The effect of various high-frequency powerful vibration (HFPV) types on fouling control of hollow fiber membrane elements in a small pilot-scale SMBR system

Abstract

During the last decade in Europe, membrane bioreactor (MBR) systems have been proven to be a very efficient technique for municipal and industrial wastewater treatment (WWT). The most obvious appeal of the MBR technology is that it produces a stable and excellent effluent quality and eliminates the need for good sludge settleability, as it is one of the basic requirements in conventional WWT plants. Due to both the compact footprint and the great potential for automation, MBR plants ensure precise control of the sludge residence time and the mixed liquor suspended solids, which are basic operating parameters. The above results in: (a) the reduction of the required reactor size, (b) the promotion of the evolution of specific nitrifying bacteria, and finally, (c) the production of less sludge. However, the effluent rate of MBRs is limited, mainly because of the membrane fouling effect. Membrane fouling is probably the most critical problem of the submerged membrane bioreactors (SMBRs), and the applied techniques to avoid this problem have as a drawback the high energy that is needed and finally the production of chemical wastes. A lot of lab studies have been published concerning the impact of mechanical action on the removal of foulants from the membranes (e.g. vibration, buck-pulse, and ultrasound). The scope of this study is to examine the feasibility of high-frequency powerful vibration (HFPV) technique, as an alternative cleaning method, applied on fouled membrane elements in a continuous operated small pilot-scale SMBR unit, treating a novel synthetic wastewater (SWW). In this work, the implementation of various HFPV types (using commercial pneumatic vibrators) on identical, parallel hollow fiber (HF) fouled membranes, showed the following: (a) a repetitive pattern for transmembrane pressure and flux values vs. time; (b) the ability to select the proper vibration type according to the fouling extend on membranes; (c) the efficiency of this technique on membrane cleaning, in a membrane module system. After HFPV implementation, this system tends to have similar behavior with that of using new membrane modules. The HFPV technique seems to be very promising with respect to energy savings, compared to conventional air cleaning systems in SMBRs because it contributes to a low air-scouring operation due to the periodic and proper HFPV implementation. Moreover, this technique copes with the handling of membrane fouling in SMBRs units, using continuous MBR operating mode.