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Biodiesel has attracted increasing interest and has proved to be a good substitute for fossil-based fuels due to its environmental advantages and availability from renewable resources such as refined and waste vegetable oils. Several studies have shown that biodiesel is a better fuel than the fossil-derived diesel in terms of engine performance, emissions reduction, lubricity and environmental benefits. The increasing popularity of biodiesel has generated great demand for its commercial production methods, which in turn calls for the development of technically and economically sound process technologies. This paper explores the applicability of ultrasound in the optimization of low-cost feedstock -in this case waste cooking oil -in the transesterification conversion to biodiesel. It was found that the conversion efficiency of the waste oil using ultrasound was higher than with the mechanical stirring method. The optimized variables of 6:1 methanol/oil ratio at a reaction temperature of 30 °C and a reaction time of 30 min and 0.75% KOH (wt/wt) catalyst concentration was obtained for the transesterification of the waste oil via the use of ultrasound.

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Advanced oxidation processes (AOPs) particularly non-thermal plasmas based on electrical discharges have been widely investigated for water and wastewater treatment. Dielectric barrier discharges (DBDs) generate large amounts of selective and non-selective reactive oxygen species (ROS) such as ozone, hydrogen peroxide, atomic oxygen, superoxide molecular anions and hydroxyl radicals, having been proved to be efficient for water decontamination among various forms of electrical discharge systems. The detection and quantification methods of these oxygen species in non-thermal plasmas have been reviewed. However, their application in dielectric barrier discharge has not been well studied. It is therefore imperative to summarise the various detection and quantification methods for oxygen-based species determination in AOPs, aqueous systems and non-thermal plasma processes. Thereafter, reviewed methods are suggested for the determination of ROS in DBD configurations to understand the consumption trend of these oxidants during treatment of water effluents and to evaluate the performance of the treatment reactor configuration towards the degradation of targeted pollutants.

The production of biofuels worldwide has been significant lately due to the shift from obtaining energy from nonrenewable energy (fossil fuels) to renewable sources (biofuels). This energy shift arose as a result of the disturbing crude petroleum price fluctuations, uncertainties about fossil fuel reserves, and greenhouse gas (GHG) concerns. With the production of biofuels increasing considerably and the current global biodiesel production from different feedstock, reaching about 6 billion liters per year, biodiesel production costs have been highly dependent on feedstock prices, ranging from 70 to 25; of total production costs, and in comparison with the conventional diesel fuel, the biodiesel is currently noncompetitive. An efficient production process is, therefore, crucial to lowering biodiesel production costs. The question of sustainability, however, arises, taking into account the African diverse conditions and how vital concerns need to be addressed. The major concern about biodiesel production costs can be reduced by finding value-added applications for its glycerol byproduct. This paper, thus, provides an overview of current research trends that could overcome the major hurdles towards profitable commercialization of biodiesel and also proposes areas of opportunity probable to capitalize the surplus glycerol obtained, for numerous applications.