Anaerobic digestion of laminaria digitata: The effect of temperature on biogas production and composition

Seaweed biomass has emerged as an alternative for the production of renewable fuels such as biogas from anaerobic digestion (AD). In relation to the biogas production rate, digester temperature setting is one of the most critical factors for an economically viable digester operation, especially in temperate countries like Ireland, as most annual temperatures are below the mesophilic range. In this study, the effect of digester temperature on biogas and methane production efficiency during the AD of Laminaria digitata was evaluated. 120 ml batch reactors were incubated at 20, 35 and 45°C for 54 days to determine a temperature profile for the AD process. Reactors incubated at 35°C produced the highest biogas and methane yields (336 ml biogas/g VS and 184 ml methane/g VS). Thermophilic reactors (45°C) produced 30% less biogas and 23.3% less methane, followed by psychrophilic reactors (20°C) which produced 41% less biogas and 39.7% less methane. A drop in pH in the mesophilic and thermophilic reactors was identified as an inhibitory factor during the first days of digestion. Psychrophilic reactors were better able to withstand the observed changes. Mesophilic temperatures will be used in further studies to examine scaling up of the process.