Study On Solid State Fermentation Of Endogenous Monosaccharides And Enrichment Of Heavy Metal Ions In Lignocellulose

Lignocellulose contains a large amounts of endogenous monosaccharides and heavy metal ions.The endogenous monosaccharides increase inhibitors' formation during the pretreatment and reduce the following cellulosic ethanol fermentaion efficiency.And heavy metal ions in lignocellulose may increase the difficulty and the cost of wastewater treatment after cellulosic ethanol fermentation,and even cause secondary pollution of heavy metal ions and reduce the effectiveness of phytoremediation.Therefore,it is necessary to reduce the content of endogenous monosaccharides in lignocellulose to increase the ethanol fermentation efficiency,and avoid the secondary pollution of heavy metal ions in the cellulosic ethanol fermentation to further enrich heavy metal ions.In order to solve these two problems,solid state fermentation in lignocellulose before pretreatment,drying of cellulosic ethanol fermentation residue and microbial transport were proposed.The first part of this thesis focused on the effect of the removal of water soluble endogenous monosaccharides in corn stover before pretreatment on cellulosic ethanol fermentation.The results showed that converting water soluble glucose and fructose into citric acid by a solid state aerobic fermentation before pretreatment can significantly reduce the 5-hydroxymethylfurfural(HMF)generation and the usage of acid catalyst in pretreatment,thus reduce the detoxification intensity and improve the cellulosic ethanol fermentation efficiency.These results provide an important reference for the actual conversion process from biomass to ethanol.The second part of this thesis focused on the utilization of lignocellulose containing cadmium by dry milling biorefinery process(DMBP)and the study of cadmium enrichment.62.3 g/L and 45.5 g/L cellulosic ethanol was obtained from the corn stover and poplar wood chip containing cadmium by DMBP,respectively.In addition,the cadmium was enriched about 5.2 and 4.5 times from corn stover and poplar wood chip,respectively,without any loss of cadmium during the DMBP,which provide a feasible direction for the treatment of lignocellulose after phytoremediation of the soil polluted by cadmium.The third part of this thesis tried to remove cadmium from wheat straw hydrolysate(WSH)by bioadsorption of three microbial strains.When the initial cadmium concentration in WSH was 0-10 mg/L,Saccharomyces cerevisiae and Corynebacterium glutamicum had stronger cadmium removal ability(higher than 43%)compared with Trichosporon cutaneum(lower than 25%).Meanwhile,the glucose consumption of Saccharomyces cerevisiae,Trichosporon cutaneum and Corynebacterium glutamicum decreased in turn.The potential of using Corynebacterium glutamicum to remove cadmium from lignocellulose hydrolysate was demonstrated,which also provide a direction for further reducing the treatment cost of lignocellulose containing cadmium.Conclusively,this study improved cellulosic ethanol fermentation efficiency by converting endogenous glucose and fructose into citric acid before pretreatment.In addition,the complete retention and effective enrichment of cadmium in the process of cellulosic ethanol fermentation from lignocellulose containing cadmium and the discovery of C.glutamate's high adsorption capacity for cadmium provide a direction for the effective treatment of lignocellulose containing cadmium and further enrichment of cadmium.