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[Display omitted] • Anammox contribution to nitrogen removal was robustly maintained at 91.3 ± 6.6 %. • Compared with stable NO 3 – → NO 2 –, NO 2 – → N 2 was sensitive to temperature reduction. • Anammox abundance was increased (0.56% to 1.22%) despite of decreased temperature. • NO 2 – accumulation at lower temperature was unexpectedly helpful to enrich anammox. Effluent quality deterioration caused by seasonal temperature reductions in wastewater treatment systems using partial anammox technology is a challenge that cannot be ignored. Here, relationships of denitrification and anammox under decreasing temperature were investigated in an anoxic moving bed biofilm reactor (MBBR). Compared with stable partial-denitrification (NO 3 – → NO 2 –), the NO 2 – reduction to N 2 was considerably inhibited when the temperature decreased, conversely helping to the competition of NO 2 – for anammox. Namely, this transformation provided sufficient substrates for anammox bacteria. Although the TIN removal decreased slightly, anammox contribution was robustly maintained at 91.3 ± 6.6 %, even increased. High-throughput sequencing results revealed that anammox bacteria were enriched (0.56 % to 1.22 %). Moreover, qPCR results showed that increased ratio of hzsB /(nirK + nirS) further supported anammox gained an enhancement. This study demonstrated partial-denitrification/anammox process using anoxic MBBR could maintain stable autotrophic nitrogen removal contribution when encountering temperature decrease, providing a new perspective on the application of mainstream anammox. [ABSTRACT FROM AUTHOR]