||This study evaluated the performance of advanced oxidation processes that combines UV, O3 and H2O2 to mineralize N-methyl-2-pyrrolidinone (NMP) in an aqueous solution. As a photoresist stripper, NMP is widely used in the semi-conductor and optoelectronics industries, and difficult to be degraded by bio-treatment of wastewater. The concentration of total organic carbon (TOC) was selected as a mineralization index of the decomposition of NMP by the advanced oxidation process.|
Results of this study indicate that UV irradiation 37.2 mWcm−2 UV(254 nm) and O3 doses of 5×10-4 mol/min causes the best 89% mineralization of NMP (20 mg/L) over a reaction time of 60 minitues and the the mineralization efficiency follows the sequence of UV/O3 (89%)＞UV/H2O2/O3 (58%)＞O3/H2O2 (48%)＞O3 (42%)＞UV/H2O2 (34%). The effect of the initial NMP concentration over the range of 20 to 80 mg/L on the mineralization rate of NMP was studied, and the experimental results indicates that the mineralization efficiency of NMP declines as the initial NMP concentration increases, the mineralization efficiencies were 89%、82%、61%、54% after a reaction time of 60 min. This result indicates that the photocatalytic mineralization of NMP by UV/O3 is not simple first-order but pseudo first-order. Since NMP generates organic acid compounds, which cannot easily be decomposed by hydroxide radicals (⋅OH ) before fully mineralization, a higher concentration of NMP results in a higher concentration of organic acid compounds. Hence, the mineralization rate of more highly concentrated NMP is lower. The pseudo first-order rate constant (kobs) is calculated between 0.0365~0.0127 min-1 and half-life (t1/2) between 18.99~54.58 minitues. The existence of the H2O2 may influence the NMP mineralization rate in the UV/O3 system, because H2O2 plays the role of initiator and scavenger at the same time. The experiment results inducate that as the concentration of H2O2 increases, the mineralization rate of NMP declines. In the UV/O3 system, the H2O2 consumed hydroxide radicals and acted as a scavenger of hydroxide radical. Adding H2O2 to the UV/O3 system has a negative effect of NMP mineralization. Adding ferrous ions is likely to reduce the mineralization rate of NMP, the mineralization efficiency reduces from 89% to 48% as the ferrous ions increses from 0 mg/L to 10 mg/L, because the ferrous ions in the solution are oxidized into the ferric hydroxide
precipitate in a UV/O3 environment and produce turbidity in the reactor. This precipitation phenomenon somewhat obstructs the penetration of UV light. UV/O3 is less capable of mineralizing NMP. The presence of ferrous ions reduces the effectiveness of UV/O3 in mineralizing NMP.
The result indicates that this pH range does not affect the mineralization process. The pseudo first-order rate constant (kobs) is calculated between 0.0349~0.0362 min-1 and half-life (t1/2) between 19.15~19.86 minitues over the range of pH:3.0 to pH:10.0 in the UV/O3 system. The pH values of the solution do not affect the mineralization efficiency of the UV/O3 process. The results also show that in highly SO42- and ClO4- ionic environment, NMP mineralization is not suppressed, indicating that a highly ionic environment does not negatively affect the generation of hydroxide radical by UV/O3 system.