Degradation Efficiency Of Nitrobenzene Research Articles

Degradation of Nitrobenzene-containing wastewater by ozone/persulfate oxidation process in a rotating packed bed

Abstract In this study, nitrobenzene was degraded using ozone/persulfate oxidation process in a rotating packed bed with semi-batch operation. NB degradation efficiencies by only using ozone or persulfate in the oxidation system were at 69.44% and 27.14%, respectively, whereas O3/Na2S2O8 system achieved degradation efficiency at 90.59% in 30 min. It was discovered that degradation efficiency of nitrobenzene was significantly affected by initial pH, high gravity factor, addition amount of persulfate or ozone, and it achieved the highest value when pH at 10, high gravity factor at 40, and initially respective concentrations of extra added persulfate and ozone at 2.5 mmol·L − 1 and 60 mg·L − 1. The production of hydroxyl radicals (·OH) and sulfate radicals (SO4·−) was directly identified in electron paramagnetic resonance tests and indirectly through capturing tests, and three ways of oxidation were determined including direct oxidation by O3, indirect oxidation by ·OH and SO4·−, within which ·OH played a significant role in oxidation process. This study also used gas chromatography-mass spectrometry to detect the intermediates in the oxidation process, and two degradation pathways were inferred based on intermediate analysis.

Oxidative degradation of nitrobenzene by a Fenton-like reaction with Fe-Cu bimetallic catalysts

De-nitrogen of organic contaminants in industrial wastewater is a great challenge for environmental remediation. In this work, alumina-supported bimetallic Fe-Cu catalysts were synthesized using a sol-gel method and exhibited high performance in catalytic degradation of nitrobenzene (NB). The bimetallic 5Fe2.5Cu-Al2O3 catalyst showed a 100% NB (100 ppm) removal within 1 h, which was superior to the NB degradation efficiency over monometallic Fe and Cu catalysts. With combination of the catalytic performance and the characterization results of X-ray photoelectron spectroscopy and H2-temperature-programmed reduction, we proposed that the synergistic effect between Fe and Cu species played a vital role in promoting the reduction of Fe3+ to Fe2+, thus enhancing the generation of hydroxyl radicals (OH) and the degradation efficiency of NB. To elucidate the degradation pathway, gas chromatography-mass spectrometry and dynamic ultraviolet-visible spectroscopy were used to detect the intermediates during the degradation process. The results indicated that the degradation predominantly occurred via electrophilic addition of aromatic ring by OH, followed by the ring opening reaction and mineralization reaction. Moreover, NB can be efficiently decomposed into less stable aniline, which is apt to degrade. This work has not only made significant progress on the development of high-performance catalysts for the degradation of NB, but also provided a deep understanding of the mechanism for NB degradation.

Degradation of nitrobenzene wastewater in an acidic environment by Ti(IV)/H2O2/O3 in a rotating packed bed.

The rotating packed bed (RPB) as a continuous flow reactor performs very well in degradation of nitrobenzene wastewater. In this study, acidic nitrobenzene wastewater was degraded using ozone (O3) combined with hydrogen peroxide and titanium ions (Ti(IV)/H2O2/O3) or using only H2O2/O3 in a RPB. The degradation efficiency of nitrobenzene by Ti(IV)/H2O2/O3 is roughly 16.84% higher than that by H2O2/O3, and it reaches as high as 94.64% in 30min at a H2O2/O3 molar ratio of 0.48. It is also found that the degradation efficiency of nitrobenzene is significantly affected by the high gravity factor, H2O2/O3 molar ratio, and Ti(IV) concentration, and it reaches a maximum at a high gravity factor of 40, a Ti(IV) concentration of 0.50mmol/L, a pH of 4.0, a H2O2/O3 molar ratio of 0.48, a liquid flow rate of 120L/h, and an initial nitrobenzene concentration of 1.22mmol/L. Both direct ozonation and indirect ozonation are involved in the reaction of O3 with organic pollutants. The indirect ozonation due to the addition of different amounts of tert-butanol (·OH scavenger) in the system accounts for 84.31% of the degradation efficiency of nitrobenzene, indicating that the nitrobenzene is dominantly oxidized by ·OH generated in the RPB-Ti(IV)/H2O2/O3 process. Furthermore, the possible oxidative degradation mechanisms are also proposed to better understand the role of RPB in the removal of pollutants. Graphical abstract ᅟ.

Degradation of nitrobenzene by sodium persulfate activated with zero-valent zinc in the presence of low frequency ultrasound

In the presence of low frequency ultrasound (US) generated from an ultrasonic cleaning bath, the degradation efficiency of nitrobenzene (C6H5NO2, NB) by Zn0-activated persulfate (PS) reached 96% within 2h, which is much higher than that by PS or Zn0 alone in the presence of US or that by Zn0-activated PS in the absence of US. The synergistic effect in the US/Zn0/PS system and the optimum degradation conditions was investigated by batch experiments. The variations of pH and concentrations of Zn2+ and SO42− over time and the removal of chemical oxygen demand (COD) and total organic carbon (TOC) in different systems were analyzed, which agreed well with the degradation pattern of NB in different systems. The formation of free radicals was measured using electron paramagnetic resonance (EPR) spectroscopy to further investigate the possible mechanism of the enhanced degradation of NB by Zn0-activated PS in the presence of low frequency US.

Influencing mechanism of bicarbonate on the catalytic ozonation of nitrobenzene in aqueous solution by ceramic honeycomb supported manganese

Abstract The influence of bicarbonate on degradation efficiency of nitrobenzene in aqueous solution by ceramic honeycomb supported manganese catalytic ozonation has been investigated. Under the lower concentration condition (25 and 50 mg L −1 ), bicarbonate enhances the degradation efficiency of nitrobenzene, while bicarbonate presents the inhibition effect at the higher concentration (100–250 mg L −1 ). The modification of ceramic honeycomb with Mn improves its resistibility to the negative effect of bicarbonate, and the inhibition effect of bicarbonate also can be decreased, respectively by increasing total applied ozone or amount of catalyst. The utilization efficiency of ozone increases with the increasing bicarbonate concentration (0–100 mg L −1 ). The formation of H 2 O 2 and the initiation of hydroxyl radical ( OH) reach a maximum at the bicarbonate concentration 75 and 50 mg L −1 , respectively. The mechanism investigation suggests that bicarbonate plays an important role as a promoter of radical chain reactions accelerating the ozone mass transformation, causing the increases in the utilization efficiency of ozone, the formation of H 2 O 2 and the initiation of OH at the lower concentration. Bicarbonate with the higher concentration exerts a negative effect on the degradation efficiency of nitrobenzene due to the predominance derived from its scavenging capacity of OH.

Aerobic biodegradation of nitrobenzene by a defined microbial consortium immobilized in polyurethane foam

An aerobic microbial consortium constructed by the combination of Rhodotorula mucilaginosa Z1, Streptomyces albidoflavus Z2 and Micrococcus luteus Z3 was immobilized in polyurethane foam and its ability to degrade nitrobenzene was investigated. Batch experimental results showed that polyurethane-foam-immobilized cells (PFIC) more efficiently degrade 200–400 mg l−1 nitrobenzene than freely suspended cells (FSC). Kinetics of nitrobenzene degradation by PFIC was well described by the Andrews equation. Compared with FSC, PFIC exhibited better reusability (over 100 times) and tolerated higher shock-loadings of nitrobenzene (1,000 mg l−1). Moreover, In the presence of salinity (≤5% NaCl, w/v), phenol (≤150 mg l−1) and aniline (≤50 mg l−1), respectively, degradation efficiency of nitrobenzene by PFIC reached over 95%. Even in the presence of both 100 mg l−1 phenol and 50 mg l−1 aniline, over 75% nitrobenzene was removed by PFIC in 36 h. Therefore, the immobilization of the defined consortium in polyurethane foam has application potential for removing nitrobenzene in industrial wastewater treatment system.

Mechanism of Influence of Initial pH on the Degradation of Nitrobenzene in Aqueous Solution by Ceramic Honeycomb Catalytic Ozonation

The influences of initial pH on the degradation efficiency of nitrobenzene in aqueous solution were investigated with a semicontinuous batch reactor in the processes of ozone alone, ozone/ceramic honeycomb, and adsorption of ceramic honeycomb. The results indicated that initial pH significantly affected the concentrations of offgas, residual ozone, and the utilization efficiency of ozone. The experiments also detected the generation of hydroxyl radicals (*OH), the removal of TOC, and the formation and evolution of byproduct at different initial pHs in the ceramic honeycomb catalytic ozonation process. It was found that the systems of different initial pHs exhibited the different extent of the conversion of pH, the leaching of effective components, and the establishment of pH at the point of zero charge (pH(PZC)) in the catalytic oxidation process. The experimental findings presented a good correlation between initial pH and terminal pH and the establishment of pHpzc with terminal pH, and indicated the relationship between the absolute value of the difference between terminal pH and terminal pH(PZC) (A) and the density of surface hydroxyl groups. Based on the correlation between the density of surface hydroxyl groups in the neutral state and A, possible mechanism of influence of initial pH on the degradation of nitrobenzene in aqueous solution by ceramic honeycomb catalytic ozonation was proposed, suggesting that the conversion of initial pH determines the establishment of pHpzc, and the synergistic effect of pH terminal and pHpzc terminal affects the density of surface hydroxyl groups in the neutral state, which controls the concentration of *OH, determining the degradation of nitrobenzene and the formation of byproduct.

Effect of pH on MnOx/GAC catalyzed ozonation for degradation of nitrobenzene

The effect of pH on MnO(x)/GAC heterogeneous catalytic ozonation was investigated. Nitrobenzene was used as a model refractory organic pollutant. It was found that in MnO(x)/GAC catalytic ozonation, the degradation efficiency of nitrobenzene was higher under low pH conditions (pH 2.74-3.52) than that under high pH conditions (pH 6.72-9.61). This result was different from the case of ozonation alone, in which higher pH had positive effect on the degradation of nitrobenzene due to the formation of hydroxyl radical. In the presence of MnO(x)/GAC catalyst, ozone decomposition was accelerated, and higher pH condition favored ozone decomposition. It was assumed that hydroxyl radicals might not be the dominating active species in the catalytic oxidation, for the presence of t-butanol did not have any influence on MnO(x)/GAC heterogeneous catalytic ozonation. Adsorption of organic micropollutants on MnO(x)/GAC catalyst was an important step and would have direct influence on the effectiveness of catalytic oxidation. It was assumed that the organic pollutants might be further decomposed on the surface of catalyst.