Investigation into the metal contamination of three rivers in the Western Cape and the subsequent application of a bioreactor system as remediation technology

Abstract

River systems can become contaminated with micro-organisms and metals and the routine monitoring of these rivers is essential to control the occurrence of these contaminants in water bodies. This study was aimed at investigating the metal contamination levels in the Berg-, Plankenburg- and Diep Rivers in the Western Cape, South Africa, followed by the remediation of these rivers, using bioreactor systems. Sampling sites were identified and samples [water, sediment and biofilm (leaves, rocks and glass, etc.)] were collected along the Berg- and Plankenburg Rivers from May 2004 to May 2005 and for the Diep River, from February 2005 to November 2005. The concentrations of aluminium (Al), copper (Cu), iron (Fe), manganese (Mn), nickel (Ni), lead (Pb) and zinc (Zn) were determined using the nitric acid digestion method and analysed by Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES). For the Berg River, the highest concentrations in water samples were recorded for Al, Mn and Fe at the agricultural area (Site A – chapter 2). In the sediment and biofilm samples, the highest metal concentrations were once again recorded for Al and Fe. The concentrations of Al and Fe were significantly higher (p < 0.05) than than Cu, Zn, Pb, Ni and Mn in water, sediment and biofilm samples, and were mostly higher than the quality guidelines recommended by the Department of Water Affairs and Forestry (DWAF, 1996) and the Canadian Council for the Ministers of the Environment (CCME, 2001). Possible sources of contamination in the Berg River could be due to the leaching or improper discarding of household waste from the informal- and established residential areas, as well as the improper discarding of pesticides at the agricultural area. For both the Plankenburg and Diep Rivers the Al and Fe concentrations were higher than all the other metals analysed for in sediment and water samples. The highest concentrations recorded in the Plankenburg River was 13.6 mg.l-1 (water - Week 18, Site B) and 15 018 mg.kg-1 (sediment - Week 1, Site C) for Al and 48 mg.l-1 (water - Week 43, Site A) and 14 363.8 mg.kg-1 (sediment - Week 1, Site A) for Fe. The highest concentrations recorded in the Diep River was 4 mg.l-1 (water - Week 1, Site A) and 19 179 mg.kg-1 (sediment - Week 1, Site C) for Al and 513 mg.l-1 (water - Week 27, Site A) and 106 379.5 mg.kg-1 (sediment - Week 9, Site C) for Fe. For most of the metals analysed the concentrations were higher than the recommended water quality

guidelines as stipulated by the Department of Water Affairs and Forestry (DWAF, 1996b), the Canadian Council for the Ministers of the Environment (CCME, 2001) and the ‘World average’ (Martin and Windom, 1991). Point sources of pollution could not conclusively be identified, but the industrial and residential areas could have influenced the increased concentrations. Metal concentrations should be routinely monitored and the guidelines should be updated and revised based on the current state of the rivers and pollution influences. Micro-organisms isolated from flow cells after exposure to varying metal concentrations were investigated for possible metal-tolerance. A site where high metal concentrations were recorded along the Plankenburg River was investigated. The micro-organisms isolated from the flow cells were cultured and identified using the Polymerase Chain Reaction (PCR) technique, in conjunction with universal 16SrRNA primers. The phylogeny of the representative organisms in GenBank, were analysed using the Neighbour-joining algorithm in Clustal X. After exposure, the channels were stained with the LIVE/DEAD BacLightTM viability probe and visualised using Epifluorescence Microscopy. The results revealed that when exposed to the highest concentrations of Al (900 mg.l-1), Fe (1000 mg.l-1), Cu (10 mg.l-1) and Mn (80 mg.l-1), the percentage of dead cells increased, and when exposed to the lowest concentrations of Al (10 mg.l-1), Cu (0.5 mg.l-1), Mn (1.5 mg.l-1) and Zn (0.5 mg.l-1), no significant differences could be distinguished between live an dead cells. When exposed to the highest concentrations of Zn (40 mg.l-1) and Ni (20 mg.l-1), no significant differences between the live and dead cell percentages, were observed. The phylogenetic tree showed that a diverse group of organisms were isolated from the flow cells and that some of the isolates exhibited multiple metal resistance (Stenotrophomonas maltophilia strain 776, Bacillus sp. ZH6, Staphylococcus sp. MOLA:313, Pseudomonas sp. and Delftia tsuruhatensis strain A90 exhibited tolerance to Zn, Ni, Cu, Al, Fe), while other isolates were resistant to specific metals (Comamonas testosteroni WDL7, Microbacterium sp. PAO-12 and Sphingomonas sp. 8b-1 exhibited tolerance to Cu, Ni and Zn, respectively, while Kocuria kristinae strain 6J-5b and Micrococcus sp. TPR14 exhibited tolerance to Mn). The efficiency of two laboratory-scale and one on-site bioreactor system was evaluated to determine their ability to reduce metal concentrations in river water samples. The laboratory-scale bioreactors were run for a two-week and a three-week

period and the on-site bioreactor for a period of ten weeks. Water (all three bioreactors) and bioballs (bioreactor two and on-site bioreactor) were collected, digested with 55% nitric acid and analysed using ICP-AES. The final concentrations for Al, Ni and Zn (bioreactor one) and Mn (bioreactor two), decreased to below their recommended concentrations in water samples. In the on-site, six-tank bioreactor system, the concentrations for Fe, Cu, Mn and Ni decreased, but still exceeded the recommended concentrations. The concentrations recorded in the biofilm suspensions removed from the bioballs collected from bioreactor two and the on-site bioreactor, revealed concentrations higher than those recorded in the corresponding water samples for all the metals analysed, except Fe. The bioballs were shown to be efficient for biofilm attachment and subsequent metal accumulation. The species diversity of the organisms isolated from the bioreactor (bioreactor two) experiment after three days (initial) differed from the organisms isolated after 15 days (final). Hydrogenophaga sp., Ochrobactrum sp, Corynebacterium sp., Chelatobater sp. and Brevundimonas sp. were present only at the start of the bioreactor experiment. The surviving populations present both in the beginning and at the end of the bioreactor experiment belonged predominantly to the genera, Pseudomonas and Bacillus. Metal-tolerant organisms, such as Bacillus, Pseudomonas, Micrococcus and Stenotrophomonas, amongst others, could possibly be utilised to increase the efficiency of the bioreactors. The bioreactor system should however, be optimised further to improve its efficacy.