Denitrification of high strength nitrate waste

The aim of the present work was to study the treatment of high strength nitrate waste (40 000 ppm NO3 i.e., 9032 ppm NO3–N) by acclimatizing sludge initially capable of degrading dilute streams (100–200 ppm NO3–N). Sludge from an effluent treatment plant of a fertilizer industry was acclimatized for 15 d each at 1694, 3388, 6774 and 9032 ppm NO3–N in a 4 L sequencing batch reactor. Complete denitrification of extremely concentrated nitrate waste (9032 ppm NO3–N) using acclimatized sludge was achieved in just 6 h. During the acclimatization period, increase in nitrite peak value from zero to 5907 ppm NO2–N was observed, as the concentration was increased from 1694 to 9032 ppm NO3–N. Kinetic analysis of the nitrate and nitrite profile could reasonably support microbiological explanations for nitrite build up and changes in sludge composition.