Enhancement of biogas production from microalgal biomass through cellulolytic bacterial pretreatment

•Microalgal biomass pretreatment by bacteria enhances liquefaction of about 18%.•Bacterial pretreatment increases the macromolecular release considerably.•Experimental microalgae improves the methane to 0.08 gCOD/gCOD comparing to control.•Methane production rate increased with hydrolysis constant of about 0.24 day−1.•A positive energy ratio of about 1.04 was achieved in experimental microalgae.

Generation of bioenergy from microalgal biomass has been a focus of interest in recent years. The recalcitrant nature of microalgal biomass owing to its high cellulose content limits methane generation. Thus, the present study investigates the effect of bacterial-based biological pretreatment on liquefaction of the microalga Chlorella vulgaris prior to anaerobic biodegradation to gain insights into energy efficient biomethanation. Liquefaction of microalgae resulted in a higher biomass stress index of about 18% in the experimental (pretreated with cellulose-secreting bacteria) vs. 11.8% in the control (non-pretreated) group. Mathematical modelling of the biomethanation studies implied that bacterial pretreatment had a greater influence on sustainable methane recovery, with a methane yield of about 0.08 (g Chemical Oxygen Demand/g Chemical Oxygen Demand), than did control pretreatment, with a yield of 0.04 (g Chemical Oxygen Demand/g Chemical Oxygen Demand). Energetic analysis of the proposed method of pretreatment showed a positive energy ratio of 1.04.

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