چكيده به لاتين
With limited reserves of fossil fuels, the world has faced an energy crisis and attention has been drawn to alternative energy sources such as biofuels. Moreover, the abundant amounts of urban, domestic and industrial wastewater, which are considered a serious threat to the environment, need to be treated. Cultivation of microalgae in wastewater provides a cost effective method producing valuable by-products, especially biomass for the production of biofuels, besides eliminating the contaminants. In the present study, synthetic wastewater was used to investigate the cultivation of mixed microalgae and their starch and lipid content under photoautotrophic, heterotrophic and mixotrophic conditions in Erlenmeyer flasks (working volume of 200 mL) and cylindrical photobioreactors (working volume of 600 mL). Effect of different organic (3574 mg/L glucose and 4883 mg/L sodium acetate) and inorganic (10000 mg/L sodium bicarbonate) carbon sources and different photoperiods (continuous light, light: dark cycle and complete darkness) using a high-pressure sodium-vapor lamp (with light intensity of 375 µmol/m2s) in Erlenmeyer flasks was studied. The mixotrophic cultivation using sodium acetate and light: dark cycle provided the optimal results (the highest starch and lipid contents of 37.7 and 15.3%, respectively). When the effect of the combination of this carbon source and sodium bicarbonate (4883 mg/L acetate+10000 mg/L bicarbonate) was studied under different photoperiods in a cylindrical photobioreactor, the mixotrophic culture using sodium acetate (as the only carbon source) and light: dark cycle was again selected as the best condition and yielded starch and lipid contents of 26.2 and 33.5%, respectively. It was also able to remove 100% of nitrate and phosphate and 95.9% of COD. Under this optimal condition, the use of a flat-plate photobioreactor (working volume of 1800 mL), having the advantage of a higher surface to volume ratio and thus higher light penetration, increased the productivities of biomass (1.4 fold), starch (2.1 fold) and lipid (1.3 fold), produced more chlorophyll (2 fold) and carotenoids (1.4 fold), and accelerated nutrients removal. The results show that the mixed microalgae used under appropriate conditions have great potential for wastewater treatment as well as renewable biofuels production.
