Nitrate Utilization Rates Research Articles

Long-term experiences with external carbon sources for nitrogen removal

Methanol and ethanol have been used for three years as external carbon sources in a nutrient removal system based on pre-precipitation and post-denitrification in a single sludge activated sludge plant. Based on these long-term experiences it has been shown that the nitrogen standards of 8 mg N/l in the effluent wastewater can be met with both carbon sources. The process entails operational flexibility and the possibility to optimize the nitrogen removal due to seasonal variations in influent wastewater characteristics. Very high specific nitrate utilization rates were measured in the system with the use of external carbon sources. Rates of around 10 mg N/g VSS.h were reached with ethanol and around 3 mg N/g VSS.h with methanol. These rates were much higher than experienced in a pre-denitrification system with the use of the influent organic material as carbon source for denitrification. A start-up with the addition of ethanol led to a direct response of the system while a start-up with methanol resulted in a much longer adaptation period before full effect of the carbon source added was reached.

Long-term experiences with external carbon sources for nitrogen removal

Methanol and ethanol have been used for three years as external carbon sources in a nutrient removal system based on pre-precipitation and post-denitrification in a single sludge activated sludge plant. Based on these long-term experiences it has been shown that the nitrogen standards of 8 mg N/l in the effluent wastewater can be met with both carbon sources. The process entails operational flexibility and the possibility to optimize the nitrogen removal due to seasonal variations in influent wastewater characteristics. Very high specific nitrate utilization rates were measured in the system with the use of external carbon sources. Rates of around 10 mg N/g VSS.h were reached with ethanol and around 3 mg N/g VSS.h with methanol. These rates were much higher than experienced in a pre-denitrification system with the use of the influent organic material as carbon source for denitrification. A start-up with the addition of ethanol led to a direct response of the system while a start-up with methanol resulted in a much longer adaptation period before full effect of the carbon source added was reached.

A steady-state model for the single sludge activated sludge system—II. Model application

Bench-scale experiments using domestic wastewater were carried out under a constant flowrate. A set of kinetic and stoichiometric coefficients was selected which resulted in a good agreement between the experimental results and the predictions of a proposed steady-state model. Units equipped with selectors showed a slower kinetics of both BOD removal and nitrification. This phenomena was attributed to the selection of different heterotrophic population or decreased mass transfer rate in the selector-equipped units. A sensitivity analysis indicate a high sensitivity of the system's size to the nitrifiers growth and decay rates and the denitrification nitrate utilization rate.

Temporal and Seasonal Trends in Nutrient Dynamics and Biomass Measures in Lakes Michigan and Ontario in Response to Phosphorus Control

Results from long-term ecological monitoring studies on Lake Michigan (1983–92) and Lake Ontario (1981–92) were compared with regard to changes in phosphorus loads. In Lake Ontario, total phosphorus (TP) loads decreased from 14 000 t∙yr−1 in 1970 to 7500 t∙yr−1 in 1981, and correspondingly, midlake TP concentration decreased from 25 to 16 μg∙L−1 From 1981 to 1991 TP loads remained around 7500 t∙yr−1; however, TP concentration continued to decline from 16 to 10 μg∙L−1. Similarly, mean summer particulate organic carbon (POC), chlorophyll a (CHLa), and nitrate utilization rate decreased by approximately 40, 20, and 50%, respectively. Conversely, silica utilization rates increased markedly after 1983. In Lake Michigan, TP loads also decreased by around 50% from 1974 to 1990 (2000 t∙yr−1); however, TP concentrations at our 100-m station in the southern basin increased during the study period from around 4 to 8 μg∙L−1 There were no distinct trends in CHLa or nutrient utilization patterns; however, POC levels decreased sharply after 1987. Overall, silica utilization rates in Lake Michigan were 50% higher than in Lake Ontario (14.7 vs. 9.6 μg∙L−1∙d−1), whereas nitrate utilization rates were only half (1.4 vs. 4.1 μg∙L−1∙d−1).

Nitrate versus Oxygen Utilization Rates in Wastewater and Activated Sludge Systems

Respiration rates for nitrate and oxygen are compared. Raw wastewaters vary much in these rates and the same holds for activated sludge systems. The denitrifying activity may range from 0-80 per cent of the oxygen activity. It is important to take these variations into consideration, when modelling complex activated sludge processes. Of similar importance are the amounts of active biomass in raw wastewater, as these amounts can exceed those produced in the activated sludge plant itself, and thus significantly can influence the overall composition of the active biomass.