DYNAMICS OF EARLY BIOFILM FORMATION IN A TURBULENT FLOW SYSTEM

Abstract

Early stages of fouling biofilm development were studied under turbulent flow conditions in a circular tube. Two separate reactor systems were used to respectively determine (1) an empirical expression describing the rate of early biofilm development and (2) estimates of individual processes contributing to net biofilm accumulation. Both objectives required the development of various detection methods sensitive to the early stages of biofilm development. The first system was a completely mixed reactor with internal recycle. It was used to determine biofilm accumulation rate as a function of three variables: suspended biomass concentration (X), Reynolds Number (Re), and reactor dilution rate (D). The change in biofilm amount with time during the early stages was described using a first order expression that was a function of biofilm amount. The first order rate constant was directly proportional to biomass concentration and dilution rate and inversely proportional to Reynolds Number. The second system consisted of two completely mixed reactors in series, the second containing an internal recycle. Perturbations in the second reactor operating conditions allowed estimates of the individual processes contributing to early biofilm accumulation. Results indicate microorganism deposition, biofilm production, and biofilm detachment to contribute significantly to early biofilm development. The relative magnitude of the contribution of these individual processes changes with prevailing operating conditions. Biofilm detection methods based on chemical analysis of a biofilm constituent (i.e., chemical oxygen demand, biofilm polysaccharide) proved to be practical, rapid, and sensitive to early biofilm development.