Udo Wiesmann

Mechanism and kinetic model for the decolorization of the azo dye Reactive Black 5 by hydrogen peroxide and UV radiation.

A kinetic model for the decolorization of C.I. Reactive Black 5 by the combination of hydrogen peroxide and UV radiation was developed based on experimental results and known chemical and photochemical reactions. The observed kinetic reaction coefficient was determined and correlated as a function of hydrogen peroxide concentration and UV intensity. The validity of the rate expression was tested experimentally in a parameterization study. The decolorization rate follows pseudo-first order kinetics with respect to dye concentration. The rate increases linearly with UV intensity and nonlinearly with increasing hydrogen peroxide concentration, going from a linear relationship at low H(2)O(2) concentrations to a maximum as hydrogen peroxide concentration continues to increase. The decolorization rate expression derived from the proposed reaction mechanism was reconciled with that used for correlating the experimental data.

Degradation kinetics of acetate and propionate by immobilized anaerobic mixed cultures

Abstract The paper presents a short review of kinetics describing the anaerobic degradation of acetate and propionate by mixed cultures of bacteria. The authors discuss their measurements in lab scale extended fixed bed reactors containing porous polyurethane particles of different sizes for the immobilization of anaerobic mixed cultures. It can be demonstrated that the influences of diffusion within the particles can be neglected for the reactors under study. The results for both acetate and propionate degradation can be fitted by Haldane kinetics using the unionized fatty acid as the actual substrate. Product inhibition of propionate degradation by acetate is shown and described as a non-competitive product inhibition.

Ozonation of polycyclic aromatic hydrocarbons in oil/water-emulsions: mass transfer and reaction kinetics

The ozonation of highly condensed polycyclic aromatic hydrocarbons (PAH) was studied in oil/water-emulsions, which are comparable to poorly water-soluble PAH in industrial wastewaters and at contaminated sites. As there was a lack of knowledge about the ozonation in oil/water-emulsions, first the ozone mass transfer was studied and optimized from the gas to the water phase and from the water to the oil phase. The ratio of mass transfer and oxidation reaction was determined by the Hatta-number and revealed a slow, quasi homogeneous reaction of ozone with PAH inside the oil droplets. Because the ozone gas concentration had no influence under the optimized conditions, the selective PAH-ozonation could be described microkinetically by a direct ozone reaction of pseudo-first order regarding PAH-concentrations. The determined PAH mean reaction rate constants of 1.02 min(-1) in oil/water-emulsions are in the upper range as found for PAH dissolved in water. These results give a new insight into the ozonation in the three-phase systems and into the treatment of highly condensed, hardly biodegradable PAH.

Selective ozonation of polycyclic aromatic hydrocarbons in oil/water-emulsions

The ozonation of three to five ring condensed polycyclic aromatic hydrocarbons (PAH) was studied in synthetic oil/water-emulsions by batch experiments. PAH can be oxidized selectively in the presence of high concentrations of dodecane as an aliphatic solvent. No oxidation of dodecane, as a representative of mineral oil, could be observed during all experiments - even at pH around 11. At acid to neutral pH high oxidation rates of the PAH were achieved due to a direct reaction with ozone. In the investigated range of 20 to 40°C no influence of temperature on the ozonation of benzo(k)fluoranthene could be found. During competitive ozonation of five PAH, the reactions are completed in the sequence of acenaphthene, pyrene and finally benzo(e)pyrene, benzo(k)fluoranthene and phenanthrene almost at the same time.

Kinetics and reaction engineering aspects of the biodegradation of dichloromethane and dichloroethane

Abstract This paper presents some new results on the aerobic degradation of dichloromethane (DCM) and 1,2-dichloroethane (DCA) in a fluidized bed reactor without direct oxygenation. Oxygen was supplied by diffusion through a synthetic membrane. High bacteria concentrations and high degradation rates were obtained. DCM degradation reached 1400 mg (1 h)−1 and DCA degradation up to 600 mg (1 h)−1. Yields for oxygen consumption and biomass production could be established. Haldane kinetics were suitable to describe the influence of DCA and oxygen concentration on the degradation rate of DCA. The DCM degradation rate is only influenced by the substrate concentration. Kinetic parameters for the Haldane model were reached in batch and extended-culture experiments. Extended-culture experiments keep the substrate concentration in the reactor constant and allow a determination of the growth rate by evaluation of the reaction volume.

Kinetics of anaerobic orthophosphate release and substrate uptake in enhanced biological phosphorus removal from synthetic wastewater

Abstract This paper presents some new results about the kinetics of orthophosphate release and substrate uptake occurring under anaerobic conditions in a lab-scale activated sludge plant consisting of an anaerobic first and an aerobic second step A/O-process. The synthetic wastewater contained acetate, peptone and yeast extract. The mixed culture was enriched from activated sludge samples from a large-scale plant with enhanced biological phosphorus removal. Anaerobic batch experiments were carried out with this enriched mixed culture using acetate as the only source for carbon and energy. In the first experiments, high acetate concentration was only partly consumed by the bacterial culture, resulting in a nearly total emptying of the poly-P-store (poly-P-limitation). In the next experiments, only a relatively low acetate concentration was added, resulting in a total acetate uptake and in partial emptying of the poly-P-store (acetate-limitation). This experimental strategy was successful in studying the complex kinetics of the anaerobic process in enhanced phosphorus removal. Most of the calculated kinetic coefficients depend on temperature; a dependence on pH cannot be postulated with certainty. A comparison with known results shows conformity but also differences.

Biomass separation from liquids by sedimentation and centrifugation

Sedimentation tanks and centrifuges are used in several biotechnological processes to separate the produced biomass from culture media. After reviewing different types of separators, methods of calculation are described, both for separation in low concentration regions (clarification) and in higher ones (thickening). Firstly, closed systems are considered which are useful for the measurement of settling rates. The hydrodynamic theory for free settling of single particles as well as the theory of the limiting flux for higher particle concentrations are discussed. Differences between ideal suspensions of rigid particles and non-ideal suspensions of flocks which were formed in many bio-suspensions are pointed out. Methods of calculation for continuous clarification and thickening in vertical flow tanks and tube centrifuges with continuous solid discharge (decanter) are described. As far as possible theoretical results are compared with experimental ones. Some examples for the application of sedimentation tanks and centrifuges in biotechnology are given. Finally some remarks about flocculation processes are added.

Effect of Chemical Reaction and Mass Transfer on Ozonation of the Azo Dyes Reactive Black 5 and Reactive Orange 96

ABSTRACT Ozonation of wastewater containing azo dye has been studied to evaluate the enhancement of ozone mass transfer from O2O3 gas into water with the presence of chemical reactions in a bubble column reactor. Experiments were performed at different initial dye concentrations and at various gas flow rates. C.I. Reactive Black 5 (RB 5) and C.I. Reactive Orange 96 (RO 96) have been chosen as representative model substances being found in wastewater from textile-finishing wastewater. Results show that the rate of ozone mass transfer increases with increasing initial dye concentration and gas flow rate. Consequently, an enhancement factor E for ozone mass transfer with chemical reaction could be calculated which increases with dye concentration. The chemical reaction between ozone and dye enhanced the mass transfer within the liquid film of the gas liquid boundary. The greatest enhancement factor for wastewater containing RO 96 of 2050 mgL−1 is E = 15.4 compared with E = 9.1 for RB 5 of 3800 mgL−1, both for gas flow rates of 19 Lh−1. For lower gas flow rates, higher enhancement factors were observed, particularly for RO 96.

Ozonation of C.I. Reactive Black 5 and Indigo

The ozone transfer for the ozonation of the azo dye Reactive Black 5 (RB5) and indigo was investigated using a bubble column at semi-batch conditions. The results were analyzed by applying film theory and surface renewal theory. The ozonation of both dyes was so fast that an instantaneous reaction directly at the bubble surface can be assumed. The ozone balance in the gas phase was used to determine the volumetric mass transfer coefficient kLa and the enhancement factor E. Besides the measured concentrations, temperature and pressure only the Henry coefficient was required for the determination of kLa and E. By varying the ozone inlet and the dye concentration the reaction regime was identified. The Hatta number Ha which requires uncertain parameters did not have to be determined.

Biologische und Chemische Behandlung Kontaminierter Grundwässer

Kontaminierte Grundwasser sind auf Bodenverunreinigungen zuruckzufuhren, die haufig schon mehrere Jahrzehnte zuruckliegen (Altlasten) und die als Folge von Ablagerungen und Versickerungen, meist organischer Schadstoffe, an Industriestandorten auftreten. Bei der Sanierung dieser Altlasten muβ das Grundwasser hochgepumt und soweit gereinigt werden, daβ es in die Kanalisation oder in den Vorfluter eingeleitet werden kann.