A spatially explicit watershed scale optimization of cellulosic biofuels production
As environmental deterioration and global warming arouses more and more attention, identifying cleaner and more environmentally friendly energy sources is of interest to society. In addition to environmental concerns, both the high price of gasoline and the fact that the United States has heavy reliance on petroleum imports has driven policymakers to find alternative energy sources. Producing biofuels from energy crops is one such alternative. They can result in relatively lower greenhouse gas emissions compared to traditional energy sources. Up to now, corn grain is the most researched energy crop. Cellulosic perennial crops such as switchgrass, miscanthus and fast growing trees are also promising energy crops and are expected to help with the energy supply. The 2007 Renewable Fuel Standard requires 16 billion gallons of a total of 36 billion gallons of renewable fuels to be cellulosic biofuels by 2022. Many studies are being done to evaluate costs and feasibility of different potential feedstocks and the first commercial-scale cellulosic biorefinery is scheduled to begin operation in 2014. This study estimates the costs of two dedicated cellulosic biofuel crops, switchgrass and miscanthus, makes comparisons with corn stover, and develops a Matlab program that uses a Genetic Algorithm to minimize production cost subject to production and pollution constraints for the Wildcat Creek Watershed in Indiana, USA. Results indicate that if the biorefinery fuelshed is limited to the boundary of the watershed, miscanthus must be planted to achieve the minimum amount of biomass production required (1,307,065 metric tons per year under thermochemical conversion) while also reducing pollutant levels (total sediment, N and P). Switchgrass has similar environmental advantages but higher cost given the crop parameterizations assumed in the accompanying Soil and Water Assessment Tool (SWAT model) simulations. Corn stover production is the cheapest among all three bio feedstocks considered and would minimize delivered feedstock cost for a biorefinery if the fuelshed is not limited to the watershed boundary. Pollutant loadings from corn stover removal scenarios vary, but they all result in higher water pollution than perennial grasses under the assumed management (tillage, nutrient replacement, stover removal rate, etc.). There is a clear tradeoff between cost and environmental quality when satisfying the Renewable Fuel Standard using different feedstocks.
Gramig, Purdue University.
Environmental economics|Agricultural economics
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