Biocrude oil and high-value metabolite production potential of the Nitzschia sp.

Diatom biomass could be an alternative feedstock for producing bio-oil through hydrothermal liquefaction (HTL) technique. Additionally, diatom biomass could have high-value metabolites, such as pigments and polyunsaturated fatty acids. Hence, this study investigated the feasibility of using indigenous marine diatom biomass as a potential feedstock for biocrude oil and high-value products. At first, different growth parameters (i.e., nutrient type and concentration, and salinity) were studied for locally isolated Amphora sp. and Nitzschia sp. diatoms in indoor experiments. For all the parameters, Nitzschia sp. showed better growth rate and biomass yield compared to Amphora sp. Therefore, Nitzschia sp. was selected as the candidate strain, and it was grown outside in a 1000-L raceway tank. The final biomass yield was 0.57 g/L, and the biomass was first concentrated using a tangential flow filtration membrane followed by a centrifuge. The harvested biomass's lipid, protein, carbohydrate, and ash contents were 22.2, 15.5, 34.4, and 27.8%, respectively. The docosahexaenoic acid and eicosatetraenoic acid contents were 13.0 and 10.9% of lipid, respectively. The carotenoid content in the biomass was 12 mg/g biomass. Next, hydrothermal liquefaction (HTL) treatment was applied to Nitzschia biomass at a temperature range of 300-400 degrees C. Biocrude yield and their higher heating values (HHV) ranged from 36.5 to 57.2% and from 24.7 to 35.1 MJ/kg, respectively; while the maximum biocrude yield was obtained at 375 degrees C, the highest HHV was obtained at 300 degrees C. The aromatics and the heterofunctional compounds were the major compounds for all the biocrude samples. The energy recovery (i.e., 64.3%) and energy return on investment (i.e., 1.68) for the biocrude samples were higher at 375 degrees C, mainly due to the higher biocrude yield at this temperature. Overall, Nitzschia sp. is a potential candidate strain for bio-oil production in a biorefinery route.