Spatial Distribution of Extracellular Polymeric Substances in Biofilms

This study investigated the spatial distribution of biofilm extracellular polymeric substances (EPS) with depth in biofilms. Heterotrophic biofilms were grown in a rotating drum biofilm reactor fed with synthetic wastewater with a COD of 150 mg/L. Biofilm was found to be heterogeneously structured, represented not only by the spatial distribution of EPS yields but also by clearly defined aerobic/anoxic zones, increased density, decreased porosity, decreased soluble COD concentrations, and decreased viable biomass concentrations along the biofilm depth. Thicker biofilms exhibited greater soluble COD concentrations, EPS yields, and viable biomass than thinner biofilms. The net EPS yields in the biofilms are proportionally related to the amount of viable biomass present, and viable biomass loses its ability to produce EPS at the deeper sections because of its lower microbial activity resulting from lower nutrient availability. Also, it is possible that the naturally produced EPS was consumed as a substrate in the deeper layers, where more readily degradable organics were absent. The results of the spatial distribution of EPS yields gained in this paper provide helpful information to achieve a more complete description of heterogeneous biofilm structure. New biofilm models need to be developed to incorporate the EPS information to accurately reflect the heterogeneity of biofilms.