Alissa Kendall

Proper accounting for time increases crop-based biofuels' greenhouse gas deficit versus petroleum

The global warming intensities of crop-based biofuels and fossil fuels differ not only in amount but also in their discharge patterns over time. Early discharges, for example, from market-mediated land use change, will have created more global warming by any time in the future than later discharges, owing to the slow decay of atmospheric CO2. A spreadsheet model of this process, BTIME, captures this important time pattern effect using the Bern CO2 decay model to allow fuels to be compared for policy decisions on the basis of their real warming effects with a variety of user-supplied parameter values. The model also allows economic discounting of climate effects extended far into the future. Compared to approaches that simply sum greenhouse gas emissions over time, recognizing the physics of atmospheric CO2 decay significantly increases the deficit relative to fossil fuel of any biofuel causing land use change.

Life-Cycle Optimization of Pavement Overlay Systems

Preservation (maintenance and rehabilitation) strategy is the critical factor controlling pavement performance. A life-cycle optimization (LCO) model was developed to determine an optimal preservation strategy for a pavement overlay system and to minimize the total life-cycle energy consumption, greenhouse gas (GHG) emissions, and costs within an analysis period. Using dynamic programming optimization techniques, the LCO model integrates dynamic life-cycle assessment and life-cycle cost analysis models with an autoregressive pavement overlay deterioration model. To improve sustainability in pavement design, a promising alternative material for pavement overlays, engineered cementitious composites (ECCs), was studied. The LCO model was applied to an ECC overlay system, a concrete overlay system, and a hot mixed asphalt (HMA) overlay system. The LCO results show that the optimal preservation strategies will reduce the total life-cycle energy consumption by 5–30%, GHG emissions by 4–40%, and costs by 0.4–12% for the concrete, ECC, and HMA overlay systems compared to the current Michigan Department of Transportation preservation strategies, respectively. The impact of traffic growth on the optimal preservation strategies was also explored.

Comparing life cycle assessments of different biofuel options.

Life cycle assessment (LCA) has shown that first generation biofuels provide a little to no benefit for greenhouse gas (GHG) reductions compared to petroleum fuels, particularly when indirect effects are considered. Second generation fuels are intended to achieve greater GHG reductions and avoid other sustainability issues. LCAs of second generation biofuels exhibit great variability and uncertainty, leading to inconclusive results for the performance of particular pathways (combinations of feedstocks and fuels). Variability arises in part because of the prospective nature of LCAs for future fuels; however, a review of recent articles on biofuel LCA methodology indicates two additional sources of variability: real sources such as spatiotemporal heterogeneity, and methodological sources such as choices for co-product allocation methods and system boundary definition.

Incorporating Time-Corrected Life Cycle Greenhouse Gas Emissions in Vehicle Regulations

Beginning with model year 2012, light-duty vehicles sold in the U.S. are subject to new rules that regulate tailpipe greenhouse gas (GHG) emissions based on grams of CO(2)-equivalent per mile (gCO(2)e/mi). However, improvements in vehicle technology, lower-carbon fuels, and improvements in GHG accounting practices which account for distortions related to emissions timing all contribute to shifting a greater portion of life cycle emissions away from the vehicle use phase and toward the vehicle production phase. This article proposes methods for calculating time-corrected life cycle emissions intensity on a gCO(2)e/mi basis and explores whether regulating only tailpipe CO(2) could lead to an undesirable regulatory outcome, where technologies and vehicle architectures with higher life cycle GHGs are favored over technologies with lower life cycle emissions but with higher tailpipe GHG emissions. Two life cycle GHG assessments for future vehicles are presented in addition to time correction factors for production and end-of-life GHG emissions. Results demonstrate that, based on the vehicle designs considered here, there is a potential for favoring vehicles with higher life cycle emissions if only tailpipe emissions are regulated; moreover, the application of time correction factors amplifies the importance of production emissions and the potential for a perverse outcome.

Life cycle analysis of biochemical cellulosic ethanol under multiple scenarios

Cellulosic ethanol is widely believed to offer substantial environmental advantages over petroleum fuels and grain‐based ethanol, particularly in reducing greenhouse gas emissions from transportation. The environmental impacts of biofuels are largely caused by precombustion activities, feedstock production and conversion facility operations. Life cycle analysis (LCA) is required to understand these impacts. This article describes a field‐to‐blending terminal LCA of cellulosic ethanol produced by biochemical conversion (hydrolysis and fermentation) using corn stover or switchgrass as feedstock. This LCA develops unique models for most elements of the biofuel production process and assigns environmental impact to different phases of production. More than 30 scenarios are evaluated, reflecting a range of feedstock, technology and scale options for near‐term and future facilities. Cellulosic ethanol, as modeled here, has the potential to significantly reduce greenhouse gas (GHG) emissions compared to petroleum‐based liquid transportation fuels, though substantial uncertainty exists. Most of the conservative scenarios estimate GHG emissions of approximately 45–60 g carbon dioxide equivalent per MJ of delivered fuel (g CO2e MJ−1) without credit for coproducts, and 20–30 g CO2e MJ−1 when coproducts are considered. Under most scenarios, feedstock production, grinding and transport dominate the total GHG footprint. The most optimistic scenarios include sequestration of carbon in soil and have GHG emissions below zero g CO2e MJ−1, while the most pessimistic have life‐cycle GHG emissions higher than petroleum gasoline. Soil carbon changes are the greatest source of uncertainty, dominating all other sources of GHG emissions at the upper bound of their uncertainty. Many LCAs of biofuels are narrowly constrained to GHG emissions and energy; however, these narrow assessments may miss important environmental impacts. To ensure a more holistic assessment of environmental performance, a complete life cycle inventory, with over 1100 tracked material and energy flows for each scenario is provided in the online supplementary material for this article.

Mass balance and life cycle assessment of biodiesel from microalgae incorporated with nutrient recycling options and technology uncertainties

This article presents mass balances and a detailed life cycle assessment (LCA) for energy and greenhouse gases (GHGs) of a simulated microalgae biodiesel production system. Key parameters of the system include biomass productivity of 16 and 25 g m−2 day−1 and lipid content of algae of 40% and 25% for low and normal nitrogen conditions respectively. Based on an oil extraction efficiency from wet biomass of 73.6% and methane yields from anaerobically digested lipid‐extracted biomass of 0.31 to 0.34 l per gram of volatile solids, the mass balance shows that recycling growth media and recovering nutrients from residual biomass through anaerobic digestion can reduce the total demand for nitrogen by 66% and phosphorus by 90%. Freshwater requirements can be reduced by 89% by recirculating growth media, and carbon requirements reduced by 40% by recycling CO2 from biogas combustion, for normal nitrogen conditions. A variety of technology options for each step of the production process and allocation methods for coproducts used outside the production system are evaluated using LCA. Extensive sensitivity and scenario analysis is also performed to provide better understanding of uncertainty associated with results. The best performing scenario consists of normal nitrogen cultivation conditions, bioflocculation and dissolved air flotation for harvesting, centrifugation for dewatering, wet extraction with hexane, transesterification for biodiesel production, and anaerobic digestion of biomass residual, which generates biogas used in a combined heat and power unit for energy recovery. This combination of technologies and operating conditions results in life cycle energy requirements and GHG emissions of 1.02 MJ and 71 g CO2‐equivalent per MJ of biodiesel, with cultivation and oil extraction dominating energy use and emissions. Thus, even under optimistic conditions, the near‐term performance of this biofuel pathway does not achieve the significant reductions in life cycle GHG emissions hoped for from second‐generation biofuel feedstocks.

Life Cycle Environmental and Cost Impacts of Using an Algal Turf Scrubber to Treat Dairy Wastewater

Using algae to simultaneously treat wastewater and produce energy products has potential environmental and economic benefits. This study evaluates the life cycle energy, greenhouse gas (GHG) emissions, eutrophication potential, and cost impacts of incorporating an algal turf scrubber (ATS) into a treatment process for dairy wastewater. A life cycle inventory and cost model was developed to simulate an ATS treatment system where harvested algae would be used to generate biogas for process heat and electricity generation. Modeling results show that using an ATS significantly reduces eutrophication impacts by reducing chemical oxygen demand, nitrogen, and phosphorus in the wastewater. With low water recirculation rates through the ATS and high algae productivity, inclusion of the ATS results in net energy displacement and a reduction of GHG emissions compared to a system with no ATS. However, if high water recirculation rates are used or if algae biosolids from the digester are dried, the system results in a net increase in energy consumption and GHG emissions. The life cycle treatment cost was estimated to be

Reducing greenhouse gas emissions through strategic management of highway pavement roughness

1.42 USD per cubic meter of treated wastewater. At this cost, using an ATS would only be cost effective for dairies if they received monetary credits for improved water quality on the order of

Life Cycle–Based Assessment of Energy Use and Greenhouse Gas Emissions in Almond Production, Part I: Analytical Framework and Baseline Results

3.83 per kilogram of nitrogen and

Wind Power as a Case Study

9.57 per kilogram of phosphorus through, for example, nutrient trading programs.