Extractive membrane bioreactors for detoxification of chemical industry wastes: process development

Pilot scale trials of an emerging membrane technology, the extractive membr ane bioreactor (EMB) are described. An EMB unit was installed at a chemical production facility to treat a spent caustic scrubber liquor containing mo nochlorobenzene (MCB). In its first configuration with 60 m(2) of membrane area the pilot unit worked well, destroying 98-99% of the organics in the M CB waste stream at a flow rate of 50 1 h(-1) with consequent evolution of c hloride ion. However, mass transfer coefficients were relatively low, aroun d 1x10(-6) m s(-1). Mass transfer experiments were undertaken at lab scale to determine the parameters limiting performance. These were found to be fl uid film resistances and the build-up of biofilms on the surfaces of the me mbrane tubes. It was also found that steady-state biofilm thickness could b e achieved through the use of fluid shear to remove biofilms. This informat ion was used to re-configure the pilot plant using a new generation of 20 m longx50 mm diameter shell and tube membrane modules. With 60 m2 of these n ew modules installed, operating at Re (tube)=1070 and Re (shell)=2140, the mass transfer coefficient was improved by an order of magnitude to between 7x10(-6) and 9x10(-6) m s(-1) MCB removal of 98-99% was obtained from a flo w of 500 1 h(-1), i.e. approximately 10 times the flow of the first configu ration, using the same membrane area. Tube-side mass transfer coefficients were well described by existing correlations. The mass transfer coefficient s on the shell side of these new modules were tested and found to be well d escribed by Sh(s) = (0.53 - 0.58 phi) * Re-s(0.53) * Sc-.(0.33) (C) 1998 Elsevier Scien ce B.V, All rights reserved.