Hydrodynamic evaluation of a biological packed-bed reactor

ABSTRACT

The effluent generation increase requires compact and efficient units to comply with quality discharge standards. Biological packed-bed reactors offer support for biomass and the establishment of oxygen gradients to foment the simultaneous growth of nitrifying and denitrifying bacteria for nitrogen removal. The reactor's performance does not only rely on microbial and enzymatic kinetics but also on the physical processes involved. The packed bed creates an uneven flow, resulting in an irregular mixture. The present study aimed to evaluate the hydrodynamics of a packed-bed reactor under distinct operational conditions. The upflow cylindrical reactor, with a volume of 10.08 L, was filled with Mini Biobob^® media and operated in hydraulic retention times (HRT) of 8, 14, and 20 h, with recirculation ratios R0, R1, and R2, with and without aeration. The flow pattern was defined as close to a complete mix, it was verified mixture increases with the reduction of HRT for the non-aerated operation, but no influence was observed for the aerated period. The experiments revealed that the mean HRT was lower than the theoretical stipulated due to flow inconsistencies. The impact on the mixture was not noticed for both operations when varying the recirculation ratio, not influencing the boundary layer thickness and mass transfer. A mean dead volume of 23.17 and 22.53% were found for the aerated and non-aerated operations, respectively. No significant statistical correlation was found for the studied variables’ parameters.

Keywords:
hydrodynamic evaluation; polyurethane foam; stimulus-response; packed bed; tracer