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OP-2 BAD SMELLING PRODUCT WATER
The reverse osmosis membrane is permeable by many gases including hydrogen sulfide, the gas
that causes rotten eggs to smell the way they do. If there are bad odors in the feed water they
will go through the membrane and the product water will be affected. Usually the source of the
odor is from the decay of planktonic creatures trapped in the sea strainer and prefilters. These
tiny oxygen loving creatures soon suffocate and die inside the prefilter housings when the unit
is shut down. Once all the available oxygen is consumed, anaerobic bacteria begin to grow,
causing the odor. If a unit being used frequently begins to make smelly water, it will be the pre-
filters that are the source of the problem. This occurs in a week or two in cold climates, but in
less than one night in very warm waters like the Sea of Cortes or the Red Sea. These bacteria
can spread throughout the watermaker, and begin to grow on the membrane, causing poor water
quality and high feed pressures.
Filling the system with fresh water after every use greatly slows this process, allowing the auto-
mated Spectra units to operate with less frequent prefilter changes. Units operated for only an
hour or so a day will probably need to have the filters changed due to odor before they are dirty
enough to restrict water flow. Prefilters can be cleaned. We recommend that you have three
sets in service, one in the unit, one set soaking overnight in a bucket of clean fresh or salt water
and one set drying for the next use. After shutting down the unit, remove the used prefilters and
install the dry set. Leave the housings full of air until the next use. On non-automated sys-
tems, open the pressure relief when starting if there is a lot of air in the system until the air is
cleared out through the brine overboard. The filters will get just as clean when soaked in sea
water, but dry much faster if soaked in fresh. Given gentle handling, prefilters can be reused
many times.
Bad smelling product water is usually caused by bad smelling feed water, but can also be
caused by a fouled membrane if the membrane has been left unpickled. If the unit makes
smelly but not salty water after a long idle period and the prefilters are new, the smell can be
eliminated by running the unit unpressurized for an hour or so to flush the membrane.
Odors in the product water can also be eliminated by adding a charcoal filter in the product wa-
ter line. Spectra offers a product water filter kit (part no. KIT-FLT-CC).
More on this subject is available on our website at www.spectrawatermakers.com.
8/17/04