In a Membrane Biofilm Reactor (MBR) gas permeable membranes are used as a substratum for bacteria to grow in. The membrane separates an oxygen containing gas space from a compartment through which wastewater is pumped. Biofilms attached to the membrane are supported with oxygen from the adhesion site, and with substrates from the bulk liquid.

The MBR is a promising tool for the aerobic treatment of industrial wastewaters. Volatile organics are kept from getting stripped into the atmosphere. Bacteria with special metabolic properties can be immobilized and exploited under controlled process conditions. By using porous membranes the bacteria are allowed to colonize not only the membrane surface but also its pores. By that, a starter culture is maintained and used as an inoculum in case biofilm gets lost through erosion, abrasion, grazing or sloughing.

Experiments have been conducted to study structure and functions of membrane bound biofilms. Visualisation of biofilms by scanning and transmission electron microscopy revealed that the pores of the membranes get densely colonized. In situ identification of microorganisms by genetic probes in cross sections of a biofilm could successfully be carried out. Oxygen concentration profiles measured by means of microelectrodes demonstrated the efficiency of the oxygen partial pressure as a parameter to control oxygen supply of membrane bound biofilms.

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