Metagenomic analysis on anaerobic digestion with reddish colour of pre-treated microalgae residues

Microalgal residues from Chlorella protothecoides were assessed as anaerobic digestion substrates for the simultaneous production of an energy carrying gas and pigments. Anaerobic runs, digesting raw heterotrophic algae, H, and pre-treated heterotrophic algae through ultrasound process, HPU, were started-up for the purpose. Pre-treatment applied to the heterotrophic algae have a positive effect on biogas/methane productions. Comparatively to H, pre-treated heterotrophic algae allow to obtain relevant increase in accumulated volume of methane. A reddish pigmentation was developed in both H and HPU, being structures of microbial communities in these units investigated by metagenomic analysis. At the end of the anaerobic digestion, Methanosaeta became the comparative dominant genus in both H and HPU units, meaning that the methane was produced through acetoclastic methanogenesis, and Rhodobacter was foun to be responsible for the coloured pigmentation.