Anaerobic digestion of mixed microalgae cultivated in secondary effluent under mesophilic and thermophilic conditions

The anaerobic digestion of mixed indigenous microalgae, grown in a secondary effluent, was evaluated in batch tests at mesophilic (35°C) and thermophilic (50°C) conditions. Under mesophilic conditions, specific methane production varied from 178 to 207 mL CH₄/g volatile solids (VS) and the maximum production rate varied from 8.8 to 26.1 mL CH₄/(gVS day), depending on the type of microalgae culture. Lower methane parameters were observed in those cultures where Scenedesmus represents more than 95% of the microalge. The culture with the lowest digestion performances under mesophilic conditions was studied under thermophilic conditions. The increase in the incubation temperature significantly increased the specific methane production (390 mL CH₄/g VS) and rate (26.0 mL CH₄/(gVS day)). However, under thermophilic conditions a lag period of 30 days was observed.