Membrane bioreactor (MBR) technology is an integration of biological treatment and membrane filtration into a single process, in which microorganisms are responsible for organic and nitrogen removal, while membranes capture biomass and suspended solids physically from the mixed liquor. The MBR process utilizes microfiltration (MF) or ultra filtration (UF) technology ranging from 0.05 to 0.4 µm to enable complete retention of bacterial flocs and suspended solids. MF membranes are responsible for removing suspended solids, algae, protozoa, and bacteria, while UF membranes can additionally retain small colloids and viruses.
There are two main MBR process configurations: submerged or immersed (iMBR), and side stream (sMBR), iMBRs are generally less energy intensive than sMBRs, as implementing membrane modules in a pumped side stream cross flow significantly increases energy demand due to high pressures and volumetric flows imposed. sMBRs typically operate at higher flux and hence tend to experience higher fouling propensity (i.e., lower permeability) than iMBRs. As such, the current trend in MBR design encourages submerged over side stream configurations.
The configuration of membrane plays a crucial role in determining the process performance. There are mainly three types of membrane configurations that are being used in MBR technologies: 1) plate-and-frame/flat sheet (FS), 2) hollow fiber (HF), and 3) multi tubular (MT). In FS membranes, the fluid flows from the membrane’s coated side towards the permeate side. In MT module, fluid flows from inside towards outside the tube (lumen to shell-side), whereas in HF configuration fluid flows from outside towards inside (shell to lumen-side).