Life cycle assessment of calcium oxide pretreatment of corn stover with carbon dioxide neutralization for ethanol production.

This work used life-cycle assessment (LCA) to determine the environmental and human health impacts of four ethanol production scenarios (S1: CaO pretreatment + H2SO4 neutralization + C6 yeast fermentation; S2: CaO pretreatment + CO2 neutralization + C6 yeast fermentation; S3: CaO pretreatment + H2SO4 neutralization + C6/C5 yeast fermentation; and S4: CaO pretreatment + CO2 neutralization + C6/C5 yeast fermentation), with the functional unit being 1 kg of 95 % ethanol. TheLCA results showed that the total ozone depletion, global warming potential, smog, acidification, eutrophication, and ecotoxicity values were comparable when CO2 or H2SO4 were used to adjust the pH of CaO-pretreated slurry. However, using CO2 for neutralization and C6/C5 yeast for fermentation demonstrated significant benefits in terms of carcinogenicity, non-carcinogenicity, respiratory effect, ecotoxicity, and fossil fuel depletion. The findings indicate that the choice of chemicals and strains plays a key role in determining environmental and human health impacts.

Isomerization of Galactose to Tagatose: Recent Advances in Non-enzymatic Isomerization.

The valorization of galactose derived from acid whey to low-calorie tagatose has gained increasing attention. Enzymatic isomerization is of great interest but faces several challenges, such as poor thermal stability of enzymes and a long processing time. In this work, non-enzymatic (supercritical fluids, triethylamine, arginine, boronate affinity, hydrotalcite, Sn-ß zeolite, and calcium hydroxide) pathways for galactose to tagatose isomerization were critically discussed. Unfortunately, most of these chemicals showed poor tagatose yields (<30%), except for calcium hydroxide (>70%). The latter is able to form a tagatose-calcium hydroxide-water complex, which stimulates the equilibrium toward tagatose and prevents sugar degradation. Nevertheless, the excessive use of calcium hydroxide may pose challenges in terms of economic and environmental feasibility. Moreover, the proposed mechanisms for the base (enediol intermediate) and Lewis acid (hydride shift between C-2 and C-1) catalysis of galactose were elucidated. Overall, it is crucial to explore novel and effective catalysts as well as integrated systems for isomerizing of galactose to tagatose.

Environmental, human health, and economic implications of landfill leachate treatment for per- and polyfluoroalkyl substance removal.

Landfill leachate is commonly treated offsite with municipal wastewater. This offsite leachate treatment may be limited or no longer applicable due to the increasingly stringent regulations and concerns related to per- and polyfluoroalkyl substance (PFAS) discharge into the environment, resulting in development of full-scale, onsite leachate treatment facilities. To help landfills prepare for the potential shift from offsite to onsite leachate treatment for PFAS compliance, this study analyzed and compared the environmental, human health, and economic performances of a typical onsite and a typical offsite leachate treatment alternative through life cycle assessment (LCA) and life cycle cost assessment (LCCA) using a landfill site located in Zhuzhou, China as a testbed. Two distinct functional units (FUs) were investigated: 1 m3 of leachate treated and 1 g of PFAS removed. Our results show that the onsite scenario offered benefits from human health and economic perspectives, while the offsite scenario generally performed better from the environmental perspective when a leachate PFAS concentration of 150,704 ng/L was assumed. The extent of this tradeoff varied when different functional units were adopted. The onsite scenario will not be competitive from all three perspectives when PFAS concentration in the raw leachate is less than 1666 ng/L.