Assessment of Waste Materials for Valorization into Biofuels

Abundant, low-cost waste materials have potential to replace the use of petroleum and they can be valorized through production of biofuels. However, waste materials contain contamination and it is unknown how these materials will perform versus pristine feedstocks. This paper describes screening of waste materials in production of either sugars (which can be fermented to biofuels) or bio-oil, the impact of contaminants found in waste materials, potential mitigation strategies to alleviate contamination effects and technoeconomic analyses to show the impact of utilizing waste resources. Five waste materials were utilized in this study including municipal solid waste paper, yard trimmings, C&D waste, logging residues and agricultural wastes. Paper, yard trimmings and agricultural wastes were screened for sugar production by treatment with sulfuric acid and enzymatic saccharification and all of the waste materials were screened for bio-oil yields by micropyrolysis. Glucose yields for paper and agricultural wastes were similar to, or in some cases higher than, yields obtained from switchgrass while glucose yields were lower for yard trimmings. Xylose yields were lower for waste materials than for switchgrass. Bio-oil yields for C&D wastes and logging residues were similar to those obtained from pine while yields were lower for paper, yard wastes and agricultural residues. Air classification and acid leaching methods were developed to remove contaminants from waste materials. Air classification was shown to remove 40-50% of soil contamination and acid leaching could remove up to 80% of contaminating metal ions. Bio-oil yields for acid leached waste paper and yard trimmings increased up to 15%. Finally, technoeconomic analyses demonstrated that C&D waste could reduce material costs by 16 to 20% over pristine pine chips. These results demonstrate that waste materials have the potential for valorization even when the materials require decontamination due to their lower cost and abundance.