Farming microalgae; the impact of nitrogen chemical species on nitrogen uptake and assimilation rates by microalgae

Abstract

Microalgal biofuel technology provides the opportunity to recover nutrients from wastewater. Nitrogen uptake and assimilation rates by microalgae were studied to understand algal growth. Both literature metadata analysis and batch experiments were carried out. Chlorella vulgaris, Scenedesmus obliquus and Micractinium pusillum were grown in shaken flasks in artificial medium containing nitrate and/or ammonia as the limiting nutrient. Nitrogen availability seems to have regulated algal growth. Exponential growth rates were not significantly different among species. Two distinct Chlorella vulgaris strains resuspended in ammonia have shown a significant higher nitrogen uptake rate per cell compared with resuspension in nitrate. The sole use of ammonia led to a decrease in pH that eventually stopped growth for all tested species. Micractinium pusillum grown in a mixture of ammonia and nitrate have preferred ammonia over nitrate. Optimization of algal growth should therefore consider the ratio of available nutrient chemical species, and control of pH.