Assessment of Chlorella sp. as a potential feedstock for biological methane production

Microalgal biomass sequestrates CO₂ and is regarded as a promising renewable feedstock for anaerobic digestion because of its adequate carbohydrate content and lignin-free structure. This study optimizes the dilute-acid pretreatment of Chlorella sp. and subsequent biomethane production using response surface methodology and central composite design with temperature, pretreatment time and solid-to-liquid ratio as variables. A temperature of 64.1 °C, pretreatment time of 1.2 h, and a solid to liquid ratio of 0.29 were the optimal pretreatment conditions and resulted in a methane yield of 302.22 mL CH₄/g COD and methane production rate of 110.04 mL CH₄/g VSS-d. The severity factor of 1.5-1.6 was adequate to render the Chlorella sp. bioavailable for high methane recovery. The results obtained from the experiments conformed to those predicted by the model. This study effectively utilizes algal biomass for biomethane production and enables the possibility of scaled-up studies using a closed-loop approach.