Optimising the climate impacts of the MBP technology

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As was shown in figure 12.6, MPB technology in addition to the recycling material including the RDF fraction leads to a product which after biological treatment is to be deposited. For suitable information on climate effects of MPB as a whole, the effect of the deposited material on the landfill has to be taken into account. A better pre-treatment comes up with lower organic residues and thus with lower landfill gas emissions. On the other hand, longer treatment requires higher energy input, e.g. for aeration, which as a consequence leads to enhanced greenhouse gas emissions in this process step. This is a typical technological compromise situation (see chapter 8) for which the best solution has to be found.

Figure 12.9 displays GHG emissions by energy consumption as well as landfill methane emission with the process duration. The sum of both curves shows a minimum which defines the best decomposition duration. Obviously it is not useful to stabilise the waste to the maximum degree as the overall result gets worse with longer process duration due to a higher total energy input. As dependent on the methane oxidation capacity of the landfill cover the minimum GHG value and therefore best process duration is between 16 and 28 hours. For 95 percent methane oxidation in the landfill layer 18 weeks is the best option.

Figure 12.9 displays GHG emissions by energy consumption as well as landfill methane emission with the process duration. The sum of both curves shows a minimum which defines the best decomposition duration. Obviously it is not useful to stabilise the waste to the maximum degree as the overall result gets worse with longer process duration due to a higher total energy input. As dependent on the methane oxidation capacity of the landfill cover the minimum GHG value and therefore best process duration is between 16 and 28 hours. For 95 percent methane oxidation in the landfill layer 18 weeks is the best option.

Landfill Waste Decomposition Curve
Process duration (weeks)

- Methane oxidation capacity 95 percent-----85 percent

75 percent

Figure 12.9 GWP as dependent on process duration (Soyez, 2001)

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