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 5 kg VS m⁻³ d⁻¹ achieving a specific methane yield (SMY) of 232 L CH₄ kg⁻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 252 L CH₄ kg⁻¹ VS but at a lower OLR of 4 kg VS m⁻³ d⁻¹. Optimum conditions for mono-digestion of both seaweeds were effected at 4 kg VS m⁻³ d⁻¹. Chloride concentrations increased to high levels in the digestion of both seaweeds but were not detrimental to operation.