Identification of some of the major groups of bacteria in efficient and nonefficient biological phosphorus removal activated sludge systems

Abstract

To investigate the bacteria that are important to phosphorus (P) removal in activated sludge, microbial populations were analyzed during the operation of a laboratory-scale reactor with various P removal performances. The bacterial population structure, analyzed by fluorescence in situ hybridization (FISH) with oligonucleotides probes complementary to regions of the 16S and 23S rRNAs, was associated with the P removal performance of the reactor. At one stage of the reactor operation, chemical characterization revealed that extremely poor P removal was occurring. However, like in typical P-removing sludges, complete anaerobic uptake of the carbon substrate occurred. Bacteria inhibiting P removal overwhelmed the reactor, and according to FISH, bacteria of the beta subclass of the class Proteobacteria other than beta-1 or beta-2 were dominant in the sludge (58% of the population). Changes made to the operation of the reactor led to the development of a biomass population with an extremely good P removal capacity. The biochemical transformations observed in this sludge were characteristic of typical P-removing activated sludge. The microbial population analysis of the P-removing sludge indicated that bacteria of the beta-2 subclass of the class Proteobacteria and actinobacteria were dominant (55 and 35%, respectively), therefore implicating bacteria from these groups in high-performance P removal. The changes in operation that led to the improved performance of the reactor included allowing the pH to rise during the anaerobic period, which promoted anaerobic phosphate release and possibly caused selection against non-phosphate-removing bacteria.

FIG. 1

Performance of SBR during stage A (A) and stage B (B) of operation. Symbols: □, phosphate P concentrations in filtered effluent samples; ○, phosphate P concentrations in filtered samples from the end of anaerobic-stage mixed liquor; ▴, P content of the sludge, expressed as a percentage of the mass of the MLSS. Labelled arrows indicate the time points during operation when sludges Q and P occurred.

FIG. 2

Profiles of soluble extracellular phosphate P concentrations (□), extracellular acetate (●), cellular polyhydroxyalkanoates (PHA) (○), and cellular carbohydrate (▴) during the anaerobic and aerobic reactor cycle stages at the time of production of the Q sludge (A) and the P sludge (B).

FIG. 3

Bacterial-community analysis of the Q and P sludges as determined by FISH cell counts. The values obtained with the probes EUB338 (▧), ALF1b (▪), BET42a (), BONE23a (▧), BTWO23a (▨), GAM42a (□), and HGC69a () are expressed as percentages of the number of cells detected with the DAPI stain.

FIG. 4

FISH of the P sludge (A and B) and the Q sludge (C). Two images are presented for each view. On the left are cells binding fluorescein-labelled bacterial probe EUB338. On the right are the corresponding views of cells binding rhodamine-labelled probes BET42a (A and C) and HGC69a (B). Bar = 10 μm (applies to all panels).