Bioconversion of algae to methane and subsequent utilization of digestate for algae cultivation: A closed loop bioenergy generation process

•A novel “closed loop process” for algae to biomethane production.•Algal biomethane production up to 317.31 ± 1.9 mL CH4 g−1 VS added.•Nutrient rich algal digestate recycled for biomass production.•Good growth and nutrient removal at 30% digestate concentration.•Significantly enhanced growth when diluted with rural sector wastewater.

The present investigation was targeted on anaerobic digestion of Chroococcus sp. and utilization of resultant “Liquid Digestate” for its further biomass production. The algal biomass has biomethane potential of 317.31 ± 1.9 mL CH4 g−1 VSfed. Regular process monitoring revealed that process was stable throughout the experiments. The “Liquid Digestate” was explored as nutrient supplement for further algal growth. Diluted “Liquid Digestate” (30% concentration) was found optimal for algal growth (0.79 ± 0.064 g L−1). Simultaneously, 69.99–89.31% removal in nutrient and sCOD was also recorded with algal growth. Interestingly, higher growth was observed when rural sector wastewater (1.29 ± 0.067 g L−1) and BG11 broth (1.42 ± 0.102 g L−1) was used for diluting the “Liquid Digestate”. The current findings have practically proven the feasibility of hypothesized “closed loop process”.

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