Fiber failure frequency and causes of hollow fiber integrity loss

Ultrafiltration (UF) and microfiltration (MF) have been successfully applied in water treatment plants to remove particles, microorganisms and viruses. Up to 5 logs removal can be obtained; nevertheless, the water quality is influenced by compromised fibers. Several methods have been developed to monitor the integrity of a membrane system, but there is no clear picture of the occurrence and causes of fiber failure. In the present study, for different commercially available membranes, an annual fiber failure rate was found, mostly between 1 to 10 per million fibers. Data were gathered from the literature and acquired by contacting membrane manufacturers and water treatment plants. An overview of factors playing a role in fiber failure is given: strength of the membrane material (reviewed from the literature), operating conditions and incidents, such as failing pre-treatment, were identified to be important. It is believed that a certain level of membrane leakage is acceptable as long as the integrated multi-barrier treatment process has sufficient disinfection credits. From our data it was concluded that fiber failure rates of UF/MF membranes are acceptable, but a further reduction of this rate can reduce repair costs and installation down-time.