MICROBIAL OXIDATION OF NAPHTHALENE TO CIS-1,2-DIHYDROXY-1,2-DIHYDRONAPHTHALENE IN A MEMBRANE BIOREACTOR

A microbial dihydroxylation process for the production of cis-1,2-dihy droxy-1,2-dihydronaphthalene from naphthalene is reported. The oxidati on reaction was initially studied in a stirred tank reactor using rest ing cells of a Pseudomonas fluorescens mutant, grown on glucose as car bon source and acetyl salicylate as inducer of the naphthalene dioxyge nase enzymatic system. In these conditions the productivity of the sys tem was limited by the efficiency of the oxygenation and by a reversib le product inhibition phenomenon. In order to overcome the inhibitory effect of the 1,2-dihydrodiol accumulation, the biotransformations wer e carried out in a stirred reactor equipped with a membrane ultrafiltr ation device. In this way, the cells and the insoluble naphthalene wer e retained and recycled into the vessel, while the soluble diol was co ntinuously removed through the membrane permeate. The diol was recover ed by selective adsorption on a column packed with an adsorbent resin, allowing the rapid and direct recycle of the reaction medium back to the enzymatic reactor. This system afforded a final yield three-fold h igher than that of the batch process, exhibiting a bioconversion rate of 1.3 g h(-1) dm(-3) for more than 16 h of continuous working.