CONVECTIVE FLOW IN METHANOGENIC GRANULES

Gas bubbles entrapped in biocatalyst particles subjected to hydrostati c pressure oscillations, e.g. during recirculation in loop reactors, w ill induce intraparticle liquid flows, and thereby enhance mass transf er in excess of diffusion. This 'breathing particle' mechanism was alr eady demonstrated in methanogenic granules from an IC reactor, and led to an average macroscopic activity increase of 13%. The existence of the alternating convective liquid flow responsible for this higher act ivity has now been established independently with pulsed field gradien t NMR, as the intraparticle water mobility during pressure oscillation s was found 16.5% larger. Micro-electrode measurements of the internal pH of a granule revealed the occurrence of a fast liquid flow through a channel between a central cavity and the periphery during pressure cycling, and the subsequent diffusive relaxation under atmospheric con ditions. (C) 1997 IAWQ. Published by Elsevier Science Ltd.