Incinerators and their accidents in Europe
At first sight, waste incinerators seem to be simple and ideal solution of the problem what to do with the huge amount of mixed municipal waste we produce every day. Through incineration, i.e. thermal decomposition by oxidation at temperatures from 600 to 1600 degrees Celsius, solid waste volume may be reduced by up to 90 %, and its weight by up to 70 %. Also pathogenicity, and, partially, also toxicity of the waste, associated with organic substances, may be eliminated through this process. Simply, mass of heterogeneous waste is converted to gases and solid residues, namely, ash, fly ash, etc.
However, if we study incineration in more detail, we find that this method of waste disposal is not free of problems, and it can have serious adverse environmental, social, as well as economic consequences. Certain part of them is described and scientifically proved. Nevertheless, the whole issue of waste incineration impacts on the environment, health, and society, has been investigated to a very small extent yet, and, thus, we can expect a high number of latent, or only theoretically described, threats. Many of them may reveal themselves in the case of incinerator accidents, which is the focus of this text.
Waste incinerators in the past and nowadays
In their beginnings, namely in the last quarter of the nineteenth century,1 waste incinerators were constructed for two main reasons. First of them was reduction of the volume of the mixed municipal waste mass, which would otherwise end in landfills. The second of them was elimination of harmful effects of rotting organic material. Their properties, as well as construction, were in accordance with that. In those times, stress was not put on recycling, composting, and other environmentally friendly methods of treatment, and particularly, utilisation of waste. It means that there took place mostly only roughly regulated, and often imperfect, incineration of unseparated, heterogeneous, and untreated mixture of materials of various origin. Because of that, the amount of released harmful emissions was huge.
In the course of the 20th century, waste incinerators developed into much more sophisticated and complicated technological complexes, however, their nature, i.e., reduction of waste volume by oxidation process of incineration, remained the same. Units for utilisation of energy from the waste were added, at first units for heat utilisation, and, subsequently, also for electricity production. Nowadays, a big part of an incinerator area is occupied by equipment necessary for reduction of toxic emissions into the air, and, usually, also a major part of the construction budget is spent for it. However, some waste incinerators in developing countries do not differ from the ones introduced in Europe in the end of the 19th century.
Before the actual incineration, waste is subjected to pre-treatment which includes separation of recyclable and compostable materials, and screening in order to identify potential sources of toxicity and other hazardous materials (explosives, etc.). Naturally, thoroughness and quality of the pre-treatment process depends on construction and properties of the specific incinerator, and, in many cases, it is completely omitted.
The subsequent incineration process may take place on the basis of various principles. Moving grate, rotary kiln, and fluidized bed technologies are the ones used most often.
Majority of incinerators are equipped by grate furnaces2, wherein the moving grate technology is used most commonly nowadays. To certain extent, this technology enables to optimize the waste movement through combustion chambers, contributing to better efficiency and completeness of incineration. The waste is introduced into the incinerator trough a throat at one end of the grate, from where it moves through furnaces to an ash pit in the other end. Incineration usually takes place at temperatures from 750 to 1000 degrees Celsius.3 The generated heat is subsequently transformed into steam, used for heating or electricity production.
The rotary kiln technology is used less often. An incinerator equipped by it has a rotating tube ensuring uniform, efficient, and complete incineration of waste, usually at the temperature from 800 to 1000 degrees Celsius, and secondary afterburner chamber, where chemical reactions of produced gases are completed, this being necessary for elimination of certain hazardous substances. Again, the released thermal energy may be used for further purposes.
The fluidized bed technology is based on the principle of incineration taking place on sand bed, maintained in move by a flow of hot air flowing from under it. The incineration, taking place at temperatures from 750 to 1000 degrees Celsius, is highly efficient, however, this technology is not used very often.
A specific kind of incinerators is represented by hazardous or medical waste incinerators. In view of expected increased toxicity of the material to be incinerated, it is necessary that these facilities be equipped with special technologies preventing releases of highly toxic substances into the environment, for example, through control of oxygen supply, and so on.
In all the cases, the incinerated waste is transformed into gases and solid residues, properties and amounts of which depend on composition of the incinerated waste, on the used incineration technology, and on the conditions in the specific incinerator. Solid residues have to be divided into ash and fly ash, because of their different characteristics. Ash is incompletely incinerated waste, remaining on the grate and in ash bins. It comprises, for instance, pieces of metal, ceramics, glass, and other materials, but also, for example, incompletely incinerated paper.
Solid and precipitable particles present in gases produced during incineration, and, subsequently, captured by filters, are designated as fly ash, or else as air pollution control residues („APC residues"). The fly ash forms about a tenth of solid residues of incineration, and it is characterised by higher homogeneity, and, in particular, by higher toxicity. Solid residues of incineration, and, in particular, fly ash from emission filters, are more concentrated than the original waste mass, as concerns toxin contents, and they may comprise heavy metals, dioxins, furans, and other hazardous substances. If this is the case, this material must be handled as hazardous waste, and deposited on special secure landfills, because of the risk of releases of toxic substances, and subsequent contamination of soil, underground water, and rivers. Also the ash, in spite of its lower toxicity, has to be deposited on landfills, because of its low usability, however, it is used as an admixture into construction materials sometimes. This often takes place also in mixture with fly ash.
As it is obvious from the preceding paragraph, use of incinerators for waste disposal does not eliminate the necessity of solid waste landfilling. Volume and weight of the incinerated waste are lower than in the case of the original material, but, on the other hand, it must be handled in a special way.
As mentioned above, big part of waste is transformed into gases during its incineration. About 5000 cubic metres of these gases are produced from each ton of the incinerated mass. Also these gases contain high amounts of pollutants, major part of which is captured in the flue gas treatment process. However, a part of them is released into the environment, and they are transferred by air into close and remote surroundings of the incinerator, where they deposit in soil and water subsequently. In addition to that, gas emissions from incinerators contribute to global warming.
The present incinerators are designated by a term „waste to energy". However, we must take this term with a pinch of salt. Although certain part of energy released during the incineration is used further, it is a relatively inefficient way. Through waste incineration, we lose the possibility to reuse, recycle, or compost it once and for all. And if we wanted to replace the incinerated material, we would consume higher amount of energy than we received from the incinerator through its incineration. Moreover, in addition to the waste, the incineration process is entered by further materials, consumption of which must be taken into consideration. In the first place, they include fossil fuels, helping to maintain the necessary (safe) temperature in the furnaces (600 - 1600 degrees Celsius) when putting the incinerator into operation and shutting it down, and during its problem operation. Further, there must be mentioned water used in filters, cleaning equipment, and coolers, and chemical agents serving for reduction of emissions.
In a comparative study based on product life cycle assessment, Jeffery Morris compared energy savings obtained by waste incineration in comparison with their recycling.5 Results showed that in the case of various paper waste, 2.4- to 7-times more energy is obtained through its recycling, in comparison with its incineration. In the case of plastics, the difference is even more marked. Recycling of plastics saves 10-times to 26-times more energy than incinerators. This is caused especially by the fact the recycling of plastics saves energy necessary for production of raw materials, which are not destroyed by recycling, but are destroyed by incineration. In other words, waste must be looked at as a raw material.
Waste incinerators as sources of releases of toxic substances into the environment
It is obvious that waste incineration is linked with the problem of solid, liquid, and gaseous materials containing high concentrations of toxic substances. This is further connected with the risk of their releases into the environment, which may take place both by means of gasses formed during the incineration, and during handling of solid residues of incineration and waste waters.
Probably the most often discussed and the most controversial problem concerning releases of toxic substances from incinerators is connected with polychloridnated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs), in short called also dioxins. These organic substances of chlorine are highly toxic, and show the ability of bioaccumulation.6 Because of their properties, both PCDDs and PCDFs were incorporated into the list of substances regulated by the Stockholm Convention on Persistent Organic Pollutants (POPs). In addition to chlorinated dioxins, also brominated and fluorinated dioxins are produced during municipal waste incineration. Although large part of PCDD/Fs in gaseous emissions is captured by filters in up-to-date incinerators, the problem of other groups of organic substances in their emissions has not been solved fully. Moreover, high dioxin concentrations are present in residues from flue gas treatment. Other problematic POPs accumulate in them, too.7
Further problematic substances, releases of which may take place in connection with waste incineration, are heavy metals that cannot be decomposed through incineration. This group includes lead, cuprum, mercury, cadmium, nickel, zinc, and further elements. Their ability to escape into the environment depends on the incineration conditions. Certain heavy metals (cadmium, mercury, chromium, lead) may be strong toxic substances as such, or may form hazardous organic substances. Others (copper, nickel) may contribute to dioxin creation in flue gases. At present, the technology of gaseous emission filters can be so advanced that the major part of heavy metals may be captured and they are subsequently present in solid incineration residues. The only exception is mercury, due to its high volatility, which is usually released into the air. Heavy metals mostly remain in solid incineration residues that are used for concrete production sometimes. In this connection, an often discussed issue is the possibility of their long-term releases from this widely used building material, possibly endangering health and environment.
Further substances are released into the air in the form of gases during incineration, too. From them, there have to be mentioned at least inorganic acid gases, such as, for example, hydrogen chloride, hydrogen fluoride, hydrogen bromide, sulphur and nitrogen oxides, etc., showing, among others, impact on development of respiratory problems. Together with gaseous emissions, incinerators release also certain amount of ultrafine solid particles (nanoparticles; PM10 and PM2.5) that may cause respiratory and cardiovascular diseases, cancer, asthma, and further problems. Because of their small size, it is very difficult to capture nanoparticles by filters, and even to monitor them. They are not captured even by such a fine filter as human lungs, and, because, of that, they penetrate into the core of the respiratory system.
Accidents of incinerators
Possible accidents represent a big danger connected with operation of incinerators. In view of nature and amount of waste to be incinerated, and handled in the incinerator premises, accidents may have a huge impact on the surroundings of these facilities, concerning both health of its inhabitants, and ecological stability of the environment.
The most often problems reported in Europe in the last twenty years are, in particular, smaller, as well as very extensive, fires and explosions. Their hazardousness resides especially in the fact that uncontrolled and unregulated burning of the waste mass may take place during them, connected with subsequent uncontrolled release of highly toxic substances into the air. According to the estimates of the United Nations Environment Programme (UNEP), up to 1000 micrograms of dioxins (expressed in TEQ) may be released into the air by uncontrolled burning of one ton of waste.
However, uncontrolled releases of toxic substances into the air, caused by poor course of the incineration process, and releases of toxic substances into soil and water during their storage, or during waste handling, are relatively common, too. There may be found many factors causing the accidents: insufficient safety standards, non-observance of the standards, defects of the equipment, human failures, but also unpredictable coincidences. Many of the accidents were accompanied by certain interest of the public and the media, however, it may be assumed that some of them were not uncovered at all. Because of that, the overview presented in this map cannot be considered exhausting, in any case.
1 First state of the art waste incinerators were constructed in the United Kingdom in 1876.
2 The waste is incinerated on grates through which incineration residues fall down, and through which air is blown into the furnaces.
3 According to the EU legislation, temperature in the flame has to reach at least 850 degrees Celsius for at least two seconds during incineration, in order to ensure thorough decomposition of toxic organic substances.
5 Morris, J. (2005). "Comparative LCAs for Curbside Recycling Versus Either Landfilling or Incineration with Energy Recovery." The International Journal of Life Cycle Assessment 10 (4): 273-284.
6 They decompose very slowly in an organism, and their amount in the body accumulates in the course of life. Accumulation takes place via the food chain, too.
7 Petrlik, J. and R. Ryder (2005). After Incineration: The Toxic Ash Problem. Prague, Manchaster, IPEN Dioxin, PCBs and Waste Working Group: 59.