Influence of enzymatic hydrolysis on the biochemical methane potential ofChlorella vulgarisandScenedesmussp.

Abstract

BACKGROUND The hard cell wall of some microalgae hampers efficient methane production when using those substrates. The present study investigated the effect of two groups of biocatalysts, namely carbohydrases and proteases, applied to Chlorella vulgaris and Scenedesmus sp. for microalgae hydrolysis prior to anaerobic digestion. RESULTS Chlorella vulgaris subjected to protease activity resulted in higher organic matter solubilisation (47%) than the carbohydrase treated samples (25–29%). Out of the carbohydrases tested, maximum carbohydrate solubilisation was reached by applying Viscozyme (84% for C. vulgaris and 36% for Scenedesmus sp.). The anaerobic digestion assays revealed that biomasses hydrolyzed with protease reached the highest methane yield. In spite of the different macromolecular composition and behavior towards the biocatalysts, protease hydrolysis before anaerobic digestion enhanced methane yield 1.72-fold and 1.53-fold for C. vulgaris and Scenedesmus sp., respectively. CONCLUSION Despite the common belief that carbohydrates are responsible for the low digestibility of microalgae, this study suggested that proteins were the main polymers hampering anaerobic digestion. The addition of enzymes to enhance anaerobic digestibility could be questionable economically-wise, however this investigation gives crucial information to elucidate the polymeric composition of two of the most common microalgae, C. vulgaris and Scenedesmus sp. © 2015 Society of Chemical Industry