Comparative environmental sustainability assessment of biohydrogen production methods.

As energy crisis is recognized as an increasingly serious concern, the topic on biohydrogen (bioH2) production, which is renewable and eco-friendly, appears to be a highly-demanding subject. Although bioH2 production technologies are still at the developmental stage, there are many reported works available on lab- and pilot-scale systems with a promising future. This paper presents various potential methods of bioH2 production using biomass resources and comparatively assesses them for environmental impacts with a special emphasis on the specific biological processes. The environmental impact factors are then normalized with the feature scaling and normalization methods to evaluate the environmental sustainability dimensions of each bioH2 production method. The results reveals that the photofermentation (PF) process is more environmentally sustainable than the other investigated biological and thermochemical processes, in terms of emissions, water-fossil-mineral uses, and health issues. The global warming potential (GWP) and acidification potential (AP) for the PF process are then found to be 1.88 kg-CO2 eq. and 3.61 g-SO2 eq., which become the lowest among all processes, including renewable energy-based H2 production processes. However, the dark fermentation-microbial electrolysis cell (DF-MEC) hybrid process is considered the most environmentally harmful technique, with the highest GWP value of 14.6 kg-CO2 eq. due to their superior electricity and heat requirements. The water conception potential (WCP) of 84.5 m3 and water scarcity footprint (WSF) of 3632.9 m3 for the DF-MEC process is also the highest compared to all other processes due to the huge amount of wastewater formation potential of the system. Finally, the overall rankings confirm that biological processes are primarily promising candidates to produce bioH2 from an environmentally friendly point of view.

Development of a new photoelectrochemical system for clean hydrogen production and a comparative environmental impact assessment with other production methods.

Hydrogen is recognized as a critical substance for diversifying the global energy supply, providing new economic opportunities and realizing a carbon-free energy sector. In the current study, a life cycle assessment is conducted on a photoelectrochemical hydrogen production process of a newly developed photoelectrochemical reactor. With a photoactive electrode area of 870 cm2, the hydrogen production rate of the reactor is 47.1 µg/s while operating with the energy and exergy efficiencies of 6.3% and 6.31%, respectively. For a Faradaic efficiency of 96%, the produced current density is evaluated as 3.15 mA/cm2. A comprehensive study is conducted for a cradle-to-gate life cycle assessment of the proposed hydrogen photoelectrochemical production system. The life cycle assessment results of the proposed photoelectrochemical system are further evaluated within a comparative analysis by considering a total of four key hydrogen generation processes, namely steam-methane reforming, photovoltaics-based and wind electricity-driven proton exchange membrane water electrolysis and the current photoelectrochemical system and studying five environmental impact categories. The global warming potential of hydrogen production via the proposed photoelectrochemical cell is evaluated as 1.052 kg CO2 equivalent per kg of produced hydrogen. In the normalized comparative life cycle assessment results, the PEC-based hydrogen production is found to be the most nature-friendly option among the considered pathways.

Economic and environmental impact assessments of a newly designed energy system for marine applications.

Marine transportation via the world's oceans is a critical way to convey goods and fuels between continents that cannot be performed cost-effectively by any other means. However, big ships heavily rely on fossil fuels, aggravating global carbon emissions. A key resolution to this dilemma is to employ clean fuels to reduce carbon emissions. This research paper introduces a new hybrid compound marine engine comprising a gas turbine, a solid oxide fuel cell, and a steam Rankine cycle. Three types of analyses, such as exergy, exergoeconomic, and exergoenvironmental analyses, are conducted on this proposed engine. It is found that the engine can produce a power of 15.5 MW, which is more than 48% compared to the traditional marine engine power, and the engine performance has up to 61% energy efficiency and 43% exergy efficiency. However, the exergetic efficiency of this engine based on fuel and product principal is 60%, which is more than 17% compared to its exergy efficiency. This engine has a 218 $/h Levelized cost rate and 139 mPt/h environmental rate. Finally, the average overall specific product exergy cost and environment are obtained to be 59 $/GJ and 20 mPt/MJ. By comparing five fuel blends, methane and hydrogen are the most economical and have the least impact on the environment; the second option is ethanol blend.

Assessment of effectiveness of optimum physical distancing phenomena for COVID-19.

Currently, COVID-19 is a global pandemic that scientists and engineers around the world are aiming to understand further through rigorous testing and observation. This paper aims to provide safe distance recommendations among individuals and minimize the spread of COVID-19, as well as examine the efficacy of face coverings as a tool to slow the spread of respiratory droplets. These studies are conducted using computational fluid dynamics analyses, where the infected person breathes, coughs, and sneezes at various distances and environmental wind conditions and while wearing a face-covering (mask or face shield). In cases where there were no wind conditions, the breathing and coughing simulations display 1-2 m physical distancing to be effective. However, when sneezing was introduced, the physical distancing recommendation of 2 m was deemed not effective; instead, a distance of 2.8 m and greater was found to be more effective in reducing the exposure to respiratory droplets. The evaluation of environmental wind conditions necessitated an increase in physical distancing measures in all cases. The case where breathing was measured with a gentle breeze resulted in a physical distancing recommendation of 1.1 m, while coughing caused a change from the previous recommendation of 2 m to a distance of 4.5 m or greater. Sneezing in the presence of a gentle breeze was deemed to be the most impactful, with a recommendation for physical distancing of 5.8 m or more. It was determined that face coverings can potentially provide protection to an uninfected person in static air conditions. However, the uninfected person's protection can be compromised even in gentle wind conditions.

Impact Assessment and Environmental Evaluation of Various Ammonia Production Processes.

In the current study, conventional resources-based ammonia generation routes are comparatively studied through a comprehensive life cycle assessment. The selected ammonia generation options range from mostly used steam methane reforming to partial oxidation of heavy oil. The chosen ammonia synthesis process is the most common commercially available Haber-Bosch process. The essential energy input for the methods are used from various conventional resources such as coal, nuclear, natural gas and heavy oil. Using the life cycle assessment methodology, the environmental impacts of selected methods are identified and quantified from cradle to gate. The life cycle assessment outcomes of the conventional resources based ammonia production routes show that nuclear electrolysis-based ammonia generation method yields the lowest global warming and climate change impacts while the coal-based electrolysis options bring higher environmental problems. The calculated greenhouse gas emission from nuclear-based electrolysis is 0.48 kg CO2 equivalent while it is 13.6 kg CO2 per kg of ammonia for coal-based electrolysis method.