Background/Objectives

To combat the adverse impacts of anthropogenic carbon-induced climate change and secure the future of energy sustainability, renewable energy from biomass sources has gained considerable attention in recent decades. Replacing corn, the most common agricultural crop grown in the riparian buffer strips of US mid-Atlantic region, with perennial bioenergy crops such as switchgrass or willow can add additional greenhouse gas (GHG) and other criteria air pollutants benefits to the buffer strips.

Approach/Activities

Riparian buffer area and their corresponding yield estimates for switchgrass and shrub willow production were fed into the Biofuel Infrastructure, Logistics and Transportation (BILT) model to identify suitable biorefinery locations and transportation distances. Yield, area, and transportation data were incorporated into a well-to-wake life cycle assessment model to estimate the life cycle GHG and other criteria air pollutant emissions. These pollution estimates were compared with the traditional corn production and corn-to-ethanol pathway. Economic benefits of energy crop production via avoiding air pollutants were estimated using values provided by US Environmental Protection Agency's BenMap - community edition. These estimates were combined with benefits from avoiding water pollution estimated by BioVEST model. Both BILT and BioVEST models were developed by the Oak Ridge National Laboratory. Life cycle assessment was conducted using GREET, developed by Argonne National Laboratory.

Results/Lessons Learned

Changing land use from traditional corn production to energy crop production provided carbon benefits via increased soil organic carbon sequestration and reduced N₂O emissions into the atmosphere. Energy crop production also resulted in lower nutrient runoff to local streams and provided water quality improvement benefits. Ethanol production from switchgrass and willow reduced GHG emissions by approximately 2.17 and 1.55 t ha^-1 (metric tonnes per hectare), respectively, compared to the baseline scenario of corn to ethanol production. Changing the land use from corn to switchgrass system increased the SOC by approximately 4.4 t ha^-1 and reduced the N₂O emissions by 0.3 t ha^-1. Same estimates were 0.7 and 0.1 t ha^-1 for corn to willow. While NOX emissions were reduced by 4.22 and 5.17 kg ha^_-1 by switchgrass and willow pathways, respectively, SO_X emissions were reduced by 6.56 and 4.08 kg ha^-1. However, on average, VOC emissions increased by 3.22 and 3.39 kg ha^-1 in switchgrass and willow pathway, respectively. PM2.5 also increased by 0.35 kg ha^-1 in both systems.

Dry milling with corn oil extraction produces DDGS which displaces corn, soybean meal, and urea. When land use is changed from corn, approximately 2,638 tonnes of corn, 1027 tonnes of soybean meal, and 92 tonnes of urea would need to be produced in switchgrass- or willow-to-ethanol pathway, to make up that demand by DDGS. This is the primary reason for the increase in VOC and PM2.5 in the perennial grass to ethanol production system and resulted in overall health cost increase when switched from corn to ethanol system. Without accounting for the benefits provided by avoiding water pollution, health costs increased by $488 and $546 ha^-1 when switched to switchgrass and willow-based system. The total health cost increase was approximately $472 million dollars. In the subsequent stages of the study, improved water quality related benefits will be included.