13-14: Biological utilization of acetic acid-rich bio-oil by microalgae for producing lipid based biofuel

The processing of lignocellulosic biomass into fuels has been categorized as either thermochemical or biochemical. However, both methods have their disadvantages, which have limited the commercial application of the biomass-to-fuel conversion. In this work, we established a hybrid processing by combining thermochemical technologies to fractionate biomass with biochemical processing to convert the resulting substrates into useful products.  

Bio-oil obtained from fast pyrolysis of biomass was recovered into five stage fractions with different compounds distributions.  Stage fraction 4 and 5 (SF 4 and 5), which are rich in acetic acid, were used as substrates for the heterotrophic growth of the microalga Chlamydomonas reinhardtii for lipid-based biofuel production. Although acetic acid serves as an ideal carbon source for the microalgae, the complex chemical compounds contained in SF4 and SF5 also severely inhibit the algal growth.  We used a metabolic evolution approach to mitigate the toxicity caused by those compounds. To date, we have successfully replace 25% acetic acid used in the original medium by SF4 and SF5 solution.  The bio-oil derived algal cell contained about 15-20% lipid.  This result demonstrates the feasibility of the hybrid process for treating lignocellulosic biomass for producing oil-based products including fuels.