Use of microalgae residues for biogas production

•Scenedesmus residues were successfully converted to methane.•Extraction methods enhanced biodegradability and methane production.•Highest methane production was obtained from amino acid-extracted biomass.•Kinetics of the process was improved by co-digestion.

In biorefineries, the extraction of metabolites from microalgae would produce great amount of organic residues that would need to be treated. In this work, Scenedesmus residues were evaluated as substrates for biogas production and compared to raw biomass (SB). Microalgae residues were generated after the extraction of amino acids (SRA) and lipids (SRL). The influence of the processes applied on physicochemical properties and anaerobic biodegradability of microalgal biomass was studied in batch digestion tests. Co-digestion of microalgae residues with carbon rich substrates was also assessed by studying synergisms and kinetics of the discontinuous process. Methane yields of SRA and SRL in mono-digestion were 272.8 ± 7.3 LCH4 kgVS−1 and 212.3 ± 5.6 LCH4 kgVS−1, respectively, increasing that of SB (140.3 ± 29.4 LCH4 kgVS−1). Kinetics of the process was also improved after the extraction of amino acids and lipids. Improvements were attributed to the disruption of microalgae cell walls and the increase in the solubilization of the organic matter. The amino acid extraction process improved the digestion process in a higher extent than lipid extraction because of its higher hydrolytic effect on biomass. Co-digestion influence on methane yield depended on the co-substrates used. However, co-digestion improved kinetics of the process.