Organic fraction of municipal solid waste as a suitable feedstock for the production of lipid by oleaginous yeast Cryptococcus aerius

• Lipid production by a robust yeast strain capable of using organic fraction of municipal solid waste.
• The MSOW introduced as suitable source for biodiesel production by yeast fermentation.
• Dilute acid and enzymatic hydrolysis, detoxification and lipid production were optimized.
• The heavy metals were reduced by the over-liming detoxification.
• The produced single cell oil by Cryptococcus aerius was similar to that of plant oils.

The detoxified pre-hydrolysate and enzymatic hydrolysate of OFMSW were used as substrates for lipid production by Cryptococcus aerius. Factorial experimental designs were employed for the optimization of dilute acid pre-hydrolysis, detoxification by over-liming, enzymatic hydrolysis, and lipid production. OFMSW pre-hydrolysis with 3% H2SO4 for 45 min was found to be the optimal treatment, resulted in total sugar concentration of 65.5 g/L (32.8% yield, based on grams of total reducing sugar per gram of OFMSW). The optimal detoxification conditions of the pre-hydrolysate by over-liming was incubation at 30 °C and pH 11 for 24 h, resulted in the reduction of total nitrogen, total phenolic compounds, and furans by 51.3%, 45.1%, and 100%, respectively. The residual solid was subjected to enzymatic hydrolysis, and the highest sugar concentration of 30.5 g/L was obtained. At optimal conditions, the yeast cultivation on the detoxified pre-hydrolysate and enzymatic hydrolysate resulted in the lipid production of 3.9 g/L (12.8% yield, based on g lipid per g consumed sugar) and 4.3 g/L (17.1% yield, based on g lipid per g consumed sugar), respectively. The elemental analysis showed the presence of heavy metals including iron (925 mg/l), zinc (59 mg/l), lead (4.7 mg/l), and nickel (3.5 mg/l) in the pre-hydrolysate, which were significantly reduced by the over-liming detoxification.

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