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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 prefilters 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 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
automated spectra units to operate with less frequent prefilter changes, but 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 systems, 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 han-
dling, 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
water line. Spectra offers a product water filter kit p/n KIT-FLT-CC.
More on this subject is available on our website at www.spectrawatermakers.com.
8/17/04