Recovery of succinic acid from fermentation broth by electrodialysis

Abstract

An experimental study was carried out on the recovery of succinic acid from model solutions and fermentation broth by a two-stage electrodialysis (ED) process of desalting ED (DSED) and water-splitting ED (WSED). In DSED for the recovery of sodium succinate, suitable membranes and the optimal operating mode were selected in the experiments with model solutions. Operations at a constant current were found to be undesirable because the voltage drastically increased at low succinate concentrations in the feed in the later part of operation. Therefore, the operation was switched from the constant current mode to a constant voltage mode when a limiting-current situation is reached. Limiting current densities at different concentrations were measured to obtain information for the switching. Effects of various factors such as operating current, concentrations in the feed and permeate, feed pH, by-products and impurities were investigated. An increase in the current resulted in a decreased operating time required for a recovery of 98% and increased energy consumption. The operating time increased and the energy consumption decreased with the feed concentration. Changes in permeate concentration, on the other hand, hardly affected the performance of electrodialysis except for the cases of a very high permeate concentration. At those high permeate concentrations, operating time and energy consumption significantly increased with the concentration most probably because of back diffusion. A decrease in the pH gave negative results such as a low recovery and a high energy consumption, etc., because the portion of un-dissociated form of succinate increased. As expected, the existence of acetic and formic acids, two major by-products, and phosphate, the major impurities lowered current efficiency and energy consumption per unit amount of succinate recovered. The DSED data for fermentation broth have been compared with those for model solutions. For WSED to acidify the succina...