A 2D tank test on remediation of nitrobenzene-contaminated aquifer using in-situ reactive zone with emulsified nanoscale zero-valent iron

Abstract

Nitrobenzene (NB) is one of the most challenging pollutants for groundwater remediation due to its great harm and recalcitrance. Emulsified nanoscale zero-valent iron (EZVI) is considered as a promising agent for in-situ remediation of contaminated groundwater for its high reactivity, good durability and low cost. In this paper, 2D tank experiment was conducted to evaluate the effectiveness of enhanced remediation of NB-contaminated groundwater with EZVI. 9 L of EZVI solution was injected into aquifer to establish in-situ reactive zone (IRZ) before 40 d of NB contamination. Results indicate that injection of EZVI leads to 90% reduction of total NB, which is mainly converted to aniline (AN). NB concentration decreases along the flow path in the tank. Fe2+ is generated from Fe0 oxidation. Significant acetate and bicarbonate are released due to emulsified oil decomposition during the whole operation time. Groundwater pH maintains in neutral value (6.6–8.2) owing to the balance between organic acids and OH− released after iron oxidation. Drastic decrease of ORP and DO indicates the transformation from oxidizing to reducing condition, leading to the reduction of oxidative species (e.g. sulfate, nitrate) in subsurface. Calculation of reducing equivalents suggests that microbial breakdown of emulsified oil provides more electrons than Fe0 oxidation does to the system. Both biotic and abiotic processes are involved in the enhanced degradation of NB.