Studies On The Fermentative Production Of Succinic Acid From Corn Stalk

Succinic acid is a C4-dicarboxylic acid. As a carbon-intermediate chemical, it can be used as a precursor of numerous products, including pharmaceuticals, food additives, green solvents, and biodegradable polymers. Studying on the fermentative production of succinic acid from corn stalk has an great significance in practical application, which not only can provide a technique for the low cost production of bio-succinic acid, but also can avoid using cereal materials, promoting utilization the residues of forestryand agricultural. In this work, the process condition of succinic acid production using corn starw hydrolysate(CSH) as a carbon source, processes of succinic acid productionby Separate hydrolysisand fermentation (SHF) and by Simultaneous saccharification and fermentation (SSF) from corn stalk were studied.The effects of various nitrogen sources on succinic acid production by A. succinogenes SF-9 were compared when CSH as a carbon source. Results showed that corn steep liquor (CSL) can instead of yeast extract as a nitrogen source of succinic acid fermentation. The optimum dosage of corn steep liquor were 20 g/L when initial sugar concentration of corn starw hydrolysate were 50 g/L in shaking flask with single-factor experiment. The effects of various initial sugar concentration of corn starw hydrolysate on succinic acid fermentation by A. succinogenes SF-9 were investigated in 5 L stirred tank bioreactor, which results indicated that the higher initial sugar concentration of corn starw hydrolysate have an inhibitory effects on cell growth. In fed-batch fermentation, 42.7 g/L succinic acid concentration and 82.7% yield were attained after 60 h incubation in a 5 L stirred tank bioreactor, and productivity achieved 0.81 g/(L·h).The composition analysis of corn stalk, enzymatic hydrolyzation and its fermentation yield of succinic acid were investigated when corn stalk were pretreated with various methods.The result showed NaOH pretreatment was the most suitable pretreatment for corn stalk. Pretreating corn stalk with 1% NaOH solution under 120℃1 hour, the removal yield of lignin is 75.4%, the total weight of fiber of the solid residue account for 88.4%.The pretreated corn stalk was enzymolysised by cellulase from submerged fermentation using Trichoderma reesei SW09-1. The optimum conditions of enzymatic hydrolysis were 80 g/L substrate concentration; 25 FPIU/g substrate; pH 4.8, and the reducing sugar concentration achieved 57.9 g/L after hydrolysis reaction 36 h, which enzymatic hydrolysis yield was 73.35% correspondingly. When adding cellobiase of 10 IU/g substrate during enzymatic hydrolysis, the reducing sugar concentration reached 67.6 g/L and enzymatic hydrolysis yield was 86.0%. By SHF with A.succinogenes SF-9,in anaerobic bottles fementation 64 h, succinic acid concentration achieved 35.08 g/L that per gram pretreated corn stalk can gain 0.439g succinic acid.Succinic acid production from NaOH-pretreated corn stalk by simultaneous saccharification and fermentation process was studied preliminarily. The effects of substrate concentration, enzyme dosage and temperature on succinic acid production were investigated. SSF by A.succinogenes SF-9 were carried out with 70 g/L NaOH-pretreated corn stalk and 20FPIU/g substrate's cellulose from T. reesei SW0901, succinic acid concentrati gain 35.53 g/L at 38℃after 72 h in anaerobic bottles, and the conversion of succinic acid was 0.507g per gram pretreated corn stalk. When SSF was operated in 5 L stirred bioreactor, succinic acid concentration of 47.36 g/L was reached in 48 h fermentation, suggested 1 g corn stalk can converted 0.722 g succinic acid.