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

Marta Nierychlo,Chenjing Jiang,Zivile Kondrotaite,Simon J Mcilroy,Mikkel Stokholm-Bjerregaard,Sergey Kucheryavskiy,Anja S Ziegler,Per Halkjær Nielsen

doi:10.3389/fmicb.2020.01214

Marta Nierychlo, Chenjing Jiang + Show 6 more

Open Access

https://doi.org/10.3389/fmicb.2020.01214

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Abstract

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.

Highlights

Filamentous bacteria are commonly observed in activated sludge in biological wastewater treatment plants (WWTPs) where they are suggested to importantly provide the structural backbone of well-settling flocs (Seviour and Nielsen, 2010)
The abundance of filamentous bacteria was surveyed in 17 Danish full-scale municipal biological nutrient removal (BNR) WWTPs over a period of 13 years using 16S rRNA gene amplicon sequencing
The genera analyzed represent all phylotypes known to contain species with a filamentous morphology (Table 1 and Figure 1, and Supplementary Figure S1), including genera that are always present in filamentous form in activated sludge (Figure 1, coral); genera with variable morphology in activated sludge (Figure 1, green); and genera, for which filamentous morphology has only been observed in pure culture, and their morphology in activated sludge is unknown (Figure 1, blue)

Summary

Introduction

Filamentous bacteria are commonly observed in activated sludge in biological wastewater treatment plants (WWTPs) where they are suggested to importantly provide the structural backbone of well-settling flocs (Seviour and Nielsen, 2010). Overgrowth of some filamentous bacteria is associated with deteriorated sludge settling, leading to sometimes serious operational problems known as sludge bulking (Liao et al, 2004; Martins et al, 2004; Lou and de los Reyes, 2005; Vervaeren et al, 2005). Some of those possessing hydrophobic cell surfaces can cause foam on the surface of process and settling tanks. Despite the available knowledge of filamentous bacteria, it is not possible to predict bulking events and the available control strategies are not always effective

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