Is there a better way to squeeze the energy from a lump of coal? An Australian researcher may have found the secret solution.
The human race is grateful to coal. The black, gritty energy source has propelled us forward at a rapid pace. But it turns out there was a dirty secret and now the relationship needs to be wound up. It will be a long and painful process.
In the meantime, can there be any harm in working out a benign method to release the latent energy in coal? At the University of NSW in Sydney, Michael Manefield thinks he has a solution.
The micro-organisms that convert food, agricultural waste and sewage to methane gas struggle when it comes to digesting coal. “Coal is a really crappy substrate for microbes to eat,” says Manefield, associate professor at the schools of chemical engineering civil and environmental engineering. “If they did want to eat it, it wouldn’t be there any more, over those time scales.”
When organic matter is formed from photosynthesis, light energy is used to form carbon-to-carbon bonds or carbon-to-hydrogen bonds. “The energy is stored in that chemistry, in those bonds,” says Manefield. If organic matter is buried and microbes don’t get to compost it, it eventually turns into coal and oil.
Looking for a catalyst
In 2009 the university was approached by Biogas Energy to find a way to accelerate the biological process that leads to gas production in coal, with some help from a grant from the Australian Research Council. If coal could be made more palatable for a microorganism, then more of that trapped energy could be released.
It’s possible to increase production of gas from a coal seam by adding nitrogen and phosphorous, which will increase microbial activity in attacking the coal. A microbial cell is essentially a cocktail of carbon and the nutrients nitrogen and phosphorous, mixed to the ratio of 100:10:1.
The simple process of encouraging methane production by adding nitrogen and phosphorous to coal works – a little bit – but Manefield and his team knew there had to be a way to enhance gas production from coal or any organic feedstock.
It was a puzzle, but the researchers made a breakthrough when they looked at the problem from another angle. Instead of regarding this complex community of different microorganisms as a living entity, why not think of it like a circuit board? “It all comes down to electrons,” says Manefield. “Life is about shuffling electrons around.”
Manefield points to his muesli bar, the source of his electrons. When he eats the bar, he needs to put the electrons somewhere, so he must breathe. “I need the oxygen to take the electrons. If I don’t have that electron transfer I can’t harvest the energy from it.”
It’s the same thing for microorganisms. They can respire oxygen but they can also respire all sorts of other stuff, like nitrate, iron, sulphate, uranium. The next step requires an understanding of chemistry beyond the scope of your correspondent, so we’ll have to take Manefield’s word for it. Here goes…
The circuit solution
Electrons come from organic feedstock, and microorganisms take those electrons. Sulphate-reducing bacteria will pass the electrons to sulphate, which isn’t useful; iron-reducing bacteria will pass the electrons to iron, which isn’t useful; nitrate-reducing bacteria will pass the electrons to nitrate, which isn’t useful. “We want those electrons to go to the organisms that produce methane,” says Manefield, drawing a diagram. “You can start to think of that as a circuit board; What’s the fate of the electrons? Where are they going to go? Can we short-circuit that and get more of those electrons to go to the methanogenic archaea [the methane-producing microbes]?”
The team started working with chemical compounds called electron shuttles that can change the fate of where an electron is headed. And that’s when it stumbled upon neutral red, an electron shuttle than can deliver electrons to the methane-producing microbes. But they needed a concentration of neutral red that was above its solubility limit and precipitated into crystals – magic crystals, as Manefield calls them, that have the remarkable property of acting like an “electron sponge”, taking electrons from cells, minerals or whatever is around them.
In a molecular-scale production line, methane-producing microorganisms will then get the electrons off the crystals because the molecule that forms the crystals is very similar to a molecule in the respiratory machinery in the biochemistry of the methane-producing microorganisms.
In the lab the process was found to boost gas production from coal tenfold after a three-month wait. “All of a sudden you get this massive increase,” says Manefield, who has been shortlisted for the PLuS Alliance Global Prize, worth $US25,000. The PLuS Alliance includes UNSW, Kings College London and the Arizona State University.
Work in progress
The potential for the researchers’ solution as a commercially viable method of extracting methane from coal persuaded the Australia-India Strategic Research Fund to invest in a project collaboration between UNSW and the Energy and Resources Institute in Delhi, with industry partners Santos, Biogas Energy and the Oil and Natural Gas Corporation in India. Working at the Lithgow State Mine in NSW, researchers have drilled five 80-metre wells into a coal seam to test different methods of extracting methane, and neutral red is working best of all.
About 30 grams of the solution is dissolved in two litres of water and feed into a 135mm-diameter well containing about 450 litres of water. The wells end about 2m into a 3m coal seam. Crystals have been observed in samples, along with a big boost in gas production.
“There is a lot of energy that’s being left in those substrates – the organic feedstocks – and it’s a question of how do you liberate it,” says Manefield. “Our treatment won’t take out the nitrate and phosphorous; it’s just a consumption of the carbon.”
The economics of success will be built on the cost of neutral red and expected boost in gas yield.
Manefield has the coal-seam gas industry in mind as a prime application for his magic crystals, but a paper published in 2016 drew enormous interest from commercial anaerobic digestion operations keen to increase gas production and survive a rollback of subsidies. Germany for example has about 16,000 anaerobic digesters, supported by government subsidies. “They can make more money if they can get more gas out of the stuff that they’re trying to extract energy out of.” These operations make most of their money from being paid to take waste, and they sell fertiliser as a byproduct. In Sydney, the Earthpower facility takes about 600 tonnes of food waste a week from supermarkets, restaurants and food processors.
Manefield looked for funding from small biogas players but has found himself managing the expectations of many while working with a budget that isn’t going quite far enough. The team needs more funding. “We’ll find it,” he says. “That’s my job.”