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MBWTs are the future exploiters of raw materials
| | In view of the imminent exhaustion of a great many deposits of raw materials accompanied by higher consumption due to population growth and increasing wealth, the recovery of raw materials from waste is becoming increasingly important. To which extent and quality raw materials can be recovered from residual waste greatly depends on the methods by which the waste is treated.
By Matthias Kühle-Weidemeier
In this regard, above all mechanical and mechanical-biological waste treatment systems (MWTs/MBWTs) and thermal treatment, i.e. waste incineration plants, stand in opposition to one other. A good 80 per cent by weight of German residual waste is currently being treated thermally and barely 20 per cent by weight using mechanical-biological methods. Will waste incineration be able to retain its supremacy?
Recycling not only conserves natural resources (energy commodities, metallic and mineral resources) but also reduces energy consumption and makes an important contribution towards climate protection. On behalf of Interseroh, in 2008 the Fraunhofer Institute Umsicht analysed the CO2 emissions produced in the manufacture of primary and secondary products made of polyethylene (PE), polyethylene terephthalate (PET), copper, aluminium, steel, wood, paper, millboard and cardboard. Massive savings were found to be possible for all of the materials analysed. However, a paper fibre can only be recycled five to seven times. As a decrease of their molecular chains result from recycling, plastics can only be recycled to a limited degree.
Will waste incineration plants be able to retain their supremacy?
The current balance of material for German MBWT plants shows that the recovery of products subjected to material recycling is not particularly high. Around 10,000 tons of non-ferrous metals and approximately 127,000 tons of ferrous metals are generated from approximately 4.9 million tons of input each year. The majority of the output consists of high-calorific fractions, which are then utilised for energetic recycling. The next largest category is landfilled (approximately 1.060 million tons).
The mechanical-biological waste treatment prior to landfilling is currently still wasting both energy and raw materials. A self-sufficient energy supply or recovery can only be achieved through the use of plants which produce biogas by means of anaerobic treatment. The fraction earmarked for landfilling contains valuable materials which could also be recovered for recycling. Even under today’s economic conditions this was partially possible before the price slump (for example with paper and wood). The high-calorific fraction also contains a high proportion of recyclable materials such as plastics, paper, millboard, cardboard and wood.
The conceptual design of the MBWT as a material-specific waste treatment plant offers ideal conditions for integrating additional separating facilities for recovering further materially recyclable fractions.
Great progress in the field of sensor-aided sorting technology will make it possible to discharge a growing percentage of materially recyclable waste components from MBWTs in the future. This applies to both the coarse and the fine fractions. Plants with wet treatment processing or dry stabilisation offer particularly favourable conditions for separating secondary raw materials. Apart from separating materially valuable components, it is also possible to separate mineral heavy fractions which would no longer have to be expensively landfilled. Wet treatment processing also facilitates the separation of a native organic fraction.
Resource-efficient core component
Thus the MBWT is a treatment concept which meets the requirements of a resource-efficient, sustainable recycling economy if its further development is worked on consistently. The percentage of residual waste that has to be landfilled will decrease considerably. This development is currently being endangered by several factors. Firstly, in Germany there is an overcapacity for the treatment of municipal waste. This currently means that incineration plants are able to acquire waste at knockdown prices. Most of the plants belong to large energy corporations which have sufficient capital to survive such situations.
The resulting price erosion and the deprivation of quantity can be ruinous for material-flow-specific, municipal or privately run medium-sized plants. However, it is a relief that MBWT plants can now supply the high-calorific fractions at far more favourable conditions (less extra payments). The current price decline on the secondary raw materials market is so dramatic that the recovery of secondary raw materials often no longer pays off. The existence of pure waste sorting plants is particularly jeopardised. Here great sustainability potential is in danger of becoming lost. However, the prices of secondary raw materials already seem to have passed their lowest levels.
The “classical” waste incineration plants for untreated residual waste are a proven and reliable method of treatment. Besides the resulting slags, which are either landfilled or utilised as building material, the waste incineration plants release energy as a further product. Due to the fact that their fuel is largely composed of water, sand and materials with low calorific value, the energy output is comparatively low. Furthermore, not all plants possess thermal use facilities.
Solid recovered fuel power plants that operate with prepared, high-calorific waste are “real” power plants, which are worthy of the name “Waste-to-Energy”. Furthermore, they are mostly adjacent to industrial facilities, so that optimal use of the combustion energy is possible by means of cogeneration.
In terms of resource conservation, the incineration of untreated residual waste destroys both energy and raw materials. Non-ferrous metals are practically irrecoverable from the incineration slag and ferrous metals suffer a reduction in quality. In the context of a sustainable resource economy, waste incineration plants are only suitable if waste is either not recyclable or recycling does not make sense. Until now, this has applied to a very high percentage of residual wastes, so that the waste incineration plants in Germany rightly became widely distributed as an expensive but reliable treatment technology.
Are waste incineration plants becoming less important?
But for all that, due to many innovations in processing and sorting technology this situation is changing. Provided that this is not hindered by dumping prices offered by the operators of incineration plants, a growing proportion of wastes will no longer be incinerated but sorted and materially recycled after the current sales crisis for secondary raw materials has been overcome.
Declining deposits of natural resources, world population growth and increasing wealth in many developing countries demand resource-oriented policies, even in waste management. This means a massive increase in the amount of recyclable waste material produced. At the same time this also helps protect the climate as less energy has to be utilised in the production of secondary raw materials and accordingly less Co2 is emitted than for the extraction of primary materials.
Enhanced MBWT technologies and sensor-aided sorting machines are the core components of a sustainable, material-flow-specific waste treatment system, which, when it comes to residual waste, have only become possible due to the technical progress seen over the last few years. The current MBWT plants are the beginning of a promising system which will lead to real separation plants that only leave small amounts of waste to be landfilled.
Thermal plants do not satisfy the requirements of a resource-oriented waste management system because they destroy raw materials and the energy expended for their production. They are only acceptable for non-recyclable waste or if recycling the waste does not make sense. Until now this has indeed applied to a very high percentage of the residual waste. With increasing ways of extracting secondary raw materials, thermal treatment will become less important.
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