Nitrogen and Organic Carbon Transformations in an Aerated Stabilization Basin, 2001 Environmental Conference Proceedings

L.B. Sonnenberg, S.L. Croghan--The addition, transformation and removal of nitrogen from wastewater treatment systems is highly important to many wastewater treatment plant operators. The purpose of these studies was to follow the transformation of added nitrogen during the treatment of a kraft mill’s wastewater and to relate these transformations to changes in organic carbon characteristics. In field and laboratory studies, ammonia, nitrate, dissolved organic nitrogen, and particulate organic nitrogen were measured after the addition of nitrogen. The distribution of organic carbon into fractions of hydrophobic acids, hydrophobic base/neutrals,hydrophilic acids, hydrophilic bases, and hydrophilic neutrals was also quantified. Kraft mill wastewater was compared to samples from an unimpacted, high-organic carbon stream.

Nitrogen and carbon results suggest that in the heterotrophic conditions of mill wastewater treatment, there is a rapid uptake of ammonia, producing organic nitrogen. Comparisons of the field and laboratory results suggest that in the ASB studied, biomass nitrogen settles and then undergoes endogenous respiration. Consequently, ammonia is released at levels equivalent to or higher than those initially added. Accompanying the nitrogen transformations, the organic carbon concentration is reduced by almost half, producing a nitrogen-enriched organic matter in the water column. All organic carbon fractions are significantly and substantially reduced, except for the basic fractions. The results indicate that the amended nitrogen is incorporated into particulate material and subsequently metabolized into dissolved hydrophilic and hydrophobic bases. By contrast to the heterotrophic mill wastewaters, in natural systems there was an increase in organic nitrogen and carbon in the stream water, indicating the dominant role of photoautotrophs, including nitrogen fixers.