Bioremediation of metal contamination in the Plankenburg River, Western Cape, South Africa

Three bioreactors (two laboratory-scale and one on-site) were evaluated for their efficiency to reduce metal concentrations in water collected from the Plankenburg River, South Africa. Water (bioreactors one, two and on-site) and bioballs (bioreactors two and on-site) collected throughout the study periods were digested and analysed using Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES). Aluminium (Al), nickel (Ni), and zinc (Zn) concentrations decreased from 0.41 mg l^-1 to 0.06 mg l^-1 (85%), 0.2 mg l^-1 to 0.07 mg l^-1 (65%) and 75 mg l^-1 to 0.02 mg l^-1 (97%), respectively (bioreactor one). Aluminium [(1.55-0.38 mg l^-1 (75%)], copper (Cu) [57% (from 0.33 mg l^-1 to 0.14 mg l^-1)], iron (Fe) [71.99-40.4 mg l^-1 (44%)] and manganese (Mn) [57% (0.07-0.03 mg l^-1)] concentrations also decreased in the water samples from bioreactor two. In the on-site, six-tank bioreactor system, concentrations for Fe, Cu, Mn and Ni decreased, while Zn and Al concentrations increased. The concentrations recorded in biofilm samples were higher than the corresponding water samples. The bioballs employed in the bioreactor were thus shown to be efficient attachment surfaces for biofilm development and subsequent metal accumulation. Potentially metal-tolerant organisms (Pseudomonas sp., Sphingomonas sp., and Bacillus sp.) were also identified using phylogeny.