Lipases were produced by a microbial consortium derived from a mixture of wastewater sludges in a medium containing solid industrial wastes rich in fats, under thermophilic conditions (temperature higher than 45 degrees C for 20 days) in 4.5-L reactors. The lipases were extracted from the solid medium using 100 mM Tris-HCl, pH 8.0 and a cationic surfactant agent (cetyltrimethylammonium chloride). Different doses of surfactant and buffer were tested according to a full factorial experimental design. The extracted lipases were most active at 61-65 degrees C and at pH 7.7-9. For the solid samples, the lipolytic activity reached up to 120,000 UA/g of dry matter. These values are considerably higher than those previously reported in literature for solid-state fermentation and highlight the possibility to work with the solid wastes as effective biocatalysts. (C) 2011 Elsevier Ltd. All rights reserved.