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Microbes for Greener Wastewater Treatment

Researchers from the National University of Singapore (NUS) have developed a new way to treat sewage that is much simpler, cheaper and greener than existing methods through a new strain of bacterium that can remove both nitrogen and phosphorous from sewage.

Research team led by Associate Professor He Jianzhong from the Department of Civil and Environmental Engineering at the Faculty of Engineering, the NUS team found a new strain of bacterium calledThauera sp. strain SND5 that can remove both nitrogen and phosphorus from sewage.

The result of this discovery was published in the journalWater Research. The new bacterium strain when used for wastewater treatment was found to significantly reduce the high operational costs and emission of greenhouse gases associated with traditional wastewater treatment methods. The team’s new treatment method was in the running for the International Water Association Project Innovation Awards 2021.

Nitrogen is present in ammonia while phosphorous is present in phosphates in sewage. High levels of either puts risk polluting of the environment, efficient removal is essential before the treated water can be released. Most existing sewage treatment systems use separate reactors for removing nitrogen and phosphorous, with different conditions for different microbes. Such a process is both bulky and expensive.

Some existing systems use a single reactor, but they are inefficient because different microbes in the same reactor will compete with one another for resources. This makes it difficult to maintain the delicate balance among the microbes, resulting in an overall lower efficiency.

Another problem with some existing sewage treatment methods is that they release nitrous oxide, a greenhouse gas. The discovery of this new microbe solves this challenge as it converts the ammonia into harmless nitrogen gas instead. Additionally, phosphates originally present in sewage water were found to be removed.

The unique SND5 bacterium was discovered in a wastewater treatment plant in Singapore. When the research team was carrying out routine monitoring, they observed an unexpected removal of nitrogen in the aerobic tanks, as well as better-than-expected phosphate removal despite the absence of known phosphorus-removing bacteria.

“This leads us to hypothesise the occurrence of a previously undescribed biological phenomenon, which we hope to understand and harness for further applications,” said Associate Professor He.

The NUS researchers then took wastewater samples from a tank, isolated various strains of bacteria, and tested each of them for their ability to remove nitrogen and phosphorus. One of the strains, which appeared as sticky, creamy, light yellow blobs on the agar medium, surprised the researchers by its ability to remove both nitrogen and phosphorous from water. In fact, it did the job faster than the other microbes that were tested. The NUS team sequenced its genes and compared them to related bacteria in a global database. They then established it to be a new strain.

Compared to conventional nitrogen removal processes of nitrification and denitrification, the NUS team’s way of using the newly identified microbe can save about 62 percent of electricity due to its lower oxygen demand. This is of great significance as the aeration system in a wastewater treatment plant can consume nearly half of the plant’s total energy.

Associate Professor He explained that with growing populations then increase in wastewater production demands the need for new technologies to reduce operation cost and overall, less waste.

Further to this current discovery the NUS researchers are looking to test their process at a larger scale, and formulate a “cocktail” of multiple microbes to boost the new microbe’s performance. [APBN]