 Sanitizing RO With Hydrogen Peroxide
Studies have shown the
effectiveness of H2O2.
By Rich Sheridan,
P.E.
From the July 1995
edition of Water Technology magazine
Anyone who has serviced
a reverse osmosis (RO) system has seen the "grunge" growing inside a
filter sump or cooling reservoir, or has felt the slime on the inside of
the tank bladder. Bacterial slimes and molds grow on the insides of filter
sumps, and on the RO membrane and storage-tank lining.
Some dealers do nothing to sanitize
systems during filter changes; they simply change the filters and check
the RO tank pressure and production rate. However, it will only be a
matter of time before complaints arise over a change and deterioration in
taste. Other dealers use surgical masks and gloves when opening filtration
equipment for filter changes, and they use liquid chlorine bleach or
hydrogen peroxide (3 percent) to sanitize the sumps, membranes, lines and
cooler reservoir.
In any case, sanitizing filtration
equipment is becoming more important from the regulatory and
product-quality/health standpoints. These issues have caused major
improvements in the RO thin-film composite (TFC) membrane, a new form of
which is now chlorine-resistant.
Bacteria-Virus Link
Heterotrophic bacteria, which is the
kind that will grow in a storage tank, cooler reservoir or filter
cartridge, have been considered by many to be harmless if ingested.
However, where there are bacteria, there are usually viruses, which are
much more likely to cause disease. As with the fecal coliform test
indicating the presence of pathogenic bacteria, the presence of
heterotrophic bacteria is a good indicator of harmful viruses.
In 1985, Pierre Payment of the
University of Quebec (now with the Institute of Virology in Montreal) was
perhaps the first to demonstrate the potential for harmful bacteria and
viruses growing in filtration systems. Other studies have demonstrated
that heterotrophic bacteria will grow in RO systems, but it was not
determined if these would make people sick.
Payment studied 600 families: 300
families had reverse osmosis systems, and 300 families drank tap water.
Early in the study, there was a 30 to 35 percent higher incidence of
gastroenteritis (intestinal illness) in those drinking tap water. Among
the RO water drinkers, 5 percent contracted illnesses early in the study
due to water contaminated by the reverse osmosis filter.
However, toward the end of the 18-month
study, Payment found a higher incidence of gastroenteritis among families
with reverse osmosis systems. The levels of bacteria in the RO systems had
increased to 100,000 per milliliter (ml) and higher. People who drank RO
water averaged 10 times the incidence of illness of those drinking the
unfiltered tap water. Payment wasn't sure if bacteria or viruses were
causing the gastroenteritis.
Pathogens Enter RO Systems
Theoretically, neither bacteria nor
viruses should be able to pass through a reverse osmosis system. Bacteria
are in the 0.1- to 10-micron range and viruses are in the 0.02-micron
range, while the openings in an RO membrane are in the 0.006-micron range.
However, RO membranes are not free of imperfection, and the probability of
total rejection is very low. Therefore, very low levels of bacteria and
viruses pass through the RO membrane and grow in the storage tank, lines
and filters.
Tests have found 99.2 to 99.5 percent
bacterial removal with feedwater containing 4,000 per ml. This level of
removal would translate to bacterial counts of 20 to 32 per ml passing on
to the RO storage tank. There is also an opportunity for bacteria to grow
from the RO faucet toward the post-carbon filter and RO storage tank.
Many dealers have experienced the
occasional complaint from customers over the initial bad taste after
system installation or a bad taste that has happened over time. The usual
procedure is to change the storage tank, change the post carbon filters or
sanitize the system again.
Liquid chlorine bleach has
traditionally been used to sanitize sumps, flush membranes and sanitize
bladder tanks and coolers. The use of bleach has not been without its
associated problems, however. Bleach will sometimes leave a residual in
the system, giving a poor taste to the water as well as possible odor. To
overcome this residual, a time-consuming component flushing is performed.
Using liquid bleach can also damage the TFC membrane.
Acceptance of Hydrogen Peroxide
Hydrogen peroxide (H2O2) is gaining
wider acceptance for sanitizing filtration systems because it virtually
eliminates the taste and odor problems associated with chlorine bleach
sanitizing. It is also a more powerful killing agent. However, it is
sometimes difficult and time- consuming to get enough 3 percent hydrogen
peroxide into the typical residential and office storage tank, RO membrane
and lines to be effective.
Food-grade hydrogen peroxide (35
percent) is over 10 times more concentrated than the "supermarket brand"
of 3 percent. Because of its higher concentration, food-grade H2O2 is a
much more powerful disinfectant. One drop per gallon of water equals a
concentration of 9 milligrams per liter (mg/l) and is equivalent to 12
mg/l ozone. There is enough food-grade hydrogen peroxide, in a small
2-ounce dropper bottle to effectively sanitize about 20 reverse osmosis/bottleless
water-cooler systems with 1-gallon cooler reservoirs.
The use of hydrogen peroxide will also
allow the reuse of the carbon filter that is usually on the back of the
cooler and the post-carbon filter that is on the RO manifold. These
polishing carbon filters receive a very light loading if not used for
chlorine removal. When the bacteria/viruses are eliminated, they continue
to produce good-tasting water.
Sanitizing an RO System
A typical bottleless water cooler
system consists of an undersink RO unit with a 1/4-inch plastic line
running 5 to 100 feet to the water cooler. The best and quickest way to
sanitize this system would be to sanitize the tank at your dealership,
bringing the sanitized tank, pre-filled with RO water, to the customer.
The rest of the system could be sanitized on site. Tank sanitizing takes
the most time and, with this method, there will be minimal interruption in
the customer's use of the system.
Tank sanitizing consists of completely
emptying the tank, adding 30 drops of 35 percent hydrogen peroxide per
3-gallon tank and partially filling with tap water (50 percent fill). Let
the tank stand at least 15 minutes, then empty and fill with RO water. If
a pre-sanitized tank is not brought out to the customer's site,
pressurized tap water must be used to flush the H2O2 through the line to
the cooler. Sanitizing the bladder tank on site will add an additional
half-hour to the service call.
When the tank is brought to the
customer's location, turn off the water line behind the cooler and
immediately switch tanks. Starting with the tank will allow determination
of the RO production rate when the tubing is disconnected from the storage
tank. Before reconnecting the tubing to the storage tank, turn off the
water supply and add 40 drops of 35 percent H2O2 into the tubing. If there
is no cooler, add 20 drops. This amount of H2O2 will sanitize the
post-carbon filter on the RO manifold, the line to the cooler, the carbon
filter on the back of the cooler and the cooler's storage tank.
Replace the sediment and pre-carbon
filters. If the sumps/housings are noticeably 'grungy' (containing mold,
for example), then clean the sump/housing in the sink with a bottle brush,
10 drops of H2O2 and hot water. After letting the housing and H2O2 stand
for 1 minute, thoroughly scrub with the brush, then pour the solution into
the drain.
When inserting the new sediment filter
into the sump, add two drops of 35 percent H2O2 into the sump. This will
kill any organisms that enter the sump during filter changing. Surgical
gloves and a mask are not necessary because anything thats enters the
housing from the air or your hands will be killed by the H2O2.
Filters and Coolers
Changing the pre-carbon filter is a
two-step process if the filter is the granular type. Granular pre-carbon
filters must be flushed to remove the harmful carbon fines. Flushing
consists of removing the RO module or the line to the RO module, and
flushing about 12 ounces of water into a jug.
After flushing, the pre-carbon filter
housing is opened and 20 drops of 35 percent H2O2 are placed inside the
carbon prefilter. If the filter is an integrated sump/filter type, place
the H2O2 into the discharge tube from the filter. This will sanitize the
RO membrane. Then turn on the feedwater and the storage tank valve.
Next go to the cooler and pull back the
float cover just enough to look inside and assess the condition inside the
cooler reservoir. If there is no noticeable slime buildup or "dust"
accumulated on the baffle, reseal the float cover. With RO bottleless
water coolers, a thorough cleaning of the tank will not be required in
most cases, and the simple addition of RO water containing H2O2 will be
sufficient. If slime and "dust" is observed, thoroughly clean the
reservoir. This involves removing the cover and baffle and cleaning all
parts with a general-purpose cleaner.
After flushing down the inside of the
cooler with tap water to remove the remaining cleaner and replacing the
cleaned baffle and cover, turn on the valve so RO water containing H2O2
flows from the RO unit to the cooler and inside the reservoir. Once the
reservoir is full, shake the cooler to have all interior surfaces of the
cooler flushed with H2O2 RO water. Let the cooler stand for at least five
minutes.
During this time you can clean the
exterior of the cooler and complete your paperwork. Turn off the valve
behind the cooler, drain all water from the cooler and turn the valve back
on.
When the cooler has refilled, taste the
water to make sure that the product is acceptable. This procedure will
effectively sanitize the entire system and save money on one and possibly
two post-carbon filters, which is especially important if you run a rental
business. If you don't run a rental business, you can possibly increase
your service fee to reflect this improved service.
For water coolers that have 4.5-gallon
storage tanks, with the RO unit also undersink, add 40 drops of H2O2 at
the RO storage tank, but also add 40 drops (1 teaspoon) directly to the
cooler reservoir if the tank appears clean. Remove 1 gallon of water from
the cooler. Then open the valve behind the cooler, allowing the cooler to
fill with the RO water flowing from the storage tank.
After filling, shake the cooler, let
stand five minutes and then drain the tank. Turn on the RO storage tank,
letting the cooler partially fill with the remaining water from the tank.
If the cooler storage tank is "dirty,"
the tank must be completely emptied, cleaned and rinsed with 1 gallon of
water containing 40 drops of H2O2. The line to the cooler is disconnected
after the carbon filter, and approximately 1 gallon of water is discharged
into a jug, sanitizing the line to the cooler and the post-carbon filters.
This line is then reconnected, and the remaining 1 to 1-1/2 gallons of RO
water is allowed to flow into the cleaned and sanitized cooler reservoir
for customer use.
Other Scenarios
If there are two or more water coolers
connected to a single RO system, the procedure of adding 40 drops of H2O2
to the line from the RO storage tank must be done for each cooler. Make
sure that the valves behind all coolers are turned off to prevent
customers from drinking water with the concentrated H2O2 solution. If
there is an RO sink faucet, remove it or put an "out-of-order" sign on it.
Also, sanitize the RO sink faucet by
placing five drops of H2O2 into both ends, rotating the faucet vertically
180 degrees to allow the peroxide to drain back through the faucet. Rinse
the peroxide out of the faucet by placing it under the tap-water faucet.
Reinstall and sanitize the short line to the RO faucet by adding 10 drops
of H2O2 to the line from the RO storage tank, and drain about 10 ounces of
water from the RO faucet.
For water coolers with the RO unit
mounted on the cooler or as an intregral part of the cooler, use the same
procedure as with the undersink system for the sediment and pre-carbon
filters.
Attempting to sanitize and reuse the
post-carbon filter in general will be too time-consuming because of the
lack of a pressurized storage tank. However, if you want to take the time,
you can temporarily switch lines and save this filter by placing the
feedwater line on the polishing filter.
Sanitize the post-carbon filter by
adding 40 drops of H2O2 into the line feeding the post-carbon filter and
allow about 1 gallon of tap water to flow through the filter to the cooler
reservoir (remove 1 gallon before sanitizing filter). The cooler's
reservoir will have to be sanitized by adding 80 drops (2 teaspoons) of
H2O2 to the filled cooler (4.5-gallon type) proceeding as above, or 40
drops (1 teaspoon) if the post-carbon filter is sanitized. After allowing
it to "set" for about five minutes, drain all 4.5 gallons.
With this type of cooler, the system
will be down for an hour or two unless the dealer brings in a separate jug
of RO water for reservoir filling. Leave a sign on the cooler saying "Out
of Order until ____". Some dealers pre-sanitize the 4.5-gallon reservoir,
bringing it out to the customer in a plastic bag. This will avoid having
to drain the 4.5-gallon tank.
Pre-sanitizing the tank requires 40
drops of H2O2 and 1 gallon of tap or RO water. The tank is then shaken up
for about 1 minute. When this method is used, you can allow the tank to be
damp with the sanitizing solution when you put it into the plastic bag.
This will cut down the time to thoroughly dry the tank and eliminate
having to re-sanitize it when it's installed.
Carbon-Filter Water Coolers
In most cases, the reservoir of a
carbon-filter bottleless water cooler will have to be throughly cleaned
and sanitized with H2O2. Observing a number of carbon filter-fed coolers
compared to RO-fed coolers should be enough of a testimonial for RO water
-- the cleaner the water, the cleaner the cooler! The consistently
"dirtier" carbon filter-fed water coolers reflect what the carbon filter
system doesn't remove.
RO systems remove essentially all of
the finer colloidal particles and most of the bacteria. In terms of
comparative sanitizing, the added requirement of RO bladder-tank
sanitizing is offset in general by the more extensive cooler tank cleaning
required by carbon filter-fed coolers.
Filter and cooler sanitizing will be
virtually the same as that for the RO system. Instead of adding 40 drops
of H2O2 to the RO storage tank discharge, add the peroxide to the sediment
filter sump. If the sumps/housing are attached to the back of the cooler
and cannot be quickly removed, inspect them to see if cleaning is
required.
If cleaning is required, half-fill with
hot water and 10 drops of H2O2, and throughly scrub with a brush in place.
Replace cover and flush 1 gallon of water through the sump without the
filter to a jug. Do not allow this water to go to the cooler. If the sumps
look clean, then flushing the 40 drops of H2O2 through the sumps and line
to the cooler will be sufficient for sanitizing.
Rich Sheridan is a twenty-year
veteran in the water and wastewater profession. He is currently a
consultant and independant contractor in Farmer's Branch, TX.
All
Content Copyright 2004.
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