A new method to determine the microbial kinetic parameters in biological air filters

This paper presents a new method to determine kinetic parameters of the biodegradation of various pollutants in a biofilter. Toluene, a readily biodegradable volatile organic compound, and methane, a hydrocarbon and a greenhouse gas, have been chosen as the target pollutants. The new protocol utilized biomass immobilized on bed pellets; these directly sampled from a continuous steady-state biofilter. The comparison of this method with the conventional experimental protocol utilizing micro-organisms suspended in a liquid medium was made using the pollutant toluene. Indeed, with both methods, the kinetic parameters have been evaluated by following the microbial growth in batch, thermostated reactors, using determined amounts of pollutant substrate. This experiment has confirmed the pertinence of the new procedure. The interesting features of the new method are that: (1) it is easy to operate (no preliminary treatment of the bed samples) and (2) it provides reproducible parameters that represent the real biofilter case more adequately than liquid cultures. In addition, modeling of the experimental specific growth rates in the case of toluene has shown that the values obtained with the use of solid extracts can be correlated by a Haldane's formulation, where mu* = 17.6 day(-1), K-h = 13.2 g m(-3), and K-i = 2.5 g m(-3). The maximum specific growth rate (3.1 day(-1)) was reached for an initial concentration of toluene near 5.0 g m(-3). The determination of the experimental specific growth rates of micro-organisms in the methane biofilter has also been performed. This study allowed highlighting two methane concentrations' ranges: from 1000 to 14500 ppmv and from 14500 to 27000 ppmv. For the first range, the Monod model proves to be suitable with the kinetic parameters: mu(max) = 0.43 day(-1) and K-m = 5.37 g m(-3). For the second range, neither the Monod nor the Haldane's formulation could directly be used. However, a mathematical adjustment of the Monod model allows to find kinetic parameters mu(max)' = 1.09 day(-1) and K-m' = 7.59 g m(-3). The biomass yields for the tested methane concentrations have also been determined and showed two different tendencies, depending on the same two ranges. For the first range of methane concentrations, the biomass yield was quite constant with an average value around 0. 36 g biomass (g methane)(-1) while for the second range, it could be approached by a polynomial second-order regression. The maximum value of the biomass yield obtained on the second range was 0.8 g biomass (g methane)(-1) at a methane initial concentration of 20000 ppmv. (C) 2008 Elsevier Ltd. All rights reserved.