Effect of thermochemical pretreatment on the solubilization and anaerobic biodegradability of the red macroalga Palmaria palmata

• With a methane potential of 308 ± 9 mL gVS−1, Palmaria palmata revealed to be attractive for biogas production.
• Palmate methane potential decreased after high temperature treatment (180–200 °C).
• Alkali pretreatments at room and low temperature (70–85 °C) enhanced the methane production of 11–13%.

The rapid development of anaerobic digestion brought with it the problem of biomass resources and supply. Marine biomass is emerging as an advantageous substrate. Such macroalgae as Palmaria palmata are promising substrates for anaerobic digestion as they possess a high methane potential (308 ± 9 mL gVS−1). The aim of this paper was to study the efficiency of the anaerobic digestion of P. palmata after a range of thermal and chemical pretreatment. The anaerobic digestion of raw and pretreated macroalgae was carried out in batch mesophilic biomethane potential tests (BMP). Thermal (between 20 and 200 °C) and thermo-chemical (addition of NaOH and HCl) pretreatment were performed on P. palmata. Thermal pretreatments at 20, 70, 85 and 120 °C and acid or soda pretreatments at 160 °C had no significant effect on P. palmata's methane potential. After high temperature pretreatment (180–200 °C), the BMP decreased with the temperature which can be explained by the formation of refractory compounds in the liquid fraction. In contrast, the addition of 0.04 gNaOH gTS−1 at 20 °C led to a release of proteins and induced an increase in the BMP from 308 ± 9 mL gVS−1 (untreated) to 365 ± 9 mL gVS−1. Thus, P. palmata can be used advantageously as a substrate for anaerobic digestion and its methane production enhanced by the addition of NaOH.