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There have been serious questions and apparent discrepancies in both laboratory and field work regarding whether chlorine dioxide is harmful to thin film composite RO membranes.[1]

The presence of metals, specifically iron, as part of the fouling deposit found on RO membranes during autopsy is well known.[2] In some cases, the amount of iron in the water entering the RO unit was very low, and yet iron was found to be concentrated in the fouling deposit.[3]

Metals, specifically iron, is known to be a catalyst for damage to RO membranes in the presence of chloramine and chlorine.[4] A similar question has been raised for chlorine dioxide (chlorite).[5]

The most comprehensive field study of this phenomenon has been made.[6] The work proceeded in three phases. In Phase 1, chlorine dioxide was generated by the chlorite: chlorine gas method.[7]

Flux increased from 22 gpm to 35 gpm in about 120 hours. Their conclusion was that impure chlorine dioxide (chlorine dioxide with some free chlorine present) was destroying the membrane. This led to Phase 2, where chlorine dioxide free from chlorine was used.

Further investigation led to the HCl: chlorite process, which is not thought to produce free chlorine, except as a short-lived intermediate.[8] Still, under these conditions, there was a rapid decrease in salt rejection. Further investigation revealed the presence of iron. This resulted in Phase 3, which employed continued use of HCl: chlorite generation method and improved iron removal in the pretreatment process.

In Phase 3, the flux was stable and salt rejection was nearly identical to results obtained without use of chlorine dioxide. Their conclusions were as follows:

  • Chlorine gas generated chlorine dioxide rapidly degraded RO membranes.
  • HCl: chlorite generation did not degrade membranes.
  • Membrane degradation appeared to be due to iron.
  • Chlorine dioxide did not degrade membrane performance in the absence of metals, specifically reduced iron.

These results suggest that the presence of metal ions in feedwater may catalyze the reaction of chlorine dioxide or chlorite ion with RO membranes and may explain the controversy surrounding the degradation of RO membranes when chlorine dioxide is used.

References

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[1]     Vos, K., Burris, F., and Riley, R., “Kinetic Study of the Hydrolysis of Cellulose Acetate in the pH Range of 2-10,” Journal of Applied Polymer Science, 10, (May 1966).

Vos, K., Nusbaum, I., Hatcher, A., and Burris, F., “Storage, Disinfection, and Life of Cellulose Acetate Reverse Osmosis Membranes,” Desalination, 5, 157(1968).

Glater, J., McCutchan, J., McCray, S., and Zachariah, M., “The Effect of Halogens on the Performance and Durability of Reverse Osmosis Membranes,” ACS Symposium Series, 153(1}, 173 (1981).

Glater, J., Zachariah, M., McCray, S., McCutchan, J., “Reverse Osmosis Membrane Sensitivity to Ozone and Halogen Disinfectants,” Desalination, 48, 1(1983).

Glater, J., McCutchan, J., McCray, S., and Zachariah, M. “The Effect of Water Pretreatment Chemicals on the Performance and Durability of Reverse Osmosis Membranes.” UCLA Report No. 831 (1983)

Zachariah, M. and Glater, J., “A Mechanistic Study of Halogen Interactions with Polyamide Reverse Osmosis Membranes,” Reverse Osmosis and Ultrafiltration, S. Sourirajan, ed., 345(1985).

McCutchan, J., and Glater, J., “The Effect of Feedwater Pretreatment Chemicals on the Performance and Durability of Reverse Osmosis Membranes,” UCLA-ENG-8004, Water Resource Center 71, January 1980.

Glater, J., McCutchan, J., McCray, S., and Zachariah, M., “Halogen Interactions with Typical Reverse Osmosis Membranes, “ AWWA Water Reuse Symposium II, Washington, DC, 2, 1339(August 1981).

McCray, S., Glater, J., and McCutchan, J., “The Effect of pH and Halogens on the Stability of Reverse Osmosis Membranes,” UCLA-ENG-8115, WRC 73, July, 1981.

McCutchan, J., Glater, J., McCray, S., Nobe, K., and Zachariah, M., “Saline Water Demineralization by Means of a Semipermeable Membrane,” Water Resources Center, Desalination Report No 75, July 1982.

McCutchan, J., Glater, J., McCray, S., Zacharian, M., and Nobe, K., “The Effect of Water Pretreatment Chemicals on the Performance and Durability of Reverse Osmosis Membranes,” Office of Water Research and Technology Report, April, 1983.

Adams, W., “The Effects of Chlorine Dioxide on Reverse-Osmosis Membranes,” Desalination, 78(3), 439 (1990).

Saad, M., “Biofouling Prevention in RO Polymeric Membrane Systems,” Desalination, 2(88), 85(1992).

Pitochelli, A., Mainz, E., and Griffith, D., “Continuous Chlorine Dioxide Use to Prevent Biofilm Formation on RO Membranes,” Ultrapure Water, 40(May/June 2005).

[2]     Jackson, J. and Landolt, D., “About the Mechanism of Formation of Iron Hydroxide Fouling Layers on Reverse Osmosis Membranes,” Desalination, 12, 361(1973).

Butt, F., Rahman, F., and Baduruthamal, U., “Characterization of Foulants by Autopsy of RO Desalination Membranes,” Desalination, 114, 51(1997).

Boubakri, A. and Bouguecha, S., “Diagnostic and Membrane Autopsy of Djerba Island Desalination Station,” Desalination, 220, 403(2008).

[3]     Dudley, L. and Darton, E., “Membrane Autopsy – A Case Study,” Desalination, 105, 135(1996).

[4]     Gabelich, C., Yun, T., Coffey, B., and Suffet, I., “Effects of Aluminum Sulfate and Ferric Chloride Coagulant Residuals on Polyamide Membrane Performance,” Desalination, 150, 15(2002).

Gabelich, C., Franklin, J., Gerringer, F., Ishida, K., and Suffet, I., “Enhanced Oxidation of Polyamide Membranes using Monochloramine and Ferrous Iron,” Journal of Membrane Science, 258, 64(2005).

Tessaro, I., da Silva, J., and Wada, K., “Investigation of Some Aspects Related to the Degradation of Polyamide Membranes: Aqueous Chlorine Oxidation Catalyzed by Aluminum and Sodium Laurel Sulfate Oxidation during Cleaning,” Desalination, 181, 275(2005).

Da Silva, M., Tessaro, I., and Wada, K., “Investigation of Oxidative Degradation of Polyamide Reverse Osmosis, Membranes by Monochloramine Solutions,” Journal of Membrane Science 282, 375(2006).

[5]     Wise, B., Marker, L., and Muellere, P., “Effectiveness of Chlorine Dioxide in Sanitizing Thin-Film Membrane Systems,” Ultrapure Water, 13 (September 2004).

[6]     Tseng, T., Cheng, R., Tanuwidjaja, D., and Wattier, K., “Evaluation of ClO2 in Seawater Desalination Pretreatment,” American Water Works Association 2009 Membrane Technology Conference, 2009.

[7]     Aieta, E. M., and Roberts, P. V., “Kinetics of the Reaction between Molecular Chlorine and Chlorite in Aqueous Solution,” Environmental Science and Technology, 20, 50(1986).

Aieta, E. M., and Roberts, P. V., “Application of Mass-Transfer Theory to the Kinetics of a Fast Gas-Liquid Reaction: Chlorine Hydrolysis,” Environ. Sci. Technol. 20(1), 44(1986).

Masschelein, W. J., “Chlorine Dioxide,” Chemical Oxidation, Technology for the Nineties, First International Symposium, Vanderbilt University, Nashville, TN, February 20-22, 1991

[8]     Pitochelli, T., “Chlorine Dioxide Generation Chemistry,” 3rd International Symposium: Chlorine Dioxide: Drinking Water, Process Water, and Wastewater Issues, New Orleans, LA., September 14-15, 1995.