Metal leachability, heavy metals, polycyclic aromatic hydrocarbons and polychlorinated biphenyls in fly and bottom ashes of a medical waste incineration facility

Medical waste from hospitals and other healthcare institutions has become an imperative environmental and public safety problem. Medical waste in Greece has become one of the most urgent environmental problems, because there are 14,000 tons produced annually, of which only a small proportion is incinerated. In the prefecture of Attica there is only one modern municipal medical waste incinerator (started 2004) burning selected infectious hospital waste (5-6 tons day(-1)). Fly and bottom residues (ashes) are collected and stored temporarily in barrels. High values of metal leachability prohibit the landfilling of these ashes, as imposed by EU directives. In the present study we determined quantitatively the heavy metals and other elements in the fly and bottom ashes of the medical waste incinerator, by inductively coupled plasma emission spectrometry (ICP) and by energy dispersive X-ray analysis (EDAX). Heavy metals, which are very toxic, such as Pb, Cd, Ni, Cr, Cu and Zn were found in high concentrations in both fly and bottom ashes. Metal leachability of fly and bottom ashes by water and kerosene was measured by ICP and the results showed that toxic metals in both ashes, such as Pb, Cr, Cd, Cu and Zn, have high leaching values. These values indicate that metals can become soluble and mobile if ash is deposited in landfills, thus restricting their burial according to EU regulations. Analysis of polychlorinated biphenyls and polycyclic aromatic hydrocarbons in fly and bottom ashes showed that their concentrations were very low. This is the first known study in Greece and the results showed that incineration of medical waste can be very effective in minimizing the most hazardous and infectious health-care waste. The presence of toxic metals with high leachability values remains an important draw back of incineration of medical waste and various methods of treating these residues to diminish leaching are been considered at present to overcome this serious technical problem.     

Residues characterisation from the fluidised bed combustion of East London’s solid recovered fuel

Waste thermal treatment in Europe is moving towards the utilisation of the combustible output of mechanical, biological treatment (MBT) plants. The standardisation of solid recovered fuels (SRF) is expected to support this trend and increase the amount of the generated combustion residues. In this work, the residues and especially the fly ashes from the fluidised bed combustion (FBC) of East London’s NCV 3, Cl 2, and Hg 1 class SRF, are characterised. The following toxicity indicators have been studied: leachable chlorine, organochlorides expressed as pentachlorobenzene and hexachlorobenzene, and the heavy metals Cu, Cr, Cd, Zn, Ni, and Pb. Furthermore the mineralogical pattern of the ashes has been studied by means of XRD and SEM–EDS. The results suggest that these SRF derived ashes have significantly lower quantities of Cu, Cd, Pb, Zn, leachable Cl, and organochlorides when compared to other literature values from traditional waste thermal treatment applications. This fact highlights the importance of modern separation technologies employed in MBT plants for the removal of components rich in metals and chlorine from the combustible output fraction of SRF resulting to less hazardous residues.     

Lysimeter washing of MSW incinerator bottom ash

Stockpiled municipal waste incinerator bottom ash is frequently considered for utilization as a construction material. Two 360 kg lysimeter experiments were conducted to study percolation washing of contaminants from stockpiled MSW bottom ash. One lysimeter was leached with a concentrated sodium hydroxide solution, as a possible pre-treatment for improvement of the bottom ash characteristics prior to utilization, while the other was leached using distilled water. The lysimeter leachate was analysed, and at the end of the 2-year leaching period, the bottom ash from each lysimeter was subjected to several laboratory tests to assess the effect of the treatments. The laboratory tests showed that distilled water leachability of both treated ashes was an order of magnitude lower than that of fresh ash, but long-term contaminant leachability under acidic conditions had not changed. Although alkaline washing clearly resulted in greater contaminant removal than did distilled water washing, the chemical properties of the alkaline-leached bottom ash were not significantly different from those of the water-leached ash.     

Characterization, leachability and valorization through combustion of residual chars from gasification of coals with pine

This paper presents the study of the combustion of char residues produced during co-gasification of coal with pine with the aim of characterizing them for their potential use for energy. These residues are generally rich in carbon with the presence of other elements, with particular concern for heavy metals and pollutant precursors, depending on the original fuel used.The evaluation of environmental toxicity of the char residues was performed through application of different leaching tests (EN12457-2, US EPA-1311 TCLP and EA NEN 7371:2004). The results showed that the residues present quite low toxicity for some of pollutants. However, depending on the fuel used, possible presence of other pollutants may bring environmental risks.The utilization of these char residues for energy was in this study evaluated, by burning them as a first step pre-treatment prior to landfilling. The thermo-gravimetric analysis and ash fusibility studies revealed an adequate thermochemical behavior, without presenting any major operational risks.Fluidized bed combustion was applied to char residues. Above 700 °C, very high carbon conversion ratios were obtained and it seemed that the thermal oxidation of char residues was easier than that of the coals. It was found that the char tendency for releasing SO₂ during its oxidation was lower than for the parent coal, while for NO_X emissions, the trend was observed to increase NO_X formation. However, for both pollutants the same control techniques might be applied during char combustion, as for coal. Furthermore, the leachability of ashes resulting from the combustion of char residues appeared to be lower than those produced from direct coal combustion.     

Leaching of metals from fly ashes in the presence of complexing agents

The leachability of some metals (Al, As, Ba, Ca, Cr, Cu, Fe, K, Mg, Mn, Ti, Zn) from fly ashes was studied in the presence of ethylenediamine tetraacetic acid (EDTA) and naturally occurring complexing agents-humic acids (HAs). Secondary complex-forming equilibria taking place in the leachates increase significantly the leached amounts of most metals. Kinetic experiments showed that almost the whole "available" amounts of metals are leached from fly ash within a time period of several hours (mostly within 20 h), with exceptions of matrix constituents (typically aluminium), which are released more slowly.     

Conversion of CCA-treated wood to ethanol: a method to reduce leaching of metals from disposed treated wood prior to disposal

The objective of this paper is to evaluate the feasibility of producing ethanol from CCA-treated wood that is highly leachable. Following the initial tests, CCA-treated wood was hydrolysed and fermented and the results showed not only that ethanol was produced during the fermentation process but that metals were taken up by the yeast. Toxicity characteristic leaching procedure tests of the hydrolysed wood leached less than 4 mg/L of As while minimal amounts of Cr and Cu remained in the hydrolysed wood which makes landfilling of hydrolysed wood acceptable and less hazardous. A slightly lower amount of ethanol from CCA-treated than untreated wood was produced (6 and 7 g/L, respectively). In general, it suggests that production of ethanol as a source of energy from a hazardous waste (CCA-treated wood) is feasible.     

A new way to stabilize fly ash from municipal incinerators

Heavy metals and toxic chlorinated organics, added to very low grain-size distributions, make fly ashes from municipal incinerators a very hazardous waste. For their disposal, the present general trend is, not only to stabilize chemically the ashes, i.e. to reduce the leachability of the toxic substances, but also to stabilize them mechanically, i.e. to convert them into massive, resistant, and unleachable solids. This paper describes various stabilization methods used on representative European fly ash samples, which led to the development of a new stabilization technique taking place in four stages: elimination of the alkali chlorides by dissolution; addition of a moderate quantity of phosphoric acid; calcination; and solidification with Portland clinker or cement. The principal advantages of the process are as follows: the polychlorodibenzodioxins-polychlorodibenzofurans are destroyed, the reactivity of the heavy metals is reduced drastically, the final solids have satisfactory mechanical properties, and the increase in weight of the waste to be disposed of does not exceed one fourth. Comparative results of TCLP extraction tests are presented.     

Contribution of individual waste fractions to the environmental impacts from landfilling of municipal solid waste

A number of LCA-based studies have reported on the environmental performance of landfilling of mixed waste, but little is known about the relative contributions of individual waste fractions to the overall impact potentials estimated for the mixed waste. In this paper, an empirical model has been used to estimate the emissions to the environment from landfilling of individual waste fractions. By means of the LCA-model EASEWASTE, the emissions estimated have been used to quantify how much of the overall impact potential for each impact category is to be attributed to the individual waste fractions. Impact potentials are estimated for 1 tonne of mixed waste disposed off in a conventional landfill with bottom liner, leachate collection and treatment and gas collection and utilization for electricity generation. All the environmental aspects are accounted for 100 years after disposal and several impact categories have been considered, including standard categories, toxicity-related categories and groundwater contamination.Amongst the standard and toxicity-related categories, the highest potential impact is estimated for human toxicity via soil (HTs; 12 mPE/tonne). This is mostly caused by leaching of heavy metals from ashes (e.g. residues from roads cleaning and vacuum cleaning bags), batteries, paper and metals. On the other hand, substantial net environmental savings are estimated for the categories Global Warming (GW; ?31 mPE/tonne) and Eco-Toxicity in water chronic (ETwc; ?53 mPE/tonne). These savings are mostly determined by the waste fractions characterized by a high content of biogenic carbon (paper, organics, other combustible waste). These savings are due to emissions from energy generation avoided by landfill gas utilization, and by the storage of biogenic carbon in the landfill due to incomplete waste degradation.     

Belgian MSWI fly ashes and APC residues: a characterisation study

Municipal Solid Waste Incineration (MSWI) produces different sorts of residues, bottom ash, fly ashes and Air Pollution Control (APC) residues. Generally, fly ashes and APC residues are mixed at the MSWI plant and manage as a sole residue. In this study, fly ashes and APC residues have been sampled separately at different Belgian MSWI plant and analysed by X-ray fluorescence in order to highlight the composition differences that may appear between the solids. Ca and Cl are found to be the major elements in most of the samples. Lithophilic elements, such as Al and Si, are richer in furnace and boiler ashes, as can be expected. Leaching tests also show differences between the residues; leachates from furnace and boiler ashes are alkaline while those from bag filter residues present a pH value of 6, which impacts the leaching of heavy metals (Pb and Zn). The results suggest that it could be advantageous to manage fly ashes and APC residues separately by adjusting the treatment to their specificities.     

Effect of sewage sludge content on gas quality and solid residues produced by cogasification in an updraft gasifier

In the present work, the gasification with air of dehydrated sewage sludge (SS) with 20wt.% moisture mixed with conventional woody biomass was investigated using a pilot fixed-bed updraft gasifier. Attention was focused on the effect of the SS content on the gasification performance and on the environmental impact of the process. The results showed that it is possible to co-gasify SS with wood pellets (WPs) in updraft fixed-bed gasification installations. However, at high content of sewage sludge the gasification process can become instable because of the very high ash content and low ash fusion temperatures of SS. At an equivalent ratio of 0.25, compared with wood pellets gasification, the addition of sewage sludge led to a reduction of gas yield in favor of an increase of condensate production with consequent cold gas efficiency decrease. Low concentrations of dioxins/furans and PAHs were measured in the gas produced by SS gasification, well below the limiting values for the exhaust gaseous emissions. NH(3), HCl and HF contents were very low because most of these compounds were retained in the wet scrubber systems. On the other hand, high H(2)S levels were measured due to high sulfur content of SS. Heavy metals supplied with the feedstocks were mostly retained in gasification solid residues. The leachability tests performed according to European regulations showed that metals leachability was within the limits for landfilling inert residues. On the other hand, sulfate and chloride releases were found to comply with the limits for non-hazardous residues.     

Comparison of leaching characteristics of heavy metals from bottom and fly ashes in Korea and Japan

The objective of this research was to compare the leaching characteristics of heavy metals such as cadmium, chromium, copper, nickel, lead, etc., in Korean and Japanese municipal solid waste incineration (MSWI) ash. The rate of leaching of heavy metal was measured by KSLT and JTL-13, and the amount of heavy metals leached was compared with the metal content in each waste component. Finally, bio-availability testing was performed to assess the risks associated with heavy metals leached from bottom ash and fly ash. From the results, the value of neutralization ability in Japanese fly ash was four times higher than that in Korean fly ash. The reason was the difference in the content of Ca(OH)(2) in fly ash. The amount of lead leached exceeded the regulatory level in both Japanese and Korean fly ash. The rate of leaching was relatively low in ash with a pH in the range of 6-10. The bio-availability test in fly ash demonstrated that the amount of heavy metals leached was Pb>Cd>Cr, but the order was changed to Pb>Cr>Cd in the bottom ash. The leaching concentration of lead exceeded the Japanese risk level in all fly ashes from the two countries, but the leaching concentration of cadmium exceeded the regulatory level in Korean fly ash only.     

Sintering characteristics of CaO-rich municipal solid waste incineration fly ash through the addition of Si/Al-rich ash residues

Thermal treatment is a promising technology for the fast disposal of hazardous municipal solid waste incineration (MSWI) fly ash in China. However, fly ash produced in grate incinerator (GFA) is rich in CaO and chlorides, which promote the formation of toxic hexavalent chromium [Cr(VI)] and ash agglomeration during the thermal process, inhibiting the thermal disposal of GFA. In this study, sintering characteristics of CaO-rich GFA were improved by adding Si/Al-rich MSWI ash residues. According to the results, ash agglomeration was well suppressed during thermal treatment of the mixed ash. Si/Al/Fe-compounds competed with un-oxidized Cr-compounds to react with CaO and suppressed Cr(VI) formation. Meanwhile, chlorides in GFA facilitated heavy metal volatilization from added ashes to the secondary fly ash, favoring the recovery of these metals. Ca-aluminosilicates was found as the main mineral phase in the thermally treated mixed ash, which has attractive potential for applications. The formation of the aluminosilicates made the heavy metals that remained in the treated mixed ash more stable than the thermally treated single ash.     

Release of salts from municipal solid waste combustion residues

Residues from fluidized bed combustion of municipal solid waste were investigated with respect to their leaching behavior and possible extraction of salts. The total water extractable amounts of Na, K, Ca, Cl(-), Br(-), F(-) and SO(4)(2-) along with the total dissolved solids of bottom, hopper, cyclone and bag house filter ashes were determined. A simple multistage washing process (using water as the extraction medium) was tested in lab scale experiments. The effect of variations in parameters, such as water to ash weight ratio, contact time, temperature and number of extraction steps was investigated. The leaching behavior of untreated and washed cyclone and bag house filter ashes was evaluated by a two-step batch-leaching test, i.e. the CEN test. The ashes investigated in this study can be arranged according to their decreasing water extractable contents and total dissolved solids as follows: filter ash > cyclone ash > hopper ash > bottom ash. A triple extraction with water at liquid to solid ratio 2 and extraction time 5 min gave the best results for the extraction of Ca, Na, K, Cl(-) and SO(4)(2-) from the cyclone as well as from the filter ashes. The leached amounts of salts in the CEN test performed on the washed cyclone ash were considerably lower than the corresponding amounts released from the unwashed ash. Thus, the washed cyclone ash was made more stable with respect to salt leachability. On the other hand, large amounts of salts were leached from the washed filter ashes as well as from unwashed filter ashes. Therefore, it can be concluded that three stage water extraction is not a suitable stabilization method for this type of filter ashes.     

Chemical stability of geopolymers containing municipal solid waste incinerator fly ash

Municipal solid waste incinerators every year produce tons of fly ashes which, differently from coal fly ashes, contain large amounts of toxic substances (heavy metals, dioxins, furans). The stabilization/solidification (S/S) technology known as geopolymerization is proposed with the purpose to bond physically and chemically incinerator fly ashes (IFA) in a solid matrix, in order to reduce pollutant mobility. The chemical stability of geopolymers with Si/Al ratio of 1.8–1.9 and Na/Al ratio of 1.0, synthesized by alkali activation of metakaolin and the addition of 20 wt% of two different kinds of IFA, is presented. The concentration of the alkaline solution, water to solid ratio and curing process have been optimized. The room temperature consolidation of IFA containing geopolymers has been tested for leachability in water for 1 day, accordingly to EN 12457 regulation and extended to 7 days to increase the water attack on solid granules. Leachable metals in the test solution, determined by ICP_AES, fall within limit values set by regulation for non-dangerous waste landfill disposal. Geopolymeric matrix evolution with leaching time has been also evaluated in terms of pH and electrical conductivity increase in solution.     

Laboratory stabilization/solidification of surrogate and actual mixed-waste sludge in glass and grout

Grout and glass formulations were developed for the stabilization of highly radioactive tank sludges. These formulations were tested in the laboratory with a surrogate and with a sample of an actual mixed waste tank sludge. The grout formulation was tested at wet-sludge loadings of 50–60 wt%, giving a volume increase of about 40–50 vol%. Dried sludge was vitrified into glass at waste oxide loadings of 40–50 wt%, giving a volume decrease of about 50–60 vol%. The Resource Conservation and Recovery Act (RCRA) metals included in surrogate testing were Ag, Ba, Cd, Cr, Ni, Pb, Se, Tl and Hg. Since vitrification would volatilize, not stabilize mercury, it was not included in the surrogates vitrified. The actual sludge sample was only characteristically hazardous for mercury by the toxic characteristic leaching procedure (TCLP) but exceeded the Universal Treatment Standard (UTS) limit for chromium. The grout and glass formulations stabilized these RCRA metals within UTS limits. In addition, a grout leachability index of about 9–10 was measured for both ⁸⁵Sr and ¹³⁷Cs, meeting the recommended requirement of >6. The glass leachability index was estimated to be >18 for cold cesium and strontium.     

The behaviour of ashes and heavy metals during the co-combustion of sewage sludges in a fluidised bed

Co-combustion tests of dry sewage sludges with coal were performed in a pilot bubbling FBC aiming at the characterization of ashes and determining the behaviour of heavy metals in the process. The tests showed compliance with the regulatory levels as far as heavy metal emissions were concerned. The bottom ashes, which accounted for about 70% of the total ash production, were obtained in a granular form, with diameters ranging from 0.5 to 4 mm. The heavy metals were distributed in ashes obtained from different locations of the installation and their concentrations were found to vary depending on the location of capture. The increase in heavy metals content in bottom ashes was not found to lead to higher leachability and ecotoxicity compared to sewage sludges, suggesting that there could be opportunities for their further use. Mercury suffered vaporisation inside the reactor, thus leaving bottom ashes free of contamination by it. However, there was observed a strong retention of mercury in cyclone ashes due to the presence of unburned carbon which probably acted as an adsorbent. The effluent mercury was also found to be mostly associated with the particulate fraction, being less than 20% emitted in gaseous forms. The results suggested that the combustion of the sewage sludge could successfully be carried out and the amount of unburned carbon leaving the combustor but captured in cyclone was large enough to ensure substantial retention of mercury at low temperatures, hence could contribute to an improvement of the mercury release which still remains an issue of great concern to resolve during combustion of waste materials.     

A study of Cr(VI) in ashes from fluidized bed combustion of municipal solid waste: leaching, secondary reactions and the applicability of some speciation methods

The use of the fluidized bed technique for the combustion of municipal solid waste is a rather new concept. This type of combustor produces ash residues with somewhat different properties than the residues generated from the traditional mass burn techniques. Therefore, chemical characterization and the investigation of toxic metals behavior during ash water reactions are necessary for the safe disposal of these residues. In the present work, the total elemental composition, mineralogy and leaching behavior of ashes from the combustion of municipal solid waste in a fluidized bed combustion boiler have been investigated. The cyclone ash and, in particular, the filter ash contained considerable amounts of soluble substances, thus giving leachates with high levels of Cl-, Na+, K+, Ca2 + and Al(IIl). On the other hand, the two ash fractions taken in the boiler, the bottom and hopper ashes, were much more stable with respect to the release of salts and heavy metals. Since Cr(VI) is mobile and toxic its release from combustion residues can pose environmental problem. Even though the total Cr contents were similar in all ashes studied, the bottom ash gave about a thousand times higher levels of Cr(VI) in test leachates than the hopper, cyclone and filter ashes. However, it was found that the leached amount of Cr(VI) from the bottom ash decreased significantly when bottom ash was mixed with the hopper ash. The most probable cause for this decrease is the coupled oxidation of Al(0) to Al(III) and reduction of dissolved Cr(VI) to Cr(III). This finding that the mixing of two ash streams from the same boiler could result in the immobilization of Cr may point at a simple stabilization method. Selective extraction of water soluble, exchangeable and sparingly soluble forms of Cr(VI) was also investigated. Extraction methods were evaluated for their suitability for ash matrixes. It was found that interferences due to the presence of reducing substances in some ash materials may occur.     

Wet extraction of heavy metals and chloride from MSWI and straw combustion fly ashes

Fly ash residues from combustion often do not meet the criteria neither for reuse as construction materials nor landfilling as non-hazardous waste, mainly because of the high concentration of heavy metals and chlorides. This work aimed to technically evaluate an innovative wet treatment process for the extraction of chloride (Cl^?), cadmium (Cd), copper (Cu), lead (Pb) and zinc (Zn) from fly ashes from a municipal solid waste incineration (MSWI) plant and from a straw combustion (SC) facility. Factors investigated were liquid/solid (L/S) ratio, full carbonation (CO₂ treatment), influence of pH and leaching time, using a two-level full factorial design. The most significant factor for all responses was low pH, followed by L/S ratio. Multiple linear regression models describing the variation in extraction data had R² values ranging from 58% to 98%. An optimization of the element extraction models was performed and a set of treatment conditions is suggested.     

Treatment and recycling of incinerated ash using thermal plasma technology

To treat incinerated ash is an important issue in Taiwan. Incinerated ashes contain a considerable amount of hazardous materials such as dioxins and heavy metals. If these hazardous materials are improperly treated or disposed of, they shall cause detrimental secondary contamination. Thermal plasma vitrification is a robust technology to treat and recycle the ash residues. Under the high temperature plasma environment, incinerated ashes are vitrified into benign slag with large volume reduction and extreme detoxification. Several one-step heat treatment processes are carried out at four temperatures (i.e. 850, 950, 1,050 and 1,150 degrees C) to obtain various "microstructure materials". The major phase to form these materials is a solid solution of gehlenite (Ca2Al2SiO7) and ?kermanite (Ca2MgSi2O7) belonging to the melilite group. The physical and mechanical properties of the microstructure materials are improved by using one-step post-heat treatment process after plasma vitrification. These microstructure materials with good quality have great potential to serve as a viable alternative for construction applications.     

Leaching of heavy metals from chromated copper arsenate (CCA) treated wood after disposal

Wood treated by preservatives is commonly found in solid waste. Among the different types of preserved wood, chromated copper arsenate (CCA) treated wood recently has received much attention due to the scale of usage and its significant role in soil and water contamination. As the ash of CCA treated wood would be hazardous if the wood were to be incinerated, this is not a good alternative, and the best available disposal method is thus landfilling in the US, Canada and Australia. Leaching of the metals from preserved wood that is disposed in unlined landfills for construction debris pollutes the soil and water environments. Several factors affecting leaching of the metals from wood, including pH of the leachant, temperature, the duration of leaching and the type of leachant, were investigated. These factors affect each of the metals, chromium, copper and arsenic, differently. A comparison of these effects on each metal was performed. The results of the experiments showed that the pH of the leachants has a significant effect on the leaching process, and sulfuric acid (pH 3) is the most effective leachant compared to nitric and acetic acid (pH 3-4-5). The amounts of leached chromium, copper and arsenic by sulfuric acid (pH 3) during 15 days were, respectively, 0.2, 0.14 and 0.15 mg more than leachates by nitric acid (pH 5) on the basis of 1g of wood (initial contents of 1.03 mg, 0.42 g and 0.8 mg per g of wood). Most of the leaching occurs in the first 5 days, and the rate of leaching decreases significantly after 5 days. Increasing temperature increases the amount of leached metals, and arsenic is the least resistant metal to the leaching when the temperature increases. Increasing the temperature from 15 degrees C to 35 degrees C during 15 days increases the amount of leached chromium, copper and arsenic by acetic acid at pH 5 by about 0.1, 0.4 and 1.2mg per g of wood, respectively.