احمد شادی

Worldwide increase in fossil fuels costs as well as global warming has resulted in voluminous researches to discover new renewable energy resources, especially bioethanol as one of the most important renewable energy resources. The present study was conducted to determine the effects of light-dark photoperiod (12-12h, 16-8h, 20-4h) and temperature (25 ?C,29 ?C, 33 ?C) on growth rate and sugar content of Parachlorella sp. microalgae needed for bioethanol production. To achieve this, microalgae was cultured in 9 different treatments (each with three replications) of specified photoperiod and temperature conditions in 20 days. Having achieved maximum growth following growth rate and biomass measurements, data analysis showed that temperature has no significant effects on all factors, i.e. growth, sugar content and biomass (p?0.05); however significant effect of photoperiod on these factors was observed (p?0.05). In addition, light-temperature interaction effect on these factors was not significant (p?0.05). The highest growth rate and sugar content was found in the 12-12h photoperiod and in a temperature of 25 ?C. Among produced monosaccharides (glucose, galactose, fructose, arabinose and xylose), in all treatments glucose and xylose were the highest and lowest with the averages of 39.4% and 3.95%, respectively. The highest biomass was achieved during the light-dark photoperiod of 16-8h and 25 ?C temperature. Having specified optimal conditions for algal growth, the algal was cultured and biomass was harvested. The algal biomass was acid treated to digest polysaccharides. The extract sugars were used as the fermentation medium for bioethanol production by Saccharomyces cerevisiae. After 24 h of anaerobic fermentation, the calculated ethanol yield by HPLC was about 18.94% (w/w) or 24% (v/w). In conclusion, in the present study, the optimal culture conditions were the light-dark photoperiod of 12-12h and 25 ?C temperature for maximum ethanol production. The produced rati