Recovery of carbon from rice straw for production of high-value products by Chlorella sorokiniana TH01 through mixotrophic cultivation

Rice straw is an abundant agricultural by-product in Viet Nam. Rice straw mainly contains carbohydrate (e.g., hemicellulose and cellulose), an abundant carbon source for biological production of high-value products, which is being used for animal feeding, burning or disposal in most suburban and rural areas of Viet Nam. The treatment of rice straw by burning and/or disposal has caused environmental pollution due to emission of greenhouse gases (e.g., CO2, CH4), toxic gases (CO, SOx, NOx) and dust. It is critical to apply technological measures replacing the traditional method to sustainably treat the huge volume of rice straw. In this study, rice straw carbohydrate was transformed to sugar-rich hydrolysate via a different chemical and enzymatic treatment methods for cultivation of Chlorella sorokiniana TH01 to produce lutein, lipid and protein. Data showed that the combined treatment of NaOH/H2SO4/Enzyme resulted in the maximal glucose and xylose hydrolysis efficiency of 96.32% and 93.43%, respectively. C. sorokiniana TH01 displayed the best growth in the hydrolysate with initial sugar concentration of 15 g/L diluted in BG-11 medium, achieving the maximal biomass concentration of 6.5 g/L (biomass yield of 0.44 g DCW/g substrate). Lutein, lipid, carbohydrate and protein contents were determined as 7.2, 350, 220 and 260 mg/g biomass, respectively. The sugar utilization efficiency by C. sorokiniana TH01 was determined as 94.67%. C. sorokiniana TH01 exhibited a promising capability in recovery of carbon from rice straw for production of high-value multiple commercial products, keeping rice straw in a circular economy and finally reaching a carbon-neutral process.