It’s unlikely that the RO membranes were damaged inadvertently during installation. While it’s possible for there to be manufacturing imperfections that allow pathogens such as viruses and bacteria to pass through, it’s not common.
In our experience, total coliform counts are high with most new membrane installations or replacements. This is because bacteria are introduced to the permeate side components (such as the membrane permeate tube and interconnectors), which will cause a high bacterial count in the permeate. This can be resolved by running the system and sending the permeate to waste for several days (usually 2 – 3 days). Alternately, a peroxide based cleaner or disinfectant can be used (peroxide solution will partially pass to the permeate side under the pressure applied during cleaning; this will disinfect the permeate side). When disinfecting with hydrogen peroxide or peracetic acid solutions such AWC D-615P, always be sure not to exceed concentrations recommended by the membrane manufacturer. In some cases, a high pH cleaning may be sufficient because hydroxide ions also partially pass through to the permeate side. We’ve had great success with similar situations using AWC C-227, a proprietary high pH cleaner designed specifically for organic and biological fouling.
In order to prevent high coliform counts after membrane loading, good hygiene must be practiced by the contractor’s staff. They should wash their hands thoroughly. Disposable gloves should be worn during membrane installation. A good practice is to dip all the interconnectors, end-cap adaptors, and other components in AWC D-615P prior to installation. Care should be taken not to introduce any type of contamination to the permeate tube of the RO membranes.
We have seen some contractors dip all the permeate-side components in sodium bisulfite solution, but that doesn’t work. Bisulfite solution is a good preservative that prevents growth of aerobic microorganisms by scavenging oxygen in the water, but has no impact on anaerobic bacteria. Bisulfite isn’t a biocide, so quickly dipping components in bisulfite solution doesn’t result in an instantaneous kill of any microorganisms.
See also:
What is the procedure for cleaning RO membranes? What CIP chemicals should be used?
A few weeks ago, we pickled all RO membranes in our trains with sodium metabisulfite for long term storage. Our membrane manufacturer recommended that we change the solution once the pH drops below 3. We measured a decrease in pH for the first two weeks, but then on the third week, the pH increased. Can you explain why the pH increased instead of decreasing?
How can we determine whether the membranes in our Reverse Osmosis system are damaged?
Can hydrogen peroxide be used effectively in place of sodium bisulfite for dechlorination of seawater RO feedwater? We are concerned about dissolved oxygen levels in the concentrate that is disposed back into the sea…