| Two types of the RBC biofilms, namely heterotrophic and nitrifying biofilms, from different full-scale secondary and tertiary wastewater treatment plants were investigated in this study.; Their physical properties and structural features such as water content, organic proportion (VS/TS), density, thickness, particle size distribution, porosity, and fractal characteristics were examined.; The results indicate that for both kinds of biofilms, the surfaces and internal pore structures could be described by the fractal concept.; However, due to the different microorganisms involved, the two kinds of biofilms existed in different physical forms. The heterotrophic biofilms have higher porosity, larger internal voids and thickness, and a faster growth and sloughing rate than the nitrifying biofilms. While the nitrifying biofilms have much higher densityTS and VS/TS ratio than the heterotrophic biofilms.; In contrast to some laboratory experimental biofilms, their structures and properties such as porosity, density, and fractals are more irregular in spatial distribution. |
