Microbial acetate oxidation in horizontal rotating tubular bioreactor.

The aim of this work was to investigate the possibility of conducting a continuous aerobic bioprocess in a horizontal rotating tubular bioreactor (HRTB). Aerobic oxidation of acetate by the action of a mixed microbial culture was chosen as a model process. The microbial culture was not only grown in a suspension but also in the form of a biofilm on the interior surface of HRTB. Efficiency of the bioprocess was monitored by determination of the acetate concentration and chemical oxygen demand (COD). While acetate inlet concentration and feeding rate influenced efficiency of acetate oxidation, the bioreactor rotation speed did not influence the bioprocess dynamics significantly. Gradients of acetate concentration and pH along HRTB were more pronounced at lower feeding rates. Volumetric load of acetate was proved to be the most significant parameter. High volumetric loads (above 2 g acetate l-1 h-1) gave poor acetate oxidation efficiency (only 17 to 50%). When the volumetric load was in the range of 0.60-1.75 g acetate l-1 h-1, acetate oxidation efficiency was 50-75%. At lower volumetric loads (0.14-0.58 g acetate l-1 h-1), complete acetate consumption was achieved. On the basis of the obtained results, it can be concluded that HRTB is suitable for conducting aerobic continuous bioprocesses.