Substrate utilization and mass transfer in an autotrophic biofilm system: Experimental results and numerical simulation

Abstract

An autotrophic biofilm has been investigated for over 10 months in a biofilm tube reactor. The objective of this investigation was the verification and improvement of a biofilm model. The use of a Clark-type oxygen microelectrode in situ allowed the determination of the substrate flux in the biofilm. Also, the population dynamics of the autotrophic bacteria could be evaluated by varying the substrate conditions. Simulation of the experimental results showed that the liquid phase of the biofilm decreased with biofilm depth. This could be described by a logistic function. The density of the inert volume fraction was found to be higher than that of the viable bacteria. This was verified in a nonsubstrate phase of 5 weeks. Growth and decay of the autotrophic bacteria could be described by the growth, endogenous respiration, and death processes. Mass transfer coefficients at the bulk/biofilm interface were evaluated. They were found to be one order of magnitude higher than those known from hydrodynamics in tubes without a biofilm.