Full scale comparison of heterotrophic and nitrifying RBC biofilms

Heterotrophic and nitrifying biofilms, from the secondary and tertiary full-scale Rotating Biological Contactor (RBC) wastewater treatment plants (WWTP) were investigated. Physical properties and structural features, such as, water content, organic portion (VS/TS), density, thickness, porosity, and fractal characteristics, including boundary/surface roughness, and Sierpinski and internal pore boundary fractals were examined. The results indicated that the heterotrophic biofilms were thicker and had higher porosity, larger internal voids, and faster growth and sloughing rates than the nitrifying biofilms. The nitrifying biofilms had much higher density(TS) and VS/TS ratio than the heterotrophic biofilms. In contrast to earlier results from laboratory scale studies, full-scale biofilms had structures and properties (porosity, density, and fractal dimensions) of more irregular spatial distribution.