Seaweed Biofuel Derived from Integrated Multi-trophic Aquaculture

Inclusion of Saccharina latissima in conventional anaerobic digestion systems

Loading macroalgae into existing anaerobic digestion (AD) plants allows us to overcome challenges such as low digestion efficiencies, trace elements limitation, excessive salinity levels and accumulation of volatile fatty acids (VFAs), observed while digesting algae as a single substrate. In this work, the co-digestion of the brown macroalgae Saccharina latissima with mixed municipal wastewater sludge (WWS) was investigated in mesophilic and thermophilic conditions. The hydraulic retention time (HRT) and the organic loading rate (OLR) were fixed at 19 days and 2.1 g l^-1 d^-1 of volatile solids (VS), respectively. Initially, WWS was digested alone. Subsequently, a percentage of the total OLR (20%, 50% and finally 80%) was replaced by S. latissima biomass. Optimal digestion conditions were observed at medium-low algae loading (≤50% of total OLR) with an average methane yield close to [Formula: see text] and [Formula: see text] in mesophilic and thermophilic conditions, respectively. The conductivity values increased with the algae loading without inhibiting the digestion process. The viscosities of the reactor sludges revealed decreasing values with reduced WWS loading at both temperatures, enhancing mixing properties.

Cascading biomethane energy systems for sustainable green gas production in a circular economy

Biomethane is a flexible energy vector that can be used as a renewable fuel for both the heat and transport sectors. Recent EU legislation encourages the production and use of advanced, third generation biofuels with improved sustainability for future energy systems. The integration of technologies such as anaerobic digestion, gasification, and power to gas, along with advanced feedstocks such as algae will be at the forefront in meeting future sustainability criteria and achieving a green gas supply for the gas grid. This paper explores the relevant pathways in which an integrated biomethane industry could potentially materialise and identifies and discusses the latest biotechnological advances in the production of renewable gas. Three scenarios of cascading biomethane systems are developed.

Biogas production generated through continuous digestion of natural and cultivated seaweeds with dairy slurry

The technical feasibility of long term anaerobic mono-digestion of two brown seaweeds, and co-digestion of both seaweeds with dairy slurry was investigated whilst increasing the organic loading rate (OLR). One seaweed was natural (L. digitata); the second seaweed (S. Latissima) was cultivated. Higher proportions of L. digitata in co-digestion (66.6%) allowed the digester to operate more efficiently (OLR of 5kgVSm(-3)d(-1) achieving a specific methane yield (SMY) of 232LCH4kg(-1)VS) as compared to lower proportions (33.3%). Co-digestion of 66.6% cultivated S. latissima, with dairy slurry allowed a higher SMY of 252LCH4kg(-1)VS but at a lower OLR of 4kgVSm(-3)d(-1). Optimum conditions for mono-digestion of both seaweeds were effected at 4kgVSm(-3)d(-1). Chloride concentrations increased to high levels in the digestion of both seaweeds but were not detrimental to operation.