Extending reaction duration has minor influence on nitrite production in partial-denitrification process

Partial denitrification (PD) is another important pathway producing nitrite for anammox, however, whether its performance is affected by overlong reaction time, a situation that often takes place is still unknown. Three sequencing batch reactors were operated for PD to evaluate this factor on nitrite production. Results indicated effluent nitrite was very close despite reaction time even extending to four times longer than control (i.e., nitrate-to-nitrite transformation ratio (NTR) of 94.4%-89.8%). Meanwhile, it was found PD could recover to the normal after suffering from high organics shocking. Cycle studies suggested produced nitrite would not be further reduced with prolonged time, as indicated by changing trend of pH and alkalinity. Microbial analysis revealed PD functional bacteria, Thauera, slightly decreased with prolonged reaction, while it was always predominated. Taken together, this study indicated overlong reaction time had minor influence on PD, demonstrating its robustness with great technological superiority in supplying nitrite for anammox.