Bioconversion of biodiesel-derived crude glycerol waste to 1,3 propanediol and gellan using adapted bacterial isolates

Abstract

The continual growth of the global biodiesel industry has resulted in a proportional increase in crude glycerol production. The by-production of glycerol waste during the manufacture of biodiesel has, with recent research, proven to hold use as a feedstock for the production of several commodity chemicals. The conversion of glycerol may be carried out by both chemical as well as biological means. The biological conversion of glycerol surpasses chemical conversion with respect to higher yield and selectivity, normal reaction conditions and the use of cheaper biological catalysts. Many microorganisms are known to convert glycerol to different value added products. This study involved the isolation of bacteria from soil and crude glycerol from a local biodiesel plant. Isolates were then used to convert crude glycerol supplemented with salts and a nitrogen source into commercially viable products. Isolates which successfully degraded glycerol were then identified via 16S PCR. A strain of Klebsiella pneumoniae, which is a known producer of 1,3-propanediol (1,3-PDO), was isolated from soil and two strains of Sphingomonas sp., which is a known gellan producer, was isolated from biodiesel waste. Gellan is an exopolysaccharide used in the food, cosmetic and pharmaceutical industries sold commercially as a product known as Gelrite or Gelzan while 1,3-PDO is an important component of fuels and polyesters (used widely in the petroleum industry) and is currently chemically produced. Using crude glycerol for producing 1,3-PDO is a good solution from an economic as well as ecological point of view. K. pneumoniae, Sphingomonas psueudosanguinis and Sphingomonas yabuuchiae were subjected to a series of shake flask fermentations in order to determine optimal growth conditions. This microoganism was able to successfully produce significant amounts of 1,3-PDO and lactic acid using crude glycerol (80 g/l), without pre-treatment (37 and 6.8 g/l respectively). S psueudosanguinis and S. yabuuchiae were both able to produce two of the highest amounts of gellan gum than that reported by other studies using crude glycerol (80 g/l) as a sole carbon source in a minimal medium (50.9 and 52.6 g/l respectively).