Calculating specific denitrification rates in pre-denitrification by assessing the influence of dissolved oxygen, sludge loading and mixed-liquor recycle

This article presents the results of an experimental study on the correlation among the specific denitrification rate (SNDR), the dissolved oxygen concentration (DO), the F:M ratio (F:M) and the mixed-liquor (ML) recycle in the pre-denitrification reactors fed by domestic sewage. The experimental curves reveal a 28.8-32.0% reduction in the SDNR at 20 °C (SDNR20°C) with DO equal to 0.1 mgO2 L-1 and F:M in the range 0.2-0.4 kgBOD5 kgMLVSS-1 d-1 . The SNDR reduction increases to 50.0-55.9% with DO = 0.3 mgO2 L-1. A mathematical correlation of these results and an equation for calculating SDNR20°C as function of the F:M as well as the average DO and BOD5 in the total flow-rate fed in the denitrification stage are proposed. The conducted experience gives useful suggestions for practical usage, in particular regarding the denitrification reactor design, and represents a good starting point for future applications with the aim to optimize the biological process in domestic sewage treatment plants.