Oxygen and carbon requirements for biological nitrogen removal processes accomplishing nitrification, nitritation,...

The oxygen and carbon savings associated with novel nitrogen removal processes for the treatment of high ammonia, low biodegradable organic matter waste streams such as the recycle streams from the dewatering of anaerobically digested sludges are well documented.This understanding may lead some to think that similar oxygen savings are possible if novel processes such as nitritation/ denitritation and partial nitritation-deammonification are incorporated into main liquid stream processes where influent biodegradable organic matter is used to denitrify residual oxidized nitrogen (nitrite and nitrate). It is demonstrated that the net oxygen required for nitrogen removal is 1.71 mg O2/mg ammonia-nitrogen converted to nitrogen gas as long as influent biodegradable organic matter is used to denitrify residual oxidized nitrogen. Less oxygen is required to produce oxidized nitrogen with these novel processes, but less biodegradable organic matter is also required for oxidized nitrogen reduction to nitrogen gas, resulting in reduced oxygen savings for the oxidation of biodegradable organic matter. The net oxygen requirement is the same since the net electron transfer for the conversion of ammonia-nitrogen to nitrogen gas is the same. The biodegradable organic matter required to reduce the oxidized nitrogen to nitrogen gas is estimated for these processes based on standard biological process calculations. It is estimated to be in the range of 3.5 to 4.0 mg biodegradable COD/mg ammonia-nitrogen reduced to nitrogen gas for nitrification-denitrification, 2.0 to 2.5 for nitritation-denitritation, and 0.5 for partial nitritation-deammonification. The resulting limiting influent wastewater carbon-to-nitrogen ratios are estimated and can be used to guide the appropriate selection of biological nitrogen removal process given knowledge of the biological process influent wastewater carbon-to-nitrogen ratio. Energy savings possible for mainstream processes incorporating these novel nitrogen removal processes include reduced process oxygen requirements from reduced biodegradable carbon loadings to the biological process and the potential that plant influent biodegradable carbon can be captured upstream of the biological nitrogen removal process and used to produce energy, for example, by conversion into biogas.