Bioremediation of effluents from biomass fractionation using microalgae: a circular economy approach

The work carried out intends to contribute to the sustainability of nanocellulose and lignin production from lignocellulosic biomass, using strong mineral acids and bases. The strategy proposed involves combination of alkaline and acid effluents to achieve neutrality and using this mixed solution for the production of microalgae. Lignocellulosic biomass from three different species-hemp, giant reed and castor bean was used for the production of nanocellulose and lignin, also yielding three mixed effluents with different compositions depending on the type of biomass processed. Bioremediation of these effluents by the microalgae Chlorella vulgaris and Tetradesmus obliquus resulted in significant reductions of chemical oxygen demand (3893 to 1094 mg O2 L^-1), total nitrogen (1090 to 279 mg.L^-1) and total phenolic compounds (19,5 to 4,1 mg.L^-1 EAG). Although exposed to high concentrations of sodium (1519 to 2021 mg.L^-1) microalgae were also able to grow and reduce the concentration of this contaminant by 27% to 45%. Microalgae productivity was around 150 mg.L^-1.day^-1 for all effluents, but this value may be improved by compensating low levels of total phosphorus (TP) as some micronutrients such as copper, zinc, or molybdenum in the effluents through medium supplementation or combination with other effluents. The results obtained indicate that bioremediation with microalgae is a feasible treatment process for the effluents of biopolymer production and may contribute to the promotion of circular economy in this growing industry of the biomass-derived nanomaterials.