The aim of the present study was to investigate the suitability of a Biological Aerated Filter (BAF) plant as an alternative process or an upgrading step for the treatment of domestic wastewater from the city of Rome, Italy. The results obtained through a three years experimental activity on a pilot-scale BAF plant fed with real wastewater showed high process efficiencies and stable performance for both carbon and ammonia oxidation. The effluent quality met. on average basis, 68 mg/L total COD (CODtot), 37 mg/L Total Suspended Solids (TSS), 3.3 mg/L ammonia-nitrogen (NH4+-N) and 21.1 mg/L nitrate-nitrogen (NO3--N). Despite the good performance, the high content of suspended solids in the influent stream caused filter bed clogging and frequent backwashing operations were required. Therefore, in the last part of the experimental activity a pre-treatment step was adopted prior to the biological step, consisting of chemical precipitation by lime addition. The influent quality parameters were consequently modified; for instance the particulate matter content was reduced by about 73%. The process efficiency of both ammonia and organic carbon oxidation did not modify appreciably; however, a beneficial effect was obtained on the frequency of the backwashing phase, which could be reduced by half. Since the new combined chemical-biological system demonstrated to be a valid alternative to the activated sludge treatment plant. a modeling activity was finally performed with the aim of evaluating the design parameters of a full-scale BAF plant fed with the same pre-treated wastewater as used in the experimental activity. The results of this phase are also herewith presented and discussed. (C) 2009 Elsevier B.V. All rights reserved.