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Life Cycle Assessment of Slurry Management Technologies

Annex B. Acidification of slurry – Life Cycle Inventory data

• B.1 System description
• B.2 In-house storage of acidified slurry
• B.3 Acidification of slurry in Infarm NH4+ system
• B.4 Production of sulphuric Acid (H2SO4)
• B.5 storage of acidified slurry
• B.6 Transport of acidified slurry to field
• B.7 Field processes (acidified slurry)
• B.8 Avoided mineral fertilisers (N, P and K)
• B.9 Avoided mineral fertilisers (S)
• B.10 Impacts on crop production

B.1 System description

This appendix contains Life Cycle Inventory data for the acidification of slurry. The slurry is acidified by the addition of sulphuric acid (H₂SO₄). The sulphuric acid reduces the pH and the chemical equilibrium between ammonium (NH₄⁺) and ammonia (NH₃) is changed which means that it is primarily in the form of ammonium (NH₄⁺). As only ammonia (NH₃) evaporates, the pH of the slurry is a determining factor for the amount of nitrogen / ammonia that volatilize in the housing system, during storage and during application to fields. Moreover, acidification of the slurry has significance for other factors that will be described in this Annex. For example the use of sulphuric acid for the acidification might be an advantage as it adds sulphur to the field which has a fertilizer effect.

The system for acidification of slurry is shown in figure B.1.

Figure B.1: Flow diagram for the scenario for acidification of slurry.

Click here to see Figure B.1

B.2 In-house storage of acidified slurry

The main part of the acidified slurry is pumped back into the housing units, and this changes the emissions from the slurry in the housing. The Life Cycle Inventory data for the in-house storage of acidified slurry are shown in table B.1.

The energy consumption for the acidification system is included under “Acidification of slurry in the Infarm NH4+ system” in section B.3 below.

Ottosen et al. (2009) investigated the microbial activity in acidified pig slurry. They found that the microbial activity, expressed as oxygen consumption, sulphate reduction and methanogenesis, was greatly reduced in acidified slurry. They state that the implications may be reduced emissions of hydrogen sulphide and methane, but increased volatilization of fatty acids.

Measurements by Dansk Landbrugsrådgivning (2004c) on cattle slurry indicate the same trend. Based on their 6 measurements (2 for non-treated slurry, 4 for acidified slurry) it can be calculated that acidification reduce the methane emissions by 32% [7-49%] and the direct nitrous oxide emissions by 83% [58-99%]. It should be emphasized that the room temperature is not the same for all the measurements and that the room temperature is significant for the microbial activity and hence the emissions. Furthermore, 6 measurements are not enough for statistical analysis, which is also emphasised by the authors of the report ¹. As it has not been possible to identify more studies covering the influence of acidification of slurry on the methane or the nitrous oxide emissions, the data from Dansk Landbrugsrådgivning (2004c) have been used, well aware that it should be regarded with care. The same estimate has been used for pig slurry. The significance is discussed under sensitivity analysis.

No data have been found for the carbon dioxide emissions. As methane is a much stronger greenhouse gas than carbon dioxide, the carbon dioxide emissions are relatively unimportant for the total contributions from the housing units. It has been assumed that the carbon dioxide emissions are reduced by the same factor as the methane emissions.

Under the acidification process the carbonate balance is affected by the low pH in the slurry, forcing the carbonate into free CO₂. This might cause a higher emission of the CO₂ during the acidification process and in the housing units. The release of CO₂ is also due to the stripping caused by the aeration of the slurry. The aspect needs further investigation. However, it is assumed that this aspect does not influence the overall conclusions of the life cycle assessment, as it supposed that the production of CO₂ by the bioprocesses in the slurry is not affected, only the release of the CO₂ contained in the slurry, and as it is assumed that this CO₂ would be released at a later stage in the life cycle of the slurry (e.g. at the field). In conclusion, it is assumed that the total amounts of CO₂ in the entire life cycle are not affected.

The ammonia emissions from acidified slurry in the housing units are reduced by 70% for pig slurry compared to untreated slurry (BAT, 2009a and Dansk Landbrugsrådgivning (2004a) (BAT byggeblad 107.04-52) and Kai et al. (2007). For cattle slurry, the ammonia emissions are reduced with 50% (Dansk Landbrugsrådgivning (2004b) (BAT byggeblad 106.04-56)).

The emission of nitrogen monoxide (NO-N) is assumed to at the same level as the direct N₂O-N emissions (Dämmgen and Hutchings, 2008), see description in Annex A.

The emission of Nitrogen (N₂-N) is assumed to be three times as high as the direct N₂O-N emissions (Dämmgen and Hutchings, 2008), see description in Annex A.

Table B.1. Life cycle Inventory data for storage of acidified slurry in the housing units (scenario F).
All data per 1000 kg of slurry “ex animal”.

As described in Annex A, it is assumed that the NO emissions cover the total NO_X emissions (NO_X = NO + NO₂) when taking the uncertainty on the rough estimate into account. Hence, additional NO₂ emissions are not added.

As for the reference scenario, the indirect N₂O emissions have been included in accordance with the IPCC (2006) recommendations, the see Appendix A.

The indirect N₂O emission corresponds to 0.01 kg N₂O–N per kg (NH₃–N + NO_X–N volatilised) (IPCC, 2006, table 11.3).

The reduction of hydrogen sulphide emissions is discussed by Ottosen et al. (2009), as mentioned above. However, it has not been possible to quantify the reduction.

The mass balances in table B.2 and B.3 are established in order to calculate the composition of the slurry ex acidification plant.

Table B.2. Calculation of the composition of acidified slurry after the acidification plant (scenario F) for pig slurry.

^a The total amount of slurry is only changed slightly – 5 kg of sulphuric acid is added, and 4.9 kg is lost as emissions. For the calculations, it is assumed that the total mass is not changed (as in the reference scenario).. The assumption has only very little significance for the concentrations.

^b Changes in total N: 0.318 kg NH₃-N + 0.0022 kg N₂O-N + 0.0022 kg NO-N + 0.0066 kg N₂-N = 0.329 kg N

^c Changes in total C: 2.34 kg CO2 * 12.011 [g/mol] /44.01 [g/mol] + 2.2 kg CH4 * 12.011 [g/mol] /16.04 [g/mol] = 2.3 kg C

^d Changes in total S: 5 kg H2SO4 * 32.054 [g/mol] / 98.077 [g/mol] = 1.63 kg S

e It is assumed that the change in VS is proportional with the loss of C i.e. 2.3 kg / 37 kg = 6.2%.

64.2 kg * 6.2% = 3.98 kg.

f It is assumed that the change in DM is identical to the VS loss and that there is no change in the Ash content.

Table B.3. Calculation of the composition of acidified slurry after the acidification plant (scenario F) for dairy cow slurry.

^a The total amount of slurry is only changed slightly – 7 kg of sulphuric acid is added, and 9.9 kg is lost as emissions. For the calculations, it is assumed that the total mass is not changed (as in the reference scenario). The assumption has only very little significance for the concentrations.

^b Changes in total N: 0.275 kg NH₃-N + 0.0024 kg N₂O-N + 0.0024 kg NO-N + 0.0072 kg N₂-N = 0.287 kg N

^c Changes in total C: 7.7 kg CO2 * 12.011 [g/mol] /44.01 [g/mol] + 1.9 kg CH4 * 12.011 [g/mol] /16.04 [g/mol] = 3.5 kg C

^d Changes in total S: 6 kg H2SO4 * 32.054 [g/mol] / 98.077 [g/mol] = 1.96 kg S

e It is assumed that the change in VS is proportional with the loss of C i.e. 3.5 kg / 55.2 kg = 6.3%.

104.2 kg * 6.3% = 6.6 kg.

f It is assumed that the change in DM is identical to the VS loss and that there is no change in the Ash content.

B.3 Acidification of slurry in Infarm NH₄⁺ system

The concept of the slurry acidification technology is to lower pH value of the slurry to 5.5 via the utilisation of sulphuric acid (H₂SO₄). The working principles on how this is done is visualised in figure B.2 and figure B.3 below.

Figure B.2 depicts an acidification installation for pig slurry, where the slurry is discharged, treated and the majority is returned to the stables. The remaining pig slurry is pumped to the outdoor slurry storage. This process is carried out approximately one time per day to ensure that the pH remain at the desired low level.

Figure B.2: An Acidification installation for pig slurry, where the pig slurry is discharged, treated and the majority is returned to the stables.

Click here to see Figure B.2

Figure B.3 illustrates an acidification installation for dairy cow slurry, where the acid is added in the mixing well just outside the housing. The mixing well is an integral part of the slurry pits, so the acidification is carried on the entire volume of slurry.

Figure B.3: An Acidification installation for cattle slurry.

Click here to see Figure B.3

The life cycle data for the acidification plant includes extra electricity for pumps and consumption of sulphuric acid. The emissions are included under the data for the in-house storage of acidified slurry in section B.2.

The electricity consumption is based on measurements by Infarm and upcoming BAT-documentation, which have been sent for public hearing until 15 April 2009 (revised version of 23 March 2009 for pig slurry and revised version of 17 March 2009) (BAT (2009a) and BAT (2009b)). In the time of writing these have not been finally approved, however, these are used as basis for the calculations in this study, as they are regarded as the most updated knowledge about the acidification installations.

As can be seen in table B.2, the energy consumption for an acidification plant for pig slurry is significant higher than for an acidification plant for cattle slurry. This is due to differences in the construction of the slurry pits below the animals. For cattle, the slurry from the slurry pits is mixed with the sulphuric acid in a relatively small pre-tank and recycled back into to slurry pits in a iterative process (the process mainly needs energy to run a mixer for recycling the slurry). The construction for pig slurry is more complicated. The slurry in the slurry pits are emptied in a batch process to a process tank, where it is stirred and mixed with the sulphuric acid before it is recycled into the slurry pits. Energy is needed for stirring and pumping amounts of slurry.

For the acidification of pig slurry, 5 kg [4-6kg] concentrated sulphuric acid is used (BAT 2009a). For the acidification of dairy cow slurry, 6 kg [5-7 kg] concentrated sulphuric acid is used (BAT 2009b).

For the production of sulphuric acid, see next section (B.4 “Production of Sulphuric Acid (H₂SO₄)”

Inventory data for the acidification of slurry are shown in table B.4.

Table B.4. Life cycle Inventory data for acidification of slurry (scenario B).
All data per 1000 kg of slurry “ex animal”.

The materials for the acidification plant are shown in table B.5. The materials for the storage tank are at the same level as the materials for the pre-tank under the housing units in the reference scenario and will be included as this.

Table B.5. Material consumption for an acidification plant.

The density of slurry roughly 1000 kg per m³ used for these estimates (as it is rough estimates anyway).

B.4 Production of sulphuric Acid (H₂SO₄)

The production of the sulphuric acid for the acidification of slurry is included in the life cycle assessment. As this life cycle is based on the consequential approach (see the method description in section 2.3) the “marginal production” of sulphuric acid should be used for the modeling. It means that the production method, that is affected when increasing the consumption of sulphuric acid should be identified – not just “the average” production.

In Denmark, sulphuric acid is produced as a by-product from the flue gas cleaning from the electricity production. However, this production of sulphuric acid is not considered to be the “marginal production”. According to Dansk Elforsyning (2006), the production of sulphuric acid as a by-product of electricity production was 5000 tons in 2006, which is a rather limited amount ². Furthermore, it could be mentioned, that if the sulphuric acid from the Danish flue gas cleaning is not bought for acidification of slurry, it would be bought by someone else and thereby replacing another production of sulphuric acid.

In this study, the production of sulphuric acid is included by the use of the Ecoinvent process ” Sulphuric acid, liquid, at plant/RER U”. However, this process is modified slightly in order to transfer the process from “average production” to “marginal production” ³.

B.5 storage of acidified slurry

In the reference scenario, the process “Storage” includes storage of slurry in the pre-tank and outdoor storage of slurry. As described in Annex A, it has not been possible to separate the pre-tank emissions from the emissions caused by the outdoor storage.

The same problem occurs in this scenario for acidification: It would have been optimal if the emissions from the acidification process tank could have been separated from the emissions from the outdoor storage. However, it is not possible. Accordingly, this process called “Storage of acidified slurry” includes emissions from:

• Storing slurry in the process tank of the acidification plant
• Storing slurry in the outdoor storage for months before application to fields

Furthermore, the energy consumption is included for stirring and pumping (other than required for the acidification of slurry).

No additional chemicals or additives are added. During the storage, rain is adding water to the slurry. Accordingly, the total amount of slurry is slightly higher after storing, as described in the mass balances chapter 3. There are no wastes or by-products from the process.

The Life Cycle Inventory data for outdoor storage of slurry is given in table B.7. The inputs to the processes are 1000 kg of slurry “ex acidification plant”. All emissions and consumptions are calculated relative to this 1000 kg of slurry going into the process.

The CH₄ emission during outdoor storage of acidified slurry is based on a very rough estimate, as practical scale measurements are not available. There is likely to be a significant reduction of CH₄ emissions when acid is added to slurry. Laboratory-scale storage of cattle slurry for 3 months showed a reduction of 90% of CH₄ emissions. Another study based on in-door storage (Hansen et al., 2008) showed a reduction of the CH₄ emissions by 67% for storage of acidified cattle slurry compared to untreated slurry. However, these indoor test results cannot be directly transferred to long-term outdoor storage of slurry and field tests are needed (personal communication with S.O. Petersen, 2009). It is difficult to assess if the relative reduction will be as high for outdoor storage, as the measurements at room temperature, as the outdoor storage during winter will be significantly lower as the emissions will be reduced by the lower temperature also for untreated slurry. Furthermore, the storage time is much longer for “real life outdoor storage” which will also affect the relative reductions. Since it has not been possible to find field data on the CH₄ emissions from acidified pig slurry, in this study the calculations will assume a reduction of 60% of the CH₄ emission (as a conservative estimate). Sensitivity analysis is carried out for reductions of 30% and 90%. No data has been found on pig slurry. The same assumptions have been made for pig slurry, i.e. a reduction of 60% and sensitivity analysis for 30% and 90%.

No data have been found for the carbon dioxide emissions. As methane is a much stronger greenhouse gas than carbon dioxide, the carbon dioxide emissions are relatively unimportant for the total contributions from the housing units. It has been assumed that the carbon dioxide emissions are reduced by the same factor as the methane emissions.

The ammonia emissions are reduced by 90% compared to untreated pig slurry (Kai et al., 2007). According to the upcoming BAT notes (BATbyggeblad . (BAT, 2009a and Dansk Landbrugsrådgivning (2004a) (BAT byggeblad 107.04-52) the ammonia emissions during storage are reduced by 50% for both cattle slurry and pig slurry. In this study, a reduction of 50% has been applied.

Nitrous oxide (N₂O) emissions were reduced by 37% in a study made by Hansen (2008). However, Hansen (2008) states that the N₂O reductions might be explained by a lower dry matter content of the acidified slurry and the by the much thicker natural crust formed on top of the untreated slurry.

Accordingly, the data is regarded as “up to 37% reduction” in this study.

A sensitivity analysis is carried out for the reduction.

The emissions of NO, NO₂ and N₂ are calculated using the same assumptions as for the in-house storage in section B.2. For the indirect N₂O emissions, see text in table B.7 and in section B.2.

The energy consumption for pumping and stirring that are not particularly related to the acidification of slurry is assumed to be identical to the energy consumption in the reference scenario in Annex A. This includes:

• Stirring slurry in the pre-tank before pumping to the outdoor storage.
• Pumping slurry from the pre-tank to the outdoor storage by a pump.
• Stirring slurry in the outdoor concrete tank when straw is added (pig slurry only)
• Stirring slurry before pumping from outdoor storage tank.
• Pumping slurry from the storage tank to the transport tank.

The energy consumption for these processes are assumed to be on the same level in the reference scenario and for the system for acidification of slurry in this Annex (see Annex A for details). In addition to this energy consumption the energy consumption for the acidification plant has been added, see table B.4.

It is assumed, that there are no emissions to water and soil from slurry storage as in the reference scenario.

Table B.6 Life cycle data for outdoor storage of acidified slurry. All data per 1000 kg of slurry “ex acidification plant”.

The mass balances in table B.7 and B.8 are established in order to calculate the composition of the slurry storage. According to Sørensen and Eriksen (2009), the NH4⁺-N/Total N ratio for acidified slurry is 0.82 for pig slurry and 0.59 for cattle slurry ex storage. The composition ex acidification plant is taken from table. B.2 and B.3.

Table B.7. Calculation of the composition of acidified slurry after outdoor storage for pig slurry.

^a For the outdoor storage, the same dilution factor is used for acidified slurry as in the reference scenario, i.e.+8.6%, see table A.4 in Annex A.

^b Changes in total N: 0.055 kg NH₃-N + 0.021 kg N₂O-N + 0.021 kg NO-N + 0.0066 kg N₂-N = 0.16 kg N

^c Changes in total C: 0.072 kg CO2 * 12.011 [g/mol] /44.01 [g/mol] + 0.78 kg CH4 * 12.011 [g/mol] /16.04 [g/mol] = 0.6 kg C

d According to Sørensen et al. (2009), the NH4+-N/Total N ratio for acidified slurry is 0.82 for pig slurry and 0.59 for cattle slurry.

e It is assumed that the change in VS is proportional with the loss of C i.e. 0.6 kg / 34.7 kg = 1.7%.
60.2 kg * 1.7% = 1.0 kg.

f It is assumed that the change in DM is identical to the VS loss and that there is no change in the Ash content.

Table B.8. Calculation of the composition of acidified slurry after outdoor storage for dairy cow slurry.

^a For the outdoor storage, the same dilution factor is used for acidified slurry as in the reference scenario, i.e.+4.4%, see table A.4 in Annex A.

^b Changes in total N: 0.065 kg NH₃-N + 0.021 kg N₂O-N + 0.021 kg NO-N + 0.063 kg N₂-N = 0.17 kg N

^c Changes in total C: 1.68 kg CO2 * 12.011 [g/mol] /44.01 [g/mol] + 0.67 kg CH4 * 12.011 [g/mol] /16.04 [g/mol] =0.96 kg C

d According to Sørensen et al. (2009), the NH4+-N/Total N ratio for acidified slurry is 0.82 for pig slurry and 0.59 for cattle slurry.

e It is assumed that the change in VS is proportional with the loss of C i.e. 0.96kg / 51.7 kg = 1.86%.
97.6 kg * 1.86% = 1.8 kg.

f It is assumed that the change in DM is identical to the VS loss and that there is no change in the Ash content.

B.6 Transport of acidified slurry to field

The transport of acidified slurry to field is assumed to be identical to the transport of untreated slurry in the reference scenario, see Annex A.

B.7 Field processes (acidified slurry)

The process “Field processes (acidified slurry)” includes the same processes as for untreated slurry in the reference scenario. The application of slurry by trail hose application tanker and the diesel consumption is assumed to be identical.

However, acidification of slurry changes some of the emissions and as the content of N in the slurry is higher in acidified slurry (due to reduced loss of NH₃ in the housing units and during storage) than for untreated slurry. This leads to that the fertilizer value of acidified slurry is higher than the fertilizer value of untreated slurry (Sørensen and Eriksen, 2009), Sørensen (2006) and Jensen (2006).

The CO₂ emissions are modeled by C-tool by B M Petersen (2009).

The CH₄ emission on the field is assumed to be negligible, as the formation of CH₄ requires anaerobic environment, and at the field is normally plenty of oxygen.

The NH₃ emissions during the very application are assumed to correspond to 33% of the NH₃ emissions from untreated slurry (Kai et al. (2008) and Hansen et al. (2008). As the NH₃ emissions during the very application are assumed to correspond 0.5% of the NH₄⁺ content of the slurry for the untreated slurry, the NH₃ emissions during the very application of acidified slurry are assumed to correspond 0.5%*0.33 = 0.165%.

Hansen et al. (2008) estimate that the NH₃ emissions from acidified slurry applied to field are is approximately 33% of the NH₃ emissions from untreated slurry.

The direct N₂O emissions from acidified slurry are calculated by the same method as for the untreated slurry, i.e. as 0.01 kg N₂O-N per kg N “ex storage” for application of animal wastes to soil, based on IPPC (2006, table 11.1), see Annex A. As the total N content of the acidified slurry is slightly higher than the total N in the untreated slurry, the N₂O emission will be slightly higher as well. It should be emphasised that this assumption (that the N₂O emissions from application of acidified slurry to field is at the same level as untreated slurry) is a rather rough assumption without any reference to measurements or testing. The composition of the slurry is rather different than untreated slurry and it might affect the N₂O emissions from the field. The area needs scientific research.

In addition, the indirect N₂O emission has been included in accordance with the IPCC (2006) guidelines, as described in section A.2, i.e. 0.01 kg N₂O–N per kg (NH₃–N + NO_X–N volatilised) (IPCC, 2006, table 11.3).

The emissions of nitrogen oxides (NO_X) and nitrogen (N₂) is based on the same assumptions as in Annex A, see this.

According to Petersen and Sørensen (2008), application of acidified slurry to fields leads to an increased need for application of lime, corresponding to 300-600 kg CaCO₃/ha per year. With 30 tons slurry per ha it corresponds to an increase of the lime consumption of 15 kg CaCO₃ per 1000 kg slurry. The Ecoinvent process “Limestone, milled, loose, at plant/CH U” has been used for the modeling. The marginal lime production has not been identified within the frames of the project, as it is insignificant for the overall results.

According to Dalgaard (2002), the amount of diesel used for applying lime to fields is 1.5 liter diesel per ha per year (corresponding to 0.05 liter diesel per 1000 kg slurry). The energy consumption for applying lime is included by the use of the Ecoinvent process “Application of plant protection products, by field sprayer/CH U” as a proxy.

The added lime is assumed to lead to a CO₂ emission corresponding to the total amount of added carbonate according to IPCC (2006, section 11.3.1). This is included in table B.9.

In order to obtain values for N leaching, we first calculate the extra N available after ammonia losses, relative to the basis scenario in Annex A. For the pig slurry basis scenario, there is 4.80 – (0.02 + 0.48) = 4.30 kg N available after ammonia losses (from tables A.5 and A.17). The corresponding figure for the cattle slurry basis scenario is 5.04 kg N available (calculated from tables A.6 and A.17). In the present scenario, there are respectively 5.43 kg N and 5.75 kg N available after ammonia losses, for respectively pig and cattle slurry (calculated from tables B.7, B.8 and B.9). The acidification is assumed to have a minute effect on the amount of organic N in the slurry, so the differences of respectively 1.13 (pig slurry) and 0.71 (cattle slurry) kg N are assumed to be in mineral form. Thereby the fates of the additional N can be considered identical to the mineral N fates of table A.14, after a small correction for the 2% ammonia volatilization assumed in this table. Hereby the additional leaching, compared to the basis scenario, for acidified pig slurry can be calculated as follows (JB3, pig slurry): 0.431 * 1.13 kg N/(1-0.02) = 0.50 kg N. The total leaching caused by 1000 kg acidified pig slurry is then 0.50 kg N + 1.91(from table A.17) = 2.41 kg N. The same principles were applied for all four combinations of soil and slurry types, as seen in table B.9.

As the main difference concerning N, relative to the untreated slurry is an increased amount of mineral N, the nitrate leaching is assumed to rise with the same marginal response as those derived from mineral fertilizer (table A.14). Concerning CO₂ , the response only differs by the effect of added production, which causes more storage of C in the soil, and hence less CO₂ emission. This effect is calculated with C-TOOL.

The life cycle inventory data for application of slurry is shown in table B.9.

Table B.9. Life cycle data for application of slurry and field processes for acidified slurry. All data per 1000 kg of slurry ex outdoor storage.

B.8 Avoided mineral fertilisers (N, P and K)

The substation of fertilizers is estimated as follows. The N content in slurry leads to a substitution of mineral N fertilizer, as described in Annex A. The use of N fertilizer is restricted by Danish law (Gødskningsbekendtgørelsen, 2008, and Gødskningsloven, 2006), and the farmers have to make accounts on their fertiliser use, and they have to include a fixed amount of the N content of the animal slurry in their fertiliser accounts. For acidified slurry, the substitution requirements states that the substitution ratio is set by the producer of the technology, however, the substitution ratio shall be at least the same as for untreated slurry, i.e. 75% for pig slurry and 70% for cattle slurry. As there is no point in setting it higher from a production viewpoint (because the farmers want to be allowed to apply as much N as possible), the substitution ration for acidified slurry is set to 75% for pig slurry and 70% for cattle slurry, as in Annex A. It has the consequence that the relative replacement of N in slurry by mineral N is the same as for untreated slurry, however, the acidified slurry has a higher content of N which means that the fields receives a higher amount of plant available N when using acidified slurry, which increases the crop yield as well as the N losses. If the N substitution had been regulated to the real fertilizer value of acidified slurry, the crop yield would presumably not increase.

According to Gødskningsbekendtgørelsen (2008), the substitution value for N is calculated in relation to the Danish Norm data (ex storage values). As the Danish Norm data (ex storage values) do not include losses due to N₂O, NO etc. the N substitution should be calculated in relation to the theoretical content of N in the slurry ex storage from the Norm Data. These are shown in table A.1 and A.2 in Annex A.

It means that the “replaced N fertilizer” is the same amount as in Annex A, in spite of that it should have been higher for acidified slurry. This gives an extra amount of N to the field. The assumptions regarding the increased crop yield is discussed in section B.10 below.

For the sensitivity analyses, it has been assumed that the Danish Law is changed, leading to a requirement that the “fertiliser replacement value” reflects the actual content of N in the acidified slurry ex storage.

Calculations of the avoided mineral N fertilisers have been carried out.

• First, the “fertiliser replacement value” for the reference system is stated (see Annex A for further details) for pig slurry: Mineral N fertiliser: 5.00 kg N per 1000 kg slurry ex storage [the value given by the Danish Norm Data, as explained in Annex A] * 1086 kg slurry ex storage per 1000 kg slurry ex animal * 75% [the replacement value according to (Gødskningsbekendtgørelsen, 2008] = 4.0725 kg mineral N fertiliser
• If the “fertiliser replacement value” for acidified pig slurry where based on measurement, the acidified pig slurry contains 5.63 kg N ex storage (table B.7). 5.63 kg N ex storage * 75% * 1086 kg slurry ex storage per 1000 kg slurry ex animal = 4.586 kg N
• Accordingly, for pig slurry, the farmer should reduce the application of mineral N fertiliser by 0.513 kg mineral N fertiliser per 1000 kg slurry ex animal (i.e. corresponding to the functional unit) (as 4.586 kg N – 4.0725 kg = 0.51 kg N). This means that additional of 0.51 kg N fertiliser is avoided per 1000 kg pig slurry ex animal.
• Then, the “fertiliser replacement value” for the reference system is stated (see Annex A for further details) for pig slurry: Mineral N fertiliser: 6.02 kg N per 1000 kg slurry ex storage [the value given by the Danish Norm Data, as explained in Annex A] * 1044 kg dairy cow slurry ex storage per 1000 kg slurry ex animal * 70% [the replacement value according to (Gødskningsbekendtgørelsen, 2008] = 4.399 kg mineral N fertiliser
• If the “fertiliser replacement value” for acidified dairy cow slurry where based on measurement, the acidified dairy cow slurry contains 6.14 kg N ex storage (table B.8). 6.14 kg N ex storage * 70% * 1044 kg slurry ex storage per 1000 kg slurry ex animal = 4.487 kg N
• Accordingly, for pig slurry, the farmer should reduce the application of mineral N fertiliser by 0.088 kg mineral N fertiliser per 1000 kg slurry ex animal (i.e. corresponding to the functional unit) (as 4.487 kg N – 4.399 kg = 0.088 kg N). This means that additional of 0.088 kg N fertiliser is avoided per 1000 kg dairy cow slurry ex animal.

The amount of P and K is unchanged for the acidified slurry.

B.9 Avoided mineral fertilisers (S)

The sulphur (S) from the sulphuric acid is assumed to replace mineral S fertilizer. It is assumed that the added sulphur in the acidified slurry can replace mineral S fertilizer corresponding to 20 kg S per ha (Birkmose, 2008). With an application of 30 tons slurry per ha it corresponds to 0.67 kg S per 1000 kg slurry. The acidified slurry will add excess amounts of sulphur to the fields, which might result in sulphur leaching (Knudsen, 2008). It has not been possible to include the environmental aspects of sulphur leaching in this life cycle assessment due to that the existing Life Cycle Methods cannot handle sulphur leaching.

No data on the production of mineral S fertiliser has been found. It is basically produced on sulphuric acid, and hence, the avoided production for S mineral fertiliser is assumed to be sulphuric acid.

B.10 Impacts on crop production

According to Sørensen (2006), the increase in fertilizer value for acidified pig slurry corresponds to 39% for winter wheat and 15% for spring barley compared to untreated pig slurry. For acidified cattle slurry, Sørensen (2006) found an increased fertilizer value of 62% for winter wheat and 3% for spring barley compared to untreated cattle slurry. Jensen (2006) found an increased yield of respectively +11.4% (winter wheat in 2001), +6.0% (winter wheat in 2002), -0.2% (decrease) (winter wheat in 2003) and + 9.4% (spring barley in 2003). The fertilizer value is not direct corresponding to the increased yield. In this study, the consequences of adding acidified slurry are modeled as an increased yield of winter wheat of 6.6% (the average of the data above). According to Sørensen (2006), the crop yield was 63.3 1hkg/ha (winter wheat 2001), 61.4 hkg/ha (winter wheat, 2002) and 59.5 hkg/ha (winter wheat, 2003) when applying untreated slurry. The average is 61.4 hkg/ha, and an increase yield of 6.6% then corresponds to 4.05 hkg/ha. With an applied amount of 30 tons slurry per ha, the increased yield corresponds to 0.135 hkg per 1000 kg slurry, i.e. 13.5 kg winter wheat per 1000 kg slurry.

In order to estimate the extra crop yield for dairy cow slurry, the extra N available after ammonia losses have been calculated:

• For pig slurry in the reference scenario, the N available after ammonia losses are 4.30 kg N per 1000 kg slurry ex storage ⁴.
• For acidified pig slurry, the N available after ammonia losses are 5.43 kg N per 1000 kg slurry ex storage ⁵.
• This corresponds to a surplus of 5.43-4.30 = 1.13 kg N
• For dairy cow slurry in the reference scenario, the N available after ammonia losses are 5.04 kg N per 1000 kg slurry ex storage ⁶.
• For acidified dairy cow slurry, the N available after ammonia losses are 5.754 kg N per 1000 kg slurry ex storage ⁷.
• This corresponds to a surplus of 5.754-5.04 = 0.714 kg N
• Accordingly, the ratio between pig slurry and dairy cow slurry is 0.714 kg N / 1.13 kg N = 0.63

Accordingly, it has been assumed that the increased yield for acidified dairy cow slurry is 13.5 kg * 0.63 = 8.5 kg winter wheat.

When calculating the yield increase with the fitted polynomials decribed in section A.5, the amount of extra mineral N (as calculated above) is utilized. For pig manure, the extra winter wheat grain yield the crops delivers at the higher fertilization level is 9.7 kg (JB3), respectively 8.8 (JB6). For cattle slurry the values are 6.4 kg, respectively 5.8 kg, because of the lower amount of extra N in acidified cattle slurry, relative to pig slurry.

It is considered to be a fairly uncertain value depending on a lot of factors, and the increased yield should be interpreted with care. The significance is discussed under sensitivity analysis.

It is considered to be a very uncertain value, depending on a lot of factors, and the increased yield should be interpreted with care. The significance is discussed under sensitivity analysis.

The increase of a crop yield of 13.5 kg winter wheat is assumed to replace 13.5 kg winter wheat produced somewhere else in Denmark. This is a very simplified assumption. The consequences of increased crop yield probably replace another crop type somewhere else in the world. It is beyond the frame of this project to identify the avoided crop as a consequence of the increased crop yield. In this report, it is assumed that the increased crop yield replace 13.5 kg winter wheat, using data from the process “Wheat, conventional, from farm“ from LCA-food data base (www.lcafood.dk).

[1] The very first sentence in the conclusion regarding methane is: ”På baggrund af de få målinger af metan er det ikke muligt at afgøre, om der er forskel mellem de undersøgte systemer.” (Dansk Landbrugsrådgivning (2004c), page 24).

[2] In rough numbers, there is used 5 kg sulphuric acid per 1000 kg pig slurry, which approximately corresponds to the slurry amount from 2 fattening pigs in their life time. Accordingly, the production of 5000 tons of sulphuric acid could at maximum acidify the slurry from 2 000 000 fattening pigs. This is of course not the case as the sulphuric acid is sold for other purposes as well and as there is not acidification plants in Denmark at farms corresponding to 2 000 000 pigs but it shows that the amount of sulphuric acid from the Danish electricity production is limited.

[3] According to the background documentation reports for the Ecoinvent database (Nemecek and Kägi, 2007), the sulphur resource for the process is mainly based on liquid sulphur obtained from desulphurization of natural gas or crude oil and cleaning of coal flue gas. In the Ecoinvent database, part of the extraction of the crude oil and natural gas is allocated to the liquid sulphur, which is not in accordance with the consequential approach: The desulphurization of natural gas and crude oil is performed to avoid damages in the refinery installations rather than with the aim of producing sulphuric acid. The liquid sulphur is a by-product which is utilized for production of sulphuric acid, not a main product. Accordingly, in this study, the contribution from the extraction of oil and gas has been deleted. Remaining is the energy and emissions from the transformation of the liquid sulphur into sulphuric acid.

Furthermore, the process is adjusted by a factor 1/0.65. under the documentation for this process, it is stated that: “Since the sulphuric acid can be considered a as byproduct from the processing of sulphide ores (other than pyrites), for this study it is considered that the sulphuric acid produced by smelter gas burning is obtained "gratis“. As mentioned above, this process contributes with 35% to the total production. Consequently, in order to subtract the contribution of this process to the overall average, all the values for inputs and outputs presented in the report have been balanced by multiplying them by 0.65.” This Ecoinvent approach is not in accordance with the consequential approach, the Ecoinvent process has been adjusted by a factor of 1/0.65 = 1.538.

[4] 4.80 kg N per 1000 kg slurry ex storage (table A.1) – 0.02 kg NH₃-N (loss during application, table A.17) - 0.48 kg NH₃-N (loss after application, table A.17) = 4.30 kg N per 1000 kg slurry ex storage.

[5] 5.63 kg N per 1000 kg slurry ex storage (table B.7) – 0.008 kg NH₃-N (loss during application, table B.9) - 0.19 kg NH₃-N (loss after application, table B.9) = 5.43 kg N per 1000 kg slurry ex storage.

[6] 5.79 kg N per 1000 kg slurry ex storage (table A.2) – 0.02 kg NH₃-N (loss during application, table A.17) - 0.73 kg NH₃-N (loss after application, table A.17) = 5.04 kg N per 1000 kg slurry ex storage.

[7] 6.14 kg N per 1000 kg slurry ex storage (table B.8) – 0.006 kg NH₃-N (loss during application, table B.9) - 0.38 kg NH₃-N (loss after application, table B.9) = 5.754 kg N per 1000 kg slurry ex storage.

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Version 1.0 July 2009, © Danish Environmental Protection Agency