ALGAL BIOPROCESSING FOR ENHANCED BIOFUEL AND BIOCHEMICAL PRODUCTION

Abstract

Scarce fossil fuels resources and environmental pollution due to their consumption is a major global concern nowadays. It has emphasized on exploring novel, ecofriendly, and renewable sources of energy. Microalgae have been established as a potential feedstock for biofuel production which is renewable as well as environmentally friendly. To date, numerous studies have been done to elucidate these organisms for large-scale biofuel and biochemical production. However, enhancing the target biomolecule (or say lipid in case of biodiesel) synthesis rate and reducing the production cost still remain a major bottleneck for its economic viability. Biofuel production from microalgae biomass is a multistep process and each process is specific to particular microalgae as well. High cost of oil extraction from algal biomass and its conversion into biodiesel poses a major challenge to its commercial viability. Recent studies on algal based biofuels production have suggested the need of extraction of other co-products like astaxanthin, lutein, β-carotene, polyhrdoxybutyrate, omega fatty acids, polysaccharides, and vitamins, from the same algal biomass following the concept of biorefinery analogous to petroleum refinery. Several studies have reported production of platform chemicals having therapeutics, nutraceuticals, and cosmetics value from the same algal biomass before and after algal oil extraction. To make microalgae-based biofuel production economic and sustainable; other microalgal high-value components extraction is termed as a promising measure. Under this direction, this study explores the bioprospecting of microalgae for production of biofuels and biochemicals. Under the first objective of this study, microalgae were isolated and identified on the basis of morphological and molecular studies. Master culture of isolated microalgae were established and used for further investigations. Microalgae isolate which showed maximum growth rate was chosen for further investigation. Out of all four chlorella strains, chlorella sorokiniana showed maximum growth rate. The amount of lipid content on cell dry weight basis was calculated for all these four select microalgae. The maximum lipid content (11% w/w dry cell weight) was found in Chlorella sorokiniana. Culture conditions including pH, temperature, and light intensity for its optimum growth rate were optimized. Also, effect of different carbon, nitrogen, and phosphorous sources were studied. Chlorella sorokiniana and Chlorella minutissima were found to have ability to grow in RO spent water facilitating the simultaneous wastewater treatment and biomass production for extraction for lipid and other valuable compounds. It can pave the way of replacing fresh water for preparation of growth medium with RO spent or reject water, thus overall reducing the cultivation cost. Further these microalgae strains were evaluated for production of polyhrdoxybutyrate, a type of bioplastic. The presence of PHB was confirmed by Sudan black staining in both Chlorella sorokiniana and Chlorella minutissima. Post confirmation, solvent extraction method was applied to quantify the amount of PHB in them. Extraction of PHB along with the lipid will enhance the economy of the algal based biodiesel production. The microalgae can be exploited not only for its high lipid content useful in production of economical biofuels, but also for high yields of essential pigments with high nutraceutical values. Algae have a unique property of accumulating high amounts of carotenoids under unfavorable conditions. There are efficient methods of subjecting the algal strain to stresses, both biotic and abiotic, that enhances the pigment production in them. The isolation and identification of economic, fast-growing, and adaptable algal strains are important. Therefore, one of the objectives of this study was to isolate locally adapted microalgal strains for prospective β-carotene production. β-carotene was qualitatively and quantitatively estimated from a novel microalgae Graesiella emersonii isolated from an industrial cement curing tank. We found high lipid content (up to 27% w/w dry cell weight) in normal growth condition. The amount of β-carotene was also higher. The co-extraction of both these chemicals can provide a sustainable algal based biofuel and biochemical production. Further scope of synthesis of silver nanoparticles from algal biomass extract and their application in wastewater treatment was evaluated. Silver nanoparticles were synthesized using Chlorella sorokiniana biomass extract and characterized using UV-spectroscopy, XRD crystallography, and Scanning electron microscopy for their morphological and structural properties. Upon confirmation of their synthesis, these nanoparticles were used for degradation of four different dyes. Also, antibacterial properties of these nanoparticles against two bacteria were evaluated. The study concludes that algal biomass can be a suitable feedstock for biodiesel production and in order to make it commercially viable other compounds along with the lipid should be co-extracted. The algal extract post cell disruption followed by lipid extraction can be used for nanoparticle synthesis which can be used for wastewater treatment. Thus, algae can be used for providing a sustainable solution to energy and environmental problems together.