Valorization of palm oil mill wastewater for integrated production of microbial oil and biogas in a biorefinery approach

This work presents an integrated biorefinery concept combining two biological platforms for the valorization of palm oil mill effluents and for simultaneous production of high market value products, such as microbial oils and bioenergy. Palm oil mill effluents were aerobically fermented to produce lipids and subsequently the effluent from the fermentation was used as influent feedstock in an anaerobic digester for biogas production. It was found that pasteurization of the wastewater before fermentation by Yarrowia lipolytica TISTR 5151 was mandatory for efficient lipid production yielding 159.2 mg lipids/g-COD. In contrast, fermentation with untreated wastewater failed to produce lipids (3.10–43.51 mg lipids/g-COD), but instead supported the growth of several indigenous bacteria (e.g., Asaia sp., Lactobacillus brevis and Acetobacter sp.) with 6.57%–65.24% of relative abundance. Regarding biogas production, a maximum of 74% of the theoretical methane yield (280 mL/g-COD) in continuous reactor operation was achieved. The dominant bacteria, Synergistales sp. (18.19%) and Bacteroidetes sp. (15.96%), found at steady state period in the biogas reactor are known for acetate, butyrate, and hydrogen production. Moreover, within archaeal population, Methanosarcina thermophila (2.27%) and Methanoculleus thermophilus (1.38%) were identified as responsible for biomethane production.