Effects of O on accumulation of nitrous and elemental sulfur and microbial community structure in double short-cut sulfur autotrophic denitrification system.

Understanding the effect of O on the accumulation characteristics of NO-N and S in the sulfur autotrophic denitrification (DSSADN) system is crucial for enhancing the denitrification efficiency of partial nitrification-anammox using DSSADN. The results revealed that in an environment without O entry, the NO-N accumulation efficiency (NiAE) and S accumulation efficiency (SAE) of the DSSADN system reached 89.40 % and 93.41 %, respectively. Once system entered O, ORP value kept increasing. When ORP increased to -59.9 mV (DO = 0.1 mg/L), soxB and nirK gene expression rose and as well NiAE and SAE continuously decreased to 48.13 % and 29.35 %. When ORP was above 30.9 mV (DO >0.2 mg/L) but below 81.0 mV (DO<0.4 mg/L), narG gene expression reduced and the relatively high sqr gene expression allowed NiAE and SAE remained at 45.08 % and 33.31 %. O promoted the synergistic effect of Thiobacillus and Azoarcus without the proliferation of nitrite oxidizing bacteria.