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Life cycle environmental performance of lignocellulosic ethanol produced through different production pathways and having different co-products has rarely been reported in the literature, with most studies focusing on a single pre-treatment and single co-product (electricity). The aim of this paper is to understand the life cycle energy use and greenhouse gas (GHG) emissions implications of alternative pre-treatment technologies (dilute acid hydrolysis, ammonia fiber expansion and autohydrolysis) and co-products (electricity, pellet, protein and xylitol) through developing a consistent life cycle framework for ethanol production from corn stover. Results show that the choices of pre-treatment technology and co-product(s) can impact ethanol yield, life cycle energy use and GHG emissions. Dilute acid pathways generally exhibit higher ethanol yields (20-25%) and lower net total energy use (15-25%) than the autohydrolysis and ammonia fiber expansion pathways. Similar GHG emissions are found for the pre-treatment technologies when producing the same co-product. Xylitol co-production diverts xylose from ethanol production and results in the lowest ethanol yield (200 L per dry t of stover). Compared to producing only electricity as a co-product, the co-production of pellets and xylitol decreases life cycle GHG emissions associated with the ethanol, while protein production increases emissions. The life cycle GHG emissions of blended ethanol fuel (85% denatured ethanol by volume) range from -38.5-37.2 g CO2 eq/MJ of fuel produced, reducing emissions by 61-141% relative to gasoline. All ethanol pathways result in major reductions of fossil energy use relative to gasoline, at least by 47%. [ABSTRACT FROM AUTHOR]

Existing life cycle assessments of concrete containing supplementary cementitious materials (SCMs) hinge on methodological procedures that might skew the results towards the conclusion that increasing the use of SCMs in concrete always decreases greenhouse gas (GHG) emissions. These procedures relate to the treatment of co-products and selection of functional units. Co-production is typically addressed via cut-off procedures and by-products are always considered to be unconstrained resources, while functional units often do not account for exposure conditions and concrete properties such as strength and workability. To address this limitation, the aim of this study was to investigate the GHG benefits of using SCMs by (1) adopting different approaches to solve multifunctionality (cut-off vs. substitution) and (2) including strength, workability and exposure conditions of concrete in the functional unit. Ontario (Canada) was used as case study, and both SCMs currently used there (i.e., slag, silica fume and metakaolin) and a wide range of alternative cementitious materials used around the world (i.e., fly ash, oil shale ash, calcium carbide residue, volcanic ash, coal bottom ash and rice husk ash) were investigated. The new contribution of this study reveals that different conclusions can be drawn when different methodological procedures are adopted. If the market for SCM is constrained (i.e., by-products are already fully utilized) and the unconstrained alternative on the market is Portland cement, the benefits of using SCM are greatly reduced, or even reversed, if the substitution approach is adopted. In contrast, unconstrained SCMs result in considerable GHG savings unless they significantly reduce the water-to-binder ratio to reach a prescribed strength and require long distance transport. • Market constraints of SCMs should be included in LCA studies of concrete. • Concrete properties and exposure conditions must be included in the functional unit. • If the SCM is constrained, overall GHG benefits of using it are greatly reduced. • Increasing SCMs in concrete does not always decrease its GHG emissions. • The use of alternative unconstrained SCMs should be further explored and promoted. [ABSTRACT FROM AUTHOR]