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Investigation of Denitrification Kinetics at Warm Temperature using Respirometer Open Access

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The Chesapeake Bay Agreement has forced many utilities in the watershed to research new and improved methods to reduce nitrogen concentrations in the bay. To achieve this goal, District of Columbia Water and Sewer Authority (DCWASA) is voluntarily exploring technologies that can help reduce its nitrogen discharge limit. Biological denitrification is an integral part of biological nitrogen removal where external carbon sources are necessary. This study focuses on the investigation of denitrification kinetics of methanol utilizing organisms that can be useful for the optimal design and upgrade of the wastewater treatment plants. A respirometer system was used to conduct experiments for measurement of kinetic parameters. The two plants that were considered in this study are Blue Plains Advanced Wastewater Treatment Plant and Alexandria Sanitation Authority Advanced Wastewater Treatment Plant. The efficiency of denitrification was evaluated with methanol and acetate as external carbon sources for denitrification. From the study, the specific denitrification rate (SDNR) with acetate was found to be 2.82 mg/g-MLVSS/hr whereas that with methanol was 3.12 mg/g-MLVSS/hr with ASA mixed liquor. With Blue Plains mixed liquor, the SDNR was 7.48 mg/g-MLVSS/hr at 20oC with an Arrhenius Coefficient of 1.087, which indicates a relatively strong temperature dependency. The relationships of the kinetic parameters were also investigated with different mixed liquor concentration. The test results indicate that the denitrification rate (DNR) was higher for high mixed liquor concentration (MLVSS), whereas the specific denitrification rate (SDNR) were very similar. The half saturation coefficient (Ks) for Blue Plains ranged from 0.10 to 2.04 mg/L and for ASA, Ks ranged from 0.02 to 0.81 mg/L. The half saturation coefficients were observed to be highly dependent on the denitrification rate and mixed liquor concentration at different temperature with R2 value ranges between 0.77 and 0.94.

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