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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 exploration of this biomass for fuel could encourage its harvesting and control. Anaerobic digestion (AD) has been suggested as one of the most promising methods of exploiting algae for biofuel. The harvesting of S. muticum is seasonal; thus, there will be a need to preserve and store seaweed to supply a year-round anaerobic digestion process. Ensiling is widely used in terrestrial agriculture, but there has been little research on ensiling seaweed. The aims of this research were to: a) study the effect of ensiling on the biomethane potential of S. muticum, b) effect of size reduction prior to ensilage on leachate and other losses during ensiling and c) examine the mass balance and energy losses of ensiling S. muticum. 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 results in losses of salt from the biomass and the virtual total loss of organic sulphur. Size reduction of seaweed prior to ensilage reduced leachate and energy loss from the biomass. Ensiling had no significant effect on methane yield. However, methane yields from S. muticum are low ≤0.11 L CH4 g−1 volatile solid (VS) at ~25 % of the theoretical maximum. Further research is needed to establish the reasons for the recalcitrance of S. muticum, but the C:N ratio of S. muticum is low (8:1), and co-digestion with a low nitrogen content substrate such as crude glycerol may be a potential method of improving methane yield.
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Ensilage and anaerobic digestion of Sargassum muticum
John J. Milledge
1
&Patricia J. Harvey
1
Received: 12 November 2015 /Revised and accepted: 19 January 2016 /Published online: 19 February 2016
#Springer Science+Business Media Dordrecht 2016
Abstract The brown seaweed Sargassum muticum is an inva-
sive 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 exploration of this biomass for fuel
could encourage its harvesting and control. Anaerobic diges-
tion (AD) has been suggested as one of the most promising
methods of exploiting algae for biofuel. The harvesting of S.
muticum is seasonal; thus, there will be a need to preserve and
store seaweed to supply a year-round anaerobic digestion pro-
cess. Ensiling is widely used in terrestrial agriculture, but there
has been little research on ensiling seaweed. The aims of this
research were to: a) study the effect of ensiling on the
biomethane potential of S. muticum, b) effect of size reduction
prior to ensilage on leachate and other losses during ensiling
and c) examine the mass balance and energy losses of ensiling
S. muticum.Ensilingwasfoundtobeaneffective,lowenergy
loss method of preserving seaweed with energy loss from the
biomass due to ensiling <8 % of the higher heating value of
seaweed feedstock. Ensiling results in losses of salt from the
biomass and the virtual total loss of organic sulphur. Size re-
duction of seaweed prior to ensilage reduced leachate and en-
ergy loss from the biomass. Ensiling had no significant effect
on methane yield. However, methane yields from S. muticum
are low 0.11 L CH
4
g
1
volatile solid (VS) at ~25 % of the
theoretical maximum. Further research is needed to establish
the reasons for the recalcitrance of S. muticum, but the C:N ratio
of S. muticum is low (8:1), and co-digestion with a low nitrogen
content substrate such as crude glycerol may be a potential
method of improving methane yield.
Keywords Sargassum muticum .Phaeophyta .Anaerobic
digestion .Ensilage .Invasive species .Algae .Macroalgae .
Japanese wireweed
Introduction
The environmental and economic costs of biological invasions
of non-native species in the early part of the last decade were
estimated to be worth ~US$ 1.4 trillion year
1
, globally, equiv-
alent to 5 % of the world economy (Engelen and Santos 2009).
For comparison, the costs of non-native species to the economy
of Great Britain alone for 2010 was £ 1.7 billion year
1
with the
specific cost of invasive marine species to shipping and aqua-
culture estimated to be in excess of £ 40 million year
1
(Cook
et al. 2013).
Sargassum muticum, Japanese wireweed, is native to the
northwest Pacific region (Edwards et al. 2014). It appeared in
Europe in the early 1970s and is now found on shorelines from
Norway to Portugal (Engelen and Santos 2009;Milledgeetal.
2015a). Since its first recorded find in the UK, on the coast of
the Isle of Wight, it has spread along the south-coast and
around the British Isles (Davison 2009;Gibson2011). The
growth rate of S. muticum is generally considerably higher
than most UK seaweed species, being over ten times higher
than that of Ascophyllum nodosum (Davison 2009).
Sargassum muticum has been described as very invasive and
perhaps the most successfulinvasive species in the UK in
terms of its rate of spread (Davison 2009).
The UK has identified S. muticum as a species of high
priority under the EUs Water Framework Directive
*John J. Milledge
j.j.milledge@gre.ac.uk
1
Algae Biotechnology Research Group, School of Science, University
of Greenwich, Central Avenue, Chatham Maritime, Kent ME4 4TB,
UK
J Appl Phycol (2016) 28:30213030
DOI 10.1007/s10811-016-0804-9
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
... The process may be particularly suited for anaerobic digestion, as experiments on agricultural crops have shown that it is able to preserve the majority of the Bio-Methane Potential (BMP) value of the biomass for up to one year [25,26]. In addition, ensiling has been shown to reduce the salt and sulphur content of seaweed, which has been suggested to have a positive impact on methane yields [27]. The kelp species Saccharina latissima is the target of experimentation for ensiling macroalgae, due to its widespread geographical cultivation potential and high carbohydrate content [23,28]. ...
... Several studies have now been published on macroalgal ensilage [13,23,[27][28][29][30][31][32], however, to better understand the process and optimise preservation; data on the microbial and chemical compositional changes over yearlong ensilage are required. Yearlong ensilage is important to enable year-round biogas production by anaerobic digestion. ...
... Heat treatment has also been shown to be an effective method to increase the availability of the present sugars from kelps [49], allowing successful fermentation of S. latissima by LAB as a food product [32,49]. Other pretreatments have been applied, such as chopping (as applied in this study) or maceration to increase fermentation efficiency by increasing the surface area for degradation and improving the compaction of the biomass [27,58]. Other pretreatments include rapid wilting (24 h) or heat treatment prior to ensilage to increase the DM and digestible sugar content [23,32,59]. ...
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... Firstly, its high moisture content dictates dewatering prior to processing [15]. Although a range of thermal, chemical and mechanical drying methods have been explored, each suffer from significant limitations [16][17][18][19][20]and are adversely impacted by seasonal changes in composition [19]. Secondly, the relatively narrow seasonal harvesting window, especially in temperate regions, of late Spring to early Summer, significantly limits availability. ...
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... Therefore, until now there was no information on the volume of leachates produced by the degradation of Sargassum spp. Milledge and Harvey (2016) performed silage as a conservation technique for Sargassum muticum and reported a leachate generation of 7.8% (w/w) in 60-day lapse (Milledge and Harvey 2016). In a study of the effect of leachate on coral larvae, Antonio-Martínez et al. (2020) reported a leachate generation in 3.5 days using 0.4 × 0.4 × 1 m fiberglass tanks, giving a leachate volume of 6.6 L/kg Sargassum spp. ...
... Therefore, until now there was no information on the volume of leachates produced by the degradation of Sargassum spp. Milledge and Harvey (2016) performed silage as a conservation technique for Sargassum muticum and reported a leachate generation of 7.8% (w/w) in 60-day lapse (Milledge and Harvey 2016). In a study of the effect of leachate on coral larvae, Antonio-Martínez et al. (2020) reported a leachate generation in 3.5 days using 0.4 × 0.4 × 1 m fiberglass tanks, giving a leachate volume of 6.6 L/kg Sargassum spp. ...
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The Sargassum phenomenon is currently affecting the Caribbean in several ways; one of them is the increase of greenhouse gases due to the decomposition process of this macroalgae; these processes also produce large amounts of pollutant leachates, in which several microbial communities are involved. To understand these processes, we conducted a 150-day study on the Sargassum spp environmental degradation under outdoor conditions, during which leachates were collected at 0, 30, 90, and 150 days. Subsequently, a metagenomic study of the microorganisms found in the leachates was carried out, in which changes in the microbial community were observed over time. The results showed that anaerobic bacterial genera such as Thermofilum and Methanopyrus were predominant at the beginning of this study (0 and 30 days), degrading sugars of sulfur polymers such as fucoidan, but throughout the experiment, the microbial communities were changed also, with the genera Fischerella and Dolichospermum being the most predominant at days 90 and 150, respectively. A principal component analysis (PCA) indicated, with 94% variance, that genera were positively correlated at 30 and 90 days, but not with initial populations, indicating changes in community structure due to sargassum degradation were present. Finally, at 150 days, the leachate volume decreased by almost 50% and there was a higher abundance of the genera Desulfobacter and Dolichospemum. This is the first work carried out to understand the degradation of Sargassum spp, which will serve, together with other works, to understand and provide a solution to this serious environmental problem in the Caribbean.
... A high C/N ratio is considered one of the factors that most inhibits the AD process and consequently the yield of the process is low (Paul and Dutta 2018). The high ash content, in our sample equal to (53.16 ± 1.93) %, is also a factor limiting the yield of the AD process (Milledge and Harvey 2016). ...
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... The rate and stability of the anaerobic digestion process is significantly affected by the particle size and the choice of equipment used for the mechanical pretreatment of the biomass [14]. A study conducted on Sargassum muticum showed that the yields of methane increased by 54.5% when the biomass was chopped [15]. A study conducted on the macroalga Sargassum fulvellum shows that the production of methane increases by 52.34% on biomass with particle size of 75-850 µm compared to that with higher particle size (106 µm, 4.75 mm) [16]. ...
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... Therefore, to mitigate the damage and costs caused by sargassum infestation, different strategies have been developed for sargassum valorization. Among them are the extraction of alginates and fucoidans [8,9], bioconversion to ethanol and methane [1,10,11], and the incorporation into formulations of agricultural fertilizers [12][13][14][15] and livestock feed [16][17][18]. However, the quantity and composition of the sargassum arriving in the Mexican Caribbean present high seasonal variability, making its collection and viable disposal difficult [6]. ...
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