Biofouling assessment using an infrared monitor.

The paper details the design of an infrared monitor for detecting biofilm accumulation on surfaces in flowing systems. It is based on the principle that the amount of infrared radiation absorbed by a biofilm, is proportional to the amount of biofilm present. The test surface in the monitor has to be transparent in order to allow the passage of the radiation, so that the radiation absorbed is solely due to the presence of the biofilm. Since the biofilm structure is very dependent upon the conditions under which it was formed, e.g. fluid flow, nutrient and cell concentrations and temperature, it cannot be made to give absolute values of biofilm accumulation. Nevertheless the device is extremely useful for comparison purposes, such as the evaluation of biocide efficacy under different operating conditions. Correlations of biofilm thickness with infrared absorbance can be made, however, for specified operating conditions. The value of the monitor is demonstrated in some typical examples. The infrared absorbance shows a clear distinction between the accumulation of biofilm under two different velocity regimes, three pH values and three chlorine concentrations at two water velocities. It is suggested that in addition to laboratory use, the monitor could be used effectively for biofilm control in cooling water circuits.