Milledge, John J. ORCID: 0000-0003-0252-6711 , Nielsen, Birthe ORCID: 0000-0002-0849-4987 and Harvey, Patricia ORCID: 0000-0001-7193-4570 (2018) Sargassum – Menace, Methane, Mouth and More. In: 3rd Medway Engineering Conference, 20 June 2018, University of Greenwich, Medway Campus.

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Abstract

Despite 72% of the Earth’s surface being covered by oceans the area used for seaweed cultivation is relatively small compared to that of land crops. Although, global utilisation of marine algae has grown to a multibillion dollar industry, primarily for food and hydrocolloids, it is a relatively small part of the current blue economy with a limited number of products available. There is tremendous potential for further exploitation of seaweed for fuel, feed, biochemicals, nutraceuticals and pharmaceuticals.

The brown seaweed Sargassum muticum is an invasive species to the coasts of the British Isles, mainland Europe and North America. Attempts at its eradication and control have generally not been successful, although time-consuming and costly. Commercial exploitation of this biomass for food, fuel and pharmaceutical products could encourage its harvesting and control. Sargassum has a naturally high content of antioxidants, carotenoids and phenols, including the well-known anti-cancer compound fucoxanthin, making this species a potential source of a range of pharmaceutically relevant materials. Macroalgae may also be a potential source of fuel. This paper discusses the some of the recent research at the University of Greenwich on Sargassum and potential process hurdles to exploit it for both fuel and high value products, but focuses particular on the on pre-treatment, preservation and conversion of the wet biomass to biogas.

Anaerobic digestion (AD) is generally the process of choice for energy production from high water content biomass, and biogas produced from AD is being used to make the most of a number of biomass wastes by turning them into renewable energy. It is a safe and cost-effective way to dispose of unwanted organic waste, and for this reason, a favoured solution for industry and governments. However, practical yields of biogas from the anaerobic digestion of macroalgae are substantially below the theoretical maximum with Sargassum muticum yielding ~25 % of the theoretical maximum. Alginates are a major component of the cell-wall of brown algae, and alginic acid and its sodium salt were found to be recalcitrant with average methane yields of equivalent to only 23% - 28% of their theoretical methane potential. Methane yield was further reduced by the presence of high concentrations (7% of substrate equivalent to 17.5 mg L-1) of the phenolics, phloroglucinol, the basis of phlorotannins, the predominant polyphenol in many seaweeds, and epicatechin. Pre-treatment by washing S. muticum did not affect overall methane production during AD, but significantly slowed down the initial rate of biomethane production.

The harvesting of S. muticum is seasonal; thus, there will be a need to preserve and store seaweed to supply a year-round processes such as anaerobic digestion for biogas production. Ensiling is widely used in terrestrial agriculture to preserve fodder. In ensilage, lactic acid fermentation under anaerobic conditions converts water soluble carbohydrates into organic acids, mainly to lactic acid; the pH decreases and the moist crop is preserved.

Ensiling was found to be an effective, low energy loss method of preserving seaweed with energy loss from the biomass due to ensiling <8 % of the higher heating value of seaweed feedstock. Ensiling had no significant effect on methane yield from AD. Pre-treatment prior to ensilage can effect leachate losses; size reduction of seaweed prior to ensilage reduced leachate and energy loss from the biomass, but washing with freshwater increased leachate losses from ensiling.

Item Type:	Conference or Conference Paper (Speech)
Uncontrolled Keywords:	Seaweed; Algae; Sargassum muticum; Biofuel; Anaerobic Digestion; Ensilage
Subjects:	Q Science > QH Natural history > QH301 Biology
Faculty / School / Research Centre / Research Group:	Faculty of Engineering & Science Faculty of Engineering & Science > Algal Biotechnology Research Group Faculty of Education, Health & Human Sciences > School of Human Sciences (HUM)
Last Modified:	09 Oct 2021 04:45
URI:	http://gala.gre.ac.uk/id/eprint/20501

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