1. School of Chemical and Metallurgical Engineering, Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, Private Bag 3, WITS, Johannesburg 2050, South Africa
2. Department of Chemical Engineering, Enugu State University of Science and Technology, Enugu, Nigeria
3. Department of Environmental Management, Federal University of Technology Owerri, Owerri, Nigeria
4. Department of Chemical Engineering, University of Pretoria, Faculty of Engineering, Built Environment and Information Technology, Private Bag X20, Hatfield, Pretoria 0028, South Africa