Sodium metabisulfite (SMBS) is not a disinfectant. SMBS dissolved in water converts to sodium bisulfite. When dosed online at high dosages, it is an oxygen scavenger and many biofilm forming bacteria are anaerobic, making oxygen scavenging useless. In many cases, such high dosages have been associated with increased biological growth, especially where the water contains high TOC levels.
SMBS does however prevent fungal growth in membranes when used as a storage solution, because most fungi can’t grow without oxygen. It goes without saying that growth of aerobic bacteria is also inhibited under these storage conditions.
Fungus requires nitrogen for growth making polyamide membranes especially susceptible to deterioration should fungal growth not be prevented. Fungi and heterotrophic bacteria obtain their energy from organic compounds, so it’s important to clean the membranes well and remove all organic foulants from the membrane surface prior to long term storage in bisulfite solution.
See also:
Under which conditions can antiscalants cause RO membrane fouling?
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?
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…
We recently installed new RO membranes in our system and observed that the permeate water tested positive for coliform bacteria. Is it possible in your experience that RO membranes could be damaged during installation and cause contamination of the water distribution system by bacteria and pathogens?