BACKGROUND: Phenol and hexavalent chromium are considered industrial pollutants that pose severe threats to human health and the environment. The two pollutants can be found together in aquatic environments originating from mixed discharges of many industrial processes, or from a single industry discharge. The main objective of this work was to study the feasibility of using phenol as an electron donor for Cr(VI) reduction, thus achieving the simultaneous biological removal/reduction of the two pollutants in a packed-bed reactor. RESULTS: A pilot-scale packed-bed reactor was used to estimate phenol removal with simultaneous Cr(VI) reduction through biological mechanisms, using a new mixed bacterial culture originated from Cr(VI)-reducing and phenol-degrading bacteria, operated in draw-fill mode with recirculation. Experiments were performed for feed Cr(VI) concentration of about 5.5mg L-1, while phenol concentration ranged from 350 to 1500mg L-1. The maximum reduction/removal rates achieved were 0.062 g Cr(VI) L-1 d(-1) and 3.574 g phenol L-1 d(-1), for a phenol concentration of 500mg L-1. CONCLUSION: Phenol removal with simultaneous biological Cr(VI) reduction is feasible in a packed-bed attached growth bioreactor. Phenol was found to inhibit Cr(VI) reduction, while phenol removal was rather unaffected by Cr(VI) concentration increase. However, the recorded removal rates of phenol and Cr(VI) were found to be much lower than those obtained from previous research, where the two pollutants were examined separately. (c) 2008 Society of Chemical Industry.