Incinerator fly ash toxicity

Fly ash from municipal waste and industrial waste incinerators contains polychlorinated dibenzo-p-dioxins (PCDDs), including tetrachlorodibenzo-/j-dioxin (TCDD) and polychlorinated dibenzofurans (PCDFs), which are lipophiles, and heavy metals, including chromium, copper, manganese, vanadium, and lead, which are hydrophilesJ29-31 These chemicals have multiple toxicities and are known to impact the human liver, immune system, respiratory system, thyroid, male reproductive function, and CNS J32 34l Several are human carcinogensJ32 35 Enhanced toxic effects are observed in the mixtures of some of theseJ21,22 36 The mixtures of toxicants present in fly ash are complex and the mechanisms for their action on the human body are largely unknown. It is known that occupational exposure to fly 

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In 1996, the vendor estimated the cost of treating incinerator fly ash and gas purification filter dust at 150 to 300 per ton. In a confidential 1996 vendor-supplied report, the cost of treating wastes containing toxic heavy metals and wet wastes was estimated at 300 to 1500 per ton. 

Show by means of a flow diagram or sketch how you would treat and dispose of the fly ash collected from a municipal incinerator. The fly ash contains toxic and nontoxic metals, nonmetallic inorganics, and organic halogen compounds. 

These results show the fate of aromatic bromine compounds during municipal waste incineration bromine is exchanged by chlorine on the surface of fly ash at the electrostatic precipitator at 250-3(X)°C. But the toxic potential at brominated dibenzodioxins and furans is not reduced by these transformations. The increase of PCDD/F concentration in MWI by adding bromine compounds has been pointed out by Lahl and coworkers (ref. 26). 

PCDDs are present as trace impurities in some commercial herbicides and chlorophenols. They can be formed as a result of photochemical and thermal reactions in fly ash and other incineration products. Their presence in manufactured chemicals and industrial wastes is neither intentional nor desired. The chemical and environmental stability of PCDDs, coupled with their potential to accumulate in fat, has resulted in their detection throughout the global ecosystem. The number of chlorine atoms in PCDDs can vary between one and eight to produce up to 75 positional isomers. Some of these isomers are extremely toxic, while others are believed to be relatively innocuous. 

Worldwide, there are numerous plasma system designs for treatment of all types of wastes. Economical considerations limit their commercial applications to the most profitable actions. Presently they commercially operate in Switzerland and Germany for low level nuclear waste vitrification, in France and the USA for asbestos waste vitrification, in the USA and Australia for hazardous waste treatment, in Japan and France for municipal fly ash vitrification. The most of installations is working in Japan because there 70% of municipal waste is incinerated and the ash can not be used as landfill. EU Regulations banning the disposal to landfill of toxic and hazardous wastes after year 2002 may cause wider use of plasma waste destruction technology in Europe. 

Another development is due to the interest in polychlorodibenzofurans, spurred by their occurrence as environmental contaminants. Polychloro-phenols are manufactured in large amounts (150,000 tons per annum) and find a wide range of uses. The usual method of manufacture involves the hydrolysis of chlorobenzenes, and side reactions, favored by high temperature, can lead to the production of polychlorodibenzofurans and poly-chlorodibenzo-p-dioxins. The Seveso incident is well known." Polychloro-biphenyls are also widely used industrial chemicals, particularly in heat exchange systems, and their pyrolysis leads to the formation of polychloro-dibenzofurans. Polychlorodibenzofurans have also been detected in the fly ash and flue gases of incinerators and industrial heating plants. The most toxic of the polychlorodibenzofurans are 2,3,7,8-tetra-, 1,2,3,7,8-penta-, and 2,3,4,7,8-pentachlorodibenzofuran, and an extensive literature exists on the environmental pollution and the results of human exposure to these substances. A particularly tragic example of the latter occurred in 1968 in the Fukuoka prefecture of Japan after consumption of rice oil contaminated with a commercial polychlorobiphenyl. 

The MelDAS technology is a modified incineration process in which high temperatures destroy organic contaminants in soil and concentrate metals into fly ash. Details of the metals immobilization process can vary based on the specific application, but the essential steps are to combine the toxic-metal containing material with the appropriate amount of sorbent, to form this mixture into pellets or briquets placing the metal compounds into intimate contact with the sorbent, and to heat treat the pellets causing a reaction to form nonleachable metal compounds. The MelDAS process requires a sorbent. 

The carbon content of MSW cannot be converted into C02 entirely, and due to incomplete combustion, minor amounts of CO and soot particles are found in the flue gases. The particulate carbon is known to be involved in the formation of volatile and toxic compounds especially poly-chlorodibenzo-dioxins and -furanes. Tests in the fully working incinerator plants revealed the presence of particulate carbon, chlorides, and Cu compounds as catalysts in the fly ash (see also Table 3). 

Incineration is often regarded as a very efficient technique for municipal solid waste (MSW) management. However, the environmental impacts of MSW incineration need to be carefully taken into account. The most relevant problem with MSW incineration is flue gas treatment. However, another often overlooked issue is the disposal of solid byproducts of the incineration process. MSW incinerators essentially produce two types of solid by-products, that is, slag, or bottom ash, and fly ash, often mixed with various other chemicals used for flue gas treatment. Bottom ash and—even more—fly ash are regarded as dangerous wastes mainly due to their potentially toxic elements (PTE) content and their tendency to leach such PTE to the environment. 

In the last twenty years, PCDD and PCDF were identified as by-products in many industrial processes which involve chlorine or chlorinated compounds. Additionally both groups of compounds were found to be formed in a broad range of combustion processes, including accidental fires. Municipal waste incineration is particularly considered to be a very important, if not the most important, of the identified source of environmental dibenzo-p-dioxin and dibenzofuran contamination. As a consequence, the evaluation and close control of new and existing installations for their dioxin releases has become a major concern. Based on this relative importance of municipal waste incinerators, and taking into account the relative toxicity data actually available for PCDD and PCDF, it was decided to prepare and certify a crude fly ash extract (CRM 429) for the twelve more toxic PCDD and PCDF [18,19]. 

Trace toxic metals may escape from the municipal incineration process. Various agents, such as 0.25 M Na-citrate, have been used to aid the removal of heavy metals during electrodialytic treatment of municipal solid waste incineration (MSWI) fly-ash (Pedersen 2002). One study found that the bottom ash in a municipal incineration system had 1000-fold higher levels of chromium(VI) in test leachates than the hopper cyclone and filter ashes (Abbas et al. 2001), but another study found the chromium in fly-ash to be mostly trivalent chromium (Coodarzi and Huggins 2001). 

Insofar as mercury and cadmium are concerned, and lead to a lesser extent, no matter how the incinerators are operated, a significant fraction of these materials will be volatilized during incineration and enter the ecosystem via the airborne path, unless recovered from the flues by fly ash precipitation and vapor condensation, methods of questionable merit for large scale MSW operations, uie remainder of the cadmium and lead will end up in the incinerator ash and in the incinerator residues, but all the mercury may be expected to be volatilized. This means that unless the reduction of the toxic materials at the source can be practiced, the incinerator residues and flues will need to be processed to remove lead and cadmium for recycling or for safe disposal in some other manner. The most effective and also the most economical way to prevent mercury from entering the environment from batteries is to phase out the use of mercury in batteries to the ftillest extent possible, an effort already instituted by the battery manufacturers, and to maintain an effective collection system for the mercury batteries still in use. 

Metals in Fly Ash Particulates from waste incinerators typically contain oxides of silicon, iron, calcium, and aluminum. The other trace metals of importance are antimony, arsenic, barium, beryllium, cadmium, chromium, lead, mercury, silver, and thallium. Carcinogenic toxic metals include arsenic, cadmium, chromium, and beryllium. Arsenic is only present in samples 7 (100% plastic) and 6 (50% nonplastic/50% plastic C) and not present in other samples. 

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