Multitasking Microbe to purify wastewater

Featured Image by Ivan Bandura on Unsplash

Researchers from NUS have developed a new way to treat sewage that is much simpler, cheaper and greener than existing methods.

Bacteria capable of simultaneous nitrification and denitrification (SND) as well as phosphate removal could eliminate the need for separate reactors to remove nutrients from wastewater. Additionally it could alleviate competition for carbon sources between different heterotrophs in wastewater treatment plants (WWTPs). This discovery was first reported in the journal Water Research on 15 October 2020.

A research team discovered the special SND5 microbe in a wastewater treatment plant based in Singapore. When they were performing the usual monitoring work, they came across a surprising removal of nitrogen present in the aerobic tanks and also the removal of phosphate, which was better than expected, in spite of the lack of familiar phosphorus-removing microorganisms.

The team subsequently collected wastewater samples from a tank, separated numerous bacterial strains and tested all of them for their potential to remove both phosphorus and nitrogen.

Photo 1: by Jemzo from Pixabay

Identification of strain SND5

Activated sludge from an anoxic tank in a wastewater treatment plant was cultivated and transferred sequentially in a denitrifying medium containing nitrate and a carbon source – lactate. Then the serial diluted culture was inoculated to agar shakes filled with the same medium. After 48 h incubation at 30 °C, creamy, convex, light-yellow, opaque colonies of approximately 2–5 mm in diameter with regular edges grew on agar shakes. The colonies were sticky and not conducive to picking.

The 16S rRNA gene was most similar to members of the genus Thauera, with the highest sequence similarity (99%) to Thauera sp. HMW3. Based on these results, the new isolate was determined to be a novel member of the genus Thauera and was designated SND5.

The researchers are mentioning three main advantages compare with the current process. It is:

  • Cheaper, because the aeration system in a wastewater treatment plant can consume nearly half of the plant's total energy.

The team has calculated that using the new bacterium in wastewater treatment plants could reduce electric power usage by about 62%, thanks to its lower oxygen demand, as compared to current techniques.

Photo 2: aeration system by Szilvia Kullai
  • Faster, because it performed the task much quicker when compared to other microorganisms that were tested by the team, furthermore phosphates originally present in sewage water were found to be removed as well.

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, expensive and takes longer. That is why they call it 2-in-1 pollutant remover. (In sewage, nitrogen is present in ammonia while phosphorous is present in phosphates.) Some other systems use only a single reactor for removing, but they are inefficient (because different microbes compete with one another for resources) and to maintain the delicate balance is also difficult among the microbes.

  • Greener, because it converts the ammonia into harmless nitrogen gas instead of nitrous oxide.

Some existing sewage treatment methods is that they release nitrous oxide, a greenhouse gas. As the conclusion of the study SND5 was isolated and found to also function as SND (simultaneous nitrification and denitrification) bacteria and a DPAO (denitrifying phosphate accumulating organisms). Strain SND5 simultaneously removes ammonium, nitrite, and nitrate without the accumulation of intermediates. It also removes phosphate from the medium whose carbon source is intracellular carbon PHB (polyhydroxybutyrate).

Szilvia Kullai

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