1,3-propanediol Production From Glycerol By Klebsiella Pneumoniae ZU-05 Under Non Anaerobic Condition

1,3-Propanediol (PDO) is a widely-applied chemical, It can be used as an important monomer for polytrimethylene terephthalate,polyester and Polyurethane. Additionally, PDO also has wide application in the field of ink, Painting,de-icer,agent and pharmaceutical products. Industrial PDO production has attracted worldwide attention. At present, with the rapid progress in the field of Biodiesel, the yield of glycerol as the major by-product of Biodiesel production, has been drastically enhanced, so the price of glycerol dropped sharply, which provides a promising opportunity for the development of PDO production by bioconversion.Bioconversion of glycerol to PDO generally processes in anaerobic condition, which requires the environment of fermentation full of nitrogen, and leads to high cost of production. In this work, an endure-oxygen Klebsiella pneumoniae strain ZU-05 was used to produce PDO from glycerol under non-strict anaerobic conditions, and the main fermentation parameters were optimized.The experiments were carried out under shaking flasks with only cotton plugs and without pumping nitrogen. Basic fermentation conditions were investigated, including cell age, the selection of nitrogen sources, temperature, initial pH, initial concentration of glycerol, nutrient salts and trace elements. Under non anaerobic condition with the optimized medium and culture parameters: initial glycerol concentration 20g/L, corn syrup 6g/L, glucose 8g/L, inoculation volume 10%,initial pH 6.7and 37℃; the molar yield of PDO and the utility of glycerol reached 51% and 90%, respectively. With CaCO₃ added in the fermentation system, the molar yield of PDO increased to 77.5%. However, the corresponding fermentation cycle will be prolonged because of the inhibitory effect of CaCO₃ to the fermenting strain.By utilizing the optimized medium and culture conditions in shaking flasks, the fermentation conditions and parameters for fed-batch culture of free Klebsiella pneumoniae ZU-05 were investigated. Applying the modified fed-batch medium and procedure, the concentration of PDO can achieve 52.14g/L and the average molar yield can reach more than 65% after fermented for 260h,.Several critical factors for the fermentation with Klebsiella pneumoniae ZU-05 in fermenter were studied. Fermentation experiments were carried out in 3.7L fermenter with Klebsiella pneumoniae ZU-05, and the optimal culture conditions in fermenter were investigated. Additionally, the finial concentration of PDO was enhanced by means of fed-batch. The experimental results suggested that agitation velocity and aeration are the two significant factors that influenced the PDO fermentation by Klebsiella pneumoniae ZU-05. In 3.7L fermenter, the optimal fermenting conditions were: agitation velocity of 300rpm, aeration of 0.2wm. After the fed-batch fermentation for 266h, the concentration of PDO arrived at 52g/L, while the average molar yield was 55.6%.Bioconversion of glycerol to PDO was conducted by utilizing the Ca-alginate Immobilized Klebsiella pneumoniae ZU-05 under non anaerobic condition(only with cotton plugs and without pumping nitrogen). The results indicated that at 37℃,with the initial glycerol concentration 40g/L, corn syrup 6g/L, glucose 8g/L, the initial pH 6.7, and the ratio of fermentation liquid to Immobilized cells 20:3(v/v) in medium, the utilization of glycerol and molar yield of PDO reached 91.4% and 52%, respectively after non-anaerobic fermentation for 72h. Comparing to fermentation with free cells, the molar yield of PDO was improved by 39%. The quality of immobilized cells was stable; after the continuous five batches fermentation experiments, the average utilization rate of glycerol and the average molar yield of PDO achieved 92.1 and 50%, respectively. The study on PDO fermentation utilizing immobilized cells is beneficial in shortening the fermentation cycle, enhancing the productivity of PDO, realizing the industrialization of PDO bioconversion.