• Energy Research

AbstractCorn stover is expected to supply much of the cellulosic biomass required to meet the 61 billion liters per year target under the US Energy Independence and Security Act. The Act also requires that cellulosic biofuels achieve a greenhouse gas (GHG) reduction of 60% compared to gasoline. If corn stover is harvested for biofuels, it can no longer help replenish soil organic matter, and net soil carbon emissions increase. So meeting the GHG reduction target is a concern. We studied the effect of stover removal on overall GHG emissions of corn stover ethanol systems in the 12‐state Corn Belt region. Even at a stover removal rate of 66%, no more than 20 billion liters can be annually produced while simultaneously satisfying the 60% GHG reduction. Moreover, no GHG reduction relative to gasoline occurs in short time periods. The GHG benefits of corn stover ethanol only appear after longer time periods. © 2017 Society of Chemical Industry and John Wiley & Sons, Ltd

A sustainable dairy manure amendment for soilless crop growth systems was evaluated for its ability to provide nutrients and serve as a major component of the growing media. After manure liquid/solid separation, the solids stream containing organic N and P was pelletized and used as a nutrient source for cherry tomato (Solanum lycopersicum var. cerasiforme) culture in soilless media. The pellets are low in moisture, odor, and pathogens, and they can be hauled at lower cost over longer distances and more easily stored than raw or composted manure. Manure pellet additions to soilless media were evaluated at 0%, 2.5%, 5%, 10%, 15%, 20%, 25%, 30%, 40%, and 50% by volume. Manure pellets had a total N content of 3.7%. Fruit size, ripeness, and biomass, plant height, nutrients value in tissue/pellets/media, and time to complete growth cycle were analyzed. Overall, manure pellet treatments improved plant height and growth rate compared to the negative control, especially when pellets were 15% to 50% of the soilless media. This indicates that the nutrients in the manure were being mineralized, and plants were able to utilize the manure-based nutrients for growth. Leaf tissue nutrient analysis revealed that N, K, Zn, and Fe in leaf tissue were not at sufficiency levels at any level of manure pellet addition. Phosphorus and Cu reached sufficiency levels with 10% or greater manure pellet additions. Calcium, Mg, S, Mn, and B were sufficient in all plants, regardless of fertilizer or manure pellet treatment. Manure pellets demonstrate the potential to be used as a substrate and partial growth medium to reduce synthetic fertilizer use for more sustainable soilless container culture.

AbstractThe current or “conventional” paradigm for producing process energy in a biorefinery processing cellulosic biomass is on‐site energy recovery through combustion of residual solids and biogas generated by the process. Excess electricity is then exported, resulting in large greenhouse gas (GHG) credits. However, this approach will cause lifecycle GHG emissions of biofuels to increase as more renewable energy sources (wind, solar, etc.) participate in grid‐electricity generation, and the GHG credits from displacing fossil fuel decrease. To overcome this drawback, a decentralized (depot‐based) biorefinery can be integrated with a coal‐fired power plant near a large urban area. In an integrated, decentralized, depot‐based biorefinery (IDB), the residual solids are co‐fired with coal either in the adjacent power plant or in coal‐fired boilers elsewhere to displace coal. An IDB system does not rely on indirect GHG credits through grid‐electricity displacement. In an IDB system, biogas from the wastewater treatment facility is also upgraded to biomethane and used as a transportation biofuel. The GHG savings per unit of cropland in the IDB systems (2.7–2.9 MgCO2/ha) are 1.5–1.6 fold greater than those in a conventional centralized system (1.7–1.8 MgCO2/ha). Importantly, the biofuel selling price in the IDBs is lower by 28–30 cents per gasoline‐equivalent liter than in the conventional centralized system. Furthermore, the total capital investment per annual biofuel volume in the IDB is much lower (by ~80%) than that in the conventional centralized system. Therefore, utilization of biomethane and residual solids in the IDB systems leads to much lower biofuel selling prices and significantly greater GHG savings per unit of cropland participating in the biorefinery system compared to the conventional centralized biorefineries.

Producing biochar from forest residues can help resolve environmental issues by reducing forest fires and mitigating climate change. However, transportation and storage of biomass to a centralized facility are often cost-prohibitive and a major hurdle for the economic feasibility of producing biobased products, including biochar. The purpose of this study was to evaluate the environmental impacts and economic feasibility of manufacturing biochar from forest residues with small-scale portable production systems. This study evaluated the environmental performance and economic feasibility of biochar produced through three portable systems (biochar solutions incorporated (BSI), Oregon Kiln (OK), and air curtain burner (ACB)) using forest residues in the United States (US). Cradle-to-grave life-cycle assessment (LCA) and techno-economic analysis (TEA) were used to quantify environmental impacts and minimal selling price (MSP) of biochar respectively considering different power sources, production sites, and feedstock qualities. The results illustrated that the global warming (GW) impact of biochar production through BSI, OK, and ACB was 0.25–1.0, 0.55, and 0.61-t CO2eq/t biochar applied to the field, respectively. Considering carbon-sequestration, 1-t of biochar produced with the portable system at a near-forest site and applied to the field reduced the GW impact by 0.89–2.6 t CO2eq. For biochar production, the environmental performance of the BSI system improved substantially (60–70%) when it was powered by a gasifier-based generator instead of a diesel generator. Similarly, near-forest(off-grid) biochar production operations performed better environmentally than the operations at in-town sites due to the reduction in the forest residues transportation emissions. Overall, the net GW impact of biochar produced from forest residues can reduce environmental impacts (i.e., 1–10 times lower CO2eq emissions) compared with slash-pile burning. The MSP per tonne of biochar produced through BSI, OK, and ACB was $3,000–$5,000, $1,600, and $580 respectively considering 100 working days per year. However, with improved BSI systems when allowed to operate throughout the year, the MSP can be reduced to below $1000/t of biochar. Furthermore, considering current government grants and subsidies (i.e.,$12,600/ha for making biochar production from forest residues), the MSP of biochar can be reduced substantially (30–387%) depending on the type of portable system used. The portable small-scale production systems could be environmentally beneficial and economically feasible options to make biochar from forest residues at competitive prices given current government incentives in the US where excess forest biomass and forest residues left in the forest increase the risk of forest fires.

Modeling the life cycle of fuel pathways for cellulosic ethanol (CE) can help identify logistical barriers and anticipated impacts for the emerging commercial CE industry. Such models contain high amounts of variability, primarily due to the varying nature of agricultural production but also because of limitations in the availability of data at the local scale, resulting in the typical practice of using average values. In this study, 12 spatially explicit, cradle-to-refinery gate CE pathways were developed that vary by feedstock (corn stover, switchgrass, and Miscanthus), nitrogen application rate (higher, lower), pretreatment method (ammonia fiber expansion [AFEX], dilute acid), and co-product treatment method (mass allocation, sub-division), in which feedstock production was modeled at the watershed scale over a nine-county area in Southwestern Michigan. When comparing feedstocks, the model showed that corn stover yielded higher global warming potential (GWP), acidification potential (AP), and eutrophication potential (EP) than the perennial feedstocks of switchgrass and Miscanthus, on an average per area basis. Full life cycle results per MJ of produced ethanol demonstrated more mixed results, with corn stover-derived CE scenarios that use sub-division as a co-product treatment method yielding similarly favorable outcomes as switchgrass- and Miscanthus-derived CE scenarios. Variability was found to be greater between feedstocks than watersheds. Additionally, scenarios using dilute acid pretreatment had more favorable results than those using AFEX pretreatment.

Spatial variability in yields and greenhouse gas emissions from soils has been identified as a key source of variability in life cycle assessments (LCAs) of agricultural products such as cellulosic ethanol. This study aims to conduct an LCA of cellulosic ethanol production from switchgrass in a way that captures this spatial variability and tests results for sensitivity to using spatially averaged results. The Environment Policy Integrated Climate (EPIC) model was used to calculate switchgrass yields, greenhouse gas (GHG) emissions, and nitrogen and phosphorus emissions from crop production in southern Wisconsin and Michigan at the watershed scale. These data were combined with cellulosic ethanol production data via ammonia fiber expansion and dilute acid pretreatment methods and region-specific electricity production data into an LCA model of eight ethanol production scenarios. Standard deviations from the spatial mean yields and soil emissions were used to test the sensitivity of net energy ratio, global warming potential intensity, and eutrophication and acidification potential metrics to spatial variability. Substantial variation in the eutrophication potential was also observed when nitrogen and phosphorus emissions from soils were varied. This work illustrates the need for spatially explicit agricultural production data in the LCA of biofuels and other agricultural products.

This study assesses the role of spatial-resolution and spatial-variations in environmental impacts estimation and decision-making for corn-stover harvesting to produce biofuels. Geospatial corn-stover yields and environmental impacts [global warming potential (GWP), eutrophication, and soil-loss] dataset for two study areas in Wisconsin and Michigan were generated through Environmental Policy Integrated Climate (EPIC) model and aggregated at different spatial-resolutions (i.e., 100; 1000; 10,000 ha). For each spatial-resolution, decision-making was accomplished using an optimization routine to minimize different environmental impacts associated with harvesting stover to meet varied biomass demands. The results of the study showed that selective harvesting at higher-resolution (or lower-aggregation level) can result in significantly lower environmental impacts, especially at low stover demand levels. Additionally, the increased spatial resolution had more impact in minimizing the environmental impacts of corn stover harvest under a more variable landscape such as terrains and its influences are more pronounced for soil-loss and eutrophication potential compared to GWP.

Replacing petroleum by biomass can be economically feasible by generating revenue from the three primary biomass constituents.