The liquid fraction free of suspended solids was treatedat 35˚C in an upflow anaerobic sludge blanket reactoroperating at an organic rate of 40.8 g COD/L·d (chemicaloxygen demand per liter reactor per day) and reaching amethane production rate of 10.3 L CH4/L·d (litre methane per litre reactor per day). The higher methane volumetric production rate was obtained for the treated liquidfraction, than a conventional anaerobic digester treatingeither unscreened or screened manure.