Biofilm Formation on Polymeric Heat Transfer Surfaces

The biofouling affinity on different polymeric surfaces (PP, PSU, PET, PEEK) in comparison with SS 1.4301 was studied using the model bacterium E.coli K12 DSM 498. A test rig with seven identical chambers allowed investigations at different system conditions (throughputs, inclination of the heat transfer cell, etc.). The biofilm mass deposited on the polymer surfaces was several magnitudes smaller compared to stainless steel. The cell counts on the polymer surfaces had an opposing trend compared to the deposited biomass. The promising low biofilm formation on the polymers was attributed to the combination of their surface properties (roughness and surface free energy) when compared to SS. INTRODUCTION River water is frequently used for cooling in industrial processes. The resulting moderate temperatures in parts of tubing, heat exchangers and cooling towers enhance biofouling. Especially in developing and third-world countries insufficient waste water treatment and warm climate conditions lead to an increased microbiological load in streaming water. The formed biofilms affect technical surfaces through inherent metabolic processes, reduce heat transfer and increase the required pump capacity by increasing friction and decreasing the tube diameter. Heat exchanger oversizing, heat losses and increased maintenance costs are common fouling related costs (Steinhagen et al., 1993). Several studies related to biofouling can be found in literature (Dreszer et al., 2014, Teodósio et al., 2011 and Teughels et al., 2006) but data in respect to polymeric based heat exchangers are scarce in respect to their biofouling affinity. The choice of polymeric films is strongly connected to bacterial adhesion properties and the ability to withstand corrosion induced by inherent metabolic processes in the biofilm matrix. An investigation of biofilm formation is given for different surfaces varying in composition, roughness and free surface energy. EXPERIMENTAL Surface Characterization In order to understand the processes taking place at the bacterial-substrate interface, two essential parameters of the used substrates were analyzed as are topology and free surface energy. The roughness profiles and respective roughness parameters were carried out according to DIN EN ISO 4287 via tactile scanning method. As decisive roughness parameters, the mean arithmetic roughness Ra and the root mean square roughness Rq were used.