Biorefinery of Dioscorea composita Hemsl with ferric chloride for saponins conversion to diosgenin and recycling the waste to biomethane

Abstract

Diosgenin is an important raw material for the synthesis of steroid hormone drug and largely required in the pharmaceutical industry. In this study, a novel process for biorefinery of Dioscorea composita Hemsl (DCH) with ferric chloride was developed to investigate the conversion of saponins to diosgenin. Furthermore, the waste, including sugary wastewater and starch residue, as recyclable biomass resources after diosgenin extraction was devoted to biomethane. Consequently, the highest yield of diosgenin (3.02%) was obtained using ethanol/water/petroleum ether (15/16/20, v/v/v) with a total volume of 255 mL containing 80 mL 5.0 g/L ferric chloride aqueous solution at 150 °C for 2 h. The yield extracted with FeCl3 was 16.6% higher than the traditional sulfuric acid hydrolysis method and was even 2.3 times more than the biphasic sulfuric acid hydrolysis method. Similarly, without consuming sulfuric acid, the yield was 79.76% higher than the control method. After fermentation, a maximum biomethane yield of 310.5 mL/g COD (chemical oxygen demand) was achieved from wastewater and the decomposition efficiency reached 91.1% with an initial COD concentration of 10,800 mg/L decreasing to 960 mg/L. The final biomethane productivity of waste residues was 278.8 mL/g VS and the VS degradation efficiency was 95.8% after a week. Therefore, the novel method with FeCl3-catalyzed acidolysis to produce diosgenin and biomethane may be an alternative much cleaner approach to better utilize dioscorea resources.