Download poster «Filamentous bacteria in a MBR»
Recent studies have suggested that the concentration of filamentous bacteria in the operation of a membrane bioreactor (MBR) should be controlled due to its negative effect on membrane fouling.Other authors found that the elevated presence of filamentous bacteria did not affect the quality of effluent or the permeability of the membranes. Identification of filamentous based on morphological identification can be ambiguous, so molecular methods such as fluorescence in situ hybridization (FISH) with oligonucleotide probes targeting different filamentous species are necessary for reliable identification. The aim of the present study was to determine the abundance of filamentous bacteria on MBR sludge samples using FISH. In the FISH analysis 16 rRNA-targeted nucleic acid probes covering phylum, class, genus and species were used. The abundance of filamentous bacteria in the 14 activated sludge samples was measured according to the subjective scoring method of Eikelboom (2000) where observations are rated on scale from 0 (none) to 5 (extensive growth). Many filaments were present in 100% of the samples, which implies that bulking still frequently occurs in MBR plants treating municipal wastewater. In 14 (100%) of the samples, several Chloroflexi (GNSB941+CFX1223 probe) filamentous species were observed. Members of Chloroflexi are responsible for degradation of soluble microbial products (SMP) including carbohydrates and cellular materials, which consequently reduces membrane fouling potential. Co-dominating (FI>5) populations of Caldilinea (probe caldi0678), Type 0803 (probe T0803-0654), Type 0092 (probe CFX197) and Candidatus “Monilibacter batavus” were observed. Type 0914 (probe CFX67a) (HHY probe) filaments were common (FI>3). Type 0092 variante B (probe CFX223) and Thiothrix (probe G123T) were observed in 10 of the samples (FI<3). Occurrence of Type 0041/0675, Haliscomenobacter hydrossis (4 samples with FI>2), and Type 1851 (4 samples with FI>5) were estimated by conventional microscopy. No fluorescence signal was detected with the probes TM7905 (Type 0041/0675), HHY (H. hydrossis), CHL1851 (Type 1851). Canonical correspondence analysis (CCA) was used to reveal the relationships between filamentous bacteria occurrence, operational parameters and influent characteristics. In the investigated range of reactor temperatures (Tr) (18-28ºC), a rise in temperature resulted in a higher Thiothrix abundance. Conversely, Type 0092 and Type 0914 were negatively related with Tr. The CCA biplot showed a positive relationship between the abundance of C. “M. batavus”and Thiothrix, and organic loading rate (OLR) and excess sludge production (ESP). The influent increase in the availability of C and N might have contribute positively to the change in relative abundance of C.”M. batavus” and Type 0092, while Thiothrix and Type 0914 were negatively related. Type 0914 was positively related with hydraulic retention time (HRT), contrary C. “M. batavus”and Thiothrix were negatively related with HRT.
Lledias, M., Zornoza, A., Alonso, J.L (2012) V International Conference on Environmental, Industrial and Applied Microbiology – BiomicroWorld 2013. Madrid, Spain.