Assessment of municipal solid waste for biochemical and thermochemical conversion pathways

Biomass feedstocks costs remain one of the largest contributors to biofuel production costs.  Municipal solid waste (MSW) represents an attractive feedstock since it is available year-round, it has an established collection infrastructure paid for by waste generators, is a low cost material and could potentially be blended with higher cost feedstocks to reduce overall feedstock costs. 

Paper waste and yard waste were examined for their applicability in both Biochemical and Thermochemical conversion pathways.  Paper waste consisted of cardboard, office paper, food packaging and magazines, while yard waste consisted of grass clippings, tree trimmings and fallen tree leaves.  Paper had glucan from 44-60%, xylan from 8-10%, and ash content from 3-25%, while yard waste was 15-23%, 4-10% and 3-13%, respectively.  The materials were acid pretreated and enzymatically hydrolyzed.  For the paper waste, glucan yields were 60% for cardboard and 95% for office paper while xylan yields were 100% for all paper types.  Grass clippings showed glucan yields from 60-100% and xylan yields from 60-80%.  As expected, the pine cones and tree trimmings gave poor glucan and xylan yields, while the tree leaves gave unexpectedly low glucan and xylan yields indicative of recalcitrance.  Ash composition and proximate/ultimate analyses were also conducted.  The majority of the ash in the paper fractions was SiO₂, Al₂O₃, and CaO, while the yard waste materials was SiO₂, K₂O, P₂O₅ and halides. Both paper and yard waste materials had heating values from 50-70% of coal.  These results show that MSW has applicability in both Biochemical and Thermochemical pathways.