Frank Stüber

Kinetic modelling of catalytic wet air oxidation of phenol by simulated annealing

A detailed reaction network for the catalytic wet air oxidation (CWAO) of phenol on a CuO/-Al2O3 catalyst is proposed in this study. The reaction network proposed accounts for all detected intermediate products of phenol oxidation overcoming the usual lumping of compounds. The model is composed by several consecutive and parallel reactions. The parameters of the model were adjusted using experimental data obtained from a continuous trickle bed reactor using air as oxidant at different temperatures (120–160 ◦ C) and oxygen partial pressures (0.6–1.2 MPa). Simple power law as well as Langmuir–Hinshelwood (L–H) expressions accounting for the adsorption effects were checked in the modelling of the reaction network. A robust non-linear multiparameter estimation approach called simulated annealing was used to simultaneously evaluate the high number of model parameters (up to 38). Approach by simple power law only succeeded in fitting phenol disappearance. Instead, when L–H expressions are incorporated for the intermediate reaction steps, the model accurately describes all the experimental concentration profiles, giving mean deviations below 8%. In addition, all estimated parameters have physical meaning. In particular, activation energies mostly agree with those reported in the literature.

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%.

Nonlinear kinetic parameter estimation using simulated annealing

The performance of simulated annealing (S-A) in nonlinear kinetic parameter estimation was studied and compared with the classical Levenberg � /Marquardt (L � /M) algorithm. Both methods were tested in the estimation of kinetic parameters using a set of three kinetic models of progressively higher complexity. The models describe the catalytic wet air oxidation of phenol carried out in a small-scale trickle bed reactor. The first model only considered the phenol disappearance reaction, while the other two included oxidation intermediate compounds. The number of model parameters involved increased from 3 to 23 and 38, respectively, for the three models. Both algorithms gave good results for the first model, although the L � /M was superior in terms of computation time. In the second case the algorithms achieved convergence, but S-A resulted in a better criterion and kinetic parameters with physical meaning. In the more complex model, only S-A was capable of achieving convergence, whereas the L � /M failed. For the second and third model the solution of S-A could be further improved, when used as an initial guess for the L � /M algorithm. # 2002 Elsevier Science Ltd. All rights reserved.

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.

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.

TiO2-sludge carbon enhanced catalytic oxidative reaction in environmental wastewaters applications

The enhanced oxidative potential of sludge carbon/TiO2 nano composites (SNCs), applied as heterogeneous catalysts in advanced oxidation processes (AOPs), was studied. Fabrification of efficient SNCs using different methods and successful evaluation of their catalytic oxidative activity is reported for the first time. Surface modification processes of hydrothermal deposition, chemical treatment and sol-gel solution resulted in improved catalytic activity and good surface chemistry of the SNCs. The solids obtained after chemical treatment and hydrothermal deposition processes exhibit excellent crystallinity and photocatalytic activity. The highest photocatalytic rate was obtained for the material prepared using hydrothermal deposition technique, compared to other nanocomposites. Further, improved removal of bisphenol A (BPA) from aqueous phase by means of catalytic ozonation and catalytic wet air oxidation processes is achieved over the solid synthesized using chemical treatment method. The present results demonstrate that the addition of TiO2 on the surface of sludge carbon (SC) increases catalytic oxidative activity of SNCs. The latter produced from harmful sludge materials can be therefore used as cost-effective and efficient sludge derived catalysts for the removal of hazardous pollutants.

Extraction of enzymes from activated sludge.

About 60–70% of the organic matter contained by domestic wastewater is formed by lipids and proteins. The microorganisms that are able to degrade this organic matter produce hydrolytic enzymes that cannot be produced by standard cultivation techniques. The extraction methods have to include detergents or ionic exchange resins to recover qualitatively and quantitatively the enzyme activity. In the present study protease was extracted by using Triton X100 alone or in combination with a cation exchange resin (CER), under stirring, mechanical or ultrasound disintegration at low temperature. It was observed that the temperature of extraction, the agitation velocity, the concentration of the detergent or the cation exchange resin, and the presence/absence of a buffer conditioned the efficiency of the extraction process and the recovery of the enzyme activity. It was also demonstrated that the preservation of the sample (cooled or frozen), and the time of withdrawal (immediately or after one day aeration) changes the activity of the enzyme recovered. The results showed that the best treatment for the recovery of protease is a combination of 60 g/g VSS of CER, 0.5% Triton and 10 mM Tris buffer pH 8, under stirring at 500 rpm during 1 h at 18oC. This process allowed to recover 6.48 protease units/g VSS.

Performance of Sludge Based Activated Carbons in Catalytic Wet Air Oxidation of Phenol

The catalytic potential of sludge based materials produced by steam or CO2 activation from non-treated dewatered raw sludge or dewatered mesophilic anaerobically digested sludge were tested in the oxidation of phenol. Batch and continuous experiments were conducted to assess activity and stability of these novel carbons in terms of phenol conversion, carbon burn-off and metal leaching. Overall, their catalytic activity can be considered satisfactory when compared to commercial carbons. However, further research on the preparation, activation and hardening of these sludge based materials is required to improve their thermal and mechanical stability and resistance to metal leaching during the catalytic wet air oxidation of phenol.