Micro-patterned PVDF membranes and magnetically induced membrane vibration system for efficient membrane bioreactor operation

Abstract

Polyvinylidene difluoride (PVDF) based membranes have been used extensively for wastewater treatment due to their chemical and mechanical stability. However, membrane fouling remains a critical factor limiting the widespread use of membrane processes. To mitigate membrane fouling, patterned PVDF membranes were prepared via spray-modified non-solvent induced phase separation (s-NIPS) which resulted in membranes with large pattern heights of 750 ± 100 μm. Patterned membrane modules were then subjected to magnetically induced membrane vibration (MMV) applied perpendicular to the direction of the pattern to reduce the foulant deposition and delay the irreversible fouling in a submerged membrane bioreactor (MBR). Mere patterning resulted in a 70–300% decrease in membrane fouling rate and a doubled critical flux as compared to the flat counterpart. The introduction of membrane vibration further improved the membrane anti-fouling potential by prevention of foulant deposition through improved hydrodynamic conditions near the membrane surface and efficient removal of foulant deposition. Introducing an axial vibration of 5 Hz frequency dropped the fouling rate by an additional 40–60% and the critical flux for irreversible fouling was almost tripled from 15 L m−2 h−1 for the flat, non-vibrating membrane to 40 L m−2 h−1 for the s-NIPS patterned, vibrating membrane. A computational fluid dynamics (CFD) simulation with mesh motion at the patterned membrane interface confirmed the formation of vortices due to vibration, which are convected away from the membrane surface. The CFD results provided a sound basis for understanding the effect of membrane topography combined with vibration. These results suggest reduced fouling without the need for intense air scouring or frequent cleaning which can result in energy- and cost-effective filtration during MBR operation.