MEMBRANE BIOREACTORS FOR WASTE-GAS TREATMENT

This review describes the recent development of membrane reactors for biological treatment of waste gases. In this type of bioreactor gaseou s pollutants are transferred through a membrane to the liquid phase, w here micro-organisms degrade the pollutants. The membrane bioreactor c ombines the advantages of membrane devices with the clean technology o f biological air purification. Two types of membrane materials can be used for gas-liquid contact: hydrophobic microporous material and dens e material, such as silicone rubber. Microporous material generally ha s a higher permeability, but dense membranes can be advantageous in th e case specific selectivity is required. Biomass is generally present as a biofilm on the membrane, but may also be suspended in the liquid phase. In a number of cases the reactor performance appears to be hamp ered by an unstable biofilm performance and/or by clogging of the liqu id channels due to excess biomass formation. So far: membrane bioreact ors for waste gas treatment have only been tested on laboratory scale. If the long-term stability of these reactors can be demonstrated, we expect membrane bioreactors to be useful tools in the treatment of gas streams containing poorly water-soluble pollutants and highly chlorin ated hydrocarbons, which are difficult to treat with the conventional methods for biofiltration. (C) 1998 Elsevier Science B.V.