Multistability and Reversibility of Aerobic Granular Sludge Microbial Communities Upon Changes From Simple to Complex Synthetic Wastewater and Back

Abstract

Aerobic granular sludge (AGS) is a promising alternative wastewater treatment to the conventional activated sludge system allowing space and energy saving. Basic understanding of AGS has mainly been obtained using simple wastewater containing acetate and propionate as carbon source. Yet, the aspect and performances of AGS grown in such model systems are different from those obtained in reactor treating real wastewater. The impact of fermentable and hydrolyzable compounds on already formed AGS was assessed separately by changing the composition of the influent from simple wastewater containing volatile fatty acids to complex monomeric wastewater containing amino acids and glucose, and then to complex polymeric wastewater containing also starch and peptone. The reversibility of the observed changes was assessed by changing the composition of the wastewater from complex monomeric back to simple. The introduction of fermentable compounds in the influent left the settling properties and nutrient removal performance unchanged, but had a significant impact on the bacterial community. The proportion of Gammaproteobacteria diminished to the benefit of Actinobacteria and the Saccharibateria phylum. On the other hand, the introduction of polymeric compounds altered the settling properties and denitrification efficiency, but induced smaller changes in the bacterial community. The changes induced by the wastewater transition were only partly reversed. Seven distinct stables states of the bacterial community were detected during the 921 days of experiment, four of them observed with the complex monomeric wastewater. The transitions between these states were not only caused by wastewater changes but also by operation failures and other incidences. However, the nutrient removal performance and settling properties of the AGS were globally maintained due to the functional redundancy of its bacterial community.

Disentangle genus microdiversity within a complex microbial community by using a multi‐distance long‐read binning method: example of Candidatus Accumulibacter

“…Biomass samples of an aerobic granular sludge (AGS) reactor were collected every week to monitor the microbial communities through 16S rRNA gene amplicon sequencing, as previously described (Adler and Holliger, 2020). Since the microbial community composition was previously shown to be variable from one granule to another (Leventhal et al, 2018), a minimum of 20 granules was estimated sufficient to have a representative sample of the bacterial community (Adler, 2019).…”

“…Since the microbial community composition was previously shown to be variable from one granule to another (Leventhal et al, 2018), a minimum of 20 granules was estimated sufficient to have a representative sample of the bacterial community (Adler, 2019). Therefore, at least 1 ml of wet biomass per sample was collected and homogenized following the protocol described in the study by Adler and Holliger (2020). In addition, four samples were chosen for metagenome DNA sequencing and assembly.…”

“…Changes in the microbial community composition were observed throughout the experiment, also within the Ca. Accumulibacter population, which already indicated a certain microdiversity of this genus (Adler, 2019;Adler and Holliger, 2020). In order to introduce additional abundance differences among the extracted metagenomic DNAs, two different extraction methods were used, extraction A, a gentle extraction preserving long DNA fragments, and extraction B, a standard method.…”

Impact of the substrate composition on enhanced biological phosphorus removal during formation of aerobic granular sludge

“…as VFAs, resulted in fast and excellent granulation(Adler & Holliger, 2020;Layer et al, 2019). Relative small granule sizes were obtained in the reference reactors (SBR A and SBR D).…”

“…A minority of studies on AGS were performed with wastewater containing polymeric substances (Adler & Holliger, 2020;Layer et al, 2019). Complex substrates will leak in the aerobic phase as they cannot be readily taken up anaerobically by bacteria before undergoing hydrolysis (de Kreuk et al, 2010).…”