RESUMEN

It has been reported that the dihydroxybenzene (DHB) driven Fenton reaction is more efficient to degrade recalcitrant substrates than the simple Fenton reaction. The enhanced reactivity of the DHB driven Fenton reaction is not clear, but it could be explained by the formation of oxidant species different from the ones formed by classical Fenton reaction or by the shift of the redox potential of the complex formed by DHB and Fe(III). The redox reaction between Fe(III) and the DHBs 1,2-dihydroxybenzene (catechol, CAT), 2,3-dihydroxybenzoic acid (2,3-DHBA), 3,4-dihydroxybenzoic acid (3,4-DHBA), and 1,2-dihydroxy-3,5-benzenedisulfonate (TIRON) was studied by cyclic voltammetry to better understand the enhanced reactivity of the DHB driven Fenton reaction. It was determined that the amount of Fe(II) produced by the redox reaction between Fe(III) and DHBs was insufficient to explain the enhanced reactivity. Cyclic voltammograms (CV) of the DHBs/Fe(III) systems show a quasi-reversible or irreversible behavior and also shifting and splitting the anodic peaks. This effect can be related to DHBs oxidation by Fe(III), but not to a real interaction.

Asunto(s)

Derivados del Benceno/química , Técnicas Electroquímicas , Compuestos Férricos/química , Peróxido de Hidrógeno/química , Hidroxibenzoatos/química , Hierro/química , Coriolaceae/química , Compuestos Ferrosos/química , Oxidación-Reducción

RESUMEN

Titanium dioxide was obtained in its pure form (TiO2) and in the presence of urea (u-TiO2) and thiourea (t-TiO2) using the sol-gel technique. The obtained powders were characterized by BET surface area analysis, Infrared Spectroscopy, Diffuse Reflectance Spectroscopy and the Rietveld refinement of XRD measurements. All the prepared catalysts show high anatase content (>99%). The a and b-cell parameters of anatase increase in the order TiO2u-TiO2>TiO2. The photocatalytic activities of the samples were determined on flumequine under solar-simulated irradiation. The most active catalysts were u-TiO2 and t-TiO2, reaching values over 90% of flumequine degradation after 15 min irradiation, compared with values of 55% for the pure TiO2 catalyst. Changing simultaneously the catalyst amount (t-TiO2) and pH, multivariate analysis using the response surface methodology was used to determine the roughly optimal conditions for flumequine degradation. The optimized conditions found were pH below 7 and a catalyst amount of 1.6 g L(-1).

Asunto(s)

Antibacterianos , Fluoroquinolonas , Luz Solar , Titanio/química , Contaminantes Químicos del Agua , Purificación del Agua/métodos , Antibacterianos/química , Antibacterianos/efectos de la radiación , Catálisis , Fluoroquinolonas/química , Fluoroquinolonas/efectos de la radiación , Fotoquímica , Contaminantes Químicos del Agua/química , Contaminantes Químicos del Agua/efectos de la radiación

RESUMEN

Increasing pulp industry production has generated additional solid waste (i.e. biological sludge, dregs, etc.) and therefore an increasing disposal problem. On the other hand, composting is emerging as an interesting alternative for the disposal of residues. The objective of this study was to evaluate the physical and chemical properties of sludge, dregs and bark and the effect on their initial conditioning stage prior to composting, using pine chips as bulking agent. After their characterization, these solid wastes were combined in different mixture proportions defined by a 32 experimental design based on the response surface methodology (RSM), in which 18 observations were required for the independent variables (dregs and bark) and the C: N ratio, moisture content and pH were the dependent variables. The characterization indicated that the dregs have alkaline properties with the presence of some essential plant nutrients, such as phosphorous (0.37%), potassium (0.76%), magnesium (1.4%) and calcium (27%). The combination of the macronutrients (phosphorous: 0.39%, potassium: 0.24%, calcium: 1.7%, magnesium: 0.44%) and micronutrients such as ferrous material (0.47%) and zinc (0.12%) found in the sludge suggest a promising alternative despite the potential problem due to the high pH of the dregs. The RSM design indicated a feasible region that satisfied the optimal dregs: bark ratio of 0.25 without exceeding the addition of 12.5% dregs, due to the alkaline properties of these inorganic wastes and the quadratic influence over the C:N ratio. The experimental results indicated that the composting process of dregs, bark and sludge is technically suitable, although the use of a rapidly available C source needs to be evaluated.

Asunto(s)

Biodegradación Ambiental , Residuos Industriales/prevención & control , Modelos Teóricos , Eliminación de Residuos/métodos , Corteza de la Planta , Eliminación de Residuos/normas , Aguas del Alcantarillado

RESUMEN

Degradation of 2.5 mM EDTA-Fe solution was performed in a coupled photocatalytic-biological reactor. The system consists of a photochemical annular reactor filled with TiO2 immobilized on glass Raschig rings coupled with an activated sludge continuous reactor. Around 50% of EDTA degradation was reached after 150 min irradiation. Simultaneously a four-fold increase in biodegradability, measured as BOD5/COD ratio, was observed. The activated sludge is not capable to degrade the complex EDTA-Fe but it removed partially the COD and efficiently the BOD5 of the photochemically treated solution.

Asunto(s)

Compuestos Férricos/aislamiento & purificación , Quelantes del Hierro/aislamiento & purificación , Contaminantes Químicos del Agua/aislamiento & purificación , Purificación del Agua/métodos , Biodegradación Ambiental , Reactores Biológicos , Catálisis , Ácido Edético/química , Ácido Edético/aislamiento & purificación , Ácido Edético/metabolismo , Ácido Edético/efectos de la radiación , Compuestos Férricos/química , Compuestos Férricos/metabolismo , Compuestos Férricos/efectos de la radiación , Quelantes del Hierro/química , Quelantes del Hierro/metabolismo , Quelantes del Hierro/efectos de la radiación , Oxidación-Reducción , Aguas del Alcantarillado , Titanio/química , Rayos Ultravioleta , Contaminantes Químicos del Agua/química , Contaminantes Químicos del Agua/metabolismo , Contaminantes Químicos del Agua/efectos de la radiación

RESUMEN

A combined chemical oxidation (catechol-driven Fenton reaction) followed by a biological treatment was used to degrade Fe(III)-EDTA (1.34 mM). The chemical treatment was inspired in fungal non-enzymatic wood rot mechanisms that use dihydroxybenzens in order to promote the Fenton reaction to breakdown wood structures. This chemical pre-oxidation used catechol (50 microM) and H202 (20 mM) and the reaction products were identified by GC-MS. In addition, a biological treatment was coupled using the baker's yeast Saccharomyces cerevisiae. The combined chemical biological treatment achieved 100% EDTA degradation, 68 % total organic carbon removal and 90% iron removal.

Asunto(s)

Quelantes/química , Ácido Edético/química , Hierro/química , Eliminación de Residuos Líquidos/métodos , Purificación del Agua/métodos , Biodegradación Ambiental , Ácido Edético/metabolismo , Hongos , Peróxido de Hidrógeno/química , Hierro/metabolismo , Oxidantes/química

RESUMEN

Dihydroxybenzenes are able to reduce Fe(III) and promote the Fenton reaction in the presence of H2O2. The catechol/Fe(III)/H2O2 system has been successfully used to degrade different compounds, being more efficient than the Fe(II)-Fenton reaction. In this paper the possibilities for using the catechol-driven Fenton reaction to degrade recalcitrant compounds such as the Fe(III)-EDTA complex and veratryl alcohol are reviewed.

Asunto(s)

Derivados del Benceno/aislamiento & purificación , Catecoles/química , Peróxido de Hidrógeno/química , Hierro/química , Purificación del Agua/métodos , Derivados del Benceno/química , Quelantes , Ácido Edético/química , Oxidación-Reducción

RESUMEN

The photocatalytic degradation of three reactive azo dyes (yellow-2, orange-16 and red-2) and one anthraquinone reactive dye (blue-19) was studied. The reactions were carried out in a reactor with recirculation using TiO2 immobilised on glass Raschig rings (system A) and compared with a batch system using the catalyst in aqueous suspension (system B). Both reaction systems were irradiated with a 125 W, lambda > 254 nm lamp. The suspended TiO2 system was also studied using a 125 W 360 nm lamp (system C). Kinetic studies indicated a rapid colour removal, following the order B > A > C. The same trend was observed in COD and TOC removal profiles. The energy consumption per order of magnitude of catalytic degradation of the dyes was lower in the batch reactor (system B) than in the reactor with recirculation and immobilised TiO2 (system A).

Asunto(s)

Compuestos Azo/química , Colorantes/química , Titanio/química , Catálisis , Oxígeno , Fotoquímica , Industria Textil , Purificación del Agua/métodos

RESUMEN

Different compounds that reduce Fe(III) and that simultaneously increase the oxidation potential of the H2O2/Fe2+ system, have been evaluated. In this work, the improving of Fenton reactions by 2,3-dihydroxybenzoic acid (2,3-DHBA), 3,4-dihydroxybenzoic acid (3,4-DHBA) or 1,2-dihydroxybenzene (CAT) were studied. The three compounds are able to reduce Fe(III) to Fe(II), but the kinetic results depend on the method used to determine the Fe(II) ion. The dihydroxybenzenes (DHBs) degrades veratryl alcohol (VA), a lignin model compound, to a greater extent than observed in a typical Fenton reaction. The rate of VA degradation was associated with the duration of the chemiluminescence (CAT > 2,3-DHBA > 3,4-DHBA) and not with the sum of integrated counts. The treatment of a cellulose pulp bleaching effluent with DHBs/Fe(III)/H2O2 was evaluated by analyzing their depolymerization at pH 4 and 7 through molecular mass distribution determinations.

Asunto(s)

Derivados del Benceno/química , Eliminación de Residuos Líquidos/métodos , Celulosa/química , Compuestos Férricos/química , Compuestos Ferrosos/química , Peróxido de Hidrógeno/química , Concentración de Iones de Hidrógeno , Hierro/química , Cinética , Oxidantes/química , Oxidación-Reducción

RESUMEN

A cellulose bleaching effluent (E1) was degraded in batch conditions by photocatalysis using TiO2 and ZnO supported on glass Raschig rings. The effluent was completely decolourised and the total phenol content was reduced by 85% after 120 min treatment with both catalysts. Partial mineralization of the organic matter was confirmed by total organic carbon (TOC) reduction, approximately 50%. The residual organic matter shows a low acute toxicity as compared to the initial values and AOX values are strongly reduced after the photocatalytic oxidation. Molecular mass distribution showed that high molecular mass compounds were almost completely degraded.

Asunto(s)

Celulosa/metabolismo , Colorantes/metabolismo , Titanio/metabolismo , Eliminación de Residuos Líquidos/métodos , Óxido de Zinc/metabolismo , Catálisis , Color , Papel , Fotoquímica

RESUMEN

The oxidation of a 186 ppm 6-chlorovanillin solution was performed using impregnated TiO2 glass rings in a 1 l photochemical reactor. Fifty per cent degradation was obtained after 60 min with recirculation of the solution. Then, oxidised samples were submitted under aerobic conditions to bacterial degradation in the Pseudomonas paucimobilis (S37) and Burkholderia cepacia (PZK). Both selected aerobic bacteria degrade more efficiently the photocatalysed samples, being PZK strain better than S37. A first-order kinetic was observed in both systems photocatalytic and bacterial degradation.

Asunto(s)

Pseudomonas/metabolismo , Microbiología del Suelo , Ácido Vanílico/metabolismo , Biodegradación Ambiental , Catálisis , Colorantes/química , Industrias , Oxidación-Reducción , Papel , Fotoquímica , Titanio/química , Ácido Vanílico/análogos & derivados , Eliminación de Residuos Líquidos

RESUMEN

The degradation, by several advanced oxidation reactions, of a pulp mill ECF bleaching effluent, was studied. The initial biodegradability of the organic matter present in the effluent, estimated as the BOD5/COD, was low (0.3). When the effluent was submitted to ozonation and to five different advanced oxidation systems (O3/UV, O3/UV/ZnO, O3/UV/TiO2, O2/UV/ZnO, O2/UV/TiO2), the biodegradability increase significantly. After five minutes of reaction, the O3/UV system appears as the most efficient in to transform the organic matter to more biodegradable forms. A similar effect was observed when the effluent was submitted to an activated sludge treatment. The COD, TOC and toxicity reduction correlated well with the biodegradability enhancement after AOPs treatments.

Asunto(s)

Residuos Industriales/efectos adversos , Residuos Industriales/análisis , Papel , Eliminación de Residuos Líquidos , Biodegradación Ambiental , Biomasa , Celulosa , Compuestos de Cloro , Oxidación-Reducción , Óxidos , Photobacterium/metabolismo

RESUMEN

Iron-chelating low-molecular-weight compounds or catecholate siderophores have been suggested to be involved in wood biodegradation. To help in understanding the mechanism involved in the enzyme-like activity of catecholate siderophores, the oxidative properties of 2,3-dihydroxybenzoic acid (DHBA) and 3, 4-dihydroxyphenylacetic acid (DHPAA) chelated with iron were studied. The pH and catechol/Fe(III) ratios were optimized for o-dianisidine oxidation, obtaining a maximum at pH 7.0, in the absence of buffer, and a catechol/Fe(III) ratio of 1:2 to DHBA and 1:1 to DHPAA was found. Under these conditions, the catechols were able to reduce Fe(III) to Fe(II) acting like siderophore models. The Fe(III) complex of DHBA and of DHPAA degraded dioxane-lignin in 60% after 2 h and 85% after 24 h, respectively. DHBA/Fe(III) oxidized the bleaching effluent (E1) in 80% in 5 min under the studied conditions.

Asunto(s)

Ácido 3,4-Dihidroxifenilacético/química , Hidroxibenzoatos/química , Quelantes del Hierro/química , Hierro/química , Lignina/análogos & derivados , Lignina/química , Dioxanos , Cinética , Oxidación-Reducción , Espectrometría de Fluorescencia , Espectrofotometría