Nitrifier Augmentation for High Ammonia Nitrogen Removal by Aerobic Granular Sludge at Low Temperatures

Aerobic granular sludge (AGS) is widely used in domestic sewage treatment, but high ammonia nitrogen removal by AGS is difficult because nitrifiers cannot work effectively at low temperatures. This study investigated the AGS performance on treating high ammonia nitrogen wastewater with the aid of an isolated pure nitrifier at low temperatures. Five isolated and identified strains possessed high ammonia nitrogen or nitrite degradation ability and good adaptability to varying temperature and pH values. AGS was formed in 33 days with a smooth surface and compact structure. However, the ammonia nitrogen removal capability was remarkably low because of the excessive influent ammonia nitrogen. With a higher hydrophobicity and better adhesion ratios, the bioaugmentation of the five strains with AGS was obvious. The chemical oxygen demand and ammonia nitrogen removal efficiencies were 90.7 and 86.3%, respectively, and the total nitrogen removal improved by a factor of 3.1. The dissolved oxygen consumption did not change after the inoculation of the five strains. However, the free ammonia concentration significantly decreased, which can facilitate a high ammonia nitrogen removal at low temperature.