Engineering aspects of nitrification with immobilized cells

Several aspects of a nitrification process with artificially immobilized cells in an airlift loop reactor have been investigated and are described in this thesis. In chapter 1 an overview of immobilization methods, suitable reactors, modelling, small-scaleapplications and scale-up strategy is given. The subjects of chapter 1 provide the starting point of the following chapters. Application of immobilized cells is beneficial for the nitrification process at high product and substrate concentrations and with a process temperature far below the optimal temperature of 30-35°C. In chapter 2 and 3 the kinetics of, respectively, Nitrosomonas europaea and Nitrobacter agilis cells at high product and substrate concentrations is presented. The results show a severe product inhibition of Nitrobacter agilis by nitrite, while Nitrosomonas europaea seems to be more sensitivefor a high osmotic pressure. In chapter 4 a theoretical background of the immobilization method and further scale-up is presented. For the immobilization method the theory for the break-up of liquid jets, with Newtonian behaviour, is evaluated and a method to apply this theory for non-Newtonian liquids like a K-carrageenan solution is presented. In chapter 6 a dynamic model for the nitrification with immobilized Nitrosomonas europaea and Nitrobacter agilis cells is presented. The model includes mass-transfer rates, kinetic behaviour of the microorganisms, and reactor and gel bead properties. Predictionsof reactor bulk concentrations of NH 4+, NO 2-and NO 3-(N-compounds) are given by the model together with concentration profiles of N-compounds, oxygen and biomass in the gel beads. A sensitivity analysis of the model parameters shows that the diffusion coefficient of oxygen in the gel beads and the radius of the gel beads are the most important parameters influencing the model output. The model is experimentally validated by means of reactor bulk concentrations and biomass profiles of Nitrosomonas europaea and Nitrobacter agilis in the gel beads. Predicted and measured values agree very well and the assumptions and equations used in the model seem to be valid. The biomass profiles of the two microorganisms co-immobilized in the gel beads are determined with immunofluorescence and a stereological method (chapter 5). The immunofluorescence technique was used to separate the Nitrosomonas europaea and Nitrobacter agilis colonies in the beads. From the position and diameter of the colonies it is possible to determine the spatial distribution of the two microorganisms in the gel beads. In chapter 7 the model is used as a tool to develop a strategy to scale-up the nitrification process with immobilized cells. A design for a large-scale application should be optimized with respect to the transport of oxygen to the immobilized cells in the gel beads. This is an advantage over the nitrification process with suspended cells, which is limited by the growth rate of the nitrifying bacteria. The growth of nitrifying bacteria is a slower process than the transport of oxygen to the cells. Some interesting aspects, which were not treated elsewhere in this thesis, are discussed in the general discussion in chapter 8.

Bibliographic Details

Main Author:	Hunik, J.H.
Other Authors:	Tramper, J.
Format:	Doctoral thesis biblioteca
Language:	English
Published:	Landbouwuniversiteit Wageningen
Subjects:	biochemistry, biotechnology, bradyrhizobiaceae, cells, chemical industry, chemical reactions, immobilization, immobilized cells, biochemie, biotechnologie, cellen, chemische industrie, chemische reacties, geïmmobiliseerde cellen, immobilisatie,
Online Access:	https://research.wur.nl/en/publications/engineering-aspects-of-nitrification-with-immobilized-cells
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