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 (SDNR), 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 degrees C (SDNR20 degrees C) with DO equal to 0.1 mgO(2) L-1 and F:M in the range 0.2-0.4 kgBOD(5) kgMLVSS(-1) d(-1). The SDNR reduction increases to 50.0-55.9% with O = 0.3 mgO(2) L-1. A mathematical correlation of these results and an equation for calculating SDNR20 degrees 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.