Cultivation of Chlorella sp. S۴ in an open raceway pond to increase biomass and carbohydrate production scale for bioethanol production

BACKGROUND AND OBJECTIVESMicroalgae are photosynthetic microorganisms with a high growth rate, high carbon fixing capability, and a short harvesting cycle. Some species have been identified as suitable sources for producing bioethanol due to their high carbohydrate content. Nutritional and environmental factors, cultivation systems (closed or open systems), and strain selection can affect the biomass and carbohydrate production of microalgae. To release the carbohydrate content, a pre-treatment procedure is necessary. Through the biological fermentation of carbohydrates, bioethanol is produced. This study aims to cultivate a native Persian Gulf isolate in an open raceway pond to increase biomass and carbohydrate production scale for bioethanol production.MATERIALS AND METHODSMicroalga cells were cultivated in a ۲۰۰ L indoor open raceway pond containing ۱۵۰ L of modified Rudic’s medium with a salinity of ۳۵ g/L. The growth was done under a photoperiod of ۱۶ h light / ۸ h dark, light intensity of ۹۰۰۰ lux, at ۲۵ °C for ۱۶ days. Stirring was produced by a paddle wheel at the speed of ۱۳ rpm. The dry biomass was pretreated using ۳% (v/v) of H۲SO۴ at ۱۲۱ °C for ۲۰ min. Saccharomyces cerevisiae (TT) cells were inoculated into a synthetic fermentation medium enriched with microalga hydrolysate and maintained at ۳۰ °C for ۴۸ h for ethanol production.RESULTS AND DISCUSSIONThe microalga was able to reach its maximum dry biomass of ۱ g/L, and carbohydrate concentration of ۰.۳ g/L in an open raceway pond. The highest ethanol concentration of ۸.۱ g/L (yield of about ۰.۴۱ g ethanol/g consumed carbohydrate) was observed after ۴۸ h. As a result, bioethanol produced from microalgae could be used in the future as a source of green energy.CONCLUSIONMicroalgae cultivation activities to produce bioenergy or other purposes could become a significant income for local people.

Keywords:

Bioethanol , Carbohydrate , Microalgae , Open raceway pond