Slurry acidification: a measure to reduce methane emission from livestock
Moset, V.a, Cerisuelo, A.b, Cambra-López, M.c, Møller H.B a
a
Department of Engineering, Aarhus University, Denmark
Centro de Investigación y Tecnología Animal, Instituto Valenciano de Investigaciones Agrarias. Pol. La Esperanza,
100. 12400 Segorbe, Castellón.
c Instituto de Ciencia y Tecnología Animal, Universitat Politècnica de València. Camino de Vera s.n. 46022 Valencia.
b
1. Introduction
The acidification of slurry by manipulation of the balance between ammonia and ammonium is an
effective measure of reducing ammonia emissions from animal slurry (Berg et al., 2006). For this
reason, in several European countries like Denmark, pig and cattle slurry acidification with sulfuric
acid (H2SO4) is being promoted.
Slurry acidification with H2SO4 can also reduce methane (CH4) emissions from the slurry during
storage; however this subject has been evaluated at a lower extent.
Ultimate CH4 yield (B0) is an important parameter to estimate CH4 emission from slurry. In fact,
countries that report their greenhouse gas emissions under the Kyoto Protocol use B0 to calculate
CH4 emissions (IPCC, 2006).
The objective of the present work was to evaluate B0 at different sulfate concentrations in pig and
cattle slurry in order to estimate CH4 emission from acidified slurries during storage.
2. Materials and Methods
The experiment was conducted in a factorial design in which two types of slurry (pig and cattle)
and ten different sulfate concentrations (treatments) were tested in a batch assay (0.5 L bottles).
Sulfuric acid was added to obtain the desired sulfate concentration in each treatment. Treatments
were tested in triplicate and three bottles of inoculum were used as blanks.
Both, pig and cattle slurries were obtained from the experimental farms at the Research Centre
Foulum (Tjele, Denmark). The initial age and composition of slurries and the inoculum is shown in
Table 1. Inoculum was collected from the thermophilic full-scale biogas reactor located at the
Research Centre Foulum and incubated at 55°C for 15 days to minimize endogenous biogas
production.
Table 1. Initial chemical composition of the substrates and inoculum used in the study.
pH
Total solids, g kg-1
Volatile solids, g kg-1
Sulfate, mgSO42- L-1
Total volatile fatty, g L-1
Pig slurry
7.51
44.7
33.4
286
13.36
Cattle slurry
8.21
93.4
77.6
670
5.29
Inoculum
7.99
23.0
14.2
330
0.19
After filling, each bottle was sealed with butyl rubber stoppers and aluminum crimps and the
headspace was flushed with pure N2 for two minutes. Bottles were then incubated at 50°C for 114
days. The measurement of biogas volume was done by inserting a needle connected to a tube with
inlet to a column filled with acidified water (pH<2) through the butyl rubber. The biogas produced
was calculated by the water displaced until the two pressures (column and headspace in bottles)
were equal.
Methane and carbon dioxide concentration in the biogas were analyzed at the time of biogas
measurements on an Agilent 7890A gas chromatograph (Agilent technologies, USA) using a
thermal conductivity detector (TCD) and a flame photometric detector (FPD).
Ultimate CH4 yield from each treatment was calculated as the cumulative CH4 produced after 114
days and expressed as mL of CH4 per gram of VS from the slurry introduced to the bottles (VSi).
Treatments effect on B0 over the 114 days study was determined using repeated measures
ANOVA (PROC MIXED) in SAS Version 9.0 (SAS, 2001).
3. Results and Discussion
Table 2 shows B0 from pig and cattle slurry with increasing sulfate concentrations. In pig slurry, the
greatest B0 was obtained in bottles with 500 mg SO42- L-1, being this significantly higher (P<0.05)
than B0 from raw slurry (0 mg SO42- L-1). However, significant reductions in B0 were observed at
sulfate concentrations of 2500 mg SO42- L-1 or higher. The CH4 inhibition in treatments with 2500,
3000, 4000 and 5000 mg SO42- L-1 in respect to raw slurry after 114 days was 58%, 78%, 93% and
94%, respectively.
In cattle slurry, the greatest B0 was also observed in the treatment with 500 mg SO42- L-1 although
this was not statistically different from raw slurry (0 mg SO42- L-1). In cattle slurry, sulfate inhibition
started at 2000 mg SO42- L-1, since CH4 production in this treatment was significantly lower than
that from raw slurry. At this SO42- concentration, the calculated CH4 inhibition with respect to raw
slurry was of 47%. For the bottles containing 2500, 3000, 4000 and 5000 mg SO42- L-1 the inhibition
was complete since CH4 production in these bottles was lower than in the blank bottles.
Table 2. Cumulative methane (CH4) production and standard error after 114 days from pig and cattle slurry
with increasing sulfate concentrations.
Sulfate
concentration
(mgSO42- L-1)
0
200
500
1000
1500
2000
2500
3000
4000
5000
[1] ]
[2]
Pig slurry
Ultimate methane
production
(ml CH4 gVSi-1)
295b[1]
310b
360a
322ab
322b
290b
123c
66d
21e
18e
Standard
error
9.6
15.8
41.5
12.4
10.0
16.1
3.8
6.5
2.1
14.2
Cattle slurry
Ultimate methane
production
(ml CH4 gVSi-1)
225ab
212ab
242a
235ab
159bc
120[c]
CI[2]
CI
CI
CI
Standard
error
14.4
51.1
21.5
16.5
9.2
18.0
-
Statistically significant differences (P < 0.05) among treatments are indicated by different superscripts within each column.
CI: complete inhibition; when CH4 production in treatment bottles was lower than the CH4 production in blank bottles.
4. Conclusion
From the results obtained herein, CH4 emission reductions occur at SO42- concentrations higher
than 2500 mg SO42- L-1 and higher than 2000 mg SO42- L-1 in pig and cattle slurry respectively.
However a SO42- concentration of 500 mg SO42- L-1 caused and increased in CH4 emission in both
slurries.
5. Acknowledgements
The research was financed by the Danish Ministry of Food, Agriculture and Fisheries as a part of a
development and research program for “Green Growth” in the Danish agricultural sector. The
authors wish to thank the slurry acidification company Infarm A/S for cooperation.
References
Berg W., R. Brunsch, I. Pazsiczki. 2006. Greenhouse gas emissions from covered slurry compared
with uncovered during storage. Agric. Ecosyst. Environ. 112: 129–134.
IPCC, 2006. Emissions from livestock and manure management. IPCC Guidelines for National
Greenhouse Gas Inventories. Volume 4. Agriculture, Forestry and Land Use. Kanagawa, Japan.
SAS. 2001. SAS User's Guide: Statics. Ver. 9.0. Cary, N.C.: SAS Institute Inc.