Technical Service Bulletin
May 2010 TSB107.19
Foulants and Cleaning Procedures for composite polyamide RO Membrane Elements (ESPA, ESNA, CPA, LFC, NANO and SWC)
This bulletin provides general information about the usual foulants affecting the performance of Hydranautics' Composite Polyamide Reverse Osmosis (RO) membrane elements and the removal of these foulants. Theinformation in this bulletin applies to 4-inch, 6-inch, 8-inch, 8.5-inch, and 16-inch diameter RO membrane elements. Note: The Composite Polyamide type of RO membrane elements may not be exposed to chlorinated water under any circumstances. Any such exposure will cause irreparable damage to the membrane. Absolute care must be taken following any disinfection of piping or equipment or the preparationof cleaning or storage solutions to ensure that no trace of chlorine is present in the feedwater to the RO membrane elements. If there is any doubt about the presence of chlorine, perform chemical testing to make sure. Neutralize any chlorine residual with a sodium bisulfite solution, and ensure adequate mixing and contact time to accomplish complete dechlorination. Dosing rate is 1.8 to 3.0 ppmsodium bisulfite per 1.0 ppm of free chlorine. It is recommended that all RO membrane cleaning operations should be closely coordinated with Hydranautics during the RO membrane element warranty period. Hydranautics field service personnel are available to be on site for cleaning assistance, should the need arise. Please contact Hydranautics for current charges for this service.
Note:The use of cationic surfactant should be avoided in cleaning solutions, since irreversible fouling of the membrane elements may occur.
If additional information is needed, please contact the Technical Services Department at:
HYDRANAUTICS 401 Jones Rd. Oceanside, CA 92058 Tel# (760) 901-2500 Fax# (760) 901-2664 e-mail: email@example.com Internet: www.membranes.com
TSB107.19 Page 2RO Membrane Fouling and Cleaning
During normal operation over a period of time, RO membrane elements are subject to fouling by suspended or sparingly soluble materials that may be present in the feedwater. Common examples of foulants are: Calcium carbonate scale Sulfate scale of calcium, barium or strontium Metal oxides (iron, manganese, copper, nickel, aluminum, etc.) Polymerized silica scaleInorganic colloidal deposits Mixed inorganic/organic colloidal deposits NOM organic material (Natural Organic Matter) Man-made organic material (e.g. antiscalant/dispersants, cationic polyelectrolytes) Biological (bacterial bioslime, algae, mold, or fungi) The nature and rapidity of fouling depends on a number of factors, such as the quality of the feedwater and the system recovery rate.Typically, fouling is progressive, and if not controlled early, will impair the RO membrane element performance in a relatively short time. Cleaning is should accur when the RO shows evidence of fouling, just prior to a long-term shutdown, or as a matter of scheduled routine maintenance. The elements shall be maintained in a clean or “nearly clean” condition to prevent excessive fouling by the foulantslisted above. Some fouling is allowed as long as: - normalized permeate flow decrease is less than 10% - normalized permeate quality decrease is less than 10% . - normalized pressure drop, as measured between the feed and concentrate headers, increase is less than 15%. Cleaning should be carried out before these values are exceeded to maintain the elements in a clean or “nearly clean” condition.Effective cleaning is evidenced by the return of the normalized parameters to their initial, Start-up, value. In the event you do not normalize your operating data, the above values still apply if you do not have major changes in critical operating parameters. The operating parameters that have to stay constant are permeate flow, permeate back-pressure, recovery, temperature, and feed TDS. If these...