Initial Investigations of Aerobic Granulation in an Annular Gap Bioreactor

Abstract

This research describes the design, construction, and characterization of a novel annular gap bioreactor. The bioreactor was conceived as a tool for the shear-based control of activated sludge floc particle size in batch and continuous-run experiments. Initial experiments on the feasibility of cultivating aerobic granular sludge in the bioreactor are described. The bioreactor was found to experience turbulent Taylor vortex flow, rather than laminar Couette flow, at all rotational speeds tested. This flow regime is the result of inner cylinder rotation. Despite turbulent flow conditions, the bioreactor was found to behave approximately as a plug-flow device when not aerated, and as a complete-mix reactor when aerated. Floc size control was found to depend on bioreactor rotational speed for two sludges tested, with higher rotational speed leading to smaller particle size. Three experimental attempts at aerobic granular sludge cultivation in the annular gap bioreactor are described in this study. Although none of the three attempts was successful at producing aerobic granules, the experiments allowed critical control issues related to bioreactor operation and influent composition to be identified and addressed. The Bacterial and Eukaryal population dynamics during each run were tracked with denaturing gradient gel electrophoresis and rDNA sequence analysis, using methods developed or streamlined in the course of this research. The foundational work described in this study culminated in the development of a series of protocols and recommendations for the next phase of aerobic granular sludge investigation with this novel annular gap bioreactor.