High biofilm activity under increased oxygen concentrations in a pressurised biofilm system

A new pressurised biofilm reactor (PBR) process with a patented disc system that enables constant biofilm control has been developed to treat concentrated wastewater with respect to easily degradable organic matter under pressures of up to 6 bar. The pressurisation enables a six-fold increase of the O₂ saturation level and aeration capacity, which potentially increases the reaction rate of COD as long as O₂ is limiting the reaction rate. Experiments performed in a pilot-scale PBR-reactor fed by synthetic wastewater were conducted to verify the potential and kinetics of heterotrophic conversion of O₂ and acetate. Under O₂-limited conditions the maximum removal rate of O₂ and COD_f was measured to r_A,O2=60 g O₂/m²/d and r_A,CODf=150 g COD_f/m²/d at 70 mg O₂/l. Experiments verified that half-order kinetics could be applied but liquid film diffusion apparently influenced the reaction rate considerably. The observed half-order rate constant was experimentally determined to K_½A,O2=7.0 (g O₂)^1/2m^−1/2d⁻¹ but this value is underestimated by 15% due to the observed liquid film diffusion. Based on this the intrinsic zero-order reaction rate was estimated at k_0f,O2=190 kg O₂/m³ biofilm/d when both liquid film and biofilm diffusion were taken into account.