Electrobioremediation of Oxyfluorfen-Polluted Soil by Means of a Fixed-Bed Permeable Biological Barrier

Abstract

This work studies the in situ electrobioremediation of an oxyfluorfen-polluted clay soil in a two-stage method. First, a fixed-bed biofilm reactor for oxyfluorfen biodegradation in wastewater was developed; it treated wastewater with 200 mg L−1 of oxyfluorfen and reached 100% of oxyfluorfen degradation in 30 h. Second, a portion of the biofilm-covered bed was included into the polluted soil and it was used as a biological permeable reactive barrier (BioPRB), whereas electrokinetics was applied to promote the contact between the pollutant and microorganisms into the soil. The electrobioremediation study was performed in a bench scale setup under 1.0 V cm−1 at room temperature and under periodic polarity reversal (2 day−1) in a 2-week batch experiment. Two reference tests were done: (i) a conventional in situ biological test without electrokinetics and (ii) a conventional in situ electrokinetic test without using microorganisms. The experimental conditions (temperature, pH, moisture) were correctly controlled in the soil and enabled the microbial activity during the process. A low oxyfluorfen removal efficiency was obtained after 2 weeks (11%) because of the low electrokinetic mobility of such non-polar pollutant into the soil. Despite this low efficiency value, it was considered that the combined biological-electrokinetic technology could be used as a bioaugmentation procedure to perform electrobioremediation processes because the results of both reference tests showed negligible removal efficiencies when using only biological or only electrochemical methods. According to these results, electrobioremediation could be considered a feasible technology although more retention time would be required to achieve successful remediation results.