Nitrogen Transformation in Activated Sludge Treatment

In a full-scale activated sludge treatment plant treating nutrient deficient pulp mill waste, the supply of supplementary nitrogen was interrupted for a period of 25 days. This interruption in nutrient supply had very little influence on the treatment efficiency but subsequently when the nutrient addition was recommenced some activated sludge was lost in the effluent and the sludge volume index increased. In this system, nitrification was completely inhibited and the only forms of nitrogen present in the system were ammonia and organic nitrogen. The concentration of ammonia in the final effluent was practically constant and independent of the addition of supplementary nitrogen. The explanation of this is that ammonia released from cellular materials occurs in proportion to the rate of endogenous respiration of the activated sludge.