Quantitative relationships for the impact of gas sparging conditions on membrane fouling in anaerobic membrane bioreactor

Abstract

Biogas sparging is one of the most commonly used strategies for membrane fouling control in anaerobic membrane bioreactors (AnMBR). However, as a cost-effective sparging pattern, high/low alternate sparging mode was seldom studied, not to mention at a quantitative level. In this study, we systematically assessed the impacts of various parameters of gas sparging (intensity, duration and interval/frequency) on membrane fouling characteristics, on the basis of orthogonal tests coupled with statistical analysis of variance and covariance. The specific gas demand in the high-intensity phase (SGDH) was identified as the key factor impacting the overall fouling rate and stagewise rate constants (Kp’ and Kc’ for pore blocking and cake layer stages respectively) with negative correlation. The product of SGDH and time, i.e. the accumulative gas amount in the high-intensity phase (QH), was identified as the key factor affecting foulant layer reversibility (η) and specific resistance (α), with logarithmic models established in terms of log QH versus log η and log α. The validity and robustness of the quantitative models with definite physical meaning were evaluated via Monte Carlo simulation of the regression. The underlying mechanisms were explained from the perspective that hydrodynamic conditions influence mixed liquor and foulant properties (particle size distribution, microbial products amount and component) and, hence, affect fouling rates and foulant layer properties, with a panorama of the interrelated factors and properties delineated by multivariate analysis. This study is expected to provide a quantitative basis for the design of gas sparging conditions, under which sustainable operation of AnMBR could be achieved with the lowest energy consumption.