OPTIMIZATION OF INDIGENOUS MICROALGAE FOR HIGH BIOMASS AND LIPIDS PRODUCTIVITY AND UTILIZATION OF ALGAL BIOMASS IN BIOREFINERY APPROACH

Abstract

Microalgae have been determined as alternative and potential feedstock for carbon neutral biofuels production over other sources due to its ability to grow at higher rates with less generation time, high-energy rich molecules formation, ability to sequester CO2 form environment and ability to treat wastewater. The abiotic stresses have been appeared as promising strategy for induction of desired metabolite in this respect. The main objective of this study was to delineate the effect of various abiotic stresses on microalgal biofuels production. Several abiotic growth factors such as temperature, pH, nitrogen and phosphorus concentration were focused in this study to facilitate the cultivation of microalgae for higher lipids production and biomass utilization in energy efficient and cost-effective way. The present study was resulted in successful isolation of four indigenous algal strains. Based on initial screening of growth characteristics and biochemical composition, two isolates FSL and F2 were selected for Identification, cultivation, optimization and biofuels production. This initial screening provided bases for further study design for strains optimization and biofuels production. The aim of this study was to enhance the specific rate of growth of Closteriopsis acicularis, (green microalgae, freshwater, family Chlorellaceae), with the impact of concentration of phosphate and pH to get optimum productivity of biomass. Present research investigated the independent and coupled impact of pH and concentration of phosphate on characteristics of photoautotrophic growth for Closteriopsis acicularis to produce bioethanol. Statistical experimental design (CCD) coupled with Response Surface Method (RSM) was utilized to optimize the growth characteristics and production of bioethanol in lab facility. The experimental outcomes revealed the high specific rate of growth and productivity of biomass as 0.342 day-1 and 0.497 g L-1 day-1 respectively, attained at high pH (9) and high concentration of phosphate (0.115 g L-1) at late exponential phase of growth. The composition of elements in optimized biomass revealed increased accumulation carbon, oxygen, phosphorus as macronutrients and sodium, magnesium, aluminum, potassium, calcium and iron other than sulfur and nitrogen as 11 micronutrients. It was observed 58% carbohydrate content in biomass after optimization and acid catalyzed saccharification resulted in 29.3 g L-1 of monosaccharides. The yield of bioethanol was calculated as 51% g ethanol/g glucose and a maximum of 14.9 g/L of ethanol, which infers the successful optimization strategy for growth of Closteriopsis acicularis to get enhanced algal yield, biomass and bioethanol production. In this study also, the Box-Behnken statistical design (BBD) of experiment was used to optimize growth parameters (N-concentration, Temperature and pH) for high biomass and lipids accumulation of indigenous microalgae Tetradesmus nygaardii. The results show that high level of parameters favors high biomass production (543 mg/L) while lipids accumulation was found maximum (272 mg/L). The Response surface methodology (RSM) assessed interaction AC (N-concentration and pH) as the strongly affecting interaction for biomass and lipids production. C16 and C18 chain length fatty acids were found dominant contributor of Tetradesmus nygaardii oil and the biodiesel properties determined were in accordance with ASTM D6751 and EN14214 standards of biodiesel specification. These results demonstrate the potential of Tetradesmus nygaardii to produce high lipids as a promising feedstock for biodiesel production. The bio-methane potential of two defatted algal biomass co-digested with eucalyptus leaves waste was assessed and the results illustrated that maximum biogas yield and methane content was obtained highest for Closteriopsis acicularis + eucalyptus leaves as 1182 mL/g VS and 74.8%, respectively, which concluded that co-digestion of microalgae with carbon rich substrate is more feasible option for cost-effective and enhanced biogas production from microalgae.