Ultrasonic-assisted membrane processes for the systematic purification of glycyrrhiza wastewater

A significant amount of glycyrrhiza wastewater is generated in the cleaning process of glycyrrhiza. The wastewater contains polysaccharide, glycyrrhizic acid, liquiritin, and other polyphenols, which is expensive for cleanup and wastes medical resources. To reduce environmental pollution from glycyrrhiza wastewater and increase the resource usage efficiency of glycyrrhiza components. According to the physicochemical properties of the component in glycyrrhiza wastewater, the ultrasonic assisted membrane separation mode was adopted to regulate the micellar state of glycyrrhizic acid and enhance the differences in membrane separation of polysaccharides, saponins, and flavones, in order to achieve the classification and separation of polysaccharides, saponins, and flavones while removing organic matter in glycyrrhiza wastewater. However, the efficiency, application, and mechanism of ultrasonic-assisted membrane technology for the separation of polysaccharides, saponins, and flavonoids from glycyrrhiza wastewater remain unclear. This study presents a green and feasible technical strategy for glycyrrhiza wastewater treatment that was developed by adjusting the parameters of ultrasonic assisted membrane separation. In this study, the systematic separation mode of ultrasonic enhanced ultrafiltration combined with nanofiltration is provided. The SCQ-9200E ultrasonic system was provided for the study with adjustable ultrasonic power, and the ultrasonic frequency was 40 kHz. The glycyrrhizic acid micelle was changed using ultrasonic power, pH, and molecular weight cut off (MWCO), and the separation differences among polysaccharide, glycyrrhizic acid, and liquiritin were enhanced. The optimal polysaccharide separation parameters used in the first step: MWCO 30 kDa, ultrasonic power 500 W and pH 5.00, and the rejections of polysaccharide, glycyrrhizic acid, and liquiritin were 87.72 %, 8.01 %, and 6.57 %, respectively. The second step included the following parameters for the separation of liquiritin and glycyrrhizic acid: MWCO 10 kDa, ultrasonic power 100 W and pH 8.00, the rejections of liquiritin and glycyrrhizic acid were 9.22 % and 40.65 %, respectively. The third step is to remove the low molecular sugar in liquiritin by nanofiltration: MWCO 800 Da, pH 8.00, retention solution diluted and separated twice, the rejection of liquiritin and total sugar were 95.72 % and 3.70 %, respectively. Ultrasonic may regulate the microtopography of glycyrrhiza wastewater with the power intensity of 50 W/L, improving the mass transfer efficiency of glycyrrhizic acid and liquiritin in the ultrafiltration separation process. As the separation volume of wastewater increased from 2.00 L to 20.00 L, the concentrations of polysaccharide, glycyrrhizic acid, and liquiritin increased by 2.5–35.4 times, 0.6–15.2 times, and 2.4–32.8 times, respectively, significantly increasing the content of index components in wastewater and solving the problem of recycling and resource utilization in glycyrrhiza wastewater.