Study On Degradation Of Nitrobenzene Using Ultrasound-Photo-Fenton System

As a toxic organic compounds, nitrobenzene(NB) is difficult to be biodegradable. In this study, a combination of ultrasound and photo-Fenton was used to treat nitrobenzene, so as to achieve the purpose of nitrobenzene complete mineralization. This research studied on nitrobenzene degradation by ultrasound(US)、ultraviolet(UV)、Fenton and other hybrid techniques. The influence of technical parameters on the reaction process and its mechanism were discussed preliminary. The synergistic strengthening effect of ultrasound with UV、Fenton and photo-Fenton were analyzed also.The study of nitrobenzene degradation by US/UV showed an obvious enhancement and synergy. The degradation of nitrobenzene was influenced by reaction time, temperature, pH and ultrasonic power. With the increase of reaction time and temperature, the nitrobenzene removal rate increased but the synergies weakened. There was little effect on UV degradating with the increase of pH. While US and US/UV degradate nitrobenzene, it found the removal rate increased at first, and then decreased with the increase of pH and the maximum removal rate appeared at pH5, which were22.61%,24.16%, respectly. Under the optimal conditions of ultrasonic power100W, the nitrobenzene degradation rates by US and US/UV were18.14%,24.29%; TOC removal rates were18.77%and25.4%.It found out existence of obvious synergies at the US/Fenton degradation of nitrobenzene. Results showed that the removal rate of nitrobenzene increased first and then be stable with the increase of H2O2concentration from75mg/L to500mg/L, and the TOC removal rate showed a tendency of increase. Both of the removal rate of nitrobenzene and TOC showed a trend of little decrease wih the increase of Fe2+concentration from10mg/L to90mg/L. The removal rate of nitrobenzene increased first and then be stable with the increase of temperature, it was stable at25℃with removal rate of83.25%. It found the removal rate increased at first, and then decreased with the increase of pH and the maximum removal rate appeared at pH3. With the ultrasonic power from the50W to200W, nitrobenzene degradation efficiency decreased at first and then rised. When the ultrasonic power was100W, the efficiency of the combined techniques of the degradation of nitrobenzene reached the maximum,84.82%, TOC removal rate was29.38%.The study of nitrobenzene degradation by US/UV/Fenton indicated that the initial H2O2concentration was the most significant factor affecting the nitrobenzene degradation and mineralization, while reaction time and ultrasonic power were significant factors and Fe2+concentration was non-significant factor. Under the conditions of500mg/L H2O2, lOmg/L Fe2+,60min reaction time and100W US power, the200mg/L of NB was completely decomposed and TOC removal achieved73.0%. The pseudo-first-order rate constants of NB degradation in Fenton, UV/Fenton and US/UV/Fenton processes were fitted to be3.37×10-2,3.81×10-2and5.10×10-2min-1,respectively.