Scientists can remove phosphorus from wastewater

(L-R) SCELSE Research Assistant Ms Hoon Hui Yi, SCELSE Research Associate Ms Sara Swa Thi, Research Fellow at SCELSE’s Integrative Analysis Unit Dr Liu Xianghui, and Prof Stefan Wuertz, who is also Research Director of SCELSE’s Environmental Engineering cluster at NTU Singapore. (Credit: NTU Singapore)

Singapore Centre for Environmental Life Sciences Engineering (SCELSE) scientists at Nanyang Technological University, Singapore (NTU Singapore) and the National University of Singapore have developed a technique to remove phosphorus from wastewater at higher temperatures than is possible using existing methods. They used bacteria to store the chemical.

Current techniques to remove phosphorus do not work well at temperatures above 25 degrees Celsius. This is a common situation now in warm countries. This is expected to extend to more countries with the advent of global warming.

Due to the diverse microbial communities in water reclamation plants in Singapore, the SCELSE-developed innovation would help to ‘future-proof’ the removal of phosphorus. It has effectively removed phosphorus from wastewater at 30 degrees Celsius and 35 degrees Celsius.

Called Candidatus Accumulibacter, the bacterial genus is not harmful to humans or the environment. It removes phosphate from wastewater and stores it internally as polyphosphate granules. The scientists say their method could be used in laboratory-scale reactors and full-scale treatment plants.

Removing phosphorus from wastewater before discharging it into bodies of fresh water is important. Its presence can result in algal bloom and a rapid increase in the algae population. Algal blooms severely lower oxygen levels in natural waters when the algae die off and sometimes release high levels of toxins. They call kill organisms that live within the waters it affects. In Singapore, wastewater is treated at water reclamation plants near coastal areas before it is discharged into the sea.

Technique for removing phosphorus from wastewater

The SCELSE-developed method to remove phosphorus from wastewater does not involve chemicals. These methods produce a large volume of inert sludge that needs to be treated and disposed of afterwards.

The bacteria-based technology extends the temperature range of enhanced biological phosphorus removal to 35 degrees Celsius. This would help to ‘future-proof’ phosphorus removal. Other methods using biological approaches work only at cooler temperatures. It would be rendered less effective as temperatures globally are expected to rise due to global warming.

The study results were published in the journal Water Research in June.

NTU Professor Stefan Wuertz, Deputy Centre Director of SCELSE, who led the study, said: “We have shown that phosphorus could be stably removed in Singapore’s water reclamation plants. We expect global water temperatures to increase further. Employing a slow-feeding strategy and sufficiently high carbon input into biological reactors, we effectively limited the carbon uptake rates of competing bacteria. This allowed Accumulibacter to flourish and benefited a stable and efficient process. It represents basic conditions suitable for future full-scale treatment plants. This will help Singapore and other countries experiencing high water temperatures prepare for climate change’s effects.” Prof Wuertz is also from NTU’s School of Civil and Environmental Engineering.

Comments from the scientists

Co-author Dr Rohan Williams, Head of the Integrative Analysis Unit in SCELSE, said: “We found that the Accumulibacter strains in the reactors were closely related to those commonly found in temperate systems, suggesting that the chosen strategy successfully preserved the microdiversity needed for a stable process.” He is also a Senior Research Fellow at the National University of Singapore Life Sciences Institute.

Dr Guanglei Qiu, a former Research Fellow at SCELSE, who also co-authored the study, said: “Operating biological reactors side by side at different temperatures provided the clues for a mechanistic understanding and underlying changes in the microbial community.” He is now an Associate Professor at the South China University of Technology.

The SCELSE-developed innovation reflects NTU’s commitment to mitigating our impact on the environment. It is one of four of humanity’s grand challenges that the University seeks to address through its NTU 2025 strategic plan.

Future of removing phosphorus from wastewater

To begin the process, the researchers enriched the bacteria from wastewater in experimental reactors with temperatures from 30 degrees Celsius to 35 degrees Celsius. They also ensured that the pH was neutral. After a six-hour cycle, the bacteria absorbed the phosphorus completely.

Over a testing period of over 300 days in a laboratory setting, they found consistent phosphorus removal. It coped with the daily infusions of fresh wastewater that contained the element.

The scientists will be conducting further research to improve their method’s efficacy. They are also looking toward using the bacteria to capture and store phosphorus. Some experts believe there could be no more phosphorus within 50 to 100 years.

Wuertz added: “Nearly all the phosphorus that farmers use today comes from a few sources of phosphate rock, mainly in the United States, China, and Morocco. Our solution could help future-proof biological phosphorus removal and store the element. In the future, they hope to re-introduce it into agricultural systems.

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