Abstract
The disposal of excess crude glycerol produced by the booming biodiesel industry and wastewater sludge solid waste has become a severe problem, and alternate routes of use and valorization of these waste byproducts are needed. The use of cheaply available wastewater sludge solids in fermentation media is very much desirable to reduce the cost of production. The strains of Yarrowia lipolytica can assimilate a wide array of waste substrates, such as crude glycerol, waste cooking oil, starch wastewater, and cellulosic. This study optimized the concentration of wastewater sludge solids (5–35 g/L) to be used with crude glycerol in fermentation media to produce microbial oil as feedstock for biodiesel production. The results indicated that 20 g/L of sludge solids with 40 g/L of crude glycerol resulted in highest lipid content of 29.35% in 96 h. Further, assuming wet extraction of lipids, it was found that at least 11.2% or higher lipid content is required for this process to have an overall positive net solid waste reduction. Insignificant inhibition was observed by the crude glycerol used in this study as compared to pure glycerol, which proves it to be an adequate source of carbon substrate for lipid production.
Highlights
Global energy demands are increasing day by day, but the non-renewable fuel resources are depleting rapidly and will be exhausted in the near future
The results indicate that sludge renders a significant inhibition to microbial growth at higher concentrations and 20 g/L of sludge solid concentration is the optimum concentration for maximum lipid accumulation by the yeast
The industrial crude glycerol used in the study imposed a slight inhibition to the microbial growth due to the matrix composition of crude glycerol as compared to pure glycerol and it is a very suitable source of carbon for lipid production
Summary
Global energy demands are increasing day by day, but the non-renewable fuel resources are depleting rapidly and will be exhausted in the near future. Biodiesel produced from microbial feedstock oil has proven itself to be a strong candidate to replace petrochemical fuels. The biodiesel industry is rapidly expanding due to increasing awareness towards the alarming situation of global warming and the “food versus fuel debate” among policymakers, stakeholders, and the scientific community, giving rise to rejuvenated interest to develop a green biotechnological process for biodiesel feedstock microbial oil. Despite its tremendous potential and ecological advantage, biodiesel production using microbial oil has been limited by the significant cost incurred by expensive carbon sources, such as glucose, to produce single-cell oil (SCO). It is essential to find cheaper carbon and nitrogen sources to make the SCO production process economical
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