Study On Xylonic Acid Fermentation Process Based On Detoxification Of Activated Carbon And Enhanced Oxygen Mass Transfer

The efficient bioconversion of xylose from hemicellulose hydrolysate is the prerequisite and key factor to realize the high value utilization of lignocellulosic bio-refining.The production of xylonic acid from xylose is considered to be one of the important ways out.The key limiting factors affecting the production efficiency of xylonic acid in hemicellulose hydrolysate are inhibitors and oxygen mass transfer.In this paper,detoxification and oxygen mass transfer are studied respectively.Firstly,this paper investigated the conditions of adsorption performance of activated carbon for adsorption of inhibitors from hydrolysate,and explored the effects of contact time,temperature,AC content and shaking speed on the adsorption performance.Secondly,this paper investigates the effects of different oxygen transfer conditions on xylonic acid production,volumetric productivity,specific oxygen consumption rate,and the relationship between oxygen transfer rate and oxygen consumption rate.Finally,this paper investigates the integration of activated carbon particles for detoxification and enhanced oxygen transfer in the production of xylonic acid by Gluconobacter oxydans.The details are as follows:1.We investigated the adsorption of inhibitors and reducing sugars in hydrolysate on activated carbon particles firstly.The optimal activated carbon detoxification conditions were obtained by response surface optimization.Higher inhibitors removal efficiencies of 100%furfural,100%HMF,18.3%acetic acid,64%formic acid and 50%levulinic acid,and lower sugars removal efficiencies of 6.4%xylose,5%glucose and 5.9%arabinose were obtained at contact time of 2.9 h,temperature of 60^oC,AC content of 15%（w/v）and shaking speed of 130rpm.For both total inhibitors and fermentable sugars,the adsorption percentage of total inhibitors could reach about 40%,while the loss of fermentable sugars was consistently below15%.2.The oxygen transfer law of the hydrolysate production xylonic acid system was investigated.The rheological behavior of hydrolysate during fermentation was measured and the rheological model of hydrolysate was established.The oxygen transfer was analyzed under different oxygen transfer coefficients k _La.When the oxygen transfer coefficient k _La<150 h^-1,the volumetric productivity of xylonic acid increased with the increase of k _La;when the oxygen transfer coefficient k _La>150 h^-1,the volumetric productivity of xylonic acid reached the maximum value of 3.5 g L^-1h^-1.The respiration intensity of Gluconobacter oxydans was related to dissolved oxygen,and the maximum cellular respiration intensity measured experimentally when hydrolysate was used as the fermentation substrate was 12 mmol g_x^-1h^-1.3.A new integrated process for the production of xylonic acids directly from lignocellulose hydrolysates is developed,using activated carbon particles to combine simultaneous detoxification and oxygen transfer enhancement.In the flask experiments,a 2.47-fold enhancement was observed at 1%（w/v）activated carbon content in the In-situ DF process.When the added activated carbon content was>1%（w/v）,the In-situ DF process had almost the same enhancement factors of xylose consumption and xylonic acid accumulation as the SDF process,but without additional detoxification and solid-liquid separation.For the fermenter experiments,a maximum volumetric productivity of 5.71g L^-1h^-1was achieved in 12 h.