Aeration pipe design for free bubbling hydrodynamic optimization of flat sheet MBRs

Abstract

An open-end aerator for free bubbling has been found previously for hydrodynamic effect enhancement. This study is focused, through two modifications, on its further optimization for aeration homogeneity in a commercial flat sheet membrane bioreactor (FSMBR). One relates to the aerators themselves, the other to the central aeration air supply pipe. The aerators are tapered, or to be more precise each one is a frustum i.e. that portion of cone which remains after the upper part has been cut off by a plane parallel to its base. A validated computational fluid dynamics (CFD) model is constructed, hydrodynamic features were predicted for various implementations of the new design. An extensive study found that to achieve a very high degree of uniformity between different aerators for a full-scale FSMBR (160 sheets), the optimal design featured frustum-designed aerators of length 180 mm with the diameter decreasing from 18 to 9 mm at the open end. Each aerator had four top nozzles of diameter 4 mm, and 20 aerators were attached to a pipe of 1760 mm. Based upon this aerator design, the central aeration pipe diameter was optimized, the shear stress was enhanced and corresponding number of effective channel coverage was enhanced by 25–75%.