The Efficacy of Ultrafiltration Treatment of the Drained Water from Steaming of Soybean in Natto Processing

Abstract

The drained water from steaming of soybean in Natto (fermented soybean) processing contains valuable components in high concentration, as the soybeans are steamed under drastic conditions of 120°C for 30-40 minutes. The efficacy of ultrafiltration for their recovery was studied from the standpoint of utilization of waste water as natural resources. lt was impossible to ultrafiltrate directly the drained water by the DDS plate-and-frame module used in this study, because of the high viscosity of the drained water causing a large pressure drop. Therefore, in order to remove the viscous components, this water was treated with isoelectric point sedimentation. The pH of the drained water was adjusted to 4.1-4.3 with hydrochloric acid followed by centrifugation. However, the separation ratio (supernatant volume/drained volume) was not satisfactory. Freezing of the pH adjusted drained water was effective in improving the separation ratio. The supernatant was subjected to ultrafiltration using three membranes of different nominal cut-off molecular weight. lsoelectric point sedimentation was greatly effective in reducing viscosity of the drained water, but was sligthly effective in reducing the BOD (93000ppm). BOD of the ultrafiltrate was 52000-68000ppm, which depended on the performance of the membrane. These treatments results in a 27-46% reduction of BOD from the drained water.