What's Driving Reuse
Growing demand and deteriorating water quality is pushing the advancement of reuse technologies
- By Glen Sundstrom
- Sep 01, 2006
Benjamin Franklin is frequently quoted as having said: "We
will never know the true value of water until the well runs dry." Although
conservation was the first attempt at preserving and maintaining limited fresh
water supplies, the idea of "reclaim, recycle, and reuse" was the
next push for managing them. Reuse is one of the hottest and most talked about
issues in the water industry today. But it is nothing new; major reuse projects
have been operational for over a decade.
For many years, the world enjoyed an abundance of high-quality fresh water that
was inexpensive to obtain, treat, and transport. Now, many communities and industries
face water shortages, deteriorating water quality, and greater demands because
of population growth, tourism, recreational use, drought, seawater intrusion,
and industrial expansion. The well, so to speak, is beginning to run dry. Many
water and wastewater treatment plants are struggling to keep up with higher
demands or achieve the quality standards set forth by regulatory agencies. And
as fresh water becomes harder to obtain and demand rises, so too does the cost
to individual consumers and industrial users.
In addition to examining the past and present drivers for reuse, this article
will highlight some of the technological advancements that have made water reuse
an economical approach for creating sustainable water supplies that benefit
communities and industries alike.
The most widely publicized and innovative reuse projects are in California and
Arizona. In California, the seriousness of water shortages more than a decade
ago led to the development of large reuse projects aimed at supplying water
for irrigation. The state reacted quickly to this new approach and developed
a regulation commonly known as "Title 22" that addressed the quality
of reclaimed wastewater. Not only does this regulation pertain to the water's
quality, but it also regulates and approves the treatment equipment used to
produce compliant water.
The next phase in California's water management program called for preventing
seawater intrusion into the aquifers by treating wastewater and injecting it
into deep wells. This created a hydraulic barrier to prevent the seawater from
contaminating the aquifers and to protect the quality of fresh water. This approach
helped increase available fresh water in the aquifers to meet the growing demands
of the surrounding communities.
Potable water has traditionally been used for non-potable uses, such as irrigating
golf courses, parks, and sports facilities. Reclaimed wastewater offers an alternative
that can easily be used to irrigate these recreational facilities, lessening
the demand on potable water sources. Municipal and industrial wastewaters have
to be treated to meet discharge requirements established by the local authorities.
This water can often be treated and reused directly rather than discharged into
a receiving body of water, only to be recollected and retreated downstream.
The West Basin Water Recycling Facility in El Segundo, Calif., is the innovation
leader in the reclaim, recycle, and reuse movement. The facility receives wastewater
from the Hyperion Wastewater Treatment Plant that serves the Los Angeles area.
Using low-pressure membrane filtration and reverse osmosis (RO), West Basin
is able to provide five different "designer" grades of water for injection,
irrigation, cooling towers, and even high-pressure boiler feedwater. Other states
and countries have studied West Basin's success and have begun implementing
similar projects to solve their water management problems and to build a sustainable
water supply for decades to come.
In other parts of the world, water reuse is becoming law. In Europe, for example,
the European Water Framework Directive places limits on the extraction of groundwater
for industrial uses, with full implementation by the year 2015. About 70 percent
of the groundwater in Europe is used for industry; the remaining 30 percent
is used for irrigation and drinking.
Similarly in China, Chapter 5 of the 2002 Water Law required all industries
to extensively reuse water and increase water recovery, especially during new
construction or plant upgrades. For the iron and steel industry, the regulations
specify water intake lower than 16 m3/ton (metric tons) of product and water
reuse ratio higher than 90 percent. In January 2005 the Chinese government imposed
a new water consumption ratio on seven different industries. These industries
can now be charged a fee for any consumption of water over the allocated amount.
If the situation is not rectified within a specified timeframe, the offending
enterprises will lose access to the water supplies.
Both of these laws affect new construction and set standards for existing plants
as well. Industrial plants are the hardest hit and need to find alternate water
sources, including reclaimed municipal wastewater, reclaiming self-generated
wastewater, and seawater.
Communities are also being pushed to reclaim, recycle, and reuse wastewater
because of their limited capacity to deliver potable water and/or treat the
increased volume of municipal wastewater. Rapid population growth, tourism,
and industrial expansion have placed heavy loads on these treatment facilities.
For instance, one Australian community was faced with upgrading its wastewater
treatment facility due to all the reasons stated above. The upgrade was to include
constructing a new pipeline to the ocean for discharge. In the early 1990s before
reuse was a standard vocabulary term, a visionary engineer realized that the
wastewater treatment plant could be upgraded with new separation technology,
and the water could be sold to the nearby electric power plant. Low-pressure
membrane filtration was installed at the treatment plant, increasing the capacity
and producing a higher quality effluent with minimal investment. And a new pipeline
did not have to be laid. The power plant installed an RO system to convert the
high-quality reclaimed wastewater to boiler feedwater and realized significant
cost savings in its water supply. This project has freed up as much as 500,000
gallons per day of fresh water for the rapidly growing community. By 2010, additional
capacity will be added that will free up nearly 1 million gallons per day (mgd)
of potable water for the community.
Similarly, Honolulu, Hawaii, faced upgrading its wastewater treatment facility
to meet growing capacity demands and tightening ocean discharge regulations.
Instead of blindly going forward with an upgrade to the treatment plant that
would just discharge the water, the city entered into a public-private partnership
to construct an advanced treatment facility that would produce water suitable
for irrigation and industrial uses. Once again, both the city and industries
enjoyed a substantial savings and freed up more 2.0 million gallons per day
(mgd) of fresh water for potable use.
Limited natural surface water and decreasing groundwater supplies, coupled with
frequent drought conditions and large fluctuations in population, drove the
city of Scottsdale, Ariz., to adopt a reuse strategy. The city has two sources
of potable water: the Colorado River and groundwater aquifers. During the winter
months, the population increases dramatically, which requires more potable water
and generates more wastewater. The city can only withdraw a fixed volume of
groundwater as dictated by the regulatory agencies, so when demand is high,
it must tap into the expensive Colorado River source. The question became what
to do with all the extra wastewater and how to obtain cost-effective potable
Although reclaiming wastewater for irrigation purposes was already common in
Scottsdale, the high influx of seasonal residents created a greater volume of
wastewater than could meet irrigation demands. To solve this problem, the Scottsdale
Water Campus treats municipal wastewater and injects it deep into the ground
to replenish the aquifers. This gives the city withdrawal "credits"
to use during peak demand seasons and reduces demand on the Colorado River.
Reclaim Technology Advancements
Multibarrier filtration systems are the original technologies used in reclaim
systems. Historically, these systems consisted of individual processes that
required a substantial amount of land space and operator attention. Today, several
unit operations such as high-rate tube settling and clarification followed by
fine granular media filtration and even ultraviolet (UV) are packed into a single
treatment step that removes residual biomass, turbidity, and micro-organisms.
Such systems are much smaller and easier to operate than their predecessors.
Low-pressure membrane filtration is now used extensively in reuse projects around
the world. These hollow-fiber membranes have a pore size of 0.04 microns that
will remove bacteria, pathogens, and turbidity. (In comparison, a human hair
is about 75 microns in diameter.) These membranes are routinely used downstream
of either a secondary or tertiary waste treatment step to provide an extremely
high-quality effluent by removing residual biomass, turbidity, and micro-organisms.
Typically, some type of disinfection step such as chlorine or UV light follows
the membranes before the water is used for irrigation or injection.
Membrane bioreactors (MBRs) are also being widely used in reuse projects. MBRs
combine the activated sludge and clarification steps in the wastewater treatment
plant into a single-unit operation. Like high-rate multibarrier filtration systems,
MBRs are compact and easy to operate. And as the technology uses the same type
of low-pressure membranes, its effluent is suitable for irrigation or injection,
following a disinfection step.
RO systems are routinely used to improve the reclaimed water quality by reducing
the dissolved solids content by 95 percent or more. Nanofiltration (NF) systems
are very similar to RO systems but do not remove as much of the dissolved solids
and, consequently, operate at lower pressures. RO and NF systems are employed
downstream of the technologies listed above. However, most are preceded by low-pressure
membranes due to their ability to provide exceptional feedwater quality to the
RO and NF membranes.
Rapid sand filtration systems are another reuse solution. These systems have
a shallow, 10-inch bed and contain 0.45-millimter (mm) fine-grain sand that
effectively captures solid particles down to 2 to 3 microns (a process known
as "surface straining"). This forms a positive barrier against solids
and turbidity. The filtered effluent meets California's tough Title 22 standard
for < 2 NTU (nephlometric turbidity units) turbidity that, after UV disinfection,
can be used for subsurface recharge. The treated effluent can also be used for
spray irrigation in citrus groves, on golf courses, on green belts, and as RO
In addition to the water treatment technologies, significant advances have been
made in reducing and transforming the residual biosolids. A biosolids reduction
process significantly reduces the generation of biological solids through a
system of interchanging solids between aerobic and non-aerobic conditions. The
process is designed to tackle two main components of solids present in the mixed
liquor of any conventional activated sludge plant: biological solids and non-readily
degradable trash, grit, and other inert materials. The biological solids production
is reduced by reconfiguring the biological treatment process. Biosolids that
would normally be wasted from a conventional plant are instead sent to the side-stream
interchange bioreactor where the unique conditioning environment of the process
Biosolids composting systems transform wastewater treatment facility sludge
into a stabilized, nutrient-rich, marketable end-product. This end-product,
which can be used for landscaping, horticulture, agriculture and land reclamation,
meets EPA Part 503 regulatory requirements for Process to Further Reduce Pathogens
(PFRP) and Vector Attraction Reduction (VAR).
Management of our global water resources is key to creating sustainable water
supplies for potable, agricultural, recreational, and industrial use. Reuse
has become an accepted water conservation and environmental preservation technique.
Many, if not all reuse facilities have proven to be an economical venture, even
when the original drivers were not solely economic in nature. Water shortages,
deteriorating water quality, and greater demands due to population growth, tourism,
recreational use, drought, seawater intrusion, and industrial expansion have
helped drive reuse in the past and will continue to do so in the future.
Several technological advancements for water reuse include multibarrier filtration
systems, low-pressure membrane filtration, MBRs, RO, and rapid sand filtration.
Biosolids-reduction processes and biosolids-composting systems treat solids
produced during the wastewater treatment process to create a marketable end-product
for land application.
This article originally appeared in the 09/01/2006 issue of Environmental Protection.