Degradation of $p$-Aminobenzoic Acid by Zero-Valent Iron Activated Persulfate System

Persulfate (PS) activated by zero-valent iron (ZVI) for the degradation of $p$-aminobenzoic acid (PABA) was investigated in this study. Compared with the removal of PABA, the degradation of ${\mathrm{PABA}}_{-\mathrm{CAP}}$ (in the presence of chloramphenicol) was not obviously affected in the ZVI/PS system. The removal of PABA (0.05 mM) and ${\mathrm{PABA}}_{-\mathrm{CAP}}$ (0.05 mM) were nearly 100% after 50 min. Moreover, the effective degradation of PABA and ${\mathrm{PABA}}_{-\mathrm{CAP}}$ were observed at a brand range of pH from 3.0 to 8.5, and the higher degradation efficiencies of PABA and ${\mathrm{PABA}}_{-\mathrm{CAP}}$ were obtained under acidic and neutral conditions. With the increase of ${\mathrm{Cl}}^{-}$ and Suwannee River humic acid (SRHA) dosage, the degradation rate of PABA decreased continuously. However, the degradation of ${\mathrm{CAP}}_{-\mathrm{PABA}}$ (in the presence of PABA) was significantly inhibited by the addition of PABA in the ZVI/PS system. The results of scavenging tests suggested that the sulfate radical (${\mathrm{SO}}_4^{•-}$) predominated the PABA and ${\mathrm{PABA}}_{-\mathrm{CAP}}$ degradation, while the hydroxyl radical (${\mathrm{HO}}^{•}$) contributing to the ${\mathrm{CAP}}_{-\mathrm{PABA}}$ removal approximated to ${\mathrm{SO}}_4^{•-}$ by the ZVI/PS system. Major intermediate products were identified during ${\mathrm{PABA}}_{-\mathrm{CAP}}$ and ${\mathrm{CAP}}_{-\mathrm{PABA}}$ degradation processes. A primary reaction pathway of ${\mathrm{PABA}}_{-\mathrm{CAP}}$ and ${\mathrm{CAP}}_{-\mathrm{PABA}}$ degradation was proposed in the ZVI/PS system.