Simultaneous Nitrification-Denitrification to Meet Low Effluent Nitrogen Limits: Modeling, Performance and Reliability

Abstract

Simultaneous nitrification-denitrification (SND) has been referred to as a biological process for nitrogen removal where nitrification and denitrification occur concurrently in the same aerobic reactor. SND facilities, investigated in this study, have been shown to remove 80 to 96 percent nitrogen without additional carbon and alkalinity. Carbon availability and bulk dissolved oxygen (DO) concentrations were found to be important process parameters for SND activity. Data suggest that a chemical oxygen demand-to-nitrogen (COD:N) ratio of at least 10.0 is required to achieve significant denitrification; and an optimum bulk DO concentration ranging from approximately 0.3 milligrams per liter (mg/L) to 0.7 mg/L appears to maximize SND activity. However, this low DO condition required for SND provides an environment more susceptible to sludge bulking as observed by the SVI data from the selected SND facilities in this study. A process simulator was used to determine important modeling parameters to predict SND performance at a pilot plant treating synthetic wastewater. Overall, the structure of the process model provided the capabilities to simulate SND performance in the pilot plant. However, important modeling parameters were modified to better predict SND performance.

Simultaneous Biological Nutrient Removal in a Single-Stage, Low Oxygen Aerobic Reactor

“…This would be anticipated since the amount of denitrification should be set by the availability of substrate (constant) and the bulk DO concentration in the reactor. Jimenez et al (2010) demonstrated that the structure of the ASDM model in the BioWin simulator (Barker and Dold, 1997) allowed the pilot plant performance to be calibrated reasonably well with minor adjustments to default parameters. The modeling results confirmed the earlier discussion about SND that the most sensitive parameters are the various halfsaturation constants, as noted by others (O'Shaugnessey et al, 1998;Insel et al, 2003 andMagbanaua et al, 2007), as well as the heterotroph maximum specific growth rate.…”

“…The results indicated that significant nitrogen removal could be realized through SND, and the two main factors affecting SND performance were organic carbon availability and operating DO concentration. Jimenez et al (2010) showed that the influent rbCOD:N ratio strongly influences denitrification in the SND process. Data suggest that an influent COD:N ratio of at least 10:1 is required to achieve near-complete denitrification through SND.…”

“…Nitrogen losses from aerated facilities have been observed frequently when suitable environmental conditions are in place (Applegate et al, 1980;Rittmann and Langeland, 1985;von Münch et al, 1996;Pochana and Keller, 1999;Daigger and Littleton, 2000;Kaempfer et al, 2000;Littleton et al, 2002;Littleton et al, 2003;Satoh et al, 2003;Daigger et al, 2007;Ju et al, 2007;Jimenez et al, 2010). This phenomenon has been referred to as simultaneous nitrification-denitrification (SND) because both biological reactions occur concurrently in the same reactor.…”

“…Parameters impacting SND predictions and those adjusted (bold) for calibration to pilot plant data(Jimenez et al, 2010) …”

N<SUB>2</SUB>O Emissions: Impact of Process Configuration and Diurnal Loading Patterns

“…However, a further consideration is that simultaneous nitrification-denitrification (SND) can be expected when nitrifying at low DO concentration, and this may mask nitrite accumulation (Jimenez et al, 2010).…”