Engineering design approaches for minimum fouling in submerged MBR

A contributor to success in managing membrane operations is to be able to identify suitable engineering design approaches to slow down the membrane fouling rate. Two such approaches were discussed in this study, namely: (1) off- site chemical and mechanical cleaning, and (2) air scouring. A longer subsequent operation time was observed after a membrane was cleaned chemically compared with mechanically. For air scouring during membrane operation, the investigation aimed at determining the crossflow velocity induced by coarse and fine bubble diffusers. Higher crossflow velocities were obtained with the latter. Uniformly distributed fine air bubbling might possibly have caused less uplift resistance and induced higher crossflow velocities. Such air scouring, at critical aeration intensity, was able to prolong the membrane operation for up to 8 months without needing chemical or mechanical cleaning.

Two design aspects, off-site cleaning and air scouring, in a submerged membrane bioreactor process and their influence on membrane fouling were investigated. The following conclusions were derived from the experimental results. 1. Off-site chemical cleaning was effective in restoring subsequent membrane performance between cleanings. While mechanical cleaning could only remove the slime layer, the use of 0.05% NaOCl probably aided in the removal of foulants deposited within the membrane or strongly on the membrane surfaces. 2. The air scouring effect was able to prolong the membrane operational lifespan by dislodging foulants from the membrane surface. Fine bubbles at critical aeration intensity induced optimum crossflow velocities, thereby creating stronger shearing effects compared to coarse bubbles.