Abstract The performance of a particulate-biofilm, expanded-bed process for nitrification of activated sludge final effluent (ASFE) is reported for a plant receiving mixed industrial and domestic wastewater. The support material for the particulate-biofilms was glassy coke, to which the nitrifying bacteria attached and formed a highly active biofilm. An average nitrification rate of 1.7±0.6 kg m −3 expanded bed d −1 was recorded during operation of the bioreactor, which had a hydraulic residence time of 15 min. On average, the ASFE contained 12.6±3.7 g m −3 NH 3–N, which was reduced to 2.6±3.3 g m −3 NH 3–N. Furthermore, transfer of 10–12% of the oxygen in air was achieved using counter-current aeration. This investigation has demonstrated that a high rate of nitrification can be achieved with a particulate-biofilm, expanded-bed process. It has also demonstrated that the process can operate without backwashing and still remove particulate material from the ASFE feed.