A spiral fiber based biofilm reactor was developed to remove nitrate and chromate simultaneously. The denitrification and Cr(VI) removal efficiency was evaluated with synthetic groundwater (NO3-N = 50 mg/L) under different Cr(VI) concentrations (0-1.0 mg/L), carbon nitrogen ratios (C/N) (0.8-1.2), hydraulic retention times (HRT) (2-16 h) and initial pHs (4-10). Nitrate and Cr(VI) were completely removed without nitrite accumulation when the Cr(VI) concentration was lower than 0.4 mg/L. As Cr(VI) up to 1.0 mg/L, the system was obviously inhibited, but it recovered rapidly within 6 days due to the strong adaption and domestication of microorganisms in the biofilm reactor. The results demonstrated that high removal efficiency of nitrate (>= 99%) and Cr(VI) (>= 95%) were achieved at lower C/N = 0.9, HRT = 8 h, initial pH = 7, and Cr(VI) = 1.0 mg/L. The technology proposed in present study can be alternative for simultaneous removal of co-contaminants in groundwater. (C) 2017 Elsevier Ltd. All rights reserved.