Nitrogen Removal by Simultaneous Nitrification and Denitrification via Nitrite in a Sequence Hybrid Biological Reactor

Abstract

Sequence hybrid biological reactor (SHBR) was proposed, and some key control parameters were investigated for nitrogen removal from wastewater by simultaneous nitrification and denitrification (SND) via nitrite. SND via nitrite was achieved in SHBR by controlling demand oxygen (DO) concentration. There was a programmed decrease of the DO from 2.50 mg·L −1 to 0.30 mg·L −1, and the average nitrite accumulation rate (NAR) was increased from 16.5% to 95.5% in 3 weeks. Subsequently, further increase in DO concentration to 1.50 mg·L −1 did not destroy the partial nitrification to nitrite. The results showed that limited air flow rate to cause oxygen deficiency in the reactor would eventually induce only nitrification to nitrite and not further to nitrate. Nitrogen removal efficiency was increased with the increase in NAR, that is, NAR was increased from 60% to 90%, and total nitrogen removal efficiency was increased from 68% to 85%. The SHBR could tolerate high organic loading rate (OLR), COD and ammonia-nitrogen removal efficiency were greater than 92% and 93.5%, respectively, and it even operated under low DO concentration (0.5 mg·L −1) and maintained high OLR (4.0 kg COD·m −3·d −1). The presence of biofilm positively affected the activated sludge settling capability, and sludge volume index (SVI) of activated sludge in SHBR never hit more than 90 ml·g −1 throughout the experiments.