Turning Slash Piles to Soil Benefit

By University of Washington
Photo by Washington DNR

Turning Slash Piles to Soil BenefitYour next bite of an organically grown apple may hold within it a tiny bit of a Washington forest.

Students at the University of Washington have teamed up on a startup that promises to turn slash piles of forest refuse into biochar, a crumbly charcoal-like product for farmers that helps their soil hold water and nutrients. Biochar is not technically a fertilizer, but often improves yield for farmers.

“Wine growers, organic farmers and gardeners of all sorts are part of the market we are targeting,” said Jenny Knoth, a doctoral student in forest resources in the UW College of the Environment. The National Science Foundation chose the project, and Knoth as key student leader, for their Innovation Corp announced Oct. 6.

After a stand of trees is harvested, the stumps and other woody debris not useful for the sawmill are collected into what are called “slash” piles, and typically burned in place because hauling the tons of material is not practical. It takes money and staff to burn the piles, and the burning produces more smoke than the new method designed by Knoth and her collaborators.

“This new product helps us manage an expensive problem,” explained principal investigator Dan Schwartz, chair and Boeing-Sutter professor of the department of chemical engineering and adjunct professor of materials science and engineering. Landowners are required to clear slash before a timber sale can close. “It is a radically simple and low cost way to turn slash piles into a source of jobs and income,” Schwartz said.

Knoth, with other team members, developed the new low-technology solution called the C6 Systems blanket, which covers and accelerates the pile’s gradual conversion into char. The blanket is designed to limit the oxygen flow to the burning pile. Lowering the oxygen getting into the pile changes the chemistry from combustion to pyrolysis. Pyrolysis describes organic material burning with low oxygen into a char.

The process can take one day for a small pile or longer for larger piles. Slash on U.S. Forest Service and tribal lands has been offered as pilot study locations.

The biochar is estimated to sell for $1,500 per ton as a soil amendment to ecologically conscious gardeners and landscapers as well as organic farmers, Schwartz said. “This could transform what is a big problem and money sink into a money-making and job-producing engine for landowners, while helping to improve soil conditions and reduce smoke.”

NSF chose this project as one of 21 nationally for a $50,000 grant to help boost the team of five students who have worked for months to develop a business plan. The project links people across the UW campus from forestry, chemical engineering and the Center for Innovation and Entrepreneurship.

Within six months, the NSF hopes the startup will prove itself ready to grow to higher commercial level.

“If we keep science in our labs, we are only doing half the work,” Knoth said. She hopes to see the team’s company, C6 Systems, become a viable commercial seller of biochar. Knoth grew up around people in the forest industry and says: “I grew up talking board feet at the dinner table.”

Another key mentor for the project was Jeffry Canin, a former entrepreneur in residence at the Center for Commercialization at the UW. He has worked with several bioenergy and energy projects as they seek to transition technology from the bench to the marketplace.

This latest project follows earlier work by Schwartz. He leads the NSF-funded Bioresource-based Energy for Sustainable Societies program at the UW. The bioenergy program brings forest resource and engineering students in to the field to solve problems that real land managers face. His students have founded or co-founded five technology companies, all of which continue to operate.

Besides Knoth, Canin and Schwartz other team members of C6 include Kenneth Faires, Derek Churchill, Nate Dorin and John Tovey, III.


  1. Chip Weinert says:

    How do they get char out of the forest and turn it into $1,500/ton?

  2. Jim Archuleta says:

    Most of the biochar producers I have talked with are selling for $2,000/t. I would also like to see if there was a quality issue with the material, as the variables are likely to be higher under this kind of conditions. Could this be why they don’t go with a higher price? Just wondering.

  3. I’d like to know more about this system. How do you regulate airflow for escaping gases, etc? How heavy is the cover and how many people are required to ‘operate’ the system? Thank you.

  4. i would also like to know more about this system. Can we get any specs on the “blanket”? Do you use several Blankets for larger piles? Are they anchored so that natural wind or wind generated by the fire doesn’t move them. Do they combust or resist the fire and are re-usable.

  5. Tom Waddell says:

    Note from FBN staff: I contacted the University of Washington to see if they might respond to your questions.

  6. Dan Schwartz says:

    Hi Commenters:

    Thanks for the interest! I am the prof at UW working with the student business team on this. Let me give a few cursory answers, and then make sure the students who have formed the company know this dialog is going on. They may chime in if there is more to add.

    Chip and Jim: I’d call the biochar price quoted “reasonable” but not certain. Unfortunately, we have not found char to have a well-established liquid market where you can look up the value of char with X volatiles, Y ash, and Z fixed carbon and know what the current and future market prices look like. Jim, if you know better than our “reasonable” number (that is, if you know the volume of char buyers want, and the specs they want, at $2000/ton), I’d love to learn from you.

    rance and Marv: Our intellectual property is around the blankets and processing conditions…what you folks are asking about, so I will be a little vague. The goal of the research was to have a low capital and operating cost process that can produce something with a price worth trucking out of the forest. The latest prototype blankets (we’ve gone through several generations) are able to take the high temperatures and are sufficiently durable to be used repeatedly. As noted, control of inlet air and exhaust is key. The blanket is designed to be handled by a small crew, something akin to the crews that would go out and burn piles. That is all I can really say.

    For all of you, we’d love to hear how you might use the product described above? The students on this team have substantial forestry experience prior to coming back to school, but I am a book-worm chemical engineer, so I’ve got lots to learn from experienced folks on FBN.
    Dan Schwartz

    • Jim Archuleta says:

      I am with the FS and been working with Fast Pyrolysis systems since 2009. The biochar produced from both Fast Pyrolysis and gasification is going for $1.00/lb. You can find producers at Sonoma Compost in CA, Biochar Solutions in CO, then there is Morris Huffman in Idaho & John Miedema in Corvallis OR @ Thompson Timber. All of the above are selling for $1.00/lb. However all are producing in a very stable environment and produce quality biochar.
      What we (FS & other agencies) are after is a cheap source of quality biochar. I used biochar (Dynomotive in Canada) on a small test in western OR, this test showed an increase of soil moisture in pumice soil, stretching out the growing season in a very droughty location. This result was a onetime application that has been sustained over two seasons. This year we extracted biomass samples and saw a visual increase in below ground biomass and greener plants associated with biochar. Samples are in the lab for testing. If your system works well it may offer a way for soil practitioners to prescribe lbs/ac of biochar in addition to fire/fuels folks perscribing t/ac treatments for wildfire risk and to buffer climate change fluctuations. I am also working with a private company who hopes to use biochar as one of the compounds in their products. This product would be sold for large reclaimations and in an ag settings. But the biochar price is too high at the moment for that to work. Please contact me directly so we may discuss further options for your technology in forest fuels reduction and/or soil reclamation projects. My email is jgarchuleta@fs.fed.us
      or cell 541-520-3998
      Hope to hear from you soon.

    • I’m a forestry consultant in the San Juan Islands, WA (CFR grad ’06)and quite interested in this technology. Up here in the islands, decay rates for slash are slow and concerns over hazardous fuels loom large. I work with logging contractors but also help conduct pre-commercial thinning operations and restoration work where we often deal with lots of slash. Mostly we pile and burn relatively small piles that have been covered with burnable wax paper for several months.
      Forest owners are desperate for some new income streams to help offset the cost of thinning and fuel reduction work. There are also a number of small farmers in the islands that are aware of the potential benefits of biochar and are eager to experiment with it on their land.
      I am fortunate to have a number of thinning projects coming up and am wondering if your lab would be interested in doing some field trials? One landowner in particular would be very receptive. Please let me know if you have a need for additional field sites or would be interested in having myself and my crews conduct some further testing.

  7. Tom Waddell says:

    Dan, thank you for your reply. It’s much appreciated. I let the readers who responded in the comments above know that you have questions and comments for them.

  8. We raise grassfed bison and grow our own hay on our high dessert Sierra’s ranch in NE California. Price is the only reason we haven’t been able to use biochar so we’re glad to see this post. If anyone would like to use our place for field trials we would be most delighted to hear from you. Pls. email us at klindner@lindnerbison.com or call us 661-254-0200. Thank you so much. Kathy & Ken Lindner

    • Dan Schwartz says:

      Kathy and Ken:
      Wonderful to hear about your application. I will ask the students to get back to learn more about your application for biochar, and how it will be used.

  9. Willibald Dressel says:

    Dear guys,
    first congratulations and deep respect for your work.

    You are talking about a heating-blanket.
    From where you get the power for the process in the start phase?
    Is this blanket available already? Please let me know and get in contact with me.
    Is the succeeding of the charing process also on a tied ground like cocrete possible?

    For answering my questions I thank you very in advance.

    Best regards
    W. Dressel

    • Dan Schwartz says:


      The heat is generated via initial combustion, followed by just enough inlet air to maintain temperature during pyrolysis. No power input needed (other than, perhaps, a propane or drip torch to get things started).

      I believe we are on experimental blanket version 4 or 5, but do not have a commercially available blanket yet. I can think of no reason producing char on concrete would cause a problem, though we normally operate on soil.


  10. I work for the US Forest Service in Oregon. I have a couple more questions: Do you intend for the blankets to be available in multiple sizes or otherwise scalable to accomodate differenet pile sizes? We burn piles ranging from small hand piles to massive landing piles. Also, what are the air impacts relative to open burning? Are the pollution/particulate levels reduced? You can also count us among your opportunities for field trials – we currently burn 6,000 to 20,000 tons a year of piled material at landings and have 100’s of acres of handpiles to burn in the near future. Good luck with this, we will be interested to see what you come up with.

    • Dan Schwartz says:

      Hi Gabe:
      Right now, version 4 of the blanket is modular, so we can add sections to accommodate different sized and shaped piles. We have heard from many potential users how valuable it would be to reduce the hydrocarbon and particulate emissions. We are examining ways to modify the design to reburn the combustible exhaust as a means to better integrate the heat and reduce emissions. I am a chemical engineer,and am working with a mechanical engineering student on this, so what you are asking about is an especially fun part of the project for me. We are working with the Forest Service (Ernesto Alvarado) on piles in the Naches District. We can’t tackle your 20,000 tons quite yet, unfortunately. I am confident we are on track to make a difference at that scale, however.

  11. Doug Thiesies says:

    As the forest manager for Hood River County Forest I would like to discuss potential field trial sites on HRC Forestland. We typically burn approximately 3000 tons of slash piles each year. A benefit of producing this product in Hood River is the proximity of agriculture in the Hood River valley which may utilize the biochar.

    • Dan Schwartz says:

      Thanks for the note, Doug. We are keen to learn more about current sites, how much it is costing you to dispose of your slash. Like so many of the others here, I will let the students know about your interest so they can follow-up.

  12. We are very interested in receiving contacts that would like to purchase high quality char at $1 per pound. Starting in August we will have 25 tons per day. Carbon 80%; very low volatiles.
    We also are working on a mobile unit.

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