AWWA MTC64577

The application of membrane filtration in the production of drinking and process water is steadily increasing. The use of spiral wound membranes for nanofiltration (NF) and reverse osmosis (RO) is often hampered by biofouling which leads to operational problems such as an increase in normalized pressure drop (NPD) and a decrease in production rate (Ridgway and Safarik, 1991). Biofouling can be limited by pretreatment of the feed water of the membrane installation, but this approach increases the total investment cost of the water treatment process. Another option is to use periodical cleaning in place (CIP) for biofouling control, in which the negative effects of biofouling are (temporarily) reversed. For a cost-effective application of membrane filtration in practice, extensive knowledge is required of the influence of cleaning methods on biomass removal. Partly due to the complexity of biofouling the determination of the optimal CIP strategy is based on "trial and error". Furthermore, data from scientific literature in many cases gives incomplete information about the interactions between the feed water quality, the type of membrane, the resulting type of membrane fouling, the cleaning method and the effect of membrane cleaning on the membrane process. An important step in elucidating the effect of membrane cleaning processes is to develop a protocol for a systematic analysis. Two approaches can be followed for evaluating the effects of a cleaning procedure: the use of operational parameters (Graham et al, 1989); and, the application of a test procedure under standardized conditions in the laboratory or in a pilot set up (Whittaker et al, 1981). Indications of effective cleaning procedures for biofouling control were obtained from a systematic approach to evaluate CIP procedures from both literature and full-scale membrane plant experience. In some cases, biofouling was effectively controlled with mixtures of complexing agents, surface active components and denaturating agents. Apart from this, the effect of a hydraulic action, e.g. by using air-water flushing, proved to be very promising in biofouling control (Cornelissen et al, 2007). The biomass removal efficacy of the air-water flushing strategy was verified with a newly developed laboratory test procedure and described in this paper. Includes 6 references, figures.