CHARACTERIZING DENITRIFICATION KINETICS AND STOICHIOMETRY AT DIFFERENT TEMPERATURES USING VARIOUS CARBON SOURCES Open Access
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Facilities across North America are designing plants to meet stringent limit of technology (LOT) treatment for nitrogen removal (3 mg/L total effluent nitrogen). The Blue Plains Advanced Wastewater Treatment Plant (AWTP) is one of many facilities in the Chesapeake Bay regions evaluating its ability to meet LOT treatment capability. The plant uses methanol as a carbon source in a post-denitrification process to achieve low effluent total nitrogen concentrations. This becomes more difficult in winter, at lower mixed liquor temperatures and higher flows, as a consequence of the kinetic behaviour of the methanol-utilizing heterotrophs.With the current demand for external carbon source addition in the Chesapeake Bay region and other parts of the country facing similar nutrient discharge limits, it is clear that other electron donors should be directly evaluated and compared to methanol in terms of denitrification rate, and the true cost-effectiveness of these substrates should be investigated. This research was designed to investigate the methods for overcoming limitations of methanol addition for full-scale facilities and to evaluate the relative benefits and constraints for using alternative carbon sources (methanol, ethanol, acetate and corn syrup) at different temperatures, between 10 to 20°C. These temperatures approximately reflect the minimum monthly and average annual temperature of wastewater in the Mid-Atlantic region of the United States. Experimental results suggest that the methanol-grown biomass could utilize acetate, corn syrup (at least not immediately) or ethanol, and denitrification rates using ethanol and acetate at Blue Plains AWTP could be tripled relative to methanol, but would not result in an immediate improvement in denitrification (using acetate). The low methanol denitrification rate at low temperatures compounded by the strong temperature dependency highlights the importance of providing sufficient anoxic Solids Retention Time (SRT) to avoid washouts in methanol addition systems. A balance may be obtained together with effective denitrification at cold temperature, by switching to a substrate such as ethanol only in the winter while using methanol the rest of the year. The results of this research are important for plants with methanol addition considering simultaneous addition of other substrates in an effort to improve denitrification performance.