Effect of the famine phase length on the properties of aerobic granular sludge treating greywater

Abstract

Sequencing batch reactors (SBR) treating high-strength greywater need an aerobic granular sludge (AGS) with good properties, such as a low sludge volume index (SVI) and high settling velocities and substrate uptake rates to yield short settling and aeration stages. To promote the formation of stable granular sludge, the length of the famine phase could be a key factor. In this regard, the effect of the duration of this variable on the AGS properties was assessed by comparing a gradual versus an abrupt reduction of the famine phase in two SBR treating greywater. The initial average famine phase of 3.3 h was gradually reduced to 0.3 h over 20 weeks in one reactor, and abruptly in another one. This condition induced filamentous outgrowth, as well as the deterioration on the properties of the sludge; being more accelerated the effect when the famine periods were abruptly shortened. In both cases the reduction on the famine periods induced increased organic loading rates, which led to degranulation events when it was higher than 2.5 g-COD g-VSS−1 d−1. Afterwards, the biomass adapted to this situation, by forming new small-filamentous aggregates with similar SVI to that of the stable AGS formed with the longest famine period.

Biological processes of nitrogen removal and modeling oxygen diffusion in flocculent sludge and in granular sequencing batch reactors

“…Famine period is required for the formation of stable granules, typically representing 65–70% of the total cycle 44 . Extended famine phase encourages granule stability according to Corsino et al 45 .…”

“…Famine period is required for the formation of stable granules, typically representing 65-70% of the total cycle. 44 Extended famine phase encourages granule stability according to Corsino et al 45 However, an excessively long starvation phase, 20 h in SBR AG1 and 22 h in SBR AG2 representing 83% and 91% of the total cycle, respectively, 24 could lead to a great consumption of EPS generating small-size granules, as was reported by Bucci et al 46 for cheese whey-fed aerobic granules.…”