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Methane emissions from the storage of liquid dairy manure: Influences
of season, temperature and storage duration
Aura Cárdenas
a
, Christian Ammon
a
, Britt Schumacher
b
, Walter Stinner
b
, Christiane Herrmann
a
,
Marcel Schneider
b
, Sören Weinrich
b
, Peter Fischer
b
, Thomas Amon
a,d
, Barbara Amon
a,c
a
Leibniz Institute for Agricultural Engineering and Bioeconomy (ATB), Potsdam, Germany
b
DBFZ Deutsches Biomasseforschungszentrum Gemeinnützige GmbH, Leipzig, Germany
c
University of Zielona Góra, Faculty of Civil Engineering, Architecture and Environmental Engineering, Poland
d
Freie Universität Berlin, Institut of Animal Hygiene and Environmental Health, Department of Veterinary Medicine, Berlin, Germany
article info
Article history:
Received 19 June 2020
Revised 17 December 2020
Accepted 18 December 2020
Keywords:
Methane emissions
GHG emissions
Cattle manure storage
Emissions reduction potential
Manure temperature
abstract
Methane emissions from livestock manure are primary contributors to GHG emissions from agriculture
and options for their mitigation must be found. This paper presents the results of a study on methane
emissions from stored liquid dairy cow manure during summer and winter storage periods. Manure from
the summer and winter season was stored under controlled conditions in barrels at ambient temperature
to simulate manure storage conditions. Methane emissions from the manure samples from the winter
season were measured in two time periods: 0 to 69 and 0 to 139 days. For the summer storage period,
the experiments covered four time periods: from 0 to 70, 0 to 138, 0 to 209, and 0 to 279 continuous days,
with probing every 10 weeks. Additionally, at the end of all storage experiments, samples were placed
into eudiometer batch digesters, and their methane emissions were measured at 20 °C for another 60 days
to investigate the potential effect of the aging of the liquid manure on its methane emissions. The exper-
iment showed that the methane emissions from manure stored in summer were considerably higher than
those from manure stored in winter. CH
4
production started after approximately one month, reaching
values of 0.061 kg CH
4
kg
1
Volatile Solid (VS) and achieving high total emissions of 0.148 kg CH
4
kg
1
VS (40 weeks). In winter, the highest emissions level was 0.0011 kg CH
4
kg
1
VS (20 weeks). The out-
comes of these experimental measurements can be used to suggest strategies for mitigating methane
emissions from manure storage.
Ó2020 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND
license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
1. Introduction
Climate change is the most important global challenge of our
era, and it is a reflection of anthropogenic processes, especially of
the increased emission of greenhouse gases (GHG) (Crowley,
2000). Considering the evidence that livestock and, in particular,
dairy production systems make an important contribution to
GHG emissions and to global warming mainly through the gener-
ation of methane (CH
4
), the transformation of our production sys-
tems has become a priority, with a particular focus on reducing
their GHG emissions (IPCC, 2001; Sommer et al., 2009; FAO,
2010; Wattiaux et al., 2019; Amon et al., 2020).
Livestock excreta constitute an important source of GHGs, espe-
cially CH
4
, which is the largest contributor to global warming from
the dairy sector and one of the most relevant gases, with an impact
28 times higher than that of carbon dioxide (CO
2
) over a hundred-
year period (IPCC, 2013). According to the EU annual GHG inven-
tory report from 2019, within EU28+ ISL, (28 EU- countries+ Ice-
land), manure management CH
4
emissions decreased
considerably, by 20% or 10.4 Mt CO
2
-eq, in the period 1990 to
2017; Germany was one of the countries with the largest decrease
in emissions mainly due to the decline in the number of animals in
the first half of the 1990s in eastern Germany. CH
4
emissions from
manure management depend on manure composition, storage
conditions and manure treatment. There is a wide range of vari-
ability in these factors, contributing to the amount of CH
4
from
manure stores including category and breed of animals, housing
system, manure removal system and method of manure treatment,
as well as the type and amount of feeding (Sommer et al., 2007;
Umweltbundesamt, 2014; Loyon et al., 2016; Purath et al., 2017;
Habtewold et al., 2018; Grossi et al., 2019).
The storage time on farms also depends on the land application
times, which depend on field crops, crop rotations, fertilizer
requirements and on the vegetation period. These factors
https://doi.org/10.1016/j.wasman.2020.12.026
0956-053X/Ó2020 The Author(s). Published by Elsevier Ltd.
This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Waste Management 121 (2021) 393–402
Contents lists available at ScienceDirect
Waste Management
journal homepage: www.elsevier.com/locate/wasman
determine the storage capacity required, resulting in on-farm
retention times of up to nine months. This stage of the manure
management process releases considerable amounts of CH
4
(Petersen et al., 2013; Purath et al., 2017; Petersen, 2018). Based
on the fact that dairy production residues are a crucial part of
the GHG emissions problem (FAO, 2010), effective treatment and
management options to reduce the emissions of these residues
would transform a problem into an opportunity by applying treat-
ment and management options to reduce emissions (Sommer
et al., 2013; Zucchella & Previtali, 2019; Treichel et al., 2020). To
improve the production chain and use all available resources
within the systems, the integration and application of new tech-
nologies such as manure treatment by means of anaerobic diges-
tion (AD) for biogas production is a valid option for reducing the
GHG footprint of farms (Rotz & Hafner, 2011).
It is well known that the temperature and storage time of liquid
manure play a decisive role in the production of CH
4
(Husted,
1994; Hill et al., 2001; Sommer et al., 2004, Sommer et al., 2007;
Baral et al., 2018). In the last 30 years, CH
4
-related studies have
focused on storage conditions, housing systems, manure mitiga-
tion and management strategies, CH
4
production and codigestion.
The target of research has turned to CH
4
emissions from manure
storage, with a special emphasis on the drivers of the emissions
process, including the effects of temperature and seasonal influ-
ences (Amon et al., 2001; Clemens et al., 2006; Elsgaard et al.,
2016; Masse et al., 2008; Petersen, 2018; Petersen et al., 2013;
Sommer et al., 2004; Moset et al., 2019; Rodhe and Ascue, 2009).
Baral et al. (2018) identified temperature and VS concentration
as the most relevant factors for CH
4
production but also stated that
additional factors such as the methanogenic potential during stor-
age must be considered. Additionally, Im et al. (2020) investigated
the effect of storage temperature on CH
4
emissions from cattle
manure stored at different temperatures (15–35 °C) for 80 d. Their
findings reveal that both variables are closely related, indicating
the highest CH
4
emissions at a storage temperature of 35 °C, while
emissions are decreased by almost half at temperatures of 20 °C.
The winter and summer time periods in the study presented in
this paper were chosen based on the typical manure spreading
times in arable regions in temperate climate zones. At the begin-
ning of the vegetation period, when soil moisture content allows
traffic with heavy machinery, manure is applied to grass, cereals
and rapeseed fields. Thus, at the beginning of spring, manure stores
are largely emptied. Dairy cattle farm crop rotations typically have
major portions of corn, as corn silage is an important part of animal
diets. As a consequence, in April and May (depending on the
region), a second phase of manure application is initiated when
the fields are prepared for corn seeding.
Even if the general influnce of temperature on CH
4
emissions is
known, an explanatory model for a better understanding of the
influence of season, temperature and storage duration on CH
4
for-
mation during liquid manure storage is still missing. For that rea-
son, the objective of the present study was to evaluate the dynamic
changes in CH
4
emissions from dairy cow liquid manure under
summer and winter conditions and to identify the threshold tem-
perature at which CH
4
production increases between the winter
and summer seasons. The following hypothesis was tested:
H1: Slurry stored under cool winter conditions has the same
methane production after temperature rise in summer as slurry
stored only under warm summer conditions.
2. Material and methods
2.1. Barn and manure sampling
Manure samples were collected at the experimental farm for
Animal Breeding and Husbandry, LVAT Groß Kreutz, Brandenburg,
Germany. Lactating German Holstein-Friesian dairy cows were fed
maize and grass silage, hay and concentrates. The housing was a
free-stall dairy barn with 1/3 slatted-floor, 2/3 solid-floor with
straw and lime as beeding materials and a manure scraper removal
system that is conveyed twice an hour via a slatted element to an
intermediate storage tank below the slats. Washing water from the
milking systems is mixed with the manure under the barn. The liq-
uid manure is stored for no more than 24 h in a collecting pit. It is
automatically stirred 3 times a day and mixed before sampling. The
manure is usually pumped to a biogas plant daily. The manure was
removed from the collection pit with a 5-L ladle and put into 12 60
L plastic barrels in May (summer sample). The same procedure was
conducted for 6 barrels of fresh manure in October (winter sam-
ple). The barrels were always transported immediately from LVAT
Groß Kreutz to DBFZ (Deutsche Biomasseforschungszentrum
gemeinnützige GmbH), Leipzig, Saxony, Germany, so that the man-
ure storage test setup at DBFZ could be filled with the manure sam-
ples. The manure storage tests were started on the same day that
the samples arrived.
2.2. Manure storage test (barrel)
To quantify the emissions during manure storage, a study was
carried out for two time periods: one long period starting in the
summer season (S0, S1, S2, S3, S4) and one short period starting
in the winter season (W0, W1, W2). Both periods ended in Febru-
ary of the following year. For both periods, the samples were col-
lected at LVAT Groß Kreutz and stored at DBFZ under ambient
temperature conditions to simulate on-farm manure storage con-
ditions from May 2018 to February 2019 and October 2018 to
February 2019. During manure storage, storage units of two
120 L barrels were connected with a gas hose. Four storage units
were 50% filled for the storage period starting in May, and two
additional storage units were filled for the storage period starting
in October. After filling, the barrels were sealed gas-tight. To inves-
tigate changes in the CH
4
emission potential of the manure over
the storage time, composite samples of the pair of barrels were
taken at every 10
th
week of storage. Sampling was conducted after
10 weeks, 20 weeks, 30 weeks and 40 weeks of storage (S0, S1, S2,
S3, S4) for the manure collected from the barn in May and after 10
and 20 weeks (W0, W1, W2) of storage for the manure collected
from the barn in October. For each sample drawing, one storage
unit was opened, thoroughly mixed and discarded after sampling.
Fig. 1 visualizes the timetable of sampling for the summer and
winter manure samples, including manure storage tests (barrels)
and the subsequent measurement of the CH
4
emission potential
at 20 °C (eudiometer).
Each storage unit was equipped with a TG05/Model No. 5 drum-
type gas meter (Dr.-Ing. RITTER Apparatebau GmbH & Co. KG,
Bochum, Germany) for the daily reading of the gas volume for
the first 3 weeks (except weekends); after the first 3 weeks, the
gas volume was read weekly. The gas volumes were standardized
(dry gas, 273.15 K, 1013.25 hPa) The humidity of the gas (formed
in the manure storage test) was calculated taking account of the
measured ambient temperature by means of the Antoine equation
(Strach, 2020a). It was assumed, that the biogas temperature in the
gas sampling lines (approximately 3 m long) between barrel and
gas meter equaled ambient temperature. The composition of the
gas was determined daily using infrared and chemical sensors in
a biogas analyzer CH
4
,CO
2
0–100% accuracy max. ± 3.0%; H
2
S0–
5000 ppm; Biogas-Analysator BM2000, Ansyco GmbH, Karlsruhe,
Germany) for the first 3 weeks (except weekends); after the first
3 weeks, the gas composition was determined weekly. The process
of measurement of gas quality took a few minutes. During the per-
iod of gas quality measuring, the inlet and outlet of the Biogas-
Analysator BM2000 were connected to the headspace of the bar-
A. Cárdenas, C. Ammon, B. Schumacher et al. Waste Management 121 (2021) 393–402
394
rels. The gas composition was corrected for the dilution within the
headspace of the barrels. A temperature sensor (PT 100 Almemo,
Ahlborn Mess- und Regelungstechnik GmbH, Holzkirchen, Ger-
many) installed in the center of one barrel per storage unit was
used for temperature measurements at 1 h intervals. All tempera-
ture sensors were connected to Almemo 2590-9 V5 data loggers
(Ahlborn Mess- und Regelungstechnik GmbH, Holzkirchen, Ger-
many). One additional temperature sensor measured the ambient
temperature in the unheated and uninsulated storage room (gar-
age) and was connected to a LT6-digi-GPRS data logger (A27083,
60.900.20/177, Umwelt- und Ingenieurtechnik GmbH, Dresden,
Germany). The barrels were insulated with an aluminum lami-
nated lamella mat made of 20 mm glass wool (SAINT-GOBAIN ISO-
VER G+H AG, Ludwigshafen, Germany) (Schumacher et al., 2020).
The barrels were insulated to prevent or buffer frequent tempera-
ture fluctuations. It was assumed, that, the temperature fluctua-
tions of the slurry during large-scale storage were also low due
to the large volume of the slurry tanks. Fig. 2 shows the piping
and instrumentation diagram of the manure storage test setups
separately for the summer (Fig. 2a) and winter samples (Fig. 2b).
2.3. Methane emission potential at 20 °C (eudiometer)
To measure the CH
4
emission potential, fresh manure samples
from the start of the experiments as well as the samples from every
10 weeks during the storage period (see Figs. 1 and 2) were placed
into eudiometer batch tests without inoculum at a temperature of
20 °C for 60 days, following the method for the residual gas tests
according to VDI 4630. 500 g of the manure samples to be tested
were weighed into 1 L bottles, implemented in triplicate. The head-
space of the filled bottles was then flushed with N
2
to expel excess
oxygen from the system and create anaerobic test conditions. The
manure storage test in barrels should give an insight into the
effects of manure aging during the seasons and of fluctuating tem-
peratures on CH
4
formation under pilot scale condictions mimicing
commercial farm conditions. A saturated, acidified saline solution
of the following composition was used as barrier fluid within the
eudiometer:
– 150 ml sulfuric acid (conc.)
– 1000 g sodium sulfate decahydrate
– 5000 ml H
2
O
dest.
– 10 ml methyl orange (0.1% in 20% alcoholic solution) was used
as a pH indicator.
After being flushed with N
2
, the bottles were connected to glass
eudiometer tubes (greased ground joint), and the eudiometers
were reset to zero. Gas was released via the gas valve at the upper
end of the eudiometer tube until the pressure within the system
had adjusted to the surrounding atmospheric pressure. The zero
position was noted as the initial value in the test protocol, and
the test was started in a water bath (incubation temperature of
20 ± 2 °C). Over the course of the test, the daily gas quantity pro-
duced was determined from the filling levels of the eudiometers.
At the time of reading, the temperature and air pressure were doc-
umented separately to standardize the gas volumes. When a level
of 250 ml of formed gas volume was reached, the eudiometers
were reset to zero by opening the gas valve. The gas volumes were
standardized (dry gas, 273.15 K, 1013.25 hPa). The humidity of the
gas (formed in the CH
4
emission potential test at 20 °C) was calcu-
lated taking account of the measured room temperature by means
of the Antoine equation (Strach, 2020a). The gas composition of the
discharged biogas was analyzed by means of a biogas monitor
equipped with infrared and chemical sensors (CH
4
,CO
2
, 0–100%
accuracy ±0.5%; H
2
S range 0–10000 ppm; Biogas-Analysator
BM5000, Ansyco GmbH, Karlsruhe, Germany). The gas composition
was corrected for dilution within the headspace volume of the bot-
tles according to VDI guideline 4630.
Fig. 1. Timetable for sampling for manure storage tests and methane emission potentials.
A. Cárdenas, C. Ammon, B. Schumacher et al. Waste Management 121 (2021) 393–402
395
2.4. Manure analysis
For the manure samples, pH, dry matter (DM), and volatile
solids (VS) analyses were carried out.
The DM content was determined by oven-drying in a drying
cabinet at 105 °C according to standard procedures (DBFZ, 2016).
Subsequently, the samples were calcined in the muffle furnace
for 30 min at 220 °C and then for 2 h at 550 °C for analyses of VS
(Strach, 2020b). The pH value of the manure samples was mea-
sured using a measuring electrode Sentix 41 and pH device 3310
(together with an accuracy of ±0.3, WTW Wissenschaftlich-
Technische Werkstätten GmbH, Weilheim, Germany).
2.5. Data analysis and modeling
In the eudiometer trials, the CH
4
production had to be adjusted
for the mass loss of manure in the barrels during storage to make
the various trials comparable on the base of initial mass (SO, WO)
of VS. For this purpose, the mass at the start of the storage exper-
iment was multiplied by the DM content and the organic DM con-
tent of the samples. The result was then divided by the mass at the
end of storage multiplied by the DM content and the organic DM
content of the samples at the end of the storage duration. The ini-
tial VS (VS
i
) could be used as long as the analyses only refer to the
storage experiments. During storage the VS content changes, and
the different storage durations lead to different initial VS contents
for the post-storage emission potential trials. A correction was nec-
essary to be able to compare the emissions during storage with the
remaining emission potential after storage. This resulted in correc-
tion factors of 0.77, 0.63, 0.66, and 0.61 for 10, 20, 30, and 40 weeks
of storage starting in summer, respectively, as well as correction
factors of 0.78 and 0.86 for 10 and 20 weeks of storage starting
in winter, respectively. The remaining gas potential between the
different storage variants S0-S4 and W0-W2 was compared with
a one-way ANOVA with heterogeneous residuals between the stor-
age variants. Post hoc multiple pairwise comparisons were then
performed using a simulation approach for adjustment of p-
values for multiple testing.
Since it could not be managed to measure gas production at the
same time every day, the methane measurements were not evenly
spaced in time. Therefore the modified Gompertz model
(Zwietering et al., 1990) was used to estimate the parameters for
Fig. 2. Piping and instrumentation diagrams for summer (a) and winter (b) seasons.
A. Cárdenas, C. Ammon, B. Schumacher et al. Waste Management 121 (2021) 393–402
396
the methane production function as prerequisites for further anal-
yses. This allowed showing the evenly spaced daily methane pro-
duction that was derived from the actual measurements in
addition to the cumulative methane production. The estimated
daily production values allowed to get daily fluxes despite not hav-
ing evenly spaced daily gas production measurements that came in
useful for the analyses relating to the daily ambient and manure
temperatures. Originally developed to describe bacterial growth,
this specific function is occasionally applied to describe cumulative
gas production during discontinuous anaerobic degradation in the
presence of a pronounced lag phase (Weinrich et al., 2020).
StðÞ¼S
res
:e
e
Rm:e
Sres
ðÞ
:ktðÞþ1
To depict the experimental results of the manure storage exper-
iments, the total residual CH
4
potential S
res
(mL g VS
1
), the max-
imum CH
4
production rate Rm (mL g VS
1
d
1
) and the specific lag
phase duration k(d) must be determined. The model implementa-
tions as well as the numeric parameter estimation (Nelder-Mead
algorithm) were realized in the software environment MATLAB
(The MathWorks, Inc., USA) by minimizing the squared differences
between the measured and simulated cumulative CH
4
yields.
A cluster analysis and a canonical discriminant analysis were
used to determine a temperature threshold for CH
4
emissions. In
the first step, a cluster analysis was conducted with the daily aver-
age manure temperature and the daily CH
4
emissions. This created
two clusters with (i) low temperature and low CH
4
emissions, and
(ii) higher temperatures with predominantly medium to high CH
4
emissions. In a second step, the clustered data were put into a
canonical discriminant analysis to create property functions for
classification of data into the two clusters based on manure tem-
perature and CH
4
emission. A data vector belongs to the cluster
that produces a higher result when the values are plugged in the
equation.
3. Results and discussion
3.1. Manure characteristics
The characteristics of the untreated manure are shown in
Table 1. The % of volatile solids of the dry matter (VS
%DM
) and
the dry matter % of the fresh matter (DM
%FM
) in the fresh liquid
manure were determined. For the summer experiment, the values
of VS
%DM
are close to the data reported by Rodhe et al. (2009) and
Le Riche et al. (2016), while the values for the dry matter (DM
%FM
),
coincide with date reported by Petersen et al. (2012). The differ-
ence in dry matter content between the periods can be related to
water consumption, which is higher in summer than in winter
due to high temperatures, thus changing the consistency of the
stored manure as a result of the increase in urine production
(Krauß et al., 2016). The amount of water used in the dairy systems
did not differ between winter and summer.
As mentioned by Petersen et al. (2016), manure storage systems
are never fully emptied, indicating that the material remaining in
the storage system functions as the inoculum for fresh material,
triggering CH
4
production at an early stage. In the present study,
no inoculum was present in the storage at filling. The physical
properties of the fresh material are very important. Measurements
of the current investigation are similar with the data reported in
the literature, regarding liquid manure properties (Masse et al.,
2008; Petersen et al., 2012; Sommer et al., 2004; Liu et al., 2018;
Masse et al., 2003; Rodhe and Ascue, 2009; Sommer et al., 2009;
Willén et al., 2016).
The concentrations of DM and VS were higher in the manure for
the winter storage experiment, than for summer storage, this can
be due to the concentration of excretion of manure with higher
dry matter and less urine excretion in the winter period. Similar
data was reported by Masse et al. (2003, 2008) illustrating the
importance of the relationship between the diet composition
(crude protein, dry matter, and neutral detergent fiber inter alia)
and CH
4
emissions from manure.
Taking into account that temperature is an important variable
in CH
4
production, we proceeded to monitor the temperature of
the liquid manure and the ambient environment. In this way, we
can demostrate the effects of seasonal temperature changes on
CH
4
productivity. Hence, the emissions data obtained from stored
manure can reflect emissions under natural conditions.
3.2. Methane emissions from stored liquid manure subjected to
ambient seasonal temperatures
During this study, CH
4
emissions from stored liquid manure and
their relationship to seasonal temperature changes were investi-
gated. For this purpose, manure and ambient temperatures were
monitored simultaneously in order to explore a correlation
between CH
4
emissions and seasonal temperatures. The outcome
of our experiments showed that the CH
4
emissions from manure
stored were higher in summer in comparison to those from the
winter trials, which is in line with the findings of other authors
(Kupper et al., 2020; Petersen et al., 2013; Sommer et al., 2013;
Sommer, 2007). The CH
4
production started after approximately
one month (Fig. 3 summer samples), reaching values of 0.061 kg
CH
4
kg
1
VS at the end of the 10 weeks and achieving a value of
0.131 kg CH4 kg
1
VS at the end of the 20 weeks. The highest level
of emissions was observed at the end of the 30 weeks of retention
with values of 0.148 kg CH
4
kg
1
VS. After the 30 weeks of reten-
tion, CH
4
emissions diminished until no CH
4
production was
observed.
Fig. 3 shows the course of the mean daily CH
4
production rates
for the whole storage period. Clearly, the CH
4
formation level cor-
responds very closely to the temperature curves. The CH
4
emis-
sions reduction for the summer trials at the end of the
experiment can be explained by multiple factors. One of these fac-
tors is the low temperatures at the end of the summer season; as
illustrated in Fig. 3, the dependencies between the behavior of
CH
4
production and temperature (ambient as well as manure)
can clearly be observed. A decrease in temperature was accompa-
nied by a decrease in CH
4
production to the extent that, when the
temperature dropped below 5 °C, CH
4
production was absent or
non-detectable. This behavior occurred towards the end of the
experiment (between weeks 30 and 40).
Table 1
Characteristics of the manure samples for the summer and winter experiment.
Characteristics Summer experiment Winter experiment
Means Std Min Max Means Std Min Max
pH 7.33 0.15 7.11 7.45 6.43 0.09 6.37 6.54
DM
%FM
7.38 1.34 6.33 9.52 11.58 1.36 10.22 12.93
VS
%DM
73.03 1.57 71.73 75.59 76.84 0.85 75.89 77.53
DM
%FM
= Dry matter% of the fresh matter; VS
%DM
= volatile solids of the dry matter
A. Cárdenas, C. Ammon, B. Schumacher et al. Waste Management 121 (2021) 393–402
397
In the case of the winter trials, the CH
4
emissions were low over
the duration of the experiment (0.0011 kg CH
4
kg
1
VS); suggest-
ing that in the winter season, the emissions from manure stored
on farms will likely be low. The low manure emissions can be
related to the seasonally cold temperatures that prevent the start
of the methanogenesis process, which optimally takes place at
approximately 20 °C and causes the release of CH
4
(Husted,
1994; Sommer et al., 2004; Elsgaard et al., 2016). Microbial com-
munities play an important role in methane formation. Some
strains responsible for methane production are subject to different
temperature levels. According to Im et al. (2020), methanogenic
activity is inhibited by storing cattle manure at low temperatures.
At low temperatures, the Methanolobus Psychrophilus strain
increases its presence, Methanocullens spp and Methanosarcine
spp are the major contributors to methanogenic activity, but it is
the hydrogenotrophic species that dominate methane production
(Barret et al., 2013; Im et al., 2020).
Our findings are similar to previous data reported in the litera-
ture; for example, Husted (1994) found values of 0.008 kg CH
4
kg
1
VS for annual emissions at 11.2 °C, while Sommer & Petersen
(2000) found, over a short storage time of 9–12 weeks in the sum-
mer season, values of 0.001 kg CH
4
kg
1
VS. Rodhe & Ascue (2009)
found 0.007 CH
4
kg
1
VS over 210 days in the summer and 0.004 kg
CH
4
kg
1
VS for winter conditions with a storage period of
157 days, Petersen et al. (2016) reported 0.011 kg CH
4
kg
1
VS from
slurry pits with retention times of 15 and 30 days. This value is
lower than the value reported in our study, because the retention
time is also shorter. Furthermore, Moset et al. (2019) published
CH
4
emissions data related to temperature (20 °C35 °C) with a
storage period of one year in which low temperatures and low
CH
4
emissions are closely related. Amon et al. (2006), reported
fluctuations over the course of one year in the net total CH
4
emis-
sions during storage, with 4.046 kg CH
4
kg
1
VS under warm con-
ditions (slurry temperature 17 °C for a storage time of 80 days).
Similarly, Clemens et al. (2006) report substantially more CH
4
being emitted under summer conditions than under winter condi-
tions and state that CH
4
production is temperature-sensitive and
therefore is also susceptible to seasonal fluctuations. Meteorologi-
cal conditions are summarized by Kupper et al. (2020), where tem-
perature and the level of emission were related. Thiss assumption
has been addressed before by Sommer et al. (2013). In their study,
not only the air temperature but also the wind speed were related
to the increase of GHG emissions including CH
4
.
3.3. Effect of storage time on CH
4
emissions
The cumulative CH
4
emissions from the storage of liquid dairy
cow manure during summer and winter were estimated by apply-
ing a modified Gompertz function. Fig. 4 shows the respective CH
4
losses for the summer and winter storage. During the summer sea-
son, a more intensive degradation of the volatile solids was
observed, compared to that in the winter season. Summer manure
had considerably lower dry matter content and was more dilute
than winter manure, however, there was a considerable lag phase
in the summer season before CH
4
production started. According to
Masse et al. (2003) and Masse et al. (2008), the lag phase and the
reduced methane production can be related to the dry matter con-
tent of manure, where CH
4
emissions from high dry matter manure
are lower in comparison to dilute manure. Rennie et al. (2018)
relate the lag phase to the design of the manure storage. The model
parameters are shown in Table 2.
The respective CH
4
loss potentials for both experiments are
shown in Fig. 4.CH
4
emissions from summer storage started
approximately 4 weeks after the start; those from winter storage
began directly after the start of the storage period. In the case of
the summer trials, the highest emissions were reached between
15 and 25 weeks, and the cumulative gas volumes remained
unchanged until the end of the experiment. This coincides with
the daily CH
4
production rates displayed in Fig. 3. In the case of
manure stored during the winter season, the CH
4
emissions were
low and constant but did not show considerable production. Given
the low temperatures, which reduced the intensity of the
methanogenesis process, the VS in the raw materials are preserved
and can be used later when conditions are favorable to activate the
CH
4
production process; however, over the entire storage period,
there were no substantial CH
4
emissions (Fig. 4). (Møller et al.,
2004), found a loss of CH
4
from cattle manure after 30 days of stor-
age. Likewise, Moset et al. (2019), found 1 L CH
4
kg
1
FM CH
4
emis-
sions from stored manure at 20 °C.
In this study, we have demonstrated that the length of storage
is a decisive factor in determining CH
4
emissions from slurry
stores, especially during summer storage conditions when temper-
atures are above 15 °C. Even a short storage period can result in the
emission of substantial amounts of CH
4
when the temperatures are
above 15 °C, while longer storage periods under cold winter condi-
tions emit little CH
4
. These findings can be useful for designing CH
4
mitigation strategies such as long winter storage, short summer
storage, cooling of slurry in the barn for ammonia and CH
4
mitiga-
Fig. 3. Methane emissions from dairy liquid manure in the summer and winter
seasons.
Fig. 4. Cumulative methane emissions from liquid manure stored over the summer
and winter seasons.
A. Cárdenas, C. Ammon, B. Schumacher et al. Waste Management 121 (2021) 393–402
398
tion. These strategies have the benefit of also supporting good agri-
cultural practices for crop production in sustainable crop rotations
that make optimum use of manure as a valuable fertilizer (Amon
et al., 2006, 2020; Masse et al., 2008; Baral et al., 2018; Petersen,
2018).
3.4. Effects of dairy cattle liquid manure aging on the methane
emission potential (20 °C)
To determine the effect of liquid manure aging on CH
4
emis-
sions and to verify the results found in the previous experiment,
subsamples were taken at a 10-week storage interval as shown
in Fig. 1. The subsamples were stored at 20 °C for 60 days in a batch
test without inoculum. The CH
4
production of each sample was
measured. Individual CH
4
yields in Fig. 5 (green bars) show the
CH
4
emission potential at 20 °C after the different storage periods
(0, 10, 20, 30 and 40 weeks) (red bars). The findings obtained from
the summer subsamples demonstrate that after a 10-week storage
period, the potential for CH
4
production was the highest, at
0.1163 g CH
4
g
1
VS, but decreased gradually to 0.0326 g CH
4
g
1
VS at week 20, to 0.0160 g CH
4
g
1
VS at week 30, and finally
to 0.0091 g CH
4
g
1
VS at week 40. This means that from week 20,
there is a remaining potential of 28% compared to week 10,
approximately 14% in week 30 and approximately 8% in week 40
of storage. The longer the retention period, the lower the potential
for daily CH
4
emissions, but the higher the accumulated CH
4
emis-
sions for the storage period. On the other hand, the results from the
winter subsample showed a strong lag phase in which CH
4
produc-
tion could not be activated during the 60 days of the experiment
even though the temperature was a constant 20 °C. A lag phase
of 250 days at 20 °C was reported by Masse et al. (2008) which
was affected by the dry matter of manure. Also Rennie et al.
(2018) reported a lag phase which they refer to the design of the
storage facilities. The difference in methanogenesis processes
between summer and winter is evident in this study and was likely
influenced by the composition of the manure. More diluted man-
ure produced more CH
4
than manure with a higher dry matter con-
tent. Manure dilution during the summer period can be related to
the cow‘s increased water intake during the warm summer period
(Masse et al., 2008; Krauß et al., 2016). We deduce that the low CH
4
production in the winter period was influenced by a multitude of
factors including manure composition and low temperatures. Our
initial hypothesis, that permanently low temperatures during the
winter months do not inhibit long-term methanogenic processes
was proven false. We showed that even under temperature condi-
tions that were favorable for methanogenesis (20 °C eudiometer)
CH
4
formation did not start again after slurry had been stored
under cool winter conditions.
During storage, the manure temperature is influenced by a
number of factors, including the climate and geographical location,
daily/seasonal variations and the storage system. Arrus et al.
(2006) and Blackwell et al. (2003) provided evidence regarding
manure storage and its effect on CH
4
emissions; the findings sug-
gest that the storage system design (aboveground systems and
underground systems) has a strong influence, depending on the
depth at which the manure is stored and the temperature range.
In the same way, Rennie et al. (2018) reported that the tempera-
ture of manure is also influenced by storage design and manage-
ment practices. Manure produced in summer and stored for a
long time (up to 30 weeks) emits more CH
4
than manure produced
and stored in winter, due to the fact that the methanogenesis activ-
ity is low at low ambient temperatures. Previous studies have
found that the storage of liquid manure for long periods under
warm conditions contributes to a greater share of the GHG emis-
sions from dairy manure management, while the share from stor-
age at low temperatures (below 10 °C) during winter is lower
Table 2
Estimated parameters from the modified Gompertz function of dairy cattle liquid manure from the winter and summer seasons.
Parameter S (mL g
1
VS)(ml/g VS) Rmax (mL g
1
VS d
1
)k(d) R2 (-)
Summer sample storage 191.116 3.049 45.056 1
Winter sample storage 1.295 0.086 4.460 0.99
S: the total residual methane emissions (mL g VS); Rm: the maximum methane emission rate (mL g
1
-VS d
1
); k: the specific lag time (days).
Fig. 5. Comparison of methane emissions at ambient temperature at various durations and their corresponding methane emission potential at 20 °C for 60 days.
A. Cárdenas, C. Ammon, B. Schumacher et al. Waste Management 121 (2021) 393–402
399
(Rodhe et al., 2009; Masse et al., 2003; Sommer, 2007). We con-
firmed these findings an added the important new finding, that
CH
4
production stays at a low level after a cool storage period even
if temperatures rise again.
The result of the cluster analysis is shown in Fig. 6. The follow-
up discriminant analysis resulted in the following equations for the
cluster 1 (low temperature) and the cluster 2 (mid-to-high
temperature).
Cluster 1¼1:21452 þ0:46638 manure temperature
1515 methane emissions
Cluster2¼19:46764 þ1:74503 manure temperature
118:11757 methane emissions
If Cluster 1 > Cluster 2, then the data point is below the temper-
ature threshold where CH
4
emissions stay low even when the man-
ure is subsequently exposed to higher temperatures (20 °C). For
the highest CH
4
emissions found in cluster 1 (0.000317174 g CH
4
gVS
1
) the temperature threshold is at 13.93 °C, given by the point
where Cluster 1 = Cluster 2.
Our experiments demonstrated that the potential for CH
4
emis-
sions from storage is markedly influenced by temperature. We
identified the threshold temperature at which CH
4
production
increases and under which CH
4
emissions are low. This factor is
important and must be considered in order to accurately estimate
and also limit CH
4
emissions from slurry stores. The highest levels
of CH
4
production occurred during the first weeks of storage. The
shorter the manure storage time is, the less CH
4
is released into
the atmosphere. For the winter period, the emissions from stored
manure are low because of the low temperatures. In general, this
outline can contribute to improve the abatement strategies and
their implication for national GHG inventories, according to the
IPCC, 2019 refinement to the 2006 IPPC Guidelines.
4. Conclusion
In this paper, relevant findings about CH
4
emissions from liquid
manure storage in the summer and winter season are presented.
Our results show that if the temperature falls below a threshold
value over a certain period of time, CH
4
production does not
increase even when the temperature rises again. CH
4
production
during winter, with temperatures below 13.93 °C, was consistently
low. Even when the manure was subsequently stored at 20 °C, CH
4
emissions did not increase after the cold winter storage. These
results show the complexity of analyzing the influence of variables
such as temperature, storage duration and season on CH
4
emis-
sions. Under summer conditions, CH
4
emissions from slurry stores
without inoculum started after a month at a temperature of 20 °C,
with a maximum production on the 100
th
day of storage and a sub-
sequent decrease until day 150, when the CH
4
production was
almost negligible. Consequently, it is necessary to build on this
work and design additional detailed experiments to gain more
in-depth understanding on the relationships of temperature, tem-
perature sums, storage length and climate season and CH
4
emis-
sions from slurry stores. These experiments shall also include
microbiological analysis to identify the microbes that contribute
to methane formation. This type of information will be helpful in
estimating emissions, designing emission mitigation options and
generating more accurate data for GHG inventories of livestock
production. Improvement of inventory reporting plays a key role
in determining relevant abatement strategies and their implica-
tions for national inventories.
Declaration of Competing Interest
The authors declare that they have no known competing finan-
cial interests or personal relationships that could have appeared
to influence the work reported in this paper.
Acknowledgment
We thank Prof. Dr. Lena Rodhe and Dr. Kristina Mjöfors from the
Research Institutes of Sweden for their valuable comments and
suggestions on the paper, Ulrich Stollberg from Leibniz-Institute
for Agricultural Engineering and Bioeconomy (ATB), Torsten Rein-
elt (DBFZ) and Carsten Tilch (DBFZ) as well as to the colleagues
from DBFZ-laboratory for their valuable contributions during the
practical experiments.
Fig. 6. Temperature threshold and methane emissions from liquid manure stored.
A. Cárdenas, C. Ammon, B. Schumacher et al. Waste Management 121 (2021) 393–402
400
Funding
The research project (funding code 22025816) was funded by
the Federal Ministry of Food and Agriculture based on a decision
of the Parliament of the Federal Republic of Germany.
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