Exploration of microalgae biorefinery: accumulation of polyhydroxyalkanoates, lipids and carbohydratesin the microalgae Scenedesmussp. under nutrient-deficient conditions

Abstract

The current global economy depends heavily on the oil-based industry, which is unsustainable in the long term, both due to the finite nature of the resources on which it is based and due to the environmental damage related to the activities involved in its processes. As an alternative to petroleum biorefineries, microalgae biorefineries are considered as a more sustainable source of bio-resources for the energy and polymer industries. In particular, polyhydroxyalkanoates, a natural form of carbon and energy storage in various microorganisms, including microalgae, are considered as potential replacements for conventional plastics, the increasing use of which has caused severe environmental damage. This study investigated the influence of glucose, N, P, Fe, and salinity over the production of PHA by Scenedesmus sp., a freshwater microalga strain not previously explored for this purpose. To assess the effect of the variables, a fractional Taguchi experimental design involving 16 experimental runs was planned and executed. Biopolymer was obtained in all the experiments in a wide range of concentrations (0.83-29.92%, w/w DW), and identified as PHB by FT-IR analysis. The statistical analysis of the response was carried out using Minitab 16 where phosphorus, glucose, and iron were identified as significant factors, together with the P-Fe and glucose-N interactions. the crucial role of iron in maintaining the continuity of the PHA synthesis process under phosphorus deficiency is highlighted. The accumulation of carbohydrates and lipids, relevant macromolecules for the production of bioethanol and biodiesel, respectively, was also assessed. After identifying the relevant factors that influence the production of each of these compounds, the conditions to achieve enhanced accumulation of the three of them were stablished. Maximum coaccumulation of up to 62.4% (28% CH, 26.3% PHA and 7.9% lipids) of the cell dry weight was achieved under phosphate and nitrogen starvation. Doing this, this work contributes to the understanding of the critical factors that control PHA production and present Scenedesmus sp. as a promising species to produce bio-resources in commercial systems.