Lipids extraction from sewage sludge for biodiesel production

Abstract

This study focuses on lipids extraction from the dewatered sludge as an alternative feedstock for biodiesel production. The first objective is to evaluate the influence of extraction parameters on the lipids yield; temperature (70, 80, 90 �C), time (2, 4, 6, 8 h), solid-to-solvent ratio (S/L) (0.05, 0.075, 0.1, 0.125, 0.15, 0.175 g/mL), particle size (4.0 mm) and cosolvent (0, 10, 13, 25, 50, 100%) using Soxhlet extractor and hexane as solvent. The optimal conditions were 70 �C, 4 h and 0.175 g/mL S/L, yielding 1.67% lipid as analysed by OFAT. Changing the particle size produced a unimodal distribution, with the highest 1.95% yield obtained with 1.0-2.0 mm. The use of methanol as a cosolvent increases the yield to 7.30%. Screening experiments with cosolvent show S/L is significant with a negative response, while other parameters are insignificant. Secondly, to determine the impact of extraction on dewatered sludge characteristics. The dewatered sludge contains 27.97% organic fractions and carbon refractories, with 3.54% of these fractions being extracted. The dewatered sludge has a dense structure with pores, gaps, and aggregation. Disaggregation during the extraction process produced a rougher surface and smaller surface particles measuring 0.74 �m � 0.08. Disaggregation reduced elements of O, P, Na, Mg, and Al and exposed C, Fe, and Si. The final objective aimed to assess the quality of lipids as oil feedstock for biodiesel production based on their profile and composition. Lipids extracted with cosolvent show the lowest fatty acids and triglycerides, as well as the highest contaminants, compared to hexane and methanol. Hexane and methanol-extracted lipids were transesterified to produce fatty acid methyl ester (FAME-hex and FAME-met). Each FAME shows a similar fatty acid profile, with C16:0, C18:0, C15:0, C17:0, C18:1n9t, C20:5n3, C18:1n9, and C18:3n3 as the major components. FAME-hex and FAME-met are inappropriate for automotive engines due to their high PUFA content (12.7 and 17.2%). However, both FAMEs can be used as pure biofuel or blended with heating and diesel fuels due to their high ester content (94.7 and 95.1%) and low linolenic content (8.0 and 0%).

only English version