PUNTO DE PARTIDA

U. lactuca is detrimental to the amenity of a bay. This paper indicates that it is a viable source of third generation gaseous biofuel. Three pre-treatments were undertaken to assess the best method of optimising digestion. A combination of washing and drying yielded the best BMP result. A yield of 250 L CH4 kg−1 VS was achieved which is equivalent

to 100 m3 CH4t-1 of substrate. This is significant. Digestion of sea lettuce can be problematic

due to the low C:N ratio. Co-digestion of fresh and dried U. lactuca with dairy slurry was assessed at various ratios. The slurry had a C:N ratio of 20. In all cases synergistic effects were noted. For example co-digestion of fresh U. lactuca and dairy slurry (75% VS in U. lactuca: 25% VS in slurry) resulted in 17% more biomethane than the sum of mono- digestion of the substrates.

Acknowledgments

This paper is based on a paper presented at the Fourth International Symposium on Energy from Biomass and Waste, Venice 2012.

The research was funded by Science Foundation Ireland (SFI), The Irish Research Council and Bord Gais Eireann (BGE).

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7 Investigation of the optimal percentage of green seaweed that may

be co-digested with dairy slurry to produce gaseous biofuel

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Investigation of the optimal percentage of green seaweed that may be co-digested with dairy slurry to produce gaseous biofuel

Eoin Allen ab_{, David M. Wall} ab_{, Christiane Herrmann} ab_{, Jerry D. Murphy,} ab

a _{Environmental Research Institute, University College Cork, Lee Road, Cork, Ireland}

b

School of Engineering, University College Cork, Cork, Ireland

Abstract

U. lactuca lactuca, a green seaweed, accumulates on beaches and shallow estuaries subject to eutrophication. As a residue, and macro-algae, it is a source of sustainable third

generation biofuel. Production of biomethane from mono-digestion of U. lactuca, however is problematic due to high levels of sulphur and low ratios of carbon to nitrogen. Fresh and dried U. lactuca were continuously co-digested with dairy slurry at ratios of 25%, 50% and 75% (by volatile solid content) in 6 number 5L reactors for 9 months. The reactors digesting a mix with 75% U. lactuca struggled to reach sustainable operating conditions. Failure was dominated by volatile fatty acid inhibition. The levels of ammonia increased with

percentage U. lactuca in the mix. Optimum conditions were observed with a mix of 25% fresh U. lactuca and 75% slurry. A yield of 170 L CH4 kg−1 VS was achieved at an organic

loading rate of 2.5 kg VS m-3 _d-1_.

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