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.
Highlights
Wastewater treatment using the enhanced biological phosphorus removal (EBPR) process is capable of achieving low effluent phosphorus (P) concentrations without addition of chemical precipitants
As EBPR systems are at times subject to failure, or periods of low efficiency, an understanding of the microbiology that underpins the process is important for knowledge-based optimization
The abundance and diversity of all proposed polyphosphate accumulating organisms (PAOs) and glycogen accumulating organisms (GAOs) were assessed in 18 Danish full-scale wastewater treatment plants with EBPR over a period of 9 years using 16S rRNA gene amplicon sequencing
Summary
Wastewater treatment using the enhanced biological phosphorus removal (EBPR) process is capable of achieving low effluent phosphorus (P) concentrations without addition of chemical precipitants. EBPR systems achieve this by utilizing the ability of polyphosphate accumulating organisms (PAOs) to take up and store excessive amounts of P. Compared to chemical precipitation, EBPR is a sustainable, effective, and economical process (Seviour et al, 2003). P-rich sludge from EBPR plants is seen as a high quality, sustainable, and economical alternative source of P (Jeanmaire and Evans, 2001; Molinos-Senante et al, 2011). As EBPR systems are at times subject to failure, or periods of low efficiency, an understanding of the microbiology that underpins the process is important for knowledge-based optimization. Many studies on the identity, diversity, and physiology of PAOs and their proposed competitors, the glycogen accumulating organisms (GAOs), have been carried out (Oehmen et al, 2007)
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