Abstract
The Turks and Caicos Islands (TCI) have been affected by sargassum inundations, with impacts on the economy and environment. Sargassum removal can be costly, but sargassum use and valorisation may generate income and offset environmental damage. A significant barrier to the valorisation of sargassum is insufficient knowledge of its chemical makeup, as well as its seasonal variation and decay after stranding. The chemical characterisation of mixed sargassum and its constituent species and morphotypes (S. natans I, S.natans VIII and S. fluitans) collected from TCI between September 2020 and May 2021 and changes in the composition of sargassum decaying (over 147 days) were studied. High ash (24.61–51.10% dry weight (DW)) and arsenic (49–217 mg kg−1) could severely hamper the use of this seaweed for food or feed purposes. Although there was some reduction in arsenic levels in decaying sargassum, levels remained high (>49 mg kg−1). Biomethane production by anaerobic digestion (AD) is a potential option. Nevertheless, the exploitation of sargassum for biogas, either fresh or as it decays on the beach, is challenging due to low methane yields (<42% of theoretical potential). Pre-treatment or co-digestion with other waste may be options to improve yield. The metal sorption ability of sargassum, which can be problematic, makes biosorption of pollutants an option for further research.
Highlights
Holopelagic sargassum, consisting of the species Sargassum fluitans and S. natans, floating in the open ocean is of extreme ecological importance [1,2,3,4]
High ash content compared to most vegetables resulting from the seawater environment and the ability of seaweed to passively and actively take up heavy metals [37] could hamper the use of sargassum in food and feed applications
High ash content is a significant challenge for seaweed biorefineries, but the build-up of salts in an anaerobic digester can inhibit microorganisms during anaerobic digestion, lowering methane yields [38].The carbon content increased in the Dec-Feb samples, which could indicate an accumulation of carbohydrate and lipid during this period
Summary
Holopelagic sargassum, consisting of the species Sargassum fluitans and S. natans, floating in the open ocean is of extreme ecological importance [1,2,3,4]. Beaches across the Caribbean and the Gulf of Mexico have experienced massive inundations of pelagic sargassum since 2011, known as ‘golden tides’, significantly impacting the environment and the local economies heavily dependent on tourism [5,7,8,9,10,11,12,13]. The breakdown of this material on the beach can lead to offensive odours and can harm human health [9,14,15,16,17]. Uses of this biomass are being sought in order to offset collection and disposal costs and the adverse effects of dumping in landfills [5,18]
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