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Miljømæssige fordele og ulemper ved genvinding af plast Summary and conclusionsThe purpose of this project is to examine the requirements to be met in order to make recycling of plastic materials more advantageous than waste incineration in respect to environment and resources. The conditions may e.g. be related to type and amount of plastics, waste (impurities, decomposition), energy consumption in connection with recovery as well as quality and application of the recovered granulate. The result of the project may support the development of sorting criteria, collection strategies and waste treatment methods that are environmentally justified. The focus of the project is transport packaging as well as household bottles and jars made of plastic. The project is based on the increasing interest in recovering plastic packaging materials which is due to the fact that Denmark through EU regulations has been committed to ensure recovery of at least 15% of all plastic packaging materials. However, a demand for further increase of this rate can be expected. The project comprises: estimation of the collection potential, i.e. amounts and types of plastic fractions that can be collected; description of the reuse potential, i.e. amounts and types of products for which the recovered plastics can be used and whether there will be downcycling. Finally, environmental impact assessment of energy consumption and environmental impacts of selected recovery scenarios is made. The environmental assessments are carried out on a screening level according to the life cycle principle. Chapter 1 is an introductory description of the background and the objective of the project. Potentials and focus areas Chapter 2 of the project deals with the collection and reuse potentials with a view to selecting focus areas for the environmental assessment. A closer analysis of the collection potential for household waste was made in the parallel project: "Collecting systems for plastic bottles and jars" which was also carried out for the Danish Environmental Protection Agency. Chapter 2 indicates that the collection potential inventory is uncertain, especially at a detailed level. In order to restrict the focus area a pre-selection of products has been made, as the packaging may be relevant, perhaps relevant or not relevant to recover. This categorizing is based on criteria such as amount and contents of a number of specific packaged product types. Out of a total potential of approx. 108.000 tons of plastic retail packaging materials a recovery of 37 % has been estimated as relevant or perhaps relevant, the major part being perhaps relevant. Out of a total potential of approx. 97.000 tons of plastic transport packaging materials a recovery of 93% has been estimated as relevant or perhaps relevant, the major part being relevant. Chapter 2 concludes that there are fractions of "clean" transport packaging materials that have a large volume potential and which are therefore relevant to recover. This especially applies to film wrapping from building sites and consumer goods as well as discarded transport boxes. Further, it is concluded that the potential volume of plastic packaging materials from households may be interesting, but that the recovery may cause environmental problems which may make waste incineration more advantageous in certain cases. This is illustrated in more detail later in the project. Methods and data of the environmental assessments Chapter 3 deals with the method of the environmental assessments and the restriction of the scenarios. The functional unity has been defined as: "1 kg packaging of the material type X for packaging the product category Y at the collection efficiency Z" Chapter 3 concentrates on explaining the various method concepts and assessed environmental impacts so that others than LCA-experts can achieve the necessary background knowledge to be able to understand the results of the project. Chapter 4 describes the data collected as part of the project. This applies especially to the data concerning collection systems and recovery of plastics. Environmental assessment of transport packaging Chapter 5 describes the environmental impact assessment of "clean" PE films and boxes which was selected as a focus area which is relevant to recover. "Clean" means that the PE packages are not mixed up with plastics that are impossible to discard during the recovery, and that the packages are free from impurities etc. which cannot be cleaned off fairly easy. For these fractions recovery will be preferred to waste incineration. The biggest advantage is achieved if regranulation without remelting will do i.e. for plastic boxes with a certain goods thickness. Further, the effect of sending the plastic waste materials to the Far East for recovery was estimated. In general, this was regarded as environmentally precarious due to the emissions of the transport, however, the individual environmental impacts are of different importance. Environmental assessment of bottles, jars and bins from households Chapter 6 describes the environmental impact assessment of household bottles, jars and bins which was selected as a focus area that is perhaps relevant to recover. Two aspects are interesting:
The degree of contamination of the used plastic packages was measured by the residues calculated into COD (Chemical Oxygen Demand), i.e. the amount of oxygen needed to decompose the organic substances, which typically make out the main part of the residual content of the packages, e.g. remaining food products. In order to recover plastics and obtain a sufficiently good quality it is important that any contamination is cleaned away. The used water shall be waste water treated no matter if the cleaning takes place within a household or in the recovery company, and COD is a key parameter for the energy consumption of the cleaning plant. Further, COD is a key parameter for the amount of energy derived from the residual content of the package in case of waste incineration. A number of general household products in plastic bottles and jars were purchased, emptied and cleaned, while registering the water consumption, package weight and weight of the residual contents. The COD amount was calculated and listed under the categories: none (clean), low, middle and high. Especially plastic bottles for oil or fat containing products turned out to be difficult to empty, and the residual contents exceeded the weight of the package. Therefore, the COD amount was high, typically corresponding to 1.5 kg per kg plastic package. The amount and type of the residual product and thus the COD impact turned out to be decisive for the question whether recovery can be justified or not. A critical COD amount was not found, but for a "medium" COD content of 0.7 kg per kg plastic, recovery does probably not pay. An example is e.g. body lotion and yoghurt in plastic bottles. Mustard, remoulade and mayonnaise are listed as "high" COD. The table below sets some guidelines as to when recovery is worth while in comparison to waste incineration when cleaning in hot and cold water respectively. During the project the packages were cleaned individually, and for this job a few litres of hot water were typically used. In order to eliminate the environmental impact of heating the water, the calculations were also made without heating the water, i.e. in cold water. However, it is hardly possible to clean used packages with high COD in cold water.
With regard to the efficiency of the collection the general conclusion is that as high a collection efficiency as possible for recovery is preferred, however, packages which are not suited for recovery (e.g. COD according to the above), should be discarded and incinerated. Environmental assessment of sensitive assumptions (sensitivity assessment) During the project a number of assumptions were made, which may be sensitive to the result of the study. Important and sensitive assumptions apply to energy. The energy assumptions are critical in regard to determining how big the advantage of recovery is, and whether recovery is advantageous in all respects. The assumptions concern choice of allocation between electricity and heating, average or marginal choice of energy scenario and future energy supply. In general, we can say that the more environmentally sound the energy displaced through waste incineration is, the less justified incineration will be in comparison to recovery. If it is assumed that the future energy supply in Denmark will become more environmentally compatible, this will consequently mean that waste incineration will be less advantageous than recovery. The results of the project with regard to the COD and collection efficiency of household packaging have been achieved on basis of idealised assumptions. The environmental assessments for COD have thus been based on a collection efficiency of 100% of separate fractions of low, middle and high COD. The environmental assessment of the significance of the collection efficiency is based on "clean" plastics. In reality though, you will have plastic waste with different CODs as well as different collection efficiency rates. Therefore a sensitivity assessment was carried out for examples of such mixtures. The result shows that there is an optimal collection efficiency for household packages, where the share for recovery and the share for waste incineration gives the least possible environmental impact for the system as a whole. With regard to resources recovery is generally an advantage. For a recovery of up to 50%, the rest being incinerated, the estimated resource consumption is almost constant. For the calculated examples of the sensitivity assessment a collection efficiency of 50% for recovery seems to be optimal. The optimal collection efficiency of reality is not defined in this project, since the statistical basis of the products is too insufficient to make a calculation of the real mixture of COD fractions of plastic waste. This will require information on the annual sale of a number of specific products. There are, however, indications towards the fact that the fraction of high COD is considerable, but that the consumers prefer to put these in the waste bin, as they are too difficult to clean.
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