Crystals increase microbes' methane emissions

UNSW researchers have discovered how to increase the amount of methane gas emitted by naturally occurring microbes living in coal seams and on food waste. Their work could extend the lifespan of coal seam gas wells, as well as improve the economics of using woody crops and leftover food as commercial sources of biogas.

Writing in the journal Energy & Environmental Science, the researchers explain that their technique involves the addition of small amounts of a synthetic dye that forms previously unobserved needle-like crystals to help the methane-producing microbes grow faster.

“If the microbes grow faster, they fart more methane,” said the study’s senior author, Associate Professor Mike Manefield.

The researchers studied a small synthetic molecule called neutral red that has been used for more than 150 years as a textile dye or for staining cells under a microscope. Associate Professor Manefield explained, “We knew it was able to shuttle electrons about, and we wondered if it could deliver them directly to the microbes that produce methane.

“When we added neutral red in the laboratory to a mixture of coal and naturally occurring groundwater microbes, in the absence of oxygen, we discovered it formed crystals that had never been seen before,” he continued.

“The crystals act as electron sponges, harvesting electrons from minerals and bacteria in the mixture and then transferring them with a lot of power to the methane-producing microbes, boosting their growth.”

The technology was also tested in a real-life environment in coal boreholes near Lithgow. Small amounts of neutral red were injected 80 m underground at three sites into the water-saturated coal seam. A fivefold to tenfold increase in methane production was observed during a 12-month period.

“Our research in the lab and in coal boreholes near Lithgow has shown that the crystals can lead to a massive leap in methane production — a tenfold increase from coal and an eighteen-fold increase from food waste,” said Associate Professor Manefield.

Biogas emitted by microbes will be vital for meeting the world’s future energy needs and helping reduce greenhouse gas emissions from the burning of other fossil fuels, according to Associate Professor Manefield, who said the discovery is “likely to be a game changer”.

“Coal seam gas wells usually have a short lifespan and spent ones litter the countryside,” he said. “Enhancing their methane production could reduce the need to build new ones.

“We also expect our approach will work with renewable feedstocks for methane-producing microbes, such as woody plant material and the by-products of municipal wastewater treatment.”

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