Alkaline treatment for detoxification of acetic acid-rich pyrolytic bio-oil for microalgae fermentation: Effects of alkaline species and the detoxification mechanisms

摘要

Bio-oil derived from Pyrolysis of lignocellulosic biomass contains appreciable amounts acetic acid, which can be used as substrate for growing microalgae Chlamydomonas rein-hardtii. However, the toxic compounds in the bio-oil inhibit the cell growth. This work is to develop alkaline treatment methods to reduce the toxicity and improve fermentability of acetic acid rich bio-oil. When growing in raw bio-oil without any detoxification treatment, the algae can only tolerate up to 0.1 wt% of bio-oil. Treatment with KOH, NaOH and Ca(OH)_2 significantly reduced the toxicity and consequently improved the fermentability of bio-oil. The bio-oil tolerant level by microalgae depended on the alkali species used. Among the three alkali species, Ca(OH)_2 proved the most effective detoxification reagent. Inhibitory compounds such as furans, phenols, ketones, aldehydes, ethers, esters, alcohols were removed by Ca(OH)_2 treatment through precipitation. The detoxification mechanisms by the Ca(OH)_2-based treatment were also explored. The synergistic effect of alkaline pH, high temperature, and presence of Ca~(2+) played an important role for the precipitation of those compounds, and the consequent detoxification. Collectively, the results shows alkali, particularly Ca(OH)_2-based, treatment is an effective for reducing the toxicity of the pyrolysis derived bio-oil as fermentative substrate for microalgae growth. The microalgae can tolerant Ca(OH)_2-treated bio-oil up to 5.5 wt%, which was 55 times higher than algal tolerance level of untreated bio-oil.