Economic evaluation of the photo-Fenton process. Mineralization level and reaction time: the keys for increasing plant efficiency

A critical review on paracetamol removal from different aqueous matrices by Fenton and Fenton-based processes, and their combined methods

Paracetamol (PCT), also known as acetaminophen, is a drug used to treat fever and mild to moderate pain. After consumption by animals and humans, it is excreted through the urine to the sewer systems, wastewater treatment plants, and other aquatic/natural environments. It has been detected in trace amounts in effluents of wastewater plant treatments, sewage sludge, hospital wastewaters, surface waters, and drinking water. PCT can cause genetic code damage, oxidative degradation of lipids, and denaturation of protein in cells, and its toxicity has been well-proven in bacteria, algae, macrophytes, protozoan, and fishes. To avoid its harmful health problems over living beings, powerful Fenton and Fenton-based treatments as pre-eminent advanced oxidation processes (AOPs) have been developed because of the inefficient treatment by conventional treatments. This paper presents a comprehensive and critical review over the application of such Fenton technologies to remove PCT from natural waters, synthetic wastewaters, and real wastewaters. The characteristics and main results obtained using Fenton, photo-Fenton, electro-Fenton, and photoelectro-Fenton are described, making special emphasis in the oxidative action of the generated reactive oxygen species. Hybrid processes based on the coupling with ultrasounds, gamma radiation, photocatalysis, photoelectrocatalysis, zero-valent iron-activated persulfate, adsorption, and microbial fuel cells, are analyzed. Sequential treatments involving the initiation with plasma gliding arc discharge and post-biological process are detailed. Comparative results with other available AOPs are also described and discussed. Finally, 13 aromatic by-products and 9 short-linear aliphatic carboxylic acid detected during the PCT removal by Fenton and Fenton-based processes are reported, with the proposal of three parallel pathways for its initial degradation.

Solar Photo-Assisted Degradation of Bipyridinium Herbicides at Circumneutral pH: A Life Cycle Assessment Approach

This study investigated the degradation of the herbicides diquat (DQ) and paraquat (PQ) by a solar photo-Fenton process that is mediated by Fe(III)-oxalate complexes at circumneutral pH = 6.5 in compound parabolic collectors (CPC)-type reactors. The photo-Fenton process operates efficiently at acidic pH; however, circumneutral operation was key to overcome drawbacks, such as acidification and neutralization steps, reagent costs, and the environmental footprint of chemical auxiliaries. This work revealed a remarkable reduction of total organic carbon for PQ (87%) and DQ (80%) after 300 min (at ca. 875 kJ L−1). Phytotoxicity assays confirmed that the treatment led to a considerable increase in the germination index for DQ (i.e., from 4.7% to 55.8%) and PQ (i.e., from 16.5% to 59.7%) using Cucumis sativus seeds. Importantly, treatment costs (DQ = USD$8.05 and PQ = USD$7.72) and the carbon footprint of the process (DQ = 7.37 and PQ = 6.29 kg CO2-Eqv/m3) were within the ranges that were reported for the treatment of recalcitrant substances at acidic conditions in CPC-type reactors. Life cycle assessment (LCA) evidenced that H2O2 and electricity consumption are the variables with the highest environmental impact because they contribute with ca. 70% of the carbon footprint of the process. Under the studied conditions, a further reduction in H2O2 use is counterproductive, because it could impact process performance and effluent quality. On the other hand, the main drawback of the process (i.e., energy consumption) can be reduced by using renewable energies. The sensitivity study evidenced that carbon footprint is dependent on the energy share of the local electricity mix; therefore, the use of more renewable electrical energy sources, such as wind-power and photovoltaic, can reduce greenhouse gases emissions of the process an average of 26.4% (DQ = 5.57 and PQ = 4.51 kg CO2-Eqv/m3) and 78.4% (DQ = 3.72 and PQ = 2.65 kg CO2-Eqv/m3), respectively. Finally, from the economic and environmental points of view, the experimental results evidenced that photo-assisted treatment at circumneutral pH is an efficient alternative to deal with quaternary bipyridinium compounds.

Treatment of a synthetic colored effluent in raceway reactors: The role of operational conditions on the environmental performance of a photo-Fenton process

This study assessed the environmental and economic performance of a photo-Fenton process in a raceway reactor at laboratory scale. For the best operational condition (BOC) identified (dye = 55.0 mg/L, H₂O₂/dye = 0.862 mg/L, Fe²⁺/dye = 0.184) a carbon footprint (CFP) of 1.335 kg CO₂ Eqv/m³ was obtained. Consumption of electrical energy, construction materials, and reagents represent 97.2% (1.298 kg CO₂ Eqv/m³) of the CFP. Similarly, ReCiPe-2016 v1.1 evidenced that these activities play an important role on the environmental performance of the process because their relative impact ranged from 96.5% to 99.7% at least in 14 of the 18 categories considered by this method. It should be noted that the CFP is scarcely sensitive to variations in the use of cement, steel, H₂O₂, and NaOH as a 50.0% increase in their expenditure increases the CFP in 4.4%, 5.0%, 5.9%, and 7.2%, respectively. A 50.0% increment in electricity consumption increased the CFP in 20.7% whereas categories related to acidification, eutrophication, resources depletion, and toxicity-related impacts had significant increments (20.0%-34.0%) in the emissions of substances used for impact characterization. BOC led to the lowest treatment cost (US$0.540/m³) and a CFP between 5- and 10-times lower than that reported for solar tubular reactors. Also, higher proportions of H₂O₂ (H₂O₂/dye = 1.200-1.800) and Fe²⁺ (Fe²⁺/dye = 0.200-0.300) increased cost in 1.9%-5.6% but reduced the CFP in 1.2%-3.7%. Finally, our results evidenced that it is possible to increase the raceway reactor's capacity by increasing the depth of the reactor without affecting the effluent quality. When the depth of the reaction medium went from 3 cm to 6 cm, the treatment capacity (TC) was increased 102.4%, and a 33.3% diminution in the CFP and of 29.1% in the treatment cost occurred. An increase from 3 cm to 9 cm rose the TC up to 204.4% and reduced the CFP (44.4%) and treatment cost (39.3%).

Techno-economic estimation of electroplating wastewater treatment using zero-valent iron nanoparticles: batch optimization, continuous feed, and scaling up studies

Electroplating manufacturing processes release industrial effluents that comprise severe levels of heavy metals into the environment. This study investigated the utilization of nanoparticles of zero-valent iron (nZVI) for the treatment of electroplating wastewater industry containing multiple heavy metal ions. In batch experiments using Cu²⁺ as a single solute, the optimum operating condition was pH 7.3, nZVI dosage 1.6 g/L, time 36 min, temperature 30 °C, and agitation speed 180 rpm, achieving almost 100% Cu²⁺ removal efficiency. The adsorption mechanisms were illustrated using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and Fourier transform infrared (FTIR) spectrometer. Moreover, continuous-feed experiments were performed to treat real electroplating wastewater industry via adsorption and sedimentation processes. The system attained removal efficiencies of 91.3% total suspended solids (TSS), 68.3% chemical oxygen demand (COD), 94.2% nitrogen (N), 98.5% phosphorus (P), 66.7% Cr⁶⁺, 91.5% Pb²⁺, 83.3% Ag⁺, 80.8% Cu²⁺, 17.4% Ni²⁺, 47.1% Mn²⁺, 54.6% Zn²⁺, 94.7% Fe³⁺, 100.0% Al³⁺, and 42.1% Co²⁺. The removal mechanisms included reduction of Meⁿ⁺ to Me^(n-x)+/Me⁰ by the Fe⁰ core, adsorption to the oxide shell as Me(OH)_x and Me-Fe-OOH, oxidation of Meⁿ⁺ to Me^(n+z)+, specific surface bonding, and sequential steps of electron transfer and precipitation. The total cost, including amortized and operating expenses for scaling up the adsorption system, was 4.45$ per m³ of electroplating wastewater. Graphical abstract.

Techno-economic and environmental approaches of Cd2+ adsorption by olive leaves (Olea europaea L.) waste

In this study, the techno-economic approach of olive leaves (Olea europaea L.) wastes for the removal of Cd²⁺ from aqueous solutions was demonstrated. The adsorption process was illustrated regarding batch experiments and scanning electron microscopy, energy dispersive X-ray, and Fourier-transform infrared characterization. The optimum pH and contact time were 6.6 and 123 min, respectively, giving Cd²⁺ removal efficiencies of 94.9% at C_o = 50 mg/L and 81.5% at C_o = 100 mg/L. The monolayer adsorption capacity of the Langmuir isotherm model was 32.6 mg/g (R² = 0.97). The adsorption mechanisms might be related to (a) ion exchange with cations (e.g., K⁺, Na⁺, and Ca²⁺), (b) formation of cadmium chloride complexes, (c) interaction with oxygen-containing functional groups, (d) physical agglomeration in the pore surface, and (e) precipitation interaction using inorganic minerals (i.e., carbonates, phosphates, and silicates). The total cost of the adsorption process for the treatment of ions-containing wastewater was 0.038 $USD/m³. Assuming a benefit-cost of tertiary treated water as 0.044 $USD/m³, the adsorption system could attain a payback period of 5.7 years. This period was shorter than the lifetime of the capital investment (i.e., 10 years), and hence, the project would be economically feasible for an application.

Photolysis of enrofloxacin, pefloxacin and sulfaquinoxaline in aqueous solution by UV/H2O2, UV/Fe(II), and UV/H2O2/Fe(II) and the toxicity of the final reaction solutions on zebrafish embryos

In this work, the photolysis of enrofloxacin (ENR), pefloxacin (PEF), and sulfaquinoxaline (SQX) in aqueous solution by UV combined with H₂O₂ or ferrous ions (Fe(II)), as well as Fenton (Fe(II)/H₂O₂) processes, was investigated. In addition, the toxicity of the final reaction solution after UV/H₂O₂/Fe(II) treatment toward zebrafish embryos was determined. The degradation of the test compounds followed pseudo-first-order reaction kinetics. The optimum concentrations of H₂O₂ for ENR, PEF and SQX removal under UV/H₂O₂ treatment were 20, 20 and 5 mM, respectively. The optimum concentrations of Fe(II) for ENR, PEF and SQX removal in the UV/Fe(II) system were 0.25, 10, and 1 mM, respectively. For the UV/H₂O₂/Fe(II) system, pH = 3 is the best initial pH for the degradation of ENR, PEF and SQX with the degradation efficiencies at 100%, 79.1% and 100% after 180 min, respectively. Considering the degradation rate and electrical energy per order of the test compounds, the UV/H₂O₂/Fe(II) process was better than the UV/H₂O₂ and UV/Fe(II) processes because of the greater OH generation. Based on major transformation products of ENR, PEF, and SQX detected during UV/H₂O₂/Fe(II) treatment, the probable degradation pathway of each compound is proposed. The fluorine atom of ENR and PEF was transformed into fluorine ion, and the sulfur atom was transformed into SO₂/SO₄^2-. The nitrogen atom was mainly transformed into NH₃/NH₄⁺. Formic acid, acetic acid, oxalic acid, and fumaric acid were identified in the irradiated solutions and all the test compounds and their intermediates can be finally mineralized. In addition, after the UV/H₂O₂/Fe(II) process, the acute toxicity of the final reaction solutions on zebrafish embryos was lower than that of the initial solution without any treatment. In summary, UV/H₂O₂/Fe(II) is a safe and efficient technology for antibiotic degradation.

Treatment of synthetic dye baths by Fenton processes: evaluation of their environmental footprint through life cycle assessment

Inorganic and organic constituents present in textile effluents have a noticeable effect on the performance of Fenton processes. However, studies have been focused on simple wastewater matrices that do not offer enough information to stakeholders to evaluate their real potential in large-scale facilities. Chemical auxiliaries, commonly present in textile wastewaters (NaCl = 30 g/L, Na₂CO₃ = 5 g/L, and CH₃COONa = 1 g/L), affect both the economic and environmental performance of the process because they increase the treatment time (from 0.5 to 24 h) and the consumption of H₂SO₄ (657%) and NaOH (148%) during conditioning steps. The life cycle assessment (LCA) performed with the IPCC-2013 method revealed that dyeing auxiliaries increase from 1.06 to 3.73 (252%) the emissions of carbon dioxide equivalent (CO₂-Eqv/m³). Electricity consumption can be considered an environmental hotspot because it represents 60% of the carbon footprint of the Fenton process. Also, the presence of auxiliaries is critical for the process because it results in the increase of the relative impact (between 50 and 80%) in all environmental categories considered by the ReCiPe-2008 method. Chemical auxiliaries increased the costs of the treatment process in 178% (US$2.22/m³) due to the higher energy consumption and the additional reagent requirements. It is worthwhile mentioning that the technical simplicity of the Fenton process and its low economic and environmental costs turn this process into an attractive alternative for the treatment of textile effluents in emerging economies.

How does intensification influence the operational and environmental performance of photo-Fenton processes at acidic and circumneutral pH

This study evaluates the technical, economical, and environmental impact of sodium persulfate (Na₂S₂O₈) as an enhancing agent in a photo-Fenton process within a solar-pond type reactor (SPR). Photo-Fenton (PF) and photo-Fenton intensified with the addition of persulfate (PFPS) processes decolorize 97% the azo dye direct blue 71 (DB71) and allow producing a highly biodegradable effluent. Intensification with persulfate allowed reducing treatment time in 33% (from 120 to 80 min) and the consumption of chemical auxiliaries needed for pH adjustment. Energy, reagents, and chemical auxiliaries are still and environmental hotspot for PF and PFPS; however, it is worth mentioning that their environmental footprint is lower than that observed for compound parabolic concentrator (CPC)-type reactors. A life-cycle assessment (LCA) confirms that H₂O₂, NaOH, and energy consumption are the variables with the highest impact from an environmental standpoint. The use of persulfate reduced the relative impact in 1.2 to 12% in 12 of the 18 environmental categories studied using the ReCiPe method. The PFPS process emits 1.23 kg CO₂ (CO₂-Eqv/m³ treated water). On the other hand, the PF process emits 1.28 kg CO₂ (CO₂-Eqv/m³ treated water). Process intensification, chemometric techniques, and the use of SPRs minimize the impact of some barriers (reagent and energy consumption, technical complexity of reactors, pressure drops, dirt on the reflecting surfaces, fragility of reactor materials), limiting the application of advanced oxidation systems at an industrial level, and decrease treatment cost as well as potential environmental impacts associated with energy and reagents consumption. Treatment costs for PF processes (US$0.78/m³) and PFPS processes (US$0.63/m³) were 20 times lower than those reported for photo-Fenton processes in CPC-type reactors.

Application of Advanced Oxidation Processes for the Treatment of Recalcitrant Agro-Industrial Wastewater: A Review

Agro-industrial wastewaters are characterized by the presence of multiple organic and inorganic contaminants of environmental concern. The high pollutant load, the large volumes produced, and the seasonal variability makes the treatment of these wastewaters an environmental challenge. A wide range of wastewater treatment processes are available, however the continuous search for cost-effective treatment methods is necessary to comply with the legal limits of release in sewer systems and/or in natural waters. This review presents a state-of-the-art of the application of advanced oxidation processes (AOPs) to some worldwide generated agro-industrial wastewaters, such as olive mill, winery and pulp mill wastewaters. Studies carried out just with AOPs or combined with physico-chemical or biological treatments were included in this review. The main remarks and factors affecting the treatment efficiency such as chemical oxygen demand (COD), biochemical oxygen demand (BOD5), total organic carbon (TOC), and total polyphenols removal are discussed. From all the studies, the combination of processes led to better treatment efficiencies, regardless the wastewater type or its physico-chemical characteristics.

Operation costs of the solar photo-catalytic degradation of pharmaceuticals in water: A mini-review

The removal of pharmaceuticals present in wastewater is receiving more and more attention since most of them are refractory to traditional biological treatments. Many advanced oxidation processes have been reported in literature. However, cost estimations are not available for most of them. Recently, more environment friendly processes using solar radiation are gaining importance. The solar photo-Fenton process has been used with different reactor configurations and scales and seems to be the most promising technology for reducing operation costs. In addition, the use of ferrioxalate-aided systems allows the use of pHs close to neutrality, that reduces costs before disposal (not calculated here). The possible use of photovoltaic panels for an energy-free process makes it very interesting for an economic evaluation. Results for the homogeneous solar photo-Fenton process show that when pure compounds are present in water, mineralization is in the range 18-21% with an estimated operation cost of 0.739-0.85 €/m³. An increase in mineralization up to 60-80.6% requires either the use of ferrioxalate (slightly increasing costs to 1.1-1.56 €/m³) or the addition of very high concentration of H₂O₂, that rises costs substantially. The presence of pharmaceuticals in a Waste Water Treatment Plant effluent reduces mineralization (maximum of 20%) also increasing costs. On the other hand, published results confirm that heterogeneous photocatalysis with TiO₂ (both suspended or immobilized) is still far to compete with homogeneous photo-Fenton process in operation costs. The development of new reactor systems and modified photo-catalysts are needed to compete as an efficient applicable technology in the near future.

Optimization of photo-Fenton process for the treatment of prednisolone

Prednisolone is a widely prescribed synthetic glucocorticoid and stated to be toxic to a number of non-target aquatic organisms. Its extensive consumption generates environmental concern due to its detection in wastewater samples at concentrations ranged from ng/L to μg/L that requests the application of suitable degradation processes. Regarding the actual treatment options, advanced oxidation processes (AOPs) are presented as a viable alternative. In this work, the comparison in terms of pollutant removal and energetic efficiencies, between different AOPs such as Fenton (F), photo-Fenton (UV/F), photolysis (UV), and hydrogen peroxide/photolysis (UV/H₂O₂), was carried out. Light diode emission (LED) was the selected source to provide the UV radiation. The UV/F process revealed the best performance, reaching high levels of both degradation and mineralization with low energy consumption. Its optimization was conducted and the operational parameters were iron and H₂O₂ concentrations and the working volume. Using the response surface methodology with the Box-Behnken design, the effect of independent variables and their interactions on the process response were effectively evaluated. Different responses were analyzed taking into account the prednisolone removal (TOC and drug abatements) and the energy consumptions associated. The obtained model showed an improvement of the UV/F process when treating smaller volumes and when adding high concentrations of H₂O₂ and Fe²⁺. The validation of this model was successfully carried out, having only 5% of discrepancy between the model and the experimental results. Finally, the performance of the process when having a real wastewater matrix was also tested, achieving complete mineralization and detoxification after 8 h. In addition, prednisolone degradation products were identified. Finally, the obtained low energy permitted to confirm the viability of the process.

Fenton treatment of bio-treated fermentation-based pharmaceutical wastewater: removal and conversion of organic pollutants as well as estimation of operational costs

The Fenton process is used as a tertiary treatment to remove organic pollutants from the effluent of bio-treated pharmaceutical wastewater (EBPW). The optimal and most appropriate Fenton conditions were determined by an orthogonal array test and single-factor experiments. The removal of chemical oxygen demand (COD) was influenced by the following factors in a descending order: H₂O₂/Fe(II) molar ratio > H₂O₂ dosage > reaction time. Under the most appropriate Fenton conditions (H₂O₂/Fe(II) molar ratio of 1:1, H₂O₂ dosage of 120 mg L^-1 and reaction time of 10 min), the COD and dissolved organic carbon (DOC) were removed with efficiencies of 62 and 53%, respectively, which met the national discharge standard (GB 21903-2008) for the Lake Tai Basin, China. However, the Fenton treatment was inadequate for removal of N compounds, and the removal of organic nitrogen led to an increment in N-NH₃ from 3.28 to 19.71 mg L^-1. Proteins and polysaccharides were completely removed, and humic acids (HAs) were partly removed with an efficiency of 55%. Three-dimensional excitation/emission matrix spectra (3DEEMs) indicated complete removal of fulvic acid-like substances and 90% reduction in the florescence intensity of humic acid-like substances. Organic pollutants with molecular weights (MW) > 10 kDa were completely removed, MW 5-10 kDa were degraded into smaller MW ones, and some low molecular weight acids (MW 0.1-1 kDa) were mineralized during the Fenton process. Some species, including pharmaceutical intermediates and solvents were detected by gas chromatography-mass spectrometry (GC-MS). The operational costs of the Fenton's treatment were estimated to be 0.58 yuan RMB/m³ EBPW based on reagent usage and iron sludge treatment and disposal.

Fenton's treatment as an effective treatment for elderberry effluents: economical evaluation

The utilization of Fenton's oxidation for the depuration of elderberry juice wastewater was studied. The aim was to select the adequate cost-effective operating conditions suitable to lead to an effluent within the legal thresholds to be discharged into the natural water courses. The treatment efficacy was assessed by chemical oxygen demand (COD), colour, phenolic content and total solids removal besides its ability to improve biodegradability (biochemical oxygen demand (BOD5)/COD). Moreover, the costs of the applied reactants were also considered. Fenton's reaction was able to abate at least 70% of COD (corresponding to a final value below 150 mg O2 L(-1)). Besides, total phenolic content degradation was always achieved. Within these conditions, the resulting effluent is able to be directly discharged into the natural hydric channels. Fenton oxidation could be successfully applied as a single treatment method with a reactant cost of 4.38 € m(-3) ([Fe(2+)] = 20 mmol L(-1), [H2O2] = 100 mmol L(-1), pH = 3 and 4 h of oxidation procedure).

Photonic efficiency of the photodegradation of paracetamol in water by the photo-Fenton process

An experimental study of the homogeneous Fenton and photo-Fenton degradation of 4-amidophenol (paracetamol, PCT) is presented. For all the operation conditions evaluated, PCT degradation is efficiently attained by both Fenton and photo-Fenton processes. Also, photonic efficiencies of PCT degradation and mineralization are determined under different experimental conditions, characterizing the influence of hydrogen peroxide (H2O2) and Fe(II) on both contaminant degradation and sample mineralization. The maximum photonic degradation efficiencies for 5 and 10 mg L(-1) Fe(II) were 3.9 (H2O2 = 189 mg L(-1)) and 5 (H2O2 = 378 mg L(-1)), respectively. For higher concentrations of oxidant, H2O2 acts as a "scavenger" radical, competing in pollutant degradation and reducing the reaction rate. Moreover, in order to quantify the consumption of the oxidizing agent, the specific consumption of the hydrogen peroxide was also evaluated. For all operating conditions of both hydrogen peroxide and Fe(II) concentration, the consumption values obtained for Fenton process were always higher than the corresponding values observed for photo-Fenton. This implies a less efficient use of the oxidizing agent for dark conditions.

Fenton-like degradation of nalidixic acid with Fe(3+)/H2O 2

The Fenton-like degradation of nalidixic acid was studied in this work. The effects of Fe(3+) concentration and initial H(2)O(2) concentration were investigated. Increasing the initial H(2)O(2) concentration enhances the degradation and mineralization efficiency for nalidixic acid, while Fe(3+) shows an optimal concentration of 0.25 mM. A complete removal of nalidixic acid and a TOC removal of 28 % were achieved in 60 min under a reaction condition of [Fe(3+)] =0.25 mM, [H(2)O(2)] =10 mM, T=35 °C, and pH=3. LC-MS analysis technique was used to analyze the possible degradation intermediates. The degradation pathways of nalidixic acid were proposed according to the identified intermediates and the electron density distribution of nalidixic acid. The Fenton-like degradation reaction of nalidixic acid mainly begins with the electrophilic attack of hydroxyl radical towards the C3 position which results in the ring-opening reaction; meanwhile, hydroxyl radical attacking to the branched alkyl groups of nalidixic acid leads to the oxidation at the branched alkyl groups.

Urban wastewater treatment plants as hotspots for the release of antibiotics in the environment: a review

Urban wastewater treatment plants (UWTPs) are among the main sources of antibiotics' release into various compartments of the environment worldwide. The aim of the present paper is to critically review the fate and removal of various antibiotics in wastewater treatment, focusing on different processes (i.e. biological processes, advanced treatment technologies and disinfection) in view of the current concerns related to the induction of toxic effects in aquatic and terrestrial organisms, and the occurrence of antibiotics that may promote the selection of antibiotic resistance genes and bacteria, as reported in the literature. Where available, estimations of the removal of antibiotics are provided along with the main treatment steps. The removal efficiency during wastewater treatment processes varies and is mainly dependent on a combination of antibiotics' physicochemical properties and the operating conditions of the treatment systems. As a result, the application of alternative techniques including membrane processes, activated carbon adsorption, advanced oxidation processes (AOPs), and combinations of them, which may lead to higher removals, may be necessary before the final disposal of the effluents or their reuse for irrigation or groundwater recharge.

Homogeneous sonophotolysis of food processing industry wastewater: Study of synergistic effects, mineralization and toxicity removal

The mineralization of industrial wastewater coming from food industry using an emerging homogeneous sonophotolytic oxidation process was evaluated as an alternative to or a rapid pretreatment step for conventional anaerobic digestion with the aim of considerably reducing the total treatment time. At the selected operation conditions ([H(2)O(2)]=11,750ppm, pH=8, amplitude=50%, pulse length (cycles)=1), 60% of TOC is removed after 60min and 98% after 180min when treating an industrial effluent with 2114ppm of total organic carbon (TOC). This process removed completely the toxicity generated during storing or due to intermediate compounds. An important synergistic effect between sonolysis and photolysis (H(2)O(2)/UV) was observed. Thus the sonophotolysis (ultrasound/H(2)O(2)/UV) technique significantly increases TOC removal when compared with each individual process. Finally, a preliminary economical analysis confirms that the sono-photolysis with H(2)O(2) and pretreated water is a profitable system when compared with the same process without using ultrasound waves and with no pretreatment.

Oxidation of aqueous pharmaceuticals by pulsed corona discharge

Oxidation of aromatic compounds of phenolic (paracetamol, beta-oestradiol and salicylic acid) and carboxylic (indomethacin and ibuprofen) structure used in pharmaceutics was studied. Aqueous solutions were treated with pulsed corona discharge (PCD) as a means for advanced oxidation. Pulse repetition frequency, delivered energy dose and oxidation media were the main parameters studied for their influence on the process energy efficiency. The PCD treatment appeared to be effective in oxidation of the target compounds: complete degradation of pollutant together with partial mineralization was achieved at moderate energy consumption; oxidation proceeds faster in alkaline media. Low-molecular carboxylic acids were identified as ultimate oxidation by-products formed in the reaction.

Solar photo-Fenton process on the abatement of antibiotics at a pilot scale: Degradation kinetics, ecotoxicity and phytotoxicity assessment and removal of antibiotic resistant enterococci

This work investigated the application of a solar driven advanced oxidation process (solar photo-Fenton), for the degradation of antibiotics at low concentration level (μg L(-1)) in secondary treated domestic effluents at a pilot-scale. The examined antibiotics were ofloxacin (OFX) and trimethoprim (TMP). A compound parabolic collector (CPC) pilot plant was used for the photocatalytic experiments. The process was mainly evaluated by a fast and reliable analytical method based on a UPLC-MS/MS system. Solar photo-Fenton process using low iron and hydrogen peroxide doses ([Fe(2+)](0) = 5 mg L(-1); [H(2)O(2)](0) = 75 mg L(-1)) was proved to be an efficient method for the elimination of these compounds with relatively high degradation rates. The photocatalytic degradation of OFX and TMP with the solar photo-Fenton process followed apparent first-order kinetics. A modification of the first-order kinetic expression was proposed and has been successfully used to explain the degradation kinetics of the compounds during the solar photo-Fenton treatment. The results demonstrated the capacity of the applied advanced process to reduce the initial wastewater toxicity against the examined plant species (Sorghum saccharatum, Lepidium sativum, Sinapis alba) and the water flea Daphnia magna. The phytotoxicity of the treated samples, expressed as root growth inhibition, was higher compared to that observed on the inhibition of seed germination. Enterococci, including those resistant to OFX and TMP, were completely eliminated at the end of the treatment. The total cost of the full scale unit for the treatment of 150 m(3) day(-1) of secondary wastewater effluent was found to be 0.85 € m(-3).

Paracetamol degradation intermediates and toxicity during photo-Fenton treatment using different iron species

The photo-Fenton degradation of paracetamol (PCT) was evaluated using FeSO(4) and the iron complex potassium ferrioxalate (FeOx) as iron source under simulated solar light. The efficiency of the degradation process was evaluated considering the decay of PCT and total organic carbon concentration and the generation of carboxylic acids, ammonium and nitrate, expressed as total nitrogen. The results showed that the degradation was favored in the presence of FeSO(4) in relation to FeOx. The higher concentration of hydroxylated intermediates generated in the presence of FeSO(4) in relation to FeOx probably enhanced the reduction of Fe(III) to Fe(II) improving the degradation efficiency. The degradation products were determined using liquid chromatography electrospray time-of-flight mass spectrometry. Although at different concentrations, the same intermediates were generated using either FeSO(4) or FeOx, which were mainly products of hydroxylation reactions and acetamide. The toxicity of the sample for Vibrio fischeri and Daphnia magna decreased from 100% to less than 40% during photo-Fenton treatment in the presence of both iron species, except for D. magna in the presence of FeOx due to the toxicity of oxalate to this organism. The considerable decrease of the sample toxicity during photo-Fenton treatment using FeSO(4) indicates a safe application of the process for the removal of this pharmaceutical.