Microalgae fermentation of acetic acid-rich pyrolytic bio-oil: Reducing bio-oil toxicity by alkali treatment



Bio-oil derived from fast pyrolysis of lignocellulosic biomass contains various substrates that can be fermented to fuels and chemicals. The goal of this research was to utilize an acetic acid-rich fraction of bio-oil for the growth and lipid production by microalga Chlamydomonas reinhardtii. As toxic compounds are contained in the bio-oil, the algae cannot survive in medium containing this bio-oil fraction even at a low level (0.05 wt %). An alkali-based treatment with sodium hydroxide was used to reduce the toxicity and enhance its fermentability by microalgae. It was found that treating the acetic acid-rich bio-oil fraction by adjusting pH to 10 greatly improved the algal growth. The algae can thrive in medium containing 4 wt % alkali-treated bio-oil fraction. When using a metabolic-evolved strain with high level of toxicity tolerance, the algae were even capable of growing in medium containing 5.5 wt % bio-oil fraction, which replaced 100% of the acetic acid in the medium. The algal biomass grown in medium containing alkali-treated bio-oil fraction exhibited fatty acid profiles similar to the culture grown in pure acetic acid, but with a lower total fatty acid content. but the total fatty acid content (∼10% DW) was lower than that of the control (∼20% DW).The benefit of alkali treatment for enhancing algal growth was confirmed to be due to the removal of toxic compounds such as furfural, acetol, phenolics, and 5-hydroxymethylfurfural (HMF). Collectively, the results showed that fast pyrolysis-microalgal fermentation is a viable approach for producing lipid from lignocellulosic biomass. Alkali-based treatment is an effective method for reducing bio-oil toxicity, and thereby, greatly enhancing the algae fermentability of bio-oil. © 2013 American Institute of Chemical Engineers Environ Prog, 32: 955–961, 2013