Performance analysis at the dynamic state of solid-liquid separation in the sequencing batch anaerobic reactor treating municipal sludge

Performances of the anaerobic sequencing batch reactor (ASBR) for municipal sludge digestion clearly demonstrated that the stability of the ASBR process to treat high-solids-content waste could be greatly affected by critical factors for solid-liquid separation. Flotation thickening occurred in mesophilic ASBR, while solid-liquid separation in thermophilic ASBR followed a gravity thickening. The hydraulic retention time (HRT) and cycle period as well as the type of thickening were key parameters to govern sludge thickenability(thickening ability) and critical solids accumulation. Thickened sludge bed volume was a critical operating variable in the ASBR with the gravity thickening, which had a poor performance because of the loss of thickened solids, and sludge interface disruption or instability of sludge bed due to internal gas evolution. A cyclic mutual effect between thickened volume and gas production was significant in the gravity thickening, whereas it was insignificant in the flotation thickening.