Ozone in post RO disinfection has been well accepted in other fields that require high purity water, such as the pharmaceutical and beverage industries. Ozone is a powerful oxidant and is extremely degrading to RO membranes and other components. Therefore, it is used in the distribution piping alone, to assist chemicals like sodium hypochlorite in maintaining disinfection in piping, and all materials in the piping need to be ozone compatible, like PEX – AL – PEX, stainless steel or Polycob. Ozone eradicates microorganisms and their byproducts, such as endotoxin, and breaks them down to carbon dioxide and water.
The half-life of ozone is 30 minutes in water and 24 hours in air. Their permissible exposure limit (PEL) in the atmosphere for ozone is 0.1ppm over an 8 hour time weighted average (TWA). In other words, as long as the exposure averages out to 0.1 ppm at any given time in an 8 hour period, the person may be exposed to higher levels, but for shorter intervals. The effective amount used in RO distribution piping has been well under the PEL. Ozone is immediately broken down with exposure to UV light. It will also degrade quickly on its own.
Formaldehyde or Formalin:
Many dialysis units are moving away from using formaldehyde because of exposure toxicity and intense OSHA regulations. For routine disinfection, a 1-2% solution is recommended. For aggressive disinfection, a 3-4% solution is recommended. Formaldehyde is
compatible with all systems and has excellent vapor phase activity; it does not, however, attack the biofilm layer. A minimum dwell time of 2 hours for 4% formaldehyde may be effective, but it is best if the formaldehyde is left in the system overnight or longer.
Formaldehyde may be used to store equipment for up to one year.
Bleach or Sodium Hypochlorite:
Never use bleach in an RO system containing thin film RO membranes. CA membranes are more chlorine-tolerant but have their individual limitations. Bleach is very aggressive toward biofilm when used to disinfect the distribution loop. A concentration of 500 parts per million, or approximately 1:100 solution, of common household strength bleach is an effective disinfectant. As a caveat, it should be remembered that bleach is very corrosive to the internal parts of the distribution loop, and dialysis machines and should be rinsed out
within 30 minutes or less. Always use high-purity bleach. Never use the “off” brands because they may contain impurities that lodge in the system.
Gluteraldehyde is not recommended for use in RO systems. It does not pass through the RO membrane in high enough concentrations to deem the system disinfected.
Sodium metabisulfite is a bacteriostatic agent. It does not kill the bacteria but simply prevents them from replicating. The recommended long term storage dose is 0.1%. For short term “disinfection”, a 1% concentration with a dwell time of 30 minutes or less is recommended. Sodium metabisulfite will degrade thin film RO membranes in higher concentrations or with longer dwell times. As with ingested sulfites in wine and salad, some people have severe reactions to sulfites. Therefore be extremely careful if you have a known
Low pH Cleaning Agents (Biosan):
Biosan is not listed as a disinfectant. It is a mineral scale deposit cleaner that has good biocidal activity. When used alternately with a disinfectant, it has been shown to prevent growth of bacteria in RO systems. It is recommended to use a 1:10 concentration of Biosan
for a minimum of 30 minutes. RO systems with thin film RO membranes may be stored for up to 2 weeks in Biosan. With CA membranes, exposure should not exceed 3 hours.
HSI and NaOH:
At least one manufacturer suggests the use of these products as alternatives for the control of bacteria. Like Biosan, these are also considered cleaners, not disinfectants, and should be used in conjunction with a disinfection regimen. The hydrochloric acid at a pH of 2
should dwell for 30 minutes, and then, once thoroughly rinsed out, the sodium hydroxide at a pH of 11 should be introduced and left to dwell for 30 minutes.
Iodine is added to the purified water via an iodinator so that a steady concentration of iodine is achieved. Iodine has also been added pre RO to prevent bacterial degradation of CA membranes. The contact times and concentrations for hemodialysis applications are not
well established. The iodine must be removed from the water before it reaches the hemodialyzer, and this can be accomplished through the use of a bed of granular activated carbon or a deionizer. However, because carbon and the deionizing resin are conducive
environments for bacterial growth, they themselves will contaminate the water with bacteria, thereby defeating the original purpose of the iodine.
Ultraviolet (UV) Irradiation:
Ultraviolet light is produced by way of low pressure mercury vapor lamps that emit a bactericidal wavelength of 254 nm. Although UV destroys the bacteria as it passes by, it can cause endotoxin levels to increase in the product water. In order to be effective, the lamp
must be replaced every 6 months to 1 year, and the protective quartz sleeve must be cleaned on a routine basis. UV resistant strains of bacteria can develop, making it necessary to use other means of disinfection.