Abstract
BackgroundCrude glycerol is a main by-product from biodiesel production, and efficient utilization of crude glycerol will bring significant economic and environmental benefits. However, the complex compositions of crude glycerol may impair the cellular growth and inhibit the crude glycerol consumption. Therefore, it is necessary to find a simple method to treat the crude glycerol and release the inhibition on cell metabolism.ResultsThe simply purified crude glycerol by activated carbon can be used as the carbon source to produce succinate in two-stage fermentation by the engineered Escherichia coli strain, MLB (ldhA−, pflB−) expressing phosphoenolpyruvate carboxykinase. In the flask experiments, succinate production from crude glycerol without treatment was less than that from pure glycerol. However, in the experiments of 1.5-L bioreactor, little succinate was produced in crude glycerol. The simply purified crude glycerol was used as carbon source for succinate production, and the glycerol consumption and succinate production were enhanced greatly. The succinate produced from the simply purified crude glycerol reached 566.0 mM, which was about ten times higher as that of non-purified one (50.3 mM). The succinate yield of the anaerobic stage achieved 0.97 mol/mol, which was 97% of the theoretical yield.ConclusionThe treatment of crude glycerol by activated carbon could effectively release the inhibition on the glycerol consumption and succinate production of the engineered E. coli strains, so that the fermentation result of the treated crude glycerol was similar as the pure glycerol. The results showed that the metabolically engineered E. coli strains have great potential to produce succinate from crude glycerol.
Highlights
Crude glycerol is a main by-product from biodiesel production, and efficient utilization of crude glycerol will bring significant economic and environmental benefits
Treatment of crude glycerol using activated carbon The chemical compositions of crude glycerol were dramatically different depending on the origin, the type of catalyst used in biodiesel production, the transesterification efficiency, other impurities in the feedstock, and whether the methanol and catalysts were recovered (Yang et al 2012; Dobrowolski et al 2016)
The contents of crude glycerol and purified crude glycerol were detected by HPLC and GC
Summary
Crude glycerol is a main by-product from biodiesel production, and efficient utilization of crude glycerol will bring significant economic and environmental benefits. The complex compositions of crude glycerol may impair the cellular growth and inhibit the crude glycerol consumption. It is necessary to find a simple method to treat the crude glycerol and release the inhibition on cell metabolism. Crude glycerol is the main by-product of biodiesel, and it will generate about 10% (w/w) glycerol in the process of biodiesel production (Vivek et al 2017). With the significant increase of biodiesel production, the price of crude glycerol decreased dramatically. The refining process of crude glycerol to pure glycerol generally consists of three stages, including neutralization/ separation, vacuum evaporation, and deep refining
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