Municipal Solid Waste As a Potential Feedstock for Biochemical and Thermochemical Conversion Processes

Biomass feedstock costs remain one of the largest contributors to biofuel production costs. Municipal solid waste (MSW) represents an attractive feedstock with year-round availability, an established collection infrastructure paid for by waste generators, low cost and the potential to be blended with higher cost feedstocks to reduce overall feedstock costs. Paper waste, yard waste and construction and demolition waste (C&D) were examined for their applicability in Biochemical and Thermochemical conversion pathways. Paper waste consisted of non-recyclable paper such as mixed low grade paper, food and beverage packaging, kitchen paper wastes and coated paper; yard waste consisted of grass clippings and C&D wastes consisted of engineered wood products obtained from a construction waste landfill. The paper and yard waste materials were tested for Biochemical conversion potential using dilute acid pretreatment and enzymatic hydrolysis with commercial enzymes. The mixed paper waste had a glucan yield of 67% and a xylan yield of 80% while the grass clippings had glucan and xylan yields of 73%.  These materials were also blended with either corn stover or switchgrass at 80% herbaceous material and 20% MSW material.  Our models show that an 80:20 blend of herbaceous and MSW materials will meet 2017 DOE cost targets.  These blends had unexpectedly higher glucan and xylan yields than would be predicted from the blend components indicating a potential synergy occurring.  All of the waste materials were tested for Thermochemical conversion potential using a bench scale fast micro-pyrolysis process.  Bio-oil yields were the highest for the C&D materials and lowest for the paper waste.  The C&D wastes had the highest level of lignin derived compounds (phenolic and cyclics) while the paper waste had higher levels of carbohydrate derived compounds (aldehydes, organic acids, ketones, alcohols and sugar derived).   However, the paper material had higher amounts of lignin derived compounds than expected based upon lignin content that is likely due to the presence of polyphenolic resins used in paper processing.  The paper and yard wastes had significantly higher levels of ash content than the C&D wastes (14-15% versus 0.5-1.3%) which further correlated to higher levels of alkali and alkaline earth metals which are known to reduce pyrolysis bio-oil yields.  There appeared to be an inverse correlation of both calcium and potassium content with the amount of product peaks which is indicative of cracking reactions occurring during product formation.