The transportation sector has been reported as a key contributor to the emissions of greenhouse gases responsible for global warming. Hence, the need for the introduction of electric vehicles (EVs) into the transportation sector. However, the competitiveness of the EVs with the conventional internal combustion engine vehicles has been a bone of contention. Life cycle cost analysis (LCCA) is an important tool that can be employed to determine the competitiveness of a product in its early stage of production. This review examines different published articles on LCCA of EVs using Scopus and Web of Science databases. The time trend of the published articles from 2001 to 2019 was examined. Moreover, the LCC obtained from the different models of EVs were compared. There was a growing interest in research on the LCC of EVs as indicated by the upward increase in the number of published articles. A variation in the LCC of the different EVs studied was observed to depend on several factors. Based on the LCC, EVs were found not yet competitive with conventional internal combustion engine cars due to the high cost of batteries. However, advancement in technologies with incentives could bring down the cost of EV batteries to make it competitive in the future.

The thermo-catalytic and biochemical conversion of biomass to hydrogen-rich syngas has been widely reported with less emphasis on the environmental implications of the processes. This mini-review presents an overview of different thermo-catalytic route of converting biomass to hydrogen-rich syngas as well as their environmental impact investigated using life cycle assessment methodology. The review revealed that most of the authors employed, biomass gasification, biomass pyrolysis, reforming and fermentative processes for the hydrogen-rich syngas production. Global warming potential was observed as the most significant environmental impact reported in the reviewed articles. The CO₂ equivalent emissions were found to varies with each of the processes and the type of feedstock used. Trends from literature shows that both thermo-catalytic and biochemical processes have competitive advantages and potential to compete favorable with the existing technology used for hydrogen production. Nevertheless, it cannot be ascertained that these technologies should be excluded from environmental burdens. This mini-review could be a quick guide to future research interest in environmental impact of hydrogen-rich syngas production by thermo-catalytic and biochemical conversion of biomass.

This study presents an overview of the economic analysis and environmental impact of natural gas conversion technologies. Published articles related to economic analysis and environmental impact of natural gas conversion technologies were reviewed and discussed. The economic analysis revealed that the capital and the operating expenditure of each of the conversion process is strongly dependent on the sophistication of the technical designs. The emerging technologies are yet to be economically viable compared to the well-established steam reforming process. However, appropriate design modifications could significantly reduce the operating expenditure and enhance the economic feasibility of the process. The environmental analysis revealed that emerging technologies such as carbon dioxide (CO₂) reforming and the thermal decomposition of natural gas offer advantages of lower CO₂ emissions and total environmental impact compared to the well-established steam reforming process. Appropriate design modifications such as steam reforming with carbon capture, storage and utilization, the use of an optimized catalyst in thermal decomposition, and the use of solar concentrators for heating instead of fossil fuel were found to significantly reduced the CO₂ emissions of the processes. There was a dearth of literature on the economic analysis and environmental impact of photocatalytic and biochemical conversion processes, which calls for increased research attention that could facilitate a comparative analysis with the thermochemical processes.

Organic-rich substrates from organic waste effluents are ideal sources for hydrogen production based on the circular economy concept. In this study, a data-driven approach was employed in modeling hydrogen production from palm oil mill effluents and activated sludge waste. Seven models built on support vector machine (SVM) and Gaussian process regression (GPR) were employed for the modeling of the hydrogen production from the waste sources. The SVM was incorporated with linear kernel function (LSVM), quadratic kernel function (QSVM), cubic kernel function (CSVM), and Gaussian fine kernel function (GFSVM). While the GPR was incorporated with the rotational quadratic kernel function (RQGPR), squared exponential kernel function (SEGPR), and exponential kernel function (EGPR). The model performance revealed that the SVM-based models did not show impressive performance in modeling the hydrogen production from the palm oil mill effluent, as indicated by the R² of −0.01, 0.150, and 0.143 for LSVM, QSVM, and CSVM, respectively. Similarly, the SVM-based models did not perform well in modeling the hydrogen production from activated sludge, as evidenced by R² values of 0.040, 0.190, and 0.340 for LSVM, QSVM, and CSVM, respectively. On the contrary, the SEGPR, RQGPR, SEGPR, and EGPR models displayed outstanding performance in modeling the prediction of hydrogen production from both oil palm mill effluent and activated sludge, with over 90% of the datasets explaining the variation in the model output. With the R² > 0.9, the predicted hydrogen production was consistent with the SEGPR, RQGPR, SEGPR, and EGPR with minimized prediction errors. The level of importance analysis revealed that all the input parameters are relevant in the production of hydrogen. However, the influent chemical oxygen demand (COD) concentration and the medium temperature significantly influenced the hydrogen production from palm oil mill effluent, whereas the pH of the medium and the temperature significantly influenced the hydrogen production from the activated sludge.

The need to mitigate CO₂ emissions from the transportation sector has necessitated the adoption of electric vehicles (EVs) and other forms of alternative vehicles. Despite the global rise of EVs demand as a complementary means of green transportations, the level of adoption in Malaysia is still not encouraging. Therefore, this study aimed to investigate the cost competitiveness of EVs in comparison with Hybrid Electric Vehicles (HEVs) and an Internal Combustion Vehicle (ICV) based on Malaysia scenarios. Using the existing data in Malaysia, life cost analysis (LCC) of two EVs was computed and compared with HEVs and ICVs. The study shows that Nissan leaf and BMW i3s EVs with LCC of $1.75 and $2.5 per km are not cost-competitive based on prevalent data available in Malaysia compared to the HEVs and ICV. Based on the sensitivity analysis, changes in the components of the operating costs significantly influence the accumulated cost of ownership of the EVs whereas the cost of ownership of the HEVs and ICVs did not experience any significant influence. The findings from this study could serve as bases for policymakers to formulate appropriate policies and strategies to improve the competitiveness of EVs in Malaysia.

Circular economy (CE) strategy is crucial in developing towards sustainable growth. It was created to promote resource utilization and the elimination of waste production. This article aimed to study the possibilities of using the CE framework in wastewater bioremediation and energy recovery using hydroponic tanks. The integration of phytoremediation with bioenergy, construction and lifespan of hydroponic tanks in phytoremediation of wastewater, selection of aquatic plants and the expected challenges in the implementation of CE in phytoremediation of wastewater were discussed. The plant-based biomass harvested and the relative growth rate (RGR) of the selected plants from the phytoremediation process was evaluated. The findings obtained indicated that the selected plants tripled in weight after 14 days cultivation period at different retention times. E. crassipes recorded the highest growth with 2.5 ± 0.03 g g⁻¹ d⁻¹, followed by S. molesta with 1.33 ± 0.05 g g⁻¹ d⁻¹ and then P. stratiotes recorded 0.92 ± 0.27 g g⁻¹ d⁻¹ at the end of the cultivation period. Therefore, the selected plants have been identified as having the potential to be used in phytoremediation as well as a source of energy production. The outcome of our review suggested the adoption of a lifecycle assessment as the CE framework for the phytoremediation of wastewater.