Removal of p-chloronitrobenzene from groundwater: Effectiveness and degradation mechanism of a heterogeneous nanoparticulate zero-valent iron (NZVI)-induced Fenton process

• p-ClNB degradation exhibited a pseudo-first-order kinetics pattern in tests.
• High NZVI, H2O2 dose, and low initial pH favored reaction.
• Anions inhibited p-ClNB degradation with order: SO42−>NO3−≈Cl−.
• Effective p-ClNB removal can be achieved by the NZVI induced Fenton process.

The removal of p-chloronitrobenzene (p-ClNB) from contaminated groundwater of certain chemical relocated site was explored by a heterogeneous nanoparticulate zero-valent iron (NZVI)-induced Fenton process. The effects of various factors, including hydrogen peroxide (H2O2), NZVI dose, and initial pH of groundwater as well as the common components in groundwater such as Cl−, NO3− and SO42− were evaluated. The results showed that p-ClNB can be completely degraded within 30 min at pH 3.0 and 30 °C with NZVI 268.8 mg/L, H2O2 4.90 mmol/L and initial p-ClNB 60 mg/L, indicating the effectiveness of the NZVI-induced Fenton process for the p-ClNB removal. The p-ClNB degradation was fitted with a pseudo-first-order kinetic model, and the rate constants were found to increase with the increasing NZVI dose (0–358 mg/L) and H2O2 dose (0–4.90 mmol/L). Acid conditions were favorable to the p-ClNB removal and elevating the initial groundwater pH (3.0–11.0) decreased the p-ClNB degradation rate. SO42− anions had negative effects on p-ClNB removal, whereas the effects of Cl− and NO3− were negligible. On the other hand, the degradation intermediates, carboxylic acids and chloride ion during the reaction process were detected by gas chromatograph/mass spectrometry (GC/MS), liquid chromatography/mass spectrometry (HPLC/MS) and ion chromatography (IC). With these findings, a degradation pathway of p-ClNB was accordingly proposed. In conclusion, the NZVI-induced Fenton process is a highly promising remediation technique for groundwater contaminated by p-ClNB, but more complex components in groundwater should be carefully considered for its practical application.