Enhanced methane production from microalgal biomass by anaerobic bio-pretreatment

• A novel anaerobic bio-pretreatment was built up for enhancing methane production.
• The bacteria Bacillus licheniformis effectively improved SCOD.
• Large amounts of VFAs especially acetic acid were produced in pretreatment.
• The methane production from Chlorella sp. increased by 22.7% in the following AD.

Anaerobic digestion (AD) of microalgal biomass is one of the most energy efficient technologies to convert microalgae to biofuels. In order to improve the biogas productivity, breaking up the tough and rigid cell wall of microalgae by pretreatment is necessary. In this work, Bacillus licheniformis, a facultative anaerobic bacterial with hydrolytic and acidogenic activities, was adopted to pretreat Chlorella sp. In the established pretreatment process, pure bacterial culture (0%, 1%, 2%, 4%, 8%, v/v) were used to pretreat Chlorella sp. under anaerobic condition at 37 °C for 60 h. The soluble chemical oxygen demands (SCOD) content was increased by 16.4–43.4%, while volatile fatty acids (VFAs) were improved by 17.3–44.2%. Furthermore, enhancement of methane production (9.2–22.7%) was also observed in subsequent AD. The results indicated that the more dosages of bacteria were used to pretreat the microalgal biomass in the range of 1–8%, the more methane was produced.