LAUSR

Abstract In this study, the effect of bubbly flow on the performance of water flux of forward osmosis (FO) membranes was investigated, in terms of membrane biofouling causing by treating wastewater under a lower flow rate operation (cross flow velocity = 0.04 m/s) in feed channel. It was found that water flux exhibited a better performance through bubbly flow (aeration rate = 0.4 L/min) in the feed channel compared to that under single-phase flow. After a 20-circle operation, the period of time required for collecting a total of 7000 ml water under bubbly flow condition was approximately half (17 d) of that under single-phase flow (36 d). Water flux dropped from 11.0 to 4.5 LMH with the presence of air bubbles, and to 2.0 LMH in the absence of air bubbles in the feed channel. In addition, it was found that the biofilm under bubbly flow condition was more homogeneous than that under single-phase flow. This finding has suggested that shear stress created by the bubbly flow has affected total biomass loading. Analysis of the characteristics of the fouling layer indicated that the fouling layer was composed of bacterial cells surrounded by scaling-like foulant, protein, polysaccharide, humic-like substances and inorganic particulates. The biofilms exhibited the dissimilarity of certain bacterial populations in the absence and presence of air bubbles. Larger molecular weight humic-like substances and inorganic particulates were present in the biofilm under single-phase flow condition. Results from this work indicated that bubbly flow condition within the feed channel can lead to intense tangential flow and uniform shear stress distribution on the vicinity of the membrane surface, and reduce the accumulation of biofoulants with higher molecular weight.