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

Abstract

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°C () with DO equal to 0.1 mgO ₂ L⁻¹ and F:M in the range 0.2–0.4 kgBOD₅ kgMLVSS⁻¹ d⁻¹. The SDNR 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 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.

Keywords:

• conversion yield
• denitrification rate
• mathematical correlation
• nitrogen control
• plant design
• wastewater treatment