FUNDAMENTAL DENITRIFICATION KINETIC-STUDIES WITH PSEUDOMONAS-DENITRIFICANS

Fundamental kinetic studies on the reduction of nitrate, nitrite, and their mixtures were performed with a strain of Pseudomonas denitrifica ns (ATCC 13867). Methanol served as the carbon source and was supplied in excess (2:1 mole ratio relative to nitrate and/or nitrite). Nitrat e and nitrite served as terminal electron accepters as well as sources of nitrogen for biomass synthesis. The results were explained under t he assumption that respiration is a growth-associated process. It was found that the sequence of complete reduction of. nitrate to nitrogen gas is via nitrite and nitrous oxide. It was found that the specific g rowth rate of the biomass on either nitrate or nitrite follows Andrews inhibitory kinetics and nitrite is more inhibitory than nitrate. It w as also found that the culture has severe maintenance requirements whi ch can be described by Herbert's model, i.e., by self-oxidation of por tions of the biomass. The specific maintenance rates at 30 degrees C a nd pH 7.1 were found to be equal to about 28% of the maximum specific growth rate on nitrate and 23% of the maximum specific growth rate on nitrite. Nitrate and nitrite were found to be involved in a cross-inhi bitory noncompetitive kinetic interaction. The extent of this interact ion is negligible when the presence of nitrite is low but is considera ble when nitrite is present at levels above 15 mg/L. Studies on the ef fect of temperature have shown that the culture cannot grow at tempera tures above 40 degrees C. The optimal temperature for nitrate or nitri te reduction was found to be about 38 degrees C. Using an Arrhenius ex pression to describe the effect of temperature on the specific growth rates, it was found that the activation energy for the use of nitrate by the culture is 8.6 kcal/mol and 7;21 kcal/mol for nitrite. Arrheniu s-type expressions were also used in describing the effect of temperat ure on each of the parameters appearing in the specific growth rate ex pressions. Studies on the effect of pH at 30 degrees C have shown that the culture reduces nitrate optimally at a pH between 7.4 and 7.6, an d nitrite at a pH between 7.2 and 7.3. (C) 1995 John Wiley and Sons, I nc.