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University of Bath

New approaches to microbial ecology in biological phosphorus removal systems

The project aims to develop new methodologies to study mixed microbial communities from biological phosphorus removal systems for better wastewater treatment.

Using biological wastewater treatment processes can deliver effective treatment.
Using biological wastewater treatment processes can deliver effective treatment.

The project aims to develop new strategies and methodologies to study the mixed microbial communities from biological phosphorus removal systems. Studying these communities is challenging as the variety of organisms and complexity of the system cannot always be studied with conventional microbiology techniques. Thus, innovative approaches to study these populations within their native communities rather than in artificial enrichments can enable a better understanding of biological phosphorus removal and lead to improved performance and efficiency of wastewater treatment.

Project outline

Using biological wastewater treatment processes can deliver effective treatment. They often promote higher efficiencies and act as a source of added-value compounds, such as phosphorous and polyhydroxyalkanoates. In particular phosphorus can be both a pollutant, contributing towards eutrophication, and a valuable resource with a shortage of extractable phosphorus resources predicted within the next 100 years. Recovery of this nutrient from wastewater is estimated to be able to meet 22% of global phosphorus demand.

Enhanced Biological Phosphorus Removal (EBPR) is often considered one of the most attractive processes for phosphorus removal from wastewater, one that does not require the addition of chemical precipitants, and with clear synergies with phosphorus recovery technologies. The uptake of phosphorus is performed mainly by a group of bacteria named polyphosphate-accumulating organisms (PAOs). However, effective phosphorus removal is often compromised by the population dynamics of the existing mixed microbial communities following variability in operational and environmental conditions, and the competition with different organisms. Also, due to the low concentration of carbon source in the wastewater, the process often requires the addition of carbon feedstocks such as acetate, which contribute to the overall process cost and carbon footprint. Hence, to ensure the resilience and effectiveness of this technology, further research is needed on the impact of process operation and different microbial stresses on the microbial ecology and phenotype of PAOs, especially “in the wild”, i.e. in real full-scale mixed liquors.

This project aims to explore some unanswered questions about the dynamics and function of the different populations composing the complex microbial communities. Although some groups of microorganisms have been identified as playing a key role in phosphorus removal, it is still not clear what the required abundance of these organisms is to ensure an efficient process. Other organisms have been identified as competitors to PAOs and detrimental to phosphorus removal, but still they are often found in well performing full-scale systems in the same abundance as PAOs. Bacteriophages constitute another group of organisms suggested to interfere with the population dynamics of the system by predating bacteria, but the extent of their impact is still unknown. With the use of strategies such as bio-augmentation of real activated sludge samples and quantification of bacteriophages, it is possible to get a better insight into these questions and mitigate biases associated with lab-scale systems. Some studies in full-scale EBPR systems will also be performed to monitor the microbial communities and correlate their composition with changes in operational conditions, response to different carbon sources in the wastewater and ultimately with the results obtained from lab-scale experiments.


The focus on developing and using innovative approaches to study the mixed communities present in EBPR will enable a more holistic understanding of the interactions and function of the microbial system. Lab-scale bioreactors will be used to promote the enrichment of the mixed microbial culture in specific groups or organisms which can then be supplemented to samples of full-scale activated sludge in bio-augmentation studies. The presence of other organisms, such as competing bacteria or bacteriophages, and the availability of different carbon sources will be considered and correlated with the populations’ dynamics in the culture.


Understanding the microbiology of EBPR with more detail can support a better control of these systems and ultimately improve phosphorus removal and process efficiency. Moreover, it can promote a wider implementation of EBPR in the UK as an efficient technology to treat wastewater, with no addition of chemical precipitation. The methodologies developed to study the different organisms in mixed microbial communities can be applied to other biological systems and environments.