Consolidated bioprocessing of microalgal biomass to carboxylates by a mixed culture of cow rumen bacteria using anaerobic sequencing batch reactor (ASBR)

•The production rates and carboxylic acid profiles were impacted by hydraulic residence time (HRT).•The proportions of longer chain carboxylic acids (C5–C6) were enhanced at long HRT.•Using cow rumen bacteria as the seed, 12-day HRT was preferred for carboxylic acid production from microalgal biomass.•Terminal Fragment Length Polymorphism (T-RFLP) analysis indicated significant changes in the bacterial community determined by HRT.•In the 5 L laboratory-scale cultures, the dominant bacterial class were Clostridia, Bacteroidia, Tissierella, and Betaproteobacteria.

This study employed mixed-culture consolidated bioprocessing (CBP) to digest microalgal biomass in an anaerobic sequencing batch reactor (ASBR). The primary objectives are to evaluate the impact of hydraulic residence time (HRT) on the productivity of carboxylic acids and to characterize the bacterial community. HRT affects the production rate and patterns of carboxylic acids. For the 5-L laboratory-scale fermentation, a 12-day HRT was selected because it offered the highest productivity of carboxylic acids and it synthesized longer chains. The variability of the bacterial community increased with longer HRT (R2 = 0.85). In the 5-L laboratory-scale fermentor, the most common phyla were Firmicutes (58.3%), Bacteroidetes (27.4%), and Proteobacteria (11.9%). The dominant bacterial classes were Clostridia (29.8%), Bacteroidia (27.4%), Tissierella (26.2%), and Betaproteobacteria (8.9%).