Dynamics of biofilms on different polymeric membranes – A comparative study using five physiologically and genetically distinct bacteria

Abstract

Biofilm formation potential of anaerobic microbes on polymeric membranes is widely acknowledged but barely investigated. In this study, the biofilm dynamics of five bacterial isolates from anaerobic sludge, against eight different polymeric membranes, was systematically characterized via scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM). Fibrous surfaces, i.e., polytetrafluoroethylene, polypropylene and polyvinyl chloride were more favorable for biofilms than the leveled porous substratum. Cellulose-based membranes, especially cellulose nitrate, and cellulose acetate-cellulose nitrate, with a relatively hydrophilic surface showed the highest resistance to biofilms among all membranes. The growth stage played a vital role in biofilm formation, as differences in biofilms of the same strain, in terms of biofilm volumes, thickness and surface coverage, across 8 different substrata, were only observed for mature biofilms. While for early-stage biofilms, the same biomass volume was developed regardless of substratum. This was largely attributed to the interactions between substrata and extracellular polymeric substances (EPS), which was not a prerequisite for initial bacterial adhesion but crucial for cell cohesion in mature biofilms, and thus deciding the morphology and thickness of mature biofilms. These findings highlight that quenching EPS production and diminishing EPS-substratum interaction are the optimum fouling control strategies in membrane-based water treatment systems.