Nitrogen Transformation During the
Activated Sludge Treatment of
Alkaline Wastewater
JERZY GANCZARCZYK, Visiting Professor
Department of Civil Engineering
University of Toronto
Toronto, Canada
INTRODUCTION
For the effective long term activated sludge treatment of the organic
wastewaters deficient in mineral nutrients, their nitrogen and phosphorus requirements have to be satisfied. The proper evaluation of these requirements was the
subject of numerous studies (1,2,3) from which it can be generally concluded that
these requirements differ for different wastewater and different degrees of their
treatment. Moreover, they also depend on the hydraulic loadings of the aeration
tanks and the mixing conditions of their contents because these factors influence the
rate of utilization of nutrients in the system or the rate of washout.
It is believed that the exogenous nitrogen supply, at some range of nitrogen to
removable organic carbon ration, is relative to the protein fraction of the activated
sludge, i.e., to the number of active bacteria in the system, and therefore influences
to some extent the effect of treatment, the possibility of increasing the loadings, and
stability of the process even at some flow and load variations.
The activated sludge process performance in some nitrogen deficient systems
was the subject of numerous laboratory studies (4,5,6,7,8,9). They showed that the
wastewater organic carbon for some period of time can be removed effectively in the
absence of exogenous nitrogen, and that this is connected with the increase of the
carbohydrate and decrease of the protein fractions of the activated sludge mass. Such
systems can be regenerated by the presence of nitrogen sources in exogenous or
endogenous conditions.
The subject of the study is full-scale activated sludge treatment of an
unbleached Kraft pulp mill nutrient-deficient effluent (10). In this plant the
nitrification is completely inhibited. Thus, the forms of the nitrogen in the system is
ammonia nitrogen introduced as a nutrient and released as a product of activated
sludge endogenous respiration, and the organic nitrogen of the cells substance. This
system in the three successive periods of time was supplied with excess of nitrogen
nutrients, no nitrogen nutrients were added, and then the supply of nitrogen was as
in the first period.
EXPERIMENTAL
The activated sludge treatment plant performance studies concerned the
treatment of an unbleached Kraft pulp mill effluent with small admixture of primary
treated town sewage at the range of the conventional loadings and in the aeration
tanks with limited longitudinal mixing (10).
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