Orange Peel Waste as Feedstock for the Production of Glycerol-Free Biodiesel by the Microalgae Nannochloropsis oculata

The bioconversion of agri-food waste into high-value products is gaining growing interestworldwide. Orange peel waste (OPW) is the main by-product of orange juice production andcontains high levels of moisture and carbohydrates. In this study, the orange waste extract (OWE)obtained through acid hydrolysis of OPW was used as a substrate in the cultivation of the marinemicroalgae Nannochloropsis oculata. Photoheterotrophic (PH) and Photoautotrophic (PA) cultivationswere performed in OWE medium and f/2 medium (obtained by supplementing OWE with macroand micronutrients of f/2 medium), respectively, for 14 days. The biomass yields in PA and PHcultures were 390 mg L-1 and 450 mg L-1, while oil yields were 15% and 28%, respectively. The fattyacid (FA) profiles of PA cultures were mostly represented by saturated (43%) and monounsaturated(46%) FAs, whereas polyunsaturated FAs accounted for about 10% of the FAs. In PH cultures, FAprofiles changed remarkably, with a strong increase in monounsaturated FAs (77.49%) and reducedlevels of saturated (19.79%) and polyunsaturated (2.72%) FAs. Lipids obtained from PH cultures weresimultaneously extracted and converted into glycerol-free biodiesel using an innovative microwaveassisted one-pot tandem protocol. FA methyl esters were then analyzed, and the absence of glycerolwas confirmed. The FA profile was highly suitable for biodiesel production and the microwaveassisted one-pot tandem protocol was more effective than traditional extraction techniques. Inconclusion, N. oculata used OWE photoheterotrophically, resulting in increased biomass and oilyield. Additionally, a more efficient procedure for simultaneous oil extraction and conversion intoglycerol-free biodiesel is proposed.