Automatic Self Cleaning Filters for Drinking Water

Automatic
Self Cleaning
Filters
for Drinking Water
Treatment
Clean Water. Clean Technology.
I
n response to consumer demand,
municipalities are being tasked to
provide the safest, most cost-effective
water with the least environmental impact.
A multi-barrier approach to filtration
is becoming increasingly important as
regulatory requirements, community
demands and the need to protect increasingly complex and costly systems mount.
However, adding the parameter of ‘least
environmental impact’ has a significant
effect on the technologies that best fit
multi-barrier systems. Operators and
other water suppliers must evaluate water treatment options not only for their
efficacy at removing a wider array of contaminants—which are continually being
detected at ever-lower levels—but also
on clean technology criteria.
This means drinking water processes must conserve energy, use minimal chemicals, occupy less space and
generate less waste. The US EPA has just
endorsed this imperative in a new guide,
Ensuring a Sustainable Future: An Energy
Management Guidebook for Wastewater and
Water Utilities, which also includes strategies to optimize all resources.
Originally developed in Israel for
irrigation applications, automatic self
cleaning filters are extremely efficient
overall. Only recently have they been recognized for their clean technology benefits in drinking water treatment.
Minimizing energy and water
consumption
The automatic self cleaning filters
integrate a set of screens to provide a
balance of strength, filtering capacity and
M AY 2 0 0 8
By Jim Lauria
fine filtration. When sediment builds up
on the inside of the filter, a self cleaning
mechanism of small nozzles is engaged
to allow the filter cake to exit the filter in
a concentrated stream. Water loss to backflush is minimal (typically less than one
percent of the flow) and the filter continues operating during the self cleaning
cycle.
Operating an automatic self cleaning filter demands minimal energy. A
fractional horsepower motor, which
draws just 0.5 amps at 220/440 VAC 3phase power, is all that is required to rotate the cleaning scanners. Because these
filters are highly focused and efficient,
they yield minimal initial head loss compared to media filters. This translates into
significant energy savings: better than 50
percent compared to sand media filters
that require more pumping to restore
head pressure after filtration.
Water consumption is also minimal
with automatic self cleaning filters. Backwash water is less than one percent of
the total flow through the filter; therefore,
automatic self cleaning filters consume
less than one-quarter of the backwash
required to clean a media filter with the
same filtration capacity.
In addition, no polymers, filter aids
or flocculating chemicals are required,
reducing costs, maintenance time and
employee exposure to chemicals. Their
filtration efficiency also often allows
water treatment providers to add less
chlorine to maintain a target disinfection
residual.
Reduced footprint (per volume of
water filtered) is another significant benefit. Automatic self cleaning filters do not
require storage tanks for water or sand
media, so they can deliver equal filtration capacity on a small fraction of the
footprint required for other filtration
technologies. Besides taking up less
space, these filters require less demand
for costly structural materials, like concrete and steel, for the same amount of
filtering capacity.
The versatility of these filters, in
terms of the particulates that they can filter, the clean technology benefits they
deliver and the scalability of the systems,
can be seen in how they provide the clean
technology benefits in three different
types of drinking water systems.
Complimenting or replacing
media filters
In municipal water treatment plants,
automatic self cleaning filters are replacing or complimenting media filtration,
offering lower levels of disinfection
byproducts and reduced energy demand.
Prefiltration with these filters significantly reduces turbidity (measured as
both TSS and NTUs) of influent water
with minimal space requirements, energy
consumption and water used in backwashing. The result is a cleaner, more
efficient operation of the main filtration
system, lower labor requirements, reduced use of chemicals and significant
reduction in the release of media filter
backwash water. Labor and maintenance
costs are similarly reduced.
Water Conditioning & Purification
Managers of one small drinking
water treatment plant in northern California conducted a trial of an automatic
self cleaning filtration system as a
prefilter to its (anthracite/sand/gravel)
media system in 2005. Algae, aquatic
weeds, crustaceans and turbidity are significant challenges in the community’s
reservoir.
The media filters must be taken offline during backflushing. During periods
of high turbidity, the community’s demand for water prevented managers
from scheduling backflushing of the media filters frequently enough. Before
prefiltration was introduced, the plant’s
crew also had to conduct a manual
‘firehose cleaning’ every 10 hours.
The water district compared several
screens to determine the optimum level
of prefiltration. The district determined
that a 50-micron screen automatically
backflushed approximately every 20
minutes when influent turbidity ranged
from five to seven NTUs. The automatic
prefiltration system reduced TSS readings by approximately 71 percent and
reduced NTU values by 21 percent. In
addition, intervals between manual
cleanings of the sand media filter were
extended to more than 27 hours.
Prefiltration protects RO and
UF membranes
Desalination and grey water reuse
have put significant emphasis on ultrafine (UF) and RO membrane technologies.
In Japan, more than 3,000 grey water reuse facilities offered approximately
400,000 cubic meters of daily capacity in
2005, from building-scale systems to industrial/regional facilities. Desalination
generates even more attention. According to Nature (March 2008), more than 40
million cubic meters of desalinated water are produced daily by approximately
15,000 desalination plants worldwide
and production is expected to rise dramatically. In California alone, plans for
at least 20 new desalination facilities are
being explored.
These outstanding systems
are extremely effective at removing suspended particles and organisms down to
Water Conditioning & Purification
the unicellular level, as well as dissolved
solids; however, they can be compromised by larger particles, which reduce
membrane life and efficiency and demand costly,
chemical-intensive cleaning.
Before RO and UF membranes, automatic self cleaning filters offer valuable
protection by removing biological organisms, organic matter and inorganic com-
pounds, such as precipitated salts, metal
hydroxides, clay, silt and other silicabased materials. Acting as a prefilter,
they increase recovery rates and lessen
chemical consumption and disposal for
membrane cleaning.
In addition to the reduction in
chemical cleaning needs, automatic self
cleaning filters provide a clean technology solution by reducing the prodigious
energy budget of the desalination process. A test program conducted in California by the Affordable Desalination
Collaboration (ADC) on six membranes
in seven element pressure vessels determined a most affordable point (MAP)
average value of 12.4 kWh/kgal. Of that
figure, more than nine percent (or 1.15
kWh/kgal) was the MAP average value
for energy for prefiltration. The more efficient the prefiltration system, the more
the energy budget can be trimmed,
bringing affordable desalination closer to
reality.
Building-scale systems
In urban environments, automatic
filters are serving as POE filtration systems to protect water and HVAC systems
in critical environments (such as hospitals) and as prefiltration for POU purification systems in high-rise buildings.
Most cities’ municipal water is of
excellent quality; however, aging infrastructure and common sediments in urban plumbing systems, primarily silt and
pipe scale, can degrade water quality after treatment. For instance, New York
City’s celebrated tap water from its reservoir systems had turbidity readings of
0.8 to 1.5 NTUs in 2006. Yet a run through
the aqueducts, underground mains and
building plumbing can lead to far more
particulate contamination. Turbidity
problems can be exacerbated by the high
velocities caused by firefighting efforts
or by work on the water system.
In some cases, such added turbidity can be a matter of life and
death. For instance, after
episodes of high turbidity
severely impacted its cartridge filter system and
upset flow to key systems, a Virginia
hospital installed an automatic self cleaning filter to protect its plumbing system
and critical patient-care equipment such
as sterilizers and X-ray developers.
Soon afterwards, a three-car fire in
the hospital’s garage caused the local fire
department to draw from hydrants on
the hospital grounds and
agitate settled sediments
in the system’s mains. The
10-micron automatic
prefiltration system went
through 20 self cleaning
cycles over the course of
the event and the
hours that followed,
safeguarding the system to the extent that
the maintenance
manager reported
no additional load
in the cartridge filters
that
the
prefilter protected.
Even where health
is not at risk, consumers
are increasingly demanding bottled-waterquality tap water. (In
fact, the most environmentally conscious of those consumers
are eager for tap water that tastes and
tests clean, so they can reduce or eliminate their consumption of plastic bottles.)
To address that demand and gain a
competitive advantage, some high-end
metropolitan developers are installing POE prefiltration systems
in luxury high-rises. This ‘twicefiltered water’ is the best tap water a city dweller can drink and
outperforms bottled water in
taste, cost and sustainability comparisons. It also enables residents
to maintain individual tap water
filtration systems, such as carbon
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filtration units, with minimal disruption.
Where green construction is the goal,
developers are integrating automatic self
cleaning filters with UV disinfection
equipment to treat collected stormwater
runoff for reuse. Such practices are being specified as integral components of
the next generation of urban water treatment systems with LEED certification
for green building applications. (Editor’s
note: visit www. usgbc.org for more on LEED
certification.)
Thread filters provide finer
filtration
Another, more advanced class of self
cleaning filters are automatic thread filters that offer surface and depth filtration in a compact design. The advanced
microfiber technology removes suspended and colloidal foulants better than
conventional treatment.
Typically, cartridges are used to remove solids in the two-to-10-micron
range to protect membranes. Based on
the unique microfiber cassettes and their
automatic cleaning cycles, these thread
filters act as a 21st century version of the
cartridge filter. Automatic thread filters
eliminate much of the total cost of cartridge use, including replacement cost,
labor costs for change-outs and the costs
for transport, storage and disposal of
consumables.
Automatic thread filters can reduce
the chemical cleaning requirement of RO
membranes by a factor of four compared
to using standard cartridge filters before
an RO system. Because of the downtime
during membrane cleaning, increased
time between cleanings translates into
greater water recovery.
Conclusion
Improvements in filtration performance—especially with regard to increasing throughput, improving selectivity and reducing clogging—have a
major impact on the economics of existing filtration applications and on their
sustainability as well. Automatic self
cleaning filters should be considered a
clean technology choice for anyone looking for a multi-barrier approach to their
filtration process.
About the author
6 Jim Lauria is Vice President of Sales &
Marketing for Amiad Filtration Systems, a
manufacturer of clean technology water filtration systems for agricultural, industrial
and municipal applications. He has over 25
years of experience in liquid/solid separation
processes and water treatment. Prior to joining Amiad, Lauria owned Team Chemistry
LLC, a consultancy that focused on developing new business opportunities for clients’
water treatment technologies and was president of an $80M filter media company. During that time, he provided peer review for the
World Health Organization’s publication on
drinking water treatment and in partnership
with a university, led a team that pioneered
arsenic reduction in drinking water. Lauria
holds a Bachelor of Chemical Engineering
Degree from Manhattan College. Contact
him via cell phone (805) 901-5524 or email
jim@amiadusa.com.
About the company
6 Access to clean water is one of the world’s
greatest challenges—for drinking, for industry and for irrigation. For more than 40
years, Amiad has helped meet this vital need
by providing outstanding filtration technology to industrial, municipal and irrigation
users around the world. Amiad filtration
systems are more than just effective and
reliable, they’re environmentally sound: no
chemicals, no polymers, a bare minimum of
backflush water and reduced energy demand.
Many of our systems don’t even require
electricity and their small footprints save
valuable installation space. It’s all part of
Amiad’s pledge to deliver clean water using
clean technology. Amiad Filtration Systems
is located at 2220 Celsius Avenue, Oxnard,
California 93030 USA, telephone (800) 9694055, fax (800) 776-3458, website www.
Amiadusa.com.
Reprinted with permission of Water Conditioning & Purification Magazine ©2008
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Automatic Self Cleaning Technology
Among the principle benefits of automatic
self cleaning filters is the capability of the filter to clean itself when needed, without demanding additional time and training on
maintenance crews, requiring consumables
such as cartridges or bags, or exposing workers to cleaning chemicals.
Suction-Scanning
Suction-scanning technology makes elegant use of simple physics. As the filter
screen captures particles, the pressure differential between the inside surface (the inlet
side) and the outside surface (the outlet side)
of the screen increases. When that pressure
differential reaches seven psi, the system
opens an exhaust valve. The exhaust valve
drains the suction scanner, a hollow 316 stainless steel tube tipped with nozzles just millimeters from the screen surface.
Opening the exhaust valve to the unpressurized outside environment causes water to
flow in a high-velocity stream backwards
across the screen into the nozzles, carrying
the captured particles (or filter cake) with it.
The nozzles concentrate the suction effect
on less than one square inch of screen at a
time, creating a powerful and highly effective
cleaning force—a phenomenon we call “focused backflushing.” The suction scanner travels down the screen in a spiral pattern at a
fixed speed, cleaning 100 percent of the screen
surface in a 25-to-40-second stroke.
The suction-scanning cleaning cycle can
be initiated by a pressure-differential switch
or by a timer.
Automatic Microfiber Technology
A new level of automatic self cleaning filtration capacity is the automatic microfiber
system.
Wound around a rigid cassette with a specially grooved base plate, densely placed polyester threads capture tiny particles as water
flows across them toward collector pipes.
As dirt builds up on the filter threads, the
pressure differential between inlet and outlet
sides of the stream increases. At a pre-set
pressure differential, a high-velocity cleaning
stream is directed through the threads. The
stream bounces off of the specially grooved
base plate, pushing the high-velocity water
back through the threads and taking the particles with it to a drain valve.
These automatic self cleaning thread filtration systems are excellent for drinking
water filtration—including the removal of
Cryptosporidium, Giardia cysts and Legionella—as well as cooling-tower, side-stream
filtration, swimming pool filtration and protecting RO systems.
Water Conditioning & Purification
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