the contribution of biogas plants to nutrient management planning

Dansk LandbrugsrådgivningLandscentret

The contribution of biogas plants to nutrient management planning

Adviser Torkild Birkmose,

DAAS, Denmark

Ph

oto

: T

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en

Sk

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, B

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Dansk LandbrugsrådgivningLandscentret

Biogas rests on tree legs

Biogas

Energy EnvironmentAgriculture

Dansk LandbrugsrådgivningLandscentret

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 LandbrugsrådgivningLandscentret

Environmental advantages

• Reduced nitrate leaching

• Reduced odour problems

• Reduced green house gas emission

• Controlled recycling of organic waste

Dansk LandbrugsrådgivningLandscentret

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

Dansk LandbrugsrådgivningLandscentret

Fertilizer value

Dansk LandbrugsrådgivningLandscentret

Ammonia evaporation in spring barley

0

10

20

30

40

50

2002 2003

NH

3-lo

ss, %

of

spre

ad N

H4-

N

Untreated pig slurry Digested pig slurry

Dansk LandbrugsrådgivningLandscentret

Improved fertilizer effect of nitrogen- trials in winter wheat

0 20 40 60 80 100

Cattle slurry, injected

Pig slurry, injected

Digested slurry, injected

Cattle slurry, trailing hoses

Pig slurry, trailing hoses

Digested slurry, trailing hoses

N-utilization, % (fertilizer equivalent)

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Fertilizer plan for nitrogen for 1 ha grass

250250N-requirement, kg

170170N in slurry, kg total

6040N-utilization, %

10268N- in slurry, utilized, kg

34

17

-

-

Saved, kg

Saved, £

148182Mineral fertilizer

Digested slurryCattle slurryPer hectare

Dansk LandbrugsrådgivningLandscentret

Digestion reduces risk of spreading diseases

Dansk LandbrugsrådgivningLandscentret

Digested slurry is low on germs

<5<5<5<5<5

1,300,000140,000690,000

9,000,00062,000

Mar. 18May 13July 15Sept. 9Nov. 11

AfterBeforeDate

Test results from Ribe Biogas,bacteria per ml. slurry (1998)

Lo

g10

ger

ms

per

ml.

slu

rry

Time, weeks

Slurry tank, 6-8°C Mesofile biogas, 35°CThermofile biogas, 53°C

10

6

5

3

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Digestion reduces odour

Dansk LandbrugsrådgivningLandscentret

Reduction of odour compounds in the biogas reactor

0

1

2

3

4

5

6

7

8

0 5 10 15 20

Days

Odour

units

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Concentration of VFA in slurry

0

200

400

600

800

1000

Iso-butanoicacid

Butanoic acid Iso-valericacid

Valeric acid

mg

per

litr

e s

lurr

y

Untreated slurry Digested slurry

Dansk LandbrugsrådgivningLandscentret

Carcass chamber for collecting air samples

Dansk LandbrugsrådgivningLandscentret

Odour concentration in air samples after spreading

0

200

400

600

800

1000

1200

20 minutes 260 minutes

Od

ou

r u

nit

s p

er

m3 o

f air

Untreated slurry Digested slurry