Synthesis of nZVI-BC composite for persulfate activation to degrade pyrene: Performance, correlative mechanisms and degradation pathways

Abstract

In order to achieve efficient adsorptive and oxidative removal of pyrene, a persulfate oxidation system with composite nZVI-BC prepared by loading nano-zero-valent iron on coconut shell biochar as an activator was established and applied. The results of adsorption experiments showed that at pH 3, when the dosages of BC, nZVI and nZVI-BC were all 1.5 g/L, the removal efficiency of pyrene reached 64.9%, 19.0%, and 61.2%, respectively after 120 min of adsorption. The best performance of nZVI-BC-persulfate system was achieved at pH 3, nZVI-BC 1.2 g/L and persulfate concentration 6 mM, and after 60 min of degradation, the removal efficiency of pyrene reached 99.4%. The pre-adsorption process was a promoting-step for pyrene degradation. The conversion of nZVI to Fe2+ and Fe3+ played an important role in the activation of persulfate to produce SO4•− and •OH, both of which were responsible for non-selectively oxidization pyrene. The support of BC could improve the dispersibility and activity of nZVI and improve of the above conversion. The intermediates with relatively lower toxicity were identified during pyrene degradation, and they were successively oxidized into CO2 and H2O finally. In summary, nZVI-BC can be a promising catalyst for persulfate activation to degrade PAHs in wastewater.