The results of FFA analyses in primary sludge showed that, after sludge acidification, the FFA content increased from 39.2% to 68.7%(on the basis of lipids) showing a good agreement with previous literature data [5]. Moreover, the increase of FFA content resulted on significant increase of saponifiable (esterifiable) lipids (from 45.3% to 70.0%),which accounts for the rise of biodiesel production from 5.9% to 18.6% (on the basis of dry sludge).