Hydrophobic Organic Compounds Research Articles

Efficient Catalytic Elimination of Toxic Volatile Organic Compounds via Advanced Oxidation Process Wet Scrubbing with Bifunctional Cobalt Sulfide/Activated Carbon Catalysts.

Advanced oxidation process (AOP) wet scrubber is a powerful and clean technology for organic pollutant treatment but still presents great challenges in removing the highly toxic and hydrophobic volatile organic compounds (VOCs). Herein, we elaborately designed a bifunctional cobalt sulfide (CoS2)/activated carbon (AC) catalyst to activate peroxymonosulfate (PMS) for efficient toxic VOC removal in an AOP wet scrubber. By combining the excellent VOC adsorption capacity of AC with the highly efficient PMS activation activity of CoS2, CoS2/AC can rapidly capture VOCs from the gas phase to proceed with the SO4•- and HO• radical-induced oxidation reaction. More than 90% of aromatic VOCs were removed over a wide pH range (3-11) with low Co ion leaching (0.19 mg/L). The electron-rich sulfur vacancies and low-valence Co species were the main active sites for PMS activation. SO4•- was mainly responsible for the initial oxidation of VOCs, while HO• and O2 acted in the subsequent ring-opening and mineralization processes of intermediates. No gaseous intermediates from VOC oxidation were detected, and the highly toxic liquid intermediates like benzene were also greatly decreased, thus effectively reducing the health toxicity associated with byproduct emissions. This work provided a comprehensive understanding of the deep oxidation of VOCs via AOP wet scrubber, significantly accelerating its application in environmental remediation.

Ongoing Laboratory Performance Study on Chemical Analysis of Hydrophobic and Hydrophilic Compounds in Three Aquatic Passive Samplers.

The quality of chemical analysis is an important aspect of passive sampling-based environmental assessments. The present study reports on a proficiency testing program for the chemical analysis of hydrophobic organic compounds in silicone and low-density polyethylene (LDPE) passive samplers and hydrophilic compounds in polar organic chemical integrative samplers. The median between-laboratory coefficients of variation (CVs) of hydrophobic compound concentrations in the polymer phase were 33% (silicone) and 38% (LDPE), similar to the CVs obtained in four earlier rounds of this program. The median CV over all rounds was 32%. Much higher variabilities were observed for hydrophilic compound concentrations in the sorbent: 50% for the untransformed data and a factor of 1.6 after log transformation. Limiting the data to the best performing laboratories did not result in less variability. Data quality for hydrophilic compounds was only weakly related to the use of structurally identical internal standards and was unrelated to the choice of extraction solvent and extraction time. Standard deviations of the aqueous concentration estimates for hydrophobic compound sampling by the best performing laboratories were 0.21 log units for silicone and 0.27 log units for LDPE (factors of 1.6 to 1.9). The implications are that proficiency testing programs may give more realistic estimates of uncertainties in chemical analysis than within-laboratory quality control programs and that these high uncertainties should be taken into account in environmental assessments.

Direct visualization of pyrene diffusion in polyethylene and polyoxymethylene passive samplers

While passive sampling of ultra-low aqueous concentrations of hydrophobic organic compounds in environmental aqueous media has emerged as a promising analytical technique, there is a lack of good understanding of the fundamental diffusive processes. In this research, we used a fluorophore, pyrene, as a model compound to track diffusion in polymers through absorption and environmental media exchange processes. We directly tracked the penetration of pyrene into polyethylene (PE) and polyoxymethylene (POM) rods during absorption from water by sectioning the rod after different stages of absorption and observing the fluorescence signal through a microscope. Diffusion profiles of pyrene in polymers were simulated by numerical integration of Fickian diffusion. The results indicated that the uptake process in PE is governed by Fick's law and the absorption and desorption kinetics are similar in this polymer. However, the observed uptake profiles of pyrene in POM were non-Fickian and the release kinetics out of POM was slower compared to uptake into the polymer. We show that slower desorption from POM makes corrections for nonequilibrium using performance reference compounds (PRCs) problematic for deployments in water or sediment where there is significant advection. However, for static sediment deployments, the overall kinetics of exchange is controlled by slow transport through sediment and the hysteretic behavior of POM may not preclude the use of PRCs to interpret equilibrium status.

Bioretention Design Modifications Increase the Simulated Capture of Hydrophobic and Hydrophilic Trace Organic Compounds.

Stormwater rapidly moves trace organic contaminants (TrOCs) from the built environment to the aquatic environment. Bioretention cells reduce loadings of some TrOCs, but they struggle with hydrophilic compounds. Herein, we assessed the potential to enhance TrOC removal via changes in bioretention system design by simulating the fate of seven high-priority stormwater TrOCs (e.g., PFOA, 6PPD-quinone, PAHs) with log KOC values between -1.5 and 6.74 in a bioretention cell. We evaluated eight design and management interventions for three illustrative use cases representing a highway, a residential area, and an airport. We suggest two metrics of performance: mass advected to the sewer network, which poses an acute risk to aquatic ecosystems, and total mass advected from the system, which poses a longer-term risk for persistent compounds. The optimized designs for each use case reduced effluent loadings of all but the most polar compound (PFOA) to <5% of influent mass. Our results suggest that having the largest possible system area allowed bioretention systems to provide benefits during larger events, which improved performance for all compounds. To improve performance for the most hydrophilic TrOCs, an amendment like biochar was necessary; field-scale research is needed to confirm this result. Our results showed that changing the design of bioretention systems can allow them to effectively capture TrOCs with a wide range of physicochemical properties, protecting human health and aquatic species from chemical impacts.

Deciphering the seasonal dynamics of microplastic morphotypes and associated co-contaminants along the northwest coast of India

In the present study, the northwest coast of India, bordering the Arabian Sea, was selected to evaluate the microplastic (MP) abundance. This is the first study to emphasize the effects of different seasons on MP distribution. The collected MPs were dried, segregated, and evaluated based on their morphotype, size, color, and polymer type. A total of 1756.6, 7326.6, and 202 particles/kg of sand were estimated in the pre-monsoon, monsoon and post-monsoon seasons, respectively, with a dominance of polypropylene (PP) type of plastic in the pre-monsoon and high-density polyethylene (HDPE) in monsoon and post-monsoon seasons. HDPE and PP collected MPs during the monsoon season were further characterized for associated contaminants. Metal absorbance was detected using SEM-EDX mapping and ICP-MS. The presence of organic compounds (OCs) was analyzed using GC-MS. MPs exhibit distinct associations with metals, among which the HDPE pellet morphotype exhibits a higher range of metal adsorption. Total 61 different OCs were associated with MPs. The HDPE pellets contained the highest amounts of hydrophobic organic compounds. PP pellets were found to contain triglycerides, fatty aldehydes, and alkaloids, along with HOCs. Among morphotypes, pellet forms of MPs were found to adsorb more contaminants. These co-contaminants infiltrate the study area through sewage runoff and shoreline debris deposition, subsequently interacting with MPs. Furthermore, the MP diversity was studied by employing the MP diversity integrated index, which suggests that most of the MP diversity was observed in the pre-monsoon period. The pollution load index employed an MP risk assessment, which presented a low degree of MP contamination. In contrast, the polymer hazard index was calculated as 21650.3 in post-monsoon, placing the area under the extreme danger category. It is evident from the data that the types of MP is more important than their number. Thus, MP morphotypes have importance in the adsorption of co-contaminants.

Development of a polyethyleneimine/poly(N-isopropylacrylamide) semi-IPN hydrogel for use in the temperature-swing adsorption and selective desorption of hydrophobic organic compounds

BackgroundA novel polyethyleneimine/poly(N-isopropylacrylamide) semi-interpenetrating polymer network (PEI/poly(NIPA) semi-IPN) hydrogel was developed as a high-performance adsorbent for use in purifying wastewater containing multiple organic compounds and recovering each organic compound. Thermosensitive poly(NIPA) with a lower critical solution temperature (LCST) of ∼33 °C in water can perform the temperature-swing adsorption, i.e., reversibly adsorb/desorb adsorbates as the temperature varies across the LCST owing to its hydrophilic/hydrophobic transition. In addition, PEI, which is a branched polymer with primary, secondary, and tertiary amine groups, can adsorb acidic adsorbates via acid-base interactions. Thus, the developed hydrogel can adsorb adsorbates via hydrophobic and/or acid-base interactions. MethodsThe PEI/poly(NIPA) semi-IPN hydrogel was prepared by free radical polymerization of NIPA and a cross-linking monomer in an aqueous solution dissolving PEI, and characterized as an adsorbent for hydrophobic organic compounds in aqueous media. FindingsThe removal (water purification) and mutual separation (recovery) of binary components (p-nitrophenol and 4-iodoaniline as model adsorbates) were demonstrated via adsorption at 50°C, followed by two-step desorption at 20°C in water and an aqueous HCl solution. This process was based on the presence or absence of hydrophobic and acid-base interactions.

Determining buffering capacity of polydimethylsiloxane-based passive dosing for hydrophobic organic compounds in large-volume bioassays

Polydimethylsiloxane (PDMS) is the most widely used material for passive dosing. However, the ability of PDMS to maintain constant water concentrations of chemicals in large-volume bioassays was insufficiently investigated. In this study, we proposed a kinetic-based method to determine the buffering capacity of PDMS for maintaining constant water concentrations of hydrophobic organic contaminants (HOCs) in large-volume bioassays. A good correlation between log Kow and PDMS-water partitioning coefficients (log KPW) was observed for HOCs with log Kow values ranging from 3.30 to 7.42. For low-molecular-weight HOCs, volatile loss was identified as the primary cause of unstable water concentrations in passive dosing systems. Slow desorption from PDMS resulted in a reduction of water concentrations for high-molecular-weight HOCs. The volume ratio of PDMS to water (RV) was the key factor controlling buffering capacity. As such, buffering capacity was defined as the minimum RV required to maintain 90% of the initial water concentration and was determined to be 0.0076–0.032 for six representative HOCs. Finally, passive dosing with an RV of 0.014 was validated to effectively maintain water concentrations of phenanthrene in 2-L and 96-h toxicity tests with adult mosquitofish. By determining buffering capacity of PDMS, this study recommended specific RV values for cost-efficient implementation of passive dosing approaches in aquatic toxicology, particularly in large-volume bioassays.

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

Predicting apparent adsorption capacity of sediment-amended activated carbon for hydrophobic organic contaminants using machine learning

In-situ stabilization of hydrophobic organic compounds (HOCs) using activated carbon (AC) is a promising sediment remediation approach. However, predicting HOC adsorption capacity of sediment-amended AC remains a challenge because a prediction model is currently unavailable. Thus, the objective of this study was to develop machine learning models that could predict the apparent adsorption capacity of sediment-amended AC (KAC,apparent) for HOCs. These models were trained using 186 sets of experimental data obtained from the literature. The best-performing model among those employing various model frameworks, machine learning algorithms, and combination of candidate input features excellently predicted logKAC,apparent with a coefficient of determination of 0.94 on the test dataset. Its prediction results and experimental data for KAC,apparent agreed within 0.5 log units with few exceptions. Analysis of feature importance for the machine learning model revealed that KAC,apparent was strongly correlated with the hydrophobicity of HOCs and the particle size of AC, which agreed well with the current knowledge obtained from experimental and mechanistic assessments. On the other hand, correlation of KAC,apparent to sediment characteristics, duration of AC-sediment contact, and AC dose identified in the model disagreed with relevant arguments made in the literature, calling for further assessment in this subject. This study highlights the promising capability of machine learning in predicting adsorption capacity of AC in complex systems. It offers unique insights into the influence of model parameters on KAC,apparent.

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.

High Cleanliness and High Hydrophobic/Hydrophilic Contrast Done by Direct Wafer Bonding for Die-to-Wafer Self-Assembly

Die-to-wafer assembly is a promising technology for 3D-integration in terms of yield. However, it is difficult to combine high placement accuracy and high throughput with a pick and place process. To overcome these issues, self-assembly and collective transfer for die-to-wafer were proposed [1].With the self-assembly technology, direct bonding is used for the assembly and the surface tension of liquid droplets drives the chips and precisely aligns them to predetermined assembly areas on carrier wafers. A good water containment on the bonding site is needed to ensure a precise alignment. It is controlled by two parameters: topographical and hydrophilic/hydrophobic contrast. A step of around 15 µm surrounding the bonding area plays the role of the topographical contrast. The hydrophilic/hydrophobic contrast is obtained by coating an hydrophobic organic compound around the hydrophilic bonding site. Collective transfer can be achieved when dies are simultaneously bonded onto a target wafer covered with bonding sites (see figure 1).The preparation of the target wafer as well as dies is a major topic of interest. As shown in figure 2 the direct bonding site is often defined by lithographic means: step and hydrophobic coating [2]. Extremely cleaned surfaces are required to ensure a good bonding quality. As a consequence, all particles and organic traces must be perfectly removed during the resist stripping step. It is here challenging as the organic resist must be removed while preserving the organic hydrophobic material. Highly aggressive and efficient stripping solutions cannot be used to obtain very clean bonding surfaces and an alternative process had to be developed.We propose an innovative process based on a temporary bonding protection of the bonding site for the hydrophobic coating. A typical flow is presented in figure 2. A standard photolithography and etching process is used to obtain steps at the edges of the bonding site. An efficient stripping based on plasma and wet cleaning yields a surface that is ready for bonding. This surface is bonded with another temporary wafer. The resulting stack is dipped in a solution of hydrophobic material and then dismounted.As a demonstration, 40 target bonding sites were defined onto a 200 mm diameter silicon wafer. First, a 2µm thick oxide layer was deposited. Then, bonding sites were defined by photolithography and etching. The step height was 15 µm and bonding areas 8x8 mm². This wafer was bonded to a temporary carrier. The acoustic picture of the resulting stack is provided in figure 3a): all bonding sites were correctly bonded on the carrier. The stack was then dipped in a fluorinated polymer solution. After dismounting the temporary carrier, the water contact angle of the surface was measured: it was around 10° on the bonding site and 90° on the surrounding area. A SEM image confirmed the presence of the hydrophobic polymer on the surrounding area but also on the sidewalls of steps (figure 3b).In the same way, 10x10 mm² dies with 8x8 mm² bonding sites were fabricated. A collective bonding between the target wafer and the 40 dies was performed: 10 µL droplets were deposited onto each bonding site. 70 % of dies were transferred onto the target wafer. The alignment performance was evaluated with dedicated marks on target and dies: 50 % of die were aligned with a precision below 1 µm. The stack withstood a 2h annealing at 400°C without any defect appearance. These results demonstrate the interest of the new process for the fabrication of high contrasted surfaces for self-assembly bonding while keeping a very high cleanliness of the hydrophilic bonding area.The authors acknowledge financial support from INTEL Corporation, United States[1] T. Fukushima, Proc. Int. Electron Dev. Meet., 2005, pp. 359–362.[2] A. Bond , 2022 IEEE 72nd Electronic Components and Technology Conference (ECTC), San Diego, CA, USA, 2022, pp. 168-176. Figure 1

Selective removal of chlorinated organic compounds from soil flushing emulsions: Adsorbent regeneration with thermal-activated persulfate and surfactant recovery

Hydrophobic organic compounds (HOCs) released into the environment can form nonaqueous phase liquids, contaminating soil and groundwater. Surfactant-enhanced aquifer remediation, followed by extracting a highly contaminated emulsion comprising surfactants and contaminants, is a promising technology for remediating polluted sites. However, the sustainable treatment of the emulsion is crucial. This study presents a two-step method for treating emulsions containing HOCs and surfactants. Firstly, pollutants are selectively adsorbed onto granular activated carbon (GAC) in a column. Secondly, spent GAC is regenerated by oxidizing adsorbed pollutants using persulfate activated at 60 °C. The emulsion was obtained from surfactant-enhanced aquifer remediation at a polluted site with lindane production waste, consisting of E-Mulse® 3 surfactant (12 g L−1) and 28 chlorinated organic compounds (COCs) at a concentration of 9.1 gCOCs L−1. Selective adsorption of COCs was observed since the adsorption kinetic constant was much higher than the E3, being 31.60 and 1.76gGAC−W·mgj−1·h−1 respectively. The adsorption-regeneration cycle was repeated three times. It was found that the GAC adsorbed 90 mgCOCs·gGAC−1 were constant after four cycles (70 % of the COCs adsorption capacity in the first step). The surfactant adsorption decreased by approximately 80 % from 108 to 26 mgE3 gGAC−1 after the third cycle, enabling surfactant recovery from the emulsion. In addition, the remaining amount of persulfate increased from 24 to 39 %, reducing oxidant consumption. Finally, the water effluent obtained after regeneration showed reduced toxicity due to the generation of nontoxic by-products, such as short-chain acids and sulphates. The results obtained proved the GAC-based adsorption/regeneration process was effective and stable over multiple cycles.

Effect of sodium dodecyl sulfate on preferential degradation of naphthalene by thermally activated persulfate: Implications for soil flushing solution reuse

Various flushing solutions that contain hydrophobic organic compounds and surfactants are generated during surfactant-enhanced soil flushing processes. How to effectively remove the target pollutants while minimizing the degradation of surfactants for reuse of the flushing solutions has become a major problem. A series of batch experiments were conducted to investigate the preferential degradation mechanisms of naphthalene by sodium dodecyl sulfate (SDS) as well as the effect of SDS concentration on the degradation efficiency using a competitive kinetic method. In addition, the effects of persulfate (PS) dosage, temperature, and pH on the degradation efficiency of naphthalene were also studied, and a prediction model based on response surface methodology (RSM) was built to optimize the preferential degradation of naphthalene. One-dimensional column flushing experiments were performed to evaluate the feasibility of reusing soil flushing solutions at the predicted PS dosage. Results show that: (i) SDS inhibited naphthalene degradation owing to competitive oxidation and micellar protection, with a decreasing degradation rate constant as SDS concentration increased. However, naphthalene was still degraded by reactive oxygen species (ROS) at a higher rate than SDS, indicating the preferential degradation of naphthalene. When the concentration of SDS increased from 5 to 10 times of critical micelle concentration (CMC; 8.2 mM), the ratio for rate constants of naphthalene to SDS (kNAP/kSDS) decreased significantly from 31.61 to 3.38, illustrating the obvious effect of SDS concentration on preferential degradation of naphthalene; (ii) The formation of single-chambered vesicles with a higher thermodynamic stability was observed at 10 CMC, compared to the spherical micelles formed at 5 CMC. The accessibility of naphthalene to ROS was greatly reduced at 10 CMC, resulting in a significant reduction in kNAP/kSDS value. Moreover, the method in which ROS attacked naphthalene in surfactant micelles varied with SDS concentration, which also impacted the preferential degradation of naphthalene; (iii) Under the optimal PS dosage predicted by the RSM model, a good reusability of SDS was observed in the soil flushing solutions after thermally activated PS oxidation, with a significant reduction on the toxic risk of soil after flushing.

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.

Microbial Biosurfactant: Candida bombicola as a Potential Remediator of Environments Contaminated by Heavy Metals.

Industrial interest in surfactants of microbial origin has intensified recently due to the characteristics of these compounds, such as biodegradability and reduced toxicity, and their efficiency in removing heavy metals and hydrophobic organic compounds from soils and waters. The aim of this study was to produce a biosurfactant using Candida bombicola URM 3712 in a low-cost medium containing 5.0% molasses, 3.0% corn steep liquor and 2.5% residual frying oil for 144 h at 200 rmp. Measurements of engine oil tension and emulsification were made under extreme conditions of temperature (0 °C, 5 °C, 70 °C, 100 °C and 120 °C), pH (2-12) and NaCl concentrations (2-12), demonstrating the stability of the biosurfactant. The isolated biosurfactant was characterized as an anionic molecule with the ability to reduce the surface tension of water from 72 to 29 mN/m, with a critical micellar concentration of 0.5%. The biosurfactant had no toxic effect on vegetable seeds or on Eisenia fetida as a bioindicator. Applications in the removal of heavy metals from contaminated soils under dynamic conditions demonstrated the potential of the crude and isolated biosurfactant in the removal of Fe, Zn and Pb with percentages between 70 and 88%, with the highest removal of Pb being 48%. The highest percentage of removal was obtained using the cell-free metabolic liquid, which was able to remove 48, 71 and 88% of lead, zinc and iron from the soil, respectively. Tests in packed columns also confirmed the biosurfactant's ability to remove Fe, Zn and Pb between 40 and 65%. The removal kinetics demonstrated an increasing percentage, reaching removal of 50, 70 and 85% for Pb, Zn and Fe, respectively, reaching a greater removal efficiency at the end of 24 h. The biosurfactant was also able to significantly reduce the electrical conductivity of solutions containing heavy metals. The biosurfactant produced by Candida bombicola has potential as an adjuvant in industrial processes for remediating soils and effluents polluted by inorganic contaminants.

Evaluation of solvent property of air-water interface based on the fluorescence spectra of 1,2'-dinaphthylamine in the aqueous solution of ultrafine bubbles.

Solvent property of air-water interface was evaluated based on the fluorescence spectra of 1,2'-dinaphthylamine in water containing ultrafine bubbles (average diameter: 103 nm, standard deviation: 38 nm). Among naphthylamine derivatives whose fluorescence spectra were responsive to microscopic hydrophobicity, 1,2'-dinaphthylamine (DN) was selected because its wavelength of the maximum emission (λmax) was significantly dependent on the concentration and microenvironment of the ultrafine bubble. The λmax value of DN in water was 486 nm, while it shifted to shorter wavelength (408nm) in the presence of 1.09 × 109 mL-1 of ultrafine bubbles. The shift of λmax value indicates that DN adsorbs on the surfaces of ultrafine bubbles and exists in hydrophobic region rather than in bulk water. By comparing with the λmax values in different solvents, the surface of ultrafine bubble was found to have similar solvent property to ethyl ether or ethyl acetate that are widely used as extracting solvents for hydrophobic organic compounds.

Genotoxicity of chlorinated hydrophobic organic compounds extracted from a source of drinking water

As precursors of disinfection by-products (DBPs), sediment hydrophobic organic compounds (HPOCs) derived from six reservoirs along the Dongjiang River were chlorinated (Cl-WS) and then fractionated into two polar components (hydrophobic organic compounds (Cl-HOCs) and hydrophilic organic compounds (Cl-HICs)) by solid phase extraction. Based on Caco-2 cell exposure study, the genotoxicity of Cl-WS, Cl-HOCs and Cl-HICs was analyzed by reactive oxygen species (ROS) analysis, comet assay and ethoxyresorufin-O-deethylase assay. Protective effects of antioxidants (catalase, vitamin C and epigallocatechin 3-gallate (EGCG)) on genotoxicity of the chlorinated samples were investigated. The results showed that Cl-WS and its two fractions (Cl-HOCs and Cl-HICs) induced ROS, DNA damage and dioxin-like toxicity (TEQbio), and Cl-HICs were a major contributor to oxidative damage and TEQbio compared with Cl-HOCs. Antioxidants significantly reduced Cl-HOCs- and Cl-HICs-induced ROS, but had insignificant effect on DNA oxidative damage and TEQbio. In addition, EGCG showed higher efficacy in reducing DNA damage induced by Cl-HICs than by Cl-HOCs. To our knowledge, this is the first study to investigate the genotoxicity of Cl-WS and its two polar components in Caco-2 cells, as well as the protective effects of antioxidants on Cl-HOCs and Cl-HICs-induced ROS, DNA damage, and TEQbio. This study provides important toxicity information for water treatment industries in differentiating DBPs of different polarity.

Stabilization of hydrophobic organic compounds in sediment using alkali-activated rice husk biochar: Enhancement of sorption by dissolved organic matter

Polycyclic aromatic hydrocarbons and phthalate esters are hydrophobic organic compounds (HOCs) that pose strong risks to aquatic and sediment ecosystems. The aim of this study was to develop a material for stabilizing (sorbing) HOCs in contaminated sediment. Activated biochar with a high surface area (called RH–NaOH) was successfully synthesized by activating rice husk biochar with an alkali (NaOH). The kinetics of HOC sorption to the RH–NaOH were described well by a three-stage intraparticle diffusion model. The sorption isotherms were adequately described by the Sips sorption model. The presence of dissolved organic matter (DOM) at environmentally relevant concentrations enhanced HOC sorption to the RH–NaOH by as much as a factor of 10, and this was mainly caused by the fulvic-acid- and humic-acid-like fractions of the DOM. The degree of sorption enhancement was predicted by the integrated volume of the fulvic-acid- and humic-acid-like fraction regions of the excitation–emission matrix that was used to characterize the DOM. The polycyclic aromatic hydrocarbon and phthalate ester stabilization efficiencies when 150 d was allowed for equilibration between the sediment and RH–NaOH to be reached were 96.5% and 94.6%, respectively. The stabilization tests indicated that HOC sorption proceeded via multiple stages with different kinetics. These stages were attributed to complex processes involving HOC and DOM sorption and desorption, HOC–DOM interactions, and HOC and HOC–DOM mixture diffusion into pores. The RH–NaOH has great potential for use as a sorbent for stabilizing HOCs in contaminated sediment.

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.