Ensilage and anaerobic digestion of Sargassum muticum
John J. Milledge
&Patricia J. Harvey
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
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
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 .
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
, 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
specific cost of invasive marine species to shipping and aqua-
culture estimated to be in excess of £ 40 million year
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 ‘successful’invasive 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 EU’s Water Framework Directive
*John J. Milledge
Algae Biotechnology Research Group, School of Science, University
of Greenwich, Central Avenue, Chatham Maritime, Kent ME4 4TB,
J Appl Phycol (2016) 28:3021–3030