Improving energy efficiency and fouling mitigation for membrane bioreactor in Al-Rustamiyah sewage treatment plant based on hydrodynamics

Abstract

In Al-Rustamiyah sewage treatment plant in the east of Baghdad city, capital of Iraq, the membrane bioreactor suffering from a severe biofouling problem. The main reason for this problem is inefficient and inadequate aeration process. The objective of this work is to control fouling and to improve the energy efficiency of the submerged membrane bioreactor. Fouling control is achieved by optimizing the two-phase hydrodynamic parameters (air bubble diameter and shear stress), while energy efficiency improved through analysis of flow field. An experimental rig similar to real plant was built, and several operating and design parameters were experimentally tested. The parameters were air flow rate (1–9 L/min), membrane sheets spacing (3, 5, and 7 mm), and air diffuser design (pipe diffuser and disk diffuser). The bubble sizes were measured experimentally using high-speed camera. It was found that larger bubbles were produced at narrow channels between the membrane sheets. Optimization using computational fluid dynamic with ANSYS FLUENT was employed; the results showed that a bubble diameter of 2.5 mm had a slug flow pattern, resulting in better energy saving for a 3 mm space between membrane sheets with a 5 L/min air flow, while maximum shear stress obtained was (4 Pa). Nutrients removal results from synthetic sewage were 97.32, 79.68, and 13% for COD, NH3–N, and PO 4 −3 , respectively, at 6 days retention time. The results obtained are quite significant in practice because it contributes to improve the efficiency of membrane bioreactor in Al-Rustamiyah sewage treatment plant.