A Critical Assessment of the Microorganisms Proposed to be Important to Enhanced Biological Phosphorus Removal in Full-Scale Wastewater Treatment Systems

Abstract

Understanding the microbiology of phosphorus (P) removal is considered essential to knowledge-based optimization of enhanced biological P removal (EBPR) systems. Biological P removal is achieved in these systems by promoting the growth of organisms collectively known as the polyphosphate accumulating organisms (PAOs). Also considered important to EBPR are the glycogen accumulating organisms (GAOs), which are theorized to compete with the PAOs for resources at the expense of P removal efficiency. Numerous studies have sought to identify the PAOs and their GAOs competitors, with several candidates proposed for each over the last few decades. The current study collectively assessed the abundance and diversity of all proposed PAOs and GAOs in 18 Danish full-scale wastewater treatment plants with well-working biological nutrient removal over a period of 9 years using 16S rRNA gene amplicon sequencing. The microbial community structure in all plants was relatively stable over time. Evidence for the role of the proposed PAOs and GAOs in EBPR varies and is critically assessed, in light of their calculated amplicon abundances, to indicate which of these are important in full-scale systems. Bacteria from the genus Tetrasphaera were the most abundant of the PAOs. The “Candidatus Accumulibacter” PAOs were in much lower abundance and appear to be biased by the amplicon-based method applied. The genera Dechloromonas, Microlunatus, and Tessaracoccus were identified as abundant putative PAO that require further research attention. Interestingly, the actinobacterial Micropruina and sbr-gs28 phylotypes were among the most abundant of the putative GAOs. Members of the genera Defluviicoccus, Propionivibrio, the family Competibacteraceae, and the spb280 group were also relatively abundant in some plants. Despite observed high abundances of GAOs (periodically exceeding 20% of the amplicon reads), P removal performance was maintained, indicating that these organisms were not outcompeting the PAOs in these EBPR systems. Phylogenetic diversity within each of the PAOs and GAOs genera was observed, which is consistent with reported metabolic diversity for these. Whether or not key traits can be assigned to sub-genus level clades requires further investigation.

Survey of full‐scale sidestream enhanced biological phosphorus removal (S2EBPR) systems and comparison with conventional EBPRs in North America: Process stability, kinetics, and microbial populations

“…Noticeably, however, 16S rRNA genes of Propionivibrio were detected at higher mean relative abundances in the conventional EBPR than S2EBPR systems. A recent study published on Danish EBPR facilities based on 16S rRNA gene sequencing (Stokholm‐Bjerregaard et al, ) showed rather consistent lower abundance of known GAOs in S2EBPR systems than the conventional plants. However, the abundance of GAOs in the Danish facilities was generally higher than observed in this study.…”

“…(d) Comparison of relative abundance of putative GAOs between conventional and S2EBPR facilities. The red point is the average relative abundance from Stokholm‐Bjerregaard et al ().…”

“…However, the abundance of GAOs in the Danish facilities was generally higher than observed in this study. This could be due to the heavy proportion of industrial load that has been observed in the Danish facilities which has been associated with increased GAO abundance (Mielczarek et al, ; Stokholm‐Bjerregaard et al, ). Differences in relative abundances observed could also be due to the small number of facilities surveyed in this study compared with Stokholm‐Bjerregaard et al ().…”

“…Amplicon data were rarefied to the minimum total sequence count (14,646 sequences) across all samples. To identify putative PAOs and GAOs (defined as organisms with glycogen-accumulating capability and no known phosphate-accumulating capability), the MiDAS field guide website (http://midas field guide.org/en/searc h/) was used (McIlroy et al, 2015;Stokholm-Bjerregaard et al, 2017). All data and statistical analyses were performed in R using the following packages: vegan (Oksanen et al, 2012), ggplot2 (Wickham., 2009), dplyr (Wickman, Francois, Henry, & Müller, 2018), and ampvis (Albertsen, Karst, Ziegler, Kirkegaard, & Nielsen, 2015).…”

“…S2EBPR has proven successful at a number of facilities worldwide; currently, there are about 80 full-scale facilities that have implemented various forms of the S2EBPR process (Barnard, Houweling, Analla, & Steichen, 2010;Copp, Belk, & Vale, 2012;Stevens, Ellsworth, Wyman, & Lambrecht, 2015;Stroud & Martin, 2001;Vale, Barnard, Thomas, & Dold, 2008;Vollertsen, Petersen, & Borregaard, 2006). A few recent studies that compared EBPR activities, rates, and microbial populations between S2EBPR and conventional EBPR facilities suggested observable differences between the two configurations (Lanham, Oehmen, et al, 2013a;Mielczarek, Nguyen, Nielsen, & Nielsen, 2013;Stokholm-Bjerregaard et al, 2017). Lanham, Oehmen, et al (2013a) compared two S2EBPR with three conventional systems and observed that the S2EBPR facilities exhibited a higher level of glycolysis activity and more efficient biological P removal than conventional systems.…”