The results obtained in the present study have demonstrated that it is possible to recover up to 23 lipase units per gram of lyophilised solid from activated sludge, in a process that comprises extraction using ultrasonication (without detergent) followed by dialysis and lyophilisation. The extracted enzymes could be used, without any further treatment, to improve the sludge degradation, thus improving the amount of biogas produced after anaerobic digestion.