Fixed-bed biological barrier coupled with electrokinetics for the in situ electrobioremediation of 2,4-dichlorophenoxyacetic acid polluted soil

Abstract

This work studies the in situ electrobioremediation (EBR) of clay soil polluted with 2,4-dichlorophenoxyacetic acid (2,4-D) in a two-stage method. First, a fixed-bed biofilm reactor able to biodegrade 2,4-D in wastewater was developed; second, a portion of the biofilm-covered bed was included in the polluted soil and used as a biological permeable reactive barrier (BioPRB), whereas electrokinetics were used to promote the contact between pollutant and microorganisms into the soil. The fixed-bed biofilm reactor successfully treated wastewater polluted with 2,4-D concentrations up to 1200 mg L−1 and under non-oxygenated conditions because of the culture ability to use nitrate as electron acceptor. A portion of the stationary biofilm was later used as a BioPRB in the polluted soil to perform in situ EBR study. The study was performed in a bench scale set-up using potentiostatic conditions (1.0 V cm−1), room temperature and periodic polarity reversal (2 d−1) in a 10 day batch experiment. The feasibility of the proposed technology was checked by the comparison with a conventional in situ bioremediation test without electrokinetics. The EBR treatment, coupling electrokinetics with the previously developed BioPRB, offered 85% removal efficiency of 2,4-D after 10 days. According to the low removal efficiency observed in the reference test, it was proved that the electrokinetic transport phenomena improved contact between pollutant and microorganisms and clearly increased 2,4-D removal rate. According to these results it is considered that the combination of electrokinetics and biobarriers could be a promising technology to achieve remediation of low permeable soils polluted with pesticides.