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Abstract: Chemical additives used in hydraulic fracturing (HF) for unconventional natural gas production can be a risk to environmental and human health (EHH). The EHH risk is affected by three factors: the chemical hazard measured, the certainty of the measured hazard, and the use frequencies of additives. Limited studies have holistically assessed the EHH risks of HF additives. This study qualitatively analyzed the EHH risks of 105 representative HF additives used in British Columbia, Canada, based on the three previously listed factors using a fuzzy clustering analysis approach. The performance of additives on these factors was converted into indices using an indexing system. The indices were grouped into seven clusters according to their relative similarities. The EHH risk of each cluster was interpreted based on the resulting indices. Results show that additives grouped in clusters 7 and 2 have relatively high EHH risks, which require special attention in HF operations. Clusters 4, 1, and 5 were identified as having moderate EHH risks, while clusters 6 and 3 are of low EHH risk concerns. Many iron control agents were classified into cluster 7, indicating that this type of additives is associated with a high EHH risk. Many friction reducers and gelling agents were classified into cluster 4 characterized by the highest hazard uncertainty. Assessment of hypothetical fracturing fluids shows that using additives grouped in clusters with a low risk could help mitigate the EHH impacts posed by HF chemicals.Graphical abstract: [ABSTRACT FROM AUTHOR]

Rapidly increasing catastrophic environmental incidents and changes in global climate have compelled researchers to take proactive measures for climate change mitigation. Consequently, reducing greenhouse gas emissions has become one of the most significant global targets. The transportation sector has a massive carbon footprint accounting for 22% of the total carbon dioxide emissions. In this regard, road transport contributes the largest fraction of the total emissions within the transportation sector. Conversely, the railway which is the cleanest form of transportation contributes slightly more than 1% of the total emissions. Moreover, since most of the rail systems are operated by government or private companies, it is relatively convenient to implement policies and replace conventional technology with environmentally friendly ones. This could be achieved by taking certain measures from technical and operational viewpoints for conserving energy to lower the carbon intensity of all transport modalities. Hence, this review paper focuses on investigating the railway sector to encourage a modal shift to the least carbon-intensive option. This study provides a critical review of the past and present rail technologies in terms of the environmental, economic, social, and technical perspectives. Moreover, a comparative assessment of the various locomotive types has been performed. The results reveal that battery-hydrogen hybrid locomotives are the best choice to be considered as a future locomotive technology. Hydrogen locomotives have the potential to be a promising alternative to diesel railway locomotives. However, certain technical barriers need to be overcome to enhance the overall system's performance and reliability to further improve the viability of its deployment in the railway sector. [Display omitted] • A critical review of the various rail technologies is provided through different viewpoints. • The assessment constitutes environmental, economic, social, and technical perspectives. • A decision-support tool for comparison of four rail technologies is also developed. • Battery-hydrogen hybrid locomotive results in the highest score of 1.47. • Standalone hydrogen locomotive results in the second highest score of 1.38. [ABSTRACT FROM AUTHOR]

Production of hydrogen fuel from municipal solid waste can serve as a potential solution to two looming environmental crises: global warming caused by undesirable emissions of greenhouse gases and the ever-increasing generation and accumulation of waste in the environment. However, the actual implementation and continuous operation of waste-to-hydrogen conversion facilities require consideration of numerous factors. This study explored the variability of several factors related to waste-to-hydrogen, such as location selection, geographic availability of municipal solid waste, pricing of by-products and waste acceptance, constantly fluctuating energy costs, and carbon credit market values from potential carbon trading systems. Four waste conversion processes previously studied for their triple-bottom-line sustainability have been used as baseline scenarios. The variability of multiple factors and their impacts were assessed via parametric analyses. The effects of these fluctuating factors on the economic and environmental performances of waste-to-hydrogen conversion and the establishment of processing facilities were captured. The results of this study will be beneficial for the industry, private investors, policymakers, and governments while making critical decisions such as location selection, deriving price formulas, and selecting plant capacity. • Implementation of four waste-to-hydrogen processes is studied. • Variabilities impacting levelized cost of hydrogen and global warming are assessed. • Economies of scale attained in all processes except waste pyrolysis. • Waste gate fee, carbon credits, and by-product sales reduce levelized costs. • Areas with high population density are suited for waste-to-hydrogen implementation. [ABSTRACT FROM AUTHOR]

The aim of the study is to conduct an ecological risk assessment of accidental release of flowback water into freshwater body. Flowback water produced from the hydraulic fracturing process has a complex combination of high concentration of salts, organic compounds and metals. The toxicity of flowback water is assessed and an exposure assessment method for the inorganic constituents of the flowback water is developed. An equation for risk is derived to characterize the risk of the flowback water to the aquatic ecology. A case study is conducted for accidental release of hydraulic fracturing flowback water in Montney unconventional play trend in northern British Columbia. The flowback water quality data for 212 wells, including the concentrations of various salt ions, metal ions, and hydrogen sulfide, is collected for the assessment. The risk quotient is found to be 0.16 (<1), proving no significant risk to the aquatic ecosystem with 90% confidence. However, the overall results of the uncertainty and scenario analysis concludes that the risk to the ecology cannot be completely overlooked. Scenario analysis was done for monthly creek discharge and a relationship between risk quotient and the ratio of spill volume to the creek discharge was derived. [ABSTRACT FROM PUBLISHER]

Building rating systems lack a methodology for assessing building's potential for becoming self-sufficient by using local resources. There is a gap in the literature for linking natural capital assessment and net-zero buildings. This paper presents a methodology for assessment of natural capital to achieve net-zero targets in buildings. The developed methodology is demonstrated through a Living Building Challenge registered building. The contribution of water, energy and building materials is discussed, and various scenarios are evaluated on how the building can become net-zero over its life cycle by using local natural resources. Results show that the building can generate 100% of its energy and 92% of its water on-site and can become net-zero with the help of materials recycling and off-site carbon offset program. [ABSTRACT FROM AUTHOR]

Thermochemical water-splitting processes are among the most promising options for producing sustainable and green hydrogen due to being extremely environmentally benign. Being extensively investigated in the literature, the thermochemical copper-chlorine cycle has demonstrated much promise in this regard as one of the most efficient options for thermochemically obtaining hydrogen. Thus, this study focuses on investigating the exergoeconomic performances of the different variants of the copper-chlorine cycle including the three-, four-, and five-step versions. All cycles are modeled and simulated in Aspen-plus software by considering a recovery of thermal energy from industrial waste flue gases in addition to internal heat recovery. Moreover, a hydrogen production capacity of 668 kg/h is considered for all cycles. The Specific Exergy Costing methodology is employed to study the exergoeconomic performance of each cycle. All cycles are initially examined in terms of the cost rates of energy transfer and hourly levelized cost rates for each step. The cycle variants are further examined through a comparative assessment of several performance parameters including hydrogen cost rates, overall cost rates of energy transfer, and overall hourly levelized cost rates. According to the performed analyses, the three-step variant of the cycle that constitutes a high-temperature electrolysis process produces hydrogen at the lowest cost rate (0.83 $/kg) while the four-step cycle produces hydrogen at the highest cost rate (1.82 $/kg). Furthermore, the hydrolysis step is found to have the highest hourly levelized cost rates for all variants of the cycle. Several factors that impact the hydrogen cost rate are also examined comprehensively. In addition, the extent to which the hydrogen cost rate is sensitive to those factors is discussed. [Display omitted] • Exergoeconomic analyses of three variants of thermochemical copper-chlorine cycle. • Thermal management schemes incorporated for each cycle. • Comparative assessment of the exergoeconomic performances of all cycles. • Hydrogen production capacity of 668 kg/h for each cycle. [ABSTRACT FROM AUTHOR]

Natural gas (NG) use is diverse and it is comparatively a cleaner fossil fuel. However, NG industry operations emit substantial levels of greenhouse gases. Hence, implementing strategies that avoid industrial emissions is necessary. The current review aims to investigate potential decarbonization strategies for the NG value chain. Three pillars of emission abatement strategies namely; industry management, technological advancements, and new business avenues are presented. Potential risks from such decarbonization investments and recommendations are provided. A road map for supply chain decarbonization strategy selection is proposed from the literature findings. The review is useful for multiple stakeholders to implement sustainable gaseous fuel futures. [Display omitted] • Review of potential emission reduction strategies and technologies for the natural gas industry. • A low-carbon natural gas supply chain is essential in achieving emission goals. • Technology improvements, industry management, and new business avenues can support decarbonization goals. • Decarbonization strategies selected based on cost and GHG reduction potential. [ABSTRACT FROM AUTHOR]