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Life Cycle Assessment of Slurry Management Technologies

2 Scope

• 2.1 Methodology
• 2.2 Reference scenarios and alternatives
• 2.3 Consequential approach
• 2.4 Basis for the comparison: The functional unit
• 2.5 System boundaries
• 2.6 Temporal, geographical and technological coverage
• 2.7 Environmental Impacts and Resources

2.1 Methodology

The environmental assessment in this study is based on the method for Life Cycle Assessments (LCA) described in the Danish EDIP method by Wenzel et al. (1997) and further updates of this method (Weidema et al. (2004), Weidema (2004), Stranddorf et al. (2005)).

Life Cycle Assessment is the assessment of the environmental impacts of a product (or service) throughout its lifespan, i.e. “from cradle to grave”. That means that the environmental impacts are followed through the whole product chain, typically from raw material extraction, through production and use, to final disposal or recycling. For agricultural products, the chain would include fertiliser production, grain production, field activities for crops, animal husbandry, slurry management, transport, storage, preparation of food and food products disposed in the households.

The method used in this study is in agreement with the standards of the International Organisation for Standardisation, ISO (ISO 14040 (2006) and ISO 14044 (2006), except that an external review has not been performed by an external LCA review panel as required by the ISO standards, as a LCA review panel was not included in the budget for the study.

The study is comparative, as environmental impacts of the new technologies are compared to the reference scenarios. This is mentioned since the ISO 14040 and 14044 standards for Life Cycle Assessment include specific requirements for comparative Life Cycle Assessments that are disclosed to the public, among these special requirements regarding a LCA review panel.

The primary data for the technologies in this study are delivered by the producers of the technologies. Background data are from the Ecoinvent database. Ecoinvent is the world's leading supplier of consistent and transparent life cycle inventory data (The Ecoinvent Centre, 2008). The database from the project will be available in SimaPro format and use requires license to SimaPro and Ecoinvent. The LCA has been performed by the use of the PC-tool SimaPro 7.1, which is the most widely used LCA software today (PRé, 2008).

2.2 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, and combinations of these. The environmental consequences of choosing alternative technologies are compared to the reference scenarios.

The alternative technologies included in this study are shown in the flow-diagrams in figure 2.1 below. It must be noticed that the flow diagrams are very rough and simplified in order to present an overview.

Figure 2.1. Overview of the slurry treatment technologies included in this study.

Click here to see Figure 2.1.

As it can be seen from figure 2.1, 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

The reference scenario is described in chapter 3, and the data for the life cycle assessment is outlined in Annex A.

Acidification of slurry in the Infarm NH4+ plant is described in chapter 4, and the data for the life cycle assessment is outlined in Annex B.

In the Samson Bimatech MaNergy 225 Energy Plant pig slurry is mechanically separated and the fibre fraction is used for producing fibre pellets. The fibre pellets are combusted for producing energy for the farm. This scenario is described in chapter 5. The data for the life cycle assessment for the mechanical separation (which is part of the Samson Bimatech MaNergy 225 Energy Plant) is described in Annex C. The data for the life cycle assessment Samson Bimatech MaNergy 225 Energy Plant is described in Annex D.

The fibre pellets from the Samson Bimatech MaNergy 225 Energy can be used for fertilising. This scenario is described in chapter 6. The data for the life cycle assessment can be found in Annex E (combined with data from Annex C and D).

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 of changed diet for the animals, the use of enzymes in the feed, the 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.

2.3 Consequential approach

This study is conducted according to the principles of consequential LCA.

The consequential LCA approach was developed during the Danish consensus project on Life Cycle Assessment in 1997-2003 (Hansen, 2007). The consequential approach is described in Weidema (2004). The ISO standards for Life Cycle Assessment (ISO 14040 and ISO 14044) recommends expanding the product system to include the additional functions related to the co-products, which is the same as the consequential approach ². In the next version of the world’s leading LCA database, Ecoinvent, the consequential approach will be the default method (Weidema, 2009) ³.

The consequential approach should be used when the goal of the study is to identify the environmental consequence of choosing one alternative over the other or, in this study, the consequence of choosing a new technology as a replacement for the conventional slurry management methods.

The consequential approach requires that the LCA is comparative, i.e. that alternatives are compared. The consequential and comparative approach ensures that all compared alternatives are equivalent and provide the same services to society, not just regarding the primary service, which is the “main function” of the system, but also on all secondary services. Secondary services are defined as products/services arising e.g. as co-products from processes in the studied systems. In this study, secondary functions are for example the nutrient value of the slurry (that can replace mineral fertilisers) or the energy content of the biogas produced from the slurry (replacing other energy production).

The consequential LCA ensures equivalence on all primary and secondary services by identifying and including the displacements of alternative products that will occur when choosing one alternative over the other. See further explanation of comparative and consequential LCA in Wenzel (1998), Ekvall and Weidema (2004) and Weidema (2004).

In order to make a reasonable comparison it is fundamental to perform the assessment in relation to the same function, i.e. the same service, which is in Life Cycle methodology called “the Functional Unit”.

2.4 Basis for the comparison: The functional unit

The primary service of all the scenarios is defined as: “Management of slurry”, which includes various kind of treatment and utilization of slurry.

The functional unit is: “Management of 1000 kg slurry”.

The reference flow is defined as 1000 kg slurry “ex animal”, i.e. right after excretion. The composition of the reference slurry is further specified in section 3.2 below.

All the scenarios in this study have additional secondary services. These are described under each scenario in chapter 3-6.

2.5 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 “upstream” 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.

As can be seen from 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.

Figure 2.2. System boundaries: The blue coloured processes and emissions are within the system boundaries and these are included in this study. The grey processes and emissions are not included.

Click here to see Figure 2.2

It is not claimed that the processes “upstream” (i.e. before the slurry excretion) have no environmental significance - it is just without the frame of this study. Other studies that have dealt with the whole food chain in an LCA perspective have concluded that the slurry management part is significant for the overall environmental impacts of meat production. Dalgaard (2007) concluded a life cycle assessment for pork production and Weidema et al. (2008) included the whole life cycle for pigs and cattle in a study entitled “Environmental Improvement Potentials of Meat and Dairy Products”. In both studies, it is concluded that the slurry and slurry management have overall significance especially for the environmental impact categories “acidification” and “eutrophication”. Dalgaard (2007) states that ammonia from the farms contributes to 83% of the acidification substances emitted from the product chain of Danish pork, and 70% of this is caused by slurry emissions in the housing system, storage and during application. When considering the whole product chain of pork, the two largest contributors to eutrophication were nitrate (63%) and ammonia (30%). According to Nielsen et al. (2008b), the agricultural sector contributed with 14% of the overall greenhouse gas emission (in CO₂equivalents) in 2006.

The emissions of CH₄ and N₂O from manure management contributed with 16% of the total emission from the agricultural sector in 2006.

According to the system boundaries in this study, the major part of the agricultural CH₄ emission originates from digestive processes (i.e. enteric fermentation) is not included in this report (as it is not affected by different types of management of the manure. This accounted for 27% of the total contribution to global warming from agricultural activities in 2006.

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, for example the consumption of energy / chemicals for acidification of the slurry in the housing units is taken into account.

In principle, all emissions and flows with significant environmental impact have to be included in a life cycle assessment. In case of lack of data, estimates have been made rather than leaving gaps.

For all the slurry management technologies, the total life cycle of the technology is included as far as possible. However, if some parts of the life cycle have shown to be insignificant for the overall environmental impacts, they have been left out. Data for equipment, machinery, and maintenance is included, primarily based on estimates or literature data.

It has not been possible to include data for “overhead activities” (i.e. office expenses, heating of offices, transport of employees to and from work for the plants producing the technologies etc). It is estimated that this omission is of minor significance for the overall results, as it is only the relative differences between the scenarios that should be included anyway.

Furthermore, all the processes “behind” this system are included, e.g. production of diesel for the tractor, extraction of oil and refinery for production of the diesel, production of the tractor itself, production of mineral fertilisers and production of chemicals for these, extraction of minerals for production of these chemicals, production of materials and electricity production. The system “behind” the product chain for slurry management is huge with hundreds of processes.

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.

2.6 Temporal, geographical and technological coverage

The study has been based on data from the most recent year for which consistent data are available. It is the intention, that data used for this study should apply for 2008 and 5-7 years ahead. As most of the alternative technologies represented in this study are fairly new, it is likely that ongoing product development will improve these technologies during the next decade.

This study covers slurry management under Danish conditions (for example the pig and cattle housing systems are typically Danish, so are the storage facilities, soil types and energy production). Furthermore, the slurry composition varies significantly within the European countries due to differences in on-farm management, e.g. for feeding (Weidema et al., 2008). The soil conditions and application of fertilisers are also different in Denmark compared to other European countries. Accordingly, it is not possible to transfer the results directly to other European countries without adjustments.

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.

2.7 Environmental Impacts and Resources

The environmental impact categories in this study are primarily based on the Danish EDIP method. Not all impact categories from the EDIP method has been included, see table 2.1.

Note, that all the categories included in this study are indicators, i.e. indicators for impacts on human beings and nature. For example, global warming (climate change) is an environmental concern in itself; however, the larger concern is usually the subsequent damages to humans, animals and plants. Global warming have many impacts, for example drought in some areas, extreme weather conditions, flooding and rising sea levels in other areas, all having potential impact on crop yields and availability of food for humans.

The Life Cycle methodology is a general approach focussing on the potentialcontributions of substances and emissions from the systems assessed to the environmental impacts, and not the actual environmental impacts. Accordingly, it is not within the frame of the LCA method to include site specific considerations of e.g. nature being particularly sensitive to specific emissions like e.g. ammonia. This is in accordance with both the ISO standards for Life Cycle Assessment (ISO 14040 and ISO 14044) and international consensus, acknowledging that it is in practice impossible to know all sites of emissions to the environment and all actual exposure pathways of the emitted substances.

From the EDIP method, the following categories have been included:

• Global warming (climate change). The main contributors are carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O).
  
  
• Acidification, which causes damage to forest, other vegetation and lakes. The primary contributors to acidification are sulphur oxides (SO₂ and SO₃), nitrogen oxides (NO_X) and ammonia (NH₃). For agriculture especially ammonia emissions are in focus.
  
  
• Eutrophication (nutrient enrichment), which causes damage to lakes and coastal marine waters. The Danish Action Plan for the Aquatic Environment III 2005-2015 (Vandmiljøplan III) is established in order to prevent eutrophication. The contributors are potentially all compounds containing nitrogen (N) and phosporus (P). When assessing the environmental impacts of slurry management, nutrient enrichment is an important impact category to include. In this study, the EDIP impact categories “Aquatic eutrophication (N)” and “Aquatic eutrophication (P)” has been included in order to illustrate the differences of the systems on leaching of nitrogen and phosphorous. The EDIP impact category “Terrestrial eutrophication” has not been included (as it generally shows the same tendencies as the category “Acidification” because it is mainly dominated by NH₃ for the scenarios included in this study).
  
  
• 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. The main contributors are nitrogen oxides (NO_X), volatile organic compounds (VOC) (including methane (CH₄)) and carbon monoxide (CO). In life cycle assessments, the main contributions normally come from transport and combustion processes. The EDIP 2003 method has two categories for this, focusing on impacts on humans and impacts on vegetation. However, the results for this study are almost identical for the two categories, and accordingly, only the category “Ozone formation, impacts on humans” has been included (representing both).

A few categories have been added to the EDIP method:

• 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. Also impacts from ammonia, nitrogen oxides and sulphur dioxide are included in this category. Airborne ammonia attaches to other airborne emissions forms small particulates that are regarded as harmful to health when inhaled (Hansen et al., 2008). In life cycle assessments transport and combustion processes normally contribute significantly to the particulates emissions. As some of the alternative technologies for slurry management in this study may reduce transport needs, as some include combustion processes, and as ammonia from slurry is significant, this category has been included. The category is based on the LCA method Impact 2002+, which is a combination of some of the best European methodologies (Jolliet et al., 2003). In the Impact 2002+ method, particulates are assessed according to size (PM₁₀ are particulates with a diameter of < 10 µm and PM_2.5have a diameter < 2.5 µm).
  
  
• Phosphorus (as a resource) has been chosen as a separate impact indicator category in addition to the general resource calculations in the EDIP method, 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. Phosphorus is in fact a core component at the basis of life (e.g. ATP and DNA molecules). Steen (1998) estimates that the current economically exploitable phosphate reserves can be depleted within approximately 100 years (within the range of 60-130 years). A significant reduction in the global crop production that would occur without phosphorus fertilisation combined with a massive increase in the world population could lead to hunger and starvation. The normalisation factor in this study is based on Nielsen and Wenzel (2005).
  
  
• Resources. The consumption of non-renewable energy resources is included as this is an indicator of the energy consumption of the system. The non-renewable energy resources are calculated by use of the LCA method Impact 2002+, which is mentioned above (Humbert et al. 2005). The unit is “MJ Primary Energy”, using the upper heating value.

An attempt to include odour as a separate impact indicator category has been made. Odour is often a problem for traditional slurry management and some of the alternative technologies are designed specifically to handle odour problems. However, the inclusion of odour is not simple. The definition of where the odour measurements should be taken can be discussed. It is probably more the neighbours of the (pig) farm that are bothered by the odour than the farmer, but the outdoor emissions from housing units to a great degree depend on the distance to the neighbours, the number of animals in the housing units, wind, temperature etc. Furthermore, the odour problem is not “mathematically linear” – an odour of 100*10⁶ OU_E for 5 days might be worse than an odour of 500*10⁶ OU_E for 1 day. The area where the odour is distributed is very significant, too. Moreover, it has been extremely difficult to find data for odour that can be related to “1000 kg slurry” especially for cattle slurry. It has been decided not to include quantitative data on odour, and odour is not included as an impact category in this study. For odour reducing technologies, the reduction is described qualitatively. The database has however been prepared for including odour at a later stage.

With regard to the aspects of slurry management, it would have been obvious to include indicators on spreading of biological contamination (spreading of bacteria and virus), hormones and medicine residues. For instance, the aspects of penicillin and resistance are widely debated. However, it has not been possible to find adequate quantitative data on these aspects; thus, they will be included qualitatively in the discussion.

Table 2.1. Included and excluded impact categories.

Table 2.2 shows the main emissions that contribute to the impact assessment categories mentioned in table 2.1. According to Sleeswijk et al. (2008), 10 emissions fully dominate the contributions to the non-toxic emission dependent environmental impacts in Life Cycle Assessments: CO₂, CH₄, SO₂, NO_X, NH₃, PM₁₀, NMVOC, and (H)CFCs emissions to air and emissions of N- and P-compounds to fresh water. 9 of these are included in this study remaining emission category, (H)CFCs, is considered not relevant for slurry management technologies, accordingly, it is not included (but not left out by principal either. Simply they do not occur for any of the technologies). In addition to the emissions recommended by Sleeswijk et al. (2008), N₂O has been included, as this is especially relevant for agricultural systems.

The emissions in table 2.2 have been included for all the “foreground processes” as far as possible (i.e. for all the processes regarding slurry management that the data have been collected for in this study). The “background processes” from the Ecoinvent database contains far more emissions than these.

Table 2.2. the emissions that data are collected for the “foreground processes” in this study.

* Among the 10 emission categories that have the main contributions to the non-toxic emission dependent environmental impacts according to Sleeswijk et al. (2008)

[2] In the ISO standards for Life Cycle Assessment (ISO 14040 and ISO 14044), the first recommended step under “Allocation procedure” is to avoid allocation by dividing the unit processes into sub-processes (which means that allocation is not necessary), and, if this is not possible, to avoid allocation by expanding the product system to include the additional functions related to the co-products, which is the same as the consequential approach.

[3] Statement from Bo Weidema, Executive Manager for the Ecoinvent Database, 2009: “We plan to improve the database with the release of version 3, which will be available in two standard versions: One is a consequential version where the inputs to each process are the ones affected on long-term by a small change in demand, and where all co-products are treated by system expansion. In addition to this consequential version, the Ecoinvent database will also be available in an attributional version where the inputs to each process are the current average suppliers, and where all co-products are treated by economic allocation.”

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Version 1.0 July 2009, © Danish Environmental Protection Agency