Development and validation of laboratory microcosms for anionic surfactant biodegradation by riverine biofilms

A laboratory system was developed for modelling the colonization of slate-discs by riverine epilithic biofilm capable of the biodegradation of anionic surfactants. Initial experiments using batch or batch-fed systems produced biofilms yielding at least 10-times fewer viable bacteria and slower surfactant biodegradation rates than occur in indigenous biofilms formed on slate-discs placed in the River Taff, South Wales. Increased aeration, and the continuous-feeding of the microcosm with nutrient-amended discharge from a sewage-treatment plant, separately gave rise to increased epilithic bacterial numbers and SDS biodegradation rates. The epilithon from a slate colonized in a microcosm, which initially had been inoculated with river water and continuously-fed at a dilution rate of 1 d−1 was compared, for a variety of characteristics, with the epilithon from a slate colonized in a polluted reach of the river Taff. On the basis of similarities in bacterial numbers and parameters specific to surfactant-biodegradation rates, and comparable bacterial metabolic capacities, the continuous-flow fed microcosm was a simple but adequate model for the colonization of slate-discs by epilithic bacteria in a polluted river, that could be used to test, in the laboratory, the effects of surfactant pollution in an environmentally-compatible system.