1. Characteristics of anaerobic-digested manure Anaerobic digestion: A way to enhance nutritional performance of animal manure
I have worked with utilization of animal manure for about 7 years. I work for Danish Agricultural Advisory Service. Projects & Field trials
Torben Ravn Pedersen
National Specialist
Biogas and Slurry Separation

2. Subejcts Danish Agricultural Advisory Service
Manure handling in Denmark
Biogas in Denmark
Nutritient value in treated manure

3. Danish Agricultural Advisory Service
51 local agricultural advisory centers and 1 national centre
3,500 thousand employees
Denmark's largest consultancy
Turnover: DKK 1.8 billion
Owned and run by farmers

4. Manure types in Denmark
Slurry systems are most common

5. How is slurry spread in Denmark?
Trailing hoses are most common

6. About 60 farmscale biogas plants in Denmark
Plants owned and driven by a single farmer. Digestion of slurry and industriel fat

7. 20 centralized biogas plants
Owned by 5 – 70 farmers, digest manure and industrial waste. Manure is hauled by trucks or pipes.

8. Biogas rests on tree legs
It is very important to understand that biogas is not just making biogas. If production of biogas was the only reason for making biogas plants, none would ever have been build in Denmark. So biogas is resting on three legs, and what happens, if one of the legs is cut off? It will tumble! We don’t want that to happen, do we? The three legs are: energy, agriculture and environment. I will concentrate on the nutritional value of the manure.
Energy
Agriculture
Environment

9. Agricultural advantages
Improved fertilizer value of nitrogen
Balanced P and K-balance in slurry
Homogeneous and light fluid
Full declaration of nutrients
Bacteria-free and seedless
Reduced costs for transportation of slurry
First an overview over the agricultural advantages:
Of course this is what the farmers are most interested in. Some of the advantages are very hard to put on a real value, and all together it may not be worth a great fortune. But keep in mind, that the farmers get the advantages for nothing, as they normally don’t pay to get the slurry digested.

10. Environmental advantages
Reduced nitrate leaching
Reduced odour problems
Reduced green house gas emission
Controlled recycling of organic waste (turns waste into valuable fertilizer)
The environmental advantages are mainly of interest for the surrounding society. For example digestion makes it easier to adapt international regulation.

11. Mixing and digesting slurry change the characteristic of the slurry
DM, %
N-tot,
kg/t
NH4-N, P, K, pH
NH4-N, %
Digested slurry
Pig slurry
Cattle slurry
4,8
5,0
7,5
4,4
3,9
3,5
2,9
2,4
1,0
1,1
0,9
2,3
7,6
7,1
6,9 81 74 61
In Denmark digested slurry is typically a mixture of pig slurry, cattle slurry and organic waste from industry.
The numbers are average content of the slurry we have used in field trials.
Reduced dry matter
Higher content of plant available nitrogen – ammonia
Higher share of ammonia
Higher pH – fatty acids are broken down
The high pH increases the risk of ammonia evaporation, but it is counteracted by the thin and light fluid which infiltrates the soil very fast. In the soil the slurry is protected from ammonia evaporation. More about that in a minute.

12. Ammonia evaporation in spring barley50 -N 40 30
-loss, % of spread NH4 20
In trials the Danish Institute of Agricultural Sciences has demonstrated, that the ammonia evaporation from a field is lower when spreading digested slurry than when spreading untreated pig slurry. These trial were made in spring barley in 2002 and The reduction of ammonia evaporation is one of the reasons for higher fertilizer value of nitrogen in digested slurry than in untreated slurry. 10
NH3
2002
2003
Untreated pig slurry
Digested pig slurry

13. 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
This figure shows the results of a great number of field trials in winter wheat. The trials were designed in a way that made it possible to measure the fertilizer value of the nitrogen in the slurry. The result is shown as the nitrogen utilization percentage, which is the utilization of nitrogen in the slurry compared to the same amount of nitrogen in mineral fertilizer. For example this means that if the nitrogen utilization is 80 percent, you can get the same yield of 80 kg nitrogen in mineral fertilizer as you can get from 100 kg N in slurry.
In all the trials the slurry is spread in April, and the method has been trailing hoses or injection. It didn’t matter if the slurry was applied with trailing hoses or with injector as the nitrogen utilization from digested slurry was higher than from pig slurry and much higher than from cattle slurry.
The reason is the high content of ammonia and the lower ammonia evaporation.
Cattle slurry, injected 20 40 60 80
100
N-utilization, % (fertilizer equivalent)

14. Fertilizer value
In Denmark we have been very focused on nitrogen utilization over a the last years. Today the consumption of nitrogen in mineral fertilizer is restricted at a level 10 percent below the economic optimum. Because of this Danish farmers are very focused on getting the highest possible fertilizer value of the manure. The higher the fertilizer value the higher yield in the field. Increasing the utilization of animal manure is a way of saving money on mineral fertilizer, but it is also a way of decreasing the negative impact on the environment. So utilization of manure and taking care of the environment works hand in hand. It makes sense to most farmers.

15. Fertilizer plan for nitrogen for 1 ha grass
Per hectare
Cattle slurry
Digested slurry
N-requirement, kg
250
250
N in slurry, kg total
170
170
N-utilization, % 40 60
N- in slurry, utilized, kg 68
102
What does this mean in practise? Well, here is an example of a simple fertilizer plan for grass with a nitrogen requirement of 250 kg N per year.
The result is that the farmer saves 27 Euro per hectare.
Mineral fertilizer
182
148
Saved, kg
Saved, Euro - 34 27

16. N, P, and K in mineral fertilizer
Prognosis
Fertiliser applications reduced

17. N-application in Denmark
450
400
350
300
250
1,000 tonne of N per year
200
150
Fertilizer
100
Manure 50
1940
1950
1960
1970
1980
1990
2000
2010

18. Injection in bare soil

19. Injection of slurry in grass

20. Digested slurry is low on bacteria6
Test results from Ribe Biogas,
bacteria per ml. slurry (1998)
Log10 germs per ml. slurry 3
Date
Before
After
Mar. 18
May 13
July 15
Sept. 9
Nov. 11
1,300,000
140,000
690,000
9,000,000
62,000
<5 5 10
This figure shows the reduction of germs over time at different temperatures during storage. Especially in a thermofile biogas reactor the reduction is very fast. But keep in mind, that a reduction also happens in a traditional slurry tank.
The table shows the content of bacteria in the slurry at Ribe Biogas before and after the process on five occasions in After the process the number was below the detection level.
Time, weeks
Slurry tank, 6-8°C
Mesofile biogas, 35°C
Thermofile biogas, 53°C

21. Digestion reduces odour
An advantage that is getting more and more important is that digestion reduces the odour problems with the slurry. For years experience has shown that the odour was lower, but only a few projects have proven it scientifically. I have got a few results of trials.

22. Slurry separation – on treated manure
Foto: Bigadan A/S.
Digested manure makes slurry separation more effective and reduces costs.
Separation has the potential to enhance nutrient value of the manure
Foto: Westfalia

23. Thank you for your attention!