Enhanced total nitrogen removal performance in a full scale Orbal oxidation ditch by a novel step aeration mode

Two aeration modes, namely point aeration and step aeration, were proposed and implemented in a full scale Orbal oxidation ditch, and nitrogen removal performance was studied. The results showed that nitrogen removal performance under point aeration mode depended on oxygen supply control. Highest total nitrogen (TN) removal efficiency of 73.2% was achieved when oxygen input in the outer, middle and inner channel accounted for 50, 25 and 25% of total oxygen supply, respectively. With the same oxygen supply, both aeration modes demonstrated complete nitrification with over 97% ammonia nitrogen removal efficiencies. However, TN removal efficiency was 78.8% under step aeration mode, which was higher than that under point aeration. The pyrosequencing results indicated that microbial community composition was affected by aeration modes and step aeration mode was beneficial to the enrichment of denitrifiers. The greater diversity and relative abundance of denitrifiers enhanced TN removal under step aeration mode.