Comparison of microbiology, filter media and plant communities within constructed wetlands treating wastewater contaminated with heavy metals

The aim was to investigate the treatment efficiency of passive vertical-flow wetland filters containing different plant communities (predominantly Phragmites Australis and/or Typha Latifolia) and granular media with different adsorption capacities in order to save capital costs, to produce high quality effluent, and to investigate the microbial interactions in the filters. Gravel, sand, granular activated carbon, charcoal and Filtralite (light expanded clay) were applied. 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 potentially pathogenic bacteria were investigated. The mean lead concentrations were 1.281mg/l and 0.028 mg/l for inflow and outflow water, respectively. The mean inflow and outflow concentrations for copper were 1.114 and 0.199 mg/l, respectively. The average BOD5 (5-day biochemical oxygen demand) was 3.2 mg/l for inflow and 0.8 mg/l for outflow water. However, after maturation of the biofilm, which dominated the top sediment, all wetlands reduced the heavy metals sufficiently and performed statistically similar (71~98% for Log10 data sets). It follows that there is no additional benefit in using adsorption media to enhance filtration performance.