A well mixed indoor recirculating channel was adopted to investigate aerobic heterotrophic biodegradation kinetics and microbial communities in drainage systems with suspended and attached biomass. Experiments were run with synthetic substrate. The biofilm function was distinguished from the suspended biomass by using the Biological Oxygen Monitor (BOM) to measure suspended biomass activity. The microbial community was overall dominated by filaments (mainly Sphaerotilus natans) due to the selection pressure of the soluble organic substrate; the biofilm was surface film-dominated because of the low flow velocity and shear stress. The channel processes were dominated by the biofilm function. However, it was found that the intrinsic Monod kinetic constants were μmax=2.8 d−1, Ks=1.8 mg/l for the suspended biomass, 1.4 d−1, 2.7 mg/l for the biofilm biomass, both at 28°C; and 0.76 d−1, 2.5 mg/l, 0.52 d−1 and 2.9 mg/l respectively for the two types of biomass, both at 200°C. The specific activity of suspended biomass was 50-100% higher than the biofilm biomass, but no significant difference was found between surface and base film biomass. Biofilm oxygen uptake rates (BUR) were around 25 gO2/m2.d at 28°C, 18 gO2/m2.d at 20°C, and velocity dependent. The observed oxygen consumption coefficient of biofilm Yo/s (gO2/ggluc) decreased from 50 to 10% when biofilm surface loading increased from 50 to 300 ggluc/m2.d. The relationship between the biomass population, intrinsic kinetics and biofilm performance is discussed.

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