Each sample of received sludge was analysed in triplicate in order to determine the total solid(TS) and volatile solid(VS)contents according to standard method 2540G, and lipid content according to standard method 5520E [10]. The results in Table 1 show that TS and VS contents were very similar for all types of sludges tested. On the other hand, the lipid contents showed clear differences between the sludges. Thus, primary sludges achieved the greatest lipid fraction, followed by blended and secondary. Primary sludge mainly consists of organic matter from non-treated raw wastewater, so it is a combination of floating grease and solids; instead, the secondary sludge is mainly composed of microbial cells and suspended solids produced during the aerobic biological treatment of the primary treated wastewater. Thus, it is expected that
primary sludge gives the highest lipid fraction as most of this fraction