Development of an in situ dissolved oxygen measurement system and calculation of its effective diffusion coefficient in a biofilm

Dissolved oxygen (DO) plays an important role in biological wastewater treatment. The DO concentration in a biofilm interior, which is controlled by its effective diffusion coefficient, determines the biochemical reaction rate. In the current study, a measurement system for the in situ determination of DO levels in a biofilm was developed. A piece of biofilm from a sequencing batch biofilm reactor was used as the experimental example. The DO distribution in the biofilm was measured and the effective diffusion coefficients in water film and in biofilm were calculated as 6.9 × 10−5 m2 d−1 and 1.7 × 10−5 m2 d−1. No anaerobic area in the biofilm was found.