Assessment of bacterial and structural dynamics in aerobic granular biofilms
David G. Weissbrodt (ETH Zürich, École Polytechnique Fédérale de Lausanne, Eawag - Swiss Federal Institute of Aquatic Science and Technology, Institute of Environmental Engineering, TU Delft - External organisation)
Thomas R. Neu (UZF - Helmholtz Centre for Environmental Research)
Ute Kuhlicke (UZF - Helmholtz Centre for Environmental Research)
Yoan Rappaz (École Polytechnique Fédérale de Lausanne)
Christof Holliger (École Polytechnique Fédérale de Lausanne)
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Abstract
Aerobic granular sludge (AGS) is based on self-granulated flocs forming mobile biofilms with a gel-like consistence. Bacterial and structural dynamics from flocs to granules were followed in anaerobic-aerobic sequencing batch reactors (SBR) fed with synthetic wastewater, namely a bubble column (BC-SBR) operated under wash-out conditions for fast granulation, and two stirred-tank enrichments of Accumulibacter (PAO-SBR) and Competibacter (GAO-SBR) operated at steady-state. In the BC-SBR, granules formed within 2 weeks by swelling of Zoogloea colonies around flocs, developing subsequently smooth zoogloeal biofilms. However, Zoogloea predominance (37-79%) led to deteriorated nutrient removal during the first months of reactor operation. Upon maturation, improved nitrification (80-100%), nitrogen removal (43-83%), and high but unstable dephosphatation (75-100%) were obtained. Proliferation of dense clusters of nitrifiers, Accumulibacter, and Competibacter from granule cores outwards resulted in heterogeneous bioaggregates, inside which only low abundance Zoogloea (