Field scale phytoremediation experiments on a heavy metal and uranium contaminated site, and further utilization of the plant residues

The remediation of large heavy metal/radionuclide (HM/R) contaminated areas by conventional remediation technologies is often too expensive. Phytoremediation can be an alternative for such areas with slight contaminations, and represents a convenient and sustainable method of remediation. Field site phytoremediation experiments were carried out at a former uranium mining area in East Germany. The test field site is slightly to moderately contaminated with HM/R; the phytoremediation was performed by combination of phytostabilization and phytoextraction methods combining microbial, soil and plant techniques both at field- and lab scale. Plant experiments with Triticale, Helianthus annuus and Brassica juncea were performed to investigate the influence of biological additives (fungi, bacteria) and soil amendment strategies (increasing pH and organic matter, fertilizing) on biomass production and plant tolerance to heavy metals. In lysimeter experiments, a minimization of HM/R accumulation in soil could be shown, and groundwater contamination as well as seepage water rate and load could be reduced. The final utilization of HM/R loaded plant residues after harvests was studied by biogas and ethanolic fermentations and by combustion of the plant material. The fate of HM/R in the different by-products was investigated. Finally, concepts were developed for the utilization of the HM/R loaded plant residues.