Removal of 1,4-dioxane from water using sonication: effect of adding oxidants on the degradation kinetics

Fe-ZSM-5 zeolite catalyst for heterogeneous Fenton oxidation of 1,4-dioxane: effect of Si/Al ratios and contributions of reactive oxygen species

Heterogeneous Fenton oxidation using traditional catalysts with H2O2 for the degradation of 1,4-dioxane (1,4-DX) still presents challenge. In this study, we explored the potential of Fe-ZSM-5 zeolites (Fe-zeolite) with three Si/Al ratios (25, 100, 300) as heterogeneous Fenton catalysts for the removal of 1,4-DX from aqueous solution. Fe2O3 or ZSM-5 alone provided ineffective in degrading 1,4-DX when combined with H2O2. However, the efficient removal of 1,4-DX using H2O2 was observed when Fe2O3 was loaded on ZSM-5. Notably, the Brønsted acid sites of Fe-zeolite played a crucial role during the degradation of 1,4-DX. Fe-zeolites, in combination with H2O2, effectively removed 1,4-DX via a combination of adsorption and oxidation. Initially, Fe-zeolites demonstrated excellent affinity for 1,4-DX, achieving adsorption equilibrium rapidly in about 10 min, followed by effective catalytic oxidative degradation. Among the Fe-ZSM-5 catalysts, Fe-ZSM-5 (25) exhibited the highest catalytic activity and degraded 1,4-DX the fastest. We identified hydroxyl radicals (·OH) and singlet oxygen (1O2) as the primary reactive oxygen species (ROS) responsible for 1,4-DX degradation, with superoxide anions (HO2·/O2·-) mainly converting into 1O2 and ·OH. The degradation primarily occurred at the Fe-zeolite interface, with the degradation rate constants proportional to the amount of Brønsted acid sites on the Fe-zeolite. Fe-zeolites were effective over a wide working pH range, with alkaline pH conditions favoring 1,4-DX degradation. Overall, our study provides valuable insights into the selection of suitable catalysts for effective removal of 1,4-DX using a heterogeneous Fenton technology.

Remedial strategies for abating 1,4-dioxane pollution-special emphasis on diverse biotechnological interventions

1,4-dioxane is a heterocyclic ether used as a polar industrial solvent and are released as waste discharges. 1,4-dioxane deteriorates health and quality, thereby attracts concern by the environment technologists. The need of attaining sustainable development goals have resulted in search of an eco-friendly and technically viable treatment strategy. This extensive review is aimed to emphasis on the (a) characteristics of 1,4-dioxane and their occurrence in the environment as well as their toxicity, (b) remedial strategies, such as physico-chemical treatment and advanced oxidation techniques. Special reference to bioremediation that involves diverse microbial strains and their mechanism are highlighted in this review. The role of macronutrients, stimulants and other abiotic cofactors in the biodegradation of 1,4-dioxane is discussed lucidly. We have critically discussed the inducible enzymes, enzyme-based remediation, distinct instrumental method of analyses to know the fate of intermediates produced from 1,4-dioxane biotransformation. This comprehensive survey also tries to put forth the different toxicity assessment tools used in evaluating the extent of detoxification of 1,4-dioxane achieved through biotransforming mechanism. Conclusively, the challenges, opportunities, techno-economic feasibility and future prospects of implementing 1,4-dioxane through biotechnological interventions are also discussed.

Hydroxyl radicals in anodic oxidation systems: generation, identification and quantification

Anodic oxidation has emerged as a promising treatment technology for the removal of a broad range of organic pollutants from wastewaters. Hydroxyl radicals are the primary species generated in anodic oxidation systems to oxidize organics. In this review, the methods of identifying hydroxyl radicals and the existing debates and misunderstandings regarding the validity of experimental results are discussed. Consideration is given to the methods of quantification of hydroxyl radicals in anodic oxidation systems with particular attention to approaches used to compare the electrochemical performance of different anodes. In addition, we describe recent progress in understanding the mechanisms of hydroxyl radical generation at the surface of most commonly used anodes and the utilization of hydroxyl radical in typical electrochemical reactors. This review shows that the key challenges facing anodic oxidation technology are related to i) the elimination of mistakes in identifying hydroxyl radicals, ii) the establishment of an effective hydroxyl radical quantification method, iii) the development of cost effective anode materials with high corrosion resistance and high electrochemical activity and iv) the optimization of electrochemical reactor design to maximise the utilization efficiency of hydroxyl radicals.

Degradation of 1,4-dioxane by biochar activating peroxymonosulfate under continuous flow conditions

1,4-Dioxane degradation under both batch-scale and column experiments has been investigated within the biochar activated peroxymonosulfate (PMS) system for in-situ remediation of 1,4-dioxane contaminated groundwater. In case of the batch experiments, the 1,4-dioxane degradation efficiencies were significantly increased with the increased biochar pyrolysis temperatures. The optimized 1,4-dioxane degradation efficiency at 89.2% was achieved with 1.0 g L^-1 of biochar (E800) and 8.0 mM PMS. In the absence of PMS, the breakthrough rates of 1,4-dioxane in biochar packed column experiments under the dynamic flow conditions were relatively slow compared with those in sand packed columns. Simultaneously, based on the integrated areas (IA) from the 1,4-dioxane breakthrough curves, the degradation efficiency at 70.2% was estimated in biochar packed column (W_E800:W_Sand = 1:9) under continuous injections of 16.0 mM PMS. Electron paramagnetic resonance (EPR) indicated that hydroxyl, sulfate and superoxide radicals were generated within the biochar/PMS systems and alcohol quenching experiments suggested that the dominated hydroxyl and sulfate radicals were responsible for 1,4-dioxane degradation. The findings of this study suggested that the biochar activated PMS system is a promising and cost-effective strategy for the remediation of 1,4-dioxane contaminated groundwater.

Single-Atom Cobalt Incorporated in a 2D Graphene Oxide Membrane for Catalytic Pollutant Degradation

We introduce a new graphene oxide (GO)-based membrane architecture that hosts cobalt catalysts within its nanoscale pore walls. Such an architecture would not be possible with catalysts in nanoscale, the current benchmark, since they would block the pores or alter the pore structure. Therefore, we developed a new synthesis procedure to load cobalt in an atomically dispersed fashion, the theoretical limit in material downsizing. The use of vitamin C as a mild reducing agent was critical to load Co as dispersed atoms (Co₁), preserving the well-stacked 2D structure of GO layers. With the addition of peroxymonosulfate (PMS), the Co₁-GO membrane efficiently degraded 1,4-dioxane, a small, neutral pollutant that passes through nanopores in single-pass treatment. The observed 1,4-dioxane degradation kinetics were much faster (>640 times) than the kinetics in suspension and the highest among reported persulfate-based 1,4-dioxane destruction. The capability of the membrane to reject large organic molecules alleviated their effects on radical scavenging. Furthermore, the advanced oxidation also mitigated membrane fouling. The findings of this study present a critical advance toward developing catalytic membranes with which two distinctive and complementary processes, membrane filtration and advanced oxidation, can be combined into a single-step treatment.

A Review on Additives-assisted Ultrasound for Organic Pollutants Degradation

In the past 2 decades, considerable attentions have been paid to the sonochemical advanced oxidation processes (SAOPs) in the fields of pollutants removal. SAOPs are powerful methods for refractory pollutants degradation due to the free radicals (e.g., •OH and •H) generated by water pyrolysis and extremely high temperature and pressure in and around cavitation bubbles. Reports on various additives for the improvement of sonochemical pollutants degradation including oxidants, inorganic anions, etc. have been made. This paper presents a comprehensive review on the ultrasound (US) alone and sono-hybrid systems for various pollutants degradation. In this paper, the degradation efficiency of various pollutants in sono-hybrid systems are elucidated in detail, and particular emphasis is placed on the reaction mechanism of additives in US for the enhancement of pollutants degradation. The problems on the applications of the current sono-hybrid systems are identified and discussed, and the outlooks for further in-depth studies on the challenges and some research needs for the applications of SAOPs for the removal of organic pollutants from aquatic systems are made at the end.

Ultrasound-assisted heterogeneous activation of persulfate and peroxymonosulfate by asphaltenes for the degradation of BTEX in water

This study investigated - for the first time - the simultaneous degradation of benzene, toluene, ethylbenzene and o-xylene (BTEX) by persulfate (PS) and peroxymonosulfate (PMS) activated by asphaltenes (Asph) under ultrasound (US) irradiation. Advantageous properties such as high thermal stability, low production cost and extensive availability make asphaltenes as an appealing carbonaceous material for heterogeneous catalysis. The application of asphaltenes in PS/US increased the degradation of BTEXs from 31%, 34%, 35%, 32%-78%, 94%, 98% and 98%, while the removal of these compounds in PMS/US system was improved from 26%, 27%, 24%, 20%-76%, 91%, 97%, 97%, respectively. PS and PMS activation followed a typical sulfate-radical based advanced oxidation processes. In terms of activation of PS and PMS, the particles of asphaltenes intensified formation of reactive radicals by creating additional centers of cavitational events. Moreover, owing to π-π stacking interaction between asphaltenes and sp²-hybridized systems of BTEX, the contaminants undergo adsorption on the surface of asphaltenes and subsequent oxidation by formed radicals. The radical route of BTEX degradation in both PS/US/Asph and PMS/US/Asph systems was mainly contributed by sulfate (SO₄^•-) and hydroxyl radicals (HO^•) and coexisting superoxide radical anions (O₂^•-) played a minor role.

Sulfate radical-induced destruction of emerging contaminants using traces of cobalt ions as catalysts

Cobalt is part of vitamin B12, which is essential to maintain human health, and trace levels of cobalt ions are ubiquitous in water and soil environments. In this study, the destruction of 1,4-dioxane (1,4-D) by peroxymonosulfate (PMS) under the catalysis of trace levels of Co²⁺ was investigated under buffered conditions. The results showed that near 100% removal of 1,4-D was achieved after reaction for 6 and 10 min with 50 and 25 μg/L Co²⁺, respectively, in the presence of 5 mM phosphate ions. Mechanism studies revealed that radicals mediated the destruction of 1,4-D and sulfate radicals were the primary reactive species. The traces of Co²⁺ had the greatest reactivity for the catalysis of PMS in neutral environments (pH 7.0). However, pH 5.5 was observed to be the best condition for 1,4-D destruction, which was probably caused by the involvement of phosphate radicals. Common water components including chloride ions and bicarbonate ions were observed to have promoting and inhibiting effects, respectively, on the removal of 1,4-D. To further demonstrate the potential of Co²⁺-PMS in practical applications, we explored the simultaneous degradation of 20 antibiotics using trace levels of Co²⁺. The results showed that all the investigated antibiotics, except for lomefloxacin, could be efficiently degraded by Co²⁺-PMS with removal rates of greater than 97%. The findings from this study demonstrate the promise of using trace levels of cobalt for environmental remediation applications, even when high concentrations of phosphate ions are co-present.

Enhanced long-term attenuation of 1,4-dioxane in bioaugmented flow-through aquifer columns

Long term natural attenuation of 1,4-dioxane (dioxane) and its enhanced biodegradation after bioaugmentation with Pseudonocardia dioxanivorans CB1190 were assessed using flow-through aquifer columns. Natural attenuation of dioxane was not observed even after 2 years of acclimation. However, dioxane removal was observed in the bioaugmented columns (34% when the influent was 200 µg/L and 92% for 5 mg/L). The thmA gene that encodes the tetrahydrofuran monooxygenase that initiates dioxane degradation by CB1190 was only detected at the inoculation port and persisted for months after inoculation, implying the resiliency of bioaugmentation and its potential to offer long-term enhanced biodegradation capabilities. However, due to extensive clumping and limited mobility of CB1190, the augmented catabolic potential may be restricted to the immediate vicinity of the inoculation port. Accordingly, bioaugmentation with CB1190 seems more appropriate for the establishment of biobarriers. Bioaugmentation efficiency was associated with the availability of oxygen. Aeration of the column influent to increase dissolved oxygen significantly improved dioxane removal (p < 0.05), suggesting that (for sites with oxygen-limiting conditions) bioaugmentation can benefit from engineered approaches for delivering additional oxygen.

Insights into the mechanism of nonradical reactions of persulfate activated by carbon nanotubes: Activation performance and structure-function relationship

This study aimed to elucidate the intrinsic mechanisms of PS activation by carbon nanotubes (CNTs). Singlet oxygen generation (¹O₂) and direct CNTs-mediated electron transfer were hypothesized to be two major pathways of the oxidation of 2,4-dichlorophenol (2,4-DCP) by PS in the presence of both unmodified and modified CNTs. For the first time, roles of CNT active sites responsible for PS activation were determined using CNT derivatization and structural characterization. By selectively deactivating the carbonyl, hydroxyl or carboxylic groups on CNTs surface and linear sweep voltammetry (LSV) analysis, CO groups were determined to be the main active sites contributing to the direct electron transfer oxidation, while singlet oxygen was generated at CNTs defects. Subsequent UV irradiation was shown to cause the recovery of surface defects with I_D/I_G of CNTs increasing by 21%. This resulted in the regeneration of the performance for the coupled system and allowed for multi-cycle activation of PS by CNTs. These results suggest that CNTs/PS system combined with regeneration based on UV irradiation can be used as an effective alternative process for continuous degradation of recalcitrant aqueous contaminants through the non-radical mechanism.

Electrochemical filtration process for simultaneous removal of refractory organic and particulate contaminants from wastewater effluents

Versatile electrochemical reactions are effective for removing a wide range of water contaminants. This study focuses on the development and testing of bifunctional electrocatalytic filter anodes as reactive and separating media for the simultaneous removal of refractory dissolved organic and particulate contaminants from real wastewater effluents. The results show that the TiO₂ particle interlayers formed between the Ti fiber support and the top composite metal oxide catalyst layers assist in reducing filter pores to an effective size range that enables removal of most particulates within the wastewater. The double-sheet design, which is a sandwich-structured module with an internal void space for permeate, prevents filter fouling, and transmembrane pressure can be maintained at a very low level of <5 kPa during batch and continuous flow reactor operations. Substantive and simultaneous removal of dissolved organics (e.g., chromophores, fluorophores, 1,4-dioxane, chemical oxygen demand, and total organic carbon) and particulate matter (i.e., turbidity) are achieved, although removal rates and efficacies differ depending on the electric current density applied. Decolorization and particulate rejection occur swiftly and immediately, but 1,4-dioxane degradation is relatively slow and quite time-dependent. Possible 1,4-dioxane degradation pathways during electrocatalysis are also proposed. Electrochemical filtration technology shows considerable promise for use in the next generation of advanced wastewater treatment solutions.

Abiotic and bioaugmented granular activated carbon for the treatment of 1,4-dioxane-contaminated water

1,4-Dioxane is a probable human carcinogen and an emerging contaminant that has been detected in surface water and groundwater resources. Many conventional water treatment technologies are not effective for the removal of 1,4-dioxane due to its high water solubility and chemical stability. Biological degradation is a potentially low-cost, energy-efficient approach to treat 1,4-dioxane-contaminated waters. Two bacterial strains, Pseudonocardia dioxanivorans CB1190 (CB1190) and Mycobacterium austroafricanum JOB5 (JOB5), have been previously demonstrated to break down 1,4-dioxane through metabolic and co-metabolic pathways, respectively. However, both CB1190 and JOB5 have been primarily studied in laboratory planktonic cultures, while most environmental microbes grow in biofilms on surfaces. Another treatment technology, adsorption, has not historically been considered an effective means of removing 1,4-dioxane due to the contaminant's low K_oc and K_ow values. We report that the granular activated carbon (GAC), Norit 1240, is an adsorbent with high affinity for 1,4-dioxane as well as physical dimensions conducive to attached bacterial growth. In abiotic batch reactor studies, 1,4-dioxane adsorption was reversible to a large extent. By bioaugmenting GAC with 1,4-dioxane-degrading microbes, the adsorption reversibility was minimized while achieving greater 1,4-dioxane removal when compared with abiotic GAC (95-98% reduction of initial 1,4-dioxane as compared to an 85-89% reduction of initial 1,4-dioxane, respectively). Bacterial attachment and viability was visualized using fluorescence microscopy and confirmed by amplification of taxonomic genes by quantitative polymerase chain reaction (qPCR) and an ATP assay. Filtered samples of industrial wastewater and contaminated groundwater were also tested in the bioaugmented GAC reactors. Both CB1190 and JOB5 demonstrated 1,4-dioxane removal greater than that of the abiotic adsorbent controls. This study suggests that bioaugmented adsorbents could be an effective technology for 1,4-dioxane removal from contaminated water resources.

Surface-bound sulfate radical-dominated degradation of 1,4-dioxane by alumina-supported palladium (Pd/Al2O3) catalyzed peroxymonosulfate

Sulfate radicals have been demonstrated as an alternative to hydroxyl radicals in advanced oxidation processes. Unfortunately, the efficient activation of peroxymonosulfate (PMS), one of the most commonly used oxidants for the generation of sulfate radicals, still relies heavily on cobalt-bearing materials that are potential carcinogens. Although copper-iron bimetallic materials are promising activators, stoichiometric amounts of metals are required to achieve satisfactory performance. In this study, we propose a real catalytic process that is capable of degrading extremely recalcitrant 1,4-dioxane using a combination of alumina-supported metallic palladium (Pd/Al₂O₃) with PMS. The metal loading-normalized pseudo-first-order constant for 1,4-dioxane degradation with Pd/Al₂O₃ was more than 16,800 times that with copper-iron bimetallic materials. Complementary to Fenton reagents, Pd/Al₂O₃-PMS had a wide effective pH range from 4.0 to 8.5. In the absence of a substrate, PMS underwent more rapid decomposition under all conditions investigated, which suggests that its activation did not likely proceed via the previously proposed non-radical mechanism. On the basis of the strong inhibitory effects of common scavengers, we instead propose that surface-bound sulfate radicals were probably the dominant active species. A near-100% conversion rate of PMS to radicals was achieved with the Pd/Al₂O₃ catalyst.

Kinetics and Mechanism of Ultrasonic Activation of Persulfate: An in Situ EPR Spin Trapping Study

Ultrasound (US) was shown to activate persulfate (PS) providing an alternative activation method to base or heat as an in situ chemical oxidation (ISCO) method. The kinetics and mechanism of ultrasonic activation of PS were examined in aqueous solution using an in situ electron paramagnetic resonance (EPR) spin trapping technique and radical trapping with probe compounds. Using the spin trap, 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), hydroxyl radical (^•OH) and sulfate radical anion (SO₄^•-) were measured from ultrasonic activation of persulfate (US-PS). The yield of ^•OH was up to 1 order of magnitude greater than that of SO₄^•-. The comparatively high ^•OH yield was attributed to the hydrolysis of SO₄^•- in the warm interfacial region of cavitation bubbles formed from US. Using steady-state approximations, the dissociation rate of PS in cavitating bubble systems was determined to be 3 orders of magnitude greater than control experiments without sonication at ambient temperature. From calculations of the interfacial volume surrounding cavitation bubbles and using the Arrhenius equation, an effective mean temperature of 340 K at the bubble-water interface was estimated. Comparative studies using the probe compounds tert-butyl alcohol and nitrobenzene verified the bubble-water interface as the location for PS activation by high temperature with ^•OH contributing a minor role in activating PS to SO₄^•-. The mechanisms unveiled in this study provide a basis for optimizing US-PS as an ISCO technology.

Mineralization of naphtenic acids with thermally-activated persulfate: The important role of oxygen

This study reports on the mineralization of model naphtenic acids (NAs) in aqueous solution by catalyst-free thermally-activated persulfate (PS) oxidation. These species are found to be pollutants in oil sands process-affected waters. The NAs tested include saturated-ring (cyclohexanecarboxylic and cyclohexanebutyric acids) and aromatic (2-naphthoic and 1,2,3,4-tetrahydro-2-naphthoic acids) structures, at 50mgL(-1)starting concentration. The effect of PS dose within a wide range (10-100% of the theoretical stoichiometric) and working temperature (40-97°C) was investigated. At 80°C and intitial pH=8 complete mineralization of the four NAs was achieved with 40-60% of the stoichiometric PS dose. This is explained because of the important contribution of oxygen, which was experimentally verified and was found to be more effective toward the NAs with a single cyclohexane ring than for the bicyclic aromatic-ring-bearing ones. The effect of chloride and bicarbonate was also checked. The former showed negative effect on the degradation rate of NAs whereas it was negligible or even positive for bicarbonate. The rate of mineralization was well described by simple pseudo-first order kinetics with values of the rate constants normalized to the PS dose within the range of 0.062-0.099h(-1). Apparent activation energy values between 93.7-105.3kJmol(-1) were obtained.

Advanced oxidation of five contaminants in water by UV/TiO2: Reaction kinetics and byproducts identification

The extent and kinetics of degradation of 1,4 dioxane, n-nitrosodimethylamine (NDMA), tris-2-chloroethyl phosphate (TCEP), gemfibrozil, and 17β estradiol in a prepared aqueous matrix by means of UV/TiO2 (ultraviolet light/titanium dioxide) oxidation was evaluated. Degussa P25 TiO2 was employed as a photocatalyst excited by UV light in a 1 L water-jacketed batch photoreactor. The rate of degradation was modeled using a pseudo-first order rate model and the Langmuir-Hinshelwood rate model with a high correlation. Degradation rate constants were found to be maximum at pH 5.0 and 1.5 g L(-)(1) TiO2 dose. For these conditions first order rate constants, values were as follows: 0.29 min(-1) for 1,4 dioxane, 0.50 min(-1) for NDMA, 0.12 min(-1) for TCEP, 0.61 min(-1) for gemfibrozil, and 0.53 min(-1) for 17β estradiol. While for the Langmuir-Hinshelwood rate model, the following constants were found: 0.11 Lmg(-1) and 2.81 mgL(-1) min(-1) for 1,4 dioxane, 0.12 Lmg(-1) and 4.35 mgL(-1) min(-1) for NDMA, 0.06 Lmg(-1) and 1.79 mgL(-1) min(-1) for TCEP, 0.21 Lmg(-1) and 3.27 mgL(-1) min(-1) for gemfibrozil, and 0.15 Lmg(-1) and 3.43 mgL(-1) min(-1) for 17β estradiol. In addition, specific byproducts of degradation were identified using GC/MS analysis. The results obtained from the kinetics analysis showed that UV/TiO2 oxidation is a promising process for treating trace organic contaminants in water, but further research is needed to better understand how to incorporate these findings into pilot and full-scale designs. The toxicity of oxidation byproducts, and their potential for interacting with other compounds should be considered in the treatment of contaminated waters using the UV/TiO2 oxidation process.

Peroxone activated persulfate treatment of 1,4-dioxane in the presence of chlorinated solvent co-contaminants

1,4-dioxane is often found as a co-contaminant with chlorinated volatile organic compounds (VOCs) at solvent release sites such as landfills, solvent recycling facilities, or fire training areas. Historically, soil and groundwater samples were not routinely analyzed for 1,4-dioxane and therefore the number of known 1,4-dioxane sites is still increasing. Due to its co-occurrence with chlorinated compounds, remediation strategies are needed that simultaneously treat both 1,4-dioxane as well as chlorinated VOC co-contaminants. In this proof of concept laboratory study, the fate of 1,4-dioxane was examined during the targeted destruction of aqueous phase VOC, using a peroxone activated persulfate (PAP) chemical oxidation method. Bench-scale experiments were carried out to evaluate the treatability of 1,4-dioxane as both a single-contaminant and in the presence of trichloroethene (TCE), and 1,1,1-trichloroethane (1,1,1-TCA). Possible dependencies on oxidant concentration and reaction kinetics were studied. The oxidative destruction of 1,4-dioxane, TCE and 1,1,1-TCA in single-contaminant batch systems followed pseudo-first-order reaction kinetics and even at the most dilute oxidant concentration lasted for at least 13 days. The rate of oxidation for each contaminant increased linearly with increasing persulfate concentration over the range of oxidant concentrations tested. The rate of oxidative destruction, from most easily degraded to least, was: TCE > 1,4-dioxane > 1,1,1-TCA. Oxidation rates were up to 87% slower in a mixture of these three compounds. Although additional tests are necessary, our data suggest that PAP oxidation of 1,4-dioxane might aid in the cleanup of VOC contaminated sites.

Membrane photoreactor treatment of 1,4-dioxane-containing textile wastewater effluent: Performance, modeling, and fouling control

A membrane photoreactor (MPR) system was investigated for the purification of textile wastewater effluent containing 1,4-dioxane for potential reuse. The effects of TiO2 dosage, alkalinity, particulate matter, and sunlight radiation on the removal of 1,4-dioxane from the effluent were evaluated. The photocatalytic 1,4-dioxane degradation followed pseudo-first order reaction kinetics. A considerably large dose of TiO2 catalyst (5 g/L) was required for maximal 1,4-dioxane degradation by MPR. The high alkalinity (∼ 550 mg/L) of the textile wastewater effluent negatively affected the 1,4-dioxane degradation rate, whereas 1,4-dioxane degradation was not impacted by the presence of particulate matter. Solar photocatalysis of 1,4-dioxane was as effective as that achieved with UV lamps in the MPR, which could lead to energy savings. Continuous flow MPR was effective for continuous degradation of 1,4-dioxane; the unsteady- and steady-state performances were well-predicted at various hydraulic residence times (HRTs). The quality of the MPR product obtained at an HRT of 8.57 h satisfied the drinking water guidelines. The transmembrane pressure (TMP) buildup, which is indicative of fouling, was dependent on the TiO2 dose and permeate flux. The TMP buildup was marginal at low flux, but increased dramatically beyond a flux level of >60 L/m(2)-h. However, the fouling layer could be sufficiently removed by periodic backwashing, even at an extremely high flux of 100 L/m(2)-h. The membrane permeability was sustained without any sign of irreversible fouling during MPR treatment of textile wastewater effluents.

Optimization of sonochemical degradation of tetracycline in aqueous solution using sono-activated persulfate process

BACKGROUND

In this study, a central composite design (CCD) was used for modeling and optimizing the operation parameters such as pH, initial tetracycline and persulfate concentration and reaction time on the tetracycline degradation using sono-activated persulfate process. The effect of temperature, degradation kinetics and mineralization, were also investigated.

RESULTS

The results from CCD indicated that a quadratic model was appropriate to fit the experimental data (p < 0.0001) and maximum degradation of 95.01 % was predicted at pH = 10, persulfate concentration = 4 mM, initial tetracycline concentration = 30.05 mg/L, and reaction time = 119.99 min. Analysis of response surface plots revealed a significant positive effect of pH, persulfate concentration and reaction time, a negative effect of tetracycline concentration. The degradation process followed the pseudo-first-order kinetic. The activation energy value of 32.01 kJ/mol was obtained for US/S2O8 (2-) process. Under the optimum condition, the removal efficiency of COD and TOC reached to 72.8 % and 59.7 %, respectively. The changes of UV-Vis spectra during the process was investigated. The possible degradation pathway of tetracycline based on loses of N-methyl, hydroxyl, and amino groups was proposed.

CONCLUSIONS

This study indicated that sono-activated persulfate process was found to be a promising method for the degradation of tetracycline.

Comparative removal of commercial diclofenac sodium by electro-oxidation on platinum anode and combined electro-oxidation and electrocoagulation on stainless steel anode

Aqueous solution of diclofenac sodium (DCFNa) from commercial analgesic pill was electro-oxidized on platinum and stainless steel (SS) anodes. On platinum anode, 66% degradation of the parent drug was achieved at pH 4.5 with a corresponding COD reduction of 49% for a specific charge of 4200 Coulombs/L. Degradation and COD reduction were less at higher pHs of 8.5 and 10.9. A number of intermediates were detected with some of them persisting at the end of the treatment. On SS anode, 84% drug removal and 80% COD decline were achieved for a specific charge of 4200 Coulombs/L at pH 10.9, owing to combined electro-oxidation and electrocoagulation. Contrary to platinum anode, here the drug removal and COD reduction were lesser at lower pHs of 8.5 and 4.5. Electrocoagulation was found to proceed with the organics directly forming complex with iron in the matrix of the SS anode with the iron oxidizing to Fe(III) at pH 10.9 and Fe(II) at pHs 8.5 and 4.5. Intermediates detected in residual liquid were much less in number and abundance.

Sonocatalytic and sonophotocatalytic degradation of Rhodamine 6G containing wastewaters

The present work deals with degradation of aqueous solution of Rhodamine 6G (Rh 6G) using sonocatalytic and sonophotocatalytic treatment schemes based on the use of cupric oxide (CuO) and titanium dioxide (TiO2) as the solid catalysts. Experiments have been carried out at the operating capacity of 2 L and constant initial pH of 12.5. The effect of catalyst loading on the sonochemical degradation has been investigated by varying the loading over the range of 1.5-4.5 g/L. It has been observed that the maximum degradation of 52.2% was obtained at an optimum concentration of CuO as 1.5 g/L whereas for TiO2 maximum degradation was observed as 51.2% at a loading of 4 g/L over similar treatment period. Studies with presence of radical scavengers such as methanol (CH3OH) and n-butanol (C4H9OH) indicated lower extents of degradation confirming the dominance of radical mechanism. The combined approach of ultrasound, solid catalyst and scavengers has also been investigated at optimum loadings to simulate real conditions. The optimal solid loading was used for studies involving oxidation using UV irradiations where 26.4% and 28.9% of degradation was achieved at optimal loading of CuO and TiO2, respectively. Studies using combination of UV and US irradiations have also been carried out using the optimal concentration of the catalysts. It has been observed that maximum degradation of 63.3% is achieved using combined US and UV with TiO2 (4 g/L) as the photocatalyst. Overall it can be said that the combined processes give higher extent of degradation as compared to the individual processes based on US or UV irradiations.

Degradation of 1,4-dioxane in water with heat- and Fe(2+)-activated persulfate oxidation

This research investigated the 1,4-dioxane (1,4-D) degradation efficiency and rate during persulfate oxidation at different temperatures, with and without Fe(2+) addition, also considering the effect of pH and persulfate concentration on the oxidation of 1,4-D. Degradation pathways for 1,4-D have also been proposed based on the decomposition intermediates and by-products. The results indicate that 1,4-D was completely degraded with heat-activated persulfate oxidation within 3-80 h. The kinetics of the 1,4-D degradation process fitted well to a pseudo-first-order reaction model. Temperature was identified as the most important factor influencing the 1,4-D degradation rate during the oxidation process. As the temperature increased from 40 to 60 °C, the degradation rate improved significantly. At 40 °C, the addition of Fe(2+) also increased the 1,4-D degradation rate. Interestingly, at 50 and 60 °C, the 1,4-D degradation rate decreased slightly with the addition of Fe(2+). This reduced degradation rate may be attributed to the rapid conversion of Fe(2+) to Fe(3+) and the production of an Fe(OH)3 precipitate which limited the ultimate oxidizing capability of persulfate with Fe(2+) under higher temperatures. Higher persulfate concentrations led to higher 1,4-D degradation rates, but pH adjustment had no significant effect on the 1,4-D degradation rate. The identification of intermediates and by-products in the aqueous and gas phases showed that acetaldehyde, acetic acid, glycolaldehyde, glycolic acid, carbon dioxide, and hydrogen ion were generated during the persulfate oxidation process. A carbon balance analysis showed that 96 and 93% of the carbon from the 1,4-D degradation were recovered as by-products with and without Fe(2+) addition, respectively. Overall, persulfate oxidation of 1,4-D is promising as an economical and highly efficient technology for treatment of 1,4-D-contaminated water.

Removal of 1,1,1-trichloroethane from aqueous solution by a sono-activated persulfate process

1,1,1-Trichloroethane (TCA), labeled as a priority pollutant by the Environmental Protection Agency (EPA) of China, can be removed from groundwater by sonochemical oxidation. The sonochemical oxidation of TCA in the presence of persulfate (PS) showed a significant synergistic effect. The operational parameters, ultrasonic frequency, PS/TCA molar ratio, radical scavenger, inorganic anions (Cl(-), CO(3)(2-), HCO(3)(-) and NO(3)(-)) and humic acid (HA), were evaluated during the investigation of the sonochemical reaction. The results showed that the degradation of TCA followed pseudo-first-order kinetics, and the rate constant was found to increase with increasing ultrasonic frequency but to decrease with both an increasing PS/TCA molar ratio and an increasing concentration of inorganic anions. With a concentration of 4.46mg/L of HA in solution, an enhanced effect was observed. Further addition of HA retarded the degradation rate of TCA. TCA could be eliminated almost completely by sono-activated persulfate oxidation, with sulfate and hydroxyl radicals serving as the principal oxidants as confirmed by the addition of radical scavengers. Eleven chlorinated degradation intermediates were detected and quantified by purge and trap gas chromatography coupled with mass spectrometry (P&T-GC-MS) in the absence of pH buffer. Three TCA degradation pathways were therefore proposed. In conclusion, the sono-activated persulfate oxidation process appears to be a highly promising technique for the remediation of TCA-contaminated groundwater.

Degradation of 1,4-dioxane using advanced oxidation processes

INTRODUCTION

In the nuclear industry 1,4-dioxane is used as a solvent in liquid scintillation technique for measuring low-energy beta-emitters such as ³H or C¹⁴ in aqueous media. Improper disposal of 1,4-dioxane can contaminate the ground and surface waters. Conventional wastewater treatment processes like chemical treatment, air stripping, carbon adsorption, and biological treatment are ineffective for the degradation of 1,4-dioxane.

METHODS

In the present study, the kinetics of degradation of 1,4-dioxane using advanced oxidation processes viz., H₂O₂ alone, Fe(II) + H₂O₂, UV (15 W) + H₂O₂, UV (15 W) + Fe(II) + H₂O₂, US (130 KHz) + Fe(II) + H₂O₂, and sunlight + Fe(II) + H₂O₂ at pH 3.0 was investigated. The optimization of Fe (II) for the processes using Fe (II) + H₂O₂ was carried out.

CONCLUSIONS

The kinetics of degradation using sunlight + Fe (II) + H₂O₂ was found to be fastest when compared to the other processes. The degradation was found to follow first-order kinetics. Formation of acidic intermediates was suspected from the observed pH changes during the degradation processes.

Destruction of some more and less hydrophobic PAHs and their toxicities in a petrochemical industry wastewater with sonication in Turkey

The effects of increasing sonication time (60-150min), NaCl (2-18g/l), S(2)O(8)(2-) (2-10mg/l) and 1-butanol (200-600mg/l) concentrations on the destructions of seven polycyclic aromatic hydrocarbons (PAHs) and acute toxicity in a petrochemical industry wastewater in Izmir (Turkey) were investigated. The yields in more hydrophobic PAHs (DahA and BghiP) were as high as in less hydrophobic PAHs (CHR, PHE, PY, BbF and ANT) at 60 degrees C after 150min sonication. The removals in all PAHs increased from 72-78% to 97-99% as the NaCl administration was increased from 1.5 to 12g/l. The degradation efficiency of seven PAHs was enhanced by 36% with 6mg/l S(2)O(8)(2-) after 150min. OH(*) is the major process for complete sonodegradation of less hydrophobic PAHs while pyrolysis is the major process for complete degradation of more hydrophobic PAHs.

Influence of alkalinity and salinity on the sonochemical degradation of estrogen hormones in aqueous solution

Ultrasound assisted degradation of estrogen hormones was examined in a batch reactor using a 2 kW (20 kHz) sonication unit. The degradation of estrogens follow a pseudo first order rate kinetics, and the order of degradation is 17alpha-dihydroequilin > equilin >17alpha-ethinyl estradiol >17alpha-estradiol >17beta-estradiol > estrone > estriol. Effect of solution alkalinity and salinity on the sonochemical degradation of estrogen hormones is examined. At alkalinity concentration of 10 mM, no adverse effect on the degradation rate constants of estradiols (17alpha-estradiol, 17beta-estradiol, and 17alpha-ethinyl estradiol) was observed, whereas equilin compounds showed a decrease in their degradation rate constants. Significant inhibitory effects were observed for all the compounds at high alkalinity concentration of 120 mM and which could be due to the scavenging of OH(*) radicals in the bulk solution. The presence of salinity (0.17 M) enhanced the estrogen degradation except for the equilin compounds. Simultaneous presence of high alkalinity (120 mM) and salinity (0.17 M) also increased the degradation of estrogen hormones than the case when only alkalinity (120 mM) was present, indicating the diffusion of analytes to the cavity interface where most of the degradation occurs under these conditions. A mechanistic approach was used to model the degradation behavior of estrogen hormones under different solution alkalinity and salinity conditions.

Sonophotocatalysis in advanced oxidation process: a short review

Sonophotocatalysis involves the use of a combination of ultrasonic sound waves, ultraviolet radiation and a semiconductor photocatalyst to enhance a chemical reaction by the formation of free radicals in aqueous systems. Researchers have used sonophotocatalysis in a variety of investigations i.e. from water decontamination to direct pollutant degradation. This degradation process provides an excellent opportunity to reduce reaction time and the amount of reagents used without the need for extreme physical conditions. Given its advantages, the sonophotocatalysis process has a futuristic application from an engineering and fundamental aspect in commercial applications. A detailed search of published reports was done and analyzed in this paper with respect to sonication, photocatalysis and advanced oxidation processes.

Ozonation combined with electrolysis of 1,4-dioxane using a two-compartment electrolytic flow cell with solid electrolyte

Ozonation combined with electrolysis (ozone-electrolysis) is a new advanced oxidation process for water treatment. The advantages of ozone-electrolysis are (1) that reagents such as hydrogen peroxide or ferrous salts are unnecessary, (2) there is less influence from chromaticity, and (3) electric power is only required for operation. However, electrolysis has a serious limitation, in that it requires electrical conductivity (EC). This research is aimed at developing an ozone-electrolysis reactor that is applicable to wastewater with low EC using a cation exchange membrane as solid electrolyte. Moreover, experimental evidence of hydroxyl radical (.OH) generation via the cathodic reduction of ozone was obtained. Competitive kinetics analysis, based on the experimental data from the ozone-electrolysis of a mixed solution of 1,4-dioxane and tert-butyl alcohol, revealed that .OH contributed to 1,4-dioxane degradation. The ozone-electrolysis reactor was successfully applicable to degradation of 1,4-dioxane in both 1,4-dioxane solution (EC: less than 0.30 microS/cm) and a landfill leachate treated by a low-pressure reverse osmosis membrane (EC: 0.06 mS/cm). The use of a solid electrolyte was also very effective in reducing the electric power required for electrolysis.