A METHOD FOR DESCRIBING BIOFILM SURFACE-ROUGHNESS USING GEOSTATISTICAL TECHNIQUES

Biofilm reactors, such as rotating biological contactors (RBCs) and tr ickling filters, have been used to treat both municipal and industrial waste streams. One fundamental property of biofilms which may affect their performance is surface roughness, or the magnitude of variabilit y in height over the structure's profile. This property has an effect on the rate of diffusion of nutrients into the biofilm for degradation through its influence on the thickness of the concentration boundary layer. The method presented here to quantify the surface characteristi cs of a biofilm involves the in situ analysis of biofilm surface profi le data collected at discrete points. For each point, a microprobe is lowered from some datum above the surface, and the distance down to th e biofilm surface is measured at that point. Statistical analysis perf ormed on the data set produces the correlation coefficient between hei ghts on the biofilm surface at various separation intervals. A graph r elating the correlation coefficient to the separation interval between heights is constructed from many points to determine tie length over which points with low correlation can be collected. A set of nearly in dependent height data collected at that length interval is then analyz ed for mean and standard deviation. The resulting statistics are chara cteristic of the magnitude of the variability between independent heig hts on the surface profile, and can be used to compare and contrast th e roughness of biofilm surfaces. This method was used to define the ro ughness of artificial and real biofilm surfaces. Artificial biofilms, which were made from agar roughed with sand paper of varying grit size , were found to have distinct and consistent roughness, as determined by this method. It was useful to compare the standard deviation (rough ness) of real biofilms to these values, because the roughness of sand paper is easily observable, and standardized.