The desulfurization-denitrification biofilm reactor with an anaerobic sulfate reduction bioreactor as pretreatment was operated for 370 days. And autotrophic and heterotrophic denitrification was found to be coexistence in this process. In anaerobic sulfate reduction reactor (AR), the influent sulfate was increased from 900 mgSO4 2-/l to 2100 mgSO4 2-/l and the sulfide generating rate was high at 97.5%. In autotrophic and heterotrophic (mixotrophic) desulfurization-denitrification reactor (MR), HRT was decreased from 6.63h to 3.31h. The sulfide was removed of 100% and predominantly oxidized to sulfur. TOC was further removed of 86.6% and the level of heterotrophic denitrification happened in MR ranged from 35.7% to 59.9%. The final average removals of sulfate and organic carbon were 93.8% and 97.8% at volumetric loadings of 7200 mgSO4 2-/(l·d) and 4800 mgC/(l·d), respectively. The sulfate was finally converted to sulfur which could be reused and would not cause secondary pollution. Furthermore, nitrate and nitrite added as electron acceptors were finally converted to nitrogen gas and the removals were both up to 100%.