Biological foaming (or biofoaming) is a frequently occurring problem in wastewater treatment plants (WWTPs) and is attributed to the overwhelming growth of filamentous bulking and foaming bacteria (BFB). Biological foaming has been intensively investigated, with BFB like
Microthrix
and
Skermania
having been identified from WWTPs and implicated in foaming. Nevertheless, studies are still needed to improve our understanding of the microbial diversity of WWTPs biofoams and how microbial activities contribute to foaming. In this study, sludge foaming at the Qinghe WWTP of China was monitored, and sludge foams were investigated using culture-dependent and culture-independent microbiological methods. The foam microbiomes exhibited high abundances of
Skermania
,
Mycobacterium
,
Flavobacteriales
, and
Kaistella
. A previously unknown bacterium,
Candidatus
Kaistella beijingensis, was cultivated from foams, its genome sequenced, and it was phenotypically characterized.
Ca
. K. beijingensis exhibits hydrophobic cell surfaces, produces extracellular polymeric substances (EPS), and metabolizes lipids.
Ca
. K. beijingensis abundances were proportional to EPS levels in foams. Several proteins encoded by the
Ca
. K. beijingensis genome were identified from EPS that was extracted from sludge foams.
Ca
. K. beijingensis populations accounted for 4–6% of the total bacterial populations in sludge foam samples within the Qinghe WWTP, although their abundances were higher in spring than in other seasons. Co-occurrence analysis indicated that
Ca
. K. beijingensis was not a core node among the WWTP community network, but its abundances were negatively correlated with those of the well-studied BFB
Sker
mania piniformis
among cross-season Qinghe WWTP communities.
Importance
Biological foaming or scumming is a sludge separation problem that has become the subject of major concern for long-term stable activated sludge operation in decades. Biological foaming was considered induced by foaming bacteria. However, the occurrence and deterioration of foaming in many WWTPs are still not completely understood. Cultivation and characterization of the enriched bacteria in foaming are critical to understand their genetic, physiological, phylogenetic, and ecological traits, as well as to improve the understanding of their relationships with foaming and performance of WWTPs.
Sludge bulking impact on relevant bacterial populations in a full-scale municipal wastewater treatment plant
