The effect of different surface conditioning layers on bacterial adhesion on reverse osmosis membranes

Reverse osmosis (RO) biofouling is a problem of biofilm development which is initiated by bacterial attachment to the membrane surface following the surface conditioning. In this study, the impact of the initial fouling layers on bacterial attachment was investigated. Both model foulants and MBR permeate water were used to simulate conditioning layers on RO membranes by performing fouling experiments at constant flux and crossflow velocity. Analysis of the properties of different conditioning layers included zeta potential, contact angle, roughness, and adhesive force. Results in this study show that the bacterial attachment was greater on pre-conditioned surfaces and the load of attached bacteria was closely correlated to the change of adhesive force rather than to the change of zeta potential and hydrophilicity. Additionally, the amount of the pre-conditioning layer also influenced the bacterial attachment. Differences in surface roughness were found to be unimportant. To examine the effect of pretreatment bacterial attachment tests were performed on a secondary effluent filtered by microfiltration or ultrafiltration. The UF pretreatment showed significantly less attachment. Results in this study confirm the role of the initial conditioning layer and highlight which surface characteristics of the conditioning layer are the most important for the initial bacterial attachment. © 2016 Elsevier B.V. All rights reserved.

This study focused on the impact of conditioning layers on the initial bacterial attachment on RO membranes. Biopolymers (polysaccharides and proteins) were found to be the main constituents in the conditioning layer formed from an MBR-permeate. Further experiments using model foulants also confirmed the findings that there is significantly more bacterial attachment on conditioned membrane surfaces. From various surface analyses, the adhesive force as measured by AFM was found to be a critical indicator of the amount of initial bacterial attachment onto RO membranes. Greater bacterial attachment was observed with increase in the amount of foulant load i.e. increase in the coverage of the conditioning layer on the membrane surface as shown by the CLSM images. Fouling control studies comparing MF and UF showed that the UF pretreatment was much more able to reduce the amount of high molecular weight biopolymers in the feed water which subsequently reduced the bacterial attachment. Acknowledgments This work is a collaborative effort between the Toray Singapore Water Research Centre (TSWRC) and the Singapore Membrane Technology Centre (SMTC) of Nanyang Technological University. SMTC is supported by Economic Development Board of Singapore.