Start-up and performance of a hybrid anoxic reactor for biological denitrification

This study was aimed at denitrification of wastewater using a hybrid anoxic reactor (HAR), which uses self immobilized microbial granules under fluidized condition. Granulation of the denitrifying biomass was studied in the HAR with methanol and acetate as carbon sources. It was observed that by the end of 15 day almost spherical granules with a settling velocity of 1.5 cm/s and a mean diameter of 0.5 mm were produced. By stepwise increment of the influent nitrate concentration, the removal rate reached 740 g NO3–N/m3 day with a removal efficiency of almost 100% at a hydraulic retention time of 6 h or higher. For complete denitrification, the ratio of the organic substrate required to amount of nitrate nitrogen removed was as low as 2.2 g COD/g NO3–N. The study was then extended to denitrifying a nitrified toxic industrial effluent. Denitrification was on par with the synthetic wastewater and efficiency of more than 95% was achieved.