Off-line chemical cleaning reduces the spatial heterogeneity of membrane fouling in full-scale membrane bioreactors: A case study

Abstract

Full-scale membrane bioreactors (MBRs) are widely employed for wastewater treatment. Nevertheless, the spatial heterogeneity of membrane fouling within full-scale MBR modules has received limited attention, especially regarding the impact of off-line chemical cleaning on this spatial heterogeneity. This study, based on 192 hollow fiber samples collected from two full-scale MBRs, investigated the spatial fouling heterogeneity before and after off-line chemical cleaning. The membrane samples were categorized into different groups based on sampling locations, and statistical tools were employed to analyze spatial fouling heterogeneity. The results of foulant mass and filtration resistance of samples confirmed the presence of spatial fouling heterogeneity within the MBR modules after 5 months of operation. The off-line chemical cleaning removed organic foulants more effectively than inorganic foulants, and interestingly, it effectively reduced the spatial fouling heterogeneity. Computational fluid dynamics analysis in the cleaning tank and the chlorine concentration distribution indicated that chemical cleaning occurred without mass transfer or reaction limitations. We further offer insights into the reduction of spatial fouling heterogeneity by clarifying the fouling layer structure and the role of off-line chemical cleaning. Our findings suggest that with an appropriate cleaning strategy, the hollow fiber filtration performance can be rebalanced before a new operation cycle.