Enhancement of 4-nitrophenol ozonation in water by nano ZnO catalyst

The removal of 4-nitrophenol [4NP] from aqueous solution by ozone combined with nano-ZnO was investigated in a laboratory-scale reactor in which pH of solution, ZnO dosage and initial 4-nitrophenol concentration were considered as variables. The degradation of 4-nitrophenol was determined using UV-Vis and HPLC methods. Interestingly, the degradation of 4-nitrophenol was high under acidic condition where the degradation was about 93% at initial phenol solution pH=3. It was due to aggregation of nano-ZnO particles above pH=6.5. This result was different from the case of ozonation alone, in which higher pH had positive effect on the degradation of 4-nitrophenol due to the formation of hydroxyl radical. As expected, degradation efficiency increased by increasing the nano ZnO dosage and initial 4-nitrophenol concentration. It was found that the nanosized ZnO enhanced the degradation of ozone and the catalytic ozonation enhanced the degradation of 4-nitrophenol on the surface of the nanosized ZnO. In addition, the degree of degradation was also determined indirectly through Total Organic Carbon [TOC] of the samples. Carbon mineralization of 4-nitrophenol was obtained as 13.68% and 60.34% during ozonation and nano-ZnO catalytic ozonation, respectively, after 30 min reaction, proving that combined ozonator and nano-ZnO for reduction of TOC is more efficient. Also a high degree of nitrogen mineralization during catalytic ozonation was achieved at pH= 3 [7.61mg/L]

Degradation of trace aqueous 4-chloro-2-nitrophenol occurring in pharmaceutical industrial wastewater by ozone

Degradation of 4-chloro-2-nitro phenol by ozonation in aqueous solution was studied in a semi batch reactor under constant ozone dosage and variable pH conditions. The effectiveness of the process was estimated based on the degree of conversion of 4-chloro-2-nitro phenol. It was observed that ozonation is more effective at alkaline reaction of medium than other conditions. The degree of conversion achieved [at the first 5 minutes of the process] at pH 9 was 99.64% compared to 99.03% and 77.35% at pH 7 and 3, respectively. Another parameter used to quantify the 4-chloro-2-nitrophenol during ozonation was the pseudo first order rate constant k [min[-1]]. Results showed that the rate constant of the process was approximately much higher at the alkaline pH compared to acidic ones. A considerable improvement in chemical oxygen demand removal was observed at pH above 7. At pH 9, the reduction in chemical oxygen demand at the end of the process reached 56.9%. The degree of organically bounded nitrogen conversion to nitrate was higher at pH 3. Of the total organic carbon reduction, 15.89% was observed at pH 9. The 4-chloro-2-nitro phenol degradation intermediate products were analyzed by mass- spectrometry. The main intermediate product was chlorophenol

Removal of Congo red from textile wastewater by ozonation

Congo red, which has a complex molecular structure with various diazo aromatic groups, is widely used in textile industry as an anionic dye. The purpose of this study was to investigate the degradation of Congo red in laboratory solution which had the chemical properties of the rinse waters of textile manufacturing dye-houses and the samples with Congo red alone wastewater by ozonation and to optimize the reaction parameters such as pH and time which influence the efficiencies of total organic carbon, total kjeldahl nitrogen and chemical oxygen demand removal. Ozonation of Congo red dye were carried out in a semi-batch reactor with constant ozone flow rate and concentration of 23 mL/sec and 13.6 mg/L, respectively. Decolorization was complete within a few minutes of ozonation possibly due to the cleavage of chromophore groups. It was observed that its structural destruction occurs predominantly at higher pHs. The reduction of chemical oxygen demand and destruction of the dye was more than 60% and 42%, respectively. Total kjeldahl nitrogen removal was accompanied by slight changes in nitrogen oxides. It can be deduced from the experimental results that: [a] the mineralization is very weak; [b] the reaction follows the indirect mechanism; i.e., the interaction of hydroxyl radicals with the dye and [c] the nitrification is rather predominant. Biological oxygen demand is declined in simulated alkalic and neutral samples respectively. At 13.6 mg O3/L, the biological oxygen demand levels were significantly enhanced. This might be attributable to the enhancement of its biodegradation at alkaline pHs