Biomethane production from anaerobic digestion of microalgae in saltwater

 Authors: Cara Fiore1, Bronson Brown1, Mark Venable1, Michael Hambourger2 

Affiliations: 1Biology Department, Appalachian State University, North Carolina, USA 

2Chemistry and Fermentation Sciences Department, Appalachian State University, North Carolina, USA 

Abstract: Anaerobic fermentation of algae is of interest for the production of biogas and natural products; however, the most common strategy requires freshwater and may incur a high freshwater footprint. Here we examined biomethane production from the anaerobic digestion of the microalgae Chlorella sp. or Nannochloropsis sp. in saltwater and attempted to adapt the initial inoculum, derived from a compost facility, to high salt conditions. Cumulative methane production was highest in the no salt or low salt (0.5% - 1.5% salt, 256 - 318 g CH4 gVS-1) digestions compared to those with high salt concentration (3.5% digestions, 101 - 128 g CH4 gVS-1). The microbial community of the digestions was also assessed at the start and end of each digestion run using 16S rRNA gene profiling. The methanogenic archaea were primarily of the genus Methanosarcinia and were variable but lower in relative abundance in the high salt digestions compared to low salt. Differential abundance analysis between low salt (0 – 1.5%) and high salt (3.5%) conditions yielded twelve significant taxa, including Anaerosalibacter that was higher in the high salt digestions, and taxa such as MBA03 (Candidatus Darwinibacteriales), which may contribute to methane production, and Syntrophomonodaceae that were higher in relative abundance in the low salt digestions. These data provide a foundation for future work to optimize biomethane production from the digestion of marine microalgae.