Modeling Hydraulic Transport and Anaerobic Uptake by PAOs and GAOs During Wastewater Feeding in EBPR Granular Sludge Reactors

New-generation bioprocesses using granular sludge aim for a high-rate removal of nutrients from wastewater with low footprint. Achieving enhanced biological phosphorus removal (EBPR) relies on the design of sludge beds and wastewater feeding conditions to optimally load the biomass and to select for polyphosphate- (PAOs) over glycogen-accumulating organisms (GAOs) and over other heterotrophs. A hydraulic–metabolic mathematical model was developed to elucidate the impact of hydraulic transport patterns and environmental conditions on the PAO/GAO competition during up-flow feeding through an EBPR granular sludge bed. Tracer experiments highlighted plug-flow regimes with dispersion under both rapid and slow feeding. Non-turbulent regimes (Rebed

Aerobic granular sludge formation and performance at 30 and 35°C in sequencing batch bubble-column reactors

Sirous Ebrahimi, Sébastien Gabus, Graciela Gonzalez Gil, Christof Holliger, Maryam Hosseini

Aerobic granular sludge-based reactors represent an attractive alternative to conventional activated sludge systems due to their small footprint and their low energy consumption and excess sludge production. The granules developed in such systems have high biomass concentration, good settling properties, high COD removal efficiencies and eventually high phosphorus removal capacity. In addition, and depending on bulk oxygen concentrations and granule size, both nitrification and denitrification can occur in the granules. Therefore sequencing batch reactors operated with granular sludge have the potential to achieve organic matter and nutrient removal in a single compact system. So far, aerobic granular sludge development has been studied at 20°C as well as at relatively low temperatures (e.g. 5 and 10°C). Compact wastewater treatment systems are especially interesting for industry. Since they often produce wastewaters with temperatures above 20°C, we investigated whether aerobic granular sludge could be developed at higher temperatures and if so, what the physical and metabolic properties of the sludge were. The formation and performance of aerobic granular sludge was studied in sequencing batch bubble-column reactors. Two start-up strategies were examined. Reactor 1 and 2 were inoculated with activated sludge from a municipal wastewater treatment plant and operated at 20°C and 30°C, respectively. After failure of Reactor 2, it was inoculated with aerobic granular sludge of Reactor 1 and operated with a stepwise temperature increase from 20 to 35°C. Granular sludge with good physical and metabolic properties was obtained in Reactor 1. Virtually all acetate was consumed during the anaerobic period with concomitant high phosphorus release suggesting the predominance of phosphate accumulating organisms (PAO). After the aerobic phase, an average of 63% of phosphate was removed. Nitrogen removal was not observed in this system, not even nitrification. In Reactor 2, a mixture of smooth granules and irregular structures was obtained. Complete COD removal was achieved, however, the sludge had low density (

2008

Linking microbial population dynamics and nutrient removal during wastewater treatment by aerobic granular sludge

Christof Holliger, Noam Shani, David Gregory Weissbrodt

Aerobic granular sludge technology is attractive for intensified biological nutrient removal from wastewater and secondary clarification in single sequencing batch reactors. A methodology combining molecular fingerprinting, pyrosequencing-based identification of phylotypes with PyroTRF-ID, and multivariate statistics was developed to investigate on the long run, with high resolution, the dynamics of bacterial populations involved in nutrient removal in this wastewater treatment system. The predominant and flanking populations present in aerobic granules belonged to the core bacteriome of activated sludge removing nutrients biologically, and were structured in two major opponent clusters. Members of the first cluster, mainly related to Accumulibacter and Nitrospira, were favored under conditions leading to efficient nutrient removal. Members of the second cluster, mainly related to Competibacter, Sphingobacteriales, Cytophaga, and Intrasporangiaceae, proliferated during periods of low performances. A third transitory cluster mainly populated by Aminobacter and abundant Xanthomonadaceae relatives was identified with weak correlations to process parameters. Based on the physiological properties referenced in literature for the detected organisms, a tentative conceptual model of the bacterial ecosystem of aerobic granules was developed. This ecological model highlighted the presence of a broad denitrifying community that was not restricted to Accumulibacter and Competibacter only, and of populations involved in the metabolism of extracellular polymeric substances. Further research will determine how these putative denitrifiers and EPS producers and consumers can thrive in the aerobic granule ecosystem under anaerobic-aerobic conditions.

2014

Aerobic granular sludge formation and performance at 30 and 35°C in sequencing batch bubble-column reactors

Sirous Ebrahimi, Sébastien Gabus, Graciela Gonzalez Gil, Christof Holliger, Maryam Hosseini

2008