A two-stage nanofiltration process for reclamation of diosgenin wastewater

Diosgenin industry is a peculiar sector in China, and has boomed in recent years. However, the traditional method of acid hydrolysis for diosgenin production generated huge amount of acidic and high COD wastewater. In addition to adoption of cleaner production technologies, a two-stage nanofiltration (TSNF) approach was designed and experimentally tested in this study to reclaim diosgenin wastewater. Since NF can intercept high molecular weight substance like sugar and filter monovalent ion, the first stage of the NF system was designed for the separation of hydrochloric acid and sugar, and the second stage for sugar concentration. At the optimal operation conditions of Volume Reduction Factor (VRF) value (2.0 and 2.5 for the two nanofiltration stages respectively), 65% sugar, 40% acid and 30% water were recovered. The wastewater was separated into three parts: sugar mixture, acid mixture and water, each of which could be recycled.