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By David
Pearson, General Manager, PCI Membrane Systems, Inc.
Providing safe drinking water in small communities is made
more difficult when the only water source available is surface
water laden with organic matter, and when skilled labor
required to run what amounts to a miniature chemical plant is
neither readily available nor affordable.
Traditional methods of removing
humic color from raw water - including flocculation,
clarification and other chemical-based approaches - can
require high staffing levels. The plant size required is
generally large and cumbersome, and the transporting of
equipment and chemicals to remote sites can sometimes be
impossible.
Fortunately, a new nanofiltration
membrane filtration process, now available in North America
from PCI Membrane Systems, Inc., Milford, OH, promises
effective water treatment without high capital costs or heavy
labor requirements. The Fyne Process, as it is called, was
first used in Scotland and has become the water treatment
technology of choice for rural communities with organic-laden
surface water from lakes or rivers as the water source. Today,
there are over 30 PCI installations running or on order with
the three Scottish Water Authorities. Systems as small as 1.8
gal/min (10 m3/day) and as large as 260 gal/min (1420 m3/day)
are currently operating. More recently, the first few North
American installations have been very successful.
SITUATION ANALYSIS
All along the rocky Canadian
Shield, in Alaska, and in the northeast U.S., it is difficult
to drill wells for drinking water, so smaller communities
often rely on surface water that tends to be heavy with
dissolved organic materials. Heavy chlorination is required
and that can lead to high TTHM (trihalomethane) and HAA(5) (haloacetic
acid) concentrations in the treated water.
Studies have shown that TTHMs and
HAA(5)s may be carcinogenic and their presence also has been
linked to miscarriages, so Canadian and US regulations limit
the presence of some or all of these byproducts in municipal
water systems. Until recently, many small communities that
rely on surface water for drinking have been exempt from these
limits. However, new, more stringent drinking water rules in
North America - including Stage 1 of the Disinfection
By-Products rule in the U.S., and new regulations in the
Canadian province of Ontario - are forcing small, rural
communities to seek solutions that effectively remove organic
matter prior to chlorination.
HOW THE PROCESS WORKS
The Fyne Process is based on a
particular membrane filtration process known as nanofiltration.
This type of filtration allows inorganic ions to pass through
the membrane with the filtrate. Organic compounds (such as
humic and fulvic acids), which cause the high color content
and disinfection by-products, are held back, along with
oocysts, bacteria viruses, and many undesirable metals,
including manganese and iron.
There are two membrane
configurations (tubular or spiral) that may be specified,
depending on plant capacity, raw water quality and recovery
required.
Spiral nanofiltration membranes
are usually required in large volume systems, but tubular
membranes are preferred whenever possible. That’s because
spiral systems require feed-water pre-filtration and frequent
chemical cleaning. Tubular membranes, which can be kept clean
by periodically passing a foam ball down the length of the
tube, need chemical cleaning only 3 to 4 times per year.
In a tubular system, the
filtration process starts with raw water, which is drawn into
the system through a coarse screen and pumped through modules
consisting of proprietary half-inch tubular membranes to
remove the undesirable dissolved organic materials. A portion
of the input water (the filtrate) crosses the membrane and
then is ready for chlorination and delivery to consumers. The
concentrate or retentate continues to flow through the
membrane tube, carrying much of the retained organic matter
with it. Because no chemicals are used in the process (in
contrast to chemical flocculation and clarification systems),
the discharge water is merely a more concentrated form of raw
water, which can be returned to the source. Thus, a tubular
membrane system achieves between 70% and 90% recovery, with
none of the expense associated with coagulant treatment or the
high maintenance costs associated with spiral membranes.
Operation is simple and automated,
so the plant can run unattended, with intervention on no more
than a weekly basis for routine maintenance. Pressure and flow
data are logged continuously and the system can even be
monitored remotely when an outside telephone line is
available.
EPA VERIFICATION
A study published as part of the
EPA’s Environmental Technology Verification (ETV) Program® has
verified the performance of a Fyne Process membrane filtration
plant tested in Barrow, AK. The study confirmed that the plant
could produce water that easily met the Disinfection
By-Product standards set by the EPA’s stringent Stage 1 D/DBP
Rule.
Barrow’s untreated water had an
average total organic carbon (TOC) level of 15mg/l and with
moderate turbidity. Over the 57-day test period, the average
TTHM concentration was reduced from 535 µg/L in chlorinated
raw water to just 31 µg/L in water chlorinated after
nanofiltration in the Fyne Process test plant. Average HAA(5)
concentrations were reduced from 398.4 µg/L to just 6.2 µg/L.
The membrane system also reduced UV254 absorbance, total
organic carbon, and turbidity - measures of water color and
clarity - by 97.5%, 95.4%, and 98.3%, respectively.
The ETV program was implemented to
assist in the development of innovative, cost-effective
environmental technologies, including packaged drinking water
treatment systems like the Fyne Process. The testing was
performed by the University of Alaska, in cooperation with the
University of New Hampshire, which is a qualified Field
Testing Organization under this ETV program.
OTHER NORTH AMERICAN RESULTS
Two Canadian installations also are demonstrating the
effectiveness of the Fyne Process.
The first system was installed in Nova Scotia in February
2000, and has been running full-time ever since. A second,
smaller system began operating in June 2000 at The Tl'azt'en
Nation community of Middle River in British Columbia.
Chapel Island is a small First
Nation Community located east of Halifax, Nova Scotia. The
plant was installed with a rated capacity 26.2 gal/min (143
m3/day), with a 20-year projected demand of 56 gpm
(305m3/day). The new installation replaced a small packaged
water treatment plant using coagulation and filtration
technology that required expansion and significant
refurbishment.
Raw water is taken from a shallow
lake with typical TOC levels of 8 mg/l and color normally in
the 40–100 TCU range. The intake is taken through a 3-mm
screen and piped to a sump under the water treatment plant
room. There is no additional filtration or treatment prior to
the membrane filter.
Reject water, which as noted is
merely a more concentrated form of raw water with no chemicals
added to it whatsoever, is fed back to the lake. When a
chemical clean is necessary, these chemicals are sent by
separate drain to a wastewater treatment lagoon where sludge
from the conventional flocculation and clarification package
plant (now removed) had previously been sent.
The system was competitively bid,
and although initial capital costs were higher, the Fyne
process was chosen from a variety of different treatment
methods because of its lower overall life cycle cost. Running
cost saving are realized as the Fyne process uses no chemicals
in the production of the water and requires significantly less
attention, allowing hard-pressed community maintenance staff
to attend to other demands. The system also is designed to
allow simple plant expansion. Additional capacity can be added
easily as and when required to meet changing needs.
The plant has been run above its
design capacity since installation, producing on average 155
m3/day, operating each day for 21.4 hrs on process. It was
cleaned only twice in the first 12 months after start up and
was to have been cleaned for the third time around its first
anniversary. The plant did experience a significant increase
in pressure over a short period, when cleaning of the inlet
works created an influx of sediment into the raw water sump.
Although the sediment remained in the inlet line for a number
of days, the membrane plant continued to produce its rated
volume of water - albeit at a higher operating pressure -
until its second partial clean a month after the incident.
This experience only served to prove the resilience of the Fyne Process to upsets in raw water quality, for whatever
reason.
MIDDLE RIVER
PERFORMANCE
The Tl'azt'en Nation community of
Middle River is a small village located on a river northwest
of Prince George, British Columbia. An isolated community two
hours from the nearest town, the site is a prime candidate for
the benefits of the Fyne process. The plant operated initially
as a 6-month pilot to test its suitability for operation in a
remote community. An engineering firm, CH2M Canada, monitors
performance of the system for the Department of Indian and
Northern Affairs Canada. At the end of the pilot period it was
decided to purchase the unit.
The Fyne plant, which has a design
capacity of 5.8 gal/min (22 l/min), operates with 6 PCI C10
filtration modules. Raw water is drawn from the nearby river.
Lift pumps provide water to the plant with a 2.5-mm screen at
the intake.
The Fyne plant was delivered in
and continues to operate in a heated and ventilated 40-ft
container, complete with membrane wash tank, chlorine dosing
and contact tanks, and 1100-gal storage. Reject from the plant
is sent to a sump tank overflowing back to the river. To
protect the environment, a separate tank is used to contain
washing chemicals that can then be taken away by tanker truck.
Since installation, performance of
the system has been very similar to the one at Chapel Island.
Corrected pressure rose at a constant rate until the first
membrane clean, which was scheduled for four months after
first operation of the plant. This clean was not entirely
effective and a second clean was performed shortly after to
establish if any significant irreversible fouling was
occurring. Cleaning concentrations and duration were increased
and the plant returned to within 96% of its early normalized
flux.
Regular analysis of feed water and
filtrate is also made. TOC reductions improved from 30% to 70%
over the first 200 hours of operation and have remained
consistently low. Iron and manganese were also significantly
reduced. While data on TTHM concentrations are limited,
formation-potential tests indicate levels well within current
Canadian guidelines.
As evidenced in these North
American installations, the Fyne Process offers distinct
advantages:
- Cost-effective for small and
medium-sized systems requiring removal of disinfection
by-products precursors; yields chlorinated water below the
limits of the EPA D/DPD Rule Stage 1 for TTHM and HAA(5).
- Low staffing requirement;
the Fyne Process can be fully automatic, including the
cleaning cycle. The plant can operate effectively
unsupervised.
- Tolerant to wide variations
in raw water quality; does not need adjustment when the feed
water quality changes.
- High recovery rate minimizes
waste of feed water.
- No chemical sludges
generated. Mechanical cleaning means cleaning chemical usage
is minimized.
- Compact design. Fyne plants
are mounted on a steel frame or skid, and units as large as
100 m3/d /(18 gpm) can be fitted into a standard 20ft or
40ft. container. Transportation to remote areas is possible
by truck, or even by helicopter.
- Single-phase supply.
Optional single-phase electrical supply for smaller plants
to suit the remotest of sites.
- Built and tested off-site.
On-site work is kept to the minimum of introducing a power
supply and connecting the unit.
- Performance guaranteed for
capacity and water quality, from a company with extensive
colored water operational experience and 25 years in other
industrial applications.
PCI expects that the Fyne Process,
with its particular advantages for remote, small communities,
will be accepted across North America as the process system of
choice, just as it has been in Scotland.
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