Fermentative Production Of Succinic Acid With Waste Fermentation Broth Of Dextran

Succinic acid, as a C4 block platform chemical, has been widely used in chemistry, food, medicine, agriculture and other fields. Waste fermentation broth of dextran(WFBD) is the residue from dextran fermentation liquid after extracting product, which contains relatively high concentrations of fructose and glucose and is usually regarded as industrial wastewater. In this work, WFBD was used as a raw material for fermentative production of succinic acid with Actinobacillus succinogenes, which not only can provide a new way for liquid waste processing emissions, also can bring extra income. The production of succinic acid from WFBD was studied in detail, including replacing MgCO3 with K2CO3 in controlling pH and adopting a fibrous-bed bioreactor to produce succinic acid repeatedly. Specific results from this work were listed as followed:First of all, succinic acid production by A.succinogenes from WFBD was studied. After comparing the effect of initial sugar concentrations on succinic acid production, Plackett-Burman experiment showed that NaH2PO4·2H2O was the most important factor in succinic acid production. Single factor experiment suggested the optimal NaH2PO4·2H2O concentration was 2.8 g·L-1. Concentrated WFBD with reducing sugar concentration of 60 g·L-1 was used as the carbon source for batch fermentation in a 3 L fermentor, and 40.5 g·L-1 succinic acid concentration was achieved after 46.8 h. In the fed-batch fermentation, an initial glucose concentration of 30 g·L-1 was added, followed by feeding concentrated WFBD, leading to a final succinic acid concentration of 55.0 g·L-1 with a productivity of 1 g·L-1·h-1 and yield of 0.83 g·g-1.Secondly, on account of operation difficulties in using MgCO3 as the pH regulator in factory and serious dilution problems associated with other carbonates, fibrous-bed bioreactor was used in optimizing fermentation process to replace MgCO3 with K2CO3 in pH control. Cotton fiber was used as the matrix for cell adhesion. A cotton fiber surface area/fermentation broth volume ratio of 1-1.5 cm2·cm-3 was found to be most efficient for cell adhesion. By comparing the structures of four fibrous-bed bioreactor, the built-in rotation fibrous-bed bioreactor was chosen. In order to examine the stability and continuous operation ability of fibrous-bed bioreactor on succinic acid production, ten batches of repeated batch fermentation was carried in this bioreactor, and results showed that the average succinic acid concentration was 39.2 g·L-1 with a yield of 0.85 g·g-1and productivity of 2.00 g·L-1·h-1. Moreover, the production rate of succinic acid did not decline in these batches. In five batches of repeated fed-batch fermentation, an average succinic acid concentration 49.8 g·L-1 was got, which was 27% increased compared to that obtained in repeated batch fermentation. The yield was 0.74 g·g-1 and the productivity was 1.14 g·L-1·h-1, with some sacrifice in continuous operation stability.Thirdly, succinic acid from WFBD was produced in the aforementioned fibrous-bed bioreactor, and preliminarily attempt to extract the fermented product was studied. An average succinic acid concentration of 53.1 g·L-1, productivity of 1.22 g·L-1·h-1 and yield of 0.82 g·g-1 was got in the repeated fed-batch fermentation with K2CO3 used as pH regulator. At the end of fermentation, the fermented liquid was treated successively by evaporation, centrifugation, destaining, acidification with sulfuric acid and two circles of crystallization, the final succinic acid crystal obtained can reach a purity higher than 99%, total recovered yield reached 62%.In conclusion, this work developed an efficient process for succinic acid production, which is based on a new raw material, facile pH control strategy with K2CO3 and combination with fibrous-bed bioreactor.