Effective membrane backwash with carbon dioxide under severe fouling and operation conditions

Abstract

Membrane fouling is an intrinsic deficiency common for all membrane processes. Fouling mitigation is therefore required to achieve sustainable membrane performance. Our study suggests a novel backwash concept which utilizes network of ultrafiltration interconnected membrane pores as a substrate for CO2 bubbles nucleation from a saturated CO2 solution which enters membrane pores from the support side. As a result, enhanced fouling removal was achieved due to additional hydrodynamic forces caused by expanded and lifted CO2 bubbles. An investigation of CO2 nucleation kinetics using a high speed camera revealed that initial CO2 nucleation rate is strongly determined by the module height and feed water type. A saturated CO2 solution backwash effectively removed bovine serum albumin (BSA) which caused both internal and external membrane fouling. A fouling reduction was also observed in BSA/seawater matrix opposite to cake layer buildup observed experiments with Milli-Q backwash. CO2 nucleation allowed to remove hydraulically irreversible fouling which was caused by transparent exopolymer particles (TEP) at pH 4 and 8. This is a promising result as TEP is biofouling precursor which tends to adsorb to a membrane surface making conventional cleaning practices inefficient. Complete transmembrane pressure recovery was achieved with a feed water containing sodium alginate and SiO2 nanoparticles with sizes compatible with membrane pores. The observed results emphasized the importance of the specific interactions in membrane/foulant/CO2 bubble triangle for a successful membrane recovery.