Chlorine Dioxide Water Treatment for Reverse Osmosis Membranes Industry
Biological fouling of reverse osmosis is a common problem leading to reduced efficiency and reduced membrane life. CleanOxide Liquid 75 is pure Chlorine dioxide which is a highly effective biocide ideal for use in reverse osmosis systems. CleanOxide Chlorine Dioxide has all the important regulatory approvals in Australia and overseas to be used in water treatment and food processing. Many strategies have been developed in an effort to control biofouling of Reverse Osmosis membranes including the use of sodium hypochlorite, non-oxidising biocides, heat and pH swings.
Oxidising biocides such as hydrogen peroxide and chloramines have also found some limited use for aggressive cleaning of Reverse Osmosis membranes when other treatments have failed. Special care is required with these oxidising agents to ensure that no iron or manganese is present in the feed water as the presence of these elements can result in membrane damage.
Free chlorine is known to damage Reverse Osmosis membranes and this has precluded the use of chlorine gas in the feedwater for Reverse Osmosis systems.
Conventional methods of generating chlorine dioxide are accompanied by the production of small amounts of free chlorine which has limited the use of chlorine dioxide for cleaning Reverse Osmosis membrane systems in the past despite the overwhelming advantages of chlorine dioxide.
When dosed into the reverse osmosis water treatment system at the recommended rate, CleanOxide will control bacteria, fungi, viruses, algae and biofilm. Higher rates will allow the control of micro-organisms on hard surfaces contacted by the irrigation spray such as workbenches, pots and glass in greenhouses.
- Effective at concentrations as low as 0.1 ppm
- Effective over a broad pH range (4-10).
- Controls pathogenic organisms such as bacteria, fungi, viruses, biofilm and algae.
- Does not react with ammonia and does not produce toxic compounds in contact with organic materials present in water.
- Not phytotoxic at the recommended dose rates.
- CleanOxide 75 is not corrosive at the recommended dose rates
- Rapidly degrades to harmless inorganic chemicals when exposed to sunlight.
CleanOxide Liquid 75 from NW Solutions is a simple modern method of generating high purity Chlorine Dioxide (ClO2) as and when required by mixing two precursor solutions.
Reverse osmosis membranes are made of a variety of polymeric materials as well as composites of several materials.
In general, chlorine dioxide has been shown to be compatible with commonly used Reverse Osmosis membrane materials at low concentrations (<3mg/L) well above the recommended rates at which CleanOxide Liquid 75 is used.
Many of the reported problems with chlorine dioxide reacting unfavourably with Reverse Osmosis membranes can be traced back to impurities in the chlorine dioxide such as free chlorine or high levels of acidity (low pH). CleanOxide is totally devoid of any free chlorine and is not acidic when diluted with water.
However, NW Solutions strongly recommends that CleanOxide Liquid 75 is tested on a small portion of the membrane at the maximum proposed rate, if there is any doubt about the compatibility of the membrane material with chlorine dioxide.
It should also be noted that because chlorine dioxide is a gas dissolved in water and is not hydrolysed by the water, it can diffuse into the membrane and pass through the membrane to provide biocidal protection downstream of the membrane. This may be of considerable advantage in some situations where the discharge water is for drinking.
In other situations, where very high purity in the discharge water is paramount, great care should be taken to use CleanOxide Liquid 75 only occasionally to control biofouling.