Elimination Of Total Organic Carbon Research Articles

Doxycycline Removal by Solar Photo-Fenton on a Pilot-Scale Composite Parabolic Collector (CPC) Reactor

In this study, the solar photo-Fenton (SPF) process was investigated for the degradation of doxycycline (DOX) using a solar compound parabolic collector (CPC) reactor and a borosilicate serpentine tube with an irradiated volume of 1.8 L. The influence of the operating parameters, such as H2O2, Fe2+ dosage, and DOX concentration, was investigated. The optimum H2O2, Fe2+ dosage, and DOX concentration were found to be 4, 0.1, and 0.06 mM, respectively. The results of photo-Fenton experiments fitted the pseudo-first-order kinetic equation (R2 = 0.99). The efficiency of the treatment under optimized conditions was analyzed by an HPLC analysis of the samples, chemical oxygen demand (COD), and total organic carbon (TOC). The results obtained showed that the solar photo-Fenton process achieved a DOX degradation of 95.07%, a COD elimination of 81.43%, and a TOC elimination of 73.05%. The phytotoxicity tests revealed a 73.32% decrease in the germination index of watercress seeds, demonstrating that the SPF process minimizes the toxicity of the chemical and did not have any negative impact on plant growth. Overall, the results of this study suggest that SPF is a promising technology for the removal of doxycycline from wastewater.

Identification of Reactive Oxygen Species and Mechanism on Visible Light-Induced Photosensitized Degradation of Oxytetracycline

This study investigated the photolysis and TiO2-assisted photosensitized degradation of oxytetracycline (OTC) under visible light, the active reactive oxygen species (ROS), and the degradation mechanisms in these two reactions. The results show that the deprotonated OTC could be photolyzed more easily under visible light because of the redshift of its absorption spectrum at high pH values. Due to the TiO2-assisted self-photosensitized degradation of OTC, OTC removal in the visible light/TiO2 system was more efficient with the addition of TiO2, as demonstrated when TiO2 was replaced with insulator SiO2. The study's ROS scavenging experiments show that superoxide radical anion (O2•-) ROS was most responsible for the self-sensitized degradation of OTC in both reactions. OTC degradation under the visible light/TiO2 system was enhanced with increasing TiO2 load, while the elimination of total organic carbon (TOC) was very limited after 5 h of visible light irradiation. Based on the eight identified transformation products found, five potential reaction mechanisms, including hydroxylation, quinonization, decarbonylation, de-methylation, and dehydration, were proposed for the photolytic and TiO2-assisted photosensitized degradation mechanisms of OTC under visible light. This study indicates that OTC can degrade under visible light with or without a semiconductor when conditions are suitable.

Influencing factors of venlafaxine degradation at boron-doped diamond anode

Degradation of the antidepressant venlafaxine by an effective electrocatalytic process, boron-doped diamond (BDD) electrode, was study. The BDD electrode was selected as the anode, and the degradation efficiency of venlafaxine under different influencing factors was systematically investigated. The preliminary grasp of the degradation law of venlafaxine by anodic electro-degradation using BDD electrode was obtained. The experimental results showed that the electrochemical oxidation technology using BDD anode can effectively degrade venlafaxine and remove total organic carbon (TOC) from the solution, complete venlafaxine degradation and TOC elimination could be achieved within 30 and 120 min of BDD oxidation process, respectively, and it has good stability and reusability. Increasing the electrolyte concentration (≤0.1 mol/L) and current density (≤100 mA/cm 2 ) within a certain range could accelerate the degradation of venlafaxine. HCO 3 – and PO 4 3− could inhibit the degradation efficiency of venlafaxine through of competing for free radicals. It is interesting that the presence of Cl − significantly promoted the degradation efficiency of venlafaxine. The results of this study suggest that the Electro-degradation treatment may provide a promising way to treat venlafaxine contaminated water.

Insight into removal TOC and NH4+ from mature landfill leachate using coupled bio-coagulation from Moringa oleifera seeds and ZVI/H2O2 process

In this research, protein was extracted from Moringa oleifera (MO) seeds using protease from Bacillus licheniformis and evaluated for effectiveness as a bio-coagulant to be applied in leachate pretreatment. Leachate samples were collected from part of a closed municipal landfill with total organic carbon (TOC) of 1465 mg/L and ammonium ion (NH4+) of 1245 mg/L. A Fenton-like reaction with a mediated zero-valent iron (ZVI) system was applied to the leachate after coagulation. A response surface methodology (RSM) based on a Box-Behnken design (BBD) was adopted to optimise the Fenton-like process. A quadratic polynomial model was used on the data, with R2 of 0.996 and 0.998 for total organic carbon (TOC) and NH4+ removal, respectively. Influence of three main factors was investigated, namely pH, molar ratio of H2O2/ZVI, and concentration of H2O2 for TOC and NH4+ removal. In optimum conditions of 30 min reaction time, pH = 3, [H2O2] =43.82 mM, molar ratio H2O2/ZVI of 3.89, effectiveness of elimination of TOC and NH4+ was 59.98 % and 98.3 %, respectively. Combined technology of bio-coagulant and Fenton-like reaction was confirmed to be a competent process for treating leachate, with 72.6 % TOC and 98.98 % NH4+ removal. Supposed operation costs for the coupling of treatments can be estimated at 5.67 $/m3. Thus, reductions in NH4+ and mineralization were achieved cost-effectively by combining bio-coagulation with protein extracted from MO seeds and a Fenton-like process activated by ZVI.

Kinetics and mechanism investigation on the destruction of oxytetracycline by UV-254 nm activation of persulfate

Oxytetracycline (OTC), an important broad-spectrum antibiotic, has been detected extensively in various environmental systems, which may have a detrimental impact on ecosystem and human health through the development of drug resistant bacteria and pathogens. In this study, the degradation of OTC was evaluated by UV-254nm activated persulfate (PS). The observed UV fluence based pseudo first-order rate constant (kobs) was found to be the highest at near neutral pH conditions (pH 5.5–8.5). Presence of various natural water constituents had different effects on OTC degradation, with a significant enhancement in the presence of bicarbonate or Cu2+. Limited elimination of total organic carbon (TOC) and PS was observed during the mineralization of OTC. Transformation byproducts in the presence and absence of hydroxyl radical scavenging agent tert-butanol (t-BuOH) were identified using ultra-high definition accurate-mass quadrupole time-of-flight liquid chromatography/mass spectrometer (LC-QTOF/MS). Potential OTC degradation mechanism was subsequently proposed revealing four different reaction pathways by SO4− reaction including hydroxylation (+16Da), demethylation (−14Da), decarbonylation (−28Da) and dehydration (−18Da). This study suggests that UV-254nm/PS is a promising treatment technology for the control of water pollution caused by emerging contaminants such as OTC.

Degradation kinetics and mechanism of oxytetracycline by hydroxyl radical-based advanced oxidation processes

In this study, the degradation kinetics and transformation mechanism of oxytetracycline (OTC) by UV-254nm and UV-254nm/H2O2 were investigated. The removal of OTC increased with increasing initial H2O2 dosage while excess H2O2 acted as an inhibitor of HO. The observed UV fluence based pseudo first-order rate constant of OTC (kobs, cm2mJ−1) decreased while the degradation rate at the initial 13min (µMmin−1) increased with increasing initial OTC concentrations. Presence of different water constituents in the reaction system had a different degree of influence on the degradation efficiency of OTC. Though after 10h irradiation, there was only a limited elimination of total organic carbon (TOC), successful transformation of OTC was demonstrated by the detection of thirty-one degradation byproducts in the UV/H2O2 system. Potential degradation mechanisms for OTC were proposed exhibiting five main pathways, including hydroxylation (+16Da), secondary alcohol oxidation (−2Da), demethylation (−14Da), decarbonylation (−28Da) and dehydration (−18Da). This study indicates that UV-254nm/H2O2 is an effective technology for the removal of OTC from an aquatic environment.

Electro-peroxone treatment of the antidepressant venlafaxine: Operational parameters and mechanism

Degradation of the antidepressant venlafaxine by a novel electrocatalytic ozonation process, electro-peroxone (E-peroxone), was studied. The E-peroxone treatment involves sparging ozone generator effluent (O2 and O3 gas mixture) into an electrolysis reactor that is equipped with a carbon-polytetrafluoroethylene cathode to electrocatalytically transform O2 in the bubbled gas to H2O2. The in-situ generate H2O2 then reacts with the bubbled O3 to yield OH, which can non-selectively degrade organic compounds rapidly in the solution. Thanks to the significant OH production, the E-peroxone treatment greatly enhanced both venlafaxine degradation and total organic carbon (TOC) removal as compared to ozonation and electrolysis alone. Under optimal reaction conditions, complete venlafaxine degradation and TOC elimination could be achieved within 3 and 120min of E-peroxone process, respectively. Based on the by-products (e.g., hydroxylated venlafaxine, phenolics, and carboxylic acids) identified by UPLC–UV and UPLC/Q-TOF-mass spectrometry, plausible reaction pathways were proposed for venlafaxine mineralization by the E-peroxone process. The results of this study suggest that the E-peroxone treatment may provide a promising way to treat venlafaxine contaminated water.

Mechanisms of enhanced total organic carbon elimination from oxalic acid solutions by electro-peroxone process

Electro-peroxone (E-peroxone) is a novel electrocatalytic ozonation process that combines ozonation and electrolysis process to enhance pollutant degradation during water and wastewater treatment. This enhancement has been mainly attributed to several mechanisms that increase O3 transformation to OH in the E-peroxone system, e.g., electro-generation of H2O2 from O2 at a carbon-based cathode and its subsequent peroxone reaction with O3 to OH, electro-reduction of O3 to OH at the cathode, and O3 decomposition to OH at high local pH near the cathode. To get more insight how these mechanisms contribute respectively to the enhancement, this study investigated total organic carbon (TOC) elimination from oxalic acid (OA) solutions by the E-peroxone process. Results show that the E-peroxone process significantly increased TOC elimination rate by 10.2–12.5 times compared with the linear addition of the individual rates of corresponding ozonation and electrolysis process. Kinetic analyses reveal that the electrochemically-driven peroxone reaction is the most important mechanism for the enhanced TOC elimination rate, while the other mechanisms contribute minor to the enhancement by a factor of 1.6–2.5. The results indicate that proper selection of electrodes that can effectively produce H2O2 at the cathode is critical to maximize TOC elimination in the E-peroxone process.

Iron-based catalysts for photocatalytic ozonation of some emerging pollutants of wastewater

A synthetic secondary effluent containing an aqueous mixture of emerging contaminants (ECs) has been treated by photocatalytic ozonation using Fe3+ or Fe3O4 as catalysts and black light lamps as the radiation source. For comparative purposes, ECs have also been treated by ultraviolet radiation (UVA radiation, black light) and ozonation (pH 3 and 7). With the exception of UVA radiation, O3-based processes lead to the total removal of ECs in the mixture. The time taken to achieve complete degradation depends on the oxidation process applied. Ozonation at pH 3 is the most effective technique. The addition of iron based catalysts results in a slight inhibition of the parent compounds degradation rate. However, a positive effect is experienced when measuring the total organic carbon (TOC) and the chemical oxygen demand (COD) removals. Photocatalytic oxidation in the presence of Fe3+ leads to 81% and 88% of TOC and COD elimination, respectively, compared to only 23% and 29% of TOC and COD removals achieved by single ozonation. The RCT concept has been used to predict the theoretical ECs profiles in the homogeneous photocatalytic oxidation process studied. Treated wastewater effluent was toxic to Daphnia magna when Fe3+ was used in photocatalytic ozonation. In this case, toxicity was likely due to the ferryoxalate formed in the process. Single ozonation significantly reduced the toxicity of the treated wastewater.

Degradation kinetics and mechanism of β-lactam antibiotics by the activation of H2O2 and Na2S2O8 under UV-254 nm irradiation

The extensive production and usage of antibiotics have led to an increasing occurrence of antibiotic residuals in various aquatic compartments, presenting a significant threat to both ecosystem and human health. This study investigated the degradation of selected β-lactam antibiotics (penicillins: ampicillin, penicillin V, and piperacillin; cephalosporin: cephalothin) by UV-254nm activated H2O2 and S2O82− photochemical processes. The UV irradiation alone resulted in various degrees of direct photolysis of the antibiotics; while the addition of the oxidants improved significantly the removal efficiency. The steady-state radical concentrations were estimated, revealing a non-negligible contribution of hydroxyl radicals in the UV/S2O82− system. Mineralization of the β-lactams could be achieved at high UV fluence, with a slow formation of SO42− and a much lower elimination of total organic carbon (TOC). The transformation mechanisms were also investigated showing the main reaction pathways of hydroxylation (+16Da) at the aromatic ring and/or the sulfur atom, hydrolysis (+18Da) at the β-lactam ring and decarboxylation (–44Da) for the three penicillins. Oxidation of amine group was also observed for ampicillin. This study suggests that UV/H2O2 and UV/S2O82− advanced oxidation processes (AOPs) are capable of degrading β-lactam antibiotics decreasing consequently the antibiotic activity of treated waters.

New insight about orange II elimination by characterization of spent activated carbon/Fe Fenton-like catalysts

This work is focused on the characterization of heterogeneous Fe-based catalysts supported on activated carbons (ACs) that are used in elimination of the azo-dye orange II (OII) from an aqueous solution. The main goal is to clarify the process of OII removal by analyzing textural and chemical surface properties of the fresh and spent activated carbon and Fenton-like catalysts upon using as adsorbents and/or catalysts. Textural changes were analyzed based on the corresponding N2 adsorption isotherms and the nature of the adsorbed products by TG-DTG and TPD. It was found that OII was adsorbed filling the microporosity without degradation, although interactions between OII molecules and the AC surface groups have been detected. The total organic carbon (TOC) removal is complete in adsorption experiments. In the catalytic experiments using different H2O2 concentrations (in the range 6–24mM) the TOC elimination was never complete and got worse when increasing the H2O2 load. The OII molecules were partially oxidized and the adsorption of these products also leads to some blockage of the porosity; higher blockage and higher TOC removals was noticed after experiments carried out with low H2O2 concentration. The different TOC removal was related to the interactions of the oxidation products with the carbon surface. When using the highest concentration of the oxidant (24mM), the highest biodegradability and the lowest toxicity of the treated solution were reached, corroborating again the different nature of the oxidation by-products formed in each case.

An innovative electrochemical degradation of 1-diazo-2-naphthol-4-sulfonic acid in the presence of Bi2Fe4O9

This paper explores the degradation of a model pollutant, 1-diazo-2-naphthol-4-sulfonic acid (1,2,4-Acid), by an advanced oxidation process that combines electrochemical degradation and Bi2Fe4O9 (BFO) oxidation. Experiments were done using a gas-diffusion cathode to produce in situ hydrogen peroxide by oxygen reduction. Column crystal semiconductor Bi2Fe4O9 was synthesized and used as a novel catalyst in the combined system. It was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Comparative experiment in two separated systems (BFO/H2O2 and BFO/Electrolysis) was conducted to determine the mechanism involved in the process. The effect of operating conditions such as applied current, solution pH, catalyst dosage on the efficacy of the process was investigated. It is shown that 1,2,4-Acid and its products can be effectively degraded by the OH radicals produced by the reaction between BFO and the electro-generated H2O2, which was further being confirmed with the electron spin resonance spin-trapping technique. Hydroxyl radicals generated in the process that led to the complete and rapid elimination of total organic carbon was observed even at low catalyst loadings. In this system, almost a complete removal of COD (89%) was achieved after 200min using 1.0gL−1 of BFO, whereas at the same time, only 39% and 32% of COD was removed by an individual process alone (electrochemical degradation and BFO adsorption, respectively). In this combined system, BFO has the principle role of adsorbing the initial substance on the surface of catalyst and catalyzing the electro-generated H2O2 to form active hydroxyl radicals. The LC-(ESI)-TOF-MS analysis indicated that the mineralization occurred simultaneous with the destruction of naphthalene ring, and 1,2,4-Acid was oxidized to colourless intermediates (mainly phthalic acid, small carbonyl species) and then to carbon dioxide.

Degradation of the biocide 4-chloro-3,5-dimethylphenol in aqueous medium with ozone in combination with ultraviolet irradiation: Operating conditions influence and mechanism

Biocides usually persist during municipal sewage treatment and are subsequently distributed into aquatic environments. To explore the capability of advanced oxidation processes for the rapid removal of biocides, we examined the total organic carbon (TOC) reduction of 4-chloro-3,5-dimethylphenol (PCMX) with a combination of UV/O 3. Moreover, the related important parameters, including the mass transfer coefficient and light utilization efficiency, in PCMX degradation were determined. The UV/O 3 experimental results showed a pronounced synergistic effect, leading to the nearly complete elimination of TOC within 75 min. Thus, the effect of operating variables was investigated as a function of pH, ozone dosage, bulk temperature and the initial concentration of PCMX. The efficiency of PCMX mineralization increased with an increase in ozone dose up to 3.1 g h −1, and a decrease in the initial concentration from 250 to 100 mg L −1. The optimal pH value was 4.0, and the preferred bulk temperature was 20 °C on the basis of the influence of temperature on reaction rate and ozone solubility. The major aromatic intermediates identified by gas chromatography/mass spectrometry were 2,6-dimethylbenzene-1,4-diol, 2,6-dimethylbenzo-1,4-quinone, 2,6-bis(hydroxymethyl)benzo-1,4-quinone, and 2,6-dimethylbenzo-1,4-aldehyde. Quantitative determination of related carboxylic acid and inorganic anions was done by ion chromatography. On the basis of the identified reaction products, a possible degradation pathway for the UV/O 3 oxidation of PCMX in aqueous media is proposed.

Effect of coagulation pretreatment on membrane distillation process for desalination of recirculating cooling water

The objective of this work was to study the performance of coagulation pretreatment and the effect of coagulation pretreatment on membrane distillation (MD) process for desalination of recirculating cooling water (RCW). In this study, RCW was desalinated by MD process after pretreated by coagulation, precision filtration, acidification and degassing. Pre-coagulation of RCW with poly-aluminum chloride (PACl) coagulant improves the elimination of total organic carbon (TOC), total phosphorus (TP) substances. The optimized pH value and PACl dosage were 7 and 15 mg/L, respectively. Compared with MD process without coagulation pretreatment, much slighter MD flux decrease was observed when coagulation pretreatment was employed for desalination of RCW using MD process. Compared with the membrane flux of MD process for the RCW without coagulation pretreatment, about 23% improvement of MD flux was obtained by employing coagulation pretreatment after 30 days operation. The variation of crystal morphology on membrane surface and hydrophobic character of PVDF hollow membranes were investigated. The results show that distorted rhombic magnesium-calcite scale formed on membrane surface when coagulation pretreatment was employed. However, the deposited magnesium-calcite on the membrane surface was loosely packed with particles of much smaller size when RCW without coagulation pretreatment was fed. It is because that the coagulation pretreatment removed most of the natural organic matter (NOM) and antiscalant additives in RCW, which act as an inhibitor to calcium carbonate crystal growth in water. After coagulation pretreatment, bigger crystal deposit formed on membrane surface with the increase in CF of RCW. It was rather difficult for bigger crystal to enter membrane pores and thus the formation of bigger crystal reduced partial wetting of membrane, which enhanced trans-membrane flux. The hydrophobic character of PVDF hollow membranes used in MD process can be easily recovered by chemical rinsing using acid–base solutions. The results indicate that the pretreatment with chemical coagulant, PACl, is effective for the desalination of RCW by MD process.

Problems of drinking water treatment along Ismailia Canal Province, Egypt

The present drinking water purification system in Egypt uses surface water as a raw water supply without a preliminary filtration process. On the other hand, chlorine gas is added as a disinfectant agent in two steps, pre- and post-chlorination. Due to these reasons most of water treatment plants suffer low filtering effectiveness and produce the trihalomethane (THM) species as a chlorination by-product. The Ismailia Canal represents the most distal downstream of the main Nile River. Thus its water contains all the proceeded pollutants discharged into the Nile. In addition, the downstream reaches of the canal act as an agricultural drain during the closing period of the High Dam gates in January and February every year. Moreover, the wide industrial zone along the upstream course of the canal enriches the canal water with high concentrations of heavy metals. The obtained results indicate that the canal gains up to 24.06x10(6) m3 of water from the surrounding shallow aquifer during the closing period of the High Dam gates, while during the rest of the year, the canal acts as an influent stream losing about 99.6x10(6) m3 of its water budget. The reduction of total organic carbon (TOC) and suspended particulate matters (SPMs) should be one of the central goals of any treatment plan to avoid the disinfectants by-products. The combination of sedimentation basins, gravel pre-filtration and slow sand filtration, and underground passage with microbiological oxidation-reduction and adsorption criteria showed good removal of parasites and bacteria and complete elimination of TOC, SPM and heavy metals. Moreover, it reduces the use of disinfectants chemicals and lowers the treatment costs. However, this purification system under the arid climate prevailing in Egypt should be tested and modified prior to application.

Low-temperature combustion of 2,4,6-trichlorophenol in catalytic wet oxidation with nanocasted Mn–Ce-oxide catalyst

The essentially complete mineralization (>95% total organic carbon elimination) of 2,4,6-trichlorophenol by a CWO is reported at a very mild operating conditions (120 °C, P O 2 = 10 bar ), with the use of a nanocasted Mn–Ce-oxide catalyst. This unique catalyst was prepared by fabrication of a thin nanometric layer of Mn–Ce oxides inside the tubular mesopores of SBA-15 silica using internal gelation of corresponding metal chlorides. Crystallization of this oxide layer at 700 °C, followed by removal of silica matrix, yielded a nanostructured mixed-oxide catalyst with surface area up to 316 m 2/g. It demonstrated superior textural, structural, and surface oxygen properties compared with a reference co-precipitated bulk Mn–Ce-oxide catalyst. This is a result of reduction and equalization of the crystal size of both oxide-phases Mn 2O 3 and CeO 2 at the level of 2–3 nm, providing the full availability of their surface for reacting molecules. The performance measured with the novel catalyst indicates a major improvement in the efficient application of CWO processes for complete purification of complex waste streams.

Comparative study of ozone and MnO 2/O 3 effects on the elimination of TOC and COD of raw water at the Valmayor station

Two oxidation processes, O 3 and MnO 2/O 3, for the degradation of precursors of trihalomethanes(THMs), humic and fulvic acids, in aqueous solution have been investigated in this paper. Total organic carbon (TOC) and chemical oxygen demand (COD) were the parameters followed to evaluate the performance of both processes of oxidation. Comparison of their effect on the enhancement of the biodegradability was studied. While ozonation was efficient to reduce 73% COD and 67% TOC at [O 3] = 47 mg/l, COD i = 205 mg/l and TOC i = 28 mg/l in 30 minutes, ozone in the presence of MnO 2 was efficient to reduce 89% COD and 79% of TOC in 30 minutes at [O 3] = 47 mg/l, COD 0 = 180 mg/l and TOC i = 38 mg/l.

Sonochemical Decomposition of Phenol: Evidence for a Synergistic Effect of Ozone and Ultrasound for the Elimination of Total Organic Carbon from Water

Advanced oxidation processes (AOPs) for water and wastewater treatment are often handicapped by their inability to completely eliminate total organic carbon (TOC). In order to explore the capability of the combination of ultrasonic irradiation with ozone for the rapid removal of TOC, we examined the degradation rates of dissolved phenol (C6H5OH) in water with high-frequency ultrasound over the range of 200-1000 kHz, with ozone and with the combined application of sonication and ozonation. When ozone and ultrasound are applied simultaneously, a pronounced synergistic effect is observed that leads to the complete and rapid elimination of TOC at enhanced reaction rates. At longer reaction times, phenol oxidation by 03 leads to oxalate and formate, which accounts for the majority of the residual TOC. However, the combination of US (ultrasound) and ozone together readily oxidizes HCO2- and C2O4(2-) to CO2 while they prove to be relatively resistant to further oxidation to CO2 by O3 alone.

Sonochemical decomposition of phenol: evidence for a synergistic effect of ozone and ultrasound for the elimination of total organic carbon

The degradation of phenol (C6H5OH) was investigated under sonication, ozonation, and the combination of sonication and ozonation. The coupling of these two oxidation processes yielded phenol degradation kinetics that are similar to those predicted from the linear combination of the individual sonication and ozonation experiments. However, synergistic effects of sonolytic ozonation were observed for the reduction of the total organic carbon (TOC) in these systems. The rate of TOC decomposition was found to be proportional to both the aqueous steady-state ozone concentration and the ultrasonic power density. At 358 kHz, sonication combined with ozonation enhanced TOC loss rates by 43% over the sum of the rates obtained by the separate treatments. Intermediate species detected during the degradation of phenol indicate that while the primary degradation products are efficiently degraded by simple ozonolysis, the simultaneous addition of ultrasonic irradiation is necessary to degrade the more recalcitrant unsaturated daughter products.

Catalytic wet air oxidation of phenol in concurrent downflow and upflow packed-bed reactors over pillared clay catalyst

An experimental study is presented for comparing the behavior of a packed bed reactor in the catalytic liquid-phase oxidation of aqueous phenol with two modes of operation, downflow and upflow. The operating parameters investigated included temperature, reactor pressure, gas flowrate, liquid hourly space velocity and feed concentration. Because of the completely wetted catalyst, the upflow reactor generally performs better for high pressures and low feed concentrations when the liquid reactant limitation controls the rate. The interaction between the reactor hydrodynamics, mass transfer, and reaction kinetics is discussed. For both operation modes, complete phenol removal and significant total organic carbon (TOC) reduction can be achieved at rather mild conditions of temperature (150–170 °C) and total pressure (1.5–3.2 MPa). The results show that the phenol and TOC conversion are considerably affected by the temperature, while the air pressure only has minor influence. Total elimination of TOC is difficult since acetic acid, as the main intermediate, is resistant to catalytic wet oxidation. All tests were conducted over extrudates of Fe–Al pillared clay catalyst, which is stable and maintains its activity during the long-term experimental process. No significant catalyst deactivation due to metal ion leaching and polymer deposition was detected.