A study of the treatment of piggery wastes using an anaerobic fixed bed reactor (AFBR) followed by a zeolite bed filtration (ZBF) was carried out at pilot scale and tropical climate conditions (temperatures between 18 and 32 degreesC) in Costa Rica. The pilot AFBR operated at two different average organic volumetric loading rates (B-v): 5.7 and 24.0 kg COD per m(3) day, which corresponded to flow-rates of 25 and 45 m(3)/day. Changes of the influent concentration did not provoke process failure. The system was able to overcome the variation of the influent strength at a fixed hydraulic retention time. COD and BOD removal efficiencies of 73 and 77%, respectively, were achieved for the highest B-v studied. Average total suspended and settleable solids removals of 63.0 and 68.1%, respectively, were achieved, the last one being virtually independent of the B-v applied. The reactor also operated as an equalisation tank reducing the variation of the influent strength, which could be favourable for the post-treatment of the final anaerobic effluent. (C) 2002 Elsevier Science Ltd. All rights reserved.