Degradation Of Hydroquinone Research Articles

Incorporation of Hydroquinone in the Synthesis of Bi2Ti2O7-TiO2 Contributes to Higher Efficiency of Hydroquinone Degradation: Preparation, Characterization, and Photocatalytic Mechanism.

In this paper, Bi-doped hydroquinone (HDQ) molecularly imprinted TiO2 (Bi-HDQ-TiO2) with the synthesis of Bi2Ti2O7-TiO2 as the main ingredient was developed. Using HDQ as an imprinted molecule, Bi(NO3)3-5H2O was introduced into the synthesis of Bi-HDQ-TiO2, which revealed that bismuth oxide was protected by HDQ in the temperature range of 0-450 °C, and during the gradual increase of the temperature up to 550 °C, the HDQ eluted completely, then the surrounding TiO2 was nucleated by bismuth oxide and bonded with the bismuth oxide, causing all of them to be transformed into Bi2Ti2O7. The excited electrons of the catalyst could be transported efficiently in various surface interfaces, meanwhile inhibiting the complexation of photogenerated carriers, thereby improving the efficiency of photocatalysis. A degradation efficiency of 96.35% of HDQ was achieved under 30 min UV irradiation, indicating that the candidate material has a promising future application in environmental purification or human health.

Bimetallic nanozyme of Cu–Mn organophyllosilicate with enhanced multi-enzyme mimetic activity for simultaneous degradation of hydroquinone and methylene blue

This work presents a highly effective multi-enzyme like nanozyme with Mn–Cu as the catalytic centers. It was employed for the degradation of methylene blue (MB) mediated by hydroquinone (HQ), resulting in satisfactory co-degradation of MB and HQ.

Fabrication of poly (quinine-co-itaconic acid) incorporated reduced graphene oxide nanocomposite and its application for electrochemical sensing and photocatalysis of hydroquinone.

In this work, we report the synthesis of poly (quinine-co-itaconic acid) incorporated graphene oxide composite that is electro-active and photo-active simultaneously. The poly (quinine-co-itaconic acid)@rGO composite was successfully utilized for electrochemical detection and photocatalytic degradation of hydroquinone (HQ). HQ is recognized as an environmental pollutant because of its high toxicity to human health even at low concentrations. The synthesized composite was characterized using different characterization techniques i.e. Fourier Transform Infrared Spectroscopy (FTIR), Energy Dispersive X-ray Spectroscopy (EDX), Scanning Electron Microscopy (SEM), X-ray Diffractometry (XRD), Brunauer-Emmett-Teller (BET) and zeta potential. The characterization studies revealed the net negative surface charge of -17.6 mV for poly (quinine-co-itaconic acid)@rGO composite that confirms its stability. Moreover, the XRD and FTIR studies confirmed the fabrication of poly (quinine-co-itaconic acid)@rGO composite. The electrochemical properties of synthesized composite were determined via cyclic voltammetry and electrochemical impedance spectroscopy which showed high conductivity and charge transfer kinetics. Under optimized condition, the sensor showed excellent response for hydroquinone i.e. potential window from -0.6 to 0.6 V at scan rate 50 mV s-1 and borate buffer of pH 8 as supporting electrolyte. The developed method was comprehensively validated and found linear between 0.1 to 40 μM of HQ, with limit of detection 0.03 μM and limit of quantification 0.1 μM, respectively. The real water and personal care products samples were used to check the applicability of developed sensor and good percent recovery was achieved. The synthesized poly (quinine-co-itaconic acid)@rGO composite was also utilized for photocatalytic degradation of HQ and the degradation efficiency was obtained as 99% with dosage of 0.5 g L-1 under optimized conditions such as solution pH 7, initial concentration of HQ 10 mg L-1, catalyst dosage of 5 mg and irradiation time of 40 min, respectively. The degradation efficiency of poly (quinine-co-itaconic acid)@rGO composite was also evaluated in real water samples from industry and river.

Hydrodynamic cavitation degradation of hydroquinone using swirl-type micro-nano bubble reactor

ABSTRACT This study reports the degradation of hydroquinone using lab-scale hydrodynamic cavitation approach (aswirl-type micro-nano bubble reactor), which is considered a green and effective method. The effects of inlet pressure, gas flow rate, pH and initial hydroquinone concentration on hydroquinone degradation were analysed based on experimental research. After experiments investigation, it was concluded that with pH 7.38, hydroquinone concentration of 50 mg/L, and int pressure of 0.2 MPa, the degradation efficiency of hydroquinone reached 91.25% in wastewater. Furthermore, this study also investigated the degradation effect of hydroquinone wastewater by hydrodynamic cavitation combined with persulfate oxidation (HC + PS). The kinetics of hydroquinone degradation by HC or PS oxidation alone and HC + PS oxidation were also examined. Compared with the degradation method alone, the degradation of hydroquinone by HC + PS was more pronounced, and the enhancement factor was 4.55, which indicates that HC greatly enhances the oxidation capacity of PS. In additon, from viewpoint of energy consumption and operating cost, the synergy of HC + PS (1.05 mM) is also the most promising combination. Based on the detection results of the Gas chromatography-mass spectrometry (GC-MS) the possible degradation pathways of hydroquinone were analysed: under the action of ·OH and the high temperature and pressure by cavitation process, the hydroquinone molecule undergoes dehydrogenation and ring-opening reaction, demethylation and decarboxylation reaction to produce intermediate products, which are finally converted into CO2 and H2O in micro-nano bubble cavitation process.

Bioelectrochemical system for enhancing anaerobic digestion of pharmaceutical-containing domestic wastewater

The unprecedented recent expansion in usage of paracetamol (AAP) has increased the need for suitable wastewater treatment technology. Furthermore, direct interspecies electron transfer promotion (DIET) offers simple and efficient approach for enhancing anaerobic digestion (AD). In this work, using AAP-containing domestic wastewater as feed, control AD reactor (RC) was operated, besides three DIET-promoted AD reactors (REV, RMC and REVMC, referring to electrical voltage “EV”-applied, nFe3O4-multiwall carbon nanotube (MCNT)-supplemented, and “EV applied + MCNT supplemented” reactor, respectively). Maximal treatable organic loading rates by RC, REV, RMC and REVMC were 3.9, 3.9, 7.8 and 15.6 g COD/L/d, corresponding to AAP loading rate of 26, 78, 156 and 312 μg/L/d, respectively. Methane production rate generated by RC, REV, RMC and REVMC reached 0.80 ± 0.01, 0.86 ± 0.04, 1.40 ± 0.07, and 3.01 ± 0.17 L/L/d, respectively. AAP expectedly followed hydroquinone degradation pathway, causing AD failure by acetate accumulation. However, this performance deterioration could be mitigated by DIET-promoted microbes with higher methanogenic activity and advanced electric conductivity. Economic evaluation revealed the favourability of MCNT addition over EV application, since payback periods for RC, REV, RMC and REVMC were 6.2, 7.7, 4.2 and 5.0 yr, respectively.

Preparation of a novel Ti/TNAs/PbO2-PVDF-Er2O3 anode by Ti3+ self-doping TNAs and its electrocatalytic performance for hydroquinone degradation

A new type of Ti/TNAs/PbO2-PVDF-Er2O3 electrode was prepared in this research via composite electrodeposition method with Ti3+ self-doped modified titanium dioxide nanotubes arrays (TNAs) as the intermediate layer, and co-deposition of PVDF and rare earth Er (Ⅲ) into PbO2, which is expected to be used for efficient degradation of hydroquinone (HQ) wastewater. The research results indicate that the Ti/TNAs/PbO2-PVDF-Er2O3 electrode is composed of more compact β-PbO2, possesses the largest hydrophobicity (97.8°) among the series electrodes. Additionally, the electrode exhibits remarkable electrocatalytic performance with the largest oxygen evolution potential (2.012 V), the largest electrochemical active surface area (ECSA), and the smallest electron transfer resistance (1.054 Ω·cm2). Furthermore, the Ti/TNAs/PbO2-PVDF-Er2O3 electrode is used for the degradation of HQ, and the experiments results reveal that the degradation process is mainly controlled by the indirectly oxidation of ·OH generated on the surface of the electrode, which is presumed to be oxidized to benzoquinone and various fatty acids by ·OH in combination with GC-MS, and finally mineralized to CO2 and H2O. Meanwhile, under the optimum degradation conditions (pH:7, temperature: 30 ℃, Na2SO4: 0.1 M, current density: 50 mA.cm‐2), the degradation rate is up to 94.5%, demonstrating the best electrocatalytic degradation efficiency.

Bimetallic FeMn-N nanoparticles as nanocatalyst with dual enzyme-mimic activities for simultaneous colorimetric detection and degradation of hydroquinone

The transition element based N-doped carbon nanoparticles (NPs) with high catalytic activity and more active centers are regards as nanozymes with great potential for colorimetric detection and environmental degradation. Here, three-dimensional (3D) hierarchically porous of manganese-amplified Fe-N-doped carbon (Fe/Mn-N-C) catalysts with more Fe/Mn-N4 and C-N active groups was synthesized via pyrolysis of manganese(II) acetyllacetonate/ferrocene@ZIF-8 nanocomposites. Owing to its excellent peroxidase-like (POD-like) and superoxide (SOD) mimicking properties, the Fe/Mn-N-C nanozymes were selected to rapid and accurate colorimetric detection of hydroquinone (HQ), and the detection limit was determined as 0.21 μM in range of 0–100 μM. In addition, the rapid degradation of HQ via hydroxyl radical (•OH) and superoxide anion (O2•-) generated between Fe/Mn-N-C nanozymes and H2O2, and the degradation efficiency reached to over 92% under the optimum reaction conditions (pH 4.0, 100 mM H2O2). The reaction mechanisms were systematically explored. The manganese-amplified Fe-N-C single atom nanozyme with excellent enzyme-like activity and chemical stability will propose a feasible way for accurate detection and removal of pollutants in actual production.

Enhanced Direct Electron Transfer Mediated Contaminant Degradation by Fe(IV) Using a Carbon Black-Supported Fe(III)-TAML Suspension Electrode System.

Iron complexes of tetra-amido macrocyclic ligands (Fe-TAML) are recognized to be effective catalysts for the degradation of a wide range of organic contaminants in homogeneous conditions with the high valent Fe(IV) and Fe(V) species generated on activation of the Fe-TAML complex by hydrogen peroxide (H2O2) recognized to be powerful oxidants. Electrochemical activation of Fe-TAML would appear an attractive alternative to H2O2 activation, especially if the Fe-TAML complex could be attached to the anode, as this would enable formation of high valent iron species at the anode and, importantly, retention of the valuable Fe-TAML complex within the reaction system. In this work, we affix Fe-TAML to the surface of carbon black particles and apply this "suspension anode" process to oxidize selected target compounds via generation of high valent iron species. We show that the overpotential for Fe(IV) formation is 0.17 V lower than the potential required to generate Fe(IV) electrochemically in homogeneous solution and also show that the stability of the Fe(IV) species is enhanced considerably compared to the homogeneous Fe-TAML case. Application of the carbon black-supported Fe-TAML suspension anode reactor to degradation of oxalate and hydroquinone with an initial pH value of 3 resulted in oxidation rate constants that were up to three times higher than could be achieved by anodic oxidation in the absence of Fe-TAML and at energy consumptions per order of removal substantially lower than could be achieved by alternate technologies.

Synthesis of dual function Fe3O4@MnO2@HKUST-1 magnetic micromotors for efficient colorimetric detection and degradation of hydroquinone

A novel and simple strategy was applied for designing and fabricating a micromotor-assisted dual-functional platform for sensitive detection and rapid degradation of hydroquinone in water.

Self-propelled Janus magnetic micromotors as peroxidase-like nanozyme for colorimetric detection and removal of hydroquinone

A Janus micromotor-assisted dual-function platform through a novel and facile method was designed and fabricated for sensitive detection and rapid degradation of hydroquinone in water.

Degradation of Hydroquinone Coupled with Energy Generation through Microbial Fuel Cells Energized by Organic Waste

Microbial fuel cell (MFC) technology has captured the scientific community’s attention in recent years owing to its ability to directly transform organic waste into electricity through electrochemical processes. Currently, MFC systems faces a number of barriers, with one of the most significant being the lack of organic substrate to provide enough energy for bacterial growth and activity. In the current work, rotten rice was utilized as an organic substrate to boost bacterial activity to produce more energy and break down the organic pollutant hydroquinone in an effort to improve the performance of MFCs. There are only a few studies that considered the waste as an organic substrate and simultaneously degraded the organic pollutant vis-à-vis MFCs. The oxidation of glucose derived from rotten rice generated electrons that were transported to the anode surface and subsequently flowed through an external circuit to the cathode, where they were used to degrade the organic pollutant hydroquinone. The results were consistent with the MFC operation, where the 168-mV voltage was generated over the course of 29 days with a 1000 Ω external resistance. The maximum power and current densities were 1.068 mW/m2 and 123.684 mA/m2, respectively. The hydroquinone degradation was of 68%. For the degradation of organic pollutants and the production of energy, conductive pili-type bacteria such as Lacticaseibacillus, Pediococcus acidilactici and Secundilactobacillus silagincola species were identified during biological characterization. Future recommendations and concluding remarks are also included.

Mechanism of Hydroquinone Oxidation by Hot Plasma Pulsed Radiation

The degradation of hydroquinone in interactions with OH• , HO2 • radicals, nitrous and peroxynitrous acids has been studied. Active species were generated using a corona electric discharge and pulsed radiation from hot plasma of a spark electric discharge. When interacting with hydroxyl radicals, hydroquinone breaks down into low molecular weight products. When interacting with species formed under the action of hot plasma radiation, chain oxidation of hydroquinone to benzoquinone occurs. This process is environmentally friendly and does not require the use of additional catalysts. Products formed under the action of radiation decompose over time.

Comparative study of dihydroxybenzene isomers degradation and bioelectricity generation using CuO as cathodic catalyst in double chambered microbial fuel cell

A double chambered microbial fuel cell (MFC) showed enormous capacity in the simultaneous degradation of synthetic wastewater and dihydroxybenzene isomers (catechol, resorcinol and hydroquinone) and concurrently with bioelectricity generation. Operating parameter such as effect of catalyst on MFC system was evaluated using bare carbon plate and copper (II) oxide (CuO) loaded carbon plate as cathodes, respectively, in terms of chemical oxygen demand (COD) and dihydroxybenzene isomers removal efficiency, maximum voltage output and power density. Results revealed that the application of CuO loaded carbon plate was more effective in the COD removal of synthetic wastewater in the anodic chamber and degradation of dihydroxybenzene isomers in the cathodic chamber. Compared with the bare carbon plate as cathode, the COD removal efficiency of synthetic wastewater, removal rate of dihydroxybenzene isomers and maximum voltage output increased 20, 100 and 31 %, respectively, when CuO was applied as cathodic catalyst. Among the dihydroxybenzene isomers, hydroquinone exhibited the best performance in both absence and presence of catalyst in the MFC. The position of the substituent of hydroxyl groups possessed significant effect on the reaction rate, reactivity and conductivity of dihydroxybenzene isomers. Hydroquinone was more susceptible to be degraded than that of catechol and resorcinol due to its lower dipole moment which eased the bond cleavage. The intermediate products of degradation of catechol, resorcinol and hydroquinone were determined using gas chromatograph-mass spectrometer and the degradation pathways were proposed.

Efficient degradation of hydroquinone by a metabolically engineered Pseudarthrobacter sulfonivorans strain.

Pseudarthrobacter sulfonivorans strain Ar51 can degrade crude oil and multi-substituted benzene compounds efficiently at low temperatures. However, it cannot degrade hydroquinone, which is a key intermediate in the degradation of several other compounds of environmental importance, such as 4-nitrophenol, g-hexachlorocyclohexane, 4-hydroxyacetophenone and 4-aminophenol. Here we co-expressed the two subunits of hydroquinone dioxygenase from Sphingomonas sp. strain TTNP3 with different promoters in the strain Ar51. The strain with 2 hdnO promoters exhibited the strongest hydroquinone catabolic activity. However, in the absence of antibiotic selection this ability to degrade hydroquinone was lost due to plasmid instability. Consequently, we constructed a hisD knockout strain, which was unable to synthesise histidine. By introducing the hisD gene onto the plasmid, the ability to degrade hydroquinone in the absence of antibiotic selection was stabilised. In addition, to make the strain more stable for industrial applications, we knocked out the recA gene and integrated the hydroquinone dioxygenase genes at this chromosomal locus. This strain exhibited the strongest activity in catabolizing hydroquinone, up to 470mg/L in 16h without antibiotic selection. In addition, this activity was shown to be stable when the strain has cultured in medium without antibiotic selection after 20 passages.

Eu/GO/PbO2 composite based anode for highly efficient electrochemical oxidation of hydroquinone

Herein, a novel europium/graphene oxide/lead oxide (Eu/GO/PbO2) composite based anode with excellent electrocatalytic performance towards degradation of hydroquinone was prepared by a facile co-electrodeposition method. The composition and micromorphology of the anode was investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) and the results confirmed that europium (Eu) and graphene oxide (GO) were successfully composited with PbO2 and a more compact structure was obtained, which was conductive to enhancing the corrosion resistance of the electrode. Besides, electrochemical measurements indicated that Eu/GO/PbO2 electrode possessed longer service lifetime (87 h), higher oxygen evolution potential (2.64 V), and lower charge transfer resistance (41.08 Ω) than GO/PbO2 and pure PbO2 electrode. The promoted electrocatalytic activity of Eu/GO/PbO2 electrode was ascribed to its stronger hydroxyl radical generation ability, more active sites and lower electron transfer resistance. Additionally, effects of initial hydroquinone concentration, applied current density and initial pH value on the degradation performance of Eu/GO/PbO2 anode were systematically investigated. The behind degradation mechanism of hydroquinone by Eu/GO/PbO2 anode was speculated on the basis of the major intermediates identified by high performance liquid chromatography-mass spectrometer (HPLC-MS). Under the continuous attack of free hydroxyl radicals, hydroquinone was finally decontaminated into CO2 and H2O. The present work demonstrated that Eu/GO/PbO2 composite anode exhibited excellent degradation performance towards hydroquinone.

Three-Dimensional Hierarchical HRP-MIL-100(Fe)@TiO2@Fe3O4 Janus Magnetic Micromotor as a Smart Active Platform for Detection and Degradation of Hydroquinone.

A novel multifunctional Janus magnetic micromotor was designed and constructed by using MIL-100(Fe)@TiO2@Fe3O4 multicore-shells modified with horseradish peroxidase (HRP) as a smart active platform to realize detection and degradation of hydroquinone (HQ). The obtained micromotor showed a unique three-dimensional (3D) hierarchical architecture with highly exposed active sites and could autonomously move at a speed of 140 ± 7.0 μm·s-1 by O2 bubbles generated from the catalytic decomposition of H2O2 fuel. Benefiting from the combination of active self-propulsive motion, high peroxidase-like activity, tuned heterojunctions with matching band structures, and a 3D hierarchical structure, an effective platform involving dynamically sensitive detection and quick removal of HQ from water was established by using the multifunctional HRP-integrated MIL-100(Fe)@TiO2@Fe3O4 Janus micromotor. The proposed multifunctional Janus magnetic micromotor had advantages of simple and feasible fabrication, sensitive detection and effective photo-Fenton degradation of HQ in a wide pH range of 4-7, and magnetic recycling, revealing potential for environmental remediation applications.

Bacterial diversity evolution process based on physicochemical characteristics of sludge treating hydroquinone during acclimation.

Hydroquinone is one of the main pollutants in coal-gasification wastewater, which is biologically toxic and difficult to remove. The aerobic biodegradation rate, organic toxicity, and microbial community structure at different acclimation stages of degradation of hydroquinone by activated sludge were investigated. In each acclimation cycle, the removal of hydroquinone reached 100% after 5 days, indicating that high-concentration hydroquinone in the activated sludge could be completely biodegraded. When the microbial flora was inhibited by the influent hydroquinone, the enzyme system experienced stress conditions and led to the secretion of secondary metabolites, extracellular protein of 5-10 kDa mainly contributing to the sludge organic toxicity. Microbial diversity analysis showed that with the increase of the concentration of hydroquinone, β-Proteus bacteria such as Azoarcus and Dechloromonas gradually accumulated, which improved the removal of hydroquinone with aerobic activated sludge in the sequencing batch reactor (SBR) system. As the inhibition degree exceeded the appropriate tolerance range of microorganisms, bacteria would secrete much more secondary metabolites, and the organic toxicity of sludge would reach a relatively high level.

Eco-friendly synthesis of g-carbon nitride coated graphene nanocomposites for superior visible photodegradation of hydroquinone: Physicochemical mechanisms and photo-Fenton effect

C3N4 coated graphene core–shell nanoparticles (g-C3N4@G) nanosheets are prepared via the combustion method to highlight their photocatalytic enhancement importance. The structural properties of g-C3N4@G samples have been defined by X-ray diffraction (XRD) and Scanning electron microscope (SEM). Diffused reflectance and its related direct and indirect optical bandgap have been studied. g-C3N4@G nanosamples were subjected to hydroquinone (HQ) photodegradation. It is observing the visible light absorption improvement until reaching the maximum at CNG-6 with 99.7 % degradation. Coating facilitates the electron-hole separation via the g-C3N4@G junction, causing more O2–, ·OH, and holes for encouraging hydroquinone degradation. Both the H2O2 and Fe2+-ion improve the photodegradation of hydroquinone in the absence and presence of g-C3N4@G. Eco-friendly g-C3N4@G are promising photocatalytic materials for the visible degradation of hydroquinone as waste from companies and laboratories. Such a low-cost photocatalyst, visible light-harvesting, would open doors for extensive applications in environmental protection.

Enhancement of laccase production from a newly isolated Trichoderma harzianum S7113 using submerged fermentation: Optimization of production medium via central composite design and its application for hydroquinone degradation

Trichoderma harzianum S7113 as an efficient fungal isolate for laccase production was identified using the 18S rRNA sequencing. T. harzianum S7113 attained its maximal laccase production level on the 14th day of static incubation at 28 °C and pH 5.0 using the inoculum size of 5 discs (14 mm), according to the one factor per time (OFT) method. The most appropriate carbon, organic and inorganic nitrogen sources to promote maximal laccase synthesis were glucose (15 g/L), beef extract (5 g/L), and ammonium chloride (4 g/L), respectively. Results of Response Surface Methodology (RSM) revealed that glucose, meat extract, and ammonium chloride concentrations of 17.54, 7.17, and 4.36 g/L respectively, at a pH value of 6.74 are the favorite conditions for high titer production. The ANOVA analysis highlighted an excellent match between the actual experimental results and the model predicted laccase production levels. The biodegradation of hydroquinone (HQ) by T. harzianum S7113 laccase was most efficient in the pH range of 5.0 to 6.5. The increase in laccase concentration led to a significant increase in the HQ conversion to get a biodegradation rate of 92 ± 2.6% with a laccase concentration of 0.75 U/mL after 3 h of reaction.

Electrochemical oxidation of hydroquinone using Eu-doped PbO2 electrodes: Electrode characterization, influencing factors and degradation pathways

A novel Eu-doped PbO 2 electrode was successfully prepared for electrochemical oxidation of hydroquinone, which gives promise for treatment of wastewater containing refractory organic pollutants. • Eu-doped PbO 2 anodes were prepared using co-electrodeposition technique. • The incorporation of Eu can enhance the electrochemical activity and stability of PbO 2 electrodes. • Electrocatalytic degradation of hydroquinone was investigated by Eu-doped PbO 2 anodes. • The intermediates were identified and a possible degradation pathway was elucidated. • The Eu-doped electrodes were promising anode materials for pollutants degradation. The Eu-doped PbO 2 electrodes were prepared using co-electrodeposition technique for electrochemical oxidation of hydroquinone. The results of electrochemical measurements, accelerated service lifetime and bulk electrolysis experiments confirmed that Eu-doped PbO 2 electrodes possessed higher oxygen evolution overpotential, stability and acetamiprid removal ratio than pure PbO 2 electrodes and Eu-PbO 2 -3 electrode was considered as the ideal anode. The promoted electrocatalytic activity of Eu-PbO 2 -3 electrode was ascribed to its stronger hydroxyl radical generation ability, more active sites and lower electron transfer resistance. Additionally, the effect of operating parameters, including current density, initial hydroquinone concentration, and pH value, on the electrochemical oxidation of hydroquinone were subjected to systematical investigation. More significantly, the intermediates generated in the degradation process were identified by HPLC-MS and a possible hydroquinone degradation mechanism was proposed accordingly. The degradation pathway can be divided into three stages with the hydroquinone initially attacked by hydroxyl radicals. Finally, all the intermediates were converted to CO 2 and H 2 O. The present work confirmed that Eu-doped electrodes could be potentially applied in removal of refractory organic contaminants from wastewater.