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Chemical Engineering

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Bacteria for wastewater treatment

| By Gerald Ondrey

Researchers from the National University of Singapore (, led by associate professor He Jianzhong, have found a new strain of bacterium called Thauera sp. strain SND5, which is capable of simultaneous nitrification and denitrification and phosphate removal from wastewater. The discovery has the potential to significantly reduce the operational costs and emission of greenhouse gases associated with traditional wastewater treatment methods.

Sewage contains nitrogen in ammonia and phosphorus in phosphates. Too much of either can pollute the environment and they must therefore be removed before the treated water can be released.

Most existing sewage treatment systems use separate reactors to remove nitrogen and phosphorus, which is a bulky and expensive process. Some existing systems use a single reactor, but they are inefficient because different bacteria in the same reactor will compete with one another, lowering the system’s overall efficiency.

Also, some existing systems release nitrous oxide, a greenhouse gas. The NUS team’s new bacterium converts the ammonia into harmless nitrogen gas instead. Compared with conventional nitrogen removal processes of nitrification and denitrification, the NUS team’s use of the new bacterium can save about 62% of electricity due to its lower oxygen demand.

The researchers are now planning to test their process at a larger scale, and formulate a “soup” of several bacteria to boost SND5’s performance even further.