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Point-source Pig Manure-management Processes in Denmark

M.Sc. Agriculture Poul Pedersen The National Committee For Pig Production

Danish Meat & Bacon Council

Danish farmers produce close to 24 millions pigs per year. 85% of this production is exported, and this makes Denmark one of the world’s largest exporters of pigmeat. It also makes pigmeat the country’s most important export product at around 6 % of total value.

Family holdings and “owner occupiers” are commonplace in Danish farming. Pig production is no exception, and Denmark has about 12,000 such producers. Over the years, larger producers have replaced the smaller ones. But in spite of fewer producers, production has nearly doubled since 1970. 30 % of the producers now account for more than 80 % of total production.

The co-operative system plays a significant role in Danish agriculture. Around 95 % of Danish pigs are slaughtered, processed and marketed by co-operative societies, owned and managed by the pig producers. Much of the further processing and other affiliated industries are also run on co-operative principles. Statistics on the Danish agricultural production is given in table 1.

Table 1. Statistical data on Danish agricultural production Total area of Denmark, hectare 4,400,000Agricultural land, hectare 2,676,000Permanent grassland, hectare 172,000Set aside, hectare 190,000Number of dairy cows 661,000Production of milk, ton 4,664,000Number of sows 1,112,000Number of produced pigs 23,985,000Number of hens 1,112,000Eggs produced 79,000Poultry – produced meat, ton 203,000Livestock total, animal units (AU) 2,349,000Total Nitrogen in animal manure, ton 230,000Total Phosphorus in animal manure, ton 49,000Total Potassium in animal manure, ton 151,000

The Danish regulatory system Danish farmers are subject to a series of laws and rules regarding the environment. Environmental rules set limits to the number of pigs that can be produced by an individual herd. The Danish regulatory system is based on animal units (AU). One AU is the number of pigs on partly slatted flooring that produce 100 kg of nitrogen (N) in livestock manure (ex slurry tank). A “critical size” for a pig farm is 250 AU, which equals a sow unit with 1150 sows producing piglets at 7 kg or a hog unit with a yearly production of 9000 hogs 30 to 100 kg.

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The local authorities must approve any expansion of pig production. For an expansion up to 250 AU it typically takes 4 to 12 months to get the permission. In the meantime the local authorities calculate ammonia emissions, the nitrate and phosphorous depletion from cropland upon spreading the slurry. In this process they evaluate the effect of the expansion on vulnerable nature, groundwater, lakes, rivers etc. If the authorities find that the pollution from the expansion exceeds the limits they have put on nature, groundwater and the water environment in general the pig producer must change his project. The time to get the permission also include a public hearing lasting 4 weeks.

Every single pig farmer in Denmark is not allowed to have more than 750 AU. If pig farmer at one site expand his production beyond 250 AU the farmer need a special permission, which typically takes 1 to 2 years to obtain. Therefore the typical way for the Danish pig farmer to expand is by having three sites with up to 250 AU.

Harmony area A balance between the number of animals in the herd and the land available on which to spread slurry is required. For each 1.4 AU the pig farmer need 1 hectare (10,000 m2) of land for spreading the slurry. It is called the harmony area. There is also a rule saying the pig farmer needs to own a certain amount of the land for harmony. Up to 120 AU the pig farmer must own 25 % of the harmony area. Between 120 and 250 AU the pig farmer must own 60 % of the harmony area and beyond 250 AU he must own the entire harmony area.

Spreading of slurry There are also fixed seasons for slurry spreading. It is forbidden to spread slurry in the period between harvest and February 1. Exception from this rule is crops like winter rapeseed where you can spread slurry in the autumn until October 1. In general, slurry contains important nutrients, which the plants can best absorb in the spring. Therefore most of the slurry is brought out on growing crops from March to May.

Broad spreading of slurry was banned August 1, 2003. In crops like winter wheat, winter barley and winter rapeseed the slurry is brought out with trailing hose technique as shown in figure 1. This technique gives an accurate spreading of slurry and compared to broad spreading it reduces ammonia losses and odour emissions. In crops like spring barley and oats some of the slurry is injected into the ground. There are also mandatory storage facilities for slurry to make sure each pig farm has enough capacity for at least 9 months of storing.

Figure 1. Spreading of slurry on winter wheat with different types of trailing hose technique

Fertiliser plans Each farm must have a fertiliser plan. For each crop you calculate the amount of nitrogen, phosphorous, potassium and some other minor nutrients needed. Due to a governmental act on reducing nitrate depletion from the soil there are limits on nitrogen application. Today the limit is set 10 % below the economical optimum for nitrogen application. The same act has also put a demand on utilization of nitrogen in livestock manure. This demand has increased in the last decade. Today 75 % of the nitrogen in the slurry has to be calculated into the fertiliser plans. Table 2 shows a typical Danish fertilizer plan for crops like winter wheat, sugar beat and spring barley on a pig farm.

This dramatic increase in utilization of the nitrogen in livestock manure has had a significant influence on the total consumption of mineral fertiliser used by the Danish farmers. Figure 2 shows the total consumption of mineral nitrogen since 1985.

Table 2. Example of a typical fertiliser plan for a pig farmer Crop Hectare Nitrogen quota

Kg per ha Total quota Kg N

Winter wheat after cereal Sugar beat Spring barley

502525

167 104 107

8,3502,6002,675

Total 100 13,625Yearly production 5,000 hogs 30 to 100 kg Yearly production of Nitrogen: 5000 hogs x 2.67 kg N per hog = 13,350 kg N Demands for utilization: 75 % 10,013Nitrogen quota: Mineral fertiliser 36 3,613

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Figure 2. Total consumption of mineral nitrogen and the nitrogen content in animal manure in Denmark since 1985.

Pig manure management Quite a number of companies are developing and marketing different ways of treating pig manure. The purpose is to reduce odour and ammonia losses from storing and spreading the slurry, reduce the volume of the slurry and improve the utilization of the nutrients in the slurry. New legislation on separation of slurry to enhance new technology reduces the amount of land a pig farmer has to own for a certain production. This legislation chooses between low technological separation and high technological separation.

Acidifying slurry by adding sulphuric acid The Danish farmer and inventor Jens Oestergaard has developed a new method of acidifying the slurry. This waste handling system is now patented and marketed by the Danish company Staring Maskinfabrik A/S. The objective of his invention was to reduce ammonia emissions not only from animal houses but also from storing and field application of slurry. Thereby as a side effect hopefully the odour emissions would be reduced too. By the end of 2004 the company will have 24 acidifying plants operating on Danish farms. It is well known from many studies and basic chemistry that reduction of pH reduces ammonia emissions. Over the years, several ways of reducing pH have been tested (Pedersen, 2003). Although there has been a significant decrease in pH and ammonia emissions, none of the tested systems have been successful from a commercial point of view so far.

In this newly developed waste handling system, slurry is acidified in a special way. Outside the building at the bottom of a small storage tank, concentrated sulphuric acid is added at a ratio of approximately five kg per tonnes of slurry. The amount of sulphuric acid is controlled by a pH-sensor. After a resting period – typically 10 minutes - a pump stirs up the treated slurry. Simultaneously, waste is aerated by injecting compressed air to prevent sulphate-ion changing

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into noxious hydrogen sulphide. This treatment reduces pH to about 5.5 and also improves the fluidity of the slurry as some of the dry matter content is degraded. Eventually the treated slurry is used to flush the waste pits and ensure that pH in the waste pits is kept at about 5.5. The number of flushings can be varied. Typically, the waste pits are flushed four to eight times a day.

The system is automatically controlled. Therefore every parameter can be varied freely. Figure 3 shows the treating system for acidifying slurry.

The results have so far shown that the newly developed acidifying system seems very efficient in reducing ammonia emissions from pig houses. In hog systems with fully slatted flooring a reduction between 70 and 80 % in ammonia emissions is reached. Unfortunately, the system does not have same potential for odour reduction. In case of breakdown and the acidifying stops for a period of time there seems to be a significant risk of an increase in odour emissions.

From a fertilizer and plant nutrient point of view, the system contains important features, which are about to be evaluated. Preliminary results have shown that pH sustains at approx. 5.5 during the storage period and also when the slurry is applied to the plants. Therefore it seems possible to obtain a significant decrease in ammonia losses from animal production facilities with this newly developed acidifying system.

Figure 3. The system for treating slurry with sulphuric acid. The tank has a capacity of 3 cubic metres – enough for storing five tonnes of concentrated sulphuric acid. In front of the tank there is a cabinet including a control unit for controlling addition of sulphuric acid and compressed air. From the cabinet, tubes lead to the bottom of the storage tank, which is situated right in front of the green container. Separation of pig slurry by adding chemicals Some Danish companies separate pig slurry by adding precipitations agents and flocculants. During this treatment a solid part is separated as shown in figure 4. This process removes 60 - 80 % of the phosphorous and 20-30 % of the nitrogen from raw pig slurry. If the same process is done on acidified slurry it is possible to remove nearly all the phosphorous from the slurry.

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100%6%

16%

90%

Figure 4. Separation of pig slurry by adding precipitations agents and flocculants. Separation of pig slurry by stationary and mobile decanting centrifuge units Decanting centrifuge is a well-known technology for separation of sludge. Especially in the Netherlands decanting centrifuge is also used for separation of pig slurry. In Denmark some pig farmers have purchased small stationary decanting centrifuges. Because of economics of scale and the high capacity of a decanting centrifuge, typically 50-100,000 cubic meters per year, mobile decanting units are the cheapest solution for the typical Danish pig farmer. A decanting centrifuge separates 60-80 % of the phosphorous and 20-30 % of the nitrogen from pig slurry.

15%

85%

15%

85%

Figure 5. A decanting centrifuge separates the slurry into a thin and a solid fraction. The mobile unit shown above has a capacity of 20 cubic meters per hour. Decanting centrifuge is quite power consuming, therefore the mobile unit needs its own generator. Funki Manura 2000 This system is a high technological separation unit shown in figure 6. Altogether the company has two separation units running in the Netherlands and one in Denmark. This unit runs quite well but it is too expensive. Therefore the company has stopped the production.

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10 %

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75 %

Figure 6. The slurry is separated into four fractions: 75 % in a “water” fraction, which can be irrigated on grassland, 2 % in a NPK-fraction, 13 % in a N-fraction and 10 % in a humus fraction. The separation system is based on a decanting centrifuge and evaporation techniques. Green Farm Energy Green Farm Energy is high technological separation concepts for treating slurry and organic waste from agricultural industry. The cost of a plant is 40 to 80 million DKK (6.5 DKK = 1 US$). Even though the company has sold four separation units in Denmark - two working and two under construction – still no results show that the system works a prescribed. A crucial point in the economics is the amount of biogas produced. In Denmark electricity produced on biogas is subsidised by the government. The price is 0.6 DKK per kWh.

Figure 7. In the Green Farm Energy concepts the organic waste is treated prior to biogas fermentation by alkali hydrolysis e.g. boiling at 160 degrees Celsius, 6 Bar and a pH about 10. After half an hour the organic matter is cooled down to 80 degrees Celsius by adding slurry. In the next step ammonia is stripped off and the suspension is ready for biogas fermentation and separation.

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Reduction of ammonia and odour emissions from pig houses The National Committee For Pig Production performs a number of studies on techniques to reduce ammonia and odour emissions from pig houses. A few are presented in this paper. Air cleaning - microbiological The Danish ventilation company SKOV and the company Perstrup Betonindustri have invented a new air cleaning system. It is a two-step air cleaning system. The air from the pig house passes through two filters. The first filter removes the dust. Both filters are moisturized periodically with water circulating from the tank. In this water and on the filters there is significant biological activity, which degrades a lot of the organic matter originating form the dust. It is possible to run the filters for months, without changing the water, but it will also reduce the performance of the filters. Preliminary results show that the filter is very efficient in reducing ammonia and odour emissions. The odour concentration is reduced significantly and the character of the odour is changed so you hardly can smell pigs at the farm – only the faint smell of the filters. There are different ways to lead the air from the pig house to the central air cleaning system as shown in figure 9 and 10.

Figure 9. Pig house with an integrated air cleaning system. The air from pig houses is led to the filter through an insulated ventilation duct in the attic space.

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Figure 10. Pig house with an integrated air cleaning system. The air from pig houses is led to the filter through a canal beneath the solid floor. Air cleaning - chemical The Danish company Scan-Airclean has invented a new air cleaning system shown in figure 11. The air from the pig house passes through filters moisturized periodically with diluted sulphuric acid with a pH at about 4. Preliminary results show that this system is very efficient in reducing ammonia emissions from the outlet air. Unfortunately, it is not very efficient in reducing odour emissions.

Figure 11. Air cleaning system from Scan-Airclean. The ammonia emissions are reduced by more than 90 %. The ammonia is collected as ammonium sulphate in the tanks outside the pig house.

REFERENCE

Pedersen, P., 2003: Reduction of gaseous emissions from pig houses by adding sulphuric acid to the slurry. Proceeding for CIGR Symposium June 1-4 2003 Bygholm Denmark.

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