Co-generation of bio-butanol and bio-lipids under a hybrid process

Abstract

A novel hybrid fermentation process for the production of biological butanol and lipids was established in this study. The ABE containing broth obtained from the two-stage fermentation was used as the substrate for the batch bio-lipids fermentation. A gas stripping unit was integrated with the bio-lipids bioreactor to separate the ABE products. The carrier gas also provided the sterilized air for the metabolism of oleaginous microorganisms. The effect of inoculation rate on the bio-lipids fermentation was evaluated and optimized. Under the optimized conditions using a synthetic medium (10% of inoculation rate with additional carbon source supplementation), about 87.9% of the initial COD in the ABE fermentation broth was degraded, while ∼6.4 g L⁻¹ of the bio-lipids and ∼82.1 g L⁻¹ of the ABE solvent cumulated in the bio-lipids bioreactor and the condensate of the gas stripping unit, respectively. Moreover, the organic acid by-products in the ABE broth could be reused as the carbon source for microbial lipid production using Rhodotorula sp., which was not reported before. The hybrid process was further performed using enzymatic hydrolysate of sweet sorghum bagasse as the substrate. When using the hydrolysate directly without detoxification, ∼62.2 g L⁻¹ of the ABE solvents and ∼2.7 g L⁻¹ of the bio-lipids were produced simultaneously with a COD degradation rate of ∼70.1% from the ABE broth. Correspondingly, 0.06 g of the bio-lipids was co-generated with 0.25 g of the ABE products from a mixture of 1 g reducing sugar in lignocellulosic hydrolysate. The hybrid biorefinery process provides an energy saving way for the manufacture of bio-fuels with environmental benefits.