Biofilms in RBC with Constant Ages and Thicknesses

AbstractWith the exception of some strict kinetic formalism, biofilm thickness constitutes a basic parameter for analyzing the mechanisms of mass transfer as a result of microbiological growth. A research gap exists, however, related to a constant (in time) biofilm thickness, a biofilm age and the system efficiency, namely the study of a biological fixed-film reactor operated with a constant biofilm age and thickness. The present work examined the influence of the biofilm age and thickness in the biodegradation process of an organic substrate. Biofilm thickness was related and measured indirectly by introducing the concept of biofilm age. This concept is commonly used in suspended biomass but is usually disregarded in fixed systems (solids retention time). In some recent studies, solids retention time is referred to only as a result of operation conditions and not a design parameter. By contrast, this work studied biofilms in a range of ages from 0.5–1 day to 5–6 days, allowing behavior comparisons of reactors operated at constant film thickness, contrary to usual procedures in continuous fixed biomass systems. A clear differentiation of microbial profiles (performed using the fluorescence in situ hybridization technique) was found for the different biofilm ages. The results showed that biofilm age can significantly influence substrate removal and those ages 0.5–1 day, 4–5 days, and 5–6 days had the most favorable results with higher substrate removal rates, indicating that operating the biomass systems with a controlled age may be advantageous. In addition to the potential benefits of efficiency, such an operation would also significantly reduce the suspended matter in the final stage of sedimentation because at those ages is not likely to experience significant biofilm detachment.