Nitrogen content reduction on scenedesmus obliquus biomass used to produce biocrude by hydrothermal liquefaction

The use of Microalgae biomass for biofuel production by hydrothermal liquefaction (HTL) has been proposed as an alternative to traditional fossil fuels. When comparing fossil fuels, Microalgae biocrude has a high nitrogen content, which is one of the challenges that affect this technology. This factor causes operational issues because it lowers the carbon fraction in the chemical composition, which reduces the calorific value and, as a result, raises NOx emissions during combustion. In this work, conditions were established for obtaining Microalgae biomass to allow the production of biocrude with low nitrogen content by HTL. The effect of the variation in nitrogen levels on the culture medium, on cell growth and nitrogen content, was evaluated in the final biomass for the Scenedesmus obliquus strain; at a laboratory scale, the best results (around 0.25 g/L NaNO3) were used at a bench scale with 20 L tubular photobioreactors (PBRs). The remaining biomass was processed through HTL then the resulting biocrude was characterized. The results show that as the nitrogen source in the culture medium increases, the percentage of nitrogen in the remaining biomass and the biocrude produced also increases. It was possible to establish a concentration of nitrogen source in the culture medium that promotes the accumulation of lipids, decreases the protein content in the final biomass and consequently, in the biocrude, without affecting production and yield, a critical factor to take into consideration when assessing the viability of the proposed process.

Automated summary

The study focused on the effect of nitrogen levels on the biomass of Scenedesmus obliquus and the resulting biocrude produced after hydrothermal liquefaction. The results indicated that increasing nitrogen source in the culture medium led to higher nitrogen content in the biomass and biocrude. By establishing an optimal concentration of nitrogen source, it was possible to enhance lipid accumulation, reduce protein content, and maintain production and yield of biocrude, which is crucial for evaluating the viability of the process.