Enhanced electrokinetic remediation for Cd-contaminated clay soil by addition of nitric acid, acetic acid, and EDTA: Effects on soil micro-ecology

Highlights: • Nitric acid and acetic acid addition were more effective in Cd removal than EDTA during EKR. • Nitric acid addition dramatically decreased the activity of βGA, URE, ACP and bacterial α-diversity. • Acetic acid addition increased the bacterial α-diversity, while only slightly decreased the activity of βGA, URE, and ACP. • The variables of reducible Cd, EC, and DOC could explain 93.42% of the total variance of microbial diversity and communities. Enhanced electrokinetic remediation (EKR) allows the rapid remediation of heavy metal-contaminated clay, but the impacts of this process on soil micro-ecology have rarely been evaluated. In this study, nitric acid, acetic acid, and EDTA were applied for enhancement of EKR and the effects on Cd removal, soil enzyme activity, and soil bacterial communities (SBCs) were determined. Nitric acid and acetic acid allowed 93.2% and 91.8% Cd removal, respectively, and EDTA treatment resulted in 40.4% removal due to the formation of negatively charged EDTA-Cd complexes, resulting in opposing directions of Cd electromigration and electroosmosis flow and slow electromigration rate caused by low voltage drop. Activities of soil beta-glucosidase, acid phosphatase, and urease, were all reduced by enhanced EKR treatment, especially nitric acid treatment, by 46.2%, 58.8% and 57.7%, respectively. The SBCs were analyzed by high-throughput sequencing and revealed significantly increased diversity for acetic acid treatment, no effect for EDTA treatment, and reduced diversity for nitric acid treatment. Compared with nitric acid and EDTA, acetic acid treatment enhanced EKR for higher Cd removal and improved biodiversity.