Levels Of Mn, Fe, Ni, Cu, Zn And Cd, In Effluent From A Sewage Treatment Oxidation Pond And A Receiving Stream - A Preliminary Study

Abstract

This study reports the results of preliminary investigation of heavy metal levels-Ni, Cd, Fe, Zn, Cu and Mn; pH; temperature and electrical conductivity in effluents from a sewage treatment oxidation pond and its receiving stream. The heavy metal concentrations were determined with Inductively Coupled Plasma-Mass Spectrometry (ICP–MS). The overall mean levels of Ni, Cd, Zn, Cu, Fe and Mn were 1.92 ± 0.66 g/L, 11.99 ± 3.45 g/L, 0.43 ± 0.32 mg/L, 0.18 ± 0.08 mg/L, 7.26 ± 1.32 mg/L and 0.43 ± 0.26 mg/L in the effluent samples and 1.64 ± 0.55 g/L, 4.74 ± 3.73 g/L, 0.19 ± 0.01 mg/L, 0.13 ± 0.07 mg/L, 4.34 ± 1.00 mg/L and 0.24 ± 0.24 mg/L in the receiving stream respectively. Thus, higher levels of these metals were generally found in the effluent samples compared with the reference sample and the receiving stream. The discharge of effluents from the sewage treatment oxidation pond into the receiving stream is therefore a major source of heavy metal pollution of the stream apart from diffuse and natural sources of these metals. The mean levels of Cd, Fe and Mn obtained for the receiving stream exceeded the WHO guideline criteria of 3.0 g/L, 1.0 mg/L and 0.5 mg/L respectively for drinking water, while the mean levels of Zn and Mn in the receiving stream exceeded the WHO guideline criteria of 20 g/L and 0.18 mg/L respectively for protection of aquatic ecosystem. Although, the overall mean temperature values of 26.8 ± 0.52 oC obtained for the receiving stream is normal, the pH levels fall below the WHO range of 7.0-8.5 for drinking water. The pH and heavy metal concentrations of the effluents indicate their potential environmental hazard on the general ecology of the receiving stream. This calls for proper management of the effluent from the oxidation pond prior to its discharge into the receiving stream. Keywords: Heavy metals, oxidation pond, effluent, influent, receiving stream IFE Journal of Science Vol. 9 (1) 2007 pp. 115-128