A novel anammox granules-circulating expanded granular sludge bed reactor for the efficient circulation and retention of floating anammox granules

Abstract

In application of anammox process, the operation of the conventional expanded granular sludge bed reactor (EGSB_conv.) is severely limited by the blocking and decay of floating anammox granules.To address this emerging issue, a novel three-phase separator configuration was designed and an anammox granules circulating EGSB (EGSB_GC) was proposed in this study. In the EGSB_GC, an influent scour on floating granules, whose effect was confirmed by simulation with a three-dimensional flow model, was obtained by integrating the external three-phase separator with the influent and the external cycle. After 166-d operation, the nitrogen removal efficiency of the EGSB_GC reached 75.6%, being 1.28-times that of the EGSB_conv. (58.9%). The sludge concentration in the main body of the EGSB_GC reached 3112 ± 65 mg/L, compared with 2613 ± 42 mg/L in the EGSB_conv. (p < 0.05). Moreover, the severe granules blockage and decay problem that is frequently encountered in the EGSB_conv. no longer occurred in the EGSB_GC. The relative abundance of anammox bacteria in granules from the three-phase separator of the EGSB_GC was 29.7%, significantly higher than that from the EGSB_conv. (16.1%, p < 0.05). The blockage and decay of granules in the three-phase separator of the EGSB_conv. led to an obvious proliferation of heterotrophic bacteria, with their relative abundance increased by 9.4% compared with the seed sludge (38.6% vs. 29.2%). This study proposed a practical three-phase separator configuration to sustain efficient and stable operation of anammox processes toward the promotion of granules circulation, retention and reaction.

Keywords: Anammox granules; Expanded granular sludge bed reactor; Granules floatation; Sludge circulation; Three-phase separator.