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

► A hybrid reactor was studied for its application to denitrification of wastewaters. ► Microbial granules developed in the reactor within 15 day of reactor start-up. ► Complete nitrate removal was possible at 740 g NO3-N/m3 day loading at an HRT of 6 h. ► Complete denitrification resulted at a COD/NO3-N ratio as low as 2.2. ► Denitrification efficiency was more than 95% on industrial wastewater.