Date of Award

Spring 1994

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Chemical Engineering - (Ph.D.)

Department

Chemical Engineering, Chemistry and Environmental Science

First Advisor

Basil Baltzis

Second Advisor

Gordon Lewandowski

Third Advisor

Ching-Rong Huang

Fourth Advisor

Piero M. Armenante

Fifth Advisor

Lily Y. Young

Abstract

This study dealt with a detailed investigation of biological denitrification of nitrate and nitrite by a pure culture of Pseudomonas denitrificans (ATCC 13867), under anaerobic conditions.

In the first part of the study, the kinetics of denitrification were studied in serum-bottle experiments. It was found that reduction of both nitrate and nitrite follows inhibitory expressions of the Andrews type. It was also found that when nitrite is present at levels above 15 mg/L, nitrite and nitrate are involved in a cross-inhibitory, non-competitive, interaction pattern. Analysis of the kinetic data has shown that the culture used has severe maintenance requirements, which can be described by the model proposed by Herbert. Experiments at different temperatures have revealed that the optimum temperature is around 38 °C. Activation energies have been determined as 8.6 Kcal/mole for nitrate, and 7.21 Kcal/mole for nitrite reduction. Studies on the effect of pH have shown that the optimal value is about 7.5.

Based on the detailed kinetic expressions determined in the first part of the study, denitrification of nitrite and nitrate/nitrite mixtures was theoretically analyzed and experimentally investigated in a continuously operated sequencing batch reactor. The theoretical analysis was based on the bifurcation theory for forced systems. The different types of the dynamical behavior of the system were found, and are presented in the form of bifurcation diagrams and two-dimensional operating diagrams. The analysis predicts that there are domains in the operating parameter space where the system can reach different periodic patterns which are determined by the conditions under which the process is started-up. The analysis also predicts that improper selection of operating parameters can lead to high nitrite accumulation in the reactor. The predictions of the theory were tested in experiments with a specially designed system. The unit involved a fully automated 2-liter reactor which operated under different inlet flowrate and concentration conditions. During the experiments the system was perfectly sealed and the medium kept under a helium atmosphere of pressure slightly higher than 1 atm. In all cases, a remarkably good agreement was found between theoretical predictions and experimental data.

The experimentally validated model can be used in process optimization studies, and preliminary scale-up calculations.

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