Removal Of M-xylene Research Articles

Effect of toluene on m-xylene removal in a biotrickling filter: Performance, biofilm characteristics, and microbial analysis

Hydrophobic volatile organic compounds (VOCs) pose a challenge to the removal efficiency in biotrickling filters (BTFs). The addition of relatively hydrophilic substances presents a promising approach for enhancing the elimination of hydrophobic VOCs. In this study, toluene was introduced into the BTF system alongside m-xylene, and their mixing ratios were changed to explore the interactions and mechanisms under different conditions. The result showed that the most pronounced synergistic interaction occurred when the mixing concentration ratio of m-xylene and toluene was 2:1. The removal efficiency (RE) of m-xylene increased from 88% to 97%, and the elimination capacity (EC) of m-xylene changed from 64 to 72 g m−3 h−1. Under this condition, there was a notable increase in biomass, extracellular polymeric substance (EPS) content, and relative hydrophobicity. Microbial diversity was enhanced observably with Berkeleyces and Mycobacterium potentially playing a positive role in co-degradation. Meanwhile, microbial metabolic function prediction indicated a significant enhancement in metabolic functions. Therefore, the introduction of relatively hydrophilic VOCs represents an effective strategy for enhancing the removal of hydrophobic VOCs in the BTFs.

Synergistic removal of m-xylene and its corresponding mechanism in a biotrickling filter

Synergism is an important strategy to enhance the bioavailability of pollutants and optimize biotrickling filter (BTF) performance. The synergistic biodegradation of m-xylene with the introduction of toluene was investigated in this study. The packing was diatomaceous earth pellets with a volume of 2411 cm3. The empty bed residence time (EBRT) of the BTF was kept constant at 25 s. The mixing ratios for toluene and m-xylene were 1:1, 1:2, 1:4, and 1:6, corresponding to the inlet loading rate (ILR) of m-xylene from about 36–216 g/m3/h, and the toluene ILR was maintained at about 36 g/m3/h. The biodegradation performance and biofilm characteristics were evaluated under these various mixture compositions. For mixing ratios of 1:1, 1:2, and 1:4, m-xylene was synergistically removed with toluene. The most pronounced synergism occurred when the ratio was 1:2; the average elimination capacity (EC) of m-xylene increased by 12.5%, from 64 g/m3/h to 72 g/m3/h. The presence of toluene promoted the growth of microorganisms and improved the hydrophobicity of the biofilm. In contrast, for the 1:6 toluene and m-xylene mixture, toluene inhibited the degradation of m-xylene. The microbial species composition analysis revealed that Burkholderia and Mycobacterium were correlated with synergistic removal of m-xylene, especially Burkholderia.

Hybrid adaptive neuro-fuzzy inference systems for forecasting benzene, toluene & m-xylene removal from aqueous solutions by HZSM-5 nano-zeolite synthesized from coal fly ash

In this research study, a mesoporous HZSM-5 nano-zeolite (SiO2/Al2O3=40) was hydrothermally synthesized from a type of coal fly ash containing high amounts of muscovite plates. The physicochemical properties of coal fly ash and HZSM-5 were examined by various characterization techniques. The synthesized HZSM-5 was applied in simultaneous removal of benzene (B), toluene (T) and m-xylene (X) from aqueous solutions. The effect of adsorption parameters such as solution pH, adsorbent dosage, contact time, initial concentration and temperature on the removal efficiencies of benzene, toluene and m-xylene were evaluated in batch-scale experiments. The maximum adsorption capacity (qmax) of synthesized HZSM-5 was achieved at optimum conditions; pH=7 and t=90 min qmax;B=9.03<T=9.16<X=9.37 mg/g. The kinetic and isotherm studies revealed that the adsorption data were well fitted with pseudo-first order kinetic and Freundlich isotherm models and the equilibrium adsorption was attained within 90 min. Thermodynamic assessments at three different temperatures of 25, 45 and 65 °C displayed that the uptakes of benzene, toluene and m-xylene onto HZSM-5 were exothermic, feasible and spontaneous at ambient temperature. Furthermore, three hybrid intelligence models comprising adaptive neuro-fuzzy inference system integrated with grid partition, subtractive clustering and fuzzy c-means were employed to estimate the removal efficiencies of benzene, toluene and m-xylene. Statistical analysis clearly proved the acceptable performance of all developed hybrid models. The highest accuracy was obtained by ANFIS-FCM models R2 >0.98 with minimum number of fuzzy rules (nR−FCM=10) which is indicative of the superiority of this method over others. The overall results suggested that the synthesized mesoporous HZSM-5 nano-zeolite could be an efficient and cost-effective adsorbent to eliminate the contamination of benzene, toluene and m-xylene from aqueous solutions.

Enhanced gas-phase photocatalytic removal of aromatics over direct Z-scheme-dictated H3PW12O40/g-C3N4 film-coated optical fibers

Environmentally benign photocatalytic oxidation is one of the most promising approaches to remove volatile, highly toxic and refractory aromatics, and the key points of gas-phase photocatalytic oxidation of aromatics are to develop efficient photocatalysts and design suitable photoreactors. Here, the custom-designed H3PW12O40/g-C3N4 film-coated optical fiber photoreactor is demonstrated for gas-phase simulated sunlight photocatalytic removal of aromatics including benzene, toluene and m-xylene. At relative humidity of 73% and air atmosphere, the H3PW12O40/g-C3N4 film-coated optical fibers with H3PW12O40 doping level of 3.2% exhibit remarkably higher photocatalytic removal efficiency of benzene, toluene and m-xylene than that of the g-C3N4 film, and apparent rate constant of the H3PW12O40/g-C3N4 film for benzene, toluene and m-xylene removal is 2.42, 1.75 and 3.67 times higher than that of g-C3N4 film. The enhanced photocatalytic activity of the H3PW12O40/g-C3N4 film is ascribed to direct Z-scheme-dictated charge carrier migration mechanism, imparting not only superior photogenerated charge carrier separation ability but also undiminished redox capability of the photogenerated electrons and holes; additionally, the increased contact area of catalyst film with the substrates and improved light harvesting ability give rise to the important contribution to gas-phase photocatalytic removal of aromatics. Moreover, the catalyst film exhibits excellent adhesion, stability and recyclability, and the activity loss is negligible after total thirty times’ catalytic runs.

Nonionic surfactant enhanced biodegradation of m-xylene by mixed bacteria and its application in biotrickling filter

ABSTRACTIn this study, m-xylene biodegradation was examined in bacteria-water mixed solution and biotrickling filter (BTF) systems amended with the nonionic surfactant Tween 80. The mixed bacteria were obtained from the activated sludge of a coking plant through a multisubstrate acclimatization process. High-throughput sequencing analysis revealed that Rhodanobacter sp. was the dominant species among the mixed bacteria. In the bacteria-water mixed solution, the bacterial density increased with increasing Tween 80 concentration. Hence, Tween 80 could be utilized as substrate by the mixed bacteria. Tween 80, with concentrations of 50–100 mg L−1, could enhance the bioavailability of m-xylene and consequently improve the degradation efficiency of m-xylene. However, further increasing the initial concentration of Tween 80 would decrease the degradation efficiency of m-xylene. At concentrations exceeding 100 mg L−1, Tween 80 was preferentially degraded by the mixed bacteria over m-xylene. In BTF systems, when the m-xylene inlet concentration was 1200 mg m−3 and the empty bed residence time was 20 sec, the removal efficiency and elimination capacity of BTF1 with Tween 80 addition were at most 20% and 24% higher than those of BTF2 without Tween 80 addition. Overall, the integrated application of the mixed bacteria and surfactant was demonstrated to be a highly effective strategy for m-xylene waste gas treatment.Implications: The integrated application of mixed bacteria and surfactant was demonstrated to be a promising approach for the highly efficient removal of m-xylene. Surfactant can activate mixed bacteria to degrade m-xylene by increasing its bioavailability. Besides, surfactant can be utilized as carbon source by the mixed bacteria so that the growth of mixed bacteria can be promoted. It is expected that the integrated application of both technologies will become more common in future chemical industry.

Equilibrium Dynamics of m-Xylene Removal from Aqueous Solution by Organoclay

In this study, calcium bentonite (Ca-bentonite) clay was beneficiated with sodium carbonate to produce sodium bentonite (Na-B) clay and subsequently modified using hexadecyltrimethylammonium bromide (HDTMABr) to obtain organoclay (OC). Both Na-B and OC were used for the removal of m-xylene from aqueous solution. The vibrational bands of the adsorbents were evaluated using Fourier transform infrared (FTIR) spectroscopy. The sorption result obtained shows the average percentage removal of m-xylene to be 81.10% for OC and 40.20% for Na-B. The monolayer sorption capacity (qm) for the organoclay and the sodium bentonite was found to be 30.30 and 12.99 mg g−1, respectively. The equilibrium data fitted well with the Freundlich isotherm model equation. The FTIR spectra confirm the intercalation of quaternary ammonium compound into the interlayer of the organoclay. This study shows that organoclays have become successful as adsorbents for oil refinery, environmental industries and petrochemical industries in the removal of effluents from the environment.

Performance of activated carbon-impregnated cellulose filters for indoor VOCs and dust control

An activated carbon-impregnated cellulose filter was fabricated, and the capacity to remove dust and volatile organic compounds was evaluated in a laboratory. The adsorption capacities for benzene, toluene, ethyl benzene and m-xylene gases were compared by an adsorption isotherm test conducted as a preliminary test, showing that m-xylene and benzene were the most and least favorable for adsorption onto activated carbon, respectively. Cellulose filters were made with four levels of activated carbon contents, and dust removal was performed with all of the filters showing 99 % and higher efficiencies stable with a small variation during the experiment. Activated carbon content of 5 g in the unit filter area (125 g/m2) was found optimum for benzene, toluene, ethylbenzene and m-xylene removal, as it appeared that higher than 5 g activated carbon content was unnecessary for the improvement of its capacity. With increasing benzene, toluene, ethylbenzene and m-xylene loading, the highest removal rates were determined as 0.33–0.37 mg/cm2 s for as short as 0.0046 s of air filter residence time. The rapid removal was possible because of the high surface area of the activated carbon-impregnated cellulose filter provided by powdered activated carbon, which is distinguished from the granular form in conventional activated carbon towers. As fixed within a cellulose scaffolding structure, the powdered activated carbon performed excellent benzene, toluene, ethylbenzene, and m-xylene adsorption (98.9–100 %), and at the same time, particular matters were removed in average 99.7 % efficiency after being filtered through the cellulose filter sheet.

Enhanced xylene removal by photocatalytic oxidation using fiber-illuminated honeycomb reactor at ppb level

The removal of volatile organic compounds (VOCs) at ppb level is one of the most critical challenges in clean rooms for the semiconductor industry. Photocatalytic oxidation is an innovative and promising technology for ppb-level VOCs degradation. We have designed a fiber-illuminated honeycomb reactor (FIHR) in which the removal efficiency of m-xylene is significantly enhanced to 96.5% as compared to 22.0% for UV irradiation only. The results indicate that photocatalysts not only play the role to substantially oxidize m-xylene, but also alter the chemical properties of xylene under UV illumination. Using the FIHR with Mn-TiO2 photocatalyst not only increased the m-xylene removal efficiency, but also increased the CO2 selectivity. Interestingly, Mn-TiO2 in FIHR also showed a very good reusability, 93% removal efficiency was still achieved in 72-h in reaction. Thus, the FIHR gave very high removal efficiency for xylene at ppb level under room temperature. The FIHR has great potential application in the clean room for the air purification system in the future.

The Potted-Plant Microcosm Substantially Reduces Indoor Air VOC Pollution: II. Laboratory Study

Indoor air-borne loads of volatile organic compounds (VOCs) are usually significantly higher than those outdoors, and chronic exposures can cause health problems. Our previous laboratory studies have shown that the potted-plant microcosm, induced by an initial dose, can eliminate high air-borne VOC concentrations, the primary removal agents being potting-mix microorganisms, selected and maintained in the plant/root-zone microcosm. Our office field-study, reported in the preceding paper, showed that, when total VOC (TVOC) loads in reference offices (0 plants) rose above about 100 ppb, levels were generally reduced by up to 75% (to < 100 ppb) in offices with any one of three planting regimes. The results indicate the induction of the VOC removal mechanism at TVOC levels above a threshold of about 100 ppb. The aims of this laboratory dose-response study were to explore and analyse this response. Over from 5 to 9 days, doses of 0.2, 1.0, 10 and 100 ppm toluene and m-xylene were applied and replenished, singly and as mixtures, to potted-plants of the same two species used in the office study. The results confirmed the induction of the VOC removal response at the lowest test dosage, i.e in the middle of the TVOC range found in the offices, and showed that, with subsequent dosage increments, further stepwise induction occurred, with rate increases of several orders of magnitude. At each dosage, with induction, VOC concentrations could be reduced to below GC detection limits (< 20 ppb) within 24 h. A synergistic interaction was found with the binary mixtures, toluene accelerating m-xylene removal, at least at lower dosages. The results of these two studies together demonstrate that the potted-plant microcosm can provide an effective, self-regulating, sustainable bioremediation or phytoremediation system for VOC pollution in indoor air.

Halide acid pretreatments of photocatalysts for oxidation of aromatic air contaminants: rate enhancement, rate inhibition, and a thermodynamic rationale

The effects of chlorine radical generation during the photocatalytic oxidation of aromatic contaminants in air can be significant. Previous studies have shown that cofeeding chlorinated olefins (TCE, PCE) may increase the removal of branched aromatics (toluene, xylenes), presumably by initiating chlorine radical chain reactions. Hydrochloric acid catalyst pretreatments produce a similar enhancement of aromatic conversions. However, both approaches were ineffective for rate enhancement toward benzene, while hydrobromic and hydriodic acid pretreatments diminished the photocatalytic oxidation of both benzene and toluene. The present study broadens this halide acid inquiry to include hydrofluoric acid catalyst pretreatments and to examine halide acid influences on the removal of m-xylene as well. Only HCl pretreatments enhanced activity, and only for the branched aromatics (toluene and m-xylene). These results appear consistent with a thermodynamic analysis proposed here, which indicates that (1) fluorine radical generation is not energetically feasible under the conditions considered, (2) bromine and iodine radical generation is energetically feasible, but the radicals are insufficiently reactive to initiate the degradation of aromatics, and (3) chlorine radicals are predicted to be sufficiently energetic to abstract hydrogen from the methyl groups of branched aromatics, but not from the more strongly bound hydrogen atoms on the aromatic ring. These calculations are all in accord with our experimental results for the photocatalytic oxidation aromatics. The consistency of these thermodynamic arguments is also further support for the presumed halide radical pathway for rate enhancement.