA’s Region 2 states, “Combined sewer overflows are a very serious public health and environmental problem in a number of New Jersey’s communities….”9 CSO’s send diluted and untreated sewage water into the Raritan waterways.  Perth Amboy has over ten CSO locations. In 2012, the EPA took action against Perth Amboy in 2012 in regard to their lack of compliance with minimum controls of CSO’s causing pollution spikes in the Raritan River.9 In 2015, the Christie Administration announced a new permit system for NJ requiring CSO reduction plans and signage for residents at discharge points noting serious health effects of overflow fluids.  Of the 217 CFO’s in NJ addressed by the 25 new permits, 16 were Perth Amboy. This step has allowed much-needed infrastructure upgrades .9

15_0003b.jpgGraphics of a CSO (by NJ Dept. of Environmental Protection)

As of 2015, the Raritan River Basin had 20 federally registered Superfund sites and 200 state-registered toxic sites.9 Thus, marine life, recreation, commercial fishing businesses and much of New Jersey’s supply of clean fresh water were highly degraded by water pollution in the Raritan Basin. That year the EPA tracked about 137 pounds of toxic chemicals in the waters of the Raritan Basin’s Middlesex County alone.5 Overall, New Jersey releases about 4.7 million pounds of toxic chemicals into its waters. This represents the most toxins per square mile of water in the U.S.5

Jones_110522_NJ_9261.jpgFly-fishing for trout in the South Branch of the Upper Raritan River, Califon NJ

The threats outlined above taken together have impacted both the creation and implementation of the CWA in the Raritan River Basin. These Raritan River issues and those of the other 2 watersheds NWNL is documenting (See Blog 1 in this CWA Series), represent threats to waterways nationwide.  Pollution of all types still carries weight today in political and legislative decisions involving the Clean Water Act. Blog 3 in this series will focus on health threats addressed by the CWA that span the U.S. as a result of water pollution, thus further highlighting the need for water safety protection.

Sources:

  1. US Environmental Protection Agency, accessed 6/19/18, published 2017, IKB, link
  2. Washington Physicians for Social Responsibility, accessed 7/11/18, published 2017, IKB, link
  3. Courthouse News, accessed 7/11/18, published 2017, IKB, link
  4. Environmental Protection Agency, accessed 7/11/18, published 2017, IKB, link
  5. The Sierra Club, accessed 7/19/18, published 2018, IKB, link. 
  6. Raritan Headwaters, accessed 7/3/18, published 2009, IKB, link
  7. The Spokesman-Review, accessed 7/26/18, published 2012, IKB, link
  8. State of New Jersey Department of Environmental Protection: Land Use Management, accessed 7/26/18, published 2018, IKB, link
  9. Rutgers University, accessed, 7/26/18, published 2018, IKB, link.