(346d) Life Cycle Assessment of Forest Biomass Energy Pathways in the Northeast US

Forest biomass is anticipated to represent a significant portion of the developing supply of bioenergy feedstocks. Increasing interest to utilize renewable and sustainable energy systems with forest biomass feedstocks necessitates an understanding of potential environmental impacts arising from these systems. Life cycle assessment (LCA) is a method used to evaluate the potential environmental impacts of a process, product, or system over its life cycle. This method is used to determine the life cycle climate change impacts, water use, and eutrophication potential of utilizing a forest biomass feedstock in electrical generation, combined heat and power (CHP), and wood chip heating systems typical to the Northeast United States. The LCA scenarios are modeled in Python code with primary data from harvest sites and energy systems in the Northeast US to define the harvest, transportation, energy conversion, and ash disposal processes. The silviculture processes are based on carbon cycling and partitioning modeling specific to hardwood forest growth and harvesting practices in New York State. The functional unit for the wood chip heating system LCA is 1 MJ of heat delivered. The functional unit for the electrical generation and CHP systems is 1 kWh, allowing for comparison to other forms of electricity generation. System expansion is used to account for the space heat coproduct of the CHP system. Coproducts of forest biomass, including sawtimber, pulpwood, and firewood, are accounted for through mass and economic allocation methods. Sensitivity and uncertainty analyses are conducted to investigate the impacts of variability in forest growth, species of harvested trees, market conditions, harvest systems, transportation distances, and energy conversion efficiencies on the life cycle environmental impacts of the studied bioenergy pathways. The life cycle environmental impacts of the forest bioenergy pathways are compared against those of conventional energy systems, and recommendations are made for system improvements for greater sustainability.