Simultaneous removal of chemical oxygen demand (COD), thiocyanate (SCN), cyanide (CN), ammonia (NH4+-N) and total nitrogen (TN) from coal process wastewater was investigated using fluidized biofilm process at a laboratory scale and commercial scale. In the laboratory scale tests, the removal efficiencies of COD, SCN, CN, ammonia and TN were 97, 99, 99, 99 and 93%, respectively, at 1.0 day of hydraulic retention time (HRT) and 3.4 kg m(-3) day(-1) of COD loading. A commercial wastewater treatment plant with 3.4 day of HRT was revised to the fluidized biofilm process with anoxic-oxic-anoxic-oxic (AOAO) reactors arrangement. The results in the revised commercial plant were similar to those in the laboratory test. (c) 2005 Elsevier Ltd. All rights reserved.