Enzymatic Cleaning of Cellulose Acetate Membrane Reverse Osmosis Systems

Abstract

A comparison was made of several methods of evaluating the efficacy of enzyme cleaning of a tubular reverse osmosis (RO) system: (a) flux restoration, (b) dissolved solids level in permeate during cleaning and (c) removal of the radioisotope 33P. Microbiological evaluation was used as the reference method. Volumetric flux restoration and dissolved solids levels in permeate during cleaning were of little value as indicators of cleaning efficiency. When these methods suggested adequate cleaning, subsequent swabs of equipment parts or determination of counts in permeate and/or concentrate at start-up 12–24 h after cleaning showed ineffective cleaning. Swab techniques were useful in identifying areas of concern. Addition of 33P-inorganic phosphate to whey resulted in immediate absorption of the isotope to the membrane surface. Measurement of the 33P-phosphate during cleaning provided a quantitative measure of soil removal that could not be achieved with other methods. The 33P-phosphate technique indicated that soil removal is cyclic in nature, with alternating removal and redeposition. The 33P technique, while of value only as a research tool, can be helpful in determining areas of minimum turbulence in a RO system and may be useful in evaluation and improvement of equipment design.