The saccharification–membrane retrieval–hydrolysis (SMRH) process: a novel approach for cleaner production of diosgenin derived from Dioscorea zingiberensis

Diosgenin (CAS number 512-04-9) production from Dioscorea zingiberensis is a very important industry in central-western China. However, treatment of the wastewater with COD up to 50,000 mg/L has been a formidable challenge for the sustainable development of diosgenin industry. A cleaner production process, called the saccharification–membrane retrieval–hydrolysis (SMRH) process, was proposed and pilot-tested by us. The new process combines traditional acid hydrolysis with enzyme hydrolysis and UF/NF technologies. It has two major advantages. (1) The starch in D. zingiberensis is degraded into low molecular weight soluble sugar which is separated and removed before acid hydrolysis of the residue. This prevents the soluble sugar from entering the wastewater; instead it can be utilized as a carbon source in the fermentation industries. (2) UF/NF membrane equipment separates the acid hydrolysis solution into three parts: (a) the colloid phase, (b) the acid solution and (c) the water. All of which can be used in this or in another industry. In this way, the new production process dramatically reduces the wastewater discharge and uses the sugar, acid, water and solid waste in other processes.