Every community produces both liquid and solids waste and air emissions. Wastewater collected from municipalities and communities ought to be ultimately returned to receiving waters, land, or potentially reused. Wastewater contains numerous pathogenic microorganisms that dwell in the human intestinal tract. Other contaminants include biodegradable organics (measured as biochemical oxygen demand “BOD” and Chemical oxygen demand “COD”) which can lead to depletion of natural oxygen resources, nutrients (such as nitrogen and phosphorous) which can stimulate the growth of undesirable aquatic life, and may contain toxic compounds that may be mutagenic or carcinogenic. For the aforementioned reasons, the immediate removal of wastewater from its source of generation, followed by treatment, reuse, or disposal into environment is necessary to protect public health and the environment.
Membrane Bioreactor Technology
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 ultrafiltration (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 sidestream (sMBR). iMBRs are generally less energy intensive than sMBRs, as implementing membrane modules in a pumped sidestream crossflow 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 sidestream 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).