BIOFILMS GROWING ON GAS-PERMEABLE MEMBRANES

In a Membrane Biofilm Reactor (MBR) gas permeable membranes are used a s a substratum for bacteria to grow in. The membrane separates an oxyg en containing gas space from a compartment through which wastewater is pumped. Biofilms attached to the membrane are supported with oxygen f rom the adhesion site, and with substrates from the bulk liquid. The M BR is a promising tool for the aerobic treatment of industrial wastewa ters. Volatile organics are kept from getting stripped into the atmosp here. Bacteria with special metabolic properties can be immobilized an d exploited under controlled process conditions. By using porous membr anes the bacteria are allowed to colonize not only the membrane surfac e but also its pores. By that, a starter culture is maintained and use d as an inoculum in case biofilm gets lost through erosion, abrasion, grazing or sloughing. Experiments have been conducted to study structu re and functions of membrane bound biofilms. Visualisation of biofilms by scanning and transmission electron microscopy revealed that the po res 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 pa rtial pressure as a parameter to control oxygen supply of membrane bou nd biofilms.