Technology for TASi: High-tech equipment for waste treatment
It wasn't a law but a simple administrative regulation in the form of a technical guideline that provided the key impulse for the diversion of waste flows in Germany away from landfill sites. In the course of the implementation of this Technical Directive on Residential Waste (TASi), the technology for treating waste underwent an extraordinary development. This is especially true of thermal processes, but it also applies to mechanical-biological methods. The forthcoming Entsorga-Enteco - International Trade Fair for Waste Management and Environmental Technology (Cologne, 24th to 27th October 2006) - will offer an excellent insight into the latest of these technological developments.
The routes taken by the roughly 50 million tons of residential waste in Germany have shifted dramatically in the last 15 years. Whereas the utilization rate for this waste was not even 15 per cent in the early 1990s, according to the German Federal Environmental Agency (Dessau), almost 60 per cent is recycled today. That represents a fourfold increase. In the same period, the capacities for waste incineration have more than doubled. The incidental incineration of wastes, such as in power stations or cement plants, has actually grown by a factor of 29. In 1990, mechanical-biological facilities for waste treatment were still on the drawing boards of the development engineers. Since then, however, the quantity of waste that ends up in landfills has fallen by more than 90 per cent.
This change in the way that residential waste is handled has been accompanied by a series of legal guidelines. Chief among them was the Commercial and Industrial Waste Management Act of 1994, which aims to 'preserve natural resources and secure the environmental friendly disposal of wastes.' Other supporting legislation included a directive on the avoidance and recycling of packaging; a directive concerning the surrender, return and environmentally friendly disposal of end-of-life vehicles, a regulation concerning the return and disposal of used batteries and accumulators, and currently, a law concerning the sale, return and environmentally friendly disposal of electrical and electronic equipment.
However, the strongest impulse for the diversion of waste flows away from the dumps came from a simple Technical Directive on Residential Waste (German abbreviation: TASi). The most important objective of this administrative regulation, which went into effect in mid-1993, is 'to ensure the environmentally friendly treatment and disposal of non-recyclable waste,' and to do so in such a way 'that the disposal problems of today are not shifted to future generations.' With this objective in mind, TASi makes the disposal of waste dependent on the fulfilment of certain requirements as regards where landfill sites are located, how they are designed, and how they are operated. Equally important, however, are its requirements for the composition of the wastes to be disposed of.
This concept is based on an awareness of the fact that downstream technical barriers don't last forever. In the technical directive, the composition of the waste therefore takes on the role of the most important barrier, ahead of even the geology of the site and its base or surface seal. To fill this principle role, wastes with biodegradable components, such as domestic refuse, comparable commercial waste, or sludge, are to be treated before they are dumped. This treatment aims to mineralise organic components to the greatest extent possible and to transform soluble pollutants into stable, indissoluble substances wherever possible. This is guaranteed by means of strict limits for the residual content of organic substances - measured in terms of incandescent heat loss and total organic carbon - and for eluates, measured in terms of leaching values, particularly for heavy metals. As of June 2005, only waste that satisfies these guidelines may be dumped in landfill sites.
What became the most important, and was initially the only, technology capable of complying with the strict limits of TASi was the method of waste treatment that had up until that point been denounced as the most notorious polluter in the country: waste incineration. It was the emissions of dioxins and furans from waste incineration facilities that caused the biggest uproar at the time. These substances belong to a group of more than 200 individual compounds that release chloracne and can cause cancer. But criticism focused on other toxic substances too, such as arsenic, cadmium, nickel, mercury and lead, and on the particulate emissions.
Today, however, these aspects are no longer a cause for concern. The reason for that is the 17th Federal Ambient Pollution Control Act on incineration facilities for wastes and other combustible substances - known by the German abbreviation 17th BImSchV - in effect since 1990. As a result of this law, the 48 waste incineration facilities of the time were equipped with sophisticated waste-air purification systems. And the 25 facilities erected since that time have naturally been equipped with such systems as well.
The optimization of the combustion technology is another key factor. According to the 17th BImSchV, it must be designed in such a way that the wastes largely burn out, so that the limits of TASi with regard to total organic carbon (TOC) and the incandescent heat loss are adhered to. For this, the minimum temperature of the combustion gases must reach 850 °Celsius. In the technology of grate furnace incineration favoured today, systems generally reach temperatures between 900 and 1050 °Celsius with exposure times of 30 to 60 minutes in the incineration chamber, depending on the composition of the wastes.
The result of this elaborate and costly technological development is not only the TASi-compatible inertisation of the wastes to be disposed of. In general, the pollutant levels in the waste air are also far lower than the prescribed limits. Consider dioxins, for example: According to the 17th BImSchV, a limit of 0.1 nanograms (ng) per toxicity unit (TU) is permitted. The Federal Ministry of the Environment reports that values of 0.005 ng per TU are now achieved.
The second important technology for the implementation of TASi is the mechanical-biological treatment of wastes. Initially, it was rough going for these methods, especially because they were - and remain - unable to adhere to the limits for the organic parameters TOC and incandescent heat loss. It wasn't until 2001 that they began to be considered serious alternatives on a par with thermal waste treatment, in the year the directive on the environmentally friendly storage of household waste (AbfAblV) came into effect. For the determination of the suitability of mechanically-biologically treated wastes for dumping, this regulation was introduced as an additional criterion the 'biological degradability of the dry residue of the original substance.' The defining parameters were the respiration activity or gas formation rate in the fermentation test.
There are now 64 mechanical-biological waste treatment facilities in operation, according to the Federal Ministry of the Environment. The processes follow the principle of material flow separation. In mechanical treatment stages, fractions of high calorific value (e.g. plastics) are first separated off for subsequent energy utilization, and ferrous metals and non-ferrous metals (aluminium) are separated for material recycling. What remains are the fractions of low calorific value, which still make up over half of the waste material. This is now subjected to a biological treatment, either by means of aerobic composting or anaerobic fermentation until the TASi values that would permit dumping are achieved. The biogas produced in the fermentation process is led off for energy utilization.
Ever since the introduction of the 30th BImSchV in 2001, mechanical-biological treatment facilities have had to satisfy strict guidelines for waste-air purification as well. For the most part, the facilities must be enclosed or encapsulated, for example. To handle highly polluted waste-air flows from the mechanical treatment or the composting, regenerative thermal oxidation (RTO) processes are generally used, according to the Working Group for Material-Specific Waste Treatment (ASA, Warendorf). The remaining waste-air flows with relatively low pollutant levels are purified with particulate filters or bio-filters.
The separated fraction of high calorific value can amount to as much as 40 per cent of the waste material delivered. It can be utilized for its energy content in various ways. One possible use is in processes of the basic materials industry, such as in the firing process for the production of cement clinkers. But it can also be used as a substitute fuel in the area of energy conversion, such as in the dust, fluidized-bed or grate-firing processes of power plants. According to the 17th BImSchV, all these activities in which wastes are incinerated as part of the process are subject to the same waste-air quality requirements as waste incineration facilities.
The state-of-the-art of the modern waste treatment technologies introduced in response to the TASi guideline can be found at Entsorga-Enteco - the International Trade Fair for Waste Management and Environmental Technology (Cologne, 24th to 27th October 2006).
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