PROPENE REMOVAL FROM SYNTHETIC WASTE-GAS USING A HOLLOW-FIBER MEMBRANE BIOREACTOR

Hollow-fibre modules containing microporous membrane material were eva luated as bioreactors for waste gas treatment. The reactors were inocu lated with the propene-utilizing strain Xanthobacter Py2, which formed a biofilm on the inner side of the fibres, The removal of the poorly soluble volatile propene from synthetic waste gas was monitored for up to 170 days. The maximum removal rates were 70-110 g propene per m(3) reactor per hour, A gas residence time of 80 s was required to remove 95% of an initial propene concentration of 0.84 g/m(3). The presence of ammonium in the liquid medium resulted in the development of an add itional population of nitrifying organisms, Therefore, nitrate was use d as the source of nitrogen in later experiments, During long-term ope ration. the propene removal rates gradually decreased, At low liquid v elocities (1-5 cm/s) clogging of individual fibres with excess biomass was observed, Elevation of the liquid velocity in the fibres to 90 cm /s resulted in the formation of a dense biofilm and prevented clogging of the fibres. However, also at this high liquid velocity a gradual d ecrease in propene removal rate was observed, These results suggest th at aging of biofilms is a very important factor in long-term operation of hollow-fibre bioreactors.