Transformation of Brewery Subproducts into Valuable Biomass Using Mixotrophic Culture of Chlorella pyrenoidosa and Associated Bacteria

Abstract

To develop a biorefinery concept applied in the brewery industry, Chlorella pyrenoidosa and a consortium of associated bacteria were cultivated mixotrophically in a continuous photobioreactor using brewery low-value subproducts as an integrative process. Beer production residues were biochemically characterized to assess the most promising options to be used as a nutrient source for microalgal cultivation. Due to its physical and chemical properties, pre-treated weak wort was used to prepare an organic complex culture medium for microalgal biotransformation. Filtration and nitrogen supplementation were necessary to improve nutrient removal and biomass productivity. Maximal removal of nitrate and phosphate obtained were 90% and 100% respectively. Depending on operation conditions, total carbohydrates depuration ranged from 50 – 80%. The initial concentration of total carbohydrates of the weak wort must be adjusted to 2 – 4g/L to maintain a stable equilibrium between microalgal and bacterial growth. The biochemical composition of produced biomass varied depending on the cultivation conditions as well as on its final use. Upon continuous mixotrophic conditions evaluated in this study, C. pyrenoidosa was composed mainly of carbohydrates and protein.