Advanced Oxidation Process System Research Articles

Pilot-scale treatment of 1,4-dioxane contaminated waters using 185 nm radiation: Experimental and CFD modeling

This work investigates the feasibility of a 185 nm advanced oxidation process (AOP) for the degradation of 1,4-dioxane from contaminated waters using a pilot-scale system operating at 6–30 L/min. Using synthetic and natural water samples with less than 20L/min, the 185 nm pilot system was able to reduce 1,4-dioxane concentration from 100 ppb to below the WHO guideline limit (i.e., 50 ppb) with no need for an exogenous chemical oxidant/catalyst. The electrical energy-per-order (EEO) analysis of the system demonstrated the cost-effectiveness of the process for 1,4-dioxane removal with EEO values close to 0.8 kWh/m3/order. Further, 1,4-dioxane degradation rate decreased by 3%-13%, depending on the flow rate, when the raw water was spiked by a second micropollutant, atrazine, which competes for hydroxyl radicals. To provide an in-depth understanding of 1,4-dioxane removal, a mechanistic computational fluid dynamic (CFD) model was developed and validated experimentally. Sensitivity analysis of the operational variables underlined the significance of flow characteristics within the photoreactors as well as the natural organic matter (NOM) concentration of the water as the key factors controlling the degradation of 1,4-dioxane. The proposed model predicted the impact of the flow rates, OH scavenging of atrazine and water matrix (NOM and alkalinity) on 1,4-dioxane degradation with less than 2% average absolute deviation, demonstrating its potential as a viable tool for the design, optimization, and scale-up of 185 nm AOP systems.

Comparison of various advanced oxidation processes used in remediation of industrial wastewater laden with recalcitrant pollutants

Due to the scarcity of water, it has become a necessity to improve the quality of wastewater that is discharged into the environment. Conventional wastewater treatment can be either a physical, chemical, and/or biological processes, or in some cases a combination of these operations. The main purpose of wastewater treatment is to eliminate nutrients, solids, and organic compounds from effluents. Current wastewater treatment technologies are deemed ineffective in the complete removal of pollutants, particularly organic matter. In many cases, these organic compounds are resistant to conventional treatment methods, thus creating the necessity for tertiary treatment. Advanced oxidation process (AOP), constitutes as a promising treatment technology for the management of wastewater. AOPs are characterised by a common chemical feature, where they utilize the highly reactive hydroxyl radicals for achieving complete mineralization of the organic pollutants into carbon dioxide and water. This paper delineates advanced oxidation processes currently used for the remediation of water and wastewater. It also provides the cost estimation of installing and running an AOP system. The costs are separated into three categories: capital, operational, and operating & maintenance.

OH-initiated transformation and hydrolysis of aspirin in AOPs system: DFT and experimental studies

Advanced oxidation processes (AOPs) are widely used in wastewater treatment of pharmaceutical and personal care products (PPCPs). In this work, the OH-initiated transformation as well as the hydrolysis of a typical PPCPs, aspirin, was investigated using density functional theory (DFT) calculations and laboratory experiments. For DFT calculations, the frontier electron densities and bond dissociation energies were analyzed. Profiles of the potential energy surface were constructed, and all the possible pathways were discussed. Additionally, rate constants for each pathway were calculated with transition state theory (TST) method. UV/H2O2 experiments of aspirin were performed and degradation intermediates were identified by UPLC-MS-MS analysis. Different findings from previous experimental works were reported that the H-abstraction pathways at methyl position were dominated and OH-addition pathways on benzene ring were also favored. Meantime, hydroxyl ASA was confirmed as the main stable intermediate. Moreover, it was the first time to use DFT method to investigate the hydrolysis mechanisms of organic ester compound.

Cryptosporidium-contaminated water disinfection by a novel Fenton process

Three novel modified advanced oxidation process systems including ascorbic acid-, pro-oxidants- and ascorbic acid-pro-oxidants-modified Fenton system were utilized to study the disinfection efficiency on Cryptosporidium-contaminated drinking water samples. Different concentrations of divalent and trivalent iron ions, hydrogen peroxide, ascorbic acid and pro-oxidants at different exposure times were investigated. These novel systems were also compared to the classic Fenton system and to the control system which comprised of only hydrogen peroxide. The complete in vitro mechanism of the mentioned modified Fenton systems are also provided. The results pointed out that by considering the optimal parameter limitations, the ascorbic acid-modified Fenton system decreased the Cryptosporidium oocytes viability to 3.91%, while the pro-oxidant-modified and ascorbic acid-pro-oxidant-modified Fenton system achieved an oocytes viability equal to 1.66% and 0%, respectively. The efficiency of the classic Fenton at optimal condition was observed to be 20.12% of oocytes viability. The control system achieved 86.14% of oocytes viability. The optimum values of the operational parameters during this study are found to be 80mgL−1 for the divalent iron, 30mgL−1 for ascorbic acid, 30mmol for hydrogen peroxide, 25mgL−1 for pro-oxidants and an exposure time equal to 5min. The ascorbic acid-pro-oxidants-modified Fenton system achieved a promising complete water disinfection (0% viability) at the optimal conditions, leaving this method a feasible process for water disinfection or decontamination, even at industrial scales.

RELIABILITY STUDY OF LABORATORY SCALE WATER TREATMENT BY ADVANCED OXIDATION PROCESSES

The application of advanced oxidation processes (AOPs) emerged as an interesting topic during the last decade. Many studies have been devoted to the complexity of phenomena imposed by AOPs, and a lot of effort was made to justify the application of AOPs. However, the reliability of AOPs has not been an issue of any extensive work. In this work, failure analysis and comparative reliability study were performed for the chosen AOP system, i.e. a laboratory scale photo- and sonoreactor, during the photocatalytic (UV/TiO2 process) and sonochemical (US/Fenton process) oxidation of model pollutants (dyes and carboxylic acids) in water. Furthermore, a three-criterion analysis approach for the risk assessment was proposed. The set criteria ; (i) probability of failure, (ii) estimated cost for the 10 000 working hours and (iii) residual organic content in the system after the applied treatment, resulted in the calculated risk scores, Srisk that enlighten all the crucial aspects of the investigated systems. In conclusion, the analysis was related to the pilot scale reactors.

Comparative life cycle assessment (LCA) study of heterogeneous and homogenous Fenton processes for the treatment of pharmaceutical wastewater

The applicability of any wastewater technology should be related not only to its degradation, mineralization or detoxification efficiency, but also to its environmental impacts. This could be particularly relevant in case of advanced oxidation processes (AOPs), which are usually highly demanding on chemicals, energy, and generating residual fluxes with specific problems and potential environmental impacts (metal ion-containing sludge, exhausted solid catalysts, etc). In this work, the life cycle assessment (LCA) has been applied for the evaluation of both homogeneous and heterogeneous Fenton processes for the treatment of a wastewater coming from a pharmaceutical industry in Toledo, Spain. The application of LCA as tool for the evaluation of AOPs is scarce found in literature, although it provides a systematic estimation of the environmental changes related to the AOP treatment, quantification of consumptions and emissions, and their effects on human health. In this work, the potential environmental impacts were calculated with Gabi 6.0 software by using ReCiPe version 1.06 and ICCP 2007 methods. Additionally, the water footprint (WF) was used in this study for the first time as tool for comparison between both AOP systems. Experimental data, directly obtained from the company and the laboratory were used to carry out the life cycle inventory (LCI) analysis, ensuring high accuracy and sensitivity of the obtained results. The obtained results showed that the recovery of the metallic sludge generated in the homogeneous Fenton process is the most contributing step to environmental impacts followed by the use of chemicals and the heat requirements. The comparison between homogeneous and heterogeneous Fenton processes revealed that the latter is a more environmental friendly alternative for the treatment of the pharmaceutical wastewater. In addition, the use of the heterogeneous process allows the reduction of the water footprint in more than 77% as compared to the homogeneous one. Besides the results regarding to both Fenton processes, this work shows the efficiency of the water footprint as a complementary parameter to the LCA for comparison between advanced wastewater treatments processes which can be intensive use of fresh water as a resource.

Rapid degradation of methyl orange using hybrid advanced oxidation process and its synergistic effect

An advanced oxidation process system to remove residual azo dye in water, called microwave-assisted UV (MDEL)/TiO2/K2S2O8 hybrid system, was developed and evaluated. The combinations of the component techniques led to increased decomposition rate constants, which are higher than the sum of each component technique. In particular, the decomposition rate constant obtained using the MDEL/TiO2/K2S2O8 hybrid system, which was the highest obtained in this study, was about 1.5 times larger than the sum of the rate constant obtained using the MDEL/K2S2O8 system and that obtained using the MDEL/TiO2 system.

Intrinsic Chemiluminescence Production during Environmentally-friendly Advanced Oxidation of Halogenated Aromatics and Its Applications

Haloaromatics (XAr) have been widely used as pesticides, personal care agents, pharmaceuticals and flame retardants, which are now ubiquitously present in our environment. The carcinogenicity coupled with their ubiquitous occurrence have raised public concerns on the potential risks to both human health and the ecosystem posed by XAr. Advanced oxidation processes (AOPs) have been increasingly employed as an environmentally-friendly technology for remediating such highly toxic and recalcitrant XAr. During these AOPs systems, the most reactive radical intermediate formed at near-ambient temperature and pressure is the hydroxyl radical ((OH)-O-center dot). Recently, we found that an intrinsic chemiluminescence can be generated during the advanced oxidation of the priority pollutant pentachlorophenol and all other XAr. Furtherly, by the complementary application of electron spin resonance (ESR) with 5,5-dimethyl-l-pyrroline-N-oxide (DMPO) as the spin-trapping agent, fluorescence method with terephthalic acid (TPA) as the (OH)-O-center dot probe, chemiluminescence analysis in the presence of classic (OH)-O-center dot scavengers and several typical (OH)-O-center dot-generating systems, the chemiluminescence was confirmed to be directly dependent on the production of the extremely reactive (OH)-O-center dot. Further studies showed that halogenated quinoid intermediates were produced during the degradation of XAr by (OH)-O-center dot-generating system, which could produce weak chemiluminescence that was greatly enhanced by addition of extra (OH)-O-center dot. We proposed that this unusual chemiluminescence generation was due to hydroxyl radical-dependent production of halogenated quinoid intermediates and electronically excited carbonyl species. In addition, the time course of chemiluminescence emission correlated well with the degradation of XAr: when the degradation level of XAr reached the maximum, no further chemiluminescence emission could be observed. Based on these findings, we developed a rapid, sensitive, simple, and effective chemiluminescence method to not only measure trace amount of XAr, but also monitor their real-time degradation kinetics. These new findings may have broad chemical, pharmaceutical, toxicological and environmental implications for future studies on remediation of these halogenated persistent organic pollutants by AOPs.

Optimization of a UV/H2O2 AOP System Using Scavenger Radicals and Response Surface Methodology

The wastewater produced by industrial processes contains many dissolved hazardous chemicals. The removal of these hazardous chemicals is a requisite for ethical environmental practices. The advanced oxidation process (AOP) is the typical technology used for the removal of these hazardous chemicals. Water treatment via photo-assisted AOP results in the production of hydroxyl radicals (HO.). Hydroxyl radicals are high reactive radicals and they react non-selectively with strong oxidation potential. The hydroxyl radical not only reacts with major contaminants but also with scavenger radicals ( free chlorine, and dissolved organic carbon (DOC)) that are present in the wastewater. Normally, water treatment is focused on a single contaminant, neglecting scavenger radicals, which results in the underprediction of the contaminant concentration after treatment. A well-proposed optimization problem that considers scavenger radicals is proposed in this work. Moreover, in an ultraviolet hydrogen peroxide (UV-HP) AOP reactor, two process inputs (lamp power and molar ratio of H2O2 to organic contaminant) are crucial. A response surface optimization methodology that optimizes these process inputs is also proposed in this research. Methylene blue (MB) was used as the major contaminant. It was observed that the overall contaminant concentration at the reactor outlet was strongly dependent upon the scavenger radicals and the lamp power. It was perceived that after a certain limit, increasing the hydrogen peroxide concentration in the wastewater matrix results in an inhibitory effect of hydrogen peroxide. The accuracy of the proposed model was validated through experimental results. The approach used in this work not only improves the existing UV-HP reactor optimization approach but also provides a better way to model other major contaminants that are present in wastewater.

Computational fluid dynamics modeling alternatives for UV-initiated advanced oxidation processes

Design and optimization of ultraviolet-initiated (UV-initiated) advanced oxidation processes (AOPs) using hydrogen peroxide (H2O2) must consider both system configuration and chemical kinetics. Alternative approaches to modeling AOP systems have been proposed in the literature; yet, due to the complex nature of the reactions involved, the literature lacks clarity in the appropriate selection of a modeling approach to help define the UV/AOP system performance. Computational fluid dynamics (CFD) was compared to the numerical solution of a system of ordinary differential equations describing the reaction mechanism for hydroxyl radical production and methylene blue destruction and to a UV dose distribution analysis produced by a Lagrangian particle track in CFD with a given dose–response curve. Similar analyses were also performed to simulate the destruction of tris(2-chloroethyl) phosphate (TCEP) and tributyl phosphate (TBP), in two different photoreactors. To validate the simulations, the results of the models were compared to pilot reactor trials for methylene blue bleaching and literature data for TCEP and TBP. Modeling results suggest that the agreement of both CFD Eulerian and Lagrangian approaches to simulating the UV/H2O2 AOP is a function of reactor design, the water matrix, and operating conditions.

Photocatalytic reactions of 2,4-dichlorophenoxyacetic acid using a microwave-assisted photocatalysis system

To use an advanced oxidation process system for the degradation of 2,4-dichlorophenoxyacetic acid (2,4-D), a series of experiments were performed in which the effects of microwave and UV irradiation were evaluated. The decomposition rate of 2,4-D increased with increasing microwave intensity, UV intensity, and the auxiliary oxidant dosage. Excessive addition of some oxidants (H2O2 and O2), however, resulted in the reduction of the decomposition rate. The effect of addition of microwave irradiation was not significant unless the ozone addition was applied together. The decomposition rate constant obtained with microwave irradiation combined with ozone addition was considerably higher than those obtained with the combinations of UV and O3, of UV and photocatalyst, or of microwave, UV and photocatalyst. The rate constant obtained with the combination of microwave, UV, photocatalyst, and ozone was the highest, being 4.5times that obtained with the microwave, UV and photocatalyst combination and more than 6times that obtained injection of ozone only. This result suggests that there is a synergy effect when the constituent techniques, i.e., microwave irradiation, UV irradiation, ozone, and photocatalysis are applied together and that the irradiation of microwave can play an important role in the O3-assisted photocatalysis of organic pollutants in water.

Identifying the factors that influence the reactivity of effluent organic matter with hydroxyl radicals

Advanced oxidation processes (AOPs) are an effective treatment technology for the removal of a variety of organic pollutants in both water and wastewater treatment. However, many background constituents in water are highly reactive towards hydroxyl radicals (HO) and decrease the efficiency of the process towards contaminant oxidation. Up to 95% of the HO scavenging can come from dissolved organic matter (OM). In this study, 28 wastewater effluent samples were analyzed to find correlations between the reactivity of HO with wastewater-derived OM (known as effluent organic matter, EfOM), water quality parameters, treatment train characteristics, and fluorescence-derived data. Rate constants for the reaction between HO and EfOM (kEfOM-HO) were measured using a bench scale UV-based AOP system with methylene blue as an HO probe and confirmed using an electron pulse radiolysis method for a subset of the samples. The EfOM was characterized using a series of physicochemical parameters, including polarity, average molecular size and fluorescence. The kinetic data were analyzed with principal component analysis and Akaike Information Criterion. Four predictors were identified as dominant: chemical oxygen demand, retention onto NH2 extraction medium, fluorescence index, and total organic carbon. These four variables accounted for approximately 62% of the variability in the value of kEfOM-HO The average kEfOM-HO value for EfOM in this study was 2.5 × 108 MC−1 s−1, which is about 31% lower than the 3.6 × 108 MC−1 s−1 value determined for natural organic matter isolates and commonly used in AOP modeling.

Treatment of industrial wastewater with high content of polyethylene glycols by Fenton-like reaction system (Fe0/H2O2/H2SO4)

The Fenton-like reaction (FLR) as advanced oxidation process system was successfully applied in the industrial wastewater pre-treatment with high content of polyethylene glycols (PEGs). Our effort was focused on the monitoring of efficiency of chemical oxygen demand (COD) removal in untreated and pre-treated wastewater using FLR (Fe0/H2O2/H2SO4) and also identification of products after treatment process. The influence of FLR pre-treatment on the biological treatment step was also studied. It was found that the COD value removal in untreated wastewater was only 37%, whereas in pre-treated wastewater the COD removal achieved 84%. High-performance liquid chromatography data have shown that during FLR the low-molecular fragments of PEGs are formed. It was also observed that high initial COD value was considerably decreased.

Degradation and toxicity changes in aqueous solutions of chloroacetic acids by Fenton-like treatment using zero-valent iron

AbstractThree priority pollutants, i.e. mono-, di-, and trichloroacetic acids, were degraded by the conventional Fenton AOP system (Fe2+ and H2O2). The results obtained suggest that the degradation decreased in the order: monochloroacetic, dichloroacetic, and trichloroacetic acid. The best of advanced oxidation processes (AOPs) for the degradation of trichloroacetic acid was reductive dechlorination with the use of zero-valent iron (Fe°). The results of Escherichia coli toxicity tests revealed that the reagents’ toxicity after the Fenton treatment process was decreased.

Compact AOP system

An all-in-one type compact Advanced oxidation process (AOP) system using UV/O3/TiO2 for water purification has been developed. Since all elements are packed in one case, portability and easy installation are facilitated. The ozonizer in this system is newly designed for generating ozone gas just before injection and the extending life time of electrodes. TOC degradation ability is confirmed by using sodium acetate solution. The performance of this AOP system is demonstrated for hydroponics. This system can kill bacteria in fertilizer solution, increase dissolved oxygen and no influence for fertilizer elements. From the results of tomato hydroponic tests, tomato growth using this system is much faster than without the system. It is clearly turned out that this AOP system is suitable for hydroponics.

Application of biological oxidation and solar driven advanced oxidation processes to remediation of winery wastewater

Biological oxidation and solar driven advanced oxidation processes (AOPs) applied as a single stages were tested at a pilot plant equipped with an immobilized biological reactor (IBR) and a photocatalytic system with compound parabolic collectors (CPCs) for the remediation of a winery wastewater (DOCaverage=882mgL−1; pH 4.1). Due to the variable nature of winery wastewater composition and quantity, the application of AOPs as a single or as preliminary stage can be an effective alternative to only conventional biological treatment. Regarding the AOPs systems tested (TiO2/H2O2/UV and Fe2+/H2O2/UV), the solar photo-Fenton reaction (optimized at pH 2.8 and 55mg Fe2+L−1) showed the highest efficiency, being necessary an UV dose of 100kJUVL−1 and 338mM H2O2 (15mg H2O2mg C−1) to achieve a COD value lower than 150mg O2L−1, which is agreement with the discharge limits into receiving waters imposed by the Portuguese Legislation (Decree-law n° 236/98). To achieve the same COD target value using only the IBR system or the combination of solar-photo-Fenton (22kJUVL−1; 80mM H2O2 consumed) and biological systems, approximately 10 and 6 days (time necessary for the biological oxidation) are required. The efficiency of the AOPs in the treatment of simulated and real winery wastewaters was also compared.

Heterogeneous Photocatalytic Degradation of Dairy Wastewater Using Immobilized ZnO

This work evaluated the efficiency and systemic application of heterogeneous photocatalytic degradation for dairy wastewater under advanced oxidation process (AOP) utilizing solar radiation and immobilized ZnO as measured by total organic carbon (TOC). The AOP system consisted of a semibatch reactor and glass tank operated with an initial volume of 3 L of dairy wastewater. ZnO was immobilized on a metal plate of mm and used as a catalyst bed. Evaporation rate was considered when effective degradation of the photocatalytic system was determined. The AOP utilized Taguchi’s L8 orthogonal array. The entry variables were pH, reaction time, initial organic load in the effluent, and ZnO coating thickness on the catalyst bed. When optimized, an effective TOC degradation of 14.23% was obtained under variable values of pH 8.0, a metal-plate coating of 100 micrometers (μm) ZnO, and total reaction time of 180 min.

Contribution of Dissolved Oxygen to Methylene Blue Decomposition by Hybrid Advanced Oxidation Processes System

Experimental results of photocatalysis under high dissolved oxygen (DO) concentration conditions are reported. Methylene blue was used as the organic pollutant to be degraded by a novel microwave/UV/DO/TiO2photocatalyst hybrid system. The degradation rate increased with TiO2nanoparticle dosages and DO concentration. However, inhibition of photocatalysis due to bubbles produced by DO generator was also observed. When the DO generator was used to increase the DO concentration in the pollutant solution treated by the microwave-assisted UV-TiO2photocatalysis, the decomposition rate constant was highest among all the experimental conditions tested in this study. This result demonstrated that high concentration of DO can enhance the photocatalytic reaction rate by causing a synergistic effect of constituent techniques.

Study on the Kinetics of NO Removal from Simulated Flue Gas by a Wet Ultraviolet/H2O2 Advanced Oxidation Process

On the basis of the steady-state approximation theory and the two-film theory, the kinetic model of NO removal by a wet ultraviolet (UV)/H2O2 advanced oxidation process (AOP) was established. The mass-transfer reaction kinetic process of NO removal was also analyzed preliminarily. The results showed that the NO removal process by the wet UV/H2O2 AOP was a pseudo-first-order reaction for NO. The NO absorption process in the wet UV/H2O2 AOP system belonged to the fast reaction kinetic region. The chemical reaction process could be completed in the liquid film. The NO absorption rate mainly depended upon the chemical reaction rate, the diffusion rate, and the NO partial pressure, but it was not affected by the liquid-phase mass-transfer coefficient. Therefore, the NO absorption rate could be increased by improving the chemical reaction conditions, increasing the gas−liquid contact area, and raising the NO partial pressure. The comparison of experimental values and model values of pseudo-first-order reaction rate constants showed that the mass-transfer reaction kinetic model deduced had good reliability.

Biofilm control in water by a UV-based advanced oxidation process

An ultraviolet (UV)-based advanced oxidation process (AOP), with hydrogen peroxide and medium-pressure (MP) UV light (H2O2/UV), was used as a pretreatment strategy for biofilm control in water. Suspended Pseudomonas aeruginosa cells were exposed to UV-based AOP treatment, and the adherent biofilm formed by the surviving cells was monitored. Control experiments using H2O2 or MP UV irradiation alone could inhibit biofilm formation for only short periods of time (<24 h) post-treatment. In a H2O2/filtered-UV (>295 nm) system, an additive effect on biofilm control was shown vs filtered-UV irradiation alone, probably due to activity of the added hydroxyl radical (OH•). In a H2O2/full-UV (ie full UV spectrum, not filtered) system, this result was not obtained, possibly due to the germicidal UV photons overwhelming the AOP system. Generally, however, H2O2/UV prevented biofilm formation for longer periods (days) only when maintained with residual H2O2. The ratio of surviving bacterial concentration post-treatment to residual H2O2 concentration played an important role in biofilm prevention and bacterial regrowth. H2O2 treatments alone resulted in poorer biofilm control compared to UV-based AOP treatments maintained with similar levels of residual H2O2, indicating a possible advantage of AOP.