Potential and challenges of osmotic membrane bioreactor (OMBR) for (potable) water reuse: A pilot scale study

Abstract

Recently, forward osmosis (FO) has been applied to the context of membrane bioreactor (MBR) and is called osmotic MBR (OMBR). This promising process relying on a dense FO membrane and osmotic gradient demonstrated higher rejections of all contaminants and lower fouling propensity than for MBR. The concept that we developed aims at (partially) retrofit existing MBR into OMBR. In addition to the use of existing MBR installation, such process also allows for combined operation of MBR and OMBR to avoid salinity build-up and to be flexible/reversible in term of operation in MBR/OMBR modes to fit with (seasonal) water quality needs. The study presented aimed at validating the proof of concept of such retrofitting which includes also the development of OMBR/FO module with similar performance than MBR/UF ones. As such, OMBR plate were designed based on Kubota MF cartridge 203 design and using new generation of thin film composite FO membrane. Then, pilot tests were conducted using a 50L MBR/OMBR pilot for two months. Stable operation was obtained in terms of depuration efficiency and water flux. Salinity build up occurred in the reactor, but conductivity was maintained below 3 mS.cm-1 thanks to the salt purge via the MBR permeate. Fouling was observed both for MBR and OMBR operation; however, for OMBR, osmotic backwash every 3 days allowed for complete removal of the fouling layer. Finally, 90% rejection of all pharmaceuticals compounds tested was observed in OMBR operation as a result of combined biological degradation and high rejection of FO membranes.