Ecology of the Microbial Community Removing Phosphate from Wastewater under Continuously Aerobic Conditions in a Sequencing Batch Reactor

Abstract

All activated sludge systems for removing phosphate microbiologically are configured so the biomass is cycled continuously through alternating anaerobic and aerobic zones. This paper describes a novel aerobic process capable of decreasing the amount of phosphate from 10 to 12 mg P liter ؊1 to less than 0.1 mg P liter ؊1(when expressed as phosphorus) over an extended period from two wastewaters with low chemical oxygen demand. One wastewater was synthetic, and the other was a clarified effluent from a conventional activated sludge system. Unlike anaerobic/aerobic enhanced biological phosphate removal (EBPR) processes where the organic substrates and the phosphate are supplied simultaneously to the biomass under anaerobic conditions, in this aerobic process, the addition of acetate, which begins the feed stage, is temporally separated from the addition of phosphate, which begins the famine stage. Conditions for establishing this process in a sequencing batch reactor are detailed, together with a description of the changes in poly-␤-hydroxyalkanoate (PHA) and poly(P) levels in the biomass occurring under the feed and famine regimes, which closely resemble those reported in anaerobic/aerobic EBPR processes. Profiles obtained with denaturing gradient gel electrophoresis were very similar for communities fed both wastewaters, and once established, these communities remained stable over prolonged periods of time. 16S rRNA-based clone libraries generated from the two communities were also very similar. Fluorescence in situ hybridization (FISH)/microautoradiography and histochemical staining revealed that "Candidatus Accumulibacter phosphatis" bacteria were the dominant poly(P)-accumulating organisms (PAO) in both communities, with the phenotype expected for PAO. FISH also identified large numbers of betaproteobacterial Dechloromonas and alphaproteobacterial tetrad-forming organisms related to Defluviicoccus in both communities, but while these organisms assimilated acetate and contained intracellular PHA during the feed stages, they never accumulated poly(P) during the cycles, consistent with the phenotype of glycogen-accumulating organisms.High levels of phosphate in effluents from activated sludge systems not designed to remove it can lead to toxic cyanobacterial blooms in receiving bodies of water. Consequently, efforts have been directed towards removing phosphate during treatment by microbiological means with a process called enhanced biological phosphorus removal (EBPR), where phosphate is removed from the wasted biomass as intracellular poly(P) (5, 37, 45). Such treatment processes are based on the underlying principle that the biomass needs to be recycled repeatedly through alternating anaerobic and aerobic stages (37), a requirement regarded as crucial for successful EBPR operation. Only after repeated recycling are poly(P)-accumulating organisms (PAO) thought to have a selective advantage over other populations, eventually allowing them to become dominant (5,37,45). In the anaerobic (feed) stage, PAO are belie...

Simple and Safe Method for Simultaneous Isolation of Microbial RNA and DNA from Problematic Populations

“…Their RNA has been difficult to recover in 16S rRNA gene clone libraries (1,12). Semiquantitative fluorescence in situ hybridization analyses of these populations (6) gave data that corresponded well with data obtained by quantitative PCR, suggesting that our method does not introduce significant extraction bias.…”

“…Increased safety and a reduced number of pipetting steps make the method suitable for high-throughput analysis. Consequently, it should prove valuable in molecular microbial ecology where current extraction protocols can fail to recover sequences from recalcitrant populations in clone libraries (1,9,12,16).…”

Characterization of the Denitrification-Associated Phosphorus Uptake Properties of “Candidatus Accumulibacter phosphatis” Clades in Sludge Subjected to Enhanced Biological Phosphorus Removal

“…Previous studies have demonstrated that members of the genera Dechloromonas and "Ca. Competibacter" have nitrate reduction abilities and can accumulate internal polyhydroxyalkanoate (PHA) throughout the SBR cycle (46,(54)(55)(56)(57)(58)(59). These results suggested that the nitrite increase observed during the early anoxic phase (Fig.…”

Dynamics of Polyphosphate-Accumulating Bacteria in Wastewater Treatment Plant Microbial Communities Detected via DAPI (4′,6′-Diamidino-2-Phenylindole) and Tetracycline Labeling

“…Since the abundances of PAOs are of great interest for EBPR processes, we propose the use of our technique for quick and reliable authentication of PAOs in WWTPs. Traditional models imply that polyphosphate accumulation occurs during aerobic growth or if the cells are exposed to stress situations such as the decrease of external pH or carbon substrate concentration (2). However, recent studies showed that some species still keep polyphosphate granules even under anaerobic conditions (36).…”