Regeneration of azo-dye-saturated cellulosic anion exchange resin by Burkholderia cepacia anaerobic dye reduction

Cellulosic strong anion exchangers are very effective for decolorizing textile wastewaters. However, the high affinity of dyes for the adsorbent make regeneration with conventional eluants impractical. Previous work demonstrated that chemical reduction of azo dyes bound to cellulosic anion exchangers facilitates adsorbent regeneration. The present study examines whether microbial azo-reductase activity could substitute for inorganic reductants. Anaerobic suspensions of Burkholderia cepacia NRRL B-14803 were tested for their ability to reduce two monoazo dyes, Orange II and hydrolyzed Remazol Red F3B, in a variety of reactor configurations. Inclusion of anthraquinone-2-sulfonate in the reaction medium greatly increased dye reduction rates, as did increased temperature and bacteria concentration. By physically separating the bacteria from the dye adsorbent using a dialysis tube, it was demonstrated that anthraquinone-2-sulfonate mediated the transfer of reducing equivalents from bacteria to adsorbent-bound dye. Furthermore, anaerobic B. cepacia suspensions can drive a large fraction of anthraquinone-2-sulfonate to the reduced state, in the absence of dye, within a 6-h incubation period. These observations suggested that a spaciotemporal disconnection of the process of adsorbent dye reduction from the azo-reductase activity of bacteria would be feasible. This possibility was confirmed by regenerating an ion exchanger bed with medium from a separately housed anaerobic reactor.