Oxone-promoted wet air oxidation of landfill leachates

Landfill leachates of the city of Badajoz (in the southwest of Spain) have been treated by wet air oxidation at high temperature (180-270 °C) and pressure (40-70 atm). Typical operating variables such as temperature and oxygen partial pressure have been investigated with no effect of any being found and moderate to low chemical oxygen demand conversions (20-30% depending on initial COD concentration). Initial pH shows a positive influence when acidic conditions are used. Addition of hydrogen peroxide (0.01 M) as a hydroxyl radical promoter is able to provide an additional 15% increase in the final COD removal achieved. If a sulfate radical promoter is used (i.e., Oxone) the process is significantly improved, with COD conversions in the range 60-80%, also depending on the initial COD of the leachates. A first attempt to comprehend the chemistry of this oxidizing system suggests an instantaneous decomposition of Oxone that initiates the radical chain also involving hydroxyl and organic radicals

Fenton-like oxidation of landfill leachate

The treatment of stabilized leachates by means of Fenton's like reagent [Fe(III)-H2O2] has been studied. It has been demonstrated that the oxidation state of the catalyst does not influence the efficacy of the process in terms of chemical oxygen demand depletion profiles. The abrupt increase in temperature experienced in oxidation experiments involves a wastage of hydrogen peroxide diminishing the fraction of this reagent addressed at removing COD. If temperature is kept constant, the hydrogen peroxide uptake is 10 mg of H2O2 consumed per mg of COD abated (from 15 to 30°C). Working temperatures above 30°C does not lead to additional COD conversion, contrarily, the percentage of wasted H2O2 is increased. A rough economic analysis of the process indicates that this treatment can be a suitable alternative to deal with this type of effluents

Stabilized leachates: sequential coagulation–flocculation + chemical oxidation process

The combined sedimentation-chemical oxidation treatment of medium-stabilized landfill leachates has been investigated. The sequence of stages implemented was: (a) coagulation–flocculation by pH decrease (pH 2) to acidic conditions (COD removal ≈ 25% related to COD0 ≈ 7500 ppm); (b) coagulation–flocculation by Fe(III) addition (0.01 M) at pH 3.5 (COD removal ≈ 40% related to COD of supernatant after step (a); (c) Fenton (Fe(III) = 0.01 M; H2O2 = 1.0 M) oxidation (COD removal ≈ 80% related to COD of supernatant after step (a); and (d) coagulation–flocculation of Fenton’s effluent at pH 3.5 (COD removal ≈ 90% related to COD of supernatant after step (a). The use of Kynch theory allows for the design of clarifiers based on the amount of solids fed. For a general example of 1000 m3 day−1 of a feeding stream, clarifier area values of 286, 111 and 231 m2 were calculated for compacting indices of 3.7, 2.67 and 2.83 corresponding to the first, second and third consecutive sedimentation processes, respectively, (steps (a), (b) and (d))

Study of different integrated physical-chemical + adsorption processes for landfill leachate remediation

Some integrated processes to deal with landfill leachates have been investigated and their efficiencies expressed in terms of chemical oxygen demand (COD) removal. The systems tested were the result of different combinations of the following single stages: acidic pH shift (elimination of humic substances), ozonation (O3), coagulation-flocculation with Fe(III) salts, Fenton's oxidation (Fe(III) + H2O2), wet air oxidation (with or without radical promoters), and adsorption onto activated carbon (commercial Norit 0.8 powdered activated carbon). COD removals obtained ranged in the interval of 80-96% for initial COD values close to 11000 mg L-1. None of the processes tested reduced the COD levels sufficiently to allow direct discharge; however, the ratio biochemical oxygen demand (BOD/COD was significantly increased (up to 1000% in some cases, i.e., from 0.1 to values above 1.0). Total carbon reduction achieved ranged from 60 to 94%, while complete decolorization (measured as the absorbance at 410 nm) was obtained in practically all the combinations investigate

Stabilized leachates: Ozone-activated carbon treatment and kinetics

Ozone has been used as a pre-oxidation step for the treatment of stabilized leachates. Given the refractory nature of this type of effluents, the conversion of some wastewater quality parameters has been moderate after 1 h of ozonation (i.e. 30% chemical oxygen demand (COD) depletion). Ozone uptake was calculated in the interval 1.3–1:5 g of ozone per gram of COD degraded. An optimum dose of ozone has been experienced in terms of biodegradability of the processed effluent (60 min of treatment, 1 103 mol L1 ozone inlet feeding concentration and 50 L h1 gas flowrate). pH and other typical hydroxyl radical generator systems exerted no influence on the efficiency of the process, suggesting the negligible role played by the indirect route of oxidation (generation of hydroxyl radicals). The ozonated effluent was thereafter treated in a second adsorption stage by using a commercial activated carbon. Removal levels up to 90% of COD in approximately 120 h were experienced for adsorbent dosages of 30 g L1 : Both steps, the single ozonation and the adsorption stage have been modelled by using different pseudoempirical models. r 2003 Elsevier Ltd. All rights reserved

Simulated solar driven photolytic ozonation for the oxidation of aqueous recalcitrant-to-ozone tritosulfuron. Transformation products and toxicity

The authors are grateful to Junta de Extremadura (Project IB16022), co-financed by the European Funds for Regional Development, for economically supporting this work. Moreover, it is also acknowledged the ‘Servicio de Análisis Elemental y Molecular (SAEM)’ of ‘Servicios de Apoyo a la Investigación de la Universidad de Extremadura (SAIUex)’ for the helping with the intermediate products analyses.This work reports the combination of ozone and solar radiation as an advanced oxidation process to remove the herbicide tritosufuron (TSF) in water. Firstly, the recalcitrance of TSF has been assessed, obtaining an ozonation second order rate constant of 5–154 M−1 min−1 in the range of pH from 5 to 8; while the rate constant with HOradical dot was found to be (1.8–3.1)·109 M−1 s−1. Secondly, the simultaneous application of simulated solar radiation in between 300 and 800 nm and ozone resulted positive in the oxidation rate of TSF. Mineralization extent was also higher. Less effective oxidation was achieved after limiting the radiation to the range 360–800 nm or 390–800 nm; also completely inappropriate for mineralization. Thirdly, the detected transformation products (TPs) demonstrated the vulnerability of TSF molecule to be attacked by HOradical dot in the sulfonylurea bridge. The combination of ozone and radiation of 300–800 nm led to the most effective removal of the TPs. Finally, after the photolytic ozonation treatment toxicity was also evaluated in terms of phytotoxicity towards the germination and root elongation of Lactuca Sativa seeds, and toxicity by immobilization tests of Daphnia Magna.Junta de Extremadura (Project IB16022)European Funds for Regional Developmen

Photocatalytic ozonation of pyridine-based herbicides by N-doped titania

The authors thank the economic support received from Gobierno de Extremadura and CICYT of Spain through Projects GRU10012 and CTQ2012-35789-C02-01, respectively. Mr. Rafael Rodríguez Solís thanks Gobierno de Extremadura, Consejería de Empleo, Empresa e Innovación, and FSE Funds for his Ph.D. grant (PD12058).BACKGROUND: A mixture of three pyridine herbicides in water (clopyralid, triclopyr and picloram) has been treated with photocatalytic processes, involving oxygen or ozone. Nitrogen doped and undoped titania were used in the process. Toxicity evolution during photocatalytic ozonation was monitored considering BOD, Daphnia parvula and fitotoxicity trials. RESULTS: N doped titania with an optimized photoactivity was tested in photocatalytic ozonation, leading to nearly 95% mineralization in 180 min. This catalyst was characterized by SEM, TEM, XRD and XPS techniques (13.5 nm crystal size, anatase phase, 1% N, and formation of O-Ti-N linkage). No loss of photocatalytic activity was observed after five consecutive runs. Although no toxicity from the parent compounds was observed, this parameter increased during the early stages of the oxidation process. When parent compounds were totally degraded and dechlorination was completed, toxicity decayed again to negligible values. CONCLUSION: N doping improves bare titania photoactivity through an optimum amount of N. Photocatalysis/ozone showed better behavior than photocatalysis/oxygen in herbicide removal and mineralization, and no significant loss of activity was observed after five runs. Toxicity initially increased due to toxic byproducts formation; however, it decreased after their abatement.Gobierno de Extremadura GRU10012CICYT of Spain CTQ2012-35789-C02-01Gobierno de ExtremaduraFSE Funds (PD12058

Synergism between peroxymonosulfate and LaCoO3-TiO2 photocatalysis for oxidation of herbicides. Operational variables and catalyst characterization assessment

Authors thank economic support received from Junta de Extremadura, CICYT of Spain and FEDER funds through Projects GR15033 and CTQ2015/64944-R, respectively. Mr Rafael Rodríguez Solís also acknowledges Gobierno de Extremadura, Consejería de Empleo Empresa e Innovación, and FSE Funds for his PhD grant (PD12058). Catalyst characterization was provided by Facility of Analysis and Characterization of Solids and Surfaces of SAIUEx (financed by University of Extremadura, Junta de Extremadura, MICINN, FEDER and FSE).BACKGROUND. This paper reports the use of novel coupled LaCoO3-TiO2 as photocatalyst with double route of peroxymonosulfate (PMS) activation. First, as a photocatalyst due to titania; and second, through PMS heterogeneous decomposition onto LaCoO3 particles. Thus, photocatalytical activity was tested for removing a mixture of four herbicides of different recalcitrance (metazachlor, tembotrione, tritosulfuron and ethofumesate). RESULTS. The presence of light and PMS highly enhanced herbicides removal rate: 3.5–5 times increases were obtained with UVA light. Oxidant concentration, catalyst load, pH and temperature were assessed. Herbicides were completely oxidized depending on their recalcitrant nature and the operational variables. 55% TOC conversion was reached using Oxone® 5 × 10−4 mol L−1. Phytotoxicity assays denoted no inhibition after 180 min of photocatalytic treatment (∼80% initial inhibition). Solid properties of Co/Ti = 0.1:1 ratio were studied by means of SEM (LaCoO3 aggregates linked to a variety of shapes and sizes of TiO2), XRF (6.1% of LaCoO3), XPS (superficial Co3+, La3+ and Ti4+), XRD (anatase, rutile and rhombohedral LaCoO3) and UV–vis diffuse reflectance (visible range absorption and bandgap of 2.88 eV for TiO2). CONCLUSION. Catalysts based on LaCoO3-TiO2 combined with peroxymonosulfate seem to be suitable for removing organic pollutants, with a moderate conversion of TOC and elimination of toxicity.Junta de Extremadura GR15033CICYT of Spain CTQ2015/64944-RFEDER foundsGobierno de ExtremaduraFSE Funds (PD12058)University of ExtremaduraJunta de ExtremaduraMICINNFS

Simulated solar photo-assisted decomposition of peroxymonosulfate. Radiation filtering and operational variables influence on the oxidation of aqueous bezafibrate

This work investigates the potential of the combination of peroxymonosulfate (PMS) and simulated solar radiation (λ > 300 nm) to remove bezafibrate from aqueous solution. Different solar light filters indicate a higher removal efficiency as the wavelength range used moves to the more energetic region of the solar spectrum. The system PMS/Daylight (300–800 nm) eliminates bezafibrate (1 mg L−1) in less than 30 min under the best conditions used in this study (CPMS = 4·10−4 M) with no pH control (acidic pH). The efficiency of the process significantly improves under alkaline conditions (pH = 10), likely due to a higher PMS photolysis rate. Experiments conducted at different initial concentration of PMS and bezafibrate suggest first order regarding PMS and different from 1 in the case of bezafibrate. Intermediates generated at the beginning of the process have been tentatively identified to propose a hypothetical reaction pathway and to estimate their toxicity