Christophe Bengoa

Catalytic removal of phenol from aqueous phase using oxygen or air as oxidant

Abstract A preliminary study of specific catalysts used to oxidize organic compounds which are hazardous to the environment is presented. The catalytic oxidation of phenol in an aqueous solution using commercially supported copper oxides was studied in a continuous trickle-bed reactor at three temperatures (120, 140 and 160°C) and under three partial pressures of oxygen (0.6, 0.9 and 1.2 MPa) using molecular oxygen or air as oxidation agents. The influence of various parameters is presented. Over the range of conditions used, the oxidation kinetics are first order with respect to phenol and COD (chemical oxygen demand) reduction and half order with respect to the partial oxygen pressure. The results are similar when using air or oxygen as an oxidizing agent. Activation energies for phenol oxidation and COD conversion were found to be 85 and 76 kJ/mol.

Bimetallic catalysts for continuous catalytic wet air oxidation of phenol

Catalytic wet oxidation has proved to be effective at eliminating hazardous organic compounds, such as phenol, from waste waters. However, the lack of active long-life oxidation catalysts which can perform in aqueous phase is its main drawback. This study explores the ability of bimetallic supported catalysts to oxidize aqueous phenol solutions using air as oxidant. Combinations of 2% of CoO, Fe2O3, MnO or ZnO with 10% CuO were supported on gamma-alumina by pore filling, calcined and later tested. The oxidation was carried out in a packed bed reactor operating in trickle flow regime at 140 degrees C and 900 kPa of oxygen partial pressure. Lifetime tests were conducted for 8 days. The pH of the feed solution was also varied. The results show that all the catalysts tested undergo severe deactivation during the first 2 days of operation. Later, the catalysts present steady activity until the end of the test. The highest residual phenol conversion was obtained for the ZnO-CuO, which was significantly higher than that obtained with the 10% CuO catalyst used as reference. The catalyst deactivation is related to the dissolution of the metal oxides from the catalyst surface due to the acidic reaction conditions. Generally, the performance of the catalysts was better when the pH of the feed solution was increased.

AQUEOUS PHASE CATALYTIC OXIDATION OF PHENOL IN A TRICKLE BED REACTOR: EFFECT OF THE pH

The catalytic oxidation of organic compounds in aqueous phase is a promising technique for waste water treatment. Obtaining efficient and durable catalysts and determining the optimal process conditions are the key to successfully implementing this treatment. Copper-based catalysts supported over either silica or γ-alumina were prepared for this purpose. This research studies the influence of the pH on the performance of these catalysts. Activity tests were conducted for nine days in a trickle bed reactor operating at 140°C using air as oxidant. The results show that the silica supported catalyst is very sensitive to the acidic medium which leads to very short lifetimes. At first, the alumina supported catalyst also quickly losses activity but subsequently it stabilises with a residual phenol conversion several times higher than that of the silica supported catalyst. For both catalysts, a higher pH reduces the rate of catalyst deactivation by preventing the leaching of the copper oxides and lengthening their lifetime. The atmosphere (air or nitrogen) during calcination does not change their performance.

Supported Cu(II) polymer catalysts for aqueous phenol oxidation

Supported Cu(II) polymer catalysts were used for the catalytic oxidation of phenol at 30 degrees C and atmospheric pressure using air and H(2)O(2) as oxidants. Heterogenisation of homogeneous Cu(II) catalysts was achieved by adsorption of Cu(II) salts onto polymeric matrices (poly(4-vinylpyridine), Chitosan). The catalytic active sites were represented by Cu(II) ions and showed to conserve their oxidative activity in heterogeneous catalysis as well as in homogeneous systems. The catalytic deactivation was evaluated by quantifying released Cu(II) ions in solution during oxidation, from where Cu-PVP(25) showed the best leaching levels no more than 5 mg L(-1). Results also indicated that Cu-PVP(25) had a catalytic activity (56% of phenol conversion when initial Cu(II) catalytic content was 200 mg L(Reaction)(-1)) comparable to that of commercial catalysts (59% of phenol conversion). Finally, the balance between activity and copper leaching was better represented by Cu-PVP(25) due to the heterogeneous catalytic activity had 86% performance in the heterogeneous phase, and the rest on the homogeneous phase, while Cu-PVP(2) had 59% and CuO/gamma-Al(2)O(3) 68%.

Immobilisation of horseradish peroxidase on Eupergit®C for the enzymatic elimination of phenol

In this study, three different approaches for the covalent immobilisation of the horseradish peroxidase (HRP) onto epoxy-activated acrylic polymers (EupergitC) were explored for the first time, direct HRP binding to the polymers via their oxirane groups, HRP binding to the polymers via a spacer made from adipic dihydrazide, and HRP binding to hydrazido polymer surfaces through the enzyme carbohydrate moiety previously modified by periodate oxidation. The periodate-mediated covalent immobilisation of the HRP on hydrazido EupergitC was found to be the most effective method for the preparation of biocatalysts. In this case, a maximum value of the immobilised enzyme activity of 127 U/g(support) was found using an enzyme loading on the support of 35.2mg/g(support). The free and the immobilised HRP were used to study the elimination of phenol in two batch reactors. As expected, the activity of the immobilised enzyme was lower than the activity of the free enzyme. Around 85% of enzyme activity is lost during the immobilisation. However, the reaction using immobilised enzyme showed that it was possible to reach high degrees of phenol removal (around 50%) using about one hundredth of the enzyme used in the soluble form.

A novel recovery process for lipids from microalgæ for biodiesel production using a hydrated phosphonium ionic liquid

The use of a hydrated phosphonium ionic liquid, [P(CH2OH)4]Cl, for the extraction of microalgae lipids for biodiesel production, was evaluated using two microalgae species, Chlorella vulgaris and Nannochloropsis oculata. The ionic liquid extraction was compared to the conventional Soxhlet, and Bligh & Dyer, methods, giving the highest extraction efficiency in the case of C. vulgaris, at 8.1%. The extraction from N. oculata achieved the highest lipid yield for Bligh & Dyer (17.3%), while the ionic liquid extracted 12.8%. Nevertheless, the ionic liquid extraction showed high affinity to neutral/saponifiable lipids, resulting in the highest fatty acid methyl esters (FAMEs)-biodiesel yield (4.5%) for C. vulgaris. For N. oculata, the FAMEs yield of the ionic liquid and Bligh & Dyer extraction methods were similar (>8%), and much higher than for Soxhlet (<5%). The ionic liquid extraction proved especially suitable for lipid extraction from wet biomass, giving even higher extraction yields than from dry biomass, 14.9% and 12.8%, respectively (N. oculata). Remarkably, the overall yield of FAMEs was almost unchanged, 8.1% and 8.0%, for dry and wet biomass. The ionic liquid extraction process was also studied at ambient temperature, varying the extraction time, giving 75% of lipid and 93% of FAMEs recovery after thirty minutes, as compared to the extraction at 100 °C for one day. The recyclability study demonstrated that the ionic liquid was unchanged after treatment, and was successfully reused. The ionic liquid used is best described as [P(CH2OH)4]Cl·2H2O, where the water is not free, but strongly bound to the ions.

Characterization and performance of carbonaceous materials obtained from exhausted sludges for the anaerobic biodecolorization of the azo dye Acid Orange II.

This work presents the preliminary study of new carbonaceous materials (CMs) obtained from exhausted sludge, their use in the heterogeneous anaerobic process of biodecolorization of azo dyes and the comparison of their performance with one commercial active carbon. The preparation of carbonaceous materials was conducted through chemical activation and carbonization. Chemical activation was carried out through impregnation of sludge-exhausted materials with ZnCl2 and the activation by means of carbonization at different temperatures (400, 600 and 800°C). Their physicochemical and surface characteristics were also investigated. Sludge based carbonaceous (SBC) materials SBC400, SBC600 and SBC800 present values of 13.0, 111.3 and 202.0m(2)/g of surface area. Biodecolorization levels of 76% were achieved for SBC600 and 86% for SBC800 at space time (τ) of 1.0min, similar to that obtained with commercial activated carbons in the continuous anaerobic up-flow packed bed reactor (UPBR). The experimental data fit well to the first order kinetic model and equilibrium data are well represented by the Langmuir isotherm model. Carbonaceous materials show high level of biodecolorization even at very short space times. Results indicate that carbonaceous materials prepared from sludge-exhausted materials have outstanding textural properties and significant degradation capacity for treating textile effluents.

Hydrolytic enzymes in activated sludge: extraction of protease and lipase by stirring and ultrasonication.

Hydrolytic enzymes released by the microorganisms in activated sludge are responsible for the organic matter degradation; however, the optimal extraction procedure of this valuable resource has not been well established until now. The present study evaluates the recovery of protease and lipase from the activated sludge by using stirring and ultrasonication, varying different parameters such as extraction time, concentration of additives (Triton X100, Cation Exchange Resin and Tris buffer), stirring velocity, ultrasonic power and sludge source. Sludge was collected from two urban wastewater treatment plants located in Prague (Czech Republic) and Reus (Spain). It was found that stirring using 2% v/v Triton X100 for 1h was enough to extract 57.4 protease units/g VSS, and that the same method using a combination of 10mM Tris pH 7.5+0.48 g/mL CER+0.5% TX100 as an additive allowed to extract 15.5 lipase units/g VSS from sludge collected from Reus Wastewater Treatment Plant. Ultrasonication allowed reducing the extraction time to 10 min for protease (using 2% v/v Triton X100 yielding 52.9 units/g VSS) and to 20 min for lipase (without any additive yielding nearly 21.4 units/g VSS), which makes this method appropriate for the extraction of enzymes from the activated sludge, and suitable to be scaled up for its application in the industry.

Degradation of model olive mill contaminants of OMW catalysed by zero-valent iron enhanced with a chelant

The aim of this study was to investigate the effect of a chelated zero valent iron as catalyst on the oxidation of six organic acids that are generally found in olive mill wastewater. The reaction was carried out in a stirred tank reactor under extremely mild conditions, a temperature of 30°C and atmospheric pressure. Solutions of 350 mg/L of the six organic compounds were treated individually using zero valent iron particles (15 g), nitrilotriacetic acid disodium salt (NTA, 100mg/L) and air. The efficiency of the process was evaluated to determine the organic compound conversion, the chemical oxygen demand (COD) reduction and the total organic carbon (TOC) reduction. The caffeic, 4-hydroxyphenylacetic and vanillic acids showed a total conversion after 180, 240 and 300 min of reaction, respectively. In turn, coumaric acid, tyrosol and cinnamic acid only reached conversions of 90, 87 and 68%, respectively, after 360 min of reaction. Four mixtures of the six acids with an initial total concentration of 1000 mg/L were also tested and gave an overall conversion of the organic compounds of 92-99% after 360 min of reaction. The COD conversions of the mixtures were always above 84%, but the TOC conversions values were lower, indicating a poorer mineralization.

Scale-up and economic analysis of biodiesel production from municipal primary sewage sludge

Municipal wastewater sludge is a promising lipid feedstock for biodiesel production, but the need to eliminate the high water content before lipid extraction is the main limitation for scaling up. This study evaluates the economic feasibility of biodiesel production directly from liquid primary sludge based on experimental data at laboratory scale. Computational tools were used for the modelling of the process scale-up and the different configurations of lipid extraction to optimise this step, as it is the most expensive. The operational variables with a major influence in the cost were the extraction time and the amount of solvent. The optimised extraction process had a break-even price of biodiesel of 1232