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Scientists from the Singapore Center for Environmental Life Science Engineering (SCELSE) at Nanyang Technological University, Singapore (NTU Singapore) and the National University of Singapore, have developed a technique to eliminate the wastewater phosphorus at higher temperatures than is possible with existing techniques, using bacteria to store the chemical.

Current phosphorus removal techniques do not work well at temperatures above 25 degrees Celsius, which currently occurs in hot countries. This should extend to other countries, with the advent of global warming.

Due to the presence of various microbial communities in water reclamation plants in Singapore, the innovation developed by SCELSE, which is based on bacteria, would thus help to “sustain” the elimination of the chemical. This is how scientists demonstrated that it effectively removed phosphorus from wastewater at 30 degrees Celsius and 35 degrees Celsius.

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

It is important to remove phosphorus from wastewater before discharging it into freshwater bodies because its presence can lead to algal blooms, which is a rapid increase in the population of algae. Algal blooms dramatically reduce oxygen levels in natural waters when the algae die and sometimes result in the release of high levels of toxins, killing organisms that live in the waters they affect. In Singapore, wastewater is treated in water reclamation plants located near coastal areas before being discharged into the sea.

Unlike other methods, the method developed by SCELSE to remove phosphorus from wastewater does not involve chemicals, such as iron and aluminum coagulants*. These methods produce a large volume of inert sludge which must be treated and subsequently disposed of.

Bacteria-based technology extends the temperature range of enhanced biological phosphorus removal to 35 degrees Celsius. This would contribute to “future-proofing” phosphorus removal, as other methods using biological approaches only work at colder temperatures and would be rendered less effective as global temperatures are expected to rise due to warming. climatic.

The results of the study have been published in the journalWater Research in June.

Professor Stefan Wuertz of NTU, Deputy Center Director of SCELSE, who led the study, said: “We have shown that phosphorus can be stably removed in Singapore’s water reclamation plants even as we expect global water temperatures to rise further. and a high enough carbon input into the biological reactors, we effectively limited the carbon uptake rates of competing bacteria. This allowed Accumulibacter to thrive and benefited from a stable and efficient process, representing baseline conditions suitable for future large-scale processing plants. This will help Singapore and other countries experiencing high water temperatures to prepare for the effects of climate change.” Professor Wuertz is also from NTU’s School of Civil and Environmental Engineering.

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

Dr. Guanglei Qiu, a former researcher at SCELSE, who is also a co-author of the study, said: “The operation of biological reactors side by side at different temperatures has provided clues for mechanistic understanding and underlying changes. underlying in the microbial community. He is now an associate professor at South China University of Technology.

The innovation developed by SCELSE reflects NTU’s commitment to lessen our impact on the environment, which is one of the four great challenges of humanity that the University seeks to address as part of its NTU 2025 strategic plan. .

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

During a test period of over 300 days in the laboratory, they found that there was a constant removal of phosphorus, coping with daily infusions of fresh sewage containing the element.

The scientists will conduct further research to further improve the effectiveness of their method. They also plan to use the bacteria to capture and store phosphorus, which some experts say could be depleted globally within 50 to 100 years.

Professor Wuertz added: “Almost all the phosphorus that farmers use today and that we consume in the foods we eat is extracted from a few phosphate rock sources, mainly in the United States, China and Morocco. Our solution could not only aid in the future-proof biological removal of phosphorus, but also store the element and then reintroduce it into agricultural systems.

* Coagulants are a substance that causes particles of a liquid to curdle and coagulate.