Phytoremediation of bark-hydrolysate fermentation effluents and bioaccumulation of added-value molecules by designed microalgal consortia

Recent years marked an increased focus towards the valorization of biorefinery side-streams for the production of various high added-value molecules and platform chemicals. The present study tackles the opportunity of using liquid ethanol fermentation effluents of bark hydrolysates for microalgal conversion to various marketable molecules. Initially, 12 green microalgae strains were screened for their ability to thrive on these substrates and uptake some of the available organic compounds. Once the most suitable strains were identified, three mixed microalgal consortia were formulated and investigated in order to maximize, either individually or both simultaneously, their biomass production and phytoremediation performances. For instance, the consortium α containing Scenedesmus obliquus, Acutodesmus obliquus, Chlorella sorokiniana and Chlorella vulgaris strains was able to consume up to 70% of C5 sugars (xylose and arabinose) and 60% of C6 sugars (fucose and hexose). The uptake of these organic compounds initially present in the fermentation effluent accounted for the removal of 27% of the total organic carbon. In addition, the microalgal community produced 55 mg/L/d, 41 mg/L/d and 26 mg/L/d of carbohydrates, lipids and proteins respectively. The photosynthetic pigments accumulated in the harvested biomass comprised of 25.8 mg/L of total chlorophyll and 5.9 mg/L of carotenoids. Finally, the pyrolysis characteristics of the algal biomass were evaluated trough thermogravimetric analysis and the elemental composition was compared with conventional lignocellulosic feedstocks. Thus, this work proves the dual opportunity of both reducing the toxicity of lignocellulosic ethanol fermentation effluents as well as generating high-value biomass by employing specifically-designed microalgal populations.