Optimization Of Fermentation Conditions And Separation Of 3-hydroxypropionic Acid From Fermentation Broth

3-Hydroxypropionic acid ?-HP)is an economically valuable platform compound from which a series of chemicals such as 1,3-propanediol,pyruvic acid and poly 3-hydroxypropionic acid can be generated.Klebsiella pneumoniae is regarded as a promising host strain for bioproduction of 3-HP mainly due to its considerable ability to metabolize glycerol and low pollution to environment.However,3-HP fermentation broth is complex and separation of 3-HP from various metabolites is pretty challenging.It is clear that downstream separation is a limiting factor for industrial production of 3-HP.This work focused on separating 3-HP from fermentation broth,involving procedures of flocculation,decolorization,resin adsorption and distillation.First,five K.pneumoniae strains were evaluated for their ability to produce 3-HP by examining biomass and metabolites concentrations.The fermentation conditions were optimized.As a result,K.pneumoniae KP-tac C was chosen as the 3-HP-producing strain.The fermentation broth was analyzed.It was found that the fermentation broth contained 78.64 g·L-1 3-HP,32.53 g·L-1 lactic acid,13.12 g·L-1 acetic acid,18.70 g·L-1 1,3-propanediol and 14.02 g·L-1 2,3-butanediol.In addition,the fermentation broth contained inorganic salts such as Cl-and Na+,bacteria,proteins as well as solid particles.Next,flocculation and decolorization processes were explored to remove bacteria,proteins and pigments in 3-HP fermentation broth.Results showed that the chitosan-sodium alginate composite flocculant was most appropriate for pretreatment of 3-HP fermentation broth.This composite flocculant removed 99.7%bacteria in the following conditions:the dosage of this composite flocculant was 1.6 g·L-1,pH at 7.0,stirring for 20 min,pause for 30 min,alternatively.For decolorization,active carbon was employed.When active carbon size was less than 178 ?m,dosage was 5.0 g·L-1,and oscillation time was 30 min,the decolorization rate reached up to 46.45%.After above pretreatment,the 3-HP in fermentation broth decreased from 78.63 g·L-1 to 76.31 g·L-1 with loss rate of 2.96%.To remove 1,3-propanediol and 2,3-butanediol from 3-HP flocculation,the mechanical strength and other properties of three resins D314,330 and D318 were examined,and the process parameters of static adsorption,dynamic adsorption and the elution of the resin showing high adsorption rate were also investigated.Results showed that resin D314 demonstrated highest absorption for 3-HP at pH=3.0,and the saturated adsorption capacity reached 0.143 g·g-1.This adsorption process is consistent with the chemical adsorption model and belongs to the monolayer adsorption.Moreover,energy was released during adsorption process.When the initial concentration of fermentation broth was 30.0 g·L-1,feed flow was 3.0 ml·min-1,and 2.0 mol·L-1 of sodium hydroxide was eluent at 3.0 ml ·min-1,dynamic adsorption was the highest.This resin showed 89.65%adsorption rate and 96.78%desorption rate toward the organic acids in fermentation broth.By resin D314 absorption,1,3-propanediol decreased from 18.70 g·L-1 to 2.54 g·L-1,and 2,3-butanediol decreased from 14.70 g·L-1 to 1.34 g·L-1.Overall these results show that D314 is an ideal resin for 3-HP separation.Finally,the effects of distillation temperature,time and other factors on removal of acetic acid from 3-HP fermentation broth were investigated.Results showed that acetic acid was reduced from 13.12 g·L-1 to 0.78 g·L-1 and the removal rate was 94.05%when the vacuum distillation temperature was 60.0 ?,and distillation time was 20.0 min.Meanwhile,vacuum distillation removed partial water from 3-HP fermentation broth,thereby leading to concentrated broth.