Assessment of Heavy Metals and Radionuclide Concentrations in Mafikeng Waste Water Treatment Plant

摘要

A study was carried out to assess the heavy metal and radionuclide concentrations of water from the waste water treatment plant in Mafikeng Local Municipality. Ten water samples were collected from various stages of water treatment (n = 2 per stage) which included sewage delivered to the plant, the two treatment stages, the effluent and the community water. Samples were analyzed for heavy metal content using Inductive Coupled Plasma Mass Spectrometer. Gross α/β activity concentrations in water samples were evaluated by Liquid Scintillation Counting whereas the concentration of individual radionuclides was measured by gamma spectroscopy. The results showed marked reduction in the levels of heavy metal concentration from 3 μg/L (As) - 670 μg/L (Na) in sewage into the plant to 2 μg/L (As) - 170 μg/L (Fe) in the effluent. The gross α activity in all the water samples (7.7 - 8.02 Bq/L) exceeded the 0.1 Bq/L limit set by World Health Organization (WHO). Gamma spectroscopy revealed very high concentrations of 235U and 226Ra in water samples, with the lowest concentrations (9.35 and 5.44 Bq/L, respectively) in the in-coming sewage and highest concentrations (73.8 and 47 Bq/L, respectively) in the community water. All the values were considerably higher than the limits of South Africa Target Water Quality Range and WHO. However, the estimated total doses of the two radionuclides for the analyzed water samples (10.62 - 45.40 μSv·yr-1) were all well below the reference level of the committed effective dose of 100 μSv·yr-1 recommended by WHO.