Effect of zero-valent iron nanoparticles on the remediation of a clayish soil contaminated with γ-hexachlorocyclohexane (lindane) in a bioelectrochemical slurry reactor

In this research we evaluated the effect of adding zero-valent iron nanoparticles (ZVI-NP) to a complete mix bioelectrochemical slurry reactors (BESR) on the remediation of a clayish soil with a high content of organic matter, contaminated with lindane. Five BESR were loaded with a clayish polluted soil (100 mg lindane/kg_ds), known concentrations of ZVI-NP, liquid medium, and sulphate-reducing inoculum to give a 33% w/v soil concentration. A one-factor experimental design was used, where the effect of nanoparticles concentration [NP] on lindane removal efficiency (η_lin) and other response variables were evaluated. The [NP] levels were 0.0 (background control with electrical connection, BCWC), 2.5 (Exp1), 5.0 (Exp2), and 7.5 gNP/kg_ds (Exp3). Maximum η_lin (95%) was attained in Exp2 (5 gNP/kg_ds). Beyond this level the η_lin slightly decreased (Exp3 with 85% η_lin.) Approximately 40%-57% of lindane was removed in the first 24 hours during a rapid kinetics phase. No metabolites of lindane degradation were detected after 30 days of operation in all the BESR. Energy production increased with [NP]; Exp3 generated 4.3 MJ/tonne_ds at 30 days, whereas the other treatments produced energy between 1.6 MJ/tonne_ds-1.2 MJ/tonne_ds. Bioelectrical energy could partially offset the requirements of BESR mixing energy. Overall performance evaluation using an ad hoc multicriteria framework indicated that BESR followed the order Exp2 > Exp3 > Exp1 ~ BCWC > ABCWOC (abiotic control without electrical connection). There was a significant, positive effect of the combined BESR and ZVI-NP technology for the remediation of heavy soils contaminated with lindane.