Adviser Torkild Birkmose,
DAAS, Denmark
Dansk Landbrugsrådgivning
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Photo: Torben Skøtt, BioPress
The contribution of biogas plants to
nutrient management planning
Biogas rests on tree legs
Biogas
Energy
Dansk Landbrugsrådgivning
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Agriculture
Environment
Agricultural advantages
• Improved fertilizer value of nitrogen
• Balanced P and K-balance in slurry
• Homogeneous and light fluid
• Full declaration of nutrients
• Free from germs and seeds
• Reduced costs for transportation of slurry
Dansk Landbrugsrådgivning
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Environmental advantages
• Reduced nitrate leaching
• Reduced odour problems
• Reduced green house gas emission
• Controlled recycling of organic waste
Dansk Landbrugsrådgivning
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Mixing and digesting slurry change
the characteristic of the slurry
DM,
P,
K,
%
N-tot, NH4N,
kg/t
kg/t
kg/t
Digested slurry
4,8
4,4
kg/t
3,5
1,0
Pig slurry
5,0
4,8
2,9
Cattle slurry
7,5
3,9
2,4
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pH
NH4N, %
2,3
7,6
81
1,1
2,3
7,1
74
0,9
3,5
6,9
61
Fertilizer value
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NH3-loss, % of spread NH4-N
Ammonia evaporation in spring barley
50
40
30
20
10
0
2002
Untreated pig slurry
Dansk Landbrugsrådgivning
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2003
Digested pig slurry
Improved fertilizer effect of nitrogen
- trials in winter wheat
Digested slurry, trailing hoses
Pig slurry, trailing hoses
Cattle slurry, trailing hoses
Digested slurry, injected
Pig slurry, injected
Cattle slurry, injected
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0
20
40
60
80
100
N-utilization, % (fertilizer equivalent)
Fertilizer plan for nitrogen for 1 ha
grass
Per hectare
N-requirement, kg
N in slurry, kg total
N-utilization, %
N- in slurry, utilized, kg
Mineral fertilizer
Saved, kg
Saved, £
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Cattle slurry
Digested slurry
250
170
40
68
182
-
250
170
60
102
148
34
-
17
Digestion reduces risk of spreading
diseases
Dansk Landbrugsrådgivning
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Log10 germs per ml. slurry
Digested slurry is low on germs
6
Test results from Ribe Biogas,
bacteria per ml. slurry (1998)
3
5
10
Time, weeks
Slurry tank, 6-8°C
Mesofile biogas, 35°C
Thermofile biogas, 53°C
Dansk Landbrugsrådgivning
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Date
Before
Mar. 18
May 13
July 15
Sept. 9
Nov. 11
1,300,000
140,000
690,000
9,000,000
62,000
After
<5
<5
<5
<5
<5
Digestion reduces odour
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Reduction of odour compounds in the
biogas reactor
8
Odour units
7
6
5
4
3
2
1
0
0
5
10
15
20
Days
Dansk Landbrugsrådgivning
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Concentration of VFA in slurry
mg per litre slurry
1000
800
600
400
200
0
Iso-butanoic
acid
Butanoic acid
Untreated slurry
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Iso-valeric
acid
Digested slurry
Valeric acid
Carcass chamber for collecting air
samples
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Odour concentration in air samples
after spreading
1000
3
Odour units per m of air
1200
800
600
400
200
0
20 minutes
Untreated slurry
Dansk Landbrugsrådgivning
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260 minutes
Digested slurry