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چکیده
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Astaxanthin-rich carotenoids were produced from Chromochloris zofingiensis green alga through an integrated biorefinery. Simultaneous effects of high light intensity and nitrogen starvation resulted in the production of 10.2 mg total carotenoids per g biomass, including 80 % astaxanthin. A novel extraction method employing ultrasonic-milling pretreatment was then used to reduce the extraction time (33.5 min) and the amount of utilized solvent (30 mL ethanol per 1 g biomass). The extraction method provided the residual biomass with the same anaerobic digestibility as the raw biomass, accumulating 315 mL/g VS methane. Additionally, the residual biomass was hydrolyzed with four commercial enzymes providing a high glucose yield (78.2 %). Overall, the biorefinery consisted of producing ethanol from the algal biomass hydrolysate and biomethane from solids remaining after hydrolysis. Also, fermentation resulted in 8260 kJ energy, in addition to 10.2 g carotenoids from 1 kg biomass. 1. Introduction Overconsumption of fossil fuels during the last decades, due to the population growth and industrialization, has resulted in several environmental issues such as global warming and desertification. So, it is important to find sustainable, renewable and clean alternative energy resources worldwide [1,2]. Among various biobased resources, microalgae are one of the most promising environmentally-friendly resources with a significant ability to produce various biochemicals such as valuable pigments (e.g., astaxanthin, lutein and beta-carotene), proteins, vitamins, lipids and carbohydrates (mainly in the form of polyglucans, without lignin and with low hemicellulose) [3–6]. They are also advantageous over higher plants due to their higher CO2 biofixation capacity as well as higher specific growth rate [7–9]. Because of these unique features, microalgae have gained much interest in both bench and commercial scales over the past few years [10]. In other words, the potential of microalga
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