In this study, zero-valent iron (ZVI) was used to pretreat para-chloronitrobenzene (p-CNB), and the major product was para-chloroaniline (p-CAN). By adding H2O2 directly, further p-CAN degradation can be attributed to Fenton oxidation because ferrous ions (Fe2+) released during the ZVI corrosion could be used as an activator for H2O2 decomposition. In the reduction process, the reduction efficiency of p-CNB as well as Fe2+ concentration increased with increasing iron dosage and decreasing solution pH. Under the optimal conditions, 25 mg L−1 of p-CNB could be transformed in 3 h when initial solution pH was 3.0 and ZVI dosage was 2.0 g L−1. A sufficient amount of Fe2+ (50.4 mg L−1) was obtained after the above reaction to activate H2O2. In the Fenton process, the oxidization of p-CAN was also more effective in acidic conditions and it increased with increasing H2O2 concentration. The control experiments showed that the sequential treatment was more effective than Fenton oxidation alone in treating p-CNB wastewater since the removal rate of total organic carbon (TOC) was improved by about 34%. It suggested that the amino function group is more susceptible to oxidative radical attack than the nitro function group. Therefore, sequential treatment using zero-valent iron reduction followed by Fenton oxidation is a promising method for p-CNB degradation.

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