Fundamental denitrification kinetic studies with Pseudomonas denitrificans

Abstract

Fundamental kinetic studies on the reduction of nitrate, nitrite, and their mixtures were performed with a strain of Pseudomonas denitrificans (ATCC 13867). Methanol served as the carbon source and was supplied in excess (2:1 mole ratio relative to nitrate and/or nitrite). Nitrate and nitrite served as terminal electron acceptors as well as sources of nitrogen for biomass synthesis. The results were explained under the 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 growth rate of the biomass on either nitrate or nitrite follows Andrews inhibitory kinetics and nitrite is more inhibitory than nitrate. It was also found that the culture has severe maintenance requirements which can be described by Herbert's model, i.e., by self-oxidation of portions of the biomass. The specific maintenance rates at 30 degrees C and 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-inhibitory noncompetitive kinetic interaction. The extent of this interaction is negligible when the presence of nitrite is low but is considerable when nitrite is present at levels above 15 mg/L.Studies on the effect of temperature have shown that the culture cannot grow at temperatures above 40 degrees C. The optimal temperature for nitrate or nitrite reduction was found to be about 38 degrees C. Using an Arrhenius expression 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. Arrhenius-type expressions were also used in describing the effect of temperature on each of the parameters appearing in the specific growth rate expressions. 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, and nitrite at a pH between 7.2 and 7.3. (c) 1995 John Wiley & Sons, Inc.

Wastewater denitrification process—the influence of methanol and kinetic analysis

“…1 3 ( Á/N/l (the stock solution was an aqueous solution of NaNO 3 containing 10 gNO 3 ( Á/N/l) and methanol were added to the original mineral medium to prepare SW. The methanol concentration during the investigation of the biomass concentrations effect on nitrate removal was 900 mg/l (MeOH/NO 3 ( Á/N weight ratio was 4.5). During optimisation of methanol to nitrate Á/nitrogen ratios, methanol concentrations were adjusted to give different MeOH/NO 3 ( Á/N weight ratios, from 1.5 to 4.5.…”

“…According to Ref. [3], 10Á/50 mgNO 3 ( Á/N/l was removed with Pseudomonas denitrificans during 4 h and denitrification of 100 mgNO 3 ( Á/N/l with the suspended bacterial cells lasted 18 h [4]. Furthermore, different industrial wastewaters contained more than 200 mgNO 3 ( Á/N/l and biological denitrification of such wastewaters usually lasted a few days [2,5 Á/7].…”

“…Furthermore, different industrial wastewaters contained more than 200 mgNO 3 ( Á/N/l and biological denitrification of such wastewaters usually lasted a few days [2,5 Á/7]. Thus, Zayed and Winter [2] investigated nitrate removal from dairy wastewater: with activated sludge removal of 250 mgNO 3 ( Á/N/l lasted 3 days, with an immobilized mixed culture the conversion of nitrate was faster, and after 2 days no nitrate or nitrite remained, and finally in the tests with the suspended pure culture 8 days were required to convert 100% of nitrate Á/N to nitrogen gas and to reduce the chemical oxygen demand (COD) from 1500 to 159 mgO 2 /l.…”

“…The nature and the amount of the organic substrate used as exogenous carbon source plays an important role in the success and price of denitrification. Various substrates have been used in many studies and a whole variety of compounds, mostly methanol [3,8,9], acetate [4,6,7], and ethanol [10]. Some studies used nutrient broth [11] and tryptic soy broth [12].…”

“…Tests with different original biomass concentrations applied for denitrification and optimisation of methanol to nitrate Á/N ratio were carried out in the batch assays. The selected MeOH/ NO 3 ( Á/N value was applied to investigate denitrification in the continuous-flow stirred reactor. A simplified kinetic analysis was performed for quantitative comparison of nitrate consumption and biomass production rates.…”