Abstract

Phytoremediation of Soil containing Mixed Contaminants

Ramin Memarian, Ph.D.
Concordia University, 2012

This study investigated the application of surfactants and chelates to enhance the removal of mixed contaminants [Cd (II), Pb (II) and used engine oil] from a sandy soil cultivated with Indian mustard plants. For chelate additives, EDTA (Ethylenediamine tetraacetic acid) was found to be more efficient than EDDS (Ethylenediamine disuccinic acid) in increasing the accumulation of metal contaminants Pb (II) in the plants. EDTA was also more capable of removing the used engine oil through rhizodegradation than EDDS. EDTA caused a sharper decrease in basal soil respiration (BSR) than EDDS, indicating that the former was much more toxic to the microbes.
For surfactant additives, the results showed that Triton X-100 and Tween 80 at concentrations higher than their critical micellar concentration enhanced phytostabilization of Pb (II). The application of Tween 80 resulted in an increase in phytoremediation of Pb (II). At the same concentrations, Tween 80 was more effective than Triton X-100 in facilitating rhizodegradation of the used engine oil. Soil basal microbiological respiration tests showed that the application of Tween 80 resulted in an increase in BSR. These tests indicated that the lower concentration of Triton X-100 had a slightly positive effect on BSR, whereas at higher concentrations, it was inhibitory to the microbes.
Empirical phytoremediation models linked to the removal of the heavy metals from the soil were formulated in the study. The two first order kinetic models were able to describe the leaching process for both Cd (II) and Pb (II). The models also revealed that the uptake of Pb (II) and Cd (II) were well described by the Freundlich type model, in the presence of surfactants. On the other hand, in the presence of chelates the uptake of Pb (II) and Cd (II) was found to follow the Langmuir type model. According to the leachability index (LI) determined in the tests, all surfactants tested can be considered as safe additives for enhancing phytoremediation. Compared to Triton X-100, Tween 80 resulted in lower diffusivity of metals tested and higher values of LI indicating that this surfactant was also safer from the point of view of reducing ground water pollution. Compared to EDTA, EDDS resulted in higher values of LI, which is desirable.