Maximum Methanol-Utilizer Growth Rate: Impact of Temperature on Denitrification

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Three AWTPs (Advanced Wastewater Treatment Plants) in the Chesapeake Bay watershed including Alexandria Sanitation Authority, Blue Plains, and Western Branch use methanol for denitrification to achieve low effluent total nitrogen concentrations. Denitrification rates are slowest in winter months due to cold temperatures which decrease the kinetic behavior of the methanol-utilizing heterotrophs. This study investigates measurement of the kinetic parameters, maximum specific growth rate (μMAX) and temperature dependency of the growth rate, used to size denitrification facilities by conducting an experimental batch test on seed mixed liquor samples obtained from full-scale single sludge, two sludge and three sludge processes. Results suggest a μMAX at 20°C of 1.25 /day with an Arrhenius coefficient, θ, of 1.13, based on a decay rate of 0.04 /day. These growth rates were the same irrespective of the process employed (single-sludge, two-sludge and three-sludge). The low growth rate (similar to that of nitrifiers) identifies that systems should be designed based on a long enough anoxic SRT to ensure stable growth and avoid washout. This is exacerbated by the strong temperature dependency for plants operating at low temperatures.

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