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Bioremediation of antimony contaminated soils

Monogyiou Sofia

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Summary

Heavy metal soil pollution is one of the most important problems worldwide and therefore the remediation of contaminated soils is of major importance. The technologies of bioremediation and phytoremediation are widely applied due to their contribution to the remediation of soils from toxic pollutants. These methods are based on the use of microorganisms and plants, aiming at removing or converting the contaminants into less toxic forms. It has been shown that another technology, oxygen nanobubbles (O2NBs), can work beneficially in combination with the above methods due to a more efficient supply of oxygen which has a positive effect on the growth of microorganisms and plants. The aim of this thesis is to remove the antimony from antimony-contaminated soils by the methods of bioremediation and phytoremediation under controlled conditions. The soils tested in the bioremediation experiment collected from three different shooting ranges in Switzerland with three different antimony concentrations (low, medium and high). These soils also contain high concentrations of iron and manganese. Preliminary experiments were performed for each soil, with and without the presence of bacteria, and with and without the use of oxygen nanobubbles, while scaling-up to a bioreactor was performed only for the soil with the highest antimony concentration since the most effective removal of antimony was observed in this soil during the preliminary experiments. The experimental results showed that microbial inoculation had a significant effect on soil remediation as it was found that about 75% of the initial antimony was mobilized. Oxygen nanobubbles were found beneficial in the absence of bacteria with 66.4% of the contaminant mobilized. Iron concentrations were not significantly affected as the residual percentages in the aqueous phase were higher in the bioaugmentation experiments. Regarding manganese concentrations, were calculated slightly lower when inoculating bacteria in combination with the use of oxygen nanobubbles. The results of the bioreactor did not show much mobilization of the pollutant compared to the flasks with the percentage reaching only 26% in the aqueous phase.In the second experimental phase of phytoremediation, the plant Nerium oleander was used. The soil was collected from the area of Kampani (Chania), specifically from a shooting range and inoculated with a concentration of 50 ppm antimony, as insufficient antimony concentration was initially detected. The nanobubble technology was also used in the phytoremediation experiment to study the effect on plant growth and subsequently on antimony removal. In addition, low and high concentration of organic acids were added to the soil during the experiment. The experimental results from the plant analyses showed that the addition of organic acids at high concentration has a significant effect on the mobilization of the contaminant from the soil to the plant, while simultaneous irrigation with oxygen nanobubbles further increases the bioaccumulation rate in plant tissues. In conclusion, the use of N. oleander with the application of appropriate soil amendments makes this plant suitable for remediation of contaminated soils.

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