Candidatus Amarolinea and Candidatus Microthrix Are Mainly Responsible for Filamentous Bulking in Danish Municipal Wastewater Treatment Plants

Marta Anna Nierychlo, Simon J. McIlroy, Sergey Kucheryavskiy, Chenjing Jiang, Anja Sloth Ziegler, Zivile Kondrotaite, Mikkel Stokholm-Bjerregaard, Per Halkjær Nielsen*

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review

21 Citations (Scopus)
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Filamentous bulking is a common serious operational problem leading to deteriorated sludge settling that has long been observed in activated sludge biological wastewater treatment systems. A number of bacterial genera found therein possess filamentous morphology, where some have been shown to be implicated in bulking episodes (e.g., Ca. Microthrix), the impact of many others is still not clear. In this study we performed a survey of 17 Danish municipal wastewater treatment plants (WWTPs) with nutrient removal using 16S rRNA amplicon sequencing over a period of 13 years, where all known filamentous bacteria from 30 genera were analyzed. The filamentous community constituted on average 13 ± 6%, and up to 43% of total read abundance with the same genera common to all plants. Ca. Microthrix and several genera belonging to phylum Chloroflexi were among the most abundant filamentous bacteria. The effect of filamentous bacteria on sludge settling properties was analyzed using measurements of the diluted sludge volume index (DSVI). Strong positive correlations with DSVI were observed only for Ca. Microthrix and Ca. Amarolinea, the latter being a novel, recently characterized genus belonging to the phylum Chloroflexi. The bulking potential of other filamentous bacteria was not significant despite their presence in many plants. Low phylogenetic diversity was observed for both Ca. Microthrix and Ca. Amarolinea, making physiological characterization of individual species and potential development of control strategies more feasible. In this study we show that, despite the high diversity of filamentous phylotypes in Danish WWTPs, only few of them were responsible for severe bulking episodes.
Original languageEnglish
Article number1214
JournalFrontiers in Microbiology
Publication statusPublished - 9 Jun 2020


  • 16S rRNA amplicon sequencing
  • filamentous bulking
  • activated sludge
  • Ca. Microthrix
  • Ca. Amarolinea


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