Optimizing biomethane production from anaerobic degradation of Scenedesmus spp. biomass harvested from algae-based swine digestate treatment

• Phycoremediation of swine digestate produces microalgae with high protein and low lipid.
• N- and P-starved microalgae have more carbohydrate and lipid contents.
• Digestion of microalgae polyculture produces 320–389 LN CH4 (kgVS)−1.
• Integration of biomethane production with microalgae-based digestate treatment.

The objective of this work was to quantify biomethane from anaerobic degradation of microalgae biomass harvested from a field-scale tank reactor simulating phycoremediation of swine wastewater. The effects of nutrients starvation on microalgae chemical cellular composition changes and its influence on biomethane generation potential were also addressed. Microalgae polyculture was dominated by uncultured Scenedesmus clone BF 063 which showed a carbohydrate, protein and lipid content of 27.6 ± 3.3, 57.6 ± 0.1 and 3.9 ± 0.6%, respectively. After 25 days exposed to N- and P-free medium, microalgae biomass composition showed 54.6 ± 2.6, 24.1 ± 2.4 and 16.9 ± 0.8% of carbohydrate, protein and lipid, respectively. Volatile solids concentration in the biomass harvested from N- and P-rich medium was lower [67 ± 1.7 g VS (kg biomass)−1] than biomass harvested from nutrient depleted medium [204.1 ± 3.1 g VS (kg biomass)−1]. Consequently, much higher biomethane production was obtained i.e., 103.5 LN CH4 (kg biomass)−1 vs 44 LN CH4 (kg biomass)−1. The results suggest that biomethane production in digesters could be improved by integrating microalgae biomass harvested from algae-based swine wastewater digestate treatment.