Analyses of Rate Data for Biofilm Studies

Data for the biodegradation of glucose and sodium benzoate in aerobic biofilms are analysed using different procedures. It was found that plots of the percentage substrate removal versus some measure of the applied substrate loading gave no insight into the processes which were occurring. In contrast, plots of mean mass flux versus some measure of the applied substrate loading were much more revealing. The results demonstrate why these plots are especially appropriate for studies of mixed substrates. The results of the studies also illustrate why quantities derived by computer matching procedures should be regarded with caution. The biodegradation of both glucose and benzoate followed zero-order kinetics. Internally consistent values were derived for the zero order rate constants using different independently prepared acclimatised bioslimes. However, intercomparisons with corresponding values from well regarded literature studies revealed differences of more than an order of magnitude between different authors. The increasing emphasis on the application of computational procedures to design indicates that efforts to produce greater consistency in the tabulated values for substrate removal rates would be a worthwhile research priority. Studies of the effect of shear on biofilm packing structures coupled with removal rate measurements, and measurements of true aerobic depth may be worthwhile.