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

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

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

Manure types in Denmark Slurry systems are most common

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

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

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

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

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.

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.

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.

Ammonia evaporation in spring barley 50 -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 2003. 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

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)

Fertilizer value In Denmark we have been very focused on nitrogen utilization over a the last 15-20 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.

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

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

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

Injection in bare soil

Injection of slurry in grass

Digested slurry is low on bacteria 6 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 1998. 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

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.

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

Thank you for your attention!