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Harvesting fertiliser from ‘bionic’ leaves

April 16, 2017, by Tim Radford

fertiliser

The technology, which means fertiliser could one day be made in the soil where the crops are grown, would transform production for subsistence farmers. Image: Likezzo via Wikimedia Commons

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Scientists working on artificial photosynthesis have adapted their “bionic leaf” so it can turn sunlight, water and air into fertiliser.

LONDON, 16 April, 2017 – The Harvard scientist who pioneered a “bionic leaf” that could generate the production of fuel has taken artificial photosynthesis a step further.

He and his colleagues have developed a bionic leaf that – with some help from friendly bacteria – can turn sunlight, water and air into fertiliser. And field tests of the new system have yielded vegetables that weigh half as much again as the same varieties in the nearby control plots.

The system is still in trials: it has yet to spread to commercial agriculture, and even more importantly to the subsistence farming of the developing world. But, by 2050, another 2 billion people will have crowded onto a planet in which climate change already threatens agricultural yields and there is room for any technology that could use existing arable land to deliver greater quantities of food without recourse to the high-energy costs of chemically produced fertilisers.

From plant technology to fertiliser

Last year Daniel Nocera, Patterson Rockwood professor of energy at Harvard University, announced the completion of a bionic leaf 10 times more efficient than natural foliage, that could split water molecules and feed the hydrogen to bacteria as the first step towards liquid fuel production: that is, it could deliver energy to drive an engine without significantly adding to the carbon dioxide ratio in the atmosphere.

But he told the American Chemical Society meeting in San Francisco that his artificial leaf  has now been converted, with help from sophisticated chemistry, and a different microbe, into something even more useful: ammonia.

“The fuels were just the first step,” Professor Nocera said. “Getting to that point showed that you can have a renewable chemical synthesis platform. Now we are demonstrating the generality of it by having another type of bacteria take nitrogen out of the atmosphere to make fertiliser.”

“The fuels were just the first step. Now we are demonstrating the generality of it by having another type of bacteria take nitrogen out of the atmosphere to make fertiliser.”

The artificial leaf uses a catalyst made of an alloy of cobalt and phosphorus to split water and release hydrogen to feed a microbial species called xanthobacter, which stores the element in its body as a bioplastic.

“I can then put the bug in the soil because it has already used the sunlight to make the bioplastic,” he said.  “Then the bug pulls nitrogen from the air and uses the bioplastic, which is basically stored hydrogen, to drive the fixation cycle to make ammonia for fertilising crops.”

Turning rubbish into fuel

And while land-based chemists pioneer a new way to make chemical fertiliser without fossil fuel energy, an ocean-going initiative has told the American Chemical Society that it has developed a mobile reactor that can turn plastic detritus into fuel. Plastic waste now litters the planet so profusely that it is likely to linger in geological strata a few million years from now as indelible evidence of human disruption.  And a colossal volume of this enduring litter – more than 9 million tons a year   –  now ends up in the oceans.

James E Holm, captain of a sailing boat, and founder of Clean Oceans International, was appalled at the evidence of global pollution.

“A few years ago, I was sailing through the Panama Canal, and when I stopped at an island on the Atlantic side, I was stunned by the amount of plastic covering the beach. I thought if I had a chance to do something about it, I should,” he said.

He joined forces with Swaminathan Ramesh, a retired chemist and founder of EcoFuel Technologies to develop a catalysis reaction that could turn plastic waste – a byproduct of crude oil technology – back into diesel fuel, on a continuous system.

“We can scale the capacity to handle anything from 200 pounds per 10-hour day to 10,000 or more pounds per 10-hour day. Because of its small size, we also can take the technological process to where the plastic wastes are,” said Dr Ramesh.

It may be some time before the technology gets to market. Both instances, however, are evidence of astonishing ingenuity in the world’s laboratories, driven by the menace of climate change and the need for technologies that do not depend on fossil fuel combustion which, ultimately, drives climate change.

To be of real use, both technologies need to be portable systems that anybody can exploit. “If we can get people around the world to pick this up and use it to shift waste plastics to fuel and make money, we are winning,” said Holm “We can even eliminate plastic waste before it gets to the oceans by creating value for it locally, on a global basis.”

The same imperative to spread the technology is true for the bionic leaf-based fertiliser. “When you have a large centralised process and a massive infrastructure, you can easily make and deliver fertiliser,” Professor Nocera said. “But if I said that now you’ve got to do it in a village in India, onsite, with dirty water  – forget it. Poorer countries in the emerging world don’t always have the resources to do this. We should be thinking of a distributed system because that’s where it’s really needed.” – Climate News Network

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