Capitalization of wastewater-grown algae in bioethanol production
2020
Ungureanu, N., University Politehnica of Bucharest (Romania) | Vladut, V., National Inst. of Research-Development for Machines and Installations Designed to Agriculture and Food Industry, Bucharest (Romania) | Biris, S.-S., University Politehnica of Bucharest (Romania)
Global environmental policies to reduce the emissions of greenhouse gases and to increase the use of renewable energy have created premises for identification and exploitation of new, economic and non-polluting resources. Algae biomass has gained interest in the production of bioethanol because it is renewable, carbon neutral, sustainable and can be cultivated in non-productive, non-arable land (without competing with production of food crops) or in fresh and grey water. Algae can grow in wastewater (in open ponds and photobioreactors), contributing to wastewater treatment, reducing nutrients (nitrogen and phosphorous), chemical oxygen demand, biochemical oxygen demand, suspended solids, heavy metals and coliforms. Algal biomass has fast growth-rate (12 days) and the doubling time during exponential growth is only 3.5 hours. Macroalgae contains carbohydrates (starch, cellulose and hemicellulose) and undergoes pre-treatments (acidic, alkaline, or enzymatic hydrolysis) to obtain reducing sugars, which are fermented with yeast to obtain bioethanol. Many strains of algae grown in wastewater, including Chlorella, Chlamydomonas, Dunaliella, Porphyridium, Spirogyra and Spirulina contain up to 50 % of their dry weight carbohydrates (starch and glycogen) and are converted into bioethanol. Global production and consumption of bioethanol are expected to increase to 134.5 billion litres by 2024. This paper presents the importance of cultivating algae in wastewater, and reviews the most recent achievements in the production of third generation bioethanol from algae strains using acid, alkali and enzymatic pre-treatments, respectively the importance of Saccharomyces cerevisiae for the fermentation of sugars extracted from algae.
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