High efficiency and stable partial nitration achieved via gel immobilization

•PN filler performance under high and low ammonia, and low temperature was evaluated.•PN filler can be rapidly reactivated after reactor breakdown or long stagnation.•Immobilization facilitated functional bacteria growth and community dominance.•The mechanism for the high efficiency and stability of the PN filler was explained.•The oxygen permeation depth model of the PN filler was established. Long-term high efficiency and stable partial nitrification (PN) performance was achieved using gel-immobilized partial nitrifying bacteria. The PN characteristics of the filler under high and low ammonia nitrogen concentrations and low temperature were comprehensively studied and the rapid reactivation was achieved after reactor breakdown or long stagnation period. The results showed that the maximum ammonia oxidation rate was 66.8 mg•(L•h)−1 and the nitrite accumulation rate was above 95 % for the filler. Efficient and stable PN performance depends on the high abundance of ammonia-oxidizing bacteria (AOB) inside the filler and dynamically microbial community. In addition, the oxygen-limited zone and competition between the microorganisms inside the filler effectively inhibited the growth of nitrite oxidizing bacteria, and the sludge outside the filler assisted in this process, which supported the dominant position of AOB in fillers. This study provides a reliable technology for the practical application of the PN nitrogen removal process.