AQUEOUS-ORGANIC MEMBRANE BIOREACTORS .2. BREAKTHROUGH PRESSURE MEASUREMENT

The effect of membrane type - structure and wettability - on the opera tion of two-phase, aqueous-organic, membrane bioreactors has been stud ied. The influence of surfactants on membrane wettability is reported. A simple, but highly sensitive, technique for the measurement of brea kthrough pressures is described. Experimental measurements of the vari ation in break through pressures as the concentration of tenside in th e system was changed are reported. On the basis of the results from th ese measurements it is concluded that: (i) hydrophilic and, highly ret entive, amphiphilic ultrafiltration membranes may be used to operate t wo-phase bioreactors, (ii) amphiphilic microfiltration membranes shoul d never be used in such reactors and (iii) PTFE membranes would always be a poor choice for use in such devices because they always have a l ow breakthrough resistance in two-liquid systems - breakthrough pressu res as low as 100 mbar were observed for the system ethyl laurate-wate r-PTFE, which contains no surface-active component. It is shown that t hese results are in general agreement with rules of thumb for the sele ction of membranes, presented earlier. The influence of membrane histo ry on its wetting behavior due to effects such as polymer surface rest ructuring - is highlighted. The limits on the utility of simple breakt hrough pressure tests in determining suitable membranes, for use in tw o-phase bioreactors, owing to possible complications resulting from th e exact mechanism of enzyme action is pointed out.