Development of separation and recovery technology of cultured Euglena gracilis using activated sludge for anaerobic digestion

Abstract

The combination of microalgae cultivation and anaerobic co-digestion of sewage sludge and microalgae is a promising system for increased energy efficiency in sewage treatment plants. This study proposed an innovative separation and recovery technology for microalgae from liquid media after culturing using combined heating and co-sedimentation with activated sludge. Sedimentation and anaerobic digestion experiments were conducted using Euglena gracilis cultures and activated sludge. Combining heating at 40 °C and co-sedimentation resulted in a maximum recovery of 92 %. Activated sludge adsorbed E. gracilis at a ratio of 0.644 μg-Chl. a/mg-MLSS. In anaerobic digestion experiments, no adverse effects such as fermentation inhibition were caused by mixing the activated sludge and E. gracilis. Total energy balance was evaluated assuming a sewage treatment plant with a capacity of 50,000 m3/day. The proposed system is shown to be energy efficient, and increase methane recovery by 24 %.