Efficacy of Sanitizers Using Unsoiled Spiral-Wound Polysulfone Ultrafiltration Membranes ¹

Sanitizing ultrafiltration and reverse osmosis systems poses unique problems for the dairy industry. Ultrafiltration and reverse osmosis membranes must be held wet and microorganisms remaining within the system could multiply under these conditions unless the holding solution is sufficiently microstatic. Two polysulfone ultrafiltration membranes as obtained from the manufacturer were used to evaluate cleaners and sanitizers. Because these membranes had not been used for processing there were no soil removal problems to interfere with sanitization. The ultrafiltration system was sanitized by recycling solutions for 10 min, and the unit containing sanitizer left idle 16 h. Stainless steel surfaces were examined by swabbing the next morning to check hygiene. Antibac B (50 ppm available chlorine), H2O₂ (0.2%, v/v) and an acid anionic surfactant (pH 2.5) were evaluated as sanitizers. None proved satisfactory based on microbiological criteria. Also, there was a loss in available chlorine from Antibac B solutions when held overnight in the retentate housing. These same problems were evident when sanitizers were circulated after cleaning solutions. Permeate flux, when used as a criterion for system cleanliness, indicated adequate cleaning and sanitization. Inability to contact all areas of membranes may be a problem in satisfactory sanitization of an ultrafiltration system.