GAS-PHASE METHYL ETHYL KETONE BIODEGRADATION IN A TUBULAR BIOFILM REACTOR - MICROBIOLOGICAL AND BIOPROCESS ASPECTS

A novel type of bioreactor was designed to clean VOCs-containing air. The operation of this reactor consists in mixing the polluted gas and a mist of nutrient solution in the presence of microorganisms in order to maximize contact and transfer between gas, liquid and microorganis ms and to promote the degradation kinetics and the relative removal ef ficiency of the pollutant. A bacterial consortium acclimatized to MEK and containing a preponderance of Alcaligenes denitrificans was establ ished under non-axenic conditions. On the tubular reactor's glass wall s, a continuous biofilm was developed. This biofilm was rapidly contam inated by two fungi able to degrade MEK: Geotrichum candidum and Fusar ium oxysporum. Their abundance in the reactor is probably linked to th e acidic conditions inside the biofilm and to their broader tolerance for low pH values concomitant with MEK degradation. In the reactor, a maximum volumetric degradation rate of 3.5 kg MEK/m(reactor)(3).d was obtained for a relative removal efficiency of 35%, whereas the latter was maintained at 70% for more modest applied loadings of 1.5 kg MEK/m (reactor)(3).d. In liquid batch cultures, a biomass originating from t he biofilm was able to degrade 0.40 g(MEK)/g(DCW).h at the optimal pH of 7. A regular cycle of detachment-recolonization was observed during the operation of the bioreactor. The maximal degradation activity was obtained with a thin biofilm and was not increased as the biofilm gre w in thickness. The overall degradation rate of the process did not ap pear to be limited by the diffusion of oxygen inside the biofilm. Over short periods of time, the MEK transfer from the gaseous phase to the biofilm was neither affected by the presence of the mist nor by the w etting of the biofilm. A better control of the biofilm pH led to impro ved performance in terms of removal rate but not in terms of relative elimination efficiency.