Environmentally sustainable second generation biofuel production through optimal land use planning

Abstract:

Biomass has emerged as a major source of energy production in many countries. In order to avoid the competition among food and fuel due to the use of grain based ethanol, there have been policies to put an upper cap on the ethanol production from grains and to meet the remaining energy requirement from second generation biofeedstocks (such as corn stover, Switchgrass and Miscanthus). However, changes in cropping practice can have long-term impacts on downstream water quality. Corn stover has emerged as a vital alternative for biofuel production since it improves the energy production without compromising on the grain production. However, stover removal causes nutrient loss and subsequent use of fertilizers, which ultimately affect the water quality downstream. In this scenario, introduction of perennial grasses is expected to be a viable alternative, since it improves the water quality compared to the row-cropped systems.Nevertheless, the high production cost associated with these crops makes them less established.Taking these issues into consideration, an environmentally and economically sustainable cropping pattern can be adopted in the watershed to minimize downstream nutrient delivery (in terms of nitrate and total phosphorus), simultaneously achieving food and biofuel production targets.

Soil and Water Assessment Tool (SWAT) model is one of the most widely used models to assess the impact of various management practices on water quality. In the present study, SWAT has been linked to an optimization algorithm known as Multi Algorithm Genetically Adaptive Method (AMALGAM) to develop a multi-objective simulation-optimization framework.The need for multiple SWAT runs during optimization was eliminated by loose coupling the calibrated SWAT model with an external exponential model for in-stream nutrient transport.The study was demonstrated using data pertaining to St. Joseph River Watershed in the USA. As expected, the results indicate that introduction of practices of corn stover removal and perennial grass planting can reduce the nitrate and total phosphorus loads at the watershed outlet to a large extent.The optimal cropping pattern (dominated by Switchgrass and corn with 50% stover removal) achieved biofuel and grain production targets with minimum production cost and minimum nutrient delivery.