Renewable energy: evaluation of low energy demand pre‐treatments to optimise methane production from microalgae.

Anaerobic digestion (AD) of microalgae is a sustainable process to produce methane‐rich biogas for bioenergy production. However, the rigid cell walls of microalgae protect them against the attack from hydrolytic bacteria, and consequently prevent efficient biodegradability and lower methane production. In this study, the effects of low energy demand enzymatic and low‐temperature thermo‐alkaline pre‐treatments on microalgae AD were investigated in batch biochemical methane potential tests. The results found that methane yields were significantly enhanced by both pre‐treatments. Microalgae Chlorella vulgaris (C. vulgaris) after enzymatic pre‐treatment enhanced methane yields the most, by 22–162%, whilst C. vulgaris pre‐treated by thermo‐alkaline pre‐treatment improved methane yields by 4–26%. In enzymatic pre‐treatment, C. vulgaris pre‐treated with mixed enzymes showed higher methane yields compared to single enzymes. In low‐temperature thermo‐alkaline pre‐treatment, the level of enhancement in methane yields depended on the alkaline dosage and pre‐treatment temperature, but the high alkaline dosages were associated with limitations such as a prolonged lag phase in the digestion process. From an energy viewpoint, both pre‐treatments showed positive energy balances for the majority of experimental conditions, and therefore both pre‐treatments are considered to be energetically efficient methods to pre‐treat microalgae for methane production via AD. [ABSTRACT FROM AUTHOR]