Stimulating methane production from microalgae by alkaline pretreatment and co-digestion with sludge.

Methane production through anaerobic digestion (AD) is a solution of energy recovery from microalgae, but some features of microalgae limit the efficiency of AD. In this study, alkaline pretreatment and co-digestion with sludge were both applied to enhance the methane production from microalgae in batch experiments. The results showed that alkaline pretreatment increased the disintegration degree of microalgae from 20% to 34% at maximum after 12-h treatment, but the specific methane production (SMP) only increased from 279 to 298 ml/g volatile solids (VS). Co-digestion with sludge stimulated methane production, and the best synergy with an SMP of 343 ml/g VS occurred when the ratio of microalgae to sludge reached 2:1 based on their VS. The yield was 12.4% and 20.0% higher than those from mono digestion of microalgae and sludge, respectively, and the synergy was evaluated at 14.8%. Therefore, co-digestion is a better choice for improving methane production from microalgae.