Biodiesel Production Using Fermented Sludge-Derived Lipids

The detrimental impacts associated with the consumption of fossil fuels to meet energy demands have led to the impetus of searching for environmentally benign alternative energy sources. Biodiesel is a sustainable fuel alternative that has gained an unprecedented increase in attention. Secondary wastewater sludge is an abundantly available and inexpensive substrate for oleaginous yeast cultivation, lipid production, and transesterification to biodiesel. In this work, primary and secondary sludge were analyzed for their physicochemical properties. The secondary sludge (thermally hydrolyzed) was found to be a suitable substrate for lipid production by Rhodosporidium toruloides and Cryptococcus curvatus. R. toruloides demonstrated better growth and lipid accumulation capabilities compared to C. curvatus; maximum biomass, lipid yield and lipid content for R. toruloides were analyzed after three days of cultivation. Lipid production was optimized for sludge concentration, pH, and inoculum volume at 30 g/L, 5.0, and 15%, respectively. The fatty acid methyl esters (FAMEs) analysis revealed that the lipids have similar fatty acid properties to conventional biodiesel feedstocks. Thus, the lipids can be used in biodiesel applications. Analysis of the biodiesel properties showed that all characteristics were in accordance with international biodiesel standards. The larger implication of this study is to reduce dependence on fossil fuels by diversifying the current energy scenario, as well as enhance wastewater treatment and mitigate sludge management issues.