Ulf Prüsse

Supported bimetallic palladium catalysts for water-phase nitrate reduction

Technologies for the removal of nitrate from drinking water and waste water will be required in the near future, and the catalytic nitrate reduction is one of the most promising methods. So far, the understanding of nitrate reducing catalysts has been very poor. Experimental trends in nitrate removal activity and selectivity for various pH values, and for different bimetallic catalysts, as well as results described in literature were used to set up a mechanistic model for the reaction. The nitrate reduction activity is determined by bimetallic ensembles, at which nitrate is adsorbed and reduced to nitrite by hydrogen, which is supposed to spillover from palladium sites to the bimetallic sites. Formic acid, on the other hand, reacts with nitrate by a transfer hydrogenation mechanism from neighboring palladium sites. The extent of positive charging of the bimetallic sites is supposed to influence the activity at different pH values. At a high pH, strongly adsorbing oxygenated species block bimetallic nitrate adsorption sites as well as palladium sites. The selectivity is determined by the ratio of nitrogen species to reductant species at monometallic palladium sites. At these sites, the reduction of nitrite and other intermediates take place, finally leading to the end products. If this ratio of nitrogen to reductant species changes, the selectivity changes as well, e.g. at different ratios of the two metals. The trends in the experimental data are well described by this model.

Improving the catalytic nitrate reduction

Abstract Technologies for the nitrate removal from drinking water and waste water will be required in the near future and the catalytic nitrate reduction is one of the most promising ones. To establish a technical-scale nitrate reduction a further improvement of the catalyst is necessary and new concepts should be introduced in the process. It is shown, that palladium–tin and palladium–indium catalysts can be much more suited for an efficient nitrate reduction than palladium–copper catalysts. Furthermore, two new innovative concepts are presented — the use of in situ buffering formic acid as reductant instead of hydrogen and the application of PVAL-encapsulated catalysts with superior diffusional properties — which may contribute to solve selectivity problems.

Comparison of different technologies for alginate beads production

This paper describes the results of the round robin experiment “Bead production technologies” carried out during the COST 840 action “Bioencapsulation Innovation and Technologies” within the 5th Framework Program of the European Community. In this round robin experiment, calcium alginate hydrogel beads with the diameter of (800 ± 100) μm were produced by the most common bead production technologies using 0.5–4 mass % sodium alginate solutions as starting material. Dynamic viscosity of the alginate solutions ranged from less than 50 mPa s up to more than 10000 mPa s. With the coaxial air-flow and electrostatic enhanced dropping technologies as well as with the JetCutter technology in the soft-landing mode, beads were produced from all alginate solutions, whereas the vibration technology was not capable to process the high-viscosity 3 % and 4 % alginate solutions. Spherical beads were generated by the electrostatic and the JetCutter technologies. Slightly deformed beads were obtained from high-viscosity alginate solutions using the coaxial airflow and from the 0.5 % and 2 % alginate solutions using the vibration technology. The rate of bead production using the JetCutter was about 10 times higher than with the vibration technology and more than 10000 times higher than with the coaxial air-flow and electrostatic technology.

Biotransformation of Poly R-478 by continuous cultures of PVAL-encapsulated Trametes versicolor under non-sterile conditions

Abstract Mycelia of Trametes versicolor were aseptically encapsulated in PVAL hydrogel beads of 1–2 mm diameter. The encapsulated mycelia were grown continuously in an aerated reactor under non-sterile conditions. After 65 days contamination of the PVAL hydrogel beads by bacteria was found only in the outer layer to a depth of 50 μm. The encapsulated fungi still expressed ligninolytic enzymes, as confirmed by the biotransformation of Poly R-478. Elimination of Poly R-478 by encapsulated Trametes versicolor reached an efficiency of up to 89%, which was due partially to biotransformation (65%) and partially to adsorption onto biomass (24%). PVAL-encapsulated mycelia of Trametes versicolor were viable for at least 6 months without nutrient supplementation, if stored at 7 °C in a refrigerator. By encapsulation Trametes versicolor was apparently protected against microbial contaminants and against mechanical stress, which is known to inactivate ligninolytic enzymes. Encapsulated Trametes versicolor might thus be applicable for bioremediation to serve as an inoculum for reactor systems or for field-side applications.

New Matrices and Bioencapsulation Processes

A PVA-matrix is presented which is capable of gelating at room temperature resulting in lens-shaped particles (LentiKats®). Immobilisation of biocatalysts in LentiKats® is possible without significant loss of biological activity. The hydrogels are long term mechanically and chemically stable and show hardly any biodegradability.