Benzene Removal Efficiency Research Articles

Novel phase transfer catalysis coupled with bifunctional oxidation for enhanced remediation of groundwater polluted with multiple NAPL: Performance and mechanisms

Structural differences among non-aqueous phase liquids (NAPLs) result in varying oxidation rates, limiting mass transfer between NAPLs and oxidants and seriously impairing the effectiveness of remediation via traditional in-situ chemical oxidation. To tackle this challenge, a novel approach is proposed for remediating multi-NAPL-polluted groundwater that leverages phase transfer catalysis (PTC) to enhance heterogeneous mass transfer by transferring oxidants from groundwater to NAPLs. Meanwhile, “oxidation-in-situ activation” is achieved through bifunctional oxidation using permanganate and peroxymonosulfate (PP). The proposed approach is referred to PTC-PP in this study. Herein, trichloroethene (TCE) and benzene serve as a representative multi-NAPL system. Experimental results indicated that PP significantly improved degradation efficiency of benzene in multi-NAPL system by at least 60.8% compared to single-oxidant systems, and further enhancement (17.6%) was achieved when PP was combined with PTC compared to PP alone. Dissolved Mn(II) and MnO2 generated by MnO4− reduction effectively activated peroxymonosulfate in PTC-PP system, with colloidal MnO2 being the most effective activator. Consequently, SO4•−, O2•− and 1O2 were formed in both NAPL and aqueous phases, while •OH was formed in aqueous phase, playing a crucial role in benzene oxidation. In phase transfer process of PTC-PP, the proportion of MnO4− transferred to benzene exceeded that to TCE. This finding illustrated that nondirectional phase transfer of oxidants posed a challenge for simultaneous promotion of TCE and benzene degradation. However, TCE and benzene removal efficiencies were both >75.7% by applying peroxymonosulfate after KMnO4 addition. These findings lay the theoretical groundwork for PTC-PP application in groundwater remediation.

A column study: Impact of redox, substrate composition and exposure order on toluene and benzene biodegradation and microbial communities

Aromatic compounds persist as hazardous contaminants in both aquatic and terrestrial environments, needing rapid and effective remediation strategies. This study evaluated toluene and benzene biodegradation under sulfate and nitrate-reducing conditions in column experiments, utilizing aquifer sediments from a contaminated site. Over a period of 36 weeks, four glass columns were operated simultaneously in an alternating flow-batch regime. Each column received either nitrate or sulfate as an electron acceptor while being exposed to different substrate compositions in varied exposure orders. A redox dependent contaminant removal efficiency was observed, with toluene removal efficiency at 81% under sulfate and 55% under nitrate-reducing conditions, and benzene removal efficiency approximately at 44% and 59%, respectively, within 4–6 weeks. The rapid removal under anaerobic conditions was attributed to the alternating flow-batch regime, allowing biomass growth in batch mode, and applying selection pressure to non-specific biodegraders during flow regime. Toluene removal remained unaffected by benzene's presence but exhibited slight inhibition in the presence of an aromatic mixture composed of BTEX, indene, indane, and naphthalene. Benzene removal efficiency dropped to 8% in the presence of toluene but remained unaffected by the mixture. Pre-exposure to a single compound enhanced breakdown efficiency when further faced with a more complex mixture. Additionally, beta-diversity analysis conducted on the four columns revealed distinct microbial community clustering between sulfate and nitrate-reducing conditions, emphasizing the determining role of redox conditions. Findings of this study can be used to develop more effective pollution cleanup strategies, specifically targeting parameters like redox conditions, substrate interactions, and pollution history, thus improving our ability to mitigate contamination across diverse environments.

In-situ treatment of gaseous benzene in fixed-bed biofilter with polyurethane foam: Functional population response and benzene transformation pathway

Volatile organic compounds emitted from landfills posed adverse effect on health. In this study, gaseous benzene was biologically treated using an in-situ biofilter without air pump. Its performance was investigated and the removal efficiency of benzene reached over 90 %. The decrease in the average benzene concentration was consistent with first-order reaction kinetics. Mycolicibacterium dominated the bacterial consortium (41–57 %) throughout the degradation. Annotation of genes by metagenomic analysis helped to deduce the degradation pathways (benzene degradation, catechol ortho-cleavage and meta-cleavage) and to reveal the contribution of different species to the degradation process. In total, 21 kinds of key genes and 13 enzymes were involved in the three modules of benzene transformation. Mycolicibacter icosiumassiliensis and Sphingobium sp. SCG-1 carried multiple functional genes critically involved in benzene biodegradation. These findings provide technical and theoretical support for the in-situ bioremediation of benzene-contaminated soil and waste gas reduction in landfills.

Performance of a novel up-flow electrocatalytic hydrolysis acidification reactor (UEHAR) coupled with anoxic/oxic system for treating coking wastewater

In this study, the performance of a novel up-flow electrocatalytic hydrolytic acidification reactor (UEHAR) and anoxic/oxic (ANO2/O2) combined system (S2) was compared with that of a traditional anaerobic/anoxic/oxic (ANA/ANO1/O1) system (S1) for treating coking wastewater at different hydraulic retention time (HRT). The effluent non-compliance rates of chemical oxygen demand (COD) of S2 were 45 %, 35 %, 25 % and 55 % lower than S1 with HRT of 94, 76, 65 and 54 h. The removal efficiency of benzene, toluene, ethylbenzene and xylene (BTEX) in S2 was 10.6 ± 2.4 % higher than that in S1. The effluent concentration of volatile phenolic compounds (VPs) in S2 was lower than 0.3 mg/L. The dehydrogenase activity (DHA) and adenosine triphosphate (ATP) of O2 were enhanced by 67.2 ± 26.3 % and 40.6 ± 14.2 % compared with O1, respectively. Moreover, COD was used to reflect the mineralization index of organic matter, and the positive correlation between COD removal rate and microbial activity, VPs, and BTEX was determined. These results indicated that S2 had extraordinary microbial activity, stable pollutant removal ability, and transcendental effluent compliance rate.

Anaerobic and microaerobic biodegradation of benzene: Effect of important intermediates

The effect of important intermediates on the anaerobic and microaerobic benzene biodegradation was investigated. An up-flow anaerobic/microaerobic sludge blanket reactor was operated at a hydraulic retention time (HRT) of 24 h and fed with water contaminated with benzene (∼4.2 mg L−1) and ethanol (1 g COD L−1). Initially, reactor operating parameters such as variation of applied flow rates, microaeration application points, and effluent recirculation were studied to optimize microaeration. Secondly, the interference of benzene degradation intermediates (phenol, benzoate, and toluene) was investigated. The addition of low concentrations of oxygen (0.5–2 mL air min−1) ensured high benzene removals (∼76–86 %), with the best obtained for a flow rate of 1 mL of air min−1, for which there was a d% removal increase compared to the anaerobic stage. Although the contact time between the air bubbles was short, the best application point was close to the feed. Effluent recirculation was necessary to maintain good mass transfer and high benzene removal efficiencies. The loss by stripping was considered negligible, even at the microaerobic stages, proving the biological removal of this compound. Finally, the intermediates added to the contaminated water reduced benzene removal, with benzoate being the compound that most negatively influenced the benzene removal process, even under microaerobic conditions. Therefore, it is a key intermediate in the benzene anaerobic and microaerobic biodegradation process.

A Study on the Gaseous Benzene Removal Based on Adsorption onto the Cost-Effective and Environmentally Friendly Adsorbent.

Removal of benzene is essential for human and environmental health because it has toxic and hazardous properties at various concentrations. Theseneed to be effectively eliminated with carbon-based adsorbents. PASACs, carbon-based adsorbents obtained from using the needles of Pseudotsuga menziesii, were produced by optimized HCl- and H2SO4-impregnated approaches. Regarding physicochemical structure, the optimized PASAC23 and PASAC35 with surface areas of 657 and 581 m2/g and total pore volumes of 0.36 and 0.32 cm3/g showed ideal temperatures of 800 °C. In order to investigate and compare internal benzene removal efficiency, PASAC23 and PASAC35 were studied separately. Initial concentrations were found to range from 5 to 500 mg/m3, and between 25 and 45 °C. The removal rate of benzene by PASAC23 and PASAC35 was 97 and 94% at low concentrations, respectively. While the highest capture amount for PASAC23 and PASAC35 was found to be at 25 °C with 141 and 116 mg/g, the adsorption capacity decreased to 102 and 90 mg/g at 45 °C. The holding capacity decreased between 22.41 and 27.66% due to increasing temperatures. After five cycles of PASAC23 and PASAC35 regeneration, we found that they could remove 62.37 and 58.46% of benzene, respectively. These results confirmed that PASAC23 is a promising environmentally adsorbent for effectively removing benzene with a competitive yield.

Performance and mechanisms of iron/copper-doped zirconium-based catalyst containing hydroxyl radicals for enhanced removal of gaseous benzene.

In the present study, novel copper-doped zirconium-based MOF (UIO-66) and copper-doped iron-based UIO-66 catalysts were prepared by hydrothermal synthesis method to improve the removal performance of gaseous benzene. The characteristics of the catalysts were analyzed by means of XRD, SEM, XPS, BET, and EPR. The copper loading catalyst had high crystallinity and irregular globular. The three kinds of catalysts with different Cu/Fe ratios had regular cubic shape. Compared with the catalyst supported with single copper, the bimetal Cu/Fe modification had a certain adjustment effect on the morphology, which specifically reflected in the uniform size and shape of catalyst particles with better dispersibility. The factors of different metal loading, dose of H2O2, and reaction temperature on benzene removal have been studied. It has been observed that in heterogeneous advanced oxidation removal of benzene, 3-Cu@UIO-66 and Cu1.5/Fe1.5@UIO-66 achieved the highest benzene removal efficiency of 81.2% and 94.6%, respectively. EPR results showed that the increase of Cu loading and different Cu/Fe ratios promoted the yield of hydroxyl radicals, thus promoted the benzene removal efficiency. The efficiency of heterogeneous oxidation removal of benzene first increased and then decreased with the increase of temperature due to H2O2 instability. DFT calculations exhibited that the Feoct-Cu-O site was a more effective activation site than the single Feoct-O site. Dissociative adsorption occurred with the O-O bond of H2O2 cracked, and the formed hydroxyls parallel adsorbed on the benzene surface. The combination of benzene and hydroxyls was strong chemisorption with the torsion angle of benzene ring obviously turned. The work was of great importance for identifying the roles of the novel catalyst for the removal of benzene pollutant from waste gases.

Fabricating core-shell of silane modified nano ZnO; Effects on photocatalytic degradation of benzene in air using acrylic nanocomposite

In this work, ZnO nanoparticles were surface modified using bis-(triethoxysilylpropyl)amine (BTPA) at different silane concentrations and applied as photocatalyst to water based acrylic film to degrade benzene in gaseous phase under UV/Vis lights. The pure and modified nanoparticles were characterized using FTIR, TGA, BET, XRD, XPS, I-V, photocurrent response and photoluminescence analysis. The results showed that the band gap of the nanoparticles decreased from 3.21 to 2.98 eV and the specific surface area increased by silanization at silane stoichiometric concentration (1X). The mechanical properties of the pure and modified ZnO containing acrylic nanocomposites were investigated. The results showed that addition of the modified nanoparticles (at 3 wt%) to the acrylic matrix increased the tensile strength by 197.9 and 123.3% and modulus by about 288.8 and 185.7% compared to the pristine and pure nanoparticle containing acrylic films. It was found that using silanized nanoparticles in acrylic film increased photocatalytic degradation of benzene in gaseous phase by about 20% compared to the pure nano ZnO containing nanocomposite. The benzene removal efficiency of about 97.28 and 85.39% was obtained for the modified acrylic nanocomposites (at 3 wt% photocatalyst loading content) under UV and visible light irradiations, respectively.

RE-NiOx (RE=Ce, Y, La) composite oxides coupled plasma catalysis for benzene oxidation and by-product ozone removal

Plasma-coupled catalysis is a promising volatile organic compounds (VOCs) removal technology because of its interactional principles of plasma decomposition and catalytic oxidation. However, the problem of harmful by-products is still in trouble. A series of rare earth doped RE-NiOx (RE = Ce, Y, La) composite oxides were synthesized by metal organic frameworks (MOFs)-derived method for coupled plasma oxidation of benzene and by-product ozone removal. Compared with plasma alone, the 1%La-NiOx catalyst shows the best enhancement of 50% for benzene conversion with complete removal of a maximum of 800 ppm ozone. The energy consumption for 90% benzene removal efficiency (η90%) is also reduced from 3600 to 1200 J/L. Characterization results of RE-NiOx catalysts indicate that the doping of La causes interaction and synergistic effect between La and Ni, and the surface oxygen and lattice oxygen with defects play crucial roles in benzene oxidation and ozone decomposition, respectively. In addition, the decomposition mechanism of benzene and ozone under plasma is proposed. Plasma is responsible for the indiscriminate bond breaking in benzene and oxygen to form a variety of organic intermediates and ozone, while the La-NiOx catalyst selectively oxidizes the intermediates to COx/H2O and decomposes the ozone into oxygen.

Efficacious removal of benzene and ammonia gases over visible light irradiated activated carbon

Removal efficiencies of benzene and ammonia were studied using as-received commercial activated carbon (AC) at 0%, 30%, and 60% relative humid (RH) conditions with and without visible light irradiation. We showed that light enhanced the removal efficiency of benzene even under nitrogen, and the enhancement effect became more pronounced in the presence of H2O and O2. We also demonstrated that the ammonia removal efficiency can be enhanced by visible light irradiation under optimum humidity conditions. We further suggested more efficient migration of NH3 through the nanoporous channels of AC facilitated by light and water. Fourier-transform infrared (FT-IR) analyses addressed the changes in surface structure of AC caused by oxidizing agents such as OH. radicals created with light irradiation and other reagents.

Performance and neural modeling of a compost-based biofilter treating a gas-phase mixture of benzene and xylene

Biofilter (BF) has been regarded as a versatile gas treatment technology for removing volatile organic compounds (VOCs) from contaminated gas streams. In order for BF to be utilized in the industrial setting, it is essential to conduct research aimed at removing VOC mixtures under different inlet loading conditions, i.e. as a function of the gas flow rate and inlet VOC concentrations. The main aim of this study was to apply artificial neural networks (ANN) and determine the relationship between flow rate (FR), pressure drop (PD), inlet concentration (C), and removal efficiency (RE) in the BF treating gas-phase benzene and xylene mixtures. The ANN model was trained and tested to assess the removal efficiency of benzene (REB) and xylene (REX) under the influence of different FR, PD and C. The model's performance was assessed using a cross-validation method. The REb varied from 20% to >60%, while the REx varied from 10% to 70% during the different experimental phases of BF operation. The causal index (CI) technique was used to determine the sensitivity of the input parameters on the output variables. The ANN model with a topology of 4-4-2 performed the best in terms of predicting the RE profiles of both the pollutants. Furthermore, the effect was more pronounced for xylene because an increase in the benzene concentration reduced xylene removal (CI = −25.7170) more severely than benzene removal. An increase in the xylene concentration had a marginally positive effect on the benzene removal (CI = +0.1178).

Morphology-modulated rambutan-like hollow NiO catalyst for plasma-coupled benzene removal: Enriched O species and synergistic effects

While catalyst morphology plays an essential role in traditional thermal catalysis, the specific effects in plasma catalysis deserve further in-depth study. In the present study, hollow NiO nanospheres with a rambutan-like structure were successfully prepared by MOFs-derived method involving morphology modulation, and employed for the in-plasma catalytic oxidation of benzene. The results show an enhancement of 60 % for benzene removal, while CO2 selectivity was increased by 20 %. The energy consumption for 95 % benzene removal efficiency (RE95%) was also reduced from 3600 J/L to 1100 J/L. Specifically, the hollow spherical shell structure is more abundant in surface oxygen species, including chemisorbed oxygen and surface lattice oxygen, which can be activated by plasma; the hollow structure also modulates the plasma discharge by shielding effect. The plasma field in turn also excites the oxidation activity of NiO, thus achieving the synergistic effect. In addition, a more comprehensive benzene decomposition pathway is proposed by analysis of the gaseous and non-gaseous intermediates (tar), where the plasma non-selectively breaks the chemical bonds of reactants and the catalyst selectively oxidizes the organic intermediates to CO2, and they promote each other to achieve synergistic effects.

Catalytic degradation of benzene over non-thermal plasma coupled Co-Ni binary metal oxide nanosheet catalysts

Non-thermal plasma (NTP) has been demonstrated as one of the promising technologies that can degrade volatile organic compounds (VOCs) under ambient condition. However, one of the key challenges of VOCs degradation in NTP is its relatively low mineralization rate, which needs to be addressed by introducing catalysts. Therefore, the design and optimization of catalysts have become the focus of NTP coupling catalysis research. In this work, a series of two-dimensional nanosheet Co-Ni metal oxides were synthesized by microwave method and investigated for the catalytic oxidation of benzene in an NTP-catalysis coupling system. Among them, Co2Ni1Ox achieves 60% carbon dioxide (CO2) selectivity (SCO2) when the benzene removal efficiency (REbenzene) reaches more than 99%, which is a significant enhancement compared with the CO2 selectivity obtained without any catalysts (38%) under the same input power. More intriguingly, this SCO2 is also significantly higher than that of single metal oxides, NiO or Co3O4, which is only around 40%. Such improved performance of this binary metal oxide catalyst is uniquely attributed to the synergistic effects of Co and Ni in Co2Ni1Ox catalyst. The introduction of Co2Ni1Ox was found to promote the generation of acrolein significantly, one of the key intermediates found in NTP alone system reported previously, suggest the benzene ring open reaction is promoted. Compared with monometallic oxides NiO and Co3O4, Co2Ni1Ox also shows higher active oxygen proportion, better oxygen mobility, and stronger low-temperature redox capability. The above factors result in the improved catalytic performance of Co2Ni1Ox in the NTP coupling removal of benzene.

Thermosensitive poly(N-isopropylacrylamide)-grafted magnetic-cored dendrimers for benzene uptake

A series of thermosensitive and magneto-responsive dendrimers was synthesized based on magnetic-cored dendrimers (MCD) and carboxylic end-capped poly(N-isopropylacrylamide) (PNIPAM) to obtain PNIPAM-g-MCD. Thermo-response profiles of the PNIPAM-g-MCD from dynamic light scattering within the temperature range of 25–45 °C indicated that the lower critical solution temperature (LCST) of the PNIPAM-g-MCD was 32 °C. The physical size of the PNIPAM-g-MCD decreased as the temperature increased above the LCST. The initial hydrodynamic size of the PNIPAM-g-MCDs at 25 °C was 298.6 nm and reached 226.4 nm at 45 °C upon heating. Adsorption of benzene onto the PNIPAM-g-MCD at 25 °C was assessed, and the results showed that hydrophobic benzene was included within the internal cavities of lipophilic PNIPAM-g-MCD to maintain a thermodynamically stable state. Entrapment effects of the PNIPAM-g-MCD were confirmed at 45 °C, and the removal efficiency of benzene increased considerably to 50% when benzene was adsorbed, and the entrapment process was added. The shrunken PNIPAM terminal groups aggregated and trapped benzenes within the cavities of PNIPAM-g-MCD to prevent escape into the aqueous solution. Un-trapped benzene was removed through coalescence with PNIPAM-g-MCD because hydrophobic interactions prevailed with increasing temperature. PNIPAM-g-MCD were also able to form emulsions below the LCST and disrupted emulsions above the LCST in oil-water emulsions.

Decomposition of benzene vapour using non-thermal plasmas: The effect of moisture content on eliminating solid residue

This study investigated the effect of power, carrier gases and moisture content on the removal of benzene in dry air and humidified air in a DBD plasma reactor. The influence of plasma power, carrier gases and humidity on benzene conversion and product selectivity were explored. The main decomposition products were CO, CO2, lower hydrocarbons (C1-C5) and solid residue in the reactor. This study reveals that benzene removal efficiency and the selectivity to CO2 increased with power in both dry and humidified air. In contrast, the selectivity to lower hydrocarbons decreased. The most important finding of this study was that the formation of solid residue in the plasma reactor can be removed in humidified air. As the amount of water vapour increased from 0% to 35% at 20 ℃, the benzene removal efficiency and CO2 selectivity increased; O3 decreased from 7.3 ppm to 0.5 ppm; NOx and solid residue were eliminated. These effects are probably due to OH radicals, and the mechanism for the various effects are proposed. The maximum benzene removal efficiency observed was 93.7%, and the maximum selectivity to CO2 was 82.4% (both at a relative humidity of 35% at 20 ℃ and 10 W). This study demonstrated that plasma-assisted benzene remediation operating in a humid condition can overcome the major drawback of plasma-assisted VOC conversion in the air by eliminating the solid residues in the reactor.

Removal of benzene vapor from the air based on novel tantalum metal-organic framework (Ta-MOF) adsorbent by gas flow solid-phase interaction before determination by gas chromatography

‌Benzene has a carcinogenic effect on the human body and adsorption from the air is the best way to control it. By this research, benzene vapor was removed from the air based on a tantalum metal-organic framework (Ta-MOF) by gas flow solid-phase interaction (GF-SPI). Benzene adsorption with Ta-MOF was studied in the static and dynamic systems at room temperature. The benzene concentration was analyzed by gas chromatography equipped with an FID detector (GC-FID). The factors affecting benzene removal efficiency like initial concentration of benzene, amount of adsorbent, exposure time, flow rate, and temperature were studied and optimized. The results showed us, the adsorption capacities range of Ta-MOF for benzene in the static and dynamic system were obtained between 90-160 mg g-1 and 65-135 mg g-1, respectively. Also, the high removal efficiency was achieved by more than 95% at 45°C, 67.5 mg L-1 benzene concentration, 0.5 g of Ta-MOF, and the flow rate of 250 mL min-1 for a dynamic system. By dynamic system, the benzene is generated in the chamber, stored in a bag, and then moved on the surface of Ta-MOF. The GF-SPI method was validated by GC-MS and spiking real samples.

Non-thermal plasma by positive corona glow discharge using nano-structured Cu/CuO coated electrodes for benzene removal from air flow; removal enhancement and energy efficiency improvement

• Benzene removal was about 67% with retention time of 5 s by Cu coating. • Cu coating showed uniform glow discharge along the discharge electrode. • The energy efficiency is increased by Cu-coating. • Glow column discharge was seen in CuO nanoparticle coating. • Benzene mineralization reached over 96% by Cu-coating. Benzene removal was investigated in the positive discharge non-thermal plasma. The wire-tube configuration was used for comparison of the discharge specifications and removal of benzene in three treatment conditions including not-coated stainless steel electrodes (D = 1 mm), Nano-hill Cu-coated stainless steel electrodes, and CuO nanoparticles coated stainless steel electrodes. A thermo-chemical electroless plating process was used for preparation of the electrodes. Comprehensive structural differences were seen between the electrodes and consequently different electrical discharge and pollution removal were observed. The results showed that the Cu was made much uniform coating and caused an obvious uniform discharge along the discharge electrode and the most removal efficiency of benzene was resulted with Cu-coated one up to 66.8 ± 2.8%, wherein the SCO 2 and the energy efficiency ( EE ) were 96.9 ± 0.1% and 1.85 ± 0.06 g/kWh, respectively. Given the results, 27.6% of energy efficiency improvement was obtained by Cu-coated reactor comparing the stainless steel. Also, it showed higher ozone destruction rate as the reaction constant [ k (L/J)] was obtained 2.9 × 10 −3 , 1.2 × 10 −3 and 1.6 × 10 −3 , respectively for Cu, CuO, and not-coated reactor.

Preparation and characterization of In-situ nano Silver/Polyvinyl alcohol membrane for pervaporative separation of benzene from model pyrolysis gasoline

Petroleum industries aim to reduce the carcinogenic benzene (confirmed by International Agency for Research on Cancer, IARC) from gasoline to meet specifications. According to Motor Source Air Toxics (MSAT) and Environmental Protection Agency (EPA), benzene present in gasoline may be around 0.62–1.3 vol%. Pyrolysis gasoline (Py gas) is generally used as an octane improver of gasoline but it generally contains high amount of benzene. Here, we have prepared an in-situ nano silver/polyvinyl alcohol membrane (in-situ nano Ag/PVA) for pervaporative separation of benzene from a model Py gas consisting of benzene (aromatic) and 1-octene (aliphatic). These fabricated membranes are characterized by Fourier transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM) and also by their swelling behaviour. The maximum separation factor and highest flux achieved with the composite membrane are 6.82 at 303 K and 4.05 Kg/m2/h respectively at 343 K. The benzene removal efficiency of this membrane is about 67%.

Enhancing benzene removal by Chlorophytum comosum under simulation microgravity system: Effect of light-dark conditions and indole-3-acetic acid

Air phytoremediation technology has been reported as a high potential technology for indoor air pollution treatment. Since 1996, NASA has supported this technology for application in the international space station. However, changes in plant physiology and hormone levels under microgravity (μG) conditions might affect air phytoremediation efficiency, especially changes of auxin hormone transportation in plants. In this study, the application of Chlorophytum comosum, high benzene removal plant species, to remove 100 ppm gaseous benzene under μG condition was studied. The experiment was operated for three days in a random positioning machine generate 6.44 × 10−4 G within 1 h. The results showed that under μG, benzene removal efficiency by C. comosum was significantly increased, with a remove more than 80% within three days under both 24 h light and dark conditions. In contrast, C. comosum growing under normal gravity (1G) can remove about 75% and 50% benzene under 24 h light and 24 h dark conditions, respectively. Surprisingly, μG conditions seem to maintain open stomata of a plant open under both 24 h light and dark conditions, and this plant will normally have closed stomata in the dark. In this case, shoot auxin hormone in the form of Indole-3-acetic acid was highly increased in the plant growing under μG. This result suggested that under μG, auxin hormone might be accumulated in the shoot part of plant. This auxin accumulation effect of maintaining open plant stomata can enhance benzene phytoremediation efficiency since stomata are the major benzene uptake pathway. Therefore, this study is the first report presenting the possibility of applying air phytoremediation technology under μG conditions.

Decomposition of gas phase benzene under different conditions in atmospheric strong ionization non–thermal plasma

Atmospheric volatile organic compounds (VOCs) from industry and automobiles are posing a serious threat to the environment and human health, and hence efficient control methods are indispensable. This paper presents a laboratory-scale study on the decomposition mechanism for benzene using strong ionization dielectric barrier discharge (DBD) at atmospheric pressure. The specific input energy (SIE), current density, and concentration were studied. The results show that the removal efficiency of benzene increased from 12% to 69% with the increase of SIE from 0.5 to 3.8 kJ/L. The decline in current density by 66.48% and 43.7% for an initial benzene concentration of 300 ppm, was due to increased oxygen content (from 2.4% to 20.9%) and relative humidity (from 18.9% to 90%), respectively, thus electron concentration and consequentially enhancing the removal efficiency over 93%. Further, the beta parameter of the VOC decomposition law decreased from 3.1 kJ/L at 300 ppm to 1.6 kJ/L at 100 ppm. This shows that •O and •OH radicals are key species for the decomposition of benzene and electron dissociation reactions principally control the process. The highest ozone concentration was detected at 5.5 mg/L when no benzene is present, while the main NOx species (NO and NO2) increased with increasing SIE. The Maxwell–Boltzmann electron energy distribution function was solved using the strong ionization discharge reactor (~10 eV), showing that approximately 84.8 % of high-energy electrons possess enough energy to cause the benzene ring cleavage and free radical production. Finally, GCMS and FTIR test results suggested that the byproducts mainly consisted of phenol and substitutions of phenol. The study results show that the strong ionization DBD reactor efficiently removes benzene from polluted air.