Studies On The Fermentation Process Of Succinic Acid

Succinic acid is a C4-dicarboxylic acid in the metabolic pathways of several anaerobic and facultative microorganisms.It can be used as a precursor of numerous products,including pharmaceuticals,food additives,green solvents,and biodegradable polymers.The production of succinic acid from petrochemical feedstocks is expensive and suffers serious pollution problems.Recent years,there has been an increasing effort on the production of succinic acid by microbial fermentation using renewable carbohydrates.Single and two stages continuous fermentation of succinic acid using Actinobacillus succinogenes SF-9 from cane molasses were studied in this work.For single continuous system,samples were taken at dilution rates of 0.06 h^-1,0.11 h^-1,0.21 h^-1,0.30 h^-1,0.42 h^-1, 0.63 h^-1 and 0.91 h^-1,and were analyzed for succinic acid production and productivity.For single stage CSTR,the maximum final succinic acid productivity[4.87 g/(L·h)]was achieved at the dilution rate of 0.63 h^-1,meanwhile the sugar conversion rate was 50.6%,succinic acid production was 7.8 g/L,and succinic acid percentage yield was 75%.For two-stage CSTR, samples were taken at total dilution rates of 0.12 h^-1,0.21 h^-1,0.30 h^-1(D₁/D₂=2).At dilution rate of 0.30 h^-1,succinic acid reached the highest productivity of 4.29 g/(L·h),with succinic acid production of 14.11 g/L,sugar conversion rate of 59.4%,and succinic acid percentage yield of 68%.In this work,the semi-continuous succinic acid fermentation by Actinobacillus succinogenes SF-9 from cane molasses with a novel two-stage and two-stream system was studied for improved succinic acid productivity.The fermentation conditions of the first stage, such as initial sugar concentration,medium addition volume,and time interval of each loading were optimized.Under the optimized condition,the maximum succinic acid productivity[2.38 g/(L·h)]was enhanced by 111%and 114%compared with those obtained in batch and fed batch fermentation,respectively.In addition,the maximum succinic acid concentration(46.0 g/L)was increased by 12.9%compared with that in batch fermentation, and reached to a comparable level of that obtained in fed batch fermentation(36 h,48.8 g/L). This process was operated stably for 39 circles without decreases both in the succinic acid concentration and productivity.During the 39 operation circles,the fermentation time of each batch(stage 1 and stage 2),the average succinic acid concentration,succinic acid productivity, succinic acid yield,and sugar conversion rate were 21 h～24 h,43.5 g/L,2.07 g/(L·h),79%, and 96.4%,respectively.In the present work,the succinic acid production by Actinobacillus succinogenes SF-9 with simultaneous saccharification of sterilized jerusalem artichoke powder by Apergillus niger SL-09 was found to be superior to separate hydrolysis and fermentation(SHF).The inhibition of the succinic acid fermentation due to a high initial sugar concentration could thus be avoided.During the fermentation process,the sugar concentration was maintained at a lower level(10 g/L～40 g/L).When fed batch fermentation was carried out in a 5-L stirred bioreactor,22.1%～77.6%higher succinic acid concentrations were obtained by simultaneous saccharification and fermentation of jerusalem artichoke in comparison with SHF.For 82.8 g/L total sugar of jerusalem artichoke with a well-balanced reducing sugar production by saccharification and sugar utilization by Actinobacillus succinogenes,the time required for the production of 71.97 g/L succinic acid with a yield of 89.8%was only 64 h.The investigation on the fermentations of succinic acid from corn straw and other fiber raw materials showed that Actinobacillus succinogenes SF-9 was able to utilize the hydrolyzed sugar present in corn straw stalk,corn cob,straw,wheat straw,sugarcane residue, and other fiber materials for the fermentation of succinic acid very well.The best results were obtained using alkalis-enzymes hydrolysis.Batch fermentation using corn straw stalk hydrolysis sugar as carbon source was conducted in 5-L stirred bioreactor,and 45.5 g/L of succinic acid and 5.75 g/L of acetic acid were attained at 48 h.When fed batch fermentation was carried out,the production of succinic acid in 48 h(52.1 g/L) was increased by 15% compared with that of batch fermentation,and sugar conversion rate,the succinic acid yield and productivity were 93.6%,81.2%and 1.09 g/(L·h),respectively.