Highly alkaline electrokinetic extraction: Characteristics of chromium mobilization, conversion and transport in high alkalinity soil.

In site chromium (Cr) contaminated soil characterized by high alkalinity and carbonate content, protons are not effectively targeted for Cr(III) mobilization but rather accelerate the reduction of easily transportable Cr(VI) within the acidification electrokinetic (EK) system. As an alternative, the highly alkaline extraction conditions (HAECs) maintained by anolyte regulation are explored owing to the ability to desorb strong binding Cr(VI) and form anionic Cr(III)-hydroxides (Cr(OH)4-, Cr(OH)52-). The results demonstrate that HAECs were more efficient in mobilizing ions in severe alkalinity and electrical conductivity soil compared to organic acid acidifying extraction conditions (OAECs). Simultaneously, a limited amount of soluble Cr(III) was produced; however, its transportation was hindered and more noticeable in the case of Cr(VI), displaying a distinct retention phase within the intermediate soil chamber. The antagonistic interplay between electromigration and electroosmotic flow was considered the main responsible factor. The conversion intensity of Cr(VI) to Cr(III) was inhibited at HAECs. The promising mobilization and low conversion intensity contributed to total Cr removal. At HAECs, enhanced electromigration and electroosmotic flow combined with a favorable oxidation environment may facilitate in situ delivery of oxidants, offering practical implications for the EK detoxification of high alkalinity site soil contaminated with Cr. The practicability of HAECs is likely to be enhanced when the cost-benefit balance of providing a simultaneous energy supply during site treatment is resolved.

Environmental and energy implications of coal-based alternative vehicle fuel pathway from the life cycle perspective.

Coal-based fuels are effective alternative vehicle fuels in coal-rich countries, but whether it is beneficial to the environment and carbon neutrality has always been a concern. This study evaluates the energy efficiency, greenhouse gas (GHG) emissions, water footprint (WF), and environmental impact of coal-based diesel, coal-based synthetic natural gas, coal-based hydrogen, and coal-based electricity pathways from the life cycle perspective. Furthermore, scenario analysis predicts the impact of coal-rich countries on energy and emissions by adjusting vehicle fuel ratio. The results show that the coal-based diesel fuel pathway has lower energy efficiency and emits more GHGs. And GHGs are concentrated in fuel production stage. In terms of WF, the coal-based electricity pathway has the greatest benefits, which gray WF is dominant. From environmental impact perspective, a single vehicle fuel pathway cannot satisfy all impact categories. But the coal-based electricity pathway has the lowest value for the end-point environmental impact categories. Scenario analysis shows that the USA, India, and the European Union can significantly save energy and water resources and reduce GHG emissions with the increase in the proportion of alternative fuel vehicle in 2030. However, even a complete ban on the use of conventional gasoline vehicle in Norway will not reduce water consumption.

Life cycle environmental impact of system irreversibility based on advanced exergy analysis: A case study.

Optimizing system irreversibility has been a major concern for the global environmental impacts of production, use, and disposal of goods in international value chains. However, the life cycle environmental impact of system irreversibility based on advanced exergy analysis is still opened problem. Using coal-to-SNG as a case study, this study conducted an integrated assessment of advanced exergy analysis and life cycle environmental impact to provide more insight into system optimization. Based on advanced exergy analysis, SNG production system still has considerable improvement potential because 61.88% of exergy destruction is avoidable. Using life cycle assessment with inventory modified by advanced exergy analysis, the improvement potentials of life cycle environmental impacts can be identified by the near-, mid-, and long-term technological optimization scenarios of SNG production process. The results show that acidification potential, global warming potential, and ozone layer depletion potential throughout the life cycle will continue to decrease, while the optimization potentials of abiotic depletion, eutrophication and human toxicity will gradually become flattened with continuous technology optimization. The potentials for reducing life cycle environmental impacts brought by improving system irreversibility are limited (15%-25%), but they are also indispensable. The results may be helpful to understand the life cycle environmental impact of system irreversibility improvement and optimize environmental performance of industrial systems.

[Ecological risk assessment of organophosphorus pesticides in aquatic ecosystems of Pearl River Estuary].

The risk quotient method and a probabilistic risk assessment method were applied for assessing aquatic ecological risk of nine organophosphorus pesticides, including thimet, dichlorovos, disulfoton, dimethoate, dimethyl parathion, chlorpyrifos, ethoprophos, sumithion and malathion on eight aquatic organisms in the Pearl River Estuary. Results using the risk quotient method revealed that the risk level of opossum shrimp was the highest among eight aquatic organisms of the Pearl River Estuary. The risk of water flea and midge was in medium level, followed by the rest six aquatic organisms, including diatom, oyster, carp, catfish and eel, which were in the low risk by the examined organophosphorus pesticides. It was found that thimet made the largest contribution to total aquatic ecological risk among nine organophosphorus pesticides to every organism. The results from probabilistic risk assessment showed that the total ecological risk in high water period was higher than that in low water period determined by the HC5 under the 95% confidence level. The largest contribution of thimet to total aquatic ecological risk subject to the HC5 in 50% confidence level was regarded as the toxic reference value. The probabilistic risk of a single contaminant showed that thimet and disulfoton were harmful to exceeded 10% organisms in the estuarine. The probabilistic risk of nine pesticides mixture in high water period was also higher than that in low water period, and both risks were greater than 5% which exceeded safety threshold for 95% organisms in the Pearl River Estuary.