Denitrification Rates: Sampling, Modeling and Design Considerations

Abstract

Biological denitrification of wastewater has been a topic of interest for several decades; however, recent nutrient reduction initiatives and the need to achieve limit-of-technology (LOT) effluent quality have renewed interest in denitrification rate research. Since readily-biodegradable chemical oxygen demand (rbCOD) drives rapid denitrification, it is essential for design efforts to include raw influent and primary effluent sampling, for different seasons if possible. However, the influent rbCOD/TKN ratio is not the only factor to consider, since rbCOD can be easily destroyed by non-optimal design and operating conditions. Two case studies are presented, each having very similar influent rbCOD/TKN ratios but very different full-scale denitrification performance. Furthermore, bench-scale tests that were conducted for the two plants yielded similar denitrification rates, which raises the question: how can engineers apply denitrification rate research to full-scale designs? Activated sludge models provide some insight to the unknown (dissolved oxygen in the mixed liquor recycle) but cannot predict rbCOD destruction due to hydraulic conditions, or fermentation due to heterogeneous mixing. This paper discusses all of the factors that affect denitrification and poses questions for future research.

Computer Simulation in Predicting Biochemical Processes and Energy Balance at WWTPs

“…Dold et al [10] used modeling to design optimal batch tests procedures, and to estimate the maximum specific growth rate of heterotrophs under anoxic conditions. Phillips et al [11] used a dynamic model to optimize the mixed liquor recycle rate and studied factors that affected nitrogen removal, including the influent wastewater readily biodegradable COD/N ratio and acetate addition. The strategies and calculations of the optimum COD/N ratios were investigated by FilaliMeknassi et al [12] (in sequencing batch reactor (SBR)) and Latimer et al [13] (in continuous flow reactor).…”

Modeling External Carbon Addition in Biological Nutrient Removal Processes with an Extension of the International Water Association Activated Sludge Model

“…The same authors demonstrated the effect of differences in denitrification kinetics for two external carbon sources, methanol and a commercial compound (MicroC TM , Environmental Operating Solutions, Inc., Bourne, Massachusetts), on the anoxic volumes needed and nitrogen removal performance for the modified Ludzak-Ettinger and 4-stage Bardenpho BNR process configurations. Phillips et al (2009) used a dynamic model to optimize the mixed liquor recycle rate and studied factors that affected nitrogen removal, including the influent wastewater readily biodegradable COD/N and acetate addition. Strategies for dosing external carbon sources and calculations of the optimum COD/N were investigated by Latimer et al (2009) (sugar addition to a continuous flow reactor) and Filali-Meknassi et al (2005) (acetate addition to a sequencing batch reactor).…”

Impact of solid residence time (SRT) on functionally relevant microbial populations and performance in full‐scale enhanced biological phosphorus removal (EBPR) systems

“… The acetate consumed by PAOs was corrected by subtracting the stoichiometric utilization of acetate by denitrification (nitrite accumulations were considered). The correction was made based on a theoretical COD/NOx‐ N ratio of 3.5 for acetate (McCarthy, Beck, & Amant, , Phillips et al, ). …”