Correlation between local TMP distribution and bio-cake porosity on the membrane in a submerged MBR

In a submerged membrane bioreactor (SMBR) the spatial distribution of bio-cake porosity on the membrane module is very important in the detection of local membrane biofouling, which is directly related to efficient membrane-cleaning and energy consumption. In this study, the local bio-cake porosity was determined experimentally and correlated with the local flux measured by a newly developed experimental method. This exercise made it possible to suggest the optimum position of an aerator in the reactor to obtain minimal membrane biofouling. The local transmembrane pressure (TMP) on the membrane module became bigger and bigger as the distance from the local position to the suction pump became nearer and nearer owing to the pressure drop inside the hollow fiber lumen. A good correlation was found between the local TMP distribution and the local porosity of bio-cake formed on the membrane surface which was measured by a confocal laser scanning microscope (CLSM) and image analysis technique. The bio-cake formed on a local position of the membrane near the suction pump was more easily compressed by higher TMP, and thus its porosity became lower. From this local porosity distribution on the membrane the effect of aerator positions on the membrane biofouling was studied. Under identical mixing intensity, the positioning of a diffused aerator near the suction pump was the most effective location for the alleviation of the membrane fouling because the porosity of bio-cake at that location was the smallest, and thus the worst biofouling took place.