Nowadays there is a continuously increasing worldwide concern for development of alternative water reuse technologies, mainly focused on agriculture and industry. In this context, Advanced Oxidation ...Processes (AOPs) are considered a highly competitive water treatment technology for the removal of those organic pollutants not treatable by conventional techniques due to their high chemical stability and/or low biodegradability. Although chemical oxidation for complete mineralization is usually expensive, its combination with a biological treatment is widely reported to reduce operating costs. This paper reviews recent research combining AOPs (as a pre-treatment or post-treatment stage) and bioremediation technologies for the decontamination of a wide range of synthetic and real industrial wastewater. Special emphasis is also placed on recent studies and large-scale combination schemes developed in Mediterranean countries for non-biodegradable wastewater treatment and reuse. The main conclusions arrived at from the overall assessment of the literature are that more work needs to be done on degradation kinetics and reactor modeling of the combined process, and also dynamics of the initial attack on primary contaminants and intermediate species generation. Furthermore, better economic models must be developed to estimate how the cost of this combined process varies with specific industrial wastewater characteristics, the overall decontamination efficiency and the relative cost of the AOP versus biological treatment.
The application of electrochemical processes for wastewater treatment has increase significantly in the last two decades. However, most of the works are focused on lab-scale systems testing in saline ...simulated solutions spiked with a reference organic compound, evidencing the scarcity of studies on actual wastewaters through a more realistic practical approach. The aim of the present work is assessing the performance of electrochemical treatments in actual matrices, considering the formation of different oxidants species, apart from hydroxyl radicals, from dissolved ions contained in target effluents as well as both, the regeneration of Fe2+ and their combination with a light irradiation source. The degradation of a mix of microcontaminants in water matrices with different complexity by solar photoelectron-Fenton at natural pH and at pilot scale has been carried out at Plataforma Solar de Almería. Higher degradation rates were obtained when focusing on the more complex and saline matrices. In addition, complex industrial wastewaters mineralization was also studied by means of solar assisted electro-oxidation, showing the crucial role of ammonium concentration in the effluent, since it acts as a competitor for active chlorine species and so reducing the mineralization rate.
•Application studies of electrochemical treatments to actual wastewaters are still very scarce.•Solar energy/electrochemical processes mean an increase in the oxidizing species generated.•Higher micro-contaminant degradation rates achieved by SPEF in actual effluents.•Ammonia in the effluent competes with the DOC for chlorine oxidant species.
Autopsy of carbon-PTFE cathodes was performed by addressing their degradation in a commercial plate-and-frame cell equipped with a Nb-BDD anode. Cell is arranged within an electrochemical pilot plant ...designed for treating wastewaters by electrochemical Fenton-like processes, thus an efficient electrocatalytic production of H2O2 is necessary to guarantee Fenton’s reaction. Significant decrease in H2O2 electrogeneration occurred during pilot plant operation, hindering the efficient performance of Fenton-like processes. Two cathodes were studied, first was operated at pH 3 and second at neutral pH by using EDDS as complexing agent to maintain iron in solution. Electrogenerated H2O2 decreased from 43 mg L−1 to 16 mg L−1 in the first cathode after 50 h of operation and from 49 mg L−1 to 24 mg L−1 in the second one after 26 h of operation. Both were cleaned with 30% (v/v) solution of HCl/water for 24 h and H2O2 production was recovered only in the second cathode (able to generate 39 mg L−1). Autopsy of the cathodes was tackled by scanning electron microscopy (SEM) and X-ray energy dispersive (EDX), evidencing a strong degradation of first cathode surface and iron oxide inlays in second one due to the decomposition of Fe3+:EDDS and consequent iron precipitation at neutral pH.
•Carbon-PTFE cathodes drastically reduced their capability to electrogenerate H2O2 after EF/SPEF.•Acid pH operation showed irreversible cathode surface degradation and loss of carbon cover.•Neutral pH provoked decrease on electrogenerated H2O2 highly recovered after cleaning (HCl/water).
Industrial wastewaters characterized by its high content in organics and conductivity entails a challenge for conventional treatments due to its low biodegradability. Electro-oxidative processes have ...been successfully applied for the treatment of this kind of wastewaters achieving high organics and ammonia removal. The degradation process is executed mainly by electrochemically generated active chlorine species, as HClO and ClO− with E0 = 1.49 V; and E0 = 0.89 V, respectively. Under solar radiation, specifically at 313 nm, the formation of Cl (E0 = 2.4 V) from ClO− is promoted, improving the oxidizing capacity of the process. In this work the combination of an electrochemical device with a solar photo-reactor has been evaluated aiming to increase the degradation rate per kWh−1. Two different complex industrial wastewaters were tested, achieving higher organics degradation when electrochemical treatment was assisted by solar light. Toxicity reduction was also assessed and biodegradability enhanced and allowing its ulterior lower-cost biological treatment.
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•Solar-assisted electro-oxidative treatment enhanced wastewater biodegradability.•Solar light promotes the formation of chlorine radicals from electrogenerated chlorine species.•Combination of solar and electrochemical processes achieved substantial organic removal.•Electro-oxidation is effective for removal of nitrogenated compounds.
► Low TiO2 concentration suitable for removal of contaminants in WWTP effluents. ► The low concentration of TiO2 limits the reaction rate due to the loss of photons. ► Contaminant degradation >85% is ...possible after a certain reaction time. ► New developments in CPC photoreactors with as large an O.D. are necessary.
The optimal photocatalyst concentration for industrial wastewater treatment in current photoreactor designs is several hundreds of milligrams per liter. However, the elimination of emerging contaminants (ECs), which are present at extremely low concentrations in waste water treatment plants (WWTP) effluents might be accomplished at much lower catalyst (TiO2) concentrations. One of the main drawbacks of reducing catalyst loading below the optimum is the loss of useful photons which instead are transmitted through the TiO2 suspension without being absorbed by the catalyst. Accordingly, in this work, laboratory and solar pilot-scale experiments were performed with real WWTP effluents to evaluate the kinetics of photocatalytic degradation of 52 emerging contaminants under realistic (ppb) concentrations. The analysis of the samples was accomplished by solid phase extraction (SPE) followed by liquid chromatography–mass spectrometry (LC–MS). In view of the results, low concentrations of TiO2 of the order of tens of milligrams per liter were found to be insufficient for the degradation of the ECs in photoreactors with a short light-path length (29cm). However, it was established that solar reactors of diameters of several hundreds of millimetres could be used for the efficient removal of ECs from WWTP effluents. The results presented show a general methodology for selecting the most efficient reactor diameter on the basis of the desired catalyst concentration.
The present study shows the results of solar photo-Fenton oxidation of paracetamol (PCT) and amoxicillin (AMX). Fe2(SO4)3 was used as the source of iron and EDDS as the iron complexing agent, ...employing different doses of hydrogen peroxide. Two aqueous matrices, a synthetic wastewater and real wastewater from El Ejido WWTP effluent (Almeria) were used. In all cases, the process was operated under conditions of natural sunlight.
Results showed that the degradation of both drugs is favoured when the aqueous matrix presents low concentration of carbonates. Under the conditions studied here, degradation percentages above 90% were obtained in the synthetic wastewater and 80% in the actual effluent. The degradation products were determined using liquid chromatography coupled to high-resolution mass spectrometry with hybrid quadrupole time-of-flight analyser. The intermediates detected throughout the oxidative process for both micro-contaminants were mainly products of hydroxylation reactions.
The toxicity of the samples was determined using the bacterium Vibrio fischeri. In the acute toxicity test, it was observed that the bacteria did not undergo inhibition in any of the cases. However, chronic toxicity studies showed that the higher the Hydraulic Retention Time (HRT) employed in the assays, the higher the bacterial inhibition.
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•Solar photo-Fenton successfully degraded microcontaminants under natural sunlight and circumneutral pH.•90% and 80% degradation percentages were obtained in the synthetic wastewater and actual effluent.•In acute toxicity tests, bacteria did not undergo inhibition in any of the cases.
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•Microcontaminants eliminated (>99%) by ozonation but acute toxicity increased.•Acute toxicity was related to microcontaminant byproducts or other water components.•D. magna ...adaptation and reduction of chronic toxicity in S. capricornutum was observed.•Ozonation and membrane technologies could be combined to treat microcontaminants.
The purpose of this work was to study the ozonation of nanofiltration (NF) retentates of real municipal wastewater treatment plant (MWTP) effluents for removal of microcontaminants (MCs) and toxicity. MCs present in these effluents were monitored using LC–MS/MS. Acute and chronic toxicity was addressed with Daphnia magna, Vibrio fischeri and Selenastrum capricornutum. Up to 40 MCs were found, most of them in concentrations over 100ng/L. 90% degradation of the sum of MCs was the critical point of comparison. When the NF membrane system was applied to MWTP effluents, treatment of NF rejection needed 2.75–4.5g O3/m3,4.5g O3/m3, which is less than 50% of the ozone needed for direct treatment of MWTP effluent. Treatment time (lower than 11min) was not influenced by MCs concentration, at least in the range tested (25–190μg/L). It has been demonstrated that consumption of ozone increased with organic load and inorganic content of different real effluents. MCs were eliminated by ozonation but acute toxicity (against V. fischeri and D. magna) increased. Chronic toxicity results were different and contrary in D. magna and S. capricornutum, due to the generation of new transformation products more toxic to D. magna than the parent contaminants. S. capricornutum inhibition percentage decreased in all cases after ozonation treatment. According to these results, before ozonation is implemented in MWTPs for the removal of MCs, the transformation products must first be examined and the treatment time or ozone doses should be extended to complete degradation if necessary.
•Antipyrine, caffeine, carbamazepine, ciprofloxacin and sulfamethoxazol were completely degraded.•Solar/Fe/H2O2 and solar/Fe/S2O82− system mediated by EDDS have been compared.•Different Fe:EDDS ...ratios, initial iron species and oxidant agents have been tested.•Best ratio for solar/Fe:EDDS/H2O2 was 1:2 and 1:1 for solar/Fe:EDDS/S2O82−.
The main purpose of this pilot plant study was to compare degradation of five microcontaminants (MCs) (antipyrine, carbamazepine, caffeine, ciprofloxacin and sulfamethoxazole at 100 μg/L) by solar photo-Fenton mediated by EDDS and solar/Fe:EDDS/S2O82−. The effects of the Fe:EDDS ratio (1:1 and 1:2), initial iron species (Fe(II) or Fe(III) at 0.1 mM) and oxidizing agent (S2O82− or H2O2 at 0.25–1.5 mM) were evaluated. The higher the S2O82− concentration, the faster MC degradation was, with S2O82− consumption always below 0.6 mM and similar degradation rates with Fe(II) and Fe(III). Under the best conditions (Fe 0.1 mM, Fe:EDDS 1:1, S2O82− 1 mM) antipyrine, carbamazepine, caffeine, ciprofloxacin and sulfamethoxazole at 100 μg/L where 90% eliminated applying a solar energy of 2 kJ/L (13 min at 30 W/m2 solar radiation <400 nm). Therefore, S2O82− promotes lower consumption of EDDS as Fe:EDDS 1:1 was better than Fe:EDDS 1:2. In photo-Fenton-like processes at circumneutral pH, EDDS with S2O82- is an alternative to H2O2 as an oxidizing agent.
In recent years, membrane technologies (nanofiltration (NF)/reverse osmosis (RO)) have received much attention for micropollutant separation from Municipal Wastewater Treatment Plant (MWTP) ...effluents. Practically all micropollutants are retained in the concentrate stream, which must be treated. Advanced Oxidation Processes (AOPs) have been demonstrated to be a good option for the removal of microcontaminants from water systems. However, these processes are expensive, and therefore, are usually combined with other techniques (such as membrane systems) in an attempt at cost reduction. One of the main costs in solar photo-Fenton comes from reagent consumption, mainly hydrogen peroxide and chemicals for pH adjustment. Thus, in this study, solar photo-Fenton was used to treat a real MWTP effluent with low initial iron (less than 0.2 mM) and hydrogen peroxide (less than 2 mM) concentrations. In order to work at neutral pH, iron complexing agents (EDDS and citrate) were used in the two cases studied: direct treatment of the MWTP effluent and treatment of the concentrate stream generated by NF. The degradation of five pharmaceuticals (carbamazepine, flumequine, ibuprofen, ofloxacin and sulfamethoxazole) spiked in the effluent at low initial concentrations (μg L−1) was monitored as the main variable in the pilot-plant-scale photo-Fenton experiments. In both effluents, pharmaceuticals were efficiently removed (>90%), requiring low accumulated solar energy (2 kJUV L−1, key parameter in scaling up the CPC photoreactor) and low iron and hydrogen peroxide concentrations (reagent costs, 0.1 and 1.5 mM, respectively). NF provided a clean effluent, and the concentrate was positively treated by solar photo-Fenton with no significant differences between the direct MWTP effluent and NF concentrate treatments.
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•Treatment of the concentrate stream generated from NF by photo-Fenton.•Solar photo-Fenton at neutral pH with complexing agents (EDDS and citrate).•EDDS as complexing agent permits that 90% of pharmaceuticals were removed.•Treatment of NF concentrate required lower UV energy.
•Solar photo-Fenton and UV highly efficient in the removal of micro-contaminants.•Comparison between solar photo-Fenton and UV must consider an economic assessment.•Solar and UV with 50mg/L of H2O2 ...and UV with 50mg/L of peroxydisulfate showed similar costs.•Total costs increase if more than 99% degradation of micro-contaminants is required.
One of the most important factors affecting the application of advanced oxidation processes (AOPs) at full scale are the high operating costs, especially those associated with the cost of the reagents. Therefore, the optimization of operating parameters, such as a reduction in reagent consumption to achieve the partial or complete decontamination of waters, is crucial in AOP application. The present study is focused on the comparison of solar and UV photo-Fenton technologies (by using H2O2 or S2O82−), for the removal of five micro-contaminants (antipyrine, caffeine, carbamazepine, ciprofloxacin and sulfamethoxazole) from simulated freshwater at very low concentrations (100ppb each one). In addition, economic assessment of the implementation of UV/H2O2, UV/S2O82−, solar/Fe(II)/H2O2 and solar/Fe(II)/S2O82− was also carried out. The total costs obtained were 0.42€/m3 for solar/Fe(II)/H2O2 with 50mg/L of initial H2O2, 0.72€/m3 for solar/Fe(II)/S2O82− with 50mg/L of initial S2O82−, 0.43€/m3 for UV/H2O2 with 50mg/L of initial H2O2, 0.49€/m3 for UV/S2O82− with 50mg/L of initial S2O82− and 0.61€/m3 for UV/S2O82− with 25mg/L of initial S2O82−. It was concluded that consumption of reagents and electricity costs coming from lamp operation in the UV process had a significant impact on the total operating cost of both technologies. Furthermore, it must be stressed that solar and UV processes promoted by H2O2 are more cost-effective than when employing S2O82−.
