Kinetic/Half-saturation Coefficient Considerations for Post Denitrification MBBR
Abstract:To understand better Moving Bed Biofilm Reactor (MBBR) post denitrification process robustness to very low level of nitrate+nitrite (NOx-N) < 1 mg/L, and possible kinetic limitations to achieve these low levels, pilot was implemented at the Blue Plains AWTP between December 2007 and early July 2008. Kinetics of microbial growth govern the utilization of the substrate and the production of the biomass; hence it was important to understand the limitations of the substrate (usually expressed as Ks (half-saturation coefficient)) on the overall denitrification rates. Total of four 100-gallon anoxic pilot reactors (each filled with 30% by volume of Hydroxyl 515® plastic media) were used for this testing. Two types of in-situ Specific Denitrification Rate (SDNR) batch tests were conducted throughout this piloting - one with NOx-N limitations and one with biodegradable soluble COD (bsCOD) limitations. Both types of tests were conducted with excess phosphorus. During the tests, SDNR was estimated by measuring the rate of consumption of NOx-N over time. At an ambient temperature of 17°C, Ks,NOx-N (Ks for nitrate limited test) was 2.5 mg/L on average, and Ks,bsCOD (Ks for bsCOD limited test) was 6.5 mg/L. During the cold temperature period (13.5°C), Ks,NOx-N was 2.4 mg/L on average while Ks,bsCOD concentration was not a definitive finding. This study supported previous reports indicating the need for residual bsCOD of 10–15 mg/L in anoxic zones. In-situ SDNR data were used to develop a reasonable model for the MBBR system, based on the double Monod relationship. It was estimated that rmax (maximum denitrification rate) = 4.7 g/m2/d, Ks,NOx-N = 3.5 mg/L and Ks,bsCOD = 9.7 mg/L. Half-saturation coefficient was found to be a very important design consideration for fixed film polishing application.
Document Type: Research Article
Publication date: January 1, 2009
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