Submerged osmotic processes: Design and operation of hollow fiber forward osmosis modules

Abstract

Submerged forward osmosis (FO) is of high interest to treat and concentrate complex streams where cross flow module suffers from limitations such as breakage of fragile compounds, viscosity issue or fouling and clogging limitations. In this study, submerged hollow fiber FO (Sub-HFFO) modules were designed using commercial HFFO membranes. Then, modules were validated, compared to commercial HFFO cross flow module, and tested in different operational conditions (draw concentration and type, feed concentration and feed tank scouring). Finally, fouling tests were performed using model foulants. Designed Sub-HFFO modules featured similar performances than commercial cross flow modules. It was demonstrated that draw circulation in Sub-HFFO can be done in pulsing mode without mass-transfer limitation due to the homogeneous flow distribution and self-supporting of the membranes, in opposition to Sub-FO plate and frame design. This study also confirmed that providing mixing near the membrane surface in the feed tank is a key factor to mitigate not only fouling but also external concentration polarization (ECP) limitation. Air scouring and recirculation tank proved to be efficient towards more sustainable operation; full recovery of initial flux after fouling was achieved thanks to osmotic backwashing cleaning.