Development of combined fouling model in a membrane bioreactor

Membrane bioreactor (MBR) system has recently become very important in wastewater treatment. However, membrane capacity during the filtration process is reduced by fouling, which is the deposition or adsorption of particles on the membrane surface or inside of the pores. For an efficient operation of MBR system, prediction of MBR fouling progress and determination of proper membrane chemical cleaning interval is necessary. Until now, four blocking models, which are complete blocking, intermediate blocking, cake filtration, and standard blocking, have typically been used to describe and predict the MBR fouling. In this study, a new combined membrane fouling model, based on the four constant flowrate blocking models, is developed to explain the combined effects of the different fouling mechanisms. This model is assumed to be more accurate in determining the chemical cleaning interval by considering variation of dominant fouling mechanisms in the filtration process. The combined fouling model is applied to data sets from a pilot-scale MBR for monitoring the variations of dominant fouling stage. By checking temporal variations of root mean square error (RMSE) values from fitting trans-membrane pressure data to four constant flowrate blocking models, the dominant fouling mechanism by each fouling stage is determined. In particular, the fouling prediction result by the new combined model of three fouling mechanisms, which are complete blocking, cake filtration, and intermediate blocking, excluding the standard blocking model has better predictive accuracy than the combined model of four mechanisms, which remarkably reduced the RMSE from 10.48 to 1.73. On the basis of the improvement, the new combined model with three mechanisms has the potential to predict MBR fouling process and to determine the optimum interval for membrane chemical cleaning. Our results would contribute the economic operation of MBR plants by suggesting the appropriate membrane cleaning interval with the filtration capacity maintained at optimal level. (C) 2011 Curtin University of Technology and John Wiley & Sons, Ltd.