초록
<P><B>Abstract</B></P> <P>The present study aimed to evaluate the energy recovery through biodiesel and bioethanol production from <I>Scenedesmus obliquus</I> in a sequential route of lipid extraction followed by fermentation, with recycling of waste glycerol (WG) as a nutrient supplement into the culture. Low WG concentrations significantly enhanced the cellular dry weight over the control, recording the maximum significant value of 3.63 g L<SUP>−1</SUP> using 2.5 g L<SUP>−1</SUP> of WG (WG2.5). In addition, the maximum carbohydrate and lipid contents were recorded in WG2.5, which represented 16.4% and 21.7%, respectively, over the corresponding control, with simultaneous reduction in protein content. Moreover, total fatty acid methyl esters (FAMEs) recovery from biomass increased after WG2.5 supplementation, recording an increase of 24.6% over the control. Fermentation of lipid-free biomass increased the rate of bioethanol production, reaching its peak of 4.82 g L<SUP>−1</SUP> at the 27<SUP>th</SUP> day. However, using of WG2.5 for microalgal growth and the residual lipid-free biomass for fermentation showed the highest bioethanol production peak of 5.58 g L<SUP>−1</SUP> at day 27. Due to the accumulation of carbohydrates under WG, the biomass treated with WG2.5 showed increase in maximum bioethanol productivity up to 0.185 g L<SUP>−1</SUP> h<SUP>−1</SUP>. However, sequential fermentation after lipid extraction enhanced the maximum bioethanol productivity by 32.3% and 15.1% over the whole cells from synthetic wastewater (WW) and lipid-free biomass from WW, respectively. The highest gross energy output of 21.4 GJ ton<SUP>−1</SUP> dry microalgae was estimated from the integrated route where <I>S. obliquus</I> was grown in WG-enriched medium and sequential fermentation was applied for the residual biomass after lipid extraction, with the highest recorded energy conversion efficiency of 62.9%. These findings provide an innovative practical integrated approach for waste recycling and high conversion efficiency of microalgal biomass for liquid biofuel production.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Cultivation of <I>Scenedesmus obliquus</I> on waste glycerol (WG) was performed. </LI> <LI> Using 2.5 g L<SUP>−1</SUP> of WG (WG2.5) enhanced lipids and carbohydrates accumulation. </LI> <LI> Biodiesel and bioethanol yields increased due to using WG2.5. </LI> <LI> The highest bioethanol production of 5.58 g L<SUP>−1</SUP> was recorded from residual biomass. </LI> <LI> The suggested route showed the highest gross energy output of 21.4 GJ ton<SUP>−1</SUP>. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>