Slaughterhouse wastewater containing pork fat particles with initial average particle sizes (D-in) ranging from 60 to 450 mum was pretreated at 25 degreesC for 5.5 h with 250 mg/l of Pancreatic Lipase 250 (PL-250). Approximately 35% of substrate neutral fat was hydrolysed during pretreatment. Enzyme pretreated and control substrates were fed to anaerobic sequencing batch reactors (ASBRs) operated at 25 degreesC. During anaerobic treatment, the first-order neutral fat hydrolysis rate averaged 0.50 +/- 0.13 and 0.63 +/- 0.07/d for pretreated and control substrates, respectively. There was no significant particle size or pretreatment effect on pork fat hydrolysis rate in the ASBR.s. Higher free long-chain fatty acid (LCFA) concentrations in the pretreated than control substrates resulted in slightly increased LCFA removal rate at the onset of anaerobic digestion with pretreated substrate. However, pretreatment had only a small overall effect on fat particle digestion at 25 degreesC, marked by a decrease of about 5% in digestion time to achieve 80% reduction in neutral fat and LCFA concentration. Crown Copyright (C) 2003 Published by Elsevier Science Ltd. All rights reserved.