Methane production from Sargassum muticum (Ochrophyta, Phaeophyceae): Modeling by experimental design methodology of the influence of size and inoculum/substrate ratio

Abstract

Marine macroalgae are present in the ocean and more particularly in the coastal zone. Their distribution is related to biotic and abiotic factors. Considered as sustainable raw materials for a wide range of value-added products and energy production, they are valued in the fields of human and plant health, agriculture, food or construction (Baghel et al., 2020). Since 2011, large rafts of brown algae of the genus Sargassum have been observed, causing strandings in West Africa, throughout the Caribbean basin and the Gulf of Mexico. These include the species S. fluitans and S. natans. Faced with this recurring phenomenon of massive seaweed strandings, the French State has made a strong commitment to the fight against these phenomena: after a first crisis management plan in 2018, a second plan (2022-2025) was deployed with a view in particular to better prevention, health monitoring and the recovery of collected algae. In Guadeloupe, there are still around 116,000 m3 of sargassum stranded each year (ADEME in Guadeloupe, 2018). At present, valorization, which is very partial (90% of the algae collected is stored without use), is mainly done by composting or manufacturing biomaterials. This untapped biomass could be valorized in the energy sector by Anaerobic Digestion (AD) for the production of a gas rich in methane (anr.fr/Projet-ANR-19-SARG-0009 “Valorisation agro-énergétique des Sargasses – SAVE”). The objective of this study is to perform AD experiments with S. muticum as a substrate, a brown alga with characteristics similar to the previously mentioned stranded species, in order to assess their Bio-Methanogenic Potential (BMP), define the experimental conditions of AD, and to propose, in the long term, an energy recovery of the co-products resulting from the biorefining of seaweed stranded or harvested at sea.