Effects of ultrafiltration membrane surface properties on Pseudomonas aeruginosa biofilm initiation for the purpose of reducing biofouling

Abstract

Biofilm fouling is one of the major obstacles hindering the use of membranes in water processing systems. There are a series of events that take place during biofilm formation, one of the most interesting and important issues of biofouling is the initial attachment of microorganisms to the surface. Therefore, effects that surface properties have on biofilm fouling are important to attachment and were examined. Hydrophobicity, surface charge and roughness were measured for several polymeric surfaces of interest in water processing membrane systems. These surfaces were then subjected to conditioning layer formation and biofilm fouling, both of which were quantified. The results show that biofilm initiation by a strain of Pseudomonas aeruginosa increases as the surface becomes more rough and more hydrophobic, while fouling is minimal when surface charge is minimized and increases with increasing charge, whether positive or negative.

Introduction

Biofilm fouling is a persistent problem for almost any water-based application. Biofilms foul ship hulls, clog water lines, reduce heat transfer in heat exchangers, infect medical implants and cause numerous other problems in water processing systems [1], [2], [3]. One of the most problematic industrial biofilm formations is the fouling of membranes. This is due to the active transport of bacteria (cause by the tangential force of the membrane flux) to the membrane surface causing biofilm formation, reducing the flux of water through the membrane [4], [5], [6]. Even a small amount of fouling can cause significant loss of flux.

The attachment of bacterial cells to the surface of the membrane is the critical first step of biofilm fouling. There are many factors affecting cellular attachment, but one of the most important is the surface property of the material. These factors affect the speed and strength of any attachment [1], [7], [8], [9]. This study, therefore, focused on the effects that surface properties have on bacterial biofilm formation.

The pH and dissolved chemically active compounds can affect the chemistry of some surfaces. Most conventional membrane materials are relatively non-reactive, so the adsorption of chemicals to the surface is responsible for most of the changes in surface properties. This adsorption is referred to as conditioning layer formation in the study of biofilm formation [9], [10], [11].

This study measured the three surface properties most closely linked to biofilm fouling, and correlated them with the adsorption of conditioning layer chemicals and the initial coverage of bacteria on the surface. Thus, hydrophobicity, surface charge and roughness, properties were measured and have all been associated with biofilm fouling [1], [12], [13], [14]. These direct quantitative measurements of surface properties in combination with measurements of conditioning layer formation and biofilm fouling area provide important direct correlations and mechanistic insights into biofilm fouling, particularly the early stages where the surface properties control biofilm formation. Measurements on some 30 samples materials confirmed that hydrophilic, electrically neutral, smooth surfaces are the least susceptible to biofilm fouling.