Hydrodynamic behavior of anaerobic biosolids during crossflow filtration in the membrane anaerobic bioreactor

Anaerobic biosolids deposition on the membrane surface has a significant effect on flux decline in membrane-coupled anaerobic bioreactors (MCAB). The aim of this study was to investigate the hydrodynamic behavior of anaerobic biosolids during crossflow ultrafiltration of digestion broth in the MCAB. A theoretical approach to predict flux decline was made considering the biosolids transport mechanism based on hydrodynamics and surface interactions. The continuous size reduction of biosolids offered an exponential flux decline at the initial stage, as the biomass cake layers being formed by the deposition of smaller particles with back-transport velocities less than the flux. Since flux recovery could not be achieved readily on the way of ultrafiltration due to irreversible biofouling, the biosolids movement toward the membrane surface should be controlled at the beginning of the MCAB operation. The optimal operating condition which prevents biosolids deposition onto the membrane surface could be predicted by the evaluation of critical flux.