The RO Renaissance:
Why
it thrives in the marketplace
|
Summary: Reverse osmosis
often seems like it's been with us forever. With its presence so
widespread in the water treatment market, it's a technology that's
easily overlooked. Here, the author explains why after five decades,
RO is stronger than ever. |
Bob Dylan's famous 1960s call to action still resonates powerfully
today, especially in the water and wastewater treatment industry. But
not necessarily in the water his lyrics suggest. Over the past two
decades, the world's water supply and the technologies used to treat it
have undergone significant changes. Due to widespread drought
conditions, population growth, urban and suburban sprawl, and an
increased presence of chemical and biological contaminants, however, the
waters aren't growing. They're shrinking or at least, access to potable
water sure is. And the world is struggling to maintain a pure, potable
supply for both municipal and industrial applications.
According to the World Bank's estimates, by 2025, as many
as 4 billion people or one half of the world's population could live
under conditions of severe water stress, especially in Africa, the
Middle East and South Asia. One sixth of the World Bank's lending
--approximately $3 billion per year is currently devoted to
water-related projects. In her book, Water Wars, expert Diane Raines
predicts the growing shortage of clean water threatens to make water,
even more than oil, the cause of political turmoil in the decades to
come.
Salt/brackish water
Adding to the challenge is the fact the majority of purification
technologies typically used for treating surface and groundwater
supplies--while they've become more economical--still aren't efficient
or cost-effective for desalinating salt water or brackish water, which
are increasingly used as source water for municipal and industrial
applications. Water and wastewater treatment experts know that change is
necessary if the world's water supply is to support future development
and population growth.
In their search for an efficient solution to the world's
clean water crisis, treatment professionals have uncovered a
purification technology that often appears to meet their needs better
than anything else on the market. The purification technology now rising
to the surface isn't new, though. It's reverse osmosis (RO).
First developed in the late 1950s as an economical method
of desalinating seawater, RO uses a semi-permeable membrane to remove
nearly all particulate matter--turbidity, bacteria, microorganisms,
salts, proteins, asbestos, and even single molecules of the heavier
organics from water. With pores ranging from 0.0005 to 0.0000002 microns
(um), the membrane "catches" the majority of the impurities while
allowing water to pass through, creating a purified water product. Of
all the commonly accepted categories of membrane filtration
systems--including RO, nanofiltration, ultrafiltration and
microfiltration--RO removes the smallest sized particles from water.
Despite the fact that RO membrane filtration has been
recognized as the most effective from of membrane filtration for some
time, it hasn't been widely used until recently. The reasons are varied
but have typically related, in the past, to high capital and energy
costs and poor efficiency when compared with other available treatment
technologies such as distillation The higher energy cost arises from the
fact that in order to remove the smallest sized particles, RO requires a
pre-determined level of pressure on the feed water stream to pass the
purified water through the microscopic pores of the semi-permeable
membrane (see Figure 1). The higher the number of dissolved solids in
the feedwater, the higher the required amount of operating pressure. The
operating pressures in an RO system can vary from 100 pounds per square
inch (psi) or 7 bar to 1,200 psi (83 bar), depending on the type of
water to be purified.
Enjoying the spotlight
Today, RO is experiencing a resurgence, thanks to
advanced technology, lower costs and higher water quality demands.
According to a recent study by The Mcilvaine Co., a consulting and
publishing firm, the U.S. RO modules and equipment market was expected
to exceed $1.3 billion last year. The RO systems market is growing at an
annual rate of 8 percent globally. In addition, desalination, one of the
primary applications for RO, is expected to grow globally at an average
of 11 percent from now until 2006. Here are some of the key reasons why
this technology is suddenly back in the spotlight.
Higher water quality standards require more
effective technologies: Increasingly sensitive instruments,
including water quality analyzers, can now measure parameters such as
aluminum, nitrate, nitrite, ammonia, dissolved oxygen, fluoride, iron,
manganese, phosphate and silica, among other water quality organics and
inorganic contaminants, in the parts per billion (ppb) range. Because RO
is able to remove the smallest of particles, it coincides with the
recent trend in more accurate instrumentation systems.
Thanks to new technology, the price is right:
According to Bob Mcilvaine, president of the The Mcilvaine Co., "Reverse
osmosis never really fell out of favor; it just wasn't the most
efficient technology on the market. The big breakthrough today comes
because of higher equipment efficiency, lower equipment costs and
reduced energy usage."
New RO pump technologies are far more
energy-efficient than previous methods: Since RO is a cross-flow
technology, some water passes through the membrane (as product water)
and some flows past it ( as reject water) carrying away impurities
during the process. The new pumps, which are equipped with energy
recovery devices, use the pressure and the flow of the reject water to
help reduce the size of the pump/motor assembly required for the system,
lowering the power requirements of the overall plant.
In addition, recent advances with RO membranes that have
higher tolerance to fouling, a higher rejection of dissolved solids and
higher flows, allow plants to operate a lower costs and higher
efficiencies. These improved membranes require less pre-treatment
chemicals, smaller pump/motor sizes and fewer membrane modules to
achieve the same output. In turn, this creates less energy waste and a
longer membrane life span. This is key because the membrane component of
an RO system can account for 20-40 percent of the system's complete
cost. The more frequently the membrane needs to be replaced, the more
expensive the system's operational cost becomes.
And that's not all. With RO costs dropping in recent
years, municipalities can provide a solution quickly without
significantly raising taxes. Coincidentally, the lower equipment costs
and reduced energy usage of RO comes at the same time that the costs of
its most popular competing purification technology--distillation --are
rising.
"The prices of distillation and RO used to be relatively
similar," said Mcilvaine. But the fuel sources for distillation have
increased in price, and will likely continue to do so. Since
distillation costs are rising and RO costs are continually dropping, RO
is rapidly becoming the preferable solution for large-scale purification
projects."
Desalination
Unusually prolonged drought conditions have afflicted the western and
southwestern United States, Africa, the Middle East and South Asia. In
addition, increases in population and industrial waste have led to the
release of a deluge of contaminants into the world's groundwater. These
and other conditions have created an urgent need for the use of RO
systems. A dozen small RO desalination plants are currently in operation
along the California coast and over 20 more are in development. " The
drought and population growth, not to mention the proliferation of
high-end resort communities in area that lack adequate water sources,
are causing us to outstrip our available water supply in many parts of
the world," said Mcilvaine. " Increased contamination and the rise in
fuel costs have raised the expense of purifying water from existing
surface sources. Thanks to the reduction in the operating cost of RO
systems, desalination of sea water has become a much more viable,
affordable option for improving the available water supply."
Grassroots awareness
Greater
public awareness through the media and the U.S. Environmental Protection
Agency has created a sense of urgency among the public to improve the
quality of its water. The public has greater awareness of
illnesses--ranging from varied cancers to Legionnaire's disease-that are
associated with biological and chemical contaminants, which can leak
form local manufacturing plants into a community's groundwater.
In addition, the public is aware of RO because of a surge
in residential or point-of-use/point-of-entry (POU/POE) water treatment
systems that are directly available to them through retailers including
Lowe's, Sears and Home Depot as well as the many U.S. franchise and
independent dealerships across the country The public's increased use of
steadily advancing home water treatment technologies has sensitized them
to water quality issues at the municipal, regional and global levels.
The consumer public has proved that water quality is a
key concern, and that they're willing to pay extra for non-municipal
sources of drinking water. Bottled water is now second only to soft
drinks as the largest-selling beverage type globally. Brackish
groundwater and highly chlorinated municipal water sources, both of
which lead to poor water taste, have led the public to demand better
water quality standards and a better drinking alternative. By using the
newly cost-and energy-efficient RO technologies, bottled water companies
can more easily provide the product at increased profits. And
consumers-residential or business-who have RO installed in their homes
or offices can have virtually the same quality water available to them
at the tap. The drought and population growth, not to mention the
proliferation of high-end resort communities in areas that lack adequate
water sources, are causing us to outstrip our available water supply in
many parts of the world.
Conclusion
Thanks to the
newfound effectiveness and performance of RO, Bob Dylan's famous lyrics
might be prophetic after all. If municipalities and industries around
the world can cost effectively use RO for desalination and other options
to better combat the looming water crisis, the waters around us might
indeed grow. Meanwhile, the nations of the world will be able to provide
clean, potable water to their populations for years to come. The times,
indeed, may be a changin'.
Back
to previous page
|
