Excellent, steady and economical nitrogen removal in highly variable mining wastewater via three-stage partial-denitrification/partial-nitrification/anammox system: A pilot-scale demonstration

In this study, a novel three-stage partial-denitrification/partial-nitrification/anammox (PD/PN/Anammox) system was established. Results showed that the excess of COD and the reduction of nitrite in PD process caused by the instability of influent nitrate are avoided through real-time influent COD/N ratio of 2.1. The extending the aeration interval in PN process enhanced the inhibition of nitrite oxidizing bacteria and promoted the activity of ammonia oxidizing bacteria under low free ammonia (FA, 1.1 ± 0.2 mg/L). In the upflow porous-plate anaerobic reactor (UPPAR), anammox bacteria (Candidatus_Kuennia) was rapid natural enriched from 0 % to 48.4 %, and granular anammox was formed by the increased of filamentous bacteria, α-d-glucose and a-helix. Moreover, the removal and robustness of ammonia nitrogen (98.9 ± 1.8 %) and total nitrogen (87.0 ± 2.3 %) in this system are better than those of the single stage PN/PD/Anammox process, and its cost of oxygen consumption, COD consumption and sludge treatment is far lower than that of nitrification denitrification process and PN/Anammox/denitrification process. This study provides a series of feasible start-up and operation strategies of PD, PN, Anammox and PD/PN/Anammox processes for the application of anammox in rare earth mining wastewater, which proposes upgrading and renovation plans for local wastewater treatment plants.