David Derbowka has long turned to trees to clean up toxic landfills, using plantations of poplars to draw contaminants from polluted soil.
Now he is teaming up with a University of British Columbia chemist in a project aimed at extracting from the trees the chemicals they absorbed through their extensive root systems. It is taking recycling to a new level, using plant metabolism and modern science to reclaim chemicals that otherwise might pollute aquifers.
“My hope is to provide hope for people on the Earth – to just show the world there is a way to repair the damage that’s been done,” Mr. Derbowka, founder and chief executive of Passive Remediation Systems Ltd., said Thursday.
His B.C.-based company has worked on projects globally and across Canada, using the natural filtration process of plants to help remediate toxic sites.
One method he’s perfected is to plant groves of hardy, fast-growing, hybrid poplar trees that flourish on landfills.
“Nowadays, a proper landfill site is built into a bowl with a big plastic liner. … The rain runs down into it and that water is collected out of the bottom. And it’s pretty nasty water. That is what I irrigate the trees with. To me, it’s a simple thing. … I’m actually just a kind of a farmer,” he said.
The trees filter chemicals and metals out of the water, storing and using the pollutants.
When the trees mature, they are cut and, through pyrolysis – a process that creates chemical reactions through the high heat of a smouldering fire – they are reduced to biochar, an organic substance that can be used to add nutrients to soil.
The process creates a useful agricultural product, but the steam generated in pyrolysis leaves a residue known commonly as “wood vinegar,” a kind of concentrated slurry of chemicals that Mr. Derbowka didn’t know what to do with.
At the UBC Okanagan campus in Kelowna recently, he met Susan Murch, a chemist with expertise in the phytochemical analysis of plants. In Mr. Derbowka’s wood vinegar waste, Dr. Murch saw great opportunity.
“There is a fair amount of science out there [about] using poplar trees to clean up volatile organics, heavy metals, phosphorous, … cadmium and a variety of environmental pollutants,” she said.
“Hybrid poplars have been bred specifically for this purpose and they are more efficient at it than many other tree species. They grow very fast and produce quite a lot of biomass, and then the question is what do you do with the leaves and the shoots and the trunks of the trees? You don’t want them to just decompose and redeposit the contaminants in the soil … so you need to harvest them and process them to extract the various chemicals back out. That’s where I come in.”
Dr. Murch said the steam from making biochar creates a “chemical cocktail” of ingredients, but exactly what’s in there isn’t known yet.
“It’s a lot like burned sugar. And maybe like a sort of runny tar. It’s a thick, dark brown liquid,” she said, describing the consistency of the wood vinegar samples she has in her lab.
Her work now, which is funded by the Natural Sciences and Engineering Research Council of Canada, is to identify the chemicals in the hybrid poplar cocktail and figure out how to make the best use of them.
Dr. Murch said it might be possible to extract directly from the trees some of the chemicals they absorbed from landfill sites, but there will also be other chemical compounds in the wood vinegar that might be useful.
“The interesting thing about this project is that this specific type of plant has the capacity to take a lot of different chemicals from the soil,” she said. “I’m hoping to find some chemistry that will be useful in growing plants, so things like organic fertilizer.”
Hybrid poplars are tough trees that are good at fending off insect attacks, Dr. Murch said, “so I’m hoping we can import some of their natural defences” to create pesticides.
There is also a growing demand for organic materials for new manufacturing technologies, she said.
“I’m hoping that we can also find some interesting molecules that feed into manufacturing processes. … 3-D printing, that kind of new technology, is requiring all kinds of new molecules to put into those systems. … So rather than using plastic-based molecules, [maybe] we can use some organic tree-based molecules,” said Dr. Murch, whose research project has just begun.