1. Department of Chemistry and Bioscience, Section of Biology and Environmental Science; Aalborg University, Fredrik BajersVej 7H; Aalborg East 9220 Denmark
2. Department of Environmental Health Sciences and Technology; Jimma University, P. O. Box 378; Jimma Ethiopia
3. School of Civil and Environmental Engineering; Jimma Institute of Technology, P.O. Box 378; Jimma Ethiopia