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Characterization of kinetic parameters and mass transfer resistance in an aerobic fixed-bed reactor by in-situ respirometry

Ordaz, Alberto, Ramirez, Rocio, Hernandez-Martinez, Gabriel R., Carrión, Manuel, Thalasso, Frédéric
Biochemical engineering journal 2019 v.146 pp. 194-202
acetates, activated sludge, biofilm, biomass, bioprocessing, hydrodynamics, liquids, mass transfer, wastewater
An airlift reactor filled with Raschig rings in the downcomer section only was designed to allow for the characterization of biofilm biomass at several superficial liquid velocities. The reactor was inoculated with activated sludge and operated with synthetic wastewater containing acetate. After steady state was reached, the kinetic parameters of the process were determined at each superficial liquid velocity by an in-situ pulse respirometry method. Subsequently, the biofilm contained in the reactor was disaggregated, resuspended in a mineral medium, and reintroduced in the reactor, without Raschig rings, i.e., a standard airlift reactor. The kinetic parameters of the bioprocess were determined again, by the same respirometry method. That strategy allowed for the estimation of apparent and intrinsic kinetic parameters; i.e., with and without mass transfer limitation, respectively. Moreover, the method also allowed for the determination of the internal and external effectiveness factors and mass transfer resistances. The results shown that the hydrodynamic conditions had a strong effect on the kinetic parameters but none on the stoichiometric parameters. The external mass transfer accounted for up to 70% of the total mass transfer resistance. It is concluded that respirometry is a useful tool for the characterization of biofilms, in actual random packing reactors.