Methane production from the microalga Scenedesmus sp. AMDD in a continuous anaerobic reactor

Methane production from the microalga Scenedesmus sp. AMDD digested in a continuously operated anaerobic reactor was studied under a range of conditions. Preliminary anaerobic toxicity assays revealed that methane yields and glucose consumption were inhibited by algae/sludge ratios in excess of 0.1 (g/g). Continuous digestions of microalgae at two hydraulic retention times (16 and 58 days) and two influent concentrations of algal feed (11 and 20 gTVS L− 1) were evaluated. Based on the amount of degraded algal biomass, a methane yield of 0.4 LCH4 gTVS‐ 1 was estimated. However, at a hydraulic retention time of 16 days only 52-53% of the algal biomass was degraded, primarily due to the limited hydrolysis of the algal cellular material. An increase of retention time to 58 days did not improve the degradation efficiency. Anaerobic decomposition of microalgae biomass appeared to affect composition of the microbial consortium in the digester, promoting the growth of sulfate-reducing bacteria leading to high levels of H2S in the biogas.