Oxygen Mass Transfer Control Technologies Of Gluconobacter Oxydans Whole Cell Catalysis And Its Applications

Gluconobacter oxydans?G.oxydans?is able to rapidly oxidize sugars and sugar alcohols to the corresponding acids and ketones depend on various membrane-bound dehydrogenases,it has already been widely used in industry.In order to address the difficulty of xylose utilization from lignocellulosic pre-hydrolysate,we researched the dynamics of oxygen supply bassed on the incompleted oxidation characteristic of G.oxydans.In this study,a compressed oxygen gas supply was connected to a sealed aerated stirred tank reactor?COS-SSTR?bio-system was put forward to improve the bio-conversion performance.By means of COS-SSTR and incompleted oxidation capability,the output and productivity of different value-added product?xylonate,1,3-dihydroxyacetone and galactonate?all could be remarkably improved.The main results were shown as follows:1.According to the researches of xylose oxidation with G.oxydans,we found that the highest specific oxygen uptake rate of the G.oxydans was about 16.2 mmolO₂/h/?g biomass?.The further researches of dissolved oxygen transfer dynamics,the highest theoretical xylonic acid production was about 5.0 g/?L·h?by the bio-conversion of 1 g/L biomass.2.Based on the oxygen balance between transfer and consumption,a new method with compressed oxygen supplied sealed aerated stirred tank reactor?COS-SSTR?was put forward.In the case of 8 g/L G.oxydans cell loaded,the productivity of xylonic acid finally was more than30 g/?L·h?.Results from the previous sections demonstrate that solutions containing higher concentrations of xylose or xylonic acid would increased the viscosity of medium and then it could inhibit xylose oxidation by G.oxydans,attributed to a sharp decline in oxygen transfer rate.To address this issue,a cell-recycle technique was employed to lift oxygen transfer restrictions.Meantime,we conducted fed-batch fermentation using recycled cells within the COS-SSTR system.After five cycles of cell recycling within 108 h,1.8 kg xylonic acid could be produced in1-L broth.3.The solid foaming issue occurred in the common agitation system was overcame by COS-SSTR which is an efficient and ideal method for in-situ fermentation of pre-hydrolysate.Finally,approximately 190 g pentonic acids could be produced starting from pre-hydrolysate produced from 1 kg corn stover.4.The calcium xylonate product was evaluated as concrete admixture without any complex purification steps.Under the same concrete fluidity conditions,the 0.2-0.3%addition dosage of calcium xylonate could decrease mixing water requirements up to 10-15%;Moreover,it also could prolong the setting-time and improve the middle and late compressive strength of concrete.5.We found that the calcium carbonate?CaCO₃?or calcium hydroxide?Ca?OH?₂?that was added to the culture for neutralizing the oxidation reaction,was precipitated as calcium galactonate with increasing concentrations of galactonic acid.The lower solubility of calcium galactonate?<30 g/L?aided its crystallization during fermentation.A successive calcium galactonate preparation method which combined fed-batch and product online crystallization-separation in the COS-SSTR was devised,and approximately 720 g calcium galactonate crystals were produced from 1L broth within 60 h.6.In this study,COS-SSTR system combined with staged culture and oxygen supply was used to improve the catalytical performance in the production of 1,3-dihydroxyacetone?DHA?from glycerol using G.oxydans.Final concentration of 301.2 g/L DHA was obtained after 32 h of fed-batch fermentation in the COS-SSTR system.The volumetric productivity for this process was 9.41 g/?L·h?,which is presently the highest obtained level of glycerol bioconversion into DHA.These results show that the application of this bioreactor would enable microbial production of DHA from glycerol at the industrial scale.