Nitrogen Removal from Dairy Waste Using Deammonification Fueled by Fermented Dairy Manure
Dairy manure contains high concentrations of organics and nutrients such as nitrogen (N) that can pollute the environment surrounding dairy operations. The objective of this research is to determine the feasibility of removing bioavailable ammonia-N (NH3-N) from dairy manure by using deammonification (nitritation combined with denitrification) coupled with dairy manure fermentation, which fuels the denitrification step. Dissolved oxygen (DO) levels of less than 1 mg/L are known to significantly reduce the growth rate of nitrite oxidizing bacteria (NOB). This can prevent nitrate (NO3 −) production, thereby reducing aeration energy requirements by 25%. Furthermore, by denitrifying from nitrite (rather than nitrate), organic carbon source requirements are reduced by approximately 40%. Therefore, we are using low DO in the deammonification phase to achieve nitritation, followed by no aeration during the denitrification phase. The fermenter, upstream of the deammonification system, provides both bioavailable NH3 (approximately 700 mg/L-N as determined from lab results) and organic acids (approximately 1,850 mg/L acetic acid chemical oxygen demand (COD) as determined from lab results) for denitrification; this corresponds with a readily biodegradable COD (rbCOD):NH3-N ratio of 3. An rbCOD to NH3-N ratio of approximately 5 is required for complete denitrification via NO3 −. However, our system is designed to process N through nitrite, and an rbCOD:NH3-N ratio of only 2 is required. Therefore, the achieved rbCOD:NH3-N ratio of 3 allows for significant nitrogen removal while reducing the cost of aeration as well as the need for an additional carbon source. The system is currently in operation. Ammonia-N removal rates approaching 100% have been observed. Fermentation-produced acetic acid concentrations of 1590 ± 310 mg/L acid COD have been generated at the pilot scale. The minimum DO level to successfully achieve stable nitritation and prevent oxidation all the way to nitrate is currently being determined and is known to be below 1.1 mg/L.
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Document Type: Research Article
Publication date: 2007-10-01
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