Studies on Rotating Packed Disc Bioreactor

Abstract

A novel rotating packed disc bioreactor (RPDB) with the maximum working volume of 65 liter is designed for biological waste water treatment. A hollow disc with radial vanes mounted on the disc was a novel design of this contactor. Stimulus-response experiments were conducted in the contactor to understand liquid mixing behavior under different operating conditions. The recycle stream was also used in the operation of the contactor. The disc design and recycle ratio had marked influence on the mixing behavior. A mathematical model was developed for the flow behavior under recycle and a good agreement was found between the model and experimental results. Moreover, the surface area available in the RPDB was about 4 times more than the surface area available in a standard rotating biological contactor (RBC) operating at similar conditions. The modified design characterized in terms of oxygen volumetric mass transfer coefficient (kLa), in the physical gas–liquid system. The oxygen volumetric mass transfer coefficients (kLa) obtained in this bioreactor are about eight times higher than the similar size of the conventional rotating biological contactors at similar operating conditions. The dimensionless empirical model is developed, by incorporating the operating parameters. In RPDB, mixed cultures of white-rot fungi (WRF), namely, P.chrysosporium and T.versicolor are used to degrade reactive black-5 (RB-5) under different rotational speeds as well as recycle ratios. Degradation mechanism of Reactive Black -5 is critically discussed and intermediate products following P.chrysosporium and T.versicolor are identified using LC-MS. The decolourization efficiency of more than 90% and chemical oxygen demand (COD) reduction of more than 85% was achieved in continuous operation. The recycle stream improved COD reduction by about 15% as compared to that without recycle. The rate of COD removal was 737.9 mg/L/h at 30 rpm and 9.75 recycle ratio in the continuous operation, which is the highest removal rate reported for a synthetic RB-5 effluent in a continuous bioreactor of size 65 liter so far in the literature.