Removal Efficiency Of Nitrobenzene Research Articles

Degradation of nitrobenzene in 3D stack Z-scheme photoelectrocatalytic system: Degradation condition, pathway analysis and synergistic mechanism

As a representative pollutant with carcinogenesis, mutagenicity and teratogenicity, nitrobenzene (NB) has devastating harm to human health. Herein, a unique three-dimensional (3D) stack Z-scheme photoelectrocatalytic (PEC) system was built by self-assembled different photoelectrodes for efficient NB removal. The effect of initial NB, bias potential, pH and electrolyte concentration on NB removal efficiency were investigated. The intermediates and oxygen-active radicals were determined and analyzed by high performance liquid chromatography (HPLC), gas chromatography-mass spectrometry (GC-MS), density functional theory (DFT) and electron paramagnetic resonance (EPR) to propose the NB degradation pathways and mechanism. The results showed that holes were utilized to produce ·OH to oxidize NB on the photoanode surface, the electrons excited from photocathode could reduce NB under UV irradiation; thereafter, the reduction product (aniline) was oxidized to phenol to achieve mineralization by the synergistic effect of anode (oxidation) and cathode (reduction). 3D stack Z-scheme PEC system exhibited a high NB degradation efficiency of 98.18% after 90 min reaction and a mineralization efficiency of 75.08% at 150 min. With ECOSAR software, the system toxicity was speculated. This study has advantages in NB removal and provides direction for other refractory organics.

The (0 0 2) exposing facets of WO3 boosting photocatalytic degradation of nitrobenzene

Photocatalysis is a potential technology for de-nitro of nitro-aromatic contaminants in wastewater. In this work, monoclinic WO3 powders and films with different exposing ratios of (002) facets were simultaneously synthesized via a hydrothermal method. Their structures and photoelectrochemical properties were investigated, and the WO3 powders were further used for nitrobenzene (NB) degradation. The NB removal efficiency increased with the increase of the exposing ratio of (002) facets of WO3, and a high efficiency of 91.65 % removal of NB was reached in 3 h reaction. Degradation mechanism was clarified with the investigation of the intermediates and final products. The (002) facets of WO3 play a crucial role in facilitating the charge carrier separation, producing more ∙OH radicals, and thus increasing the efficiency for NB degradation. Moreover, the reaction kinetics analysis revealed that the first phenolation step of NB is the slowest step in the tandem photocatalytic degradation of NB.

Enhanced anaerobic reduction of nitrobenzene at high salinity by betaine acting as osmoprotectant and regulator of metabolism

Anaerobic technology is extensively applied in the treatment of industrial organic wastewater, but high salinity always triggers microbial cell dehydration, causing the failure of the anaerobic process. In this work, betaine, one kind of compatible solutes which could balance the osmotic pressure of anaerobic biomass, was exogenously added for enhancing the anaerobic reduction of nitrobenzene (NB) at high salinity. Only 100 mg L−1 betaine dosing could significantly promote the removal efficiency of NB within 35 h at 9% salinity (36.92 ± 4.02% without betaine and 72.94 ± 6.57% with betaine). The relieving effects on salt stress could be observed in the promotion of more extracellular polymeric substances (EPS) secretion with betaine addition. Additionally, the oxidation-reduction potential (ORP), as well as the electron transfer system (ETS) value, was increased with betaine addition, which was reflected in the improvement of system removal efficiency and enzyme activity. Microbial community analysis demonstrated that Bacillus and Clostridiisalibacter which were positively correlated with the stability of the anaerobic process were enriched with betaine addition at high salinity. Metagenomic analysis speculated that the encoding genes for salt tolerance (kdpB/oadA/betA/opuD/epsP/epsH) and NB degradation (nfsA/wrbA/ccdA/menC) obtained higher relative abundance with betaine addition under high salt environment, which might be the key to improving salt tolerance of anaerobic biomass. The long-term assessment demonstrated that exogenous addition betaine played an important role in maintaining the stability of the anaerobic system, which would be a potential strategy to achieve a high-efficiency anaerobic process under high salinity conditions.

Cu2O nanoparticles modified BiO2-x nanosheets for efficient electrochemical reduction of nitrate-N and nitrobenzene from wastewater

Nitrogen-polluted wastewater posed great threat to the environment and human beings. Bismuth-based materials have presented high potentials for wastewater treatment. However, it suffers from unsatisfactory electrocatalytic efficiency, especially for nitrate-N removal. Considering the superior performance of copper in electrochemical reduction reactions, Cu2O nanoparticles modified BiO2-x nanosheets (Cu2O NPs/BiO2-x NSs) were designed and synthesized through a one-step hydrothermal method for wastewater purification. The obtained Cu2O NPs/BiO2-x NSs presents enhanced electrocatalytic activity towards nitrate removing, since the introduced Cu2O NPs not only increased the active sites but also decreased the electrical resistance. The effect of reaction parameters (current density, initial concentration, initial pH, supporting electrolyte, and dissolved oxygen) was also studied to optimize the operation conditions. Meanwhile, the electrochemical and scavenging experiments illustrated the mechanism that both the direct electron transfer and atomic H* played important roles in nitrate reduction. Furthermore, when applying Cu2O NPs/BiO2-x NSs for the treatment of nitrobenzene (NB), it achieved nearly 90% removal efficiency of NB in 30 min. Therefore, the designed Cu2O NPs/BiO2-x NSs shows a wide range of potential for removing both nitroaromatic and inorganic nitrogen pollutants.

Enhanced nitrobenzene removal in soil by biochar supported sulfidated nano zerovalent iron: Solubilization effect and mechanism

Sulfidated nano zerovalent iron (S-nZVI) is reported to be effective in removal of aqueous organic contaminants. However, little is known about its potential use in reductive degradation of soil-sorbed contaminants. In this study, biochar (BC) supported S-nZVI (S-nZVI@BC) was successfully synthesized through sulfidation and carbon loading modification, which effectively combined the solubilization characteristics of BC and high reduction characteristics of S-nZVI. Transmission electron microscopy (TEM) with an energy-dispersive X-ray spectroscopy (EDS) analysis suggested that sulfur and iron were evenly distributed throughout BC matrix. The degradation of nitrobenzene (NB) in soil was achieved more efficiently with the as-synthesized S-nZVI@BC composites. Results indicated that S-nZVI@BC with S-nZVI/BC mass ratio of 3:1, dosage of 10 mg/g exhibited superior NB removal (98%) and aniline (AN) formation (90%) efficiency within 24 h without formation of other intermediates, higher than those of S-nZVI. Meanwhile, the surface FeSX layer enhanced the antioxidant capacity of S-nZVI@BC and participated in the reduction of NB. The soil-sorbed NB decreased from 14% to 1.4%, indicating that the addition of BC played an important role in solubilization of NB from soil. Solubilization-reduction was the dominant mechanism for NB removal. This research indicated that S-nZVI@BC held the potential to enhance in-situ remediation of NB-contaminated soil.

Photocatalytic Decomposition of Nitrobenzene in Aqueous Solution by Ag/Cu2O Assisted with Persulfate under Visible Light Irradiation

The mineralization of nitrobenzene was executed using an innovative method, wherein Ag/Cu2O semiconductors stimulated by visible light irradiation were supported with persulfate anions. Batch-wise experiments were performed for the evaluation of effects of silver metal contents impregnated, persulfate concentrations and Ag/Cu2O dosages on the nitrobenzene removal efficiency. The physicochemical properties of fresh and reacted Ag/Cu2O were illustrated by X-ray diffraction analyses, FE-SEM images, EDS Mapping analyses, UV–Vis diffuse reflectance spectra, transient photocurrent analyses and X-ray photoelectron spectra, respectively. Because of intense scavenging effects caused by benzene, 1-propanol and methanol individually, the predominant oxidant was considered to be sulfate radicals, originated from persulfate anions via the photocatalysis of Ag/Cu2O. As regards oxidation pathways, nitrobenzene was initially transformed into hydroxycyclohexadienyl radicals, followed with the production of 2-nitrophenol, 3-nitrophenol or 4-nitrophenol. Afterwards, phenol compounds descended from denitration of nitrophenols were converted into hydroquinone and p-benzoquinone.

Substantially enhanced degradation of nitrobenzene by biosponge iron system: Process and mechanisms

Considering the high reactivity, cost-efficiency, environmental friendliness, the zero-valent iron-microbe (bio-ZVI) technology for refractory organic wastewater treatment has obtained worldwide attentions. This paper submerged sponge iron (SFe, a typical ZVI material) in activated sludge to form biological sponge iron (bio-SFe) systems, while the iron sludge and ordinary activated sludge systems were taken as blank control. To study the strengthening effect and degradation mechanism of bio-SFe systems, Nitrobenzene (NB) was chose as a target contaminant. The interaction between SFe and microorganisms improved the NB removal efficiency, prompted the formation of Fe(II)/ROS and facilitated the biodegradation process. Specifically, the Fenton-like effects for NB removal increased from 3.6 % in mono-SFe system to 11.79 % in SFe coupled with iron sludge system. This facilitated the production of OH could constantly attack and eventually mineralize NB. Additionally, biodegradation of NB was the predominant pathway (64.25 %), when iron sludge combined with SFe, the removal of NB could ascend to 92.11 %. SFe created a more favorable environment for certain core functional genera related to recalcitrant pollutants reduction and iron cycle. According to the accumulation of NH4+-N content and the identification of the degradation intermediates of NB in bio-SFe system, the partial reduction biodegradation of NB was finally confirmed.

The removal mechanism of nitrobenzene by the Cu-Fe/Carbon material under different aeration conditions

Zero-valent Cu-Fe bimetallic porous carbon materials were successfully applied to remediate organic wastewater. In this work, we successfully recycled the layered double hydroxides (LDHs) adsorbed with Orange II (OII) to form a zero-valent Cu-Fe bimetallic porous carbon material (CuFe/Carbon). The characterization results showed that CuFe/Carbon was a zero-valent Cu-Fe bimetallic porous graphene-like carbon material. In the course of the experiment, we found that aeration condition had a great influence on the activity of CuFe/Carbon. The removal efficiency of nitrobenzene (NB) was 100 % in nitrogen system and 48 % in air system. The active species of O2− and OH was formed under air condition, while there was no active species under nitrogen condition. NB was reduced to aniline directly under nitrogen condition. We proposed there were reduction and oxidation mechanisms under different aeration conditions. This work mainly investigated the conversion process of a novel material under different reaction conditions, which provided theoretical support for the removal of organic matters.

Influence of plant radial oxygen loss in constructed wetland combined with microbial fuel cell on nitrobenzene removal from aqueous solution

This study investigated the effects of radial oxygen loss (ROL) of three different plants on nitrobenzene (NB) wastewater treatment and bioelectricity generation performance in constructed wetland-microbial fuel cell (CW-MFC). ROL and root biomass from wetland plants showed positive effects on NB wastewater compared to unplanted CW-MFC. Scirpus validus exhibited higher tolerance to NB than Typha orientalis and Iris pseudacorus at 20−200 mg/L NB. As NB concentration reached 200 mg/L, the CW-MFC with Scirpus validus had relatively high DO (2.57 ± 0.17 mg/L) and root biomass (16.42 ± 0.18 g/m2), which resulted in the highest power density and voltage (19.5 mW/m2, 590 mV) as well as NB removal efficiency (93.9 %) among four reactors. High-throughput sequencing results suggested that electrochemically active bacteria (EAB) (e.g., Geobacter, Ferruginibacter) and dominant NB-degrading bacteria (e.g., Comamonas, Pseudomonas) could be enhanced by wetland plants, especially in CW-MFC with Scirpus validus. Therefore, Scirpus validus was a good option for simultaneously treating NB wastewater and producing bioelectricity.

Enhanced nitrobenzene reduction by modified biochar supported sulfidated nano zerovalent iron: Comparison of surface modification methods

In our previous study, biochar (BC) supported sulfidated nano zerovalent iron (S-nZVI@BC) was prepared for nitrobenzene (NB) reduction. In this study, in order to further improve the reduction performance of S-nZVI@BC, BC was modified before the loading of S-nZVI through three methods: oxidant (H2O2) pretreatment, alkali (NaOH) pretreatment and acid (HCl) pretreatment. The results indicated that S-nZVI could be evenly distributed onto HCl-BC due to increased surface area, negative surface charge and increased acidic functional groups on HCl-BC. At an initial concentration of 200 mg L−1, NB could be completely removed by S-nZVI@HCl-BC within a reaction time as short as 60 min, indicating rather excellent performance of S-nZVI@HCl-BC. NB reduction performance followed the order: S-nZVI@HCl-BC > S-nZVI@NaOH-BC > S-nZVI@BC > S-nZVI@H2O2-BC. The mass ratio of S-nZVI and HCl-BC was optimized in terms of NB removal efficiency, with 3:1 being identified as the best mass ratio. Furthermore, the mechanism involved in the enhanced NB reduction by S-nZVI@HCl-BC was proposed. This study demonstrated that S-nZVI@HCl-BC is a promising alternative for efficient NB removal from wastewater.

Catalytic ozonation by Si-doped α-Fe2O3 for the removal of nitrobenzene in aqueous solution

Si-doped α-Fe2O3 by controlling the atom ratio of Si/Fe was synthesized for catalytic ozonation of nitrobenzene in aqueous solution. Basing on the results of batch oxidation experiments, the catalysts in Si/Fe ratios of 0.1, 0.5, 1.0, and 2.0 showed various activities for ozone decomposition into hydroxyl radical (OH), which obviously enhanced the removal efficiency of nitrobenzene in aqueous solution compared with sole ozonation. The best Si/Fe ratio was 0.5 in present study. The dose of the catalyst, solution pH and reaction temperature can significantly affect the removal efficiency of nitrobenzene. Moreover, the catalyst was composed of Si–Fe binary oxides and α-Fe2O3. With the increase of Si/Fe ratio, the surface relative content of Si-Fe binary oxides increases and the relative content of α-Fe2O3 decreases, which promotes the ozone adsorption-desorption on the surface of the catalyst. The generation of hydroxyl radical in catalytic ozonation was dependent on the synergy of ozone adsorption-desorption by Si–Fe binary oxides and ozone decomposition by α-Fe2O3 on the surface of the catalyst.

Enhanced removal efficiency and influencing factors of nitrobenzene in soil by foam flushing

Laboratory scale experiments were conducted to investigate the removal efficiency of nitrobenzene in soil by different kinds of flushing liquid. In addition, the influencing factors, such as foam injection rate, foam quality and permeability of medium for the removal efficiency of nitrobenzene in soil were discussed in the paper. The results showed that the residual rates of nitrobenzene in soil were 62.15%, 63.18%, and 2.65%, while the flushing liquid were water, SDS solution, and SDS foam, respectively. The removal efficiency of nitrobenzene was found to be greatly increased by using a foam-enhanced surfactant solution flooding approach, probably because of the reduction in the channeling flow effect. These data demonstrated that by the use of foam, the nitrobenzene recovery efficiency can be significantly improved. Within the scope of the study, the foam quality and foam injection rate has little effect on the total removal efficiency of nitrobenzene in soil. Moreover, the total removal efficiency of nitrobenzene for low permeability (0.1∼0.25mm, 0.25∼0.5mm) is greater than that in high permeability medium. Because of the time necessary for distribution of foam through the soil and desorption process is much longer for soil with a low hydraulic conductivity, this technique is more effective in soil with lower hydraulic conductivity and higher porosity.

Activation of zero-valent iron through ball-milling synthesis of hybrid Fe0/Fe3O4/FeCl2 microcomposite for enhanced nitrobenzene reduction.

To activate zero-valent iron (ZVI) for efficient nitrobenzene (NB) reduction, a hybrid Fe0/Fe3O4/FeCl2 microcomposite (hZVIbm) was synthesized via simple ball-milling of the ternary mixture of ZVI, Fe3O4, and FeCl2·4H2O (hZVI). SEM-EDX and time-of-flight secondary ion mass spectroscopy (ToF-SIMS) indicated the hZVIbm microcomposite (10-20 μm) consisted of Fe0 core covered by ∼3.3 μm-thick shell decorated with Fe3O4/FeCl2 fine particles (0.1-2 μm). Efficient removal (>95%) of NB (200 mg/L) was achieved by hZVIbm (2.0 g Fe/L) in 30 min over a wide pH range from 3 to 9. Notably, the NB removal efficiency of hZVIbm was over 30 times higher than the virgin ZVI or over three times higher than hZVI. The enhanced reactivity synergistically resulted from both chemical and physical aspects. Chemically, the Fe3O4/FeCl2-inlaid shell and the Fe(II) components played significant activation roles, as observed from the comparative experiments in their absence via pretreatments of hZVIbm by sonication and rinsing, respectively, with direct evidence of depassivation effect by XRD analysis. Physically, the ball-milling-induced inter-particle compaction effect was considered crucial to facilitate the interfacial mass/electron transfer processes during the reduction. The reduction pathway from NB to aniline via two intermediates was analyzed by liquid chromatography.

Effects of glucose and starch on the toxicity of nitrobenzene to plants and microbes in constructed wetlands

Photosynthetic pigment content, antioxidant enzyme activities of plants, microbial enzyme activities and community structure were analyzed to investigate the effects of glucose and starch on the toxicity of nitrobenzene (NB) to plants and microbes in constructed wetlands (CWs). As the influent NB concentration increased from 10 mg/L to 100 mg/L, the NB removal efficiency of the blank group decreased from 97.1% to 75.02%. However, the NB removal efficiencies of the external carbon source groups were maintained at nearly 100%. External carbon sources accelerated the transformation process of NB to aniline (AN), thus decreasing NB toxicity to the microbes and plants. When the influent NB concentration reached 100 mg/L, the NB removal rates and NB reductase activities of the external carbon source groups were 2.4 times and 4 times higher, respectively, than those of the blank group. Most of the dominant genera found in the three CWs could reduce nitroaromatics to the corresponding aromatic amines according to the results of high-throughput sequencing. The performance of NB removal in the CWs indicated the potential of CWs for NB treatment and the necessity of external carbon sources under high NB concentrations.

Effect of surfactants on the removal of nitrobenzene by Fe-bearing montmorillonite/Fe(II)

Nonionic and anionic surfactants often occur in anaerobic environments, but their roles in the removal of organic contaminants by Fe-bearing mineral/Fe(II) have not been determined. In this study, batch experiments were performed to investigate the effects of a nonionic surfactant (TX-100) and an anionic surfactant (SDBS) on the removal of nitrobenzene (NB) by Fe-bearing montmorillonite (FM)/Fe(II). Mössbauer spectrum and XPS were applied to analyze the edge surface bound Fe(II) and secondary minerals formed on FM. The contribution of surfactant to the enrichment of NB on FM was studied. The results showed that TX-100 and SDBS had opposite effects on the removal of NB by FM/Fe(II) at neutral pH. The presence of TX-100 improved the removal efficiency of NB from 36.4% to 70.0%, and increased the initial removal rate by 1.7 times. This enhancement effect was mainly attributed to the formation of more active edge surface bound Fe(II) that can reduce more NB to aniline. Formation of more magnetite on FM and selective enrichment of NB on the reactive surface also contributed to the removal of NB. In contrast, the presence of SDBS reduced the amount of edge surface bound Fe(II) via formation of SDBS-Fe(II) complex, which decreased the removal efficiency of NB.

Fabrication of a hydrophobic SDBS-PbO2 anode for electrochemical degradation of nitrobenzene in aqueous solution

In present work, a hydrophobic PbO2 electrode modified by sodium dodecyl benzene sulfonate (SDBS-PbO2) was fabricated using electrodeposition method. The effect of SDBS concentration in electroplating bath on the surface morphology, structure, electrochemical properties, hydrophilicity, OH generation ability and stability of SDBS-PbO2 electrodes was studied using scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), water contact angle, fluorescence probe technique, and accelerated life test, respectively. Results showed that SDBS modification not only increased the electro-catalytic activity, but also prolonged the service life of PbO2 electrode. The electrode prepared from the electroplating bath containing 10 mg/L SDBS (SDBS-PbO2-10 mg/L) showed the highest electrocatalytic activity and the longest service life. The electrochemical degradation of nitrobenzene (NB) in simulated wastewater was used to evaluate the potential application of SDBS-PbO2 electrodes for wastewater treatment. The highest NB removal efficiency and total organic carbon (TOC) removal efficiency of 89.35% and 52.62% were both obtained by SDBS-PbO2-10 mg/L anode. Thus, the SDBS-PbO2-10 mg/L anode was used to systematically investigate the effects of applied current density, initial NB concentration, temperature, and pH value on the reaction kinetics and mineralization current efficiency (MCE) of NB degradation. It was found that the increase of applied current density and the reduction of initial NB concentration exerted a prominent effect on the degradation of NB, but caused the decrease of MCE, while high temperature and low pH value improved both NB degradation rate and MCE. These results show that the SDBS-PbO2-10 mg/L electrode may become a promising anode for organic pollutant degradation.

Removal of sulfamethoxazole, ibuprofen and nitrobenzene by UV and UV/chlorine processes: A comparative evaluation of 275 nm LED-UV and 254 nm LP-UV

The aim of this study is to evaluate the micropollutant removal capacity of a 275 nm light-emitting diode (LED)-UV/chlorine system. The sulfamethoxazole, ibuprofen, and nitrobenzene removal efficiencies of this system were compared with those of a conventional 254 nm low-pressure (LP)-UV system as a function of the UV dose. In a direct photolysis system, the photon reactivity of sulfamethoxazole is higher than that of nitrobenzene and ibuprofen at both wavelengths. The molar absorption coefficients and quantum yields of each micropollutant were as follows: sulfamethoxazole (εSMX, 275 nmprotonated = 17,527 M−1 cm−1, ΦSMX, 275 nmprotonated = 0.239, εSMX, 275 nmdeprotonated = 8430 M−1 cm−1, and ΦSMX, 275 nmdeprotonated = 0.026), nitrobenzene (εNB, 275 nm = 7176 M−1 cm−1 and ΦNB, 275 nm = 0.057), and ibuprofen (εNB, 275 nm = 200 M−1 cm−1 and ΦIBF, 275 nm = 0.067). The photon reactivity of chlorine species, i.e., HOCl and OCl-, were determined at 275 nm (εHOCl, 275 nm = 28 M−1 cm−1, ΦHOCl, 275 nm = 1.97, εOCl−, 275 nm = 245 M−1 cm−1, and ΦOCl−, 275 nm = 0.8), which indicate that the decomposition rate of OCl− is higher and that of HOCl is lower by 275 nm photolysis than that by 254 nm photolysis (εHOCl, 254 nm = 60 M−1 cm−1, ΦHOCl, 254 nm = 1.46, εOCl−, 254 nm = 58 M−1 cm−1, and ΦOCl−, 254 nm = 1.11). In the UV/chlorine system, the removal rates of ibuprofen and nitrobenzene were increased by the formation of OH and reactive chlorine species. The 275-nm LED-UV/chlorine system has higher radical yields at pH 7 and 8 than the 254 nm LP-UV/chlorine system.

Incorporation of nanoscale zero-valent iron particles in monodisperse mesoporous silica nanospheres: Characterization, reactivity, transport in porous media

In this study, nanoscale zerovalent iron (nZVI) was incorporated inside the channels of monodisperse mesoporous silica nanospheres (MSN). The techniques of TEM, XRD, FTIR, N2 adsorption-desorption and XPS were conducted to characterize the composition and structure of the composite materials. Results revealed that nZVI was well dispersed in the channels of MSN, and the synthesized Fe/Si composite materials (nZVI@MSN) remained monodisperse nanospheres with the size of 100 nm which was in the optimal size range for transport through porous media. The loading of Fe (wt %) in nZVI@MSN was 4.3% and the BET surface area of nZVI@MSN was 743.49 m2/g. Batch experiment results revealed that the removal efficiency of nitrobenzene (NB) by nZVI@MSN was 42.9% higher than that of bare nZVI. Lower initial solution pH could favour the removal of NB. Most of the common ions including Na+, K+, Cl−, NO3− and SO42- presented no obvious effect on NB removal. While, Ca2+, Mg2+ and HCO3− showed promoted inhibitory effect on NB degradation with the increased of ion concentration. After seven cycles of reduction, the removal efficiency of NB by nZVI@MSN was higher than 86%, indicating its high stability and durability. Transport experiments showed that nZVI@MSN performed better mobility in porous aquifer media than bare nZVI.

Extraction of nitrobenzene from aqueous solution in impinging stream-rotating packed bed

A liquid-liquid extraction of nitrobenzene (NB) in impinging stream-rotating packed bed (IS-RPB) was proposed using cyclohexane as an extractant, presented for its improvement of micromixing and mass transfer performance. The effects of pH, phase ratio (the flow rate of organic phase/aqueous phase) and rotating speed of IS-RPB on removal efficiency and extraction stage efficiency of NB were investigated experimentally in IS-RPB. The experimental result showed that the removal rate of NB reached 94.93%, and extraction stage efficiency was 99.99% in IS-RPB, respectively, under the following experimental conditions including: a pH of 6.4, a temperature of 25 °C, a phase ratio of 1:1, a liquid flow rate of 50 L/h, a rotating speed for IS-RPB of 400 r/min, and an initial impinging velocity of 7.88 m/s. Besides, IS, RPB and IS-RPB were compared based on the removal rate of NB and extraction stage efficiency in the same experimental conditions. Compared with other mixing devices, IS-RPB has better extraction stage efficiency and shorter extraction time than other extraction devices, proving that high gravity technology can be utilized to effectively improve the extraction stage efficiency and has a good application prospect.

Simultaneous formation of nanoscale zero-valent iron and degradation of nitrobenzene in wastewater in an impinging stream-rotating packed bed reactor

A novel process based on an impinging stream-rotating packed bed (IS-RPB) was proposed for preparing nanoscale zero-valent iron (NZVI) and degrading nitrobenzene (NB) simultaneously. The obtained NZVI particles were characterized by scanning electron microscopy (SEM), high-resolution transmission electron microscopy experiments (HRTEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The experimental results showed that the NB removal efficiency increased with the augment of liquid flow rate and initial reactant concentrations. The NZVI prepared with Fe2+ as an iron source had high reactive activity and its removal efficiency of NB could be maintained at a high level in acidic or a weakly basic condition (pH<8). Compared with the traditionally mixing method, the IS-RPB could reduce the iron dosing amounts by 49.6% and the prepared NZVI could achieve 100% efficiency of the NB removal. Considering the operational cost and treatment efficiency, the optimal ratio between NaBH4 and iron concentration could be in the range of 2.0–3.0. Through the strong micro-mixing intensification performance of IS-RPB, the reported approach has compensated for the shortcomings of the traditional nanoparticles production such as complicated procedures and the potential oxidation of Fe0. This study encourages further optimization and development of the high gravity system towards industrial production of NZVI and large-scale NB-containing wastewater treatment.