Incinerator accidents in European countries
At first glance, waste incineration seem to be a simple and ideal solution to the problem of what to do with the massive amounts of mixed municipal waste we produce every day. By burning, that is, through thermal decomposition using oxidation at temperatures ranging from 600 to 1600 degrees Celsius, it is possible to reduce the volume of solid waste by up to 90% and its weight by up to 70%. This process also eliminates pathogenicity—disease-causing potential—and partially reduces the toxicity associated with organic compounds. The mass of heterogeneous waste is simply converted into gases and solid residues, namely ash, dust, and other residues.
However, if we look at incineration in more detail, we find that this method of waste disposal is not without problems and can have serious negative environmental consequences. Some of these are well documented and scientifically proven. The entire issue of the impact of waste incineration on the environment, health, and society has been explored only to a very limited extent, and therefore, we can assume the existence of many latent or only theoretically described threats. Many of these may manifest during incinerator accidents.
Waste Incineration Plants: Then and Now
In their early days, in the last quarter of the 19th century, waste incineration plants were designed for two main reasons. The first was to reduce the volume of mixed municipal waste that would otherwise end up in landfills. The second was to eliminate the harmful effects of rotting organic material. These purposes were reflected in their design and construction. At that time, there was no emphasis on recycling, composting, or other environmentally friendly methods of processing and utilizing waste, so the incineration of unsorted, heterogeneous, and untreated mixtures of materials of various origins was often poorly regulated and imperfect. As a result, the amount of harmful emissions released was enormous.
During the 20th century, waste incineration plants evolved into far more sophisticated and complex technological facilities, but their essence, which is the reduction of waste volume through the oxidation process of burning, remained the same. Units for utilizing energy from waste were added, first for heat and later for electricity generation. Today, a large part of incineration plants is dedicated to equipment necessary for reducing toxic emissions into the air, which usually consumes most of the construction budget. Some incinerators in developing countries, however, differ little from those established in Europe at the end of the 19th century.
Before incineration, waste undergoes preparation, including the sorting of recyclable and compostable materials and screening to identify potential sources of toxicity or other hazardous materials (explosives, etc.). The thoroughness and quality of the preparatory process naturally depend on the design and characteristics of the specific incinerator, and in many cases, it is entirely omitted.
The subsequent incineration process can be based on various principles, the most common being technologies like moving grates, rotary kilns, and fluidized beds. Most incinerators are equipped with grate furnaces, where waste is burned on grates through which combustion residues fall and air is blown into the furnaces. Today, the most commonly used technology is the "moving grate," which to some extent allows for the optimization of waste movement through the combustion chambers, contributing to better efficiency and completeness of combustion. Waste is fed into the combustion mechanism through an inlet on one side of the grate, where it moves through the furnace to the ash pit on the other side. Combustion typically occurs at temperatures between 750 and 1000 degrees Celsius. The heat generated is then transformed into steam used for heating or electricity generation.
Less frequently, the "rotary kiln" technology is used. Incinerators equipped with this technology have a rotating drum that ensures uniform, efficient, and complete combustion of waste at typical temperatures between 800 and 1000 degrees Celsius, along with a secondary combustion chamber where the chemical reactions of the gases formed are completed, which is necessary to eliminate certain hazardous substances. The released thermal energy can again be used for other purposes.
The fluidized bed technology is based on combustion taking place on a sand bed kept in motion by a stream of hot air flowing from beneath it. Such combustion, occurring at temperatures between 750 and 1000 degrees Celsius, is highly efficient, but it is not widely used.
A special type of incinerator is one designed for hazardous or medical waste. Due to the presumed increased toxicity of the materials being burned, these facilities must be equipped with special technologies that prevent the release of highly toxic substances into the environment, for example, by controlling the oxygen supply and other similar measures.
In all cases, the incinerated waste is transformed into gases and solid residues, the properties and quantities of which depend on the composition of the waste, the incineration technology used, and the conditions in the specific incinerator. Solid residues need to be divided into bottom ash and fly ash due to their different properties. Bottom ash refers to imperfectly burned waste that remains on the grates or in ash bins. This includes pieces of metal, ceramics, glass, or other materials, as well as incompletely burned paper.
The solid and coagulated particles dispersed in the gases released during combustion and subsequently captured in filters are referred to as fly ash or also as APC residues (Air Pollution Control residues). These make up about one-tenth of the solid residues from combustion and are characterized by greater homogeneity and especially higher toxicity. Solid combustion residues, particularly the fly ash from emission filters, are more concentrated in toxic chemicals than the original waste mass and can contain heavy metals, dioxins, furans, and other hazardous substances. If this is the case, this material must be treated as hazardous waste and stored in special secured landfills because of the risk of releasing toxic substances and subsequent contamination of soil, groundwater, and rivers. Bottom ash, despite its lower toxicity, also has limited usability and must often be landfilled, though it is sometimes used as an additive in construction materials, often in a mixture with fly ash.
From the previous paragraph, it is clear that using incinerators to dispose of waste does not eliminate the need to store solid waste. The volume and weight of burned waste are indeed smaller than the original material, but it still requires special handling.
We have already mentioned that during waste incineration, a large part is converted into gases. About 5,000 cubic meters of gases are released from each ton of burned material. These gases also contain large amounts of pollutants, which are mostly captured during the cleaning process. However, some of them escape into the environment and are carried by the air to both nearby and distant areas of the incinerator, where they settle in the soil and water. Moreover, the gaseous emissions from incinerators contribute to global climate change.
Incinerators and the Release of Toxic Substances into the Environment
It is evident that waste incineration is associated with the production of solid, liquid, and gaseous materials with high concentrations of toxic substances. This also involves the risk of their release into the environment, which can occur through the gases released during combustion, as well as during the handling of solid combustion residues and wastewater.
Probably the most discussed and controversial issue related to the release of toxic substances from incinerators is polychlorinated dibenzo-p-dioxins (PCDD) and dibenzofurans (PCDF), also known simply as dioxins. These chlorinated organic compounds are highly toxic and have the ability to bioaccumulate, meaning they break down very slowly in the body and their amounts accumulate over a lifetime. Both PCDD and PCDF have been classified as substances regulated under the Stockholm Convention on Persistent Organic Pollutants (POPs). In addition to chlorinated dioxins, brominated or fluorinated dioxins are also produced during the incineration of municipal waste. Although PCDD/F from gaseous emissions in modern incinerators are captured by filters, the issue of other groups of organic compounds in their emissions is not entirely resolved. High concentrations of dioxins also remain in the residues from flue gas cleaning, where other problematic POPs accumulate.
Other problematic substances that can be released during waste incineration are heavy metals, which cannot be broken down by burning. This group includes lead, copper, mercury, cadmium, nickel, zinc, and other elements. Their ability to escape into the environment depends on the conditions of combustion. Some heavy metals (cadmium, mercury, chromium, lead) can be highly toxic by themselves or can form dangerous organic compounds. Others (copper, nickel) can contribute to the formation of dioxins in flue gases. Currently, the technology of flue gas filters is advanced enough to capture most heavy metals, so they remain in the solid residues from combustion. The only exception is mercury, which usually escapes into the air due to its high volatility. Heavy metals typically remain in the solid combustion residues, which are sometimes used in concrete production. In this context, there is often a discussion about the potential long-term release of these metals from this widely used construction material, which could pose a threat to health and the environment.
During combustion, other gases are released into the atmosphere, including inorganic acidic gases such as hydrogen chloride, hydrogen fluoride, hydrogen bromide, sulfur oxides, nitrogen oxides, and others, which, among other things, can cause respiratory problems. Incinerators also release certain amounts of ultrafine particulate matter (nano-particles PM10, PM2.5 and PM1), which can cause respiratory or cardiovascular diseases, cancer, asthma, and other problems. These nano-particles are very difficult to capture with filters due to their small size, and even monitoring them is challenging. Not even as fine a filter as human lungs can catch them, so they penetrate deep into the respiratory system.
Incinerator Accidents
A significant danger associated with the operation of incinerators is the potential for accidents. Given the nature and quantity of the waste that is meant to be incinerated and handled within incinerator facilities, accidents can have a tremendous impact on the surrounding area, affecting both the health of residents and the ecological stability of the environment.
The most common issues in Europe over the past twenty years have primarily been fires and explosions, ranging from minor incidents to very extensive ones. The danger of these events lies mainly in their potential to cause uncontrolled and unregulated combustion of waste material, leading to the release of highly toxic substances into the air. According to estimates from the United Nations Environment Programme (UNEP), the uncontrolled burning of one ton of waste can release up to 1000 micrograms of dioxins into the air (expressed in TEQ).
However, uncontrolled releases of toxic substances into the air due to poor combustion processes or leaks of toxic substances into soil and water during storage or waste handling are also relatively common. Many factors can cause accidents: inadequate safety standards, failure to comply with standards, equipment defects, human error, and even unpredictable combinations of circumstances. Many accidents have attracted public and media attention, but it can be assumed that some have gone entirely undetected. Therefore, this overview should not be considered exhaustive.
