This paper reports on the ability of an enzymatic pre-treatment to significantly improve the conditioning of wastewater sludges (biosolids) significantly using by a polymeric flocculant. Experiments used anaerobically digested biosolids samples from two different municipal wastewater treatment facilities, and a formulation containing several different hydrolytic enzymes. Samples were incubated at 35 degrees C for 16 h then conditioned with the cationic polymer solution. A laboratory scale mechanical dewatering unit, which simulates full-scale belt filter presses, was used in dewatering of,the biosolids. Dewaterability was evaluated using capillary suction time (CST), solid content of final cake product, filtrate turbidity, and suspended solids analysis. The enzyme additions enhanced dewaterability of the polymer conditioned samples in terms of CST and solids content of final product, demonstrating the possibility of significant volume reductions using enzymatic treatment at full-scale. The biosolids structures with the additions of enzyme, polymer, and both additives were determined using field emission scanning electron microscopy. (c) 2004 Elsevier Ltd. All rights reserved.