Methane microprofiles in a sewage biofilm determined with a microscale biosensor

Microprofiles of the methane concentration in a 3.5-mm-thick sewage outlet biofilm were measured at high spatial and temporal resolution using a microscale biosensor for methane. In the freshly collected biofilm, methane was building up to a concentration of 175 mu mol l(-1) at 3 mm depth with a total methanogenesis of 0.14 mu mol m(-2) s(-1), as compared to an aerobic respiration (including methane oxidation) of 0.80 mu mol m(-2) s(-1). A model biofilm was established by homogenisation of an in situ biofilm and 12 days of incubation with surplus sodium acetate. The homogenised biofilm was able to maintain 50% of the methanogenic activity in the absence of external electron donor. Oxygen had only a minor effect on the methane production, but aerobic respiration consumed a substantial part of the produced methane and was thus an important control on methane export from the biofilm. A concentration of 2 mmol l(-1) nitrate was shown to inhibit methanogenesis only in the upper layer of the biofilm, whereas a further addition of 2 mmol l(-1) sulphate inhibited methanogenesis in the entire biofilm. The study demonstrated the power of the methane microsensor in the study of microhabitats with concurrent production and consumption of methane. (C) 2001 Elsevier Science Ltd. All rights reserved.