Achieving stable nitrogen removal performance of mainstream PN-ANAMMOX by combining high-temperature shock for selective recovery of AOB activity

This paper describes the new concept of the mainstream partial nitritation (PN)-anaerobic ammonium oxidation (ANAMMOX) combined with a high-temperature shock strategy for the selective recovery of ammonia-oxidizing bacteria (AOB) activity. In the preliminary test, the temperature shock condition for PN was optimized (60 °C and > 20 min). Based on this, the implementation strategy in a continuous stirred tank reactor (CSTR) system was studied further, and the polyvinyl alcohol (PVA)/sodium alginate carrier exposure ratio (ER) and dissolved oxygen (DO) concentration were considered as primary variables. The AOB activity was recovered selectively when the ER of the carrier ranged from 20 to 40%, and the DO was higher than 2.3 mg O2/L. This was not the case for nitrite-oxidizing bacteria (NOB) (AOB: 1.17±0.1 gNH4+-N/LCarrier/d, NOB: 0.34±0.1 gNO3−-N/LCarrier/d). As a result, the activity of AOB was recovered selectively with a decrease in Nitrospira spp., which was verified by kinetic and microbial analyses for the AOB (KS, DO = 3.89 mgO2/L) and NOB (KS, DO = 1.14 mgO2/L). Eventually, the mainstream PN-ANAMMOX was achieved with a nitrogen removal efficiency of 81.5±3.3% for 95 days. The findings provide insight to establishing a stable mainstream PN-ANAMMOX process using a high-temperature shock strategy. [Display omitted] •Mainstream ANAMMOX combined with high temperature shock was well implemented.•Exposure at 60 °C for 20 min was effective for selective recovery of AOB activity.•The population of Nitrospira spp. was selectively inhibited by the strategy.•Ca. Brocadia sp. 40 was predominant in the mainstream ANAMMOX reactor.•Effluent TN concentration of 5.7±1.3 mg/L was achieved with a HRT of 4.5 h.