Hydrophobic Volatile Organic Compounds Research Articles

Absorption of n-butyl acetate from tannery air emissions by waste vegetable oil/water emulsions

Tanning industries emit a huge quantity of Volatile Organic Compounds (VOCs), including hydrophilic and hydrophobic solvents. In this study, vegetable oil/water emulsions with 2 and 5 vol% of corn oil (O) or waste cooking oil (WCO) were prepared. Their potential as absorbents of n-butyl acetate (BA), in place of water, was investigated to increase the efficiency of tannery wet scrubbers. BA was selected as a representative component of hydrophobic VOC emissions derived from leather finishing processes. Static and dynamic absorption tests were performed with a BA concentration of 500 ppmv (2.6 g/m3) and a flowrate of 3.0 L/min to evaluate Henry’s law constant, absorption efficiency, absorption capacity, and saturation time of the various investigated absorbents. The feasibility of the absorbent regeneration was also studied by hot stripping with nitrogen. The results showed that Henry’s constant of BA in oil/surfactant/water or oil/water emulsions (5 vol% oil), regardless of the oil used, were significantly lower than those in water (3.6 versus 15.9 atm), and BA absorption capacity (0.84 g/L) was four times higher than the value in water. The presence of the surfactant (0.2–0.8 vol%) contributed to improving the oil/water emulsions stability without having a significant effect on BA absorption capacity. Almost complete BA desorption from the saturated emulsions was obtained by flowing hot N2 at 80°C, demonstrating the absorbent regeneration's feasibility followed by recovery and reuse. Therefore, the oil/water emulsions containing 5 vol% of WCO are efficient and sustainable absorbents of BA, with potential use in VOC emission treatment systems.

Enhancing the Biodegradation of Hydrophobic Volatile Organic Compounds: A Study on Microbial Consortia Adaptation and the Role of Surfactants

Enhancing the Biodegradation of Hydrophobic Volatile Organic Compounds: A Study on Microbial Consortia Adaptation and the Role of Surfactants

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.

Absorption of hydrophobic volatile organic compounds in renewable vegetable oils and esterified fatty acids: Determination of gas-liquid partitioning coefficients as a function of temperature

Air scrubbing is an effective technology to treat industrial polluted air loaded with VOCs. Water is the most widely used absorbent liquid, but when hydrophobic pollutants are treated, mass transfer between the gas phase and the liquid phase is limited. Therefore, organic solvents are an attractive option to improve the removal efficiency of hydrophobic VOCs. In this study, four esterified fatty acids (isopropyl isostearate, isopropyl laurate, isopropyl myristate and methyl oleate) and three vegetable oils (corn oil, peanut oil and sunflower oil) were evaluated as suitable absorption liquids for seven hydrophobic VOCs, i.e., toluene, m-xylene, ethylbenzene, butane, pentane, hexane and heptane. In addition, one synthetic silicone oil (polydimethylsiloxane) was used as a reference absorption liquid. Dimensionless gas-liquid partitioning coefficients (KGL, 1.3×10−4 – 2.4×10−2) were determined as a function of temperature (25–50 °C) by an optimized dynamic absorption method (DynAb) using Selected-Ion Flow Tube Mass Spectrometry (SIFT-MS). Our experimental results show that, in all the absorption liquids tested, the lowest KGL coefficients were obtained for m-xylene + ethylbenzene, followed by toluene. Isopropyl myristate was found to be the most efficient liquid to absorb the target VOCs, except for heptane where methyl oleate was better. Knowledge of the KGL coefficients of hydrophobic VOCs in these absorption liquids is crucial for process optimization and modeling. Moreover, the effect of temperature is relevant for industrial applications where KGL temperature dependence relations are often lacking. This study evaluates for the first time the use of three renewable vegetable oils and four esterified fatty acids as pure solvents for the absorption of industrially widely used hydrophobic VOCs, where except for toluene, very little or no research had been carried out.

Biofilm metagenomic characteristics behind high coulombic efficiency for propanethiol deodorization in two-phase partitioning microbial fuel cell

Hydrophobic volatile organic sulfur compounds (VOSCs) are frequently found during sewage treatment, and their effective management is crucial for reducing malodorous complaints. Microbial fuel cells (MFC) are effective for both VOSCs abatement and energy recovery. However, the performance of MFC on VOSCs remains limited by the mass transfer efficiency of MFC in aqueous media. Inspired by two-phase partitioning biotechnology, silicone oil was introduced for the first time into MFC as a non-aqueous phase (NAP) medium to construct two-phase partitioning microbial fuel cell (TPPMFC) and augment the mass transfer of target VOSCs of propanethiol (PT) in the liquid phase. The PT removal efficiency within 32 h increased by 11–20% compared with that of single-phase MFC, and the coulombic efficiency of TPPMFC (11.01%) was 4.32–2.68 times that of single-phase MFC owing to the fact that highly active desulfurization and thiol-degrading bacteria (e.g., Pseudomonas, Achromobacter) were attached to the silicone oil surface, whereas sulfur-oxidizing bacteria (e.g., Thiobacillus, Commonas, Ottowia) were dominant on the anodic biofilm. The outer membrane cytochrome-c content and NADH dehydrogenase activity improved by 4.15 and 3.36 times in the TPPMFC, respectively. The results of metagenomics by KEGG and COG confirmed that the metabolism of PT in TPPMFC was comprehensive, and that the addition of a NAP upregulates the expression of genes related to sulfur metabolism, energy generation, and amino acid synthesis. This finding indicates that the NAP assisted bioelectrochemical systems would be promising to solve mass-transfer restrictions in low solubility contaminates removal.

Effect of inoculum type, packing material and operational conditions on the biofiltration of a mixture of hydrophobic volatile organic compounds in air

The emission of volatile organic compounds (VOCs) into the atmosphere causes negative environmental and health effects. Biofiltration is known to be an efficient and cost-effective treatment technology for the removal of VOCs in waste gas streams. However, little is known on the removal of VOC mixtures and the effect of operational conditions, particularly for hydrophobic VOCs, and on the microbial populations governing the biofiltration process. In this study, we evaluated the effect of inoculum type (acclimated activated sludge (A-AS) versus Rhodococcus erythropolis) and packing material (mixture of compost and wood chips (C + WC) versus expanded perlite) on the removal of a mixture of hydrophobic VOCs (toluene, cyclohexane and hexane) in three biofilters (BFs), i.e., BF1: C + WC and R. erythropolis; BF2: C + WC and A-AS; and BF3: expanded perlite and R. erythropolis. The BFs were operated for 374 days at varying inlet loads (ILs) and empty bed residence times (EBRTs). The results showed that the VOCs were removed in the following order: toluene > cyclohexane > hexane, which corresponds to their air-water partitioning coefficient and thus bioavailability of each VOC. Toluene is the most hydrophilic VOC, while hexane is the most hydrophobic. BF2 outperformed BF1 and BF3 in each operational phase, with average maximum elimination capacities (ECmax) of 21 ± 3 g toluene m−3 h−1 (removal efficiency (RE): 100 %; EBRT: 82 s), 11 ± 2 g cyclohexane m−3 h−1 (RE: 86 ± 6 %; EBRT: 163 s) and 6.2 ± 0.9 g hexane m−3 h−1 (RE: 96 ± 4 %; EBRT: 245 s). Microbial analysis showed that despite having different inocula, the genera Rhodococcus, Mycobacterium and/or Pseudonocardia dominated in all BFs but at different relative abundances. This study provides new insights into the removal of difficult-to-degrade VOC mixtures with limited research to date on biofiltration.

Use saponins to enhance the removal of benzene vapors in a foam bioscrubber system

Surfactants are often used to enhance the efficacy of bioreactors in treating waste air streams containing hydrophobic volatile organic compounds (VOCs). In this study, biosurfactant - saponins was innovatively applied in a self-designed reflux foam bioscrubber (RFB) to remove benzene vapor from waste gas stream. The optimal operating parameters and long-term performance of this saponins enhanced RFB were investigated. The important optimal operational conditions are as follows: saponins concentrations of 40–50 mg/L, defoam liquid reflux rate of 60% and pH range of 6.5–7. A 90-day experiment was conducted to evaluate the stability of this system, and benzene removal rates stabilized at around 99.52 ± 0.03% after day 7. Microbial characteristics in this bioreactor were also investigated using 16 S rRNA gene sequencing technologies. The relative abundance of benzene-degrading microbial species, such as Actinobacteria and Saccharibacteria, increased significantly after 90 days of the experiment. Furthermore, the analysis of metabolic pathways revealed the presence of abundant degradation enzymes and diverse degradation pathways in the RFB system. This study is believed to be the first to investigate such metabolic pathways in the context of biotechnological treatment of VOCs. Together, the lessons learned from this study suggest that the application of saponin is a viable enhancement for the reflux foam bioscrubber system in removing hydrophobic VOCs gases.

Synthetic microbial consortia to enhance the biodegradation of compost odor by biotrickling filter

Composting generates odorous gases, including ammonia (NH3), hydrogen sulfide (H2S), and volatile organic compounds (VOCs). The Biological Trickling Filter (BTF) is effective for odor treatment, but it may have limitations with hydrophobic VOCs. In this study, a strain of Bacillus subtilis with ammonia-reducing ability, a strain of Bacillus cereus with desulfurization ability and a strain of Schizophyllum commune with the ability to degrade dimethyl disulfide were isolated and screened. The three strains were combined to create synthetic microbial consortia for enhancing odor treatment in the BTF. Compared to the activated sludge control, the BTF with synthetic microbial consortia removed 92.43% ammonia, 92.75% hydrogen sulfide. Furthermore, it demonstrated a significant improvement in the removal rates of p-methyl mercaptan, methyl sulfide, and dimethyl disulfide. High-throughput sequencing was conducted on the fillers of the synthetic microbial consortia-inoculated BTF to analyze the microbial community composition.

Differences in the Effect of Water on Deep Eutectic Solvents Based on Choline Chloride/Lauric Acid and Choline Chloride/Myristic Acid: Molecular Dynamics Simulations at Three Different Temperatures

AbstractApplication of deep eutectic solvents based on fatty acids in different fields of biological and therapeutic sciences, such as novel hydrophobic Volatile organic compounds (VOC) absorbents, etc. However, industries need knowledge and precise investigation of the structural and dynamic properties of these solvents. In this work, the effect of water on the dynamical and structural properties of the binary mixtures of choline chloride+two types of Fatty acids; Lauric (LUA), and Myristic (MRA) acids have been investigated at T=343 K, 443 K, 543 K. An additional NPT production run of 30 ns was considered for the binary mixtures. In order to understand the effective interactions in the formation of the eutectic mixture based on fatty acid and choline chloride, the combined distribution functions (CDFs) involving the radial distribution functions (RDFs) and the angular distribution functions (ADFs), the hydrogen‐bonding network, and spatial distribution functions (SDFs), interaction energies between species were calculated for the binary mixtures. Also, the dynamical properties of DESs have been evaluated by calculating the mean‐square displacement (MSD), the velocity autocorrelation function (VACF) of the centers of mass of the molecules, and the self‐diffusion coefficient.

Influence of water vapor on the separation of volatile organic compound/nitrogen mixture by polydimethylsiloxane membrane

In the industrial treatment of waste volatile organic compound (VOC) streams by membrane technology, a third impurity, generally, water vapor, coexists in the mixture of VOC and nitrogen or air, and can affect membrane performance and the design of the industrial process. This study focused on the investigation of the effect of water vapor on the separation performance of the separation of VOC/water/nitrogen mixtures by a polydimethylsiloxane (PDMS) membrane. Three types of VOCs: water-miscible ethanol, water-semi-miscible butanol, and water-immiscible cyclohexane, were selected for the study. Different operating parameters including, concentration of the feed VOC, feed temperature, and concentration of the feed water were compared for the separation of binary and ternary VOC/nitrogen mixtures. The interaction between the VOC and water was analyzed to explain the transportation mechanism after analyzing the difference in the membrane performance for the separation of binary and ternary mixtures. The results indicated that the interaction between the VOC (or nitrogen) and water is the key factor affecting membrane performance. Water can promote the permeation of hydrophilic VOC but prevent hydrophobic VOC through the membrane for the separation of ternary VOC/water/nitrogen mixtures. These results will provide fundamental insights for the design of the recovery application process for industrial membrane-based VOCs, and also guidance for the investigation of the separation mechanism in vapor permeation.

Bibliometrics and Knowledge Map Analysis of Research Progress on Biological Treatments for Volatile Organic Compounds

The emission of volatile organic compounds (VOCs) has resulted in increasingly severe harm to the environment and human health. In recent years, biological methods have become the preferred technology for VOC removal due to their environmental friendliness and economic advantages. Based on the theory of bibliometrics, this study analyzed research articles and reviews on biological methods for VOC removal published in the Web of Science Core Collection (WOSCC) database from 1966 to 2021. The knowledge map visualization software CiteSpace was utilized to analyze research progress in different countries, co-citation clustering, co-citation bursts, and keyword clustering in the literature data. The results indicated that early research on VOC biological treatment focused on the removal of odorous gases and single components of volatile organic waste gases. Subsequently, benzene contents (BTEX), hydrophobic VOCs, and multi-component VOCs have gradually become the focus of research. In recent years, improving VOC removal efficiency by studying packing materials and microbial communities has become an important research topic both domestically and internationally. Future research should focus on continuously improving the performance of reactors, developing novel reactors, and investigating technologies for treating complex and recalcitrant VOCs.

Efficient biodechlorination at the Fe3O4-based silicone powder modified chlorobenzene-affinity anode

The treatment of chlorinated volatile organic compounds faces challenges of secondary pollution and less-efficiency due to the substitution of chlorine. Microbial fuel cells (MFCs) provide a promising opportunity for its abatement. In this study, a novel Fe3O4 nanoparticles and silicone-based powder (SP) were integrated and immobilized on carbon felt (CF+Fe3O4@SP), which was further used as anode in the chlorobenzene (CB) powered MFC. Owing to the cooperation between SP and Fe3O4, the anode exhibited excellent performance for both biodechlorination and power generation. The results indicated that the CF+Fe3O4@SP anode loaded MFC achieved 98.5% removal of 200 mg/L CB within 28 h, and the maximum power density was 675.9 mW/m3, which was a 45.6% increase compared to that of the bare CF anode. Microbial community analysis indicated that the genera Comamonadaceae, Pandoraea, Obscuribacteraceae, and Truepera were dominated, especially, the Comamonadaceae and Obscuribacteraceae showed outstanding affinity for Fe3O4 and SP, respectively. Moreover, the proportion of live bacteria, secretion of extracellular polymer substances, and protein content in the extracellular polymer substances were significantly increased by modifying Fe3O4@SP onto the carbon-based anode. Thus, this study provides new insights into the development of MFCs for refractory and hydrophobic volatile organic compounds removal.

Effect of nitrogen source and spray conditions on the integral biotrickling filter operation for hydrophobic volatile organic compounds

A nutrient solution containing major and trace elements plays a crucial role in biotrickling filter (BTF) operation in practical applications. This study conducted a series of experiments on the BTF packed with integral filters using two types of nitrogen sources under different spray conditions. The rapid start-up was observed in the BTF feeding with ammonium tartrate-N (AT-N) nutrient solution. Heterotrophic nitrification and denitrification were observed by monitoring the concentration of ammonia-N, nitrite-N, nitrate-N, PO43− and SO42− in the nutrient solution. The BTF performance under two different types of the nutrient solutions were detected up to ∼90% at the inlet toluene concentration of 300–700 mg∙m−3. The BTF packed with integral filters exhibited the stable performance with the change of nitrogen source and could be steadily operated at a wide pH range of 5.5–8.5. To illustrate the effect of the two types of nitrogen sources on the biofilm, metagenomic sequencing was used to assess the microbial diversity and functional genes of biofilm on the integral filters. The results showed that the application of AT-N nutrient solution increased the functional genes of denitrification in the microorganisms on the filters. Furthermore, the more stable performance of BTF was achieved by using the AT-N nutrient solutions, which might be beneficial to the long-term operation of BTF packed with honeycomb integral packing.

Enhanced removal of mixed VOCs with different hydrophobicities by Tween 20 in a biotrickling filter: Kinetic analysis and biofilm characteristics

Mass transfer limitation usually causes the poor performance of biotrickling filters (BTFs) for the treatment of hydrophobic volatile organic compounds (VOCs) during long-term operation. In this study, two identical lab-scale BTFs were established to remove a mixture of n-hexane and dichloromethane (DCM) gases using non-ionic surfactant Tween 20 by Pseudomonas mendocina NX-1 and Methylobacterium rhodesianum H13. A low pressure drop (≤110 Pa) and a rapid biomass accumulation (17.1 mg g−1) were observed in the presence of Tween 20 during the startup period (30 d). The removal efficiency (RE) of n-hexane was enhanced by 15.0%− 20.5% while DCM was completely removed with the inlet concentration (IC) of 300 mg·m−3 at different empty bed residence times in the Tween 20 added BTF. The viable cells and the relative hydrophobicity of the biofilm were increased under the action of Tween 20, which facilitated the mass transfer and enhanced the metabolic utilization of pollutants by microbes. Besides, Tween 20 addition enhanced the biofilm formation processes including the increased extracellular polymeric substance (EPS) secretion, biofilm roughness and biofilm adhesion. The kinetic model simulated the removal performance of the BTF with Tween 20 for the mixed hydrophobic VOCs, and the goodness-of-fit was above 0.9.

Interactive effects of dual short-chain n-alkanes on removal performances and microbial responses of biotrickling filters

Enhanced biotrickling filtration at the presence of surfactants could be competitive in treatment of waste gas streams polluted by hydrophobic volatile organic compounds (VOCs) such as light hydrocarbons, while few such reports are available. Herein, biotrickling filters (BTFs) were applied to investigate the removal performances for binary-component n-alkanes (n ≤ 6) at the presence of sodium dodecyl benzene sulfonate (SDBS), and the microbial responses were also examined. Interestingly, results showed that the existence of shorter chain n-alkanes promoted the removal of longer chain n-alkanes, as the elimination capacities (EC) of BTF for n-hexane increased by 44 ± 1.2 % when there was methane in incoming gas stream. While the presence of longer chain n-alkanes antagonistically affected shorter chain n-alkane removal, as EC for methane decreased by 65 ± 8.1 % at the presence of n-hexane. Additionally, the presence of SDBS improved the mixed n-alkane removal. EC of the BTF with 15 mg/L SDBS for mixed propane and n-hexane reached 55 ± 1.4 and 31 ± 0.5 g/m3·h respectively, which increased by 90 ± 4.6 % and 47 ± 0.9 % compared with those without SDBS. The richness of Bacillus and Sporosarcina was improved in the BTF fed with SDBS. Moreover, the presence of SDBS improved the content of hydrophobic proteins and the activity of fluorescent substances inextracellular polymeric substances. Also, both the activities of ATPase and the antioxidant capacity of microbial cells exhibited higher than that when SDBS was not added. These data could lead to a better understanding and more reasonable design of biotrickling filtration to remove n-alkanes from waste gas streams of refinery wastewater treatment plants.

Effect of (bio)surfactant type and concentration on the gas-liquid equilibrium partitioning of hydrophobic volatile organic compounds.

The biological removal of hydrophobic volatile organic compounds (VOCs) is limited by their low water solubility and, therefore, low bioavailability. The addition of surfactants is a promising strategy, but to gain understanding and broaden its applicability, its effect on the solubility of hydrophobic VOCs should be investigated. This study evaluates the effect of 2 synthetic surfactants (sodium dodecyl sulfate (SDS) and Tween 80) and 3 biological surfactants (surfactin, rhamnolipid and saponin) on the gas-to-liquid equilibrium partitioning coefficient (KGL) of 7 hydrophobic VOCs at different critical micelle concentrations (CMC). For all VOCs, a decrease in their KGL was observed when a (bio)surfactant was added at 1 and 3 CMC. The highest decrease in KGL (71 - 96%) was observed for all compounds when SDS was added at 3 CMC, whereas the smallest effect was noticed when Tween 80 or surfactin (5.1 - 75%) were added at both concentrations. The results are explained in terms of the (bio)surfactant and VOC physical-chemical properties (e.g. CMC and polarity). This is the first study evaluating the effect of biological surfactants on KGL. These fundamental data are essential to improve the design and modeling of air treatment systems using (bio)surfactants.

Fungal co-culture improves the biodegradation of hydrophobic VOCs gas mixtures in conventional biofilters and biotrickling filters

The present study systematically evaluated the potential of Candida subhashii, Fusarium solani and their consortium for the abatement of n-hexane, trichloroethylene (TCE), toluene and α-pinene in biofilters (BFs) and biotrickling filters (BTFs). Three 3.2 L BFs packed with polyurethane foam and operated at a gas residence time of 77 s with an air mixture of hydrophobic volatile organic compounds (VOCs) were inoculated with C. subhashii, F. solani and a combination of thereof. The systems were also operated under a BTF configuration with a liquid recirculating rate of 2.5 L h-1. Steady state elimination capacities (ECs) of total VOCs of 17.4 ± 0.7 g m−3 h−1 for C. subhashii, 21.2 ± 0.8 g m−3 h−1 for F. solani and 24.4 ± 1.4 g m−3 h−1 for their consortium were recorded in BFs, which increased up to 27.2 ± 1.6 g m−3 h−1, 29.2 ± 1.9 g m−3 h−1, 37.7 ± 3.3 g m−3 h−1 in BTFs. BTFs supported a superior biodegradation performance compared to BF, regardless of the VOCs. Moreover, a more effective VOC biodegradation was observed when C. subhashii and F. solani were grown as a consortium. The microbial analysis conducted revealed that the fungi initially introduced in each BF represented the dominant species by the end of the experiment, with C. subhashii gradually overcoming F. solani in the system inoculated with the fungal consortium.

Performance and mechanism of innovative two-phase partitioning microbial fuel cell for effective propanethiol treatment

A two-phase partitioning microbial fuel cell (TPPMFC) was first time constructed to enhance the mass transfer and removal efficiency of hydrophobic volatile organic sulfur compounds by adding silicone particles as solid non-aqueous phase. The results indicated that the output voltage was gradient increased with the concentration of selected mode propanethiol increased from 100 mg/L to 500 mg/L, but the complete degradation cycle of PT was extended from 12 h to 78 h. The obvious enhancement of microbial fuel cell performance was achieved with 2 % (v/v) 0.4 mm silicone particle. The output voltage increased by 95.6 % ± 12 %, the removal efficiency of 500 mg/L of propanethiol increased from 67 % ± 3 % to 91 % ± 4 % within 24 h, and the maximum power density was 26.23 mW/m2 (72.5 % improvement). The live microorganism on the anodic biofilm was maintained at 95 % after a long-term operation, which was benefited from the fluid shear force caused by agitated anolyte and solid non-aqueous phase. Moreover, the dominant microbial in the TPPMFC were Pseudomonas, sulfate-reduced Aquamicrobium, and Acinetobacter, and the propanethiol was biodegraded by them via two different pathways compared with the traditional ones. Finally, the mechanisms of propanethiol removal and power generation in the TPPMFC were analyzed. It is believed that the results provide insight into the application of two-phase distribution technology for the removal of hydrophobic volatile organic compounds in bioelectrochemical systems.

Newly isolated Enterobacter cloacae sp. HN01 and Klebsiella pneumoniae sp. HN02 collaborate with self-secreted biosurfactant to improve solubility and bioavailability for the biodegradation of hydrophobic and toxic gaseous para-xylene.

The gas-liquid mass transfer rate of hydrophobic volatile organic compounds (VOCs) is the limiting step in a biological treatment system. The present study aimed to utilize self-producing biosurfactants to enhance the bioavailability of hydrophobic gaseous VOCs. Two novel gram-negative rod-shaped bacteria, Enterobacter cloacae strain HN01 and Klebsiella pneumoniae strain HN02 were successfully isolated from sewage sludge by using blood agar and methylene blue agar plates. The two strains can use para-xylene (PX), a hydrophobic VOC model, as the only carbon source for biosurfactant production. Both strains can produce glycolipid biosurfactants, as confirmed by the emulsification index, Nuclear magnetic resonance, and Fourier transform infrared spectroscopy. Results indicated that PX can be completely decomposed at an initial concentration of 15.50mgL-1, pH value of 7.0, and temperature of 30°C within 36h. The Yano model is suitable for the prediction of the growth kinetics of strains over the entire PX concentration range. Gas chromatography/mass spectrometry analysis indicated that PX was converted into four and four intermediates in the presence of the strains HN01 and HN02, respectively, and the possible mechanisms were proposed. The results can be used in purifying industrial hydrophobic gaseous VOCs and improving the bioavailability of VOCs with self-produced biosurfactants.

Simultaneous acidic air biofiltration of toluene and styrene mixture in the presence of rhamnolipids: Performance evaluation and neural model analysis

Biotrickling filters (BTFs) supplied with di-rhamnolipids have been proven to improve biodegradability and bioavailability of singly fed hydrophobic volatile organic compounds (VOCs). However, BTFs performance could be significantly impacted for multi-component mixtures. Herein, the performance of lab-scale fungal-BTF was evaluated for the co-treatment of toluene-styrene gas-phase mixture and compared to previous single runs of both VOCs. For equal ratios of the VOCs, the total removal efficiencies (REtotal) ranged from 89.1% to 74% by varying the total inlet loading rates (LRtotal) from 199.1 to 295.2 g m−3 h−1 at empty bed residence times (EBRT) of 90 and 60 s. Both VOCs were efficiently removed (up to RE 90%) at 199.1 g m−3 h−1 inlet LRtotal and 90 s EBRT. Shortening EBRT to 60 s revealed that styrene degradation was kinetic-limited, whereas toluene was less impacted, indicating styrene inhibition and preferential toluene utilization. Increasing toluene:styrene ratio to 2:1 (v./v.) improved styrene biodegradation and mineralization. Neural network model was developed for the binary mixture which highlighted the interaction effects between input and output variables. The model provided high predictive accuracy (R2-0.993) and revealed significant information towards improving future BTFs design.