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Globally, there has been rising interest in using microalgae as a potential source of biofuel. This is due to higher growth rates and the potential to accumulate higher amounts of lipids than conventional oil crops in per unit area. Microalgae are also known for their metabolic flexibility which means that by varying the cultivation conditions of algae, regulation of variation in biochemical composition of the biomass can be achieved. The major parameters determining the possibility of using microalgae as a potential source of biofuels are economic viability achieved through biomass productivity, lipid productivity and type of fatty acids. In the present study, two different algal strains (Monoraphidium sp. and Scenedesmus sp.) were grown alternatively in accordance with their seasonal tolerance. Temperature, light and pH of the culture strains were studied in order to understand their seasonal tolerance. Thus, it presented a two strain approach wherein, Monoraphidium sp. and Scenedesmus sp. were grown to obtain an optimum growth rate at large scale. While it is documented in the literature that lipid production is more under stress conditions and stress can also be created by various factors including nutrient deficiency, studies on nutrient removal efficiency and uptake rates are limited. Therefore, more research is required so as to understand the mechanism of growth and lipid accumulation. In our study, nutrient requirement of the strains were studied and optimized in a way to maximize lipid production by reducing the amount of nutrients or by using alternative nutrients especially as a measure to reduce cost. For Monoraphidium sp., nitrate concentration was reduced by 66.6% to achieve optimum lipid productivity whereas, in case of Scenedesmus sp, alternate sources for nitrate and phosphate were used to achieve maximum lipid productivity. These parameters were optimized under laboratory conditions and then applied on large scale in a 1000L raceway pond. Our study also reports of a higher average daily algal productivity (25.79 g/m2/day) for Scenedesmus sp. in comparison to previous studies. Monoraphidium sp. was observed to give an average aerial productivity of 17.2 g/m2/day from October 2015 to February 2016. The paddlewheel driven raceway pond was operated in a semi-continuous mode and the cultures were harvested after achieving maximum biomass concentration of approximately 0.5 g/l. Studies were also conducted to understand the mechanism of settling (pH of the culture was explored) and harvesting of the algal cultures with respect to lipid productivity. For Scenedesmus sp., pH 7.8 exhibited higher growth and biomass productivity, and gave maximum settling efficiency (88%), whereas, maximum growth rate and biomass productivity with a settling efficiency of 91% was obtained for Monoraphidium sp. when pH 8.8 was maintained continuously. The cultures were made to settle and harvested at an appropriate time so as to maximize extraction. Increase in culture time was observed to give maximum lipid productivity. Thus, this study puts forward an efficient way to cultivate microalgae species with higher aerial productivity at large scale and provides a competent harvesting technique without compromising lipid productivity considering the extreme temperature conditions in Delhi-NCR.
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