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US researchers and forest industry look for new ways to use forestry residues

A forester demonstrates the size of slash piles, which researchers hope to turn into usable biomass for the bioenergy industry
A forester demonstrates the size of slash piles, which researchers hope to turn into usable biomass for the bioenergy industry

A potential revolution is unfolding on out-of-the-way logging roads.

Foresters and researchers are innovating unique ways to make use of forest residues, or low quality trees, tree tops, limbs, and chunks that formerly would have been left in slash piles and burned, or worse, left to rot.

Last year, Humboldt State University (HSU) and 15 regional partners in California, US, began the Waste to Wisdom project after receiving a $5.88 million (€5.17m) grant from the US Department of Energy (DOE) to expand biomass research.

The grant is part of the Biomass Research and Development Initiative, a collaborative effort between the DOE and the US Department of Agriculture.

Now, initial research from that project is beginning to show promising results.

Researchers have long known forest residues – also referred to as woody biomass – have the potential to be used in energy production, but logistics have stood in the way.

‘Due to the high cost of collection and transportation, woody biomass is a promising but widely untapped source of renewable energy,’ says Arne Jacobson, one of the principal investigators on the Waste to Wisdom project who is focusing on developing new biomass-to-energy conversion technologies.

‘Our approach is different. We’re adapting our operations to take advantage of the opportunity the waste materials present,’ says Han-Sup Han, HSU forestry professor and one of the project’s lead researchers.

‘Processes such as briquetting and torrefaction of wood chips at or near the forestry sites add value to existing bio-products.’

According to researchers, the innovations centre on improving collection of forest residues and reducing transportation costs.

For example, gathering forest residues into dense bails improves the economics of handling, storing, and transporting the raw materials.

Beyond analysing logistics, researchers hope to also to better understand the environmental impacts of processing forest residues on site, and how the forest products market will receive the new products.

Utilising forestry residues with these new methods has the potential to sequester carbon, speed up the replanting process at cut sites, and boost the economy in rural communities, all while reducing the US’ overall dependence on fossil-based energy.

In June, the research team and partners demonstrated new collection and transportation techniques to community members and stakeholders at a meeting in Humboldt County, California.

The demonstration, one of the largest of its kind, guided participants through every step of the forest residue’s journey, from slash pile to finished briquettes and biochar wood chips.

In today’s forestry practices, it’s the sawlog – a tree that’s been felled, stripped of its branches, and topped so it can be milled into lumber – that generates profit.

The leftover forest residues are lumped into slash piles, and for many reasons forest land managers often aren’t able to process the heaps of branches and stumps as burn permits can be hard to obtain, and weather often causes delays.

The piles end up sitting, attracting pests, increasing the risk of wildfire, and delaying foresters from reseeding cut sites.

Chipping and transporting the slash to a processing site is often economically unfeasible, since in today’s market forest residues processed this way are worth about $40 to $50 per bone dry ton.

The new methods being developed by the Waste to Wisdom group will make a range of bio-products worth from $150 to as much as $2,000 a ton.

Bio-products include a charcoal-like product called biochar – torrefied wood chips that have been heated to drive off moisture – and briquettes made from compressed biomass that can be used directly for energy production.

Recent research has highlighted the effectiveness of biochar as a soil amendment in helping to achieve higher levels of carbon sequestration in agriculture and forestry.

The project will directly affect the development of new policies and strategies in minimising greenhouse gas emissions through the substitution of fossil fuels and petroleum-based fuels.

Researchers will also evaluate the economic feasibility, along with the social and environmental impacts, of biomass conversion technologies.

A life cycle analysis will be performed to identify trade-offs between uses from both an economic and environmental perspective, and a final component of the project will analyse the environmental and economic impacts of bioenergy and biobased products.

A forester demonstrates the size of slash piles, which researchers hope to turn into usable biomass for the bioenergy industry