This study evaluates the kinetic parameters of biochemical reaction in three-phase fluidized bed biofilm reactor from the steady state values of the response of the system to step changes in inlet concentration. It was observed from the outlet biological oxygen demand (BOD5) plot of the response of the system that as the inlet BOD5 was increased, the outlet BOD5 also increased, reached a peak value and then decreased until it leveled to a new steady state value corresponding to the new inlet concentration level. The increase in BOD5 was attributed to the accumulation of substrate within the reactor as well as the decrease in biofilm substrate consumption rate as the microorganisms adjusted to the new environment. Using the substrate balance at steady state and assuming Monod kinetics, an equation relating the substrate consumption rate to substrate concentration (BOD5) and total biofilm surface area had been established. Monod kinetic parameters were found to be K = 2.20 g/m2/day, K(m) = 17.41 g/m3 and K/K(m) = 0.13 m/day. The ratio K/K(m) can be taken as the indicator for biofilm substrate degradation effectiveness at low substrate concentrations. (C) 2000 Elsevier Science S.A.
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