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(T/MF197) Comparison of biofilms, filter media and plants within constructed wetlands treating wastewater containing heavy metals.. Xu, Jing1,2, Scholz, Miklas2, Funk, Marcus2, Dodson, Hilary2, 1 2 ABSTRACT- The aim was to investigate the treatment efficiency of passive vertical-flow wetland filters containing different plant communities (predominantly Phragmites australis and Typha latifolia) and granular media with different adsorption capacities in order to save capital costs, to produce high quality effluent and to determine how these wetland filters would develop the ecological characteristics of natural wetlands. Gavel, sand, granular activated carbon, charcoal and Filtralite (light expanded clay) were used as filter material. Lead and copper sulphate were added to polluted urban beck inflow water in order to simulate pre-treated mine wastewater, landfill leachate or highway runoff and to test the toxicity of lead and copper to wetland biota. The interactions between growth media, microbial and plant compositions and the reduction of predominantly lead, copper, biochemical oxygen demand and pathogenic bacteria were investigated. The average lead (copper) concentrations were 1.28 (1.11) mg/l and 0.03 (0.20) mg/l for inflow and outflow water, respectively. The average five-day biochemical oxygen demand was 3.2 mg/l for inflow and 0.8 mg/l for outflow water. An additional PlasmaQuad3 High Performance Quadrupole ICP-MS analysis suggested that lead and copper accumulate as colloidal and particulate compounds in the litter and charcoal zones. Therefore, the toxicity effect of the reduced dissolved fraction of these metals was low for micro-organisms and plants. For filters containing media with limited adsorption capacities a breakthrough of copper was only recorded during the first nine weeks. However, after maturation of the biofilm, which dominates the top sediment, all wetlands reduced the performance parameter sufficiently and performed significantly similar. It follows that there is no additional benefit in using adsorption media to enhance biofilm performance. Key words: wetlands, biofilms, lead, copper |
