Studies on biomass and lipid production of seven diatom species with special emphasis on lipid composition of Nitzschia palea (Bacillariophyceae) as reliable biodiesel feedstock
Abdel-Hamid, Mohammed I.; El-Refaay, Dina A.; Abdel-Mogib, M.; Azab, Yehia A.
Seven different pennate diatom species namely, Nitzschia palea, N. hungarica, N. angustata, N. amphibia, N. capitellata, N. denticula and Navicula confervacea were isolated from water samples collected from delta region of the River Nile in Egypt. The effects of two standard nutrient media and vitamins supplement on growth and lipid content (n-hexane extract) were investigated. The experimental results showed that NAV nutrient medium supported relatively higher biomass production of most of the test diatoms. Combined vitamins (B12, B1 and vitamin B7) addition did not induce potential increase in dry weight biomass. Neither medium type nor vitamins supplement exhibits any significant effects on lipid production. Marked decline in concentration of N, P and Si of nutrient medium was evident at the end of 6 days incubation period. The pennate diatom N. palea maintained relatively higher biomass and lipid production; therefore it was selected as a model test diatom for further experimental work. Effects of Nualgi® and initial N concentration on growth and lipid production of N. palea were investigated. The GC/Ms analysis indicated that the n-hexane lipid fraction of N. palea was mainly composed of C16:0 palmitic acid (41.13 %), followed by C16:1 palmitoleic (29.25 %), C14:0 myristic acid (9.01 %), C15:0 pentadecyclic acid (8.26 %), C18:0 stearic acid (2.32 %) and C18:1 oleic acid (3.22 %). The gel permeation chromatography (GPC) analysis revealed that lipid fraction was mainly composed of free carboxylic acids (28.9 %), diglycerides (27.3 %), triglycerides (24.3 %) and monoglycerides (16.3 %). Except high values of FFA (28.9 %) and acid value (57.6 mg KOH/g oil), other characteristics including, for instance, specific gravity (0.83 g cm-3) and flash point (230 °C) are within ranges accepted by the European Standards EDIN 51605 for oil feedstock of biodiesel. Based on GC/MS fatty acid profile and physical and chemical characteristics the n-hexane lipid fraction of the pennate diatom N. palea seems promising feedstock of biodiesel.