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Life Cycle Assessment of Slurry Management Technologies

Summary and conclusions

• Objectives of the study
• Reference scenarios and alternatives
• Basis for the comparison: The functional unit
• System boundaries
• Temporal, geographical and technological coverage
• Environmental Impacts and Resources
• Reference scenarios
  • System description for the reference scenarios
  • Data for the reference scenario
  • Results of the impact assessment
• Scenario for the Infarm NH4+ acidification of slurry
  • Goal
  • System description
  • Results of the impact assessment
• Scenario for the Samson Bimatech Energy Plant
  • Goal
  • System description
  • Results of the impact assessment
• Scenario for fibre pellets used as fertiliser
  • Goal
  • System description
  • Results of the impact assessment

Objectives of the study

The objective of this study is to establish a foundation for Life Cycle Assessments of slurry management technologies in Denmark.

The LCA foundation consists of:

• A database containing Life Cycle Data for selected slurry management technologies,
• A reference model for conventional slurry management, which is expanded with models for alternative technologies and data from the contribution of participating companies. The models are part of the database.
• This report, containing examples and results of Life Cycle Assessments performed for selected slurry management technologies.

The LCA foundation can be used by the contributing companies for evaluating the environmental sustainability of a specific technology from a holistic Life Cycle perspective. The goal of the study is to answer the question for each alternative technology: “What are the environmental benefits and disadvantages of introducing this technology for slurry management?”

From a societal perspective the results can contribute to a clarification of which slurry management technologies (or combination of technologies) having the largest potential for reducing the overall environmental impacts.

Reference scenarios and alternatives

In this study, the reference scenarios are:

• Slurry from fattening pigs, stored in the slurry pits below the animals in the housing units, stored in a concrete slurry tank (covered by a natural floating layer), transported and applied to field.
• Slurry from dairy cows, stored in the slurry pits below the animals in the housing units, stored in a concrete slurry tank (covered by a natural floating layer), transported and applied to field.

A detailed description of the reference scenarios are specified in chapter 3.

The reference scenarios serve as a basis for the assessment of the environmental impacts of the alternative technologies for slurry management. The environmental consequences of choosing alternative technologies are compared to the reference scenarios.

The slurry treatment technologies included in this report are:

• Acidification of slurry and subsequent storage and application of the acidified slurry to field (Infarm NH4+ plant).
• Mechanical separation of slurry into a fibre fraction and a liquid fraction (Samson Bimatech Separation plant):
  • Use of the fibre fraction for fibre pellets production and use of the pellets for:
    • Application to field
    • Heat production in a Samson Bimatech Energy Plant
  • Application of the liquid fraction directly to the field

For a fully understanding of the preconditions and the systems, reading of the Annexes is required.

There is a huge variety of alternative technologies for slurry management. It has not been possible to include all of these various alternatives within the framework of this study. For example, it has not been possible to include the environmental impacts changed management of the slurry in the housing system or the various technologies for application of slurry to the field. The exclusion should notbe seen as these technologies are regarded as unimportant – some of them most likely have huge significance for the overall environmental impacts – they are only excluded due to the time and budget constraints of the project.

Biogas production will be included in an upcoming report.

Basis for the comparison: The functional unit

The new technologies are compared to the reference system based on the same “functional unit”, which means that they all start with the same amount of pig slurry (or dairy cow slurry) with the same composition. This is necessary in order to make the scenarios comparable.

The functional unit in this study is: “Management of 1000 kg slurry ex animal”.

The composition of the reference slurry is specified in the tables below:

Characteristics of slurry from fattening pigs and from dairy cows in the reference scenario.

Per 1000 kg of slurry “ex animal”, “ex housing” and “ex storage”.

System boundaries

In principle, all environmental impacts from all processes in the entire chain have to be included; however, when comparing alternatives, it is not necessary to include processes that are identical in the compared systems.

In this study, focus has been put on the differences, and the processes, that are identical for the reference scenarios and the alternative technologies have been left out.

Common for all the scenarios in this study are all the processes “up-stream” of the slurry excretion, i.e. production of pigs and cattle, production of feed, medicine, hormones, housing systems etc. Also the energy consumption within the housing system is assumed to be the same, and all common processes are excluded. Furthermore, methane emissions from the cattle in the housing units are not included. These are left out as they are identical in all scenarios, but also as they are not relevant for the goal of the study (“What are the environmental benefits and disadvantages of introducing slurry management technology X?”). The starting point is, thus, the slurry excreted in the housing units. In other words, the system starts when the slurry leaves the pig or the cow and hits the floor or the slurry pits in the housing system, see figure 2.2.

Gaseous emissions (methane, carbon dioxide) from the animals are not included within the system boundaries (as changed slurry management has no influence on the enteric fermentation and on the respiration).

Included are only the gaseous emissions from the slurry and the emissions from all the slurry management that follows; in-house handling, pumping, storage, transport and application to the field. These are the focus of this report.

Included within the system boundaries for the reference scenario are emissions from the slurry in the housing units and in the pre-tank, outdoor storage, transport, application to field, avoided / reduced production of mineral fertilisers due to the fertiliser value of the slurry and organic matter incorporation in the soil which include carbon sequestration. A flow diagram for the reference scenario is shown in figure 3.1 in chapter 3.

In principle, the crops on the field are not included within the system boundaries. However, it has been necessary to include small amounts of “increased crop production” for some of the new technologies when the slurry management actually leads to an increase of the crop yield. This is elaborated later. In order to specify the emissions from the field, a reference s crop rotation for pig farms and cattle farms has been set up in the system description in section 3.1. This has been necessary in order to estimate the input and output from the fields.

The energy consumption for all the slurry management technologies is included, for example the energy consumption for pumping, for the separation processes or for transport. The energy consumption in the housing units is generally not included, however, the extraenergy consumption for the “add-on” technology in the housing system is included, and for example the consumption of energy / chemicals for acidification of the slurry in the housing units is taken into account.

In some Life Cycle Assessments, biogenic carbon dioxide (CO₂) is not included as it is regarded as “neutral” (Crops take up CO₂ when growing, and when the crop is incinerated, the CO₂ ends back in the environment). In this Life Cycle Assessment biogenic CO₂ is included. First of all, biogenic CO₂ contributes exactly as much to global warming as CO₂ from fossil fuels. Secondly, it is very important for the results of this study to identify how much of the carbon applied to the soil that will be incorporated in the soil and how much that is emitted as CO₂. As the amount of biogenic CO₂ emissions are different from the various technologies, it is important to include the biogenic CO₂ and the global warming potential caused by it. In this way, the difference between the biogenic CO₂ and the C stored in the soil is included in the comparison between the reference scenario and the scenarios for each of the new technologies.

It should be emphasized that the Life Cycle Assessment methodology is a simplified model of the environmental impacts. A lot of the processes in the slurry management chain are complex and dependent upon many variables, especially the field processes. The simplified Life Cycle Assessment methodology is not capable of handling dynamic modelling. In LCA, these dynamic data are translated into a set of discrete parameters and values that are carefully chosen in order to represent the situation as well as possible (as done in section 3 when defining the reference scenarios), and these parameters can be changed for analysing the uncertainty. However, LCA is not suitable as e.g. a dynamic model for the analysis of the development during the next 10-20 years, showing the results year by year.

Temporal, geographical and technological coverage

The intended technology level for the reference scenario is to set up a “typical Danish scenario”, based on “average technology”. The scenario should represent “state of the year 2008”. The intended technology level for the alternative technologies is “Best available technology” (BAT), as these technologies are representing the future technologies. This study covers slurry management under Danish conditions (cattle housing systems, storage facilities, soil types, application methods, and energy production) and it is not possible to transfer the results directly to other European countries without adjustments.

Environmental Impacts and Resources

The environmental impact categories in this study are primarily based on the Danish EDIP method, supplied with two impacts from the method “Impact 2002+”:

• Global warming (climate change) (EDIP).
• Acidification, which causes damage to forest, other vegetation and lakes (EDIP).
• Eutrophication (nutrient enrichment), which causes damage to lakes and coastal marine waters (EDIP).
• Photochemical ozone formation (“smog”) , which is caused by reactive compounds forming ozone on the lower layer of the atmosphere, i.e. at the human breathable level, causing respiratory problems for humans and potentially reducing growth of crops. It is commonly known as “smog” in large cities (EDIP).
• Respiratory inorganics (particulates) are commonly known as small particles or dust that causes respiratory problems (and death) for humans with asthma or respiratory diseases. Especially particles from diesel cars and wood stoves are known from the media. Impacts from ammonia, nitrogen oxides and sulphur dioxide are included in this category (Impact 2002+).
• Phosphorus (as a resource) has been chosen as a separate impact indicator category, as the phosphorus resource issue and recycling of phosphorus is particularly relevant for this project. Phosphorus is an essential element for plant and animal nutrition. In case of depletion there could be a serious problem for the global food production since phosphorus is such an essential ingredient in fertilisers, especially because there are no substitutes.
• Resources. The consumption of non-renewable energy resources is included as this is an indicator of the energy consumption of the system (Impact 2002+)

Reference scenarios

System description for the reference scenarios

The reference scenarios in this report do not represent an average of the slurry management systems in Denmark, but should rather be seen as a representative of “typical” systems. Accordingly, an attempt to identify the most commonly used methods has been made. The reference scenarios do not cover all situations and possibilities.

There are two reference scenarios: one for fattening pigs and one for dairy cows. In short, the main preconditions for the reference scenario are:

• The reference scenario for fattening pigs is based on a housing system with “Fully slatted floor” for fattening pigs and “cubicle housing system with slatted floor (1.2 m channel)” for dairy cows.

• From the pre-tank in connection with the housing units the slurry is pumped to the outdoor storage in concrete slurry tanks and covered by a floating layer.

• The transport distance from storage to application to fields has been estimated to 10 km.

• The slurry is applied with trail hose tankers to the field in the reference scenarios.

• Relevant soil types in Denmark are clay soil and sandy soil. In the modelling, soil type JB3 has been used representing sandy soil and soil type JB6 has been used representing clayey soil ¹.

• It is assumed that the slurry is applied to all crops in the crop rotation pattern (six year rotation). Crop types relevant for respectively pig slurry and dairy cow slurry are specified. As mentioned above, the crops are not included within the system boundaries. They are only defined, as the uptake and emissions of N and P in slurry depends on the crop, and in order to model the further fate of the N not removed with harvested products.

Data for the reference scenario

Data for the reference scenario is to a high degree based on two main references: Data from the Danish Normative system for assessing manure composition (Poulsen et al. (2001), DJF (2008a) and DJF (2008b)) and IPCC (2006). These data should be regarded as rather “static and rough estimates”. These data have been used as these are widely used for national and international statistics for Green House Gas calculations, and as the budget for this study could not include sophisticated modelling of the emissions. However, it is has not without problems using the Danish Normative system for assessing manure composition together with data from IPCC (2006). First of all, the two references are not in accordance regarding mass balances and emissions (the loss of C due to CH₄ emissions in IPCC (2006) is not in accordance with the DM loss estimated by DJF (2008b)). Secondly, the data is rather “static”. The Danish Normative system do not specify the retention time in the housing units, the pre-tank or the outdoor storage. Furthermore, there is no specification of the emissions from the pre-tank (it is assumed to be included under “storage”, which is included in the data for outdoor storage in this study).

Results of the impact assessment

It should be emphasised that essential assumptions and data in this report are chosen to represent Danish conditions only. Results cannot be immediately transferred to other countries due to differences in housing systems, retention time for the slurry in the housing units and in the outdoor storage, differences in how the slurry is stored (covered / uncovered), differences in temperatures, slurry composition (due to differences in the feeding of the animals), temperature and other weather conditions (during and after application), soil types and many other factors.

The conclusions are only valid for the preconditions described in this report! For example, differences in application method to the field, uncovered outdoor storage or differences in the slurry composition will significantly affect the results.

Contributions to global warming mainly come from CH₄ from in-housing storage, outdoor storage and from CO₂ and N₂O emissions after application of the slurry to the field. Scientific research is needed in the area.

The contribution to acidification is totally dominated by NH₃ emissions in the housing units, during outdoor storage and after application of the slurry to the field.

Aquatic eutrophication (N) is dominated by N leaching. NH₃ emissions also contribute to some extent (contributions from the indoor storage are due to NH₃ emissions).

The results for aquatic phosphorous eutrophication (P) are affected by huge uncertainty, and the results should be interpreted with care. Accordingly it cannot be concluded that there is a “net saving on P leaching” by applying pig slurry or dairy cow slurry! The discussion of P leaching from slurry vs. mineral fertilisers is beyond the scope of this study.

The main contributor to ozone formation is the CH₄ emissions from the in-house storage of slurry and the outdoor storage of slurry.

The contributions to the impact “Respiratory inorganics” are totally dominated by contributions from NH₃.

The electricity consumption (for pumps and stirring) is rather insignificant (but for resource consumption).

Transport has a small contribution to the category “Resource consumption” due to the fuel consumption. The contributions to the impact “Photochemical ozone formation” are rather small, and so are the contributions to the category “Respiratory inorganics” (caused by small particles emitted during driving). Transport is totally insignificant for the rest of the impact categories.

The difference between soil type JB3 and JB6 is only noteworthy for aquatic eutrophication (N) (nitrate leaching).

Scenario for the Infarm NH4+ acidification of slurry

Goal

A comparative life cycle assessment has been performed in to answer the question: “What are the environmental benefits and disadvantages of acidification of slurry in the Infarm NH4+ plant compared to the reference scenario for slurry?”. This is done by comparing the environmental impacts from the scenario for acidification of slurry in the Infarm NH4+ plant to the environmental impacts from the reference scenario.

The environmental impacts and conclusions in this chapter build to a great extent on data and information delivered by the producer of the technology, Infarm, or on data made for Infarm. The conclusions rely on this information, and the authors have not had the possibility of verifying the data.

System description

In the Infarm NH4+ Acidification plant, pig or cattle 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; for example might the use of sulphuric acid for the acidification be an advantage as it adds sulphur to the field which can have a fertiliser effect.

Results of the impact assessment

The results of the comparative life cycle assessment show that:

• Acidification of slurry reduces the NH₃ emissions significantly. As NH₃ gives the main contributions to the environmental impact categories “Acidification” and “Respiratory inorganics”, the total contributions to these are reduced considerably when comparing the acidification scenario to the reference. The contribution to “Acidification” is reduced by 40-90% compared to the contribution from the reference system for pig slurry and by 30-66% compared to the contribution from the reference system for dairy cow slurry. The contribution to “Respiratory inorganics” is reduced by 30-90% compared to the contribution from the reference system for pig slurry and by 20-70% compared to the contribution from the reference system for dairy cow slurry.
  
  
• Acidification of slurry reduces the CH₄ emissions, probably due to that the biological activity is inhibited at the low pH. This leads to a reduction of the contributions to the environmental impacts “Global warming and “Photochemical ozone formation”. The contribution to “Global warming” is reduced by 10-36% compared to the contribution from the reference systems for pig and dairy cow slurry.
  
  
• As the acidified slurry contains more N when applied to fields than untreated slurry (due to the reduced losses of NH₃ during storage), the contribution to nitrate leaching is higher for acidified slurry. The higher amount of N will lead to a higher crop yield. When comparing systems in life cycle assessments, it is very important that the outputs of the compared systems are equal (otherwise they are not comparable. For example, a system that produces 1 kg wheat shall not be compared to at system that produces 1 kg wheat plus 2 kg rye). In order to make the system for acidification of slurry equal to the reference system, a corresponding amount of crop yield has been subtracted from the system, which will to some extent counterbalance the higher nitrate leaching (however, these data are rather uncertain). When taking the replaced crop yield into consideration, there is no significant difference between the acidification scenario and the reference scenario on a 10 year basis due to uncertainties. On a 100 year basis, the contribution to nitrate leaching is increased by 10-30% when comparing with the contribution from the reference system.
  
  
• Acidification of slurry does not affect “Aquatic phosphorous eutrophication” or the resource consumption of phosphorus, as acidification does not affect the content of phosphorus in the slurry.
  
  
• The consumption of non-renewable energy resources is not significant higher for the acidification scenario as the extra consumption due to the electricity consumption is counterbalanced by the subtraction of the higher crop yield, as explained above.
  
  
• The difference between soil type JB3 and JB6 is only noteworthy for aquatic eutrophication (N) (nitrate leaching). The difference is not significant for the overall results.

Scenario for the Samson Bimatech Energy Plant

Goal

A comparative Life Cycle Assessment has been performed in order to answer the question: “What are the environmental benefits and disadvantages of utilising pig slurry for producing fibre pellets in a Samson Bimatech Plant MaNergy 225 and utilising the fibre pellets for heat production - compared to the reference scenario for pig slurry?”.

The environmental impacts and conclusions in this chapter to a great extent build on data and information delivered by the producer of the technology, Samson Bimatech, and on data made for Samson Bimatech (laboratory measurements of the slurry composition). The conclusions rely on this information, and the authors of this study have not had the possibility of verifying the data.

System description

The fibre pellets are produced in a number of steps, which include mechanical separation of pig (or cattle) slurry, drying of the fibre fraction and pressing the dried fibres into pellets. The pellets can be used for heat production at the farm in a Samson Bimatech Energy Plant. The drying process of the wet fibres requires heat and this consumes approximately 40% of the energy produced by combustion of the fibre pellets. The produced heat replaces heat production by light fuel oil (or by the use of straw or wooden pellets in the sensitivity analysis) and the “replaced heat” is subtracted from the system.

The assessment includes pig slurry only, as measurement for cattle slurry was not available at the time of collecting data. Data on cattle slurry has been collected just before finalizing the project (May 2009) however, it was not possible to include this within the time frames of this study.

Results of the impact assessment

The results of the Life Cycle Assessment show that:

The overall contributions to global warming for the system with the Energy Plant are at the same level as the contributions from the reference system (when keeping the high uncertainty on the data in mind). The CO₂ emissions from the combustion of fibre pellets from the Energy Plant is partly counterbalanced by the reduced CO₂ emissions from applying the liquid fraction to field (compared to applying untreated slurry to field) and the CO₂ emissions from the replaced heat production (the Energy Plant produces heat that can be utilized for heating the farmer’s private house. The energy that would have been used for heating the farmer’s house has been subtracted from the system).

The NH₃ emissions is reduced in the Energy Plant scenario compared to the reference scenario due to reduced NH₃ emissions from the application of the liquid fraction to field compared to untreated slurry in the reference scenario. The reduced NH₃ emissions lead to a small reduction in the overall contributions to the environmental impact “Acidification“.

The contribution to aquatic eutrophication (N) is slightly reduced for the Energy Plant scenario, as a smaller total amount of N from the slurry ends at the field because some of the N is removed to the fibre fraction, converted to fiber pellets and combusted.

The contribution to aquatic eutrophication (P) is unchanged.

The scenario for the Energy Plant has a higher contribution to the environmental impact category “photochemical ozone formation” due to emissions of nitrogen oxides during the combustion of the fibre pellets. This is only partly counterbalanced by a slight decrease of CH₄ emissions from the outdoor storage of the liquid fraction compared to the outdoor storage of the reference slurry due to a lower content of C a in the liquid fraction. There are significant uncertainties on the emissions of nitrogen oxides from the Energy Plant due to the fact that the technology is undertaking ongoing product development.

The contribution to the impact category “respiratory inorganics” is at the same level for the scenario with the Energy Plant as for the reference scenario (taking the uncertainties into consideration). The Energy Plant scenario has increased contributions to respiratory inorganics caused by the emissions of nitrogen oxides (and partly by the emissions of particles). The nitrogen oxides are discussed above. However, the contributions from the field processes are lower for the Energy Plant scenario than for the reference scenario due to the reductions of NH₃ as explained above.

The Energy Plant technology is undergoing continuous product development and the technology should be seen as being “in its child-hood”. On one hand it means that it has been difficult to obtain “high quality data” on air emissions and separation indexes. The data on air emissions has significant influence on the nitrogen oxide emissions. On the other hand it probably means that there are plenty of possibilities for improving the technology. The NO_X emissions could probably be reduced significantly by implementing known NO_X reducing technology in the Energy Plant. The separation has huge influence on the overall environmental impacts, as the main contributions come from storage and application of the liquid fraction to field – which to a great extent depend on the proportion of N and C transferred to the fibre fraction. For the mechanical separation, 29.6% of the DM and 6.8% of N is transferred to the fibre fraction (see table C.2). This means that 70.4% of the DM and 93.2% of the N stays in the liquid fraction. Increasing the part of DM and N that is separated to the fibre fraction during the separation by “product development” would reduce the overall environmental performance of the system.

Scenario for fibre pellets used as fertiliser

Goal

A comparative Life Cycle Assessment has been performed in order to answer the question: “What are the environmental benefits and disadvantages of utilising pig slurry for producing fibre pellets in a Samson Bimatech Energy Plant and utilising the fibre pellets for fertilising the field - compared to the reference scenario for pig slurry?”.

The environmental impacts and conclusions in this chapter build to a great extent on data and information delivered by the producer of the technology, Samson Bimatech and on data made for Samson Bimatech (laboratory measurements of the slurry composition). The conclusions rely on this information, and the authors do not have had the possibility of verifying the data.

System description

The system in this chapter is very alike the system for the “Energy Plant scenario” mentioned above. However, the fibre pellets are not used for heat production as the “Energy Plant scenario”, but for application to the field as fertiliser.

It should be emphasised that this scenario is mostly performed as “a test of a future possibility”, as fibre pellets are not used for fertilising today.

Results of the impact assessment

When keeping the overall uncertainty on the data in mind, there is no significant difference between the overall contributions to global warming, aquatic eutrophication (P), “respiratory inorganics” and the consumption of phosphorus as a resource when comparing the “Fibre Pellets used for fertilising”-scenario compared to the reference system.

The “Fibre Pellets used for fertilising”-scenario has a slightly reduced contribution to the environmental impact “Acidification” and to aquatic eutrophication (N) than the reference system due to the reduced NH₃ emissions and N leaching from the liquid fraction applied to field compared to untreated slurry.

The contribution to “photochemical ozone formation” is slightly higher from the “Fibre Pellets used for fertilising”-scenario compared to the reference system.

The consumption of non-renewable energy resources is considerably higher caused by the electricity consumption by the Energy Plant.

[1] JB3 has a clay content of 5 – 10 %, a silt content < 25 % and a fine sand content <40 %. JB6 has a clay content of 10 – 15 %, a silt content < 30 % and a fine sand content of 40 – 90 %

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Version 1.0 July 2009, © Danish Environmental Protection Agency