Anaerobic co-digestion of microalgae Scenedesmus sp. and Opuntia maxima

Resumen

Microalgae are being studied worldwide as biomass source for energetic purposes due to their high productivity. The aim of this study was to evaluate the application of anaerobic digestion to Scenedesmus sp. microalgal biomass as single substrate and in co-digestion with cladodes of Opuntia maxima to increase C/N ratio. Batch assays were conducted to evaluate possible synergistic effects and to determine the best mix ratio. The mixture with highest methane productivity was digested in semi-continuous mode at 6%VS concentration to study possible inhibition processes. Mixture composed of 75% Opuntia maxima and 25% Scenedesmus sp. (VS basis), with a C/N ratio of 15.6, had the highest methane yield (233.6±16.4 L CH4 kgVS-1), increasing 66.4% that of Scenedesmus biomass digested alone. In semi-continuos mode the highest methane yield obtained was 0.291±0.018 L CH4 gVS-1 at an organic loading rate of 4 gVS L-1d-1 and an hydraulic retention time of 15 days. The addition of Opuntia maxima to Scenedesmus sp. biomass enhanced the anaerobic digestion process and avoided inhibition related to low C/N ratio of substrates.