The contribution of biogas plants to nutrient management planning

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The contribution of biogas plants to nutrient
management planning

• Adviser Torkild Birkmose,
• DAAS, Denmark

Photo Torben Skøtt, BioPress
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Biogas rests on tree legs
Energy
Environment
Agriculture
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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

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Environmental advantages

• Reduced nitrate leaching
• Reduced odour problems
• Reduced green house gas emission
• Controlled recycling of organic waste

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Mixing and digesting slurry change the
characteristic of the slurry
DM, N-tot, kg/t NH4-N, kg/t P, kg/t K, kg/t pH NH4-N,
Digested slurry Pig slurry Cattle slurry 4,8 5,0 7,5 4,4 4,8 3,9 3,5 2,9 2,4 1,0 1,1 0,9 2,3 2,3 3,5 7,6 7,1 6,9 81 74 61
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Fertilizer value
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Ammonia evaporation in spring barley
50
-N
4
40
30
-loss, of spread NH
20
10
3
NH
0
2002
2003
Untreated pig slurry
Digested pig slurry
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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
0
20
40
60
80
100
N-utilization, (fertilizer equivalent)
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Fertilizer plan for nitrogen for 1 ha grass
Digested slurry
Cattle slurry
Per hectare
250
250
N-requirement, kg
170
170
N in slurry, kg total
60
40
N-utilization,
102
68
N- in slurry, utilized, kg
148
182
Mineral fertilizer
34 17
- -
Saved, kg Saved,
10
Digestion reduces risk of spreading diseases
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Digested slurry is low on germs
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Test results from Ribe Biogas, bacteria per ml.
slurry (1998)
Log10 germs per ml. slurry
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After
Before
Date
lt5 lt5 lt5 lt5 lt5
1,300,000 140,000 690,000 9,000,000 62,000
Mar. 18 May 13 July 15 Sept. 9 Nov. 11
10
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Time, weeks
Slurry tank, 6-8C
Mesofile biogas, 35C
Thermofile biogas, 53C
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Digestion reduces odour
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Reduction of odour compounds in the biogas reactor
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Concentration of VFA in slurry
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Carcass chamber for collecting air samples
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Odour concentration in air samples after spreading