Green energy from marine algae: biogas production and composition from the anaerobic digestion of Irish seaweed species

Abstract

Marine algae have emerged as an alternative feedstock for the production of a number of renewable fuels, including biogas. In addition to energy potential, other characteristics make them attractive as an energy source, including their ability to absorb carbon dioxide (CO2), higher productivity rates than land-based crops and the lack of water use or land competition. For Ireland, biofuels from marine algae can play an important role by reducing imports of fossil fuels as well as providing the necessary energy in rural communities. In this study, five potential seaweed species common in Irish waters, Saccorhiza polyschides, Ulva sp., Laminaria digitata, Fucus serratus and Saccharina latissima, were co-digested individually with bovine slurry. Batch reactors of 120 ml and 1000 ml were set up and incubated at 35°C to investigate their suitability for production of biogas. Digesters fed with S. latissima produced the maximum methane yield (335 ml g volatile solids−1 (gVS−1)) followed by S. polyschides with 255 ml gVS−1. L. digitata produced 246 ml gVS−1 and the lowest yields were from the green seaweed Ulva sp. 191 ml gVS−1. The methane and CO2 percentages ranged between 50–72% and 10–45%, respectively. The results demonstrated that the seaweed species investigated are good feedstocks candidates for the production of biogas and methane as a source of energy. Their use on a large-scale process will require further investigation to increase yields and reduce production costs.