is originally formed by fats whereas lipids from secondary sludge come from the cells after breaking their structure. As blended sludge is a mixture of primary and secondary, with a higher fraction of the first one, it results in the intermediate lipid content.Comparingboth primary sludges, some differences in the TS, VS and lipids can be observed (Table 1). As the primary sludges were collected in different days, this indeed implies variations in their composition.
The fluctuations may be the result of climate changes or by deviations in the amount and quality of the wastewater received in the WWTPprimary sludge gives the highest lipid fraction as most of this fraction