Influence of reactor type and shear stress on aerobic biofilm morphology, population and kinetics

The influence of flow pattern on the microbial community of biofilm systems is relevant for process analysis, reactor selection and microbial ecology control. The interaction between reactor type, shear stress, microbial population, intrinsic kinetics, and biofilm performance for biofilm systems was studied by comparing experimental results of three reactors: a batch reactor representing plug flow, and a CSTR and an indoor channel reactor with recirculation, two configurations of continuous stirred tank reactors but with different shear stress. Cocci co-existed with filaments (mainly Sphaerotilus natans) in the batch reactor biofilm, whereas filaments predominated in the other two reactors. The values of the Monod constants μmax and Ks of the biofilm biomass of the batch reactor were 2.8 day−1 and 54 mg(glucose)/l at 28°C, whereas in the CSTR and channel they were 1.3 day−1 and 2.9 mg/l, and 1.5 day−1 and 2.7 mg/l, respectively. The oxygen consumption coefficients of biofilm decreased from 50 to 10% (gO2/gglu), when biofilm surface loading increased from 50 to 400 gglu/m2•.day in the CSTR and channel reactors. An analogy was found between intrinsic microbial kinetics and the corresponding macroscopic biofilm kinetics. A conceptual model of these interactions was proposed.