A Blind Spot of Efficient Anaerobic Reactor: Ecological Distribution of Anaerobic Granular Sludge

Abstract

The practical organic loading rates (OLRs) of anaerobic reactors are usually lower than expectation, indicating an uncovered crux to be revealed. Herein, two anaerobic reactors with (EAR) and without (PAR) vertical partition setting were developed. It was found that EAR achieved a much higher OLR than PAR (>100 vs 45 kg/m3·d). Further, the vertical distribution characteristics of anaerobic granular sludge were different, which could be ascribed to two vertical distribution patterns of ecological and physical distributions dominated in EAR and PAR. Generally, habitat selection could promote the ecological distribution via substrate availability, resulting in a high OLR. While hydraulic selection enhanced the physical distribution via granule settleability, causing negative effects on the habitat selection. Therefore, the vertical partition set in EAR weakened the hydraulic selection by restricting liquid back-mixing and granule migration, leading to its good performance. This study could offer a novel concept for reactors' development towards high OLRs.

Keywords: anaerobic reactor, granular sludge, vertical distribution, habitat and hydraulic selections, ecological and physical distributions