From seaweed to safe digestate: integrating anaerobic digestion and genotoxicity assessment to evaluate digestate quality as an agricultural substrate

Abstract

Seaweed is a valuable feedstock for anaerobic digestion, yet integrated evaluation of methane production and digestate quality across multiple species remains limited in Morocco. This study presents the first assessment of biogas production and the biostimulant potential of digestate derived from seaweed collected from the southern coast of Morocco. Anaerobic digestion was optimized at an organic loading rate of 8 g VS/L and substrate to inoculum ratio of 1:2, yielding a maximum biomethane potential of 171.18 ± 12.74 Nml CH 4 /g VS. Under these conditions, 11 seaweed species were used, with C. galeatum (116.85 ± 14.67 Nml CH 4 /g VS) exhibiting the highest methane yield followed by N. larix (102.09 ± 7.05 Nml CH 4 /g VS). Digestate bioassays showed that P. cartilagineum and S. muticum significantly enhanced seed germination index, while all digestates displayed low genotoxicity effects, making them safe for agricultural use. Overall, these findings indicate that seaweed can be effectively valorized for both methane and high value digestate production in Morocco.