Surface analysis for the identification of effective strategies to fight marine biofouling

Abstract

ABSTRACT Biofouling tremendously reduces performance of polymer membranes in desalination. The underlying processes involve multiple organisms and there is no complete picture of the involved interactions yet. Defined and reproducible testing strategies are therefore critically important in the successful development of effective cleaner systems. To address this need, we have introduced a two-stage approach to mimic the initial fouling process on membrane surfaces in contact with seawater. Based on thin films of membrane polymers, we established: (i) a molecular fouling model layer containing proteins, humic acids, and polysaccharidic substances and (ii) a bacterial layer of the marine micro-organism Cobetia marina. With our developed approach, we were able to quantify selectively both the stability of preadsorbed biomolecules and of attached micro-organisms and the extracellular polymeric substances (EPS) they secrete. Surface sensitive techniques including ellipsometry and various microscopy techniques (scanning electron microscopy, atomic force microscopy [AFM], and confocal laser scanning microscopy) were applied. Biofilm quantification and dissection of the different contributions of bacteria and matrix (EPS) to the film formation was achieved by fluorescence staining followed microscopic or spectroscopic analysis. After application of various cleaning agents, their efficiency to remove the fouling layer could be independently determined for both cellular and matrix components via a spectrofluorometeric plate reader technique, while high-resolution AFM studies revealed details on their cleaning mechanism. Exploiting this set of analytical methods, a combination of surfactant and protease could be identified as effective cleaning mixture that removed both bacterial cells and EPS under mild conditions. Conclusively, together with the advanced techniques for characterization, the established bacterial fouling layer could serve as a model system to screen for effective antifouling and cleaning strategies.