Strategies for the electrobioremediation of oxyfluorfen polluted soils

Abstract

This work compares three strategies for the in-situ remediation of oxyfluorfen polluted clay soil, based on the combination of biological processes and electrokinetics (EK): (i) EK-biostimulation, in which the action of microorganisms contained in soil is promoted without the use of biological permeable barriers, (ii) EK-bioaugmentation with fixed culture of microorganisms (BB1), which enhanced the natural bioremediation by including a microbial fixed biofilm reactor as permeable biobarrier, and (iii) EK-bioaugmentation with suspended culture of microorganisms (BB2), which improves the natural remediation by including a mixture of soil and a microbial suspension as permeable biobarrier. To do this, two-week batch electro-bioremediation tests were carried out using bench scale set-ups. In each case, a constant electric field (1 V cm−1) was applied, and electrode polarity was reversed periodically, every 12 h. In addition, a microbial consortium acclimated to oxyfluorfen biodegradation was used. The best oxyfluorfen removal efficiency (15%) was obtained using the option (i). Permeable biobarriers allowed the introduction of microorganism and nutrients into the soil, and the biological activity reached the whole soil positions. However, the insertion of these biobarriers caused an excessive decrease in the electro-osmotic flow (approximately 80%) which, in turn reduced the mobilization of the pollutants. Despite of that, results show that permeable reactive biobarriers may result in a successful alternative for in-situ EK-bioaugmentation, although higher retention times would be needed to obtain higher removal efficiencies.