Methane production from marine microalgae Isochrysis galbana

•Methane production from marine microalgae Isochrysis galbana was assessed.•Mechanical pretreatment resulted in a 61.7% increase in soluble COD.•Best hydrolysis condition was 40 °C/0.2% (v/v) acid/16 h (9.27 L CH4/kg VS).•Low methane yields were attributed to inhibitory sodium concentrations.•Biomass prewashing eliminated inhibitory sodium and increased methane yield in 71.5%.

Methane production from marine microalgae Isochrysis galbana was assessed before and after mechanical and chemical pretreatments. Mechanical pretreatment resulted in a 61.7% increase in soluble Chemical Oxygen Demand. Different hydrolysis conditions were evaluated by varying temperature – T, sulfuric acid concentration – AC and biomass suspension concentration (measured as particulate COD – CODp) using an experimental design. The most significant interaction occurred between AC and T and the hydrolysis condition that showed the best result in the anaerobic digestion step was the condition at 40 °C with addition of 0.2% (v/v) acid for 16 h (9.27 L CH4/kg VS). The low methane yields were attributed to inhibitory sodium concentrations for anaerobic digestion. Eliminating inhibitory sodium in the anaerobic digestion by biomass prewashing, there was a 71.5% increase in methane yield for biomass after acid hydrolysis, demonstrating the need for pretreatment and reduction in sodium concentration in the anaerobic digestion.

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