Interactions between electrokinetics and rhizoremediation on the remediation of crude oil-contaminated soil

An electrokinetics (EK)-enhanced phytoremediation system with ryegrass was constructed to remediate crude oil-polluted soil. The four treatments employed in this study included (1) without EK or ryegrass (CK-NR), (2) EK only (EK-NR), (3) ryegrass only (CK-R), and (4) EK and ryegrass (EK-R). After 30d of ryegrass growth, EK at 1.0 V.cm(-1) with polarity reversal (PR-EK) was supplied for another 30d. The electric current was recorded during remediation. The pH, electrical conductivity, total petroleum hydrocarbon content (TPH), 16S rDNA, functional genes of AlkB, Nah, and Phe, DGGE, and dehydrogenase activity in soil were measured. The physical-chemical indexes of the plant included the length, dry mass, and chlorophyll contents of the ryegrass. Results showed that EK-R removed 18.53 +/- 0.53% of TPH, which was higher than that of other treatments (13.34-14.31%). Meanwhile, the values of 16S rDNA, AlkB, Nah, Phe, and dehydrogenase activity in the bulk soil of EK-R all increased. Further clustering analysis with numbers of genes and DGGE demonstrated that EK-R was similar to the ryegrass rhizosphere soils in both EK-R and CK-R, while the EK treatment of EK-NR was similar to that of CK-NR without EK and ryegrass. These results indicate that the PR-EK treatment used in this experiment successfully enlarged the existing scale of the rhizosphere microorganisms, improved microbial activity and enhanced degradation of TPH. (C) 2019 Elsevier Ltd. All rights reserved.