Influence of hydraulic retention time on advanced synergistic nitrogen removal using internal carbon source

Hydraulic retention time (HRT) is a significant operational eter of denitrifying filter (DF). The influence of HRT on the performance and mechanism of advanced synergistic nitrogen removal (ASNR) of partial-denitrification anammox (PDA) and denitrification was investigated, consuming the hydrolytic and oxidation products of refractory organics in the secondary effluent (SE) as carbon source. When the HRT was 8, 6, 4 and 2 h, the filtered effluent total nitrogen (TN) was 1.47, 3.47, 4.17 and 4.49 mg/L, and the effluent CODcr was 8.12, 9.95, 9.40 and 9.87 mg/L, respectively. Removing 1 mg of TN actually consumed 0.87–0.96 mg CODcr, and the contribution rate of PDA to TN removal was 62.10–70.02 %. A variety of manganese oxidizing (MnOB), hydrolytic, anammox and denitrifying bacteria were identified, and their abundance was obviously affected by the HRT. The lack of carbon source was the main factor limiting the ASNR efficiency, rather than the HRT. [Display omitted] •CODcr, organic nitrogen, NH4+-N, NO2--N, NO3--N and TN were removed by the ASNR.•Carbon source amount was the main factor affecting the TN removal efficiency.•The actual CODcr consumption for removing 1 mg TN was significantly reduced.•BMOs, MnOB, Anammox, denitrifying, and hydrolytic bacteria coexisted in the DF.•Anammox bacteria had priority over denitrifying bacteria in removing NO2--N.