Final Report - Ohio Department of Transportation

5. Conclusions and Recommendations
This study was designed to evaluate the fundamental feasibility of producing useful
quantities of bitumen from yard waste carbonization. To accomplish this, the research evaluated
the moisture, organic, and char content of nearly 50 distinct yard waste components, and
evaluate the recovery efficiencies of the bio-char and byproducts. The overall average byproduct
generation rate was 60.4% (28.8 % aqueous and 31.6 % organic). Of this, approximately 57%
was recovered by the collection system used in this project.
The variability of moisture content, organic content, and byproduct collection were
grouped by type of yard waste. This was done to investigate whether any typical yard waste
component would be more beneficial for bitumen production. In the comparison between
branches and leaves, neither type has a significantly higher organic fraction (0.34 and 0.32,
respectively). This fact is relevant in that, if collecting bitumen from yard waste carbonization
was implemented at a larger scale, extensive feedstock separation would not be necessary.
The benefit of drying feedstock prior to carbonization was also investigated. In comparing
byproduct collection of unaltered samples and pre-dried samples, pre-drying decreased the total
byproduct collection. This was partly due to the increased viscosity of the off-products after
drying. In looking at the same relationship between byproduct collection and moisture content
over all samples tested, a sample’s moisture content seemed to have little impact on byproduct
production.
In retrospect, the laboratory apparatus used was more effective at accomplishing the
carbonization process (i.e. the basic pyrolysis step) than managing the recovery and separation of
byproducts. Improvements were made during the course of the project by installing heating
elements to control gas discharge temperatures in strategic sections of the discharge piping, and
these helped stabilize and improve recovery. However, the off gas management system should
be further improved. Such improvements would increase the production of the organic fraction
and could help reduce the potential air discharge complications of the process.
The difficulties arising from transferring bitumen from collection flasks to storage containers
or bottles also warrant more attention. Although in an aqueous solution, a portion of higher
viscosity bitumen in the flasks could not be transferred to separate containers without an acetone
wash. Of those bitumen samples that were transferred to separate containers, they were
eventually consolidated for the creation of a larger sample. They were easily transferred as they
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