Synergistic degradation of chloramphenicol by ultrasound-enhanced nanoscale zero-valent iron/persulfate treatment

Ultrasonic (US) was used to activate persulfate (PS) in presence of nanoscale zero-valent iron (nZVI) to degrade chloramphenicol (CAP) in solution. Synergistic effects were observed of US and nZVI on PS activation (US-nZVI/PS) compared to US/PS, nZVI/PS, or US-nZVI alone, while replacement of nZVI with Fe(II) or Fe(III) ion was less efficient to degrade CAP. The US-nZVI/PS treatment exhibited a rapid and continuous oxidation of CAP in solution. Both (OH)-O-center dot and SO4 center dot- were considered to be primary reactive species responsible for CAP degradation, of which SO4 center dot- had a higher contribution than (OH)-O-center dot. Our results indicated that Fe2+ was continuously being recycled by reaction of nZVI and PS, accompanied by generation of SO4 center dot-. US accelerated the corrosion of nZVI and removed passive films on the nZVI surface. Under optimal conditions, 98.1% of CAP was degraded during 90 min. This was established in presence of 0.5 g/L nZVI and 1.0 mM PS, with an US intensity of 0.36 W/mL at 40 kHz and a pH of 7.0. When present, inorganic anions and natural organic matter partly inhibited CAP degradation, which was mainly attributed to their scavenging effects for SO4 center dot- and (OH)-O-center dot. The reusability of nZVI was examined in five consecutive cycles, showing a decrease in efficiency with each cycle. Seven major intermediate products were identified, and these indicated two degradation pathways. Finally, in-situ regeneration of CAP-saturated powdered activated carbon using US-nZVI/PS process was evaluated.