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Forestry waste put to use

June 13, 2014, Jönköping – Canadian Forest Industries made the long treck to Sweden last week to attend World Bioenergy 2014. It was an opportunity to learn how the Swedish forest industry is able to make use of forestry waste to produce heat, power and biogas throughout the country.

In the forest

A typical logging operation in Sweden doesn't differ much from what can be observed in Canada where cut to length logging is practiced. But once the sawlogs have been harvested and piled by the roadside, slash piles are left to dry under tarps to keep the rain off them. These tops and limbs are left to dry throughout the summer before a contractor comes to chip the piles for delivery to the end user.

On the warm spring day, Canadian Forest Industries visited the harvesting site, a contractor had driven a compact European-sized truck that sported a small loader and grinder combination with an open back to catch the biomass. The pile was a good six feet in height and 30 feet long and about 10 feet wide. He had worked through a good portion of the pile in the couple of hours before we arrived and expected to be finished in a couple more hours.

The operator's skill was evident as he made quick work of the pile. The loader sliced through the covering into the slash pile and dropped it into the grinder that was able to reduce even large trunks into chips that sprayed into the top of the trailor. The compact combo was efficient and powerful and matched the operator to make it a productive team. He would have a European-sized truck full of wood chips in about four hours, deliver it to the client and return to the forest for a second load at another site.

In high demand

Residuals aren't always chipped in the forest. Sometimes it makes more sense to bring the slash pile to the sawmill where it can be chipped along with material from other sites but whether the harvest byproducts are processed in the forest or at the mill, it is a valuable commodity that is in demand. In fact, one of the sessions at World Bioenergy shared a study that sought to look for more sources of biomass in a typical harvest site. It's conclusion was that the best source of unused biomass is in the stump – a controvercial practice that brings up the question, how much biomass can be sustainably removed?

Sveaskog's Jan Wintzell explained that the solution to responsible stump harvesting means one should only take the central part of the stump and leave the roots. "It's good for both the extracted volume and quality of biomass and it's good for the carbon in the ground. With new technique that's more efficient, we could get it out," he said.

His solution leaves about 70 per cent of the stump to provide nutrients to the forest floor – an important consideration for sustainable forestry. And harvesting only the core of the stump should mean less stones would end up in the grinding equipment.

At the mill

Forestry residuals are in high demand but Swedish researchers found another potential source of fuel and Canadians should take note. Karin Granström is a researcher who was looking into the rumoured substrate shortage in her country. She found a wealth of underused feedstocks in pulp and paper mill sludge and municipal waste.

In Sweden, it is forbidden to dump organic waste in landfills but what's the best use of this watery waste? She found that rather than going through the expensive process of dewatering it, it should be used for anaerobic digestion for biogas.

Combining municipal sewage treatment with food industry, agriculture, sorted food waste and manure and adding it to pulp and paper mill sludge generates more methane than those feedstocks would generate on their own. Pulp and paper mill sludge combines particularly well with municipal sewage sludge to balance nitrogen and carbon. Her research also found that pure pulp and paper sludge produced the most methane of the test groups but adding up to 50 per cent sewage sludge to the mix worked well too.

Biogas is in great demand in Sweden where it is used for public transportation (buses) and still it remains a large, untapped resource for biogas production. Granström explained that in Sweden, there was a lot of positive response to the idea of using sludge from the mills to make biogas but when her researchers approched the pulp and paper mill owners, the response was hesitant.

In Canada, we're looking to extract value from every part of the tree harvested and we're making progress but until we begin to use the sludge from our pulp and paper mills, municipal waste and trash, a valuable resource is escaping our grasp.

For more about World Bioenergy 2014, go to http://www.canadianbiomassmagazine.ca/content/view/4585/57/.

June 13, 2014  By  Amie Silverwood

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