Effective degradation of para-chloronitrobenzene through a sequential treatment using zero-valent iron reduction and Fenton oxidation

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.