Denitrification of highly alkaline nitrate waste using adapted sludge

Uranium extraction and regeneration of ion exchange resin generates concentrated nitrate effluents (typically 500 to 10,000 ppm NO(3)-N) that are highly alkaline in nature (pH 9.0 to 11.0). It is difficult to remove nitrate from such solutions using standard physiochemical and biological methods. This paper reports denitrification of such wastes using preadapted sludge (biomass), which was acclimatized to different influent pH (7.5 to 11.5) in a sequencing batch reactor (4 l) for 2 months. Performance of the developed consortia was studied under different pH (7.5 to 12). Biomass denitrified the synthetic wastewater containing 1,694 ppm NO(3)-N at a pH of 10.5. Decrease in nitrite build up was observed at higher pH, which differs from the reported results. Kinetic analysis of the data showed that specific rate of nitrate reduction was highest (78 mg NO(3)-N/g MLSS/h) at higher pH (10.5). This was attributed to the acclimatization process. Thus, high-strength nitrate wastewater, which was highly alkaline, was successfully treated using preadapted sludge.