Optimization ofS/Fe ratio for enhanced nitrobenzene biological removal in anaerobicSystem amended withSulfide-modified nanoscale zerovalent iron.

Anaerobic reduction of nitrobenzene (NB) can be efficiently enhanced bySupplementing withSulfide-modified nanoscale zerovalent iron (S-nZVI). In thisStudy,S/Fe ratio ofS-nZVI was further optimized for enhancing biological NB removal in anaerobicSystem amended withS-nZVI and inoculated by anaerobicSludge. The results indicated that the performance andStability of the coupled anaerobicSystem for NB reduction and aniline formation were remarkably improved byS-nZVI atS/Fe molar ratio of 0.3 (0.3S-nZVI). TheSecretion of extracellular polymericSubstances (EPS), transformation of volatile fatty acids (VFAs), yield of methane and activity ofSeveral key enzymes could be efficiently improved by 0.3S-nZVI. Furthermore,Species related to NB reduction, fermentation, electroactivity and methanogenesis could be enriched in 0.3S-nZVI coupled anaerobicSystem, with remarkable improvement in the biodiversity observed. ThisStudy demonstrated thatSulfidation would be a promising method to improve the performance of nZVI in coupled anaerobicSystems for the removal of recalcitrant nitroaromatic compounds from wastewater.

Substantially enhanced anaerobic reduction of nitrobenzene by biochar stabilized sulfide-modified nanoscale zero-valent iron: Process and mechanisms.

Nanoscale zero-valent iron (nZVI), although being increasingly used in anaerobic systems for strengthening the removal of various refractory pollutants, is limited by various inherent drawbacks, such as easy precipitation, passivation, poor mass and electron transfer. To address the above issues, biochar stabilized sulfide-modified nZVI (S-nZVI@BC) was added into an up-flow anaerobic sludge blanket (UASB) to investigate the enhancement of anaerobic biodegradation of nitrobenzene (NB) and its impacts on microbial community structure. The results demonstrated that both NB reduction and aniline formation could be substantially facilitated in S-nZVI@BC coupled system compared to other anaerobic ones coupled with nZVI or S-nZVI. The dosage of S-nZVI@BC resulted in the formation of densely packed aggregates, evidently increased the extracellular polymeric substances content, promoted the volatile fatty acids transformation and stimulated the methane yield. Furthermore, species related to fermentation (Bacteroides and Longilinea), methanogenesis (Methanosarcina and Methanomethylovorans), electroactivity (Pelobacter, Thiobacillus and Phaselicystis) as well as reduction (Desulfovibrio) were considerably enriched in S-nZVI@BC coupled system. The activities of electron transport, total adenosine triphosphate, nitroreductase and NAD(P)H, which were closely related to microbial activity and NB transformation, were increased noticeably in S-nZVI@BC coupled anaerobic system. This study demonstrated the promising potential for long-term operation and full-scale application of S-nZVI@BC coupled system for the treatment of NB containing wastewater.

Effective stabilization and distribution of emulsified nanoscale zero-valent iron by xanthan for enhanced nitrobenzene removal.

The reactivity and delivery of remediants and treatment of organic contaminants in heterogeneous aquifer are particularly challenging issues for injection-based remedial treatments. Our objective was to enhance the reactivity and delivery of nanoscale zero-valent iron (nZVI) and improve the sweeping efficiency of nZVI into low permeable zones (LPZs) to reduce nitrobenzene (NB). This was accomplished by conducting batch and transport experiments that quantified NB degradation by different modified nZVI and the ability of emulsified nZVI (EZVI) or xanthan carried EZVI (XG-EZVI) to penetrate and cover a lens. By incorporating the xanthan and emulsified oil with nZVI, it possessed higher stability and stronger reactivity to reduce NB. Results showed that the stability of EZVI was improved by xanthan, and there were no adverse effects on NB removal in use of XG-EZVI at limited xanthan addition of ≦100 mg L-1. By the injection of XG-EZVI in 2D-tank experiments, the degradation of NB was 8 times that of EZVI added, while NB adsorption on media was only 1/50 of initial NB. 1205 mg of NB totally entered into the tank, the quality of aniline in effluent was approximately 90.0 mg in addition of XG-EZVI at 40 h, but not detected in presence of EZVI. The greater NB reduction by XG-EZVI resulted from higher sweeping efficiency in LPZ. These observations support the couple use of xanthan and emulsified oil for modifying nZVI as a means of achieving greater stability and reactivity and enhancing nZVI delivery into LPZs for the treatment of NB.

Study on the removal effect and influencing factors of nitrobenzene reduction by iron carbonate precipitates.

To investigate the activity of iron carbonate precipitates produced by long-term operation of Fe0 permeable reactive barriers, three kinds of precipitates, namely Fe6(OH)12CO3, Fe2(OH)2CO3, and FeCO3, were prepared to reduce the pollutant nitrobenzene. We studied the reduction effects of these iron carbonate precipitates on nitrobenzene by considering three factors, namely the initial nitrobenzene concentration, initial pH, and precipitate dosage, and established the kinetic degradation using pseudo-first-order kinetics model. The results showed that all three precipitates can reduce nitrobenzene, and the order of reducing capability is Fe6(OH)12CO3 > Fe2(OH)2CO3 > FeCO3; moreover, the removal efficiency values of nitrobenzene are 68.08, 53.00, and 50.29%. A high initial nitrobenzene concentration and high pH value are beneficial to nitrobenzene reduction, and removal efficiency was increased when pH was increased from 4 to 9. In addition, the increased precipitate addition in the Fe6(OH)12CO3 and Fe2(OH)2CO3 systems increased removal efficiency. Furthermore, the dosage did not significantly influence the removal rate in the FeCO3 system. Fe6(OH)12CO3 and Fe2(OH)2CO3 mainly relied on the precipitate itself with the structural Fe(II) to reduce nitrobenzene, and FeCO3 mainly relied on the dissolved Fe2+. The reaction of all three precipitates in reducing nitrobenzene followed the first-order reaction kinetics.

Nitrobenzene reduction using nanoscale zero-valent iron supported by polystyrene microspheres with different surface functional groups.

Three polystyrene (PS) resin microspheres supported nanoscale zero-valent iron (nZVI), i.e., nZVI@PS, nZVI@PS-Cl, and nZVI@PS-N, were prepared and characterized by FT-IR, XPS, SEM, EDS, and weighing method. The functional groups on the carriers showed obvious influence on the loading quantity, the micro morphology, and the reduction efficiency of these supported nZVI. The best hybrid reducer was nZVI@PS-N. The load quantity of nZVI was 0.2476 g/g, and some of them were dispersed and the others remained as particles (≤ 50 nm). At optimal reaction conditions, i.e., initial solution pH = 3, 25 °C, 100 r/min stirring, 99% nitrobenzene (NB) in 250 mL 123.1 mg/L NB solution could be totally reduced into AN by 1.31 g fresh nZVI@PS-N within 20 min. The excellent reduction efficiency and fast degradation rate of nZVI@PS-N were mainly attributed to the synergistic effects between the good adsorption property of its carrier and the high reduction activity of nZVI particles. NZVI@PS-N was reproducible and recycled, and 90.6% degradation ratio of NB was till obtained at its seventh recycle. The results showed that nZVI@PS-N had high potential practical application value in the reductive degradation and emergency rescue of nitrobenzene pollutant.

Enhanced Fenton-like removal of nitrobenzene via internal microelectrolysis in nano zerovalent iron/activated carbon composite.

The efficiency of Fenton-like catalysis using nano zerovalent iron (nZVI) is limited by nZVI aggregation and activity loss due to inactive ferric oxide forming on the nZVI surface, which hinders electron transfer. A novel iron-carbon composite catalyst consisting of nZVI and granular activated carbon (GAC), which can undergo internal iron-carbon microelectrolysis spontaneously, was successfully fabricated by the adsorption-reduction method. The catalyst efficiency was evaluated in nitrobenzene (NB) removal via the Fenton-like process (H2O2-nZVI/GAC). The results showed that nZVI/GAC composite was good for dispersing nZVI on the surface of GAC, which permitted much better removal efficiency (93.0%) than nZVI (31.0%) or GAC (20.0%) alone. Moreover, iron leaching decreased from 1.28 to 0.58 mg/L after reaction of 240 min and the oxidation kinetic of the Fenton-like reaction can be described well by the second-order reaction kinetic model (R2=0.988). The composite catalyst showed sustainable catalytic ability and GAC performed as a medium for electron transfer in internal iron-carbon microelectrolysis to promote Fe2+ regeneration and Fe3+/Fe2+ cycles. Therefore, this study represents an important method to design a low cost and high efficiency Fenton-like catalyst in practical application.

Cooperative role of electrical stimulation on microbial metabolism and selection of thermophilic communities for p-fluoronitrobenzene treatment.

A novel thermophilic bioelectrochemical system (TBES) based on electrical stimulation was established for the enhanced treatment of p-fluoronitrobenzene (p-FNB) wastewater. p-FNB removal rate constant in the TBES was 78.6% higher than that of the mesophilic BES (MBES), the elevation of which owing to high-temperature overtook the rate improvement of 50.8% in the electrocatalytic system (ECS). Additionally, an overwhelming mineralization efficiency of 91.96% ± 5.70% was obtained in the TBES. The superiority of TBES was attributed to the integrated role of electrical stimulation and high-temperature. Electrical stimulation provided an alternative for the microbial growth independent energy requirements, compensating insufficient energy support from p-FNB metabolism under the high-temperature stress. Besides, electrical stimulation facilitated microbial community evolution to form specific thermophilic biocatalysis. The uniquely selected thermophilic microorganisms including Coprothermobacter sp. and other ones cooperated to enhance p-FNB mineralization.

Application of ultraviolet, ozone, and advanced oxidation treatments to washwaters to destroy nitrosamines, nitramines, amines, and aldehydes formed during amine-based carbon capture.

Although amine-based CO(2) absorption is a leading contender for full-scale postcombustion CO(2) capture at power plants, concerns have been raised about the potential release of carcinogenic N-nitrosamines and N-nitramines formed by reaction of exhaust gas NO(x) with the amines. Experiments with a laboratory-scale pilot unit suggested that washwater units meant to scrub contaminants from absorber unit exhaust could potentially serve as a source of N-nitrosamines via reactions of residual NO(x) with amines accumulating in the washwater. Dosage requirements for the continuous treatment of the washwater recycle line with ultraviolet (UV) light for destruction of N-nitrosamines and N-nitramines, and with ozone or hydroxyl radical-based advanced oxidation processes (AOPs) for destruction of amines and aldehydes, were evaluated. Although <1000 mJ/cm(2) UV fluence was generally needed for 90% removal of a series of model N-nitrosamines and N-nitramines, 280-1000 mJ/cm(2) average fluence was needed for 90% removal of total N-nitrosamines in pilot washwaters associated with two different solvents. While AOPs were somewhat more efficient than ozone for acetaldehyde destruction, ozone was more efficient for amine destruction. Ozone achieved 90% amine removal in washwaters at 5-12 molar excess of ozone, indicating transferred dosage levels of ∼100 mg/L for 90% removal in a first-stage washwater unit, but likely only ∼10 mg/L if applied to a second-stage washwater. Accurate dosage and cost estimates would require pilot testing to capture synergies between UV and ozone treatments.

[Kinetic study of 4-chloronitrobenzene degradation by zero-valent iron].

4-chloronitrobenzene as a representative material of nitroaromatic compounds was used in this study to investigate the degradation reaction rate and products by different concentrations of zero-valent iron (ZVI) under anoxic condition. According to stoichiometry, different reaction rates of products were obtained by fitting the experimental data. Products of ZVI were measured by Mössbauer technique. The results show that reduction of 4-chloronitrobenzene corresponds to the concentration of ZVI. The production and transformation rates of intermediate products, 4-chloronitrosobenzene and 4-chloro phenyl hydroxylamine, can be achieved. The 4-chloronitrobenzene reduction reaction is the fastest when the ZVI concentration is 1.04 g x L(-1). The reaction rate constant is 0.189 min(-1). Ferrous iron ions generated during reaction are sorbed on the ZVI surfaces in the early age of the reaction. Formation and reduction reaction rates of different products depend on the reactive sites of ZVI and the mass transfer between each other.

Determination of seven nitrobenzene compounds in mainstream cigarette smoke with heart-cutting two-dimensional gas chromatography.

A heart-cutting two-dimensional gas chromatography (GC) method was developed for the determination of nitrobenzene compounds (NBCs) in mainstream cigarette smoke. For the method, the particulate matter of cigarette smoke was extracted with cyclohexane, purified with a silica solid-phase extraction (SPE) cartridge and analyzed by heart-cutting two-dimensional GC equipped with two electron capture detectors. The heart-cutting two-dimensional GC was achieved by a single-column GC oven equipped with a microfluidic pressure balanced device (Deans switch). Two-dimensional GC was compared to single-dimensional GC and found to be clearly better for the separation of seven NBCs from a complex smoke matrix. The limits of detection ranged from 1.28 to 9.83 ng/mL, spiked recoveries were between 88.3 and 106.8% and relative standard deviation ranged from 2.79 to 12.78%. The NBCs yields of six kinds of Chinese and international cigarettes brands, which were all smoked according to two smoking protocols (International Organization for Standardization and Health Canada Intense smoking regimens), were determined and compared.

[Investigation of nitrobenzene removal by iron sulfide (FeS)].

The nitrobenzene removal performance by iron sulfide was investigated in batch experiments. The effects of different factors were studied. The results showed that the removal efficiency of nitrobenzene was 90% as initial nitrobenzene concentration was 0.96 mmol x L(-1), dosage of FeS was 1.2 g and the reaction time was 180 minutes. Initial nitrobenzene concentration, dosage of FeS, temperature and reused times of FeS had a significant influence on the removal efficiency of nitrobenzene. As the initial nitrobenzene concentration was in range of 0.74 to 1.74 mmol x L(-1), the removal efficiency of nitrobenzene decreased by 4.7% with every 0.1 mmol x L(-1) increasing of initial nitrobenzene concentration. As the dosage of FeS was in the range of 0.3 to 1.5 g, the removal efficiency of nitrobenzene increased by 20% with every 0.3 g increasing of FeS. As the dosage of FeS was 1.8 g, the removal efficiency of nitrobenzene was 100%. In the temperature range of 10 to 25 degrees C, the removal efficiency of nitrobenzene increased by 1.6% with 1 degrees C increasing. As the temperature was 30 degrees C, the removal efficiency of nitrobenzene was 100%. The removal efficiency of nitrobenzene decreased as the reused times of FeS increased. Rotational speed hardly had any influence on the removal efficiency of nitrobenzene. As the rotational speed was in the range of 10 to 80 r x min(-1), the removal efficiency of nitrobenzene was around 75%. The nitrobenzene removal performance by iron sulfide was satisfied in the treatment of simulated chemical industrial wastewater, and after 60 min, the removal efficiency of nitrobenzene was 100%.

Zero-valent aluminum for oxidative degradation of aqueous organic pollutants.

Oxidative degradation of aquatic organic contaminants using zero-valent aluminum (ZVAl) in the presence of dissolved oxygen (O2) was investigated. The metal corrosion process in acidic conditions (pH < 4) was accompanied by electron transfer from ZVAl to O2, which led to the simultaneous generation of Al3+ and hydrogen peroxide (H2O2). The oxidation of 4-chlorophenol (4-CP), a model substrate, was initiated by the generation of hydroxyl radicals (HO*) via electron transfer from Al0 to H2O2. Degradation was initiated after an induction period of about 2 h, during which the native oxide layer was dissoluted. The HO*(-) mediated oxidation reaction was completely quenched by adding methanol as a radical scavenger. Systematic studies on the effects of ZVAl loading, pH, and surface oxide content revealed that the oxide layer dissolution controlled the Al0-mediated oxidation of 4-CP. The proposed process is similarly compared with the zero-valent iron (ZVI) system, but the ZVAl/O2 system showed a higher oxidation capacity compared with ZVI/O2 because of the stability of aquo-complexed Al3+ ions over a wider pH range. The degradation of phenol, nitrobenzene, and dichloroacetate was also successfully achieved with ZVAl. The present study proposes the ZVAl/O2 process as a viable method of oxidative water treatment.

[Simultaneous remediation of Cr (VI) and p-NCB by nanosacle iron].

Nanoscale Fe and Ni/Fe, which were prepared by chemical deposition, were utilized as catalyst for remediation of Cr(VI) and pNCB in contaminated water. The interactions between Cr( VI) and p-NCB in contaminated water during the simultaneous remediation process were analyzed. It is demonstrated from the experiment that p-NCB can be degradated into p-CAN by nanoscale iron, but cannot exhibit the effect of dechlorination, and that there is a competitive relationship between Cr( VI) and p-NCB in the remediation process. The nanoscale Nil Fe bimetals could be applied in simultaneous remediation of p-NCB with Cr( VI) and give rise to a good remediation efficiency, where the products are only Cr(III) and p-CAN without any intermediate products. It was found that the conditions of higher Ni(II) concentration can promote the degradation rate of p-NCB. The optimum Ni/Fe ratio is 1:50. Whereas, the higher concentrations of Cr(VI) and p-NCB will lead to the lower degradation rate. Under the condition that concentration of Cr (VI) was 20 mg/L, the corresponding maximum dechlorination of p-NCB was 43.0%; under the condition that concentration of p-NCB was 40 mg/L, the corresponding maximum removal efficiency of Cr(VI) was 71.4%.

Large-scale synthesis of the bifunctional chelating agent 2-(p-nitrobenzyl)-1,4,7,10-tetraazacyclododecane-N,N',N'',N'''-tetr aacetic acid, and the determination of its enantiomeric purity by chiral chromatography.

The attachment of radiometals to monoclonal antibodies for medical applications requires extreme stability under physiological conditions, with no significant release of metal. Chelators that can hold radiometals like 111In, 67Ga, and 90Y with high stability under these conditions are essential for radiotherapy or immunoscintigraphy. 2-(p-Nitrobenzyl)-1,4,7,10-tetraazacyclododecane- N,N',N'',N'''-tetraacetic acid (nitrobenzyl-DOTA) is one of the most promising bifunctional chelating agents. A large-scale synthesis of nitrobenzyl-DOTA is described. The overall yield for the nine-step synthesis sequence starting from nitrophenylalanine is 5.6%. Synthesis of nitrobenzyl-DOTA according to the new procedure yields up to approximately 10 g without special apparatus. Both enantiomers of the chiral chelate nitrobenzyl-DOTA have been prepared, and their enantiomeric purity has been checked by chiral chromatography.

Identification, occurrence and mutagenicity in Salmonella typhimurium of two synthetic nitroarenes, musk ambrette and musk xylene, in Indian chewing tobacco and betel quid.

During N-nitrosamine analysis of extracts of betel quid with tobacco and of the saliva of chewers of betel quid with tobacco for N-nitrosamines using a Thermal Energy Analyzer, two unknown compounds were detected. They were identified as synthetic nitro musks, musk ambrette (5-tert-butyl-1,3-dinitro-4-methoxy-2-methylbenzene, CAS No. 83-66-9) and musk xylene, (1-tert-butyl-3,5-dimethyl-2,4,6-trinitrobenzene, CAS No. 81-15-2), by gas chromatography-mass spectrometry and Fourier transform nuclear magnetic resonance spectroscopy. These compounds were detected in several samples of betel quid with tobacco and in perfumed tobacco used for chewing in India in amounts ranging from 0.45-23.5 mg/g wet weight. Musk ambrette was found to be mutagenic in Salmonella typhimurium TA100 requiring metabolic activation by rat-liver postmitochondrial supernatant but musk xylene lacked mutagenicity.