THE CHALLENGES OF BIODIESEL PRODUCTION FROM OSCILLATORIA SP

Marwa Gamal Saad 1,2 and Hesham Mohamed Shafik 2 . 1. Department of Electrical and Computer Engineering, Texas A&M University, College Station, Texas, 77843, USA. 2. Department of Botany, Science College, Port Said University, Port Said, 42536, Egypt. ...................................................................................................................... Manuscript Info Abstract ......................... ........................................................................ Manuscript History

At the lowest concentration of nitrogen and phosphorus, the microalgal cell tends to produce high lipid content (Hidayat, 2008). As described by many authors that under nutrient limitation, many algae stop growth and division to use all their energy to make lipids as storage products for survival (Hidayat, 2008).
Since the various fatty acid profiles influence biodiesel fuel properties, it is important to possess data on how the presence of nitrogen and the period of cultivation can influence the profile of produced fatty acids from algae. This study aimed to compare between the effect of nitrogen limitation and starvation on fatty acid profiles and biomass productivity of Oscillatoria sp. to enhance biodiesel production.

Materials and Methods: -
Isolation, Purification and Identification of Oscillatoria sp.: -Under aseptic conditions, four Oscillatoria species were isolated from fresh water bodies at Port Said, Egypt. Then they were purified using steak method on solid BG-11 medium. Identification done by binocular light microscopy (SME-F4D, Rating: 85 V to 265 V, 50/60 Hz, Halogen lamp: 60 V 20 W, Delay-action fuse: 1 A) according to Smith (2010) (Fig. 1).

Experimental design:-
A touch having many filaments from the agar plates were transferred separately to standard BG-11 liquid medium and left to grow at 27±1 °C with continuous lighting 82.62 µmol -2 sec -1 . These cultures used as a stock culture for next experiments.
Cultivation of algae in standard medium:-Constant weights were transferred separately from each species to 100ml sterile BG-11 medium then left to grow for 39 days in the same culture conditions as previous. Biomass as dry cell weight (DCW) detected after 3, 7, 22, 36 and 39 days of cultivation.

Cultivation of alga (Osci. 2) in different N concentrations:-
Constant weights were transferred to 1l sterile BG-11 medium with different nitrogen concentrations; 1500, 375, 186, 94, 47, 23 and 0.0 mgl -1 NaNO 3 , separately then left to grow for 21 days in the same culture conditions as previous. Biomass as dry cell weight (DCW), Biomass productivity recorded weekly and fatty acid analysis after 7 days for all concentrations, 14 days for 186 and 375mgl -1 NaNO 3 and 21 days for 375mgl -1 NaNO 3.

Dry cell weight: -
Certain volume of culture was filtered on pre-weighted glass fiber filter paper then dried at 60°C until constant to detect Dry cell weight (DCW).

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Oil extraction: -A definite dry weight of Oscillatoria sp. was poured all night into hexane: ether (1:1, V: V) to extract oil, this step is repeated until the extract became hyaline. The extract evaporated in vacuum to release solvents using rotary evaporator (Diagonal Condenser-RE300, vacuum 1 mm Hg, made in U.K.) (Hossain & Salleh, 2008).

Fatty Acid Analysis:-
Extracted oil converted into fatty acid methyl ester according to Luddy et al. (1960) and measured using gas chromatography (Perkin Elmer Auto system XL) equipped with Flame Ionization Detector (FID), fused silica capillary column DB-5 (60 m × 0.32 mm i.d.). The oven temperature was maintained initially at 150 °C and programmed from 150 °C to 240 °C at rate 3 °C/min, then held at 240 °C for 30 min. The injector temperature was 230 °C. Detector temperature was 250 °C and carrier gas was Helium with flow rate of 1 ml/min.  (Table 1).

Results:-
Nitrate residue detected almost every 2 days, the results clarified that Oscillatoria sp. did not consume all nitrate in short period cultures and it will take more time to start starvation (Fig. 2).

Discussion:-
Many researchers believe that the choice of microalgae for biodiesel production needs a balance between species that grow quickly and produce oil in large quantities (Chisti, 2007). While others see that to choose microalgae for biodiesel, production needs to search about species that grow with large biomass and produce high concentration of target fatty acids because not all fatty acid types are suitable for biodiesel production.
Biodiesel quality and quantity produced from microalgae affected by biomass productivity, lipid productivity and target fatty acids percent. Thomas et al. (1984)  BG-11 medium is a blue green medium. It is known as a good medium not only for blue green algae but also for some green algae. It contains nitrogen in a nitrate form. It is important to possess data about rate of nitrate consuming by all cultured species and when the starvation started. According to results of DCW and biomass productivity, there were no big differences between cultures cultivated in 1500 and 375 mgl -1 NaNO 3 . While with lower nitrate concentrations, the lower dry cell weights and biomass productivity were observed.
The fatty acid profiles of Oscillatoria sp. were detected in pure batch cultures experiments. Osci.2 tended to produce diverse of fatty acid patterns; saturated (myristic acid (C14.0), palmitic acid (C16.0) and stearic acid (C18.0)) and unsaturated fatty acids (oleic acid (C18.1), linoleic acid (C18.2), linolenic acid (C18.3) and eicosapentaenoic acid (C20.5)) with different amounts related to nitrate occurrence that leaded to the difference in the percent of significant fatty acids for biodiesel production. So, the results show that the type and amount of fatty acids affected by the period of cultivation and mode of nitrogen supply.
Both growth and lipid content depend not only culture conditions like nutrients but also on algal strain and period of cultivation. Reviewers consistent with our results where; the fatty acids profile could be control not only by starvation but also by the level of limitation and biomass productivity is a good indicator of suitability for biodiesel production.
From presented results, twenty-one days of cultivation with NaNO 3 concentration of 375 mgl -1 was the suitable condition to cultivate Oscillatoria sp. with maximum percent of biomass productivity and target fatty acids for biodiesel production.