Microalga Isochrysis galbana biorefinery: Obtaining fucoxanthin and biogas after supercritical fluid extraction

Isochrysis galbana is a microalga that is a potential source of several 'compounds of interest' for food and nutraceutical industries. The procurement of these compounds of interest and the generation of bioenergy is a novel and interesting application of microalgae. The present study evaluated the valorization of the microalga I. galbana through the extraction of the carotenoid fucoxanthin and polyunsaturated fatty acids using supercritical fluid extraction (SFE). The spent or extracted microalga I. galbana was valorized through anaerobic digestion (AD) to produce biogas through the integration of the concepts of biorefinery and the circular economy. The biochemical composition of the extracted microalga exhibited a marked decrease in the carbohydrates by approximately ninefold after the SFE, while the proteins and lipids were decreased only to nearly half of their initial contents. The methane (CH4) yields obtained for non-extracted I. galbana and supercritical fluid-extracted I. galbana were 104 +/- 5 L-STP CH4 kg(-1) VS and 90 +/- 2 L-STP CH4 kg(-1) VS (VS: volatile solids), respectively, indicating the methane yield loss of only 14.2% when using the extracted microalga. In order to increase methane production, different co-digestion mixtures of I. galbana and olive mill solid waste (OMSW) were evaluated. The methane yield increased to 134 + 4 and 189 +/- 5 mL(STP) CH4 g(-1) VS for the VS/TKN ratio (w/w) of 20 and 30, respectively (TKN: Total Kjeldahl Nitrogen). These results were encouraging due to the positive synergism established between the co-substrates.

Automated summary

The study evaluated the extraction of fucoxanthin and polyunsaturated fatty acids from Isochrysis galbana using supercritical fluid extraction (SFE) and valorized the spent microalga through anaerobic digestion (AD) to produce biogas. The results showed that co-digestion with other substrates increased methane production.