Development of an artificial phytoremediation technology for soils contaminated by toxic metals

Abstract

Globally, contamination of soil and groundwater by toxic metals (Pb, As, Cr, Ni, Zn, etc.) are becoming increasingly problematic for both ecosystems and human health. Currently, phytoextraction and phytoaccumulation are studied for the decontamination of metals because they offer a treatment option at low cost. From a biomimetic approach, the general objective of this work is to propose, at a conceptual level, a new technology based on physical-chemical mechanisms of transport of contaminants by plants. In order to fulfill these objectives, an experimental arrangement was constructed in the laboratory to test some materials and operating factors. The seven metals studied and analyzed by ICP-MS were aluminum, arsenic, cadmium, chromium, nickel, lead and zinc. A cellulosic fibre (M1) and a polyester-polyamide (M2) were used as capillary means of transport due to the fact that they have a diameter similar to that of xylem vessels on the transport system of vascular plants. On the basis of a negative pressure gradient of 0.02 MPa⋅m-1, reported for vascular plants, the studied pressures were 0.011, 0.022, 0.045, 0.090 and 0.18 MPa⋅m-1, while the pH solutions were studied at 4 and 8. The results show that the highest metal ion transport was obtained at pH 4, in ascending order: Cr <Pb = Al <As <Ni <Zn <Cd to M1 and Cr <Pb = Al = As <Ni = Zn = Cd to M2. Differences on ion transport between M1 and M2, expressed as the percentage of transported ion, are attributed to the chemical composition of the materials, due to unequal amount of active sites on the surface of each material, as well as to the effect of pH on the ions in solution. Under negative pressure, the materials showed similar behaviour to that of membranes, thus, the solution rate of flow (mL⋅h-1) increases with the pressure while the concentration of metal ions (mg⋅L-1) exhibited no significant variation. In addition, a transport coefficient (TCHM), in function of the metal and the material, was obtained. A value of TCHM=1 means that there are no interactions between the metal ion and the material and, at the same time, this value will place the material at the level of a plant species identified as hyperaccumulator; the indicator is useful to assess indirectly the concentration of metal in the soil. By integrating the laboratory results in a simplified conceptual model, the principles of the artificial phytoremediation technology were highlighted. This technology should be the basis for the development of a new family of technologies that can help reduce some negative impacts caused by the traditional methods of soils decontamination.

Date	22 Jul 2013
Original language	American English
Awarding Institution	École de technologie supérieure
Supervisor	Robert Hausler (Supervisor) & Mathias Glaus (Co-supervisor)