Anaerobic Digestion Under Alkaline Conditions from Thermochemical Pretreated Microalgal Biomass

Microalgae biomass can be a feedstock for anaerobic digestion, but the recalcitrance of the cell wall limits fully exploiting this source of organic matter. Alkaline pretreatments modify the structure of the cell wall facilitating bacterial attack and solubilizing the organic matter content. It is unknown whether alkaline hydrogen peroxide can help to improve biogas production from microalgae biomass compared to other alkaline pretreatments. This work focused on methane production at alkaline conditions (pH 9) with pretreated microalgal biomass (Scenedesmus obtusiusculus). Alkaline hydrogen peroxide (AHP) was used for the thermo-alkaline pretreatment and compared with pretreatments using NaOH or CaO. The pretreatment with 15% CaO solubilized the highest carbohydrates (22.1%) and proteins (18.3%), while the microalgal biomass pretreated with 4 M NaOH or 1.5% AHP attained the highest yields of methane (227.1 mL and 208.4 mL CH4/g VS, respectively), improving the methane potential between 34 and 46%, and producing biogas with methane content up to 91%. A preliminary techno-economic and energy analysis showed energy savings of 40% with 4 M NaOH and 31% with 1.5% AHP; therefore, AHP could be considered a suitable option for the pretreatment of microalgal biomass.