Preliminary Investigation into Occurrence and Removal of Arsenic, Cadmium, Mercury, and Zinc in Wastewater Treatment Plants in Cape Town and Stellenbosch

Abstract

The results of metals determination using inductively coupled plasma mass spectrometry (ICP-MS) for wastewater, sludges, freshwater, and sediment from six treatment plants and rivers in Cape Town and Stellenbosch are presented. The possible impacts of waste effluent on the freshwater systems are also assessed. The concentrations of the respective metals can be ranked in the order mercury < cadmium < arsenic < zinc. Occurrence of metals in influent wastewater ranged from 4.04-28.19, 1.64-17.39, 0.64-2.2, and 684.94- 5128.31 µg·l-1 for arsenic, cadmium, mercury and zinc, respectively. Average metal removal efficiency in WWTP is listed as mercury > zinc > cadmium > arsenic, with removal efficiency ranging from 28% for arsenic at Plant B and 90.25% for As at Plant D. Sludges from the six treatment plants exhibited particularly high con- tents of heavy metals, above the permissible utilization and disposal of sewage sludge guidelines. Metal con- tent of sediment and freshwater samples were also above the acceptable limits for aquatic ecosystems