In order to optimize the enzymatic dosage and microalgae biomass loads subjected to enzymatic hydrolysis prior anaerobic digestion of Chlorella vulgaris, organic matter solubilisation and methane production were investigated. Experimental data using protease dosage of 0.585 AU g DW-1 showed that increasing biomass loads up to 65 g L-1 did not affect markedly the hydrolysis efficiency (51%). Enzymatically pretreated biomasses subjected to anaerobic digestion enhanced methane production by 50-70%. The attempt of decreasing the enzymatic dosages revealed diminished hydrolysis efficiency concomitantly with a decreased methane production enhancement. In agreement with the good results observed for organic matter conversion into biogas, total nitrogen mineralization was attained for enzymatically pretreated biomass. Despite the high protein content of the biomass and the biocatalyst used in the present study no ammonia inhibition was detected. (C) 2014 Elsevier Ltd. All rights reserved.