No abstract

In order to have an efficient operation, sequencing batch reactors (SBR) must support granular biomass with high conversion rates, settling properties, and be able to deal with the inherent variability of the composition of real wastewaters. In this study, the effect of the influent composition and the specific organic loading rate (Bx) on the granulation process was evaluated in two SBRs, fed with greywater (GW) and a synthetic medium (SM). The feeding with SM led to the formation of compact granular biomass, with a sludge volume index (SVI) of 22.4 mL g, and a zone settling velocity (ZSV) of 13.1 m h. In contrast, feeding with GW induced the formation of filamentous granules, with lower settling properties (SVI = 165 mL g and ZSV = 10 m h), when the system was operated at high Bx (4.4 kg COD kg VSS d). However, the reduction of the average Bx to 2 kg COD kg VSS d induced an improvement in the morphology and properties of the granules (SVI = 98 mL g and ZSV = 13 m h). Furthermore, the kinetic analysis indicated that granules cultivated with SM were formed by fast growing microorganisms with a high cell yield, whereas those cultivated in GW presented a much lower cell yield.

Modelado de la biodegradación en biorreactores de lodos de hidrocarburos totales del petróleo intemperizados en suelos y sedimentos (Biodegradation modeling of sludge bioreactors of total petroleum hydrocarbons weathering in soil and sediments)

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.