(305g) Activated Sludge Oil: Identification and Characterization of Components

The demand for alternative sources to petroleum is growing. Recently, sewage sludge as a raw material for biodiesel production has been demonstrated in our group^1-2. In this present study, activated sludge oil (ASO) extracted from activated sludge was characterized to provide information for activated sludge oil refinement. The refinement process aims for activated sludge to be considered as a feedstock for biodiesel production and as a possible source of value-added products. Fractionation of the ASO extract with solvents of varying polarities gave five ASO solvent fractions. The % composition of the ASO hexane (HX), chloroform (CHCl₃), acetone (ACE), methanol (MeOH) and methanol/ammonium hydroxide (HPC) fractions were 7.0, 26.0, 32.0, 31.0 and 4 %, respectively. The ASO HX fraction was found to contain a homologous series of n-alkanes and squalene. The ASO CHCl₃ fraction was found to contain free fatty acids (C14:0-C20:0), tocopherols, monoglyceride, free sterols, diglyceride, wax esters, steryl esters and triglycerides. The ASO ACE fraction contained two unknown glycolipids. Approximately 1.3% of the ASO ACE fraction is carbohydrates with glucose (57%) as the main glycosyl moiety present. Majority of the ASO ACE fraction are sterols or steryl derivatives. The ASO MeOH fraction was 35 % phospholipids based on ³¹P NMR. Phosphatidylethanolamine at 18% was the major phospholipid component detected. Conversion into fatty acid methyl esters was at 38, 18 and 15 % for ASO CHCl₃, ACE and MeOH fractions, respectively. The fatty acid profiles show C14:0, C16:0, C16:1, C18:0 and C18:1 as the dominant fatty acids in all three major ASO solvent fractions. However, longer and unsaturated FAMEs were observed in the ASO MeOH fraction. ASO extract (13%) of dry AS is a source of biodiesel but simultaneously can be refined to obtain value-added products such as squalene and tocopherols. Although the utilization of activated sludge oil can reduce the cost for feedstocks, the actual process requires additional expense for refinement but may be compensated by the separation and purification of high value-added compounds of nutraceutical or biologically importance.

¹Dufreche S, Hernandez R, French T, Sparks D, Zappi M, Alley E. 2007 J Amer Oil Chem Soc 84, 181-187.

²Mondala A, Liang K, Toghiani H, Hernandez R, French T. 2009 Biores Technol 100, 1203-1210.