A draft-tube spouted-bed (DTSB) reactor was equipped with an auxiliary aeration device to provide air into the annular region and thereby improve the oxygen transfer efficiency. The effects of the total air flow rate and its distribution between spout and annulus, the liquid phase viscosity (water and carboxymethyl cellulose solutions), and the solid holdup (glass and cyclodextrin polymer beads) on the oxygen transfer efficiency were discussed. The oxygen transfer coefficient increased with the air flow rate and the ratio of air flowing through the annulus, whereas it decreased with increasing viscosity and solid holdup. A correlation was proposed to predict the transfer coefficient in DTSB reactors with primary and auxiliary aeration. A good fitting was achieved between the experimental data and those estimated with the model.

A draft-tube spouted bed bioreactor was developed to investigate the microbial degradation of aqueous phenol using a cyclodextrin-based support material. Bacteria from activated sludge were acclimated to phenol in a continuous stirred tank bioreactor, and then immobilized onto the hydrogel particles within the spouted bed bioreactor. Microorganisms obtained under different operating conditions in both bioreactors were isolated and characterized. Batch phenol degradation assays performed on isolated dominant strains showed that Acinetobacter baumannii was the most resistant to phenol. Microbial population distribution in bioreactors was not only affected by phenol concentration, but also by oxygen availability, the system configuration and the presence of intermediates formed during phenol metabolization. A maximum elimination capacity of 2.79 kg-phenol/m(3) d was achieved in the spouted bed bioreactor, with Comamonas acidovorans being the dominant strain during high degradation periods.