According to the Madison Water Utility, throughout 2017 the city of Madison, Wis....
Contrary to the belief of many, desalination is not new to
The largest growth in global desalination has taken place in
the Arabian Gulf, which often makes it seem like a distant solution. We often
hear that only oil rich states such as Saudi Arabia can afford such technology,
but this is far from the truth. While we may not be facing desertification, the
stress on our traditional water supplies is making desalination increasingly
widespread much closer to home. The reality is that when utilization of
traditional water sources is maximized, desalination (and related applications
such as reuse and recycle) become key components of sustained development.
The International Desalination Association (IDA) tracks
approximately 10,000 desalination facilities worldwide. Each of these
facilities has at least one machine capable of producing more than 13,210
gallons per day (50 m3/d) using one of several desalination processes. More
than 24 percent of these are located in North America but most surprising is
that almost 2,000 are in the United States. The exact operating status of all
these units is difficult to say, but a steady number of new systems for new
projects keeps being added to the database.
On average there are 50 to 75 significant desalination
projects per year in the United States with an average capacity of
approximately 1 million gallons per day. The majority of these projects utilize
membrane processes such as nanofiltration (NF) or reverse osmosis (RO). There
also are other processes used for specific applications including vapor
compression (VC), which is more robust than RO and can be used for higher
salinity situations such as meeting zero liquid discharge requirements with
water chemistry that prohibits membrane processes.
This steady growth in the use of desalination goes back a
long way. Many people may recall that Key West had desalination units installed
in the 1960s using the multi-stage flash (MSF) process and then again in the
1980s using the RO process. Not many people know that the first desalination
unit was installed there in 1861 and operated until the 1900s. The modern road
access to Key West has allowed the water supply to be piped down to the island
but only so long as South Florida has sufficient water.
The U.S. Virgin Islands do not have the luxury of
considering a pipeline and have utilized desalination for almost 50 years.
Other islands have an even longer history of continuous desalination for
municipal water supply; the islands of Aruba and Curacao both recently celebrated
70 years of desalination.
North American companies have been and continue to be at the
forefront of the science and technology of desalination and water reuse. Today
American and Canadian companies are world leaders in membrane technology and
also in the technology and application of reuse and recycling.
Processes and Technology
The technology today can be focused on providing the best
solution for each application. As an example, thermal desalination processes
can utilize waste heat from petro-chemical facilities or power plants,
increasing overall thermodynamic efficiency of the "host" process and
yielding excellent economics. This can be a wonderfully holistic approach to
desalination and is applied in several Caribbean installations.
Membrane processes are unrivaled for treatment of brackish
waters and seawater. They work particularly well for stand-alone "water
Hybrid process designs also are becoming more common.
-- Mechanical vapor compression can be used to treat the
brine reject from RO plants increasing system water recovery.
-- Seawater RO and distillation process (MSF or MED/TVC) can
be utilized in cogeneration facilities yielding improved economics via enhanced
utilization with fluctuating water to power demand ratios. (An Asian
manufacturer is participating in the first major project of this type in the
RO is a type of membrane process that could be considered as
"pressure driven," but there are several types of membranes that can
be used with different results. The toughest application for membranes is to
remove salt; seawater membranes are different from brackish membranes. A less
difficult pressure membrane application is the removal of other ion species
(which are not classically considered salt) or small suspended particulates. An
example of this is known as NF, which can be used to remove ions that are
larger and have higher molecular weights than salts and also other materials
such as viruses and bacteria.
Other types of membranes can be used to remove troublesome
particulate matter, and these systems are known generically as membrane
filtration. "Dual membrane systems integrating the use of porous, low
pressure-high flux microfiltration (MF) pretreatment with reverse osmosis are
able to effectively treat secondary sewage to meet ultrapure water standards
and may more accurately be described as 'repurification' systems," says
Tom Pankratz, author of Environmental Dictionary & Directory. While this
membrane reuse application has been widely utilized for wastewater and some
brackish water desalination, it now is beginning to find use in higher salinity
applications. Pretreatment continues to be the Achilles' heel of SWRO systems
and MF (or NF) certainly shows promise as a process improvement; the economics
now are being evaluated.
A new class of hybrid process utilizes NF as a pretreatment
for thermal desalination processes allowing the distillation to occur at
temperatures that previously would have led to the deposition of
process-inhibiting mineral scale.
The desalination industry not only continues to grow but,
more importantly, it moves from an obscure technical possibility to mainstream,
accepted practice. There are many technical measures of the improved technology
and economics of desalination, but nonscientific analyses also are possible.
Whether referred to by the industry terminology, desalination, or the more
common usage of desalinization, the word is out: desalination is viable. People
are beginning to get the message on a large scale via mass media.
Not a desalination conference goes by without more
discussion about desalinated total water costs (TWC) and what is the best
metric to compare TWC and overall economics. The scope of one project may
differ greatly from another. There is great variation from locale to locale in
the value of energy and the cost of capital. Comparing water costs often is
"apples and oranges." Continued construction of large-scale
desalination projects in preference to traditional water treatment as the method
of choice is proof of the economics.
Trinidad, where the largest seawater desalination plant in
the Americas recently was commissioned, considered desalination and traditional
water sources. Many people in Trinidad feel their traditional source of water
from the mountains to be adequate. However, the cost of pipelines and the
environmental impact of dams could not compete with desalination or the
potential for drought.
In the United States, water-rich central states provide
water across multiple state borders to reach the arid southwest. Transportation
of water in this manner requires a large capital investment and significant
operating cost. These arrangements are not drought proof, especially if the
drought were to be "politically" created. The water rich regions
currently providing water to the southwest are beginning to reconsider this
practice as their water wealth dwindles.
The political sensitivity of water transportation is more
critical when national borders are crossed. In these cases, even when water is abundant,
it can be denied for political reasons. A desalination facility was built at
the U.S. Naval Base at Guantanamo Bay when the government of Cuba stopped the
flow of fresh water for political reasons. Much of the local water supply for
Singapore comes from neighboring Malaysia--a desalination solution is planned
to create water self-sufficiency for Singapore.
Tampa Bay, Fla., has a 25 million gpd desalination project
that will be operational by the end 2002. This project has attracted a lot of
attention, specifically about the cost of water that is less than $2.00/1,000
U.S. gallons. Environmental concerns about the use of a bay rather than open
seawater failed to convince the courts of their merit, so the project proceeds.
The environmental issues related with developing traditional water sources was
a less publicized concern. It was the overall economics and drought proof
operation that led to successful selection of desalination.
The unavoidable fact is that desalination is competitive and
is being implemented in more diverse locations. The naysayers can no longer
claim desalination is possible only in oil rich nations. In June 2002, the
island of Aruba celebrated 70 years of desalination. Today, Aruba prospers
mainly from tourism, which relies entirely on desalination on an otherwise very
arid island. "Many people all over the world know of the local nickname
for our very pure water, Balashi Cocktail," said Filomena Marchena, the
One of the things that has made the recent growth possible
is the incorporation of "financial engineering" into desalination
projects. For decades, desalination systems were financed like other pieces of
process equipment--industrial bank loans that typically have a five-year repayment
schedule. We now have the situation where bond financing (or other long-term
financial instruments) has greatly reduced the cost of desalinated water and
allow "apples to apples" comparisons with traditional water sources.
The durability of the equipment and stability of the processes have reached the
point where investors in utilities now can consider desalination as a viable
Financial engineering in desalination is the true milestone
achieved by the Tampa and Trinidad projects. Further evidence of this is in the
privatization of large power and desalination projects in UAE and Qatar. These
same financing models are being utilized for the upcoming projects in Israel,
Singapore and Australia. These projects will become milestones, not for technical
reasons, but rather for being commercial breakthroughs for new models of
public-private cooperation on large-scale utility projects.
Desalination now is at the point the electricity-generating
industry reached decades ago. Access to new types of financing and the
resulting benefits lead directly from being able to compete as the water supply
for large municipalities and the ability to reflect upon decades of reliable
As populations continue to grow and migrate to coastal
regions, desalination someday will be a word on the lips of most Americans.