New insight into the granule formation in the reactor for enhanced biological phosphorus removal

Anna Pelevina; Evgeny Gruzdev; Yulia Berestovskaya; Alexander Dorofeev; Yury Nikolaev; Anna Kallistova; Alexey Beletsky; Nikolai Ravin; Nikolai Pimenov; Andrey Mardanov

doi:10.3389/fmicb.2023.1297694

New insight into the granule formation in the reactor for enhanced biological phosphorus removal

Front Microbiol. 2023 Dec 14:14:1297694. doi: 10.3389/fmicb.2023.1297694. eCollection 2023.

Affiliations

¹ Winogradsky Institute of Microbiology, Federal Research Center of Biotechnology, Russian Academy of Sciences, Moscow, Russia.
² K.G. Skryabin Institute of Bioengineering, Federal Research Center of Biotechnology, Russian Academy of Sciences, Moscow, Russia.

Abstract

While granulated activated sludge exhibits high productivity, the processes of granule formation are incompletely studied. The processes of granule formation and succession of communities were investigated in a laboratory sequencing batch reactor (SBR) under conditions for enhanced biological phosphorus removal (EBPR) using microbiological and molecular techniques. Active consumption of acetate, primarily by the phosphate-accumulating organisms (PAO), commenced at day 150 of cultivation. This was indicated by the high ratio of molar P-released/acetate uptake (0.73-0.77 P-mol/C-mol), characteristic of PAO. During this period, two types of granule-like aggregates formed spontaneously out of the activated sludge flocs. The aggregates differed in morphology and microbial taxonomic composition. While both aggregate types contained phosphorus-enriched bacterial cells, PAO prevailed in those of morphotype I, and glycogen-accumulating organisms (GAOs) were predominant in the aggregates of morphotype II. After 250 days, the elimination of the morphotype II aggregates from the reactor was observed. The subsequent selection of the community was associated with the development of the morphotype I aggregates, in which the relative abundance of PAO increased significantly, resulting in higher efficiency of phosphorus removal. Metagenomic analysis revealed a predominance of the organisms closely related to Candidatus Accumulibacter IС and IIС and of Ca. Accumulibacter IIB among the PAO. Based on the content of the genes of the key metabolic pathways, the genomes of potential PAO belonging to the genera Amaricoccus, Azonexus, Thauera, Zoogloea, Pinisolibacter, and Siculibacillus were selected. The patterns of physicochemical processes and the microbiome structure associated with granule formation and succession of the microbial communities were revealed.

Keywords: Candidatus Accumulibacter; EBPR; formation of granule-like aggregates; phosphate-accumulating bacteria (PAO); phosphorus removal.

Grants and funding

The author(s) declare financial support was received for the research, authorship, and/or publication of this article. The reactors construction and operation, and chemical analyses were supported by the Ministry of Science and Higher Education of the Russian Federation (goszadanie). Metagenomic analysis and 16S rRNA sequencing were supported by the Russian Science Foundation (grant no. 21-64-00019).