Differences in populations of filamentous bacteria involved in foaming and bulking of activated sludge

Bulking and foaming of activated sludge are related to excessive proliferation of a specific group of activated sludge biocenosis – filamentous bacteria. The research was carried out to compare filamentous bacteria populations in foam and activated sludge in a full-scale municipal wastewater treatment plant located near Warsaw (Poland). Fluorescent in situ hybridization (FISH) – a quantitative, culture-independent, molecular method was applied to evaluate the structure of filamentous populations. Activated sludge and foam were examined for the abundance of eleven groups of these microorganisms, which occur in wastewater treatment plants in Europe. Filamentous bacteria constituted 18% and 24% of all bacteria detected in sludge and foam, respectively. The structures of filamentous bacteria populations in sludge and foam were different, although the same bacteria were found in both types of samples. The most abundant filaments belonged to phylum Chloroflexi (targeted by the CFXmix probe) and genus Microthrix (targeted by the MPAmix probe) in sludge and foam, respectively. The third significantly abundant bacteria was Haliscomenobacter hydrossis (targeted by HHY654).