1. Department of Environmental Engineering, School of Water and Environment, Chang’an University, Xi’an, Shaanxi Province 710064, P.R China
2. Faculty of Education, Eastern Technical University of Sierra Leone, Combema Road, Kenema City 00232, Sierra Leone
3. School of Highway, Chang’an University, Xi’an, Shaanxi Province 710064, P.R China
4. College of Economics and Management, Jilin Agricultural University, Changchun 130118, China
5. Department of Geography-Environment and Natural Resources Management, Faculty of Social and Management Sciences, Ernest Bai Koroma University of Science and Technology, Magburaka City 00232, Sierra Leone
6. School of Economics and Management, Chang’an University, Xi’an 710064, China