Efficiency Of Advanced Oxidation Processes Research Articles

Electric-Field-Driven Nanoparticles Produce Dual-Functional Bipolar Electrodes and Nanoelectrolytic Cells for Water Remediation

Advanced oxidation processes (AOPs) represent one of the most powerful strategies for dealing with the ever-growing water pollution problem. However, their application is hindered by high cost and risk of handling catalysts and sacrificial chemicals, as well as the low efficiency of electron transfer to peroxides. Here, we report that the addition of nanoparticles (NPs) into the electric field facilitates electron transfer on the surface of NPs to generate reactive oxidizing species (ROS) without the use of sacrificial chemicals. Electrostatic induction can drive the charge separation of individual NPs. Because of the polarization, NPs are turned into numerous bipolar electrodes, which activate the electrogenerated H 2 and O 2 to form ROS, thereby efficiently enabling their fast reaction with the adjacent pollutants. This discovery may provide a general methodology that is fundamental for AOPs and has wide applications for real-life water remediation. A general AOP strategy is reported Electric field drives NPs, creating bipolar electrodes and nanoelectrolytic cells NPs promote electron transfer to make numerous reactive oxidizing species This efficient AOP may address the common drawbacks of AOPs Devising electric-field-driven nanoparticulate oxidation provides a general and powerful strategy to address the common drawbacks of the advanced oxidation process. Guo et al. report the synergistic effect of electrochemistry with nanotechnology. The nanoparticles are subjected to a spontaneous separation of charge under electric field, forming bipolar electrodes and nanoelectrolytic cells, thus facilitating electron-transfer efficiency. This work provides a general methodology for water remediation applications.

Surface dual redox cycles of Mn(III)/Mn(IV) and Cu(I)/Cu(II) for heterogeneous peroxymonosulfate activation to degrade diclofenac: Performance, mechanism and toxicity assessment

Advanced oxidation processes (AOPs) based on heterogeneous catalytic activated peroxymonosulfate (PMS) have been becoming alternatives to conventional wastewater treatment technologies to directly degrade chemical contaminants. To build dual/multi redox cycles of different metal ions may be an effective means for better PMS activation. Herein, this study designed Mn3O4/CuBi2O4 with dual redox cycles of Mn(III)/Mn(IV) and Cu(I)/Cu(II) to activate PMS for efficiently decomposing and mineralizing diclofenac sodium (DCF). Under optimal reaction conditions, DCF (50 mg/L) was degraded totally within 10 min, and TOC removal rate reached up to 74.3%. The possible mechanism of PMS activation by Mn3O4/CuBi2O4 was proposed, wherein dual redox cycles of Mn(III)/Mn(IV) and Cu(I)/Cu(II) on Mn3O4/CuBi2O4 effectively facilitated PMS activation to generate ·O2−, 1O2, SO4·− and ·OH, which was responsible for DCF degradation. Moreover, combined with degraded products detected by high resolution liquid chromatography coupled to mass spectrometry and corresponding toxic assessment results, the possible degradation pathways of DCF were proposed and the relative toxicity of degraded products was evaluated. This work may be useful for developing stronger heterogeneous activators of PMS to construct more efficient AOPs for purifying wastewater.

Improving the Imazapyr Degradation by Photocatalytic Ozonation: A Comparative Study with Different Oxidative Chemical Processes

The degradation of imazapyr (C13H15N3O3), an active element in the aqueous solution of commercial herbicide, was investigated. This study was the first to evaluate in a comprehensive manner the efficiency of advanced oxidation processes for imazapyr degradation. Results showed that Imazapyr degradation is significantly affected by operational conditions such as TiO2 concentration, ozone concentration, initial concentration of imazapyr and pH. The kinetics of Imazapyr consumption was the first order with respect to Imazapyr concentration and zero order with respect to ozone concentration with a constant rate of 0.247 min−1 and 0.128 min−1 for photocatalytic ozonation and heterogeneous photocatalysis, while it was the first order with respect to Imazapyr and the first order with respect to ozone concentrations when only ozone was used with a constant rate of 0.053 mol L−1 min−1 at pH 7. The results revealed that more than 90 percent of the removal efficiency representing the elimination of imazapyr was held up to 7 μM. Further increase in the concentration of imazapyr leads to a drop in the removal efficiency, however the total imazapyr degradation was reached in 20 min utilizing photocatalytic ozonation for 5 μM of Imazapyr in the presence of 100 mg L−1 of TiO2, 10 mg L−1 of ozone at pH 7. Photocatalytic ozonation and heterogeneous photocatalysis utilizing TiO2 as a semiconductor process appeared possible and well suited for the treatment of organic contaminants such as imazapyr herbicides, although at certain dosages of pH and common time for wastewater treatment, imazapyr was not degraded with ozonation on its own. The association of two oxidation processes, ozonation and photocatalysis, has improved oxidation efficiencies for water treatment under optimal conditions, leading to the development of non-selective hydroxyl and more reactive radicals in the oxidation medium, as well as the resulting synergistic effects between photocatalysis and ozonation that react more rapidly with imazapyr herbicide.

Evaluating the efficiency of advanced oxidation processes for textile wastewater treatment: Electro‐kinetic, sonochemical and persulfate

AbstractThe aim of this study was to evaluate the electro‐kinetic/ultrasonic/persulfate (EK/US/PS) process efficiency for textile wastewater treatment. The concentration of persulfate (0.5, 0.75, 1, 1.25, 1.5 mM), reaction time (30, 60, 90 and 120 min were studied consecutively, according to one factor at the time methodology. Result was indicated that the highest removal efficiency of 38% was achieved at pH 5. The chemical oxygen demand (COD) removal efficiency at electrolyte concentration of 6, 8 and 10 g/L were 56, 58 and 59% respectively. Results were showed that by increasing the ultrasonic power up to 300 W, the removal efficiency increased from 78 to 96% at a reaction time of 90 min and from 92 to 96% at a reaction time of 120 min. The correlation coefficient for pseudo‐first‐order kinetic model and pseudo‐second‐order kinetic models were obtained 0.96 and 0.87, respectively. Therefore, according to the results of this study, it was suggested to use EK/US/PS process for treatment of textile wastewater.

Ionothermal Carbonization of Biomass to Construct Fe, N-Doped Biochar with Prominent Activity and Recyclability as Cathodic Catalysts in Heterogeneous Electro-Fenton

Heterogeneous electro-Fenton is an efficient advanced oxidation process for the degradation of refractory organic contaminants in wastewater, and its efficiency is governed by cathodic catalysts. I...

Inhibition of bromate formation in the O3/PMS process by adding low dosage of carbon materials: Efficiency and mechanism

Ozone/peroxymonosulfate (O3/PMS), firstly proposed by our group, is an efficient advanced oxidation process for the degradation of organic pollutants. However, the elevation of bromate formation was the main problem in the treatment of bromide-containing water. In this work, adding low dosage of powdered activated carbon (PAC), carbon nanotube (CNT) and graphene oxide (GO) in the inhibition of bromate formation and the enhanced degradation of organic pollutants during the O3/PMS process were firstly investigated. As 10 mg/L of PAC, CNT and GO were added, the bromate conversion efficiency (25.1%) was decreased to 15.9%, 14.1%, and 8.8% at pH = 7.0, 50 μM PMS addition and 1.135 mg min−1 ozone injection after 25 min reaction. It is shown that the carbon materials played a crucial role in reducing intermediate products (HOBr/OBr−) in the reaction, thereby blocked the bromate formation. This may be due to the defects such as vacancies and zigzag/armchair-like edges on the graphene boundary, which were reported as active sites for oxygen reduction reaction. Meanwhile, the addition of three carbon materials would also promote the degradation of oxalic acid and para-chlorobenzoic acid, and the effect of GO was better than the other two. According to the release of TOC in the reaction, the stability of GO was obviously stronger than that of PAC and CNT, which was attributed to that GO had a relatively stable lamellar structure. Finally, compared with the deionized water, the water matrices that would trap free radicals in actual water samples can significantly inhibit the bromate formation. Therefore, adding low dosage of carbon materials is an effective way to control the bromate formation and promote the degradation of organic pollutants in the O3/PMS process.

Electrochemical-driven carbocatalysis as highly efficient advanced oxidation processes for simultaneous removal of humic acid and Cr(VI)

Electrochemical advanced oxidation processes (AOPs) represent an efficient and promising strategy for dealing with the ever-growing water pollution. Meanwhile, carbocatalysis has long and widely been applied in the fields of synthesis and catalysis because of high activity and selectivity. In this work, we combined the advantages of these two methods and for the first time proposed a conceptual new, novel and promising approach of electrochemical-driven carbocatalysis as highly efficient AOPs for water remediation, which was simply performed by adding carbon-based particles into the electrochemical system. This method shows great potentials for the simultaneous removal of both humic acid (HAC) and Cr(VI) in water, in which HAC was effectively mineralized with a TOC removal efficiency as high as 90% and Cr(VI) was completely removed with a total Cr removal beyond 90%. The presence of carbon particulate materials and their physicochemical properties were first indicated to play critical roles in the developed electrochemical AOPs. These added carbonaceous particles such as activated carbon (AC) and a series of modified AC materials, on one side exerted an important carbocatalytic function with typical AOPs features and on another side, they behaved like numerous galvanic cells with quasi-homogeneous catalytic properties, greatly facilitating mass and electron transfers in the electrochemical system and resulting in a synergistic effect for the removal of combined pollutants. The physicochemical properties of these carbon particulate catalysts facilitated the simultaneous occurrence of adsorption and carbocatalysis, where a synergistic effect between adsorption and catalytic oxidation was confirmed in this electrochemical-driven carbocatalysis system. Moreover, the catalytic performances and mechanisms of this system were found to be dependent on the carbon structures (e.g., surface area, functional groups and hybridization structure, etc.). Very importantly, the energy-effective feature and the carbon materials stability showed a promising prospect of this approach with energy consumption much lower than the ever-reported electrochemical AOPs. This work details the first insight into electrochemical-driven carbocatalysis and provides a new, green and promising approach for effective water remediation, as well as gives new evidence for the synergistic effect between adsorption and catalytic oxidation.

Solar light-assisted remediation of domestic wastewater by NB-TiO2 nanoparticles for potable reuse

Water reuse has become a worldwide necessity due to scarcity of fresh water supplies. Recently, advanced oxidation processes (AOPs) has been incorporated into water reuse treatment train to destroy residual organics in water before its discharge. Yet, the currently applied ultraviolet/H2O2 AOP is associated with high electrical demand by the UV process in addition to transport and storage problems of H2O2. Accordingly, the current work investigates the use of solar light/NB-TiO2 as an efficient AOP for water reuse industry. The technology was developed and tested for degradation of five contaminants of emerging concern (CECs) spiked in Milli-Q water and different wastewater samples. All CECs were successfully removed from individual and quinary systems, even in presence of natural levels of common inorganic quenching agents. Roles of different reactive species involved on the degradation of CECs were explored. Using mass spectroscopy, transformation products from CECs degradation were identified and degradation pathways were hypothesized.

Catalytic degradation of organic pollutants in Fe(III)/peroxymonosulfate (PMS) system: performance, influencing factors, and pathway.

This study demonstrated, for the first time, Fe(III)/peroximonosulphate (PMS) could be an efficient advanced oxidation process (AOP) for wastewater treatment. Bisphenol A (BPA) was chosen as a model pollutant in the present study. Fe(III)-activated PMS system proved very effective to eliminate 92.18% of BPA (20 mg/L) for 30-min reaction time at 0.50 mM PMS, 1.5 g/L Fe(III), pH 7.0. The maximum degradation of BPA occurred at neutral pH, while it was suppressed at both strongly acidic and alkaline conditions. Organic and inorganic ions can interfere with system efficiency either positively or negatively, so their interaction was thoroughly investigated. Furthermore, the presence of organic acids also affected BPA degradation rate, especially the addition of 10 mM citric acid decreased the degradation rate from 92.18 to 66.08%. Radical scavenging experiments showed that SO4•- was the dominant reactive species in Fe(III)/PMS system. A total of 5 BPA intermediates were found by using LC/MS. A possible degradation pathway was proposed which underwent through bridge cleavage and hydroxylation processes. Acute toxicity of the BPA degradation products was assessed using Escherichia coli growth inhibition test. These findings proved to be promising and economical to deal with wastewater using iron mineral for the elimination of organic pollutants. Graphical abstract.

Electrochemically-driven dosing of iron (II) for autonomous electro-Fenton processes with in situ generation of H2O2

Reliance of Fenton processes to hazardous chemicals diminishes the range of niche applications of this highly efficient advanced oxidation process due to risks associated to transport, storage, and handling of chemicals. In this work, an alternative approach towards independent Fenton systems integrating (1) per demand in situ production of H2O2 from oxygen cathodic reduction and (2) electrochemically-driven iron (II) dosing system is explored as a novel strategy. For this purpose, a dual-cell system was designed to fulfill individual current needs of both processes while avoiding excessive iron sludge production observed in peroxicoagulation treatments. Experimental results indicate high reproducibility and resilience of the proposed dual-cell electro-Fenton system, which attained complete organic methylene blue dye decolorization in 80 ​min of treatment and over 80% mineralization in only 120 ​min of electro-Fenton treatment. These results showcase a new approach that opens alternative pathways for possible implementation of low-physical footprint electro-Fenton systems as point-of-entry treatments or even to treat effluents of small and mid-sized industries.

Microwave/Persulphate assisted ZnO mediated photocatalysis (MW/PS/UV/ZnO) as an efficient advanced oxidation process for the removal of RhB dye pollutant from water

Microwave (MW), ultraviolet (UV) light and MW-UV combination are tested as sources of activation for the ZnO-mediated, persulphate (PS)-assisted (MW/PS/UV/ZnO) degradation/mineralization of the pollutant dye Rhodamine B (RhB) in water. The simultaneous irradiation by MW and UV is more efficient and synergistic for the mineralization of the dye compared to the respective individual energy sources. The degradation is influenced by catalyst dosage, concentration of the dye, pH of the medium, presence of contaminant salts, dissolved oxygen etc. The synergy of the MW/PS/UV/ZnO process in comparison to the respective individual processes (MW/PS and UV/ZnO) is attributed to the ‘nonthermal’ and ‘specific’ effect of MW which induce increased formation of reactive oxygen species (ROS) such as O2-, and OH radicals. Formation of surface defects which inhibits the recombination of photoinduced electrons and holes in ZnO is another major reason for the synergy. MW enhances the degradation/mineralisation of RhB even in systems with less dissolved oxygen because of the efficient transference of oxygen from the bulk of the catalyst to the surface. Another interesting observation is that simultaneous MW + UV irradiation of ZnO suspensions deaerated with N2 results in N-doped ZnO, with extended absorption in the visible range of sunlight. The potential of this simple convenient method without any cumbersome procedure for preparing N-doped ZnO needs further in-depth investigation. The study demonstrated the potential use of the combination process ‘microwave-photocatalysis’ for the efficient decontamination of water from dye pollutants.

Gamma Radiation and Hydrogen Peroxide Based Advanced Oxidation Process for the Degradation of Disperse Dye in Aqueous Medium

Abstract In view of promising efficiency of advanced oxidation process (AOP), gamma radiation in combination with H2O2 was employed for the degradation of disperse red 73 (DR73) dye. Cs-137 gamma radiation source was used for dye aqueous solution irradiation. The process variables such as pH (3–9), H2O2 concentration (0.3–0.9 mL), gamma radiation absorbed dose (1–20 kGy) and DR73 initial concentration (50–150 mg/L) were optimized for maximum degradation of dye. The efficiency of AOP was evaluated on the basis of dye degradation, water quality parameters and toxicity reduction. Degradation of DR73 was achieved 69% using gamma radiation absorbed dose of 20 kGy and at the same dose 96.3% degradation was achieved in the presence of 0.9 mL/L H2O2. The dye degradation found to be dependent on dye initial concentration and pH of the medium. The radiolytic progress of DR73 was monitored by Fourier transform infrared (FTIR) and UV-Visible spectroscopy. The chemical oxygen demand (COD) and biological oxygen demand (BOD) were reduced significantly in response of treatment of dye at optimum conditions of process variables. The toxicity of treated and un-treated dye solution was monitored by haemolytic and Ames assays. Results revealed that the toxicity of DR73 dye was also reduced significantly after treatment. Findings revealed that the gamma radiation based AOPs are promising and could possibly be used for the remediation of textile wastewater contains toxic dyes.

ZnO/UV/H2O2 Based Advanced Oxidation of Disperse Red Dye

Abstract In view of promising efficiency of advanced oxidation process, ZnO/UV/H2O2 based advanced oxidation process (AOP) was employed for the degradation of Disperse Red-60 (DR-60) in aqueous medium. The process variables such as concentration of catalysts, reaction time, pH, dye initial concentration and H2O2 dose were evaluated for maximum degradation of dye. The maximum degradation of 97% was achieved at optimum conditions of H2O2 (0.9 mL/L), ZnO (0.6 g/L) at pH 9.0 in 60 min irradiation time. The analysis of treated dye solution revealed the complete degradation under the effect of ZnO/UV/H2O2 treatment. The water quality parameters were also studied of treated and un-treated dye solution and up to 79% COD and 60% BOD reductions were achieved when dye was treated with at optimum conditions. The dissolved oxygen increased up to 85.6% after UV/H2O2/ZnO treatment. The toxicity was also monitored using hemolytic and Ames tests and results revealed that toxicity (cytotoxicity and mutagenicity) was also reduced significantly. In view of promising efficiency of UV/H2O2/ZnO system, it could possibly be used for the treatment of wastewater containing toxic dyes.

A novel graphene oxide-carbon nanotubes anchored α-FeOOH hybrid activated persulfate system for enhanced degradation of Orange II

Persulfate activation has been applied as one of the efficient advanced oxidation processes (AOPs) to remediate polluted environments. In this study, a novel α-FeOOH anchored by graphene oxide (GO)-carbon nanotubes (CNTs) aerogel (α-FeOOH@GCA) nanocomposite activated persulfate system (α-FeOOH@GCA + K2S2O8) was applied for decolorization of Orange II (OII). The decolorization of OII was remarkably enhanced to a level of ~99% in this system compared with that of pristine α-FeOOH (~44%) or GO-CNTs (~18%). The enhanced catalytic activity of α-FeOOH@GCA was due to the formation of a heterojunction by α-FeOOH and GO-CNTs as confirmed by the presence of Fe–O–C chemical bonds. The degradation intermediates of OII were comprehensively identified. The proposed degradation pathway of OII begins with the destruction of the conjugated structures of OII by the dominant reactive oxygen species, surface-bound SO4•−. The decolorization efficiency of OII by the α-FeOOH@GCA activated persulfate system decreased from the first to third cycle of recycling. Ultraviolet (UV) irradiation or introduction of a small amount of Fe2+ could restore the activation of this system. The results show that the α-FeOOH@GCA persulfate activation system promises to be a highly efficient environmental remediation method for organic pollutants.

Understanding the role of mediators in the efficiency of advanced oxidation processes using white-rot fungi

Τhe coupling of biological with advanced oxidation processes for the removal of 13 pharmaceuticals is reported in this study. The efficiency of this system was examined by using two ligninolytic fungi, Trametes versicolor and Ganoderma lucidum. Pharmaceuticals’ removal was examined by using four different quinone substances (1,4-benzoquinone, 2,6-dimethoxy-1,4-benzoquinone, 2-methyl-1,4-naphthoquinone and gallic acid). The quinone redox cycling mechanism of the fungal species promotes the production of hydrogen peroxide for subsequent decomposition to non-selective and highly oxidizing hydroxyl radicals in presence of Fe(III)-oxalate. Results evidenced that the most effective mediators for T. versicolor and G. lucidum were 2,6-dimethoxy-1,4-benzoquinone (DMBQ) and gallic acid (GA), respectively. Time-course experiments showed that higher concentrations of Fe(II) were produced using DMBQ and GA, suggesting that the efficiency of the mediator in reducing Fe(III) is linked to the removal of pharmaceuticals. The application of DMBQ in the redox cycling process of T. versicolor resulted to 60–100% removal for all the pharmaceuticals, due to the high affinity of laccase enzyme for DMBQH2. The advanced bio-oxidation of T. versicolor was tested for hospital wastewater treatment. Results showed a decrease of the elimination degree for pharmaceuticals as compared to the previous bioassays conducted with a synthetic medium. Nevertheless, significant removals (30–100%) were achieved by using DMBQ and GA as mediators of the redox cycle for T. versicolor under the non-sterilized conditions of the hospital wastewater. The use of GA is of great importance since its phenolic form, equivalent to the hydroquinone form, is considered as a critical parameter in Fe(III) reduction.

Elimination kinetics and detoxification mechanisms of microcystin-LR during UV/Chlorine process

Microcystin-LR (MC-LR), a toxin produced by cyanobacteria, is very toxic and poses a threat to public health when entering water treatment works. In this study, UV/chlorine process, as an advanced oxidation process (AOP), has been demonstrated for effective elimination of MC-LR levels and associated toxicity. At a chlorine dose of 3.0 mg L−1 and UV fluence of 125 mJ cm−2, MC-LR (initial concentration 1.0 μM) was reduced by 92.5%, which was much higher than 20.3% removal under UV irradiation alone and 65.1% removal during dark chlorination. Enhanced degradation was attributed by hydroxyl radicals (HO) and reactive chlorine species (RCS), mainly Cl2- and ClO. Increasing chlorine doses or lowering pH favored MC-LR removal. Increased bicarbonate and natural organic matter concentrations inhibited MC-LR removal, but bromide ions enhanced MC-LR removal instead. MC-LR elimination rates in natural waters were roughly two times smaller than those in ultrapure water. The reactive radicals promoted hydroxylation of both diene of Adda moiety and double bond of Mdha moiety in MC-LR. UV exposure enhanced the dechlorination of chloro-MC-LR via the cleavage of CCl bond. The toxicity was evaluated by a protein phosphatase (PP2A) inhibition assay. At a chlorine dose of 3.0 mg L−1 and UV fluence of 125 mJ cm−2, the toxicity of the treated water was reduced by 75.0%, which was also higher than 25.7% and 46.7% removal under UV irradiation alone and during dark chlorination, respectively. These results highlight UV/chlorine is an efficient AOP for MC-LR degradation and detoxification.

Comparative study of the toxicity between three non-steroidal anti-inflammatory drugs and their UV/Na2S2O8 degradation products on Cyprinus carpio

The efficiency of advanced oxidation processes (AOPs) for disposing of non-steroidal anti-inflammatory drugs (NSAIDs) has been widely studied, but the environmental fates and effects of the NSAIDs and their degradation products (DPs) are poorly understood. In this study, the efficiency of ultraviolet light/Na2S2O8 (UV/PS) in degrading three NSAIDs—diclofenac, naproxen, and ibuprofen—and the toxicity of their DPs on Cyprinus carpio (C. carpio) was investigated. Results showed that the three NSAIDs can be completely removed (removal rate > 99.9%) by UV/PS, while the mineralization rate of the NSAIDs was only 28%. When C. carpio were exposed to 0.1 μM NSAIDs, 10 μM persulfate (PS), and 0.1 μM DPs of the NSAIDs for 96 h, respectively, the toxicity effects are as the NSAID DPs > PS > NSAIDs. Research results into the time-dependent effect of NSAID DPs on C. carpio demonstrated that obvious toxicity effects were observed in the first 48 hours, and the toxicity effects strengthened over time. NSAID DPs may have more severe toxicity effects than NSAIDs on C. carpio; therefore, the operating conditions of UV/PS must be optimized to eliminate the ecotoxicity of DPs.

Degradation of the pharmaceuticals nimesulide and ibuprofen using photo-Fenton process: toxicity studies, kinetic modeling and use of artificial neural networks

The growth of pollution in aquatic environments increases every day, causing compounds like pharmaceuticas to be detected in surface waters. Thus, tecniques such as advanced oxidation processes (AOP) have been used to degrade this compounds. In this work, the efficiency of AOP in the degradation of nimesulide and ibuprofen pharmaceuticals was evaluated through chromatographic analysis as well as organic matter through the levels of chemical oxygen demand (COD) and total organic carbon (TOC). It was verified that the photo-Fenton process presented the bests results, degrading 89.70% of nimesulide and 93.35% of ibuprofen. This same process managed to reduce COD by 91.60% and mineralize 90.04% of the TOC. The kinetic study showed a good linear fit (R2=0.993) for the clustered kinetic model, as well as a good fit to the mathematical model of artificial neural networks (ANNs), with a value of R2=1.000 for the MLP4-4-1 BFGS 4567 model. Finally, the toxicity of the solution after treatment was verified against the seeds of Lactuta sativa, Cichorium endívia, Ocimum basilicum and American Hard grain. It was found that the seeds that received the solution before treatment had a lower germination amount than the ones where the post AOP treatment solution was added. Then, the root growth was evaluated, in which a relative toxic effect was observed.

Evaluation of a New Electrochemical Concept for Vacuum Toilet Wastewater Treatment - Comparison with Ozonation and Perozone Processes

Over the last several years, the removal of more than 150 micropollutants was investigated. Many pharmaceuticals are persistent and pass the conventional wastewater treatment plants (WWTP). According to literature, the removal efficiency of various pharmaceuticals is between 0 and 50 % in activated sludge processes. For a standard analgesic such as Diclofenac, the removal efficiency is approx. 30 %. Therefore, additional treatment such as 4th treatment step is necessary, which is already implemented in some WWTPs in Europe, to save water bodies as much as possible. Options for the 4th treatment step are, for example, activated carbon adsorption, nanofiltration and advanced oxidation processes (AOP). By far one of the most cost efficient AOP is the ozonation. However, it is not able to remove X-ray contrast media sufficiently. For this purpose, electrochemical oxidation processes (EAOP) based on boron-doped diamond electrodes are much more effective. Keeping in mind that AOPs are still an emerging technology, especially for water reuse options and also might cause even toxic intermediates, one of the biggest disadvantages are the relatively high operational costs due to the electrical energy demand. Especially electrochemical reactors, which are based on two boron-doped diamond (BDD) electrodes are very cost-intensive, particularly in comparison to ozonation or perozone (ozone plus peroxide) processes. For that reason, a new electrochemical reactor concept, which promises lower CAPEX and OPEX costs, was investigated. This reactor concept consists mainly of one BDD electrode as anode and a gas diffusion electrode (GDE) as cathode. The innovative reactor concept combines the generation of highly reactive hydroxyl radicals on the anode surface and simultaneously hydrogen peroxide on the cathode surface, which is very efficient as there is a double use of the same applied power. Both electrodes are mounted in a membrane-less flow-through reactor in pilot-scale for direct treatment of wastewater. Due to the direct contact between the surfaces of both electrodes, the wastewater gets treated specifically, which leads to a high energy efficiency. First results already prove the more energy efficient removal of COD in an artificial wastewater with the new reactor concept. For a detailed evaluation, a defined artificial wastewater with compounds and concentration equal to vacuum toilet wastewater was treated by the new reactor concept as well as by ozonation and perozone process (ozone plus peroxide). COD removal as well as the associated energy demand were measured after defined intervals in each step of the treatment to determine the performance of the different processes. A comparison was made between the different kind of treatments (EAOP, ozonation, perozone) concerning COD degradation and the power demand. The evaluation is based on electrical energy per order (EEO) conception as well as degradation for given reaction kinetics.

Trace Organic Pollutant Removal by VUV/UV/chlorine Process: Feasibility Investigation for Drinking Water Treatment on a Mini-Fluidic VUV/UV Photoreaction System and a Pilot Photoreactor.

The vacuum-ultraviolet/ultraviolet/chlorine (VUV/UV/chlorine) process, with a VUV/UV mercury lamp used as the light source, was found to be a highly efficient advanced oxidation process (AOP) in a previous study. Hence, its application feasibility for trace organic pollutant removal from drinking water becomes attractive. In this work, a bench-scale mini-fluidic VUV/UV photoreaction system was used to determine the degradation kinetics of sulfamethazine (SMN), a model sulfonamide antibiotic frequently detected with trace levels in aquatic environments. Results indicated that SMN (0.1 mg L-1) could be degraded rapidly by VUV/UV/chlorine, and a synergism was observed between the VUV/UV and UV/chlorine processes. Photon-fluence based rate constants of SMN degradation were determined to be 6.76 × 103 and 8.51 × 103 m2 einstein-1 at chlorine doses of 0.05 and 0.5 mg L-1, respectively. The presence of natural organic matter in real waters significantly inhibited SMN degradation. In addition, pilot tests were conducted to explore the practical performance of the VUV/UV/chlorine process, thereby allowing electrical energy per order to be calculated for cost evaluation. The effect of flow pattern on photoreactor efficiency was also analyzed by computational fluid dynamics simulations. Both bench- and pilot-scale tests have demonstrated that the VUV/UV/chlorine process, as a new AOP, has potential applications to trace organic pollutant removal in small-scale water treatment.