Exploiting Local Algal Diversity for Bio-Diesel Production

Abstract

Algae is proven potential resources for eco-friendly bio-diesel production. But research efforts are still required for worthwhile results. The present study aims to utilize locally available algae biomass resources for bio-diesel production. The samples were collected from the air, water depositories and soil within the Institute campus. Further purification, culture, morphological identification, preservation, lipid extraction, transesterification and bio-diesel properties estimation were also conducted.
In the first set of experiment, water strains were collected, isolated up to the molecular level and utilized for vitrification protocol development. The isolated Oocystis sp. and Anabaena sp. confirm an improvement in survival percentage over conventional encapsulation-vitrification method. The viability concentration was also enhanced further by the addition of 2-mercaptoethanol and glutathione. The developed methodology further used for the preservation of collected and isolated cells during the study.
Further, the study compared the pre-treatment strategies for improvement in overall lipid extraction rate. Comparison were done for dry vs. wet, with cell disruption vs. without cell disruption and conventional Soxhlet method vs. Folch’s methods. Results show that the combination of dried algal biomass with the Folch’s method yields more than 27% lipid which was comparatively higher than the traditional Soxhlet methodology i.e. 15%. The mixed population includes Chlorella, Anabaena, Euglena, Oocystis and Sphaerocystis species. Fatty acids present in lipid consist majorly of the C-18 molecule i.e. linolenic acid (C18:3), linoleic acid (C18:2) and oleic acid (C18:1). The other varieties of comparatively short carbon chain fatty acids were also observed which were considered to give the best fuel properties. Therefore, this local algal mixed diversity was found to be suitable for biofuel as well as various other fatty acids production.
Similarly, dominant airborne species throughout the year in this locality were found to be Scenedesmus sp., Chlorella sp., Pteromonas, Sphaerocystis sp., Oocystis sp., Oedogonium sp., Anabaena, Pseudanabaena sp., Gloeocapsa sp., Microcystis sp., Naviculoid Diatoms, Mastogloia, Striatella sp., Euglena sp., Phacus sp. and two unidentified species. Availability of algae was found to be maximum during post monsoon and minimum in rainy season. Lipid estimation and FAME analysis were conducted by spectrofluorometry, CHNS, FTIR, GC-MS. Basic bio-diesel properties were also performed to know the suitability of extracted oil as raw material for bio-diesel production. Further, probable sugars, acids and alcohol were also estimated from methanol layer after lipid extraction. As varieties of algae were found in the month of October, therefore, overall lipid content and other functional groups were also found higher in the analysis. Summarizing, the obtained airborne algal oil fraction was suitable to use as bio-diesel. As the airborne algae were also oleaginous, hence these could not be considered as contamination during large scale open culture system.
In the further experiments, bio-diesel and other co-products were produced using soil algal biomass. All the three layers during lipid extraction i.e. chloroform:methanol:residual layers were considered for this study. The dominant species include Chlorella, Euglena, Oocystis, Anabaena, Pseudomonas and one unreported species. Bottom chloroform layer consists of lipid which was transesterified and analyzed by GC-MS for the presence of FAME and phytol. Phytol is hydrolyzed component of chlorophyll molecule and precursor of vitamin E, and K. HPLC of methanol layer shows the presence of various carbohydrates, acids and other commercially valuable components. Therefore, methanol layer could be further purified and utilize as the source of carbohydrates and other useful chemicals. The cell debris was physically activated to use it as bio-char. Comparative characterization of raw algae, residual algae and algae biochar by proximate, elemental, TGA, FTIR, XRD, SEM-EDX were done. The results show that volatile matter was depleted after lipid extraction but fixed carbon increases. Peaks of FTIR study identified many chloroalkanes repeat in all the three states which were consistent with EDX analysis. EDX shows the presence of high amount of carbon, oxygen along with few inorganic substitutes like chlorine, calcium, etc. SEM and XRD pattern reveals the surface morphology of raw, residue and bio-char of algae. The residual algae are much crystalline in comparison to other two states which may be due to the extraction of intracellular components. Hence raw and residual algal biomass could not be utilized directly as the adsorbent. The further physical treatment creates the pores in crystalline surface hence could be used as the adsorbent. Organic and inorganic materials present in algal biomass shows that it can also be utilized as fertilizer for agricultural purpose. Further, methylene blue dye adsorption study was also conducted to know the suitability of biochar as the adsorbent. More than 90% of the dye was absorbed after the interval of one hour. In summary, the algae are very valuable biomass, and wise utilization could provide various value added products for human benefit.