Effect of pretreatments on biogas production from microalgae biomass grown in pig manure treatment plants

• Published in: Bioresource technology 2018-06, Vol.257, p.30-38
• Main Authors: Martín Juárez, Judit, Riol Pastor, Elena, Fernández Sevilla, José M., Muñoz Torre, Raúl, García-Encina, Pedro A., Bolado Rodríguez, Silvia
• Format: Article
• Language: English
• Subjects: Anaerobic digestion; Fertilizer; Inhibition; Kinetic model; Methane
• ISSN: 0960-8524; 1873-2976
• DOI: 10.1016/j.biortech.2018.02.063

•Pretreatments solubilised volatile solids but also inhibited biogas production.•Alkali pretreatment increased 2.3 times the methane production of the raw material.•The removal of pretreated liquids did not improve the global methane production.•Gompertz model fitted the results of methane production controlled by inhibition.•Composition of digestates allows their possible valorisation as fertilizers. Methane production from pretreated and raw mixed microalgae biomass grown in pig manure was evaluated. Acid and basic pretreatments provided the highest volatile solids solubilisation (up to 81%) followed by alkaline-peroxide and ultrasounds (23%). Bead milling and steam explosion remarkably increased the methane production rate, although the highest yield (377 mL CH4/g SV) was achieved by alkali pretreatment. Nevertheless, some pretreatments inhibited biogas production and resulted in lag phases of 7–9 days. Hence, experiments using only the pretreated solid phase were performed, which resulted in a decrease in the lag phase to 2–3 days for the alkali pretreatment and slightly increased biomass biodegradability of few samples. The limiting step during the BMP test (hydrolysis or microbial inhibition) for each pretreatment was elucidated using the goodness of fitting to a first order or a Gompertz model. Finally, the use of digestate as biofertilizer was evaluated applying a biorefinery concept.