(125a) Mechanisms And Control Of Biological Fouling Of Microfiltration Membranes

The first part of this presentation will focus on the initial stages of convection-dominated deposition of bacteria on microfiltration membranes. It will be demonstrated that before bacteria secrete extracellular polymeric substances (EPS) and before cake formation, fouling is quantitatively explained by the phenomenon of intermediate blocking. Next, the simultaneous effects of cake growth and compression was investigated by performing constant flux experiments. New blocking laws for compressible cake filtration were derived and verified experimentally using Brevundimonas diminuta and Serratia marcescens.

Finally, a 2:1 molar ratio preparation of bismuth with a lipophilic dithiol (3-dimercapto-1-propanol, BAL) significantly reduced EPS expression by B. diminuta in suspended cultures at levels just below the minimum inhibitory concentration (MIC). Total polysaccharides and proteins secreted by B. diminuta decreased by approximately 95% over a 5-day period when exposed to the bismuth-BAL chelate (BisBAL) at near MIC (12 uM). Fourier-transform infrared spectroscopy (FTIR) suggested that a possible mechanism of biofilm disruption by BisBAL is the inhibition of carbohydrate O acetylation. FTIR also revealed extensive homology between EPS samples with and without BisBAL treatment, with proteins, polysaccharides, and peptides varying predominantly only in the amount expressed. EPS secretion decreased following BisBAL treatment as verified by atomic force microscopy and scanning electron microscopy. Without BisBAL treatment, a slime-like EPS matrix by B. diminuta resulted in biofouling and inefficient hydrodynamic backwashing of microfiltration membranes. The undesirable role of EPS in establishing biofilms and biological fouling of microfilters commonly employed for environmental and biotechnological separations were thus confirmed.