6 Fibre Pellets used as fertiliser

Life Cycle Assessment of Slurry Management Technologies

This chapter contains a life cycle assessment for a scenario where pig slurry is use for producing fibre pellets in a Samson Bimatech MaNergy 225 Energy Plant and these are used as fertiliser at the field. The “Fibre Pellets for fertilising”-scenario is compared with the reference scenario from chapter 3. The life cycle assessment is 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?”.

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.

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.

6.1 System description

The system in this chapter is very alike the system in chapter 5. However, the fibre pellets are not used for heat production as in chapter 5, but for application to the field as fertiliser.

The system is shown in figure 6.1. The process numbers refer to the heading of the sections in this Annex E.

Figure E.1. Flow diagram for the scenario with production of fibre pellets for fertilising.

Click here to see Figure 6.1

6.2 Results of the Impact Assessment

6.2.1 Overall results of the comparison

In figure 6.2, the environmental impacts from the “Fibre Pellets as fertiliser scenario” have been compared to the environmental impacts from the “reference system” described in chapter 3. The results are discussed in the following sections.

Figure 6.2. Environmental impacts for the scenario with fibre pellets used for fertilising (fibre pellets pellets produced the Samson Bimatech Energy Plant) with the reference system (both based on soil type JB3) – pig slurry.

Click here to see Figure 6.2

6.2.2 Sensitivity analysiss

Sensitivity analysis has been carried out for a number of possible variations of the Energy Plant scenario and uncertainties related to the data.

In this section, the results of sensitivity analysis are shown for the difference between soil type JB3 and JB6. As can be seen from figure 6.3, the difference between soil type JB3 and JB6 has no significance for the overall conclusions.

The significance of applying a 10 years horizon or 100 year horizon is shown in figure 6.2, however only for global warming, as the 100 year leaching values cannot be calculated for N leaching.

In general, this scenario is very alike the “Energy Plant Scenario” in chapter 5, and the same uncertainties apply. Accordingly, these are not repeated here but should be read in chapter 5.

6.2.3 Global warming

The discussion regarding the contributions to global warming is generally the same as in chapter 5. The difference from chapter 5 is that only 40% of the fibre pellets are combusted, leading to a smaller contribution of CO₂ from the Energy plant (50% of the contributions from chapter 5), however, as 60% of the fibre pellets ends at the field, the CO₂ is emitted here instead (see figure 6.2). Detailed explanations can be found in Annex E. The overall conclusion is the same; there is no difference between the system for Fibre pellet production and the reference system when taking the uncertainties into consideration.

As there is no heat production (no heat surplus by the Energy Plant), replaced heat production has not been subtracted from this system.

6.2.4 Acidification (environmental impact)

The conclusion regarding the acidification is generally the same as in chapter 5. The contribution from the Energy Plant is reduced by 50% due to a smaller amount of fibre pellets being combusted. However it does not change the conclusion: The scenario with the Fibre Pellet used for fertilising contributes slightly less to acidification than the reference system, due to the reduced emissions from the liquid fraction.

Figure 6.3. Sensitivity Analysis: Difference between soil type JB3 and JB6. Environmental impacts for the scenario with fibre pellets used for fertilising (fibre pellets pellets produced the Samson Bimatech Energy Plant) compared to the reference system – pig slurry.

Click here to see Figure 6.3

6.2.5 Aquatic eutrophication (N) and (P)

The conclusions regarding aquatic eutrophication (N) is different than in chapter 5.The system with pellet production in the Energy plant contributes slightly less to the environmental impact aquatic eutrophication (N) than the reference system (due to the smaller amount of N in the liquid fraction).

Furthermore, the N leaching from the fibre pellets are very low. In short, the C:N ratio of the fibre pellets is very high, which has the consequence that most of the N will be build into the humus rather than being available for crops. The fibre pellets are more suitable as “soil improvement agent” (for building up humus) than as N fertiliser. Accordingly, the net contribution to aquatic eutrophication (N) from the system with Fibre pellet production for fertilising is slightly lower than the reference system.

6.2.6 Aquatic eutrophication (P)

As all the phosphorous from the original reference slurry ex animal end at the field, there is no change in the contributions to aquatic eutrophication (P).

6.2.7 Photochemical ozone formation (“smog”)

The contribution to the impact category “photochemical ozone formation” is slightly higher for the scenario with the Energy Plant as for the reference scenario. The explanations runs parallel to the explanations in chapter 5 but the emissions from the Energy Plant itself is reduced by 50% due to a smaller amount of fibre pellets being combusted (not for the total system).

6.2.8 Respiratory inorganics (small particles)

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 explanations runs parallel to the explanations in chapter 5 but here the emissions from the Energy Plant is reduced by 50% due to a smaller amount of fibre pellets being combusted.

6.2.9 Non-renewable energy resources

As can be seen on figure 6.2, the consumption of non-renewable energy resources is increased considerably for the “Fibre Pellets as fertiliser”-scenario compared to the reference system. This is due to the energy consumption of the Energy Plant.

6.2.10 Consumption of phosphorus as a resource

There is no difference regarding the consumption of phosphorus as a resource between the “Fibre Pellets as fertiliser”-scenario and the reference scenario.

All the phosphorus that was originally in the slurry “ex animal” is distributed to fields – by the liquid fraction, by the fibre pellets and in the ash from the combusted fibre pellets.

However, as the fibre pellets contain some of the phosphorus, and as the ash contains another part of the phosphorus, there could be future possibilities for redistributing some of the phosphorus with these two fractions. As discussed in chapter 5, approximately 9% of the phosphorus is transferred to the fibre fraction and from this to the fibre pellets (60%) and to the ash (40%).

The modelling of the fate of this phosphorus if redistributed to other fields with more need for phosphorus has been above the time and budget of this project. However, it is recommended to include aspects of this in a future project.

6.3 Conclusion

The results of the comparison are shown in table 6.1 and figure 6.4 below.

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.

Table 6.1. Comparison of the impacts from the scenario with fibre pellets used for fertilising (fibre pellets pellets produced the Samson Bimatech Energy Plant) to the reference scenario for pig slurry. The number of digits is not an expression of the uncertainty. The uncertainty of the net contribution is based on an estimate with regard to the uncertainty on the data the forms the foundation for the LCA.

Environmental impact / resource consumption	Reference scenario	“Fibre Pellets as fertiliser” scenario	Net contribution i.e. ” Fibre Pellets as fertiliser scenario” minus ”Reference scenario”
Global warming (during 10 years) [kg CO₂ eq.]	From slurry: 284 kg From fertiliser: -36 kg Net: 248 kg	From slurry: 288 kg From fertiliser: -36 kg Net: 252 kg	4 [-4 – +11 kg CO₂ eq. No significant difference
Global warming (during 100 years) [kg CO₂ eq.]	From slurry: 304 kg From fertiliser: -47 kg Net: 257 kg	From slurry: 310 kg From fertiliser: -47 kg Net: 263 kg	5 [-5 – +16] kg CO₂ eq. No significant difference
Acidification [m² UES, i.e. area of unprotected ecosystem]	From slurry: 50.3 m² From fertiliser: -5.5 m² Net: 44.8 m²	From slurry: 44.4 m² From fertiliser: -5.5 m² Net: 38.9 m²	-5.9 [-3.5- -8.3] m² UES 7-16% reduction of contribution from slurry
N-eutrophication (aquatic) (during 10 years) [kg N - amount reaching aquatic recipients]	From slurry: 1.51 kg From fertiliser: -0.93 kg Net: 0.59 kg	From slurry: 1.43 kg From fertiliser: -0.93 kg Net: 0.50 kg	-0.08 [-0.042 - -0.13] kg N 2.7-8.0% reduction of contribution from slurry
N-eutrophication (aquatic) (during 100 years) [kg N - amount reaching aquatic recipients]	From slurry: 1.63 kg From fertiliser: -1.03 kg Net: 0.61 kg	Could not be modelled	Could not be modelled
P-eutrophication (aquatic) [kg P - amount reaching aquatic recipients]	From slurry: 0.0069 kg From fertiliser: -0.0086 kg No significant difference	From slurry: 0.0069 kg From fertiliser: -0.0086 kg No significant difference	No difference
Photochemical ozone formation [person.ppm.hr - see section 3.4.7]	From slurry: 0.18 p.p.h From fertiliser: -0.014 p.p.h Net: 0.17 p.p.h	From slurry: 0.19 p.p.h From fertiliser: -0.014 p.p.h Net: 0.17 p.p.h	0.007 pers.ppm.hr [0.003-0.009] 2-5% increase of contribution from slurry
Respiratory Inorganics [kg PM2.5 eq, i.e. kg equivalents of 2.5 µm size particles]	From slurry: 0.29 kg From fertiliser: - 0.05 kg Net: 0.24 kg	From slurry: 0.27 kg From fertiliser: - 0.05 kg Net: 0.22 kg	No significant difference
Non-renewable energy [MJ primary energy]	From slurry: 151 MJ From fertiliser: - 369 MJ Net: -217 MJ	From slurry: 359 MJ From fertiliser: - 370 MJ Net: -11 MJ	20o [ 100 – 300 ] MJ 70-200% increase of contribution from slurry
Phosphorus Resources [kg P]	From slurry: 0 kg From fertiliser: - 1.3 kg Net: - 1.3 kg	From slurry: 0 kg From fertiliser: - 1.3 kg Net: - 1.3 kg	No difference
Carbon stored in soil during 10 years [kg C] (Corresponding to this amount of CO₂-eq.)	From slurry: 7.5 kg C From fertiliser: - 3.9 kg C Net: 3.6 kg C From slurry: 27.6 kg CO₂ From fertiliser: -14.3 kg CO₂ Net: 13.2 kg CO₂	From slurry: 8.0 kg C From fertiliser: - 3.9 kg C Net: 4.1 kg C From slurry: 29.3 kg CO₂ From fertil.: -14.4 kg CO₂ Net: 14.9 kg CO₂	0.5 [0.3 – 0.6 ] kg C 1.7 [ 1.2 – 2.3] kg CO2 4-8% increase of contribution from slurry
Carbon stored in soil during 100 years [kg C] (Corresponding to this amount of CO₂-eq.)	From slurry: 2.1 kg C From fertiliser: - 1.1 kg C Net: 1.0 kg C From slurry: 7.8 kg CO₂ From fertiliser: -4.0 kg CO₂ Net: 3.8 kg CO₂	From slurry: 2.1 kg C From fertiliser: - 1.11 kg C Net: 1.9 kg C From slurry: 7.8 kg CO₂ From fertiliser: -4.1 kg CO₂ Net: 3.7 kg CO₂	-0.02 [-0.01 – -0.03 ] kg C -0.08 [ -0.06 - -0.11] kg CO2 0.7-1.4% decrease of contribution from slurry

Figure 6.4. Environmental impacts for the scenario with fibre pellets used for fertilising (fibre pellets pellets produced the Samson Bimatech Energy Plant) compared to the reference system (both based on soil type JB3) – pig slurry.

Clck here to see Figure 6.4