Study And Techno-economic Analysis Of Butyric Acid Production From Cassava Starch By Clostridium

Butyric acid is a chemical which is widely used in industry,food and medicine industries.Although bio-based butyric acid has the advantages of resource-saving and environment-friendly and can be used as a good substitute for petroleum-derived butyric acid,its industrial application is restricted by the unsustainable feedstock,high process cost,and limited report about technical and economic analysis.Cassava is an underutilized starchy crop that can be grown on poor soils where the yield of other crops is low.Using it as a raw material can reduce substrate costs and avoid competition with food production.Therefore,in this study,three processes for butyric acid production by Clostridium using cassava starch were established:1)butyric acid production from cassava starch hydrolysate through simultaneous saccharification and fermentation(SSF)by C.tyrobutyricum ATCC 25755 which has a strong butyric acid production capacity but cannot directly use starch;2)butyric acid production from raw cassava starch through consolidated bioprocessing(CBP)by C.butyricum SCUT 620 which has a weak butyric acid production capacity but can utilize raw starch directly.In addition,C.butyricum itself can be used as a high-value by-product;3)Overexpressing theα-amylase and glucoamylase genes from C.tyrobutyricum SCUT 620 and C.acetobutylicum ATCC 824 in C.tyrobutyricum by metabolic engineering to make C.tyrobutyricum has the ability to directly utilize cassava starch and produce butyric acid through consolidated bioprocessing.Based on these,the technical and economic analysis of three different butyric acid production processes from cassava starch was carried out by constructing process model,which could provide basic data for industrial production of bio-based butyric acid.The main findings are as follows:The first process is SSF of cassava starch to butyric acid by C.tyrobutyricum.The results showed that the growth of C.tyrobutyricum was inhibited by 140 g/L cassava starch hydrolysate,which could be relieved by SSF.Under the optimal fermentation conditions(37°C,p H 6.0 and50 U/g glucoamylase),the butyric acid concentration,yield,selectivity and productivity reached 65.22 g/L,0.37 g/g,92.2%and 0.54 g/L·h from 200 g/L liquefied cassava starch.The second process is CBP of cassava starch to butyric acid by C.butyricum.Under the optimal fermentation parameters(37°C,5 g/L yeast extract,80 g/L raw cassava starch,p H 6.0),the butyric acid concentration,yield,selectivity and productivity reached 21.72 g/L,0.29 g/g,72.3%,0.30 g/L·h from raw cassava starch and the alternative nitrogen source fish meal.Furthermore,the concentration and activity of by-product microbial agent were 5.06 g/L and3.50×10~8 CFU/g,respectively.The third process is CBP of cassava starch to butyric acid by the engineered C.tyrobutyrium.The results showed that the engineered bacteria exhibited the starch utilization ability that the wild type did not have.The optimal process conditions and fermentation results were as follows:30.40 g/L butyric acid was produced with a yield of 0.31 g/g,selectivity of100%and productivity of 0.25 g/L·h by CTAA05 which overexpressed theα-amylase gene amy BIII of C.butyricum and glucoamylase gene glu of C.acetobutylicum from 100 g/L gelatinized cassava starch through CBP at p H 5.5.Based on the experimental data,the technical and economic analysis of these three processes is carried out,and all the processes showed an ideal industrial application prospect.In the sensitivity analysis,the unit operating cost was more sensitive to cassava starch price,production scale,butyric acid concentration and yield.Among different processes,the first process has the advantages of high butyric acid concentration and yield,and the second process has the advantages of simple process operation and high value of by-product.And the more economically promising process is to use the metabolically engineered strains,which has a higher butyric acid production ability,for butyric acid production from raw cassava starch through CBP.In summary,through optimizing the fermentation parameters and performing the technical and economic analysis for different butyric acid production processes from cassava starch,this study not only provide basic data for bio-based butyric acid production,but also provide theory guidance and basis for the design,development and evaluation of the industrial production of butyric acid.