| Front Page | | Contents | | Previous | | Next |

Miljøvurdering af alternative bortskaffelsesveje for bionedbrydelig emballage

3 English summary

Composting of biodegradable packaging is not the environmentally optimal solution

Should biodegradable packaging be composted or is it just as good for the environment to incinerate them and utilise the energy for electricity and district heating? This question is the subject of the project "Environmental assessment of alternative ways of disposing of biodegradable packaging." The question is fairly easy to answer when considered from a life cycle perspective. Each of the systems to be compared consists of only a few process-chains, and each of these is characterized by some typical environmental effects. Thus, the question can be answered without extensive and detailed calculations. The main conclusion of the project is that incineration is generally preferable since it allows for better utilisation of the energy content of the materials.

The background for the project is the appearance of new plastic materials that can be degraded biologically, also known as compostable or biodegradable. Today, these materials will simply be treated together with the general household waste, which means that they will be incinerated. The question is whether there would be any environmental advantage by composting the packaging instead, and whether biodegradability in itself is therefore a property of packaging that should be promoted.

The project has been performed as a simplified life cycle assessment based on selected publicly available data. The calculations show that incineration of the biodegradable packaging gives a smaller contribution to global warming, acidification than composting.

The main conclusion is that incineration is preferable, because it displaces emissions from an alternative energy production. This conclusion is relatively stable to changes in the basic system assumptions. As long as the heat from incineration is utilised, and other environmental effects than global warming are not given extreme weights (e.g. 5 times more than global warming, or including other effect categories than those included here), the conclusion will be stable.

Whether the biodegradable packaging is composted or incinerated, the main process is the same, namely a decomposition of carbon-chains. This can take place at low temperature (composting and subsequent metabolism in soil) or quickly at high temperature (incineration), but the CO₂-emission is practically the same, when assuming completely aerobic composting and metabolism (i.e. without methane-emission).

The main difference between composting and incineration is that the energy content of the packaging material can be recuperated upon incineration and utilised for production of district heating and electricity so that the overall demand for incineration of fossil fuels for this purpose is reduced. In a life cycle assessment this is shown by subtracting the emissions from the displaced fossil energy production from the emissions from incineration of the packaging. When the packaging is composted the material is decomposed without recuperation of energy (in principle heat could be recuperated from the composting process, but this is assessed as not economically feasible due to the relatively low temperatures of the composting process).

Even though the CO₂-emissions from decomposition of the carbon chains are the same, the composting process and the incineration process have different emissions of e.g. NOx, VOC and dioxins. NOx and dioxins have been included as examples of emissions that only occur in incineration. By waste incineration a smaller fraction of the chlorine in the waste contributes to the formation of toxic dioxins. At the lower temperatures in the composting process this reaction does not take place. In the same way, NOx is formed by incineration but not by composting. Thus, it is an advantage of composting that these emissions are avoided.

The energy content in the packaging could also be utilised if Denmark decides to use waste gasification instead of incineration. However, this requires that the packaging is also biodegradable under the anaerobic conditions in the biogas reactor. This can be ensured by demanding that the packaging is compliant with the CEN-standard 13432, which covers both aerobic composting and anaerobic decomposition. However, it is voluntary to perform the anaerobic tests. It is therefore important to investigate whether these have been performed if the packaging is to be used in a gasification system.