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This paper presents the reviews of scientific papers published in 2018 issues on the effects of anthropogenic pollution on the aquatic organisms dwelling in freshwater ecosystem at global scale. The first part of the study provides the summary of relevant literature reviews followed by field and survey based studies. The second part is based on categories of different classes/sources of pollutants which affect freshwater organism. This is composed of several sections including metals and metalloids, wastewater and effluents, sediments, nutrients, pharmaceuticals, polycyclic aromatic hydrocarbons, flame retardants, persistent organic pollutants, pharmaceuticals and illicit drugs, emerging contaminants, pesticides, herbicides, and endocrine disruptors. The final part of the study highlights the reviews of published research work on new pollutants such as microplastics and engineered nanoparticles which affect the freshwater organisms.Practitioner points Heavy metals concentrations should be assessed at nano‐scale in aquatic environment. Air pollutants could have long‐term effects on freshwater ecosystem. Future studies should focus on bioremediations of freshwater pollution.

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AbstractDue to increasing concerns about global warming and dwindling oil supplies, the world’s attention is turning to green processes that use sustainable and environmentally friendly feedstock to produce renewable energy such as biofuels. Among them, biodiesel, which is made from nontoxic, biodegradable, renewable sources such as refined and used vegetable oils and animal fats, is a renewable substitute fuel for petroleum diesel fuel. Biodiesel is produced by transesterification in which oil or fat is reacted with short chain alcohol in the presence of a catalyst. The process of transesterification is affected by the mode of reaction, molar ratio of alcohol to oil, type of alcohol, nature and amount of catalysts, reaction time, and temperature. Various studies have been carried out using different oils as the raw material; different alcohols (methanol, ethanol, butanol); different catalysts; notably homogeneous catalysts such as sodium hydroxide, potassium hydroxide, sulfuric acid, and supercritical fluids; or, in some cases, enzymes such as lipases. This article focuses on the application of heterogeneous catalysts for biodiesel production because of their environmental and economic advantages. This review contains a detailed discussion on the advantages and feasibility of catalysts for biodiesel production, which are both environmentally and economically viable as compared to conventional homogeneous catalysts. The classification of catalysts into different categories based on a catalyst’s activity, feasibility, and lifetime is also briefly discussed. Furthermore, recommendations have been made for the most suitable catalyst (bifunctional catalyst) for low-cost oils to valuable biodiesel and the challenges faced by the biodiesel industry with some possible solutions.

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Food waste is a major constituent in municipal solid wastes and its accumulation or disposal of in landfills is problematic, causing environmental issues. Herein, a techno-economic study is carried out on the potential of biogas production from different types of food waste generated locally. The biogas production tests were at two-time sets; 24-h and 21-day intervals and results showed a good correlation between those two-time sets. Thus, we propose to use the 24-h time set to evaluate feedstock fermentation capacity that is intended for longer periods. Our approach could potentially be applied within industry as the 24-h test can give a good indication of the potential substrate gas production as a quick test that saves time, with minimal effort required. Furthermore, polynomial models were used to predict the production of total gas and methane during the fermentation periods, which showed good matching between the theoretical and practical values with a coefficient of determination R2 = 0.99. At day 21, the accumulative gas production value from mixed food waste samples was 1550 mL per 1 g of dry matter. An economic evaluation was conducted and showed that the case study breaks-even at $0.2944 per cubic metre. Any prices above this rate yield a positive net present value (NPV); at $0.39/m3 a discounted payback period of six years and a positive NPV of $3108 were calculated. If waste management fee savings are to be incorporated, the total savings would be higher, increasing annual cash flows and enhancing financial results. This economic evaluation serves as a preliminary guide to assess the economic feasibility based on the fluctuating value of methane when producing biogas from food waste via anaerobic digestion, thus could help biogas project developers investigate similar scale scenarios .