D. C. Hempel

Oxidation of tri- and perchloroethene in aqueous solution with ozone and hydrogen peroxide in a tube reactor

The reaction between trichloroethene (TCE) and perchloroethene (PCE) as micropollutants in water with ozone and hydrogen peroxide has been studied in a tube reactor. During the course of the reaction the micropollutants were nearly completely mineralized, as indicated by a stoichiometrical release of the organic chlorine as chloride ions. A mathematical model describing the kinetics of the oxidation was developed based on known reactions of the ozone/hydrogen peroxide system. Experiments with demineralized water that was spiked with bicarbonate and with drinking water have shown that the model is sufficient to predict the concentration profiles of the pollutants, ozone and hydrogen peroxide at different pH values and inorganic carbon concentrations.

Effective diffusivities and mass fluxes in fungal biopellets

Mass transport within biological aggregates is a key process that can determine overall turnover rates in submerged cultivations. A parameter commonly used for its description is the effective diffusion coefficient D eff, which is highly dependent on biomass density and structure. Different approaches have been used to estimate or measure D eff, yet the data still shows broad scattering. This study provides experimental data on effective diffusivities of oxygen within fungal pellets. A correlation is found with the hyphal gradient (dh/dr), which is a morphological parameter describing the structure of the pellet periphery. Furthermore, the dependency of D eff on fluid dynamic conditions at the pellet is investigated. The comparison of the results with data from literature clearly demonstrates the influence of the experimental methodology applied for determination of D eff. Moreover, it is shown that while diffusion limitation of whole pellets is mainly a function of size, the influence of advection in the outer zone of pellets that is supplied with oxygen is actually rather high. Thus, it is concluded that the effective diffusion coefficient might not be sufficient for the description of mass transport within the pellet periphery for a broad range of realistic fluid dynamic conditions during cultivation. Nevertheless, although actual mass transport rates inside pellets are unknown, mass fluxes can be calculated on the basis of spatially resolved data of oxygen and biomass distribution within the pellet. Biotechnol. Bioeng. 2009;103: 1202–1213.