Abstract
The balance of the nitrogen cycle depends on the combined activities of nitrogen fixation, nitrification, denitrification, nitrogen assimilation and dissimilation. The removal of ammonia-nitrogen in wastewater treatment plants is dominated by two mechanisms: a conversion pathway to nitrogen gas via the related processes of nitrification and denitrification, and an assimilatory pathway for the formation of bacterial biomass. For combined nitrification-denitrification, there are at least two routes: anaerobic ammonia oxidation (the Anammox process), and the autotrophic nitrification. Under typical wastewater treatment conditions—10-20°C, with the presence of organic material—the autotrophic nitrification followed by heterotrophic denitrification is the dominant mechanism for the biological nitrogen removal. In the design of a nitrogen-removing plant, the capital cost is usually dominated by the size of the reactor used and its associated solid-liquid separation unit. The dominant factors in the operating cost include aeration, sludge removal, pumping cost (primarily for any recycle stream required), and the chemical dosage requirement.
Published Version
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