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.

丝状膨胀是一种常见的严重操作问题，导致污泥沉降恶化，长期以来在活性污泥生物废水处理系统中观察到这种现象。其中发现的许多细菌属具有丝状形态，其中一些已被证明与膨胀事件有关（例如，约。 Microthrix），其他许多因素的影响仍不清楚。在这项研究中，我们使用 16S rRNA 扩增子测序对 17 个丹麦城市污水处理厂 (WWTP) 进行了为期 13 年的调查，其中对 30 个属的所有已知丝状细菌进行了分析。丝状群落平均占所有植物共有的相同属的总读数丰度的 13 ± 6%，最高可达 43%。约。 Microthrix 和属于 Chloroflexi 门的几个属是最丰富的丝状细菌之一。通过测量稀释污泥体积指数（DSVI）来分析丝状细菌对污泥沉降特性的影响。仅观察到与 DSVI 的强正相关性约。微丝菌和约。 Amarolinea，后者是新近鉴定的属，属于 Chloroflexi 门。尽管其他丝状细菌存在于许多植物中，但它们的膨大潜力并不显着。观察到两者的系统发育多样性较低约。微丝菌和约。 Amarolinea，使个体物种的生理特征和控制策略的潜在开发更加可行。 在这项研究中，我们表明，尽管丹麦污水处理厂的丝状系统发育型具有高度多样性，但只有少数丝状系统发育型导致了严重的膨胀事件。