Potential of selected microalgae in the bioremediation of wastewater impacted dam water: A case of Goreangab Dam in Windhoek, Namibia

Abstract

The study was aimed at determining the efficacy of freshwater microalgae in the treatment of polluted dam water with respect to the reduction of pathogen loads, as well as heavy metals and nutrients concentrations. Microalgae were collected from the Klein Windhoek River, as well as the Avis and Goreangab Dams in Windhoek, Namibia. Identification of the microalgae species revealed the presence of the Microcystis species in the Goreangab Dam (control), Anabaena species in the Klein Windhoek River (treatment 1) and the Scenesdesmus species as well as the Anabaena species in the Avis Dam (treatment 2). During treatment, the water samples were assessed on day 0, day 6 and day 12 for faecal and total coliform bacteria, heavy metals (Pb and Cd) as well as nutrients (phosphorous and nitrates). A one-way analysis of variance (ANOVA) indicated that there were no statistical differences between the mean values of Pb (p = 0.346) and Cd (p = 0.940) concentrations after treatment with microalgae. The Kruskal Wallis tests indicated statistical differences between the mean values of the nitrate levels (H(3) = 8.597, p = 0.035) before and after treatment with microalgae. However, the ANOVA indicated that there were no significant differences between the mean values of total phosphate uptake (p = 0.052) after treatment with microalgae. The results for pathogen loads in the wastewater samples indicated statistically significant differences between the mean values of total coliforms ((H(3) = 10.352, p = 0.015) as well as faecal coliforms (H(3) = 10.421, p = 0.015) before and after treatment with microalgae. We conclude that while our microalgae species were not effective in the removal of heavy metals from the dam water, they were nonetheless effective in the removal of microbial contaminants as well as excessive nutrients from wastewater.