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An excess level of nitrate in drinking water is responsible for methemoglobinemia, or 'blue baby' disease. Consequently, management of nitrate in drinking water is universally of public health interest. In this study, clinoptilolite functionalised with cationic surfactant hexadecyltrimethyl ammonium (HDTMA) was used for the removal of nitrate from drinking water. The effects of surfactant loading, adsorbent dosage, pH, coexisting ions, temperature and environmental water quality on the adsorption of nitrate were investigated. It was found that adsorption was optimum when the initial concentration of the functionalising surfactant was 3 000 mg•ℓ-1. An increase in adsorbent dosage raised the percentage removal of nitrate. The valency of the coexisting anion had a major effect on nitrate removal, with the presence of phosphate (a trivalent anion) leading to the lowest removal ability. Temperature and pH had negligible effects on adsorbent performance. Environmental water samples (natural groundwater samples from Limpopo Province, South Africa) were tested and it was found that the World Health Organisation (WHO) regulatory compliance can be achieved even when the initial concentration of nitrate exceeds 300 mg•ℓ-1. Equilibrium data was modelled using the Freundlich and Langmuir isotherms and the data conformed well to the Freundlich isotherm, indicating the heterogeneous nature of the active sites. Kinetically, nitrate adsorption was best described by the pseudo-second rate equation.

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Due to the increased population growth in South Africa, particularly in urban areas, the generation of municipal solid waste has increased and so is the demand of energy. Municipal solid waste can be considered a good candidate for electricity generation in South Africa. This approach does not only have the benefit of recovering electricity from municipal waste, but also contributes to the integrated waste management system. This study aimed to investigate the economic feasibility of hybrid of anaerobic digestion and gasification of municipal waste for electricity generation in South Africa. The research developed a techno-economic model to evaluate the financial profitability of waste-to-energy of gasification, anaerobic digestion and a hybrid system of both waste-to-energy technologies. A spreadsheet was developed to evaluate the financial profitability of waste-to-energy of gasification, anaerobic digestion and hybrid system of both waste-to-energy technologies. The technoeconomic model provides cost estimates for the implementation of waste-to-energy technologies in South Africa. This is carried out through a set of financial indicators, namely payback period (PBT), net present value (NPV), profit index (PI), internal rate of return (IRR), levelised cost of electricity (LCOE) and levelised cost of waste (LCOW). Hybrid of gasification and anaerobic digestion manifested positive results across all the financial indicators. The study concluded that a hybrid of anaerobic digestion and gasification waste-to-energy is economically viable. In addition, the hybrid system also provides optimal solution for energy recovery and waste disposal, based on the IRR, LCOE and LCOW values. Sensitivity analysis showed that, energy price and capital expenditure are the major variables affecting the hybrid plant's investment decision.

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