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Grassland – a European Resource? 487
The biogas potential of Juncus effusus L. using solid phase fermentation technique
Müller J.1, Jantzen C. 1 and Kayser M.2
1
Working Group Landscape Ecology and Site Evaluation, Faculty of Agricultural and Envi-
ronmental Sciences, University of Rostock, Justus-von-Liebig-Weg 6, 18059 Rostock, Germany
2
Department of Crop Sciences, Institute of Grassland Science, University of Göttingen,
Von-Siebold-Strasse 8, D-37075 Göttingen, Location 49337 Vechta, Germany
Corresponding author: juergen.mueller3@uni-rostock.de
Abstract
Wet grassland sites are often infested with Juncus effusus L. (soft rush). A high coverage of
soft rush will lead to a restricted use in traditional animal-based farming systems. Therefore
alternative options of biomass use are required urgently. Biogas production using solid-phase
fermenters could be a promising alternative for the use of soft rush-infested swards. In our experi-
ment, we varied the amount of soft rush (100% Juncus; 50% Juncus + 50% grasses and herbs;
100% grasses and herbs) in the substrate and analysed the substrate compaction. We then de-
termined the methane production and a range of chemical and physical substrate parameters
before and after anaerobic digestion. Methane yields of Juncus (100%) were smaller than that
of the accompanying grassland vegetation. The methane yield of the grass-Juncus-mixture was
higher than expected from the energy content. We found that Juncus contributed to substrate
stability and presumably to gaseous diffusion of methane through the substrate stock.
Keywords: soft rush, biomass utilization, biogas, methane
Introduction
Wet grassland sites are often infested with soft rush (Juncus effusus L.) due to wetland
restoration measures (Nielsen and Hald, 2010). To sustain typical wet grassland vegetations
and to avoid further succession towards reeds and shrubs, a regular utilisation is necessary.
However, a high coverage of soft rush will lead to a limited biomass quality (Odeyinka
et al., 2006), with a restricted use in traditional animal-based farming systems (Cherrill,
1995). To maintain wet grasslands, alternative options of biomass use are required urgently.
Biomass use via methanogenesis for energetic purposes is often regarded as an option. Wet
fermentation plants are widespread, but not well suited to substrates rich in lignocellulos-
es. The solid phase fermentation technique (SPFT) is better adapted to high-fibre substrates
than common wet fermentation techniques. Therefore the aim of our investigations was to
study the capability of soft rush as a substrate for SPFT.
Materials and methods
The experiments on the methanogenesis potential of soft rush, that is the substrate performance
in an SPFT percolation process, were conducted in 10 laboratory-scale batch fermenters (120
l). The experimental set-up is given in Figure 1. We tested five substrates which originated from
peat grassland swards with high coverage of Juncus effusus (Table 1). Biomass was collected
from an autumn growth, chopped by hand to an average length of 5 cm and ensilaged in plastic
tubs. Material from each substrate was filled in two 120 l fermenters. The methanogenesis was
started by sprinkling process water over the stacked biomass. The temperature in the fermenter was
controlled and kept in the mesophilic range over the 60 d measuring period.
Each fermenter was percolated three times per day. The total volume of biogas produced
was measured daily by a drum-type gas meter.
488 Grassland Science in Europe, Vol. 17
Table 1. Substrate classification and composition (percentage of dry matter)
Location ID Grasses (%) Herbs (%) Soft rush (%) Classification
Emsland I 1 1 98 Juncus
Emsland II 40 10 50 Mix
Darß III 100 0 0 Grass
Darß IV 50 0 50 Mix
Darß V 0 0 100 Juncus
The biogas composition was analysed by infrared detection (Bernt DGA 3) for CH4, CO2,
and O2. Biogas and methane yields were converted to standard conditions (T = 273.15 K;
P = 101.325 kPa).
Results
Methane yields of Juncus were smaller than that of the accompanying grassland vegeta-
tion (Figure 2). Methane yield of the mixed substrate did not differ significantly from that
of either Grass extensive or Juncus, but was higher than expected from estimations based
on feed analysis according to Kaiser (2007).
The substrate compaction had an effect on feedstock specific biogas yield (Figure 3). With
increasing substrate compaction the biogas yield per unit of oDM of the Juncus substrates
declined (Figure 3a) while that of the mixed substrate increased (Figure 3b).
The Juncus substrate yielded lowest in methane, but production of biogas continued to the
end of the 60 d measuring period.
Figure 1. Experimental setup – schematic view of a single 120 l fermenter
Figure 2. Substrate specific methane
production in a solid phase fermenta-
tion process (retention time 60 days, er-
ror bars are the standard deviations and
different letters indicate significant dif-
ferences of the means (P < 0.05; T-test),
* = estimated methane yields according
to Kaiser, l
N
kg
–1
oDM
–1
= norm litre
per kg organic dry mass, reference sub-
strates “Grass intensive” and “Maize”
were frequently percolated)
Grassland – a European Resource? 489
Discussion and conclusions
The feedstock specific methane yields of silages from pure stands of Juncus were small-
er than those from pure grass stands, but still within a range of common late-cut biomass
from extensive grasslands (Prochnow et al., 2009). Juncus substrate in this experiment
was cut at a relatively late physiological stage. If young Juncus would be used and would
than be preconditioned and percolated more frequently there seems to be a realistic po-
tential of improved methane yields from Juncus dominated grassland swards. Moreover,
there seems to be a positive additional effect of Juncus as a component in a mixture with
grass dominated substrates. Ashekuzzaman and Poulsen (2010) have also shown that using
multi-component substrates increases the methane yield by more than would be expected
from the digestion of single substrates. We assume that in our experiments this was due to
the specific physical-structural properties of soft rush. A greater stability in the stack ac-
companies a higher percolate absorption ability. The gas exchange in the mixed-treatment
stacks might have been improved by the presence of tubular aerenchyma from the soft
rush particles. We conclude that biogas production using a solid-phase fermenter can be
a promising alternative for the use of soft rush infested swards once substrate conditioning
as well as the fermentation process management have been optimised.
References
Ashekuzzaman S.M. and Poulsen T.G. (2010) Optimizing feed composition for improved methane yield
during anaerobic digestion of cow manure based waste mixtures. Bioresource Technology 102(3), 2213–2218.
Cherrill A. (1995) Infestation of improved grasslands by Juncus effusus L. in the catchment of the River Tyne,
Northern England: a field survey. Grass and Forage Science 50, 85–91.
Kaiser F. (2007) Einfluss der stofflichen Zusammensetzung auf die Verdaulichkeit nachwachsender Rohstoffe
beim anaeroben Abbau in Biogasreaktoren. PhD thesis. Technical University of Munich, 176 pp.
Nielsen A.L. and Hald A.B. (2010) Shortcut strategies to improve plant species richness after years of
intensive management in moist grassland. Grassland Science in Europe 15, 1052–1054.
Odeyinka S.M., Hector B.L. and Ørskov E.R. (2006) Nutritive evaluation of some trees and browse species
from Scotland. European Journal of Scientific Research 14(3), 311–318.
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permanent grassland – a review: 1. Biogas. Bioresource Technology 100(21), 4931–4944.
Figure 3. The relationship between substrate compaction and biogas yield in SPFT (with trend line,
g DM l–1 = g of substrate dry mass per litre; lN g–1 oDM–1 = norm litre per g organic dry mass)
