Mercury leaching characteristics of waste treatment residues generated from various sources in Korea

In this study, mercury (Hg) leaching characteristics of the waste treatment residues (fly ash, bottom ash, sludge, and phosphor powder) generated from various sources (municipal, industrial, medical waste incinerators, sewage sludge incinerator, oil refinery, coal-fired power plant, steel manufacturing plant, fluorescent lamp recycler, and cement kiln) in Korea were investigated. First, both Hg content analysis and toxicity characteristic leaching procedure (TCLP) testing was conducted for 31 collected residue samples. The Hg content analysis showed that fly ash from waste incinerators contained more Hg than the other residue samples. However, the TCLP values of fly ash samples with similar Hg content varied widely based on the residue type. Fly ash samples with low and high Hg leaching ratios (R_L) were further analyzed to identify the major factors that influence the Hg leaching potential. Buffering capacity of the low-R_L fly ash was higher than that of the high-R_L fly ash. The Hg speciation results suggest that the low-R_L fly ashes consisted primarily of low-solubility Hg compounds (Hg₂Cl₂, Hg⁰ or HgS), whereas the high-R_L fly ashes contain more than 20% high-solubility Hg compounds (HgCl₂ or HgSO₄).     

Characterisation of polycyclic aromatic hydrocarbons in flue gas and residues of a full scale fluidized bed combustor combusting non-hazardous industrial waste

This paper studies the fate of PAHs in full scale incinerators by analysing the concentration of the 16 EPA-PAHs in both the input waste and all the outputs of a full scale Fluidized Bed Combustor (FBC). Of the analysed waste inputs i.e. Waste Water Treatment (WWT) sludge, Refuse Derived Fuel (RDF) and Automotive Shredder Residue (ASR), RDF and ASR were the main PAH sources, with phenanthrene, fluoranthene and pyrene being the most important PAHs. In the flue gas sampled at the stack, naphthalene was the only predominant PAH, indicating that the PAHs in FBC’s combustion gas were newly formed and did not remain from the input waste. Of the other outputs, the boiler and fly ash contained no detectable levels of PAHs, whereas the flue gas cleaning residue contained only low concentrations of naphthalene, probably adsorbed from the flue gas. The PAH fingerprint of the bottom ash corresponded rather well to the PAH fingerprint of the RDF and ASR, indicating that the PAHs in this output, in contrast to the other outputs, were mainly remainders from the PAHs in the waste inputs. A PAH mass balance showed that the total PAH input/output ratio of the FBC ranged from about 100 to about 2600 depending on the waste input composition and the obtained combustion conditions. In all cases, the FBC was clearly a net PAH sink.     

Water washing effects on metals emission reduction during municipal solid waste incinerator (MSWI) fly ash melting process

This study investigated that water washing effects on the metals emission reduction in melting of municipal solid waste incinerator (MSWI) fly ash. Experimental conditions were conducted at liquid-to-solid (L/S) ratio 10, 20, and 100 for water-washing process and its subsequent melting treatment at 1450 °C for 2 h. The simple water-washing process as a pre-treatment for MSWI fly ash can remove most of the chlorides, leachable salts, and amphoteric heavy metals from the MSWI fly ash, resulting in the washed ash having lowered chlorine content. MSWI fly ashes washed by L/S ratio 10 and above that were melted at 1450 °C produced slag containing relatively high vitrificaton ratio of Cu and Pb. Besides, the vitrification ratios of Na, K, Ca, and Mg in washed MSWI fly ash were also higher than that of MSWI fly ash. The results indicated that washed MSWI fly ash can reduce the emission of metallic chlorides during its subsequent melting treatment.     

Characterisation of agroindustrial solid residues as biofuels and potential application in thermochemical processes

In the present work, selected agroindustrial solid residues from Brazil – biosolids from meat processing wastewater treatment and mixture of sawdust with these biosolids; residues from apple and orange juice industries; sugarcane bagasse; açaí kernels (Euterpe oleracea) and rice husk – were characterised as solid fuels and an evaluation of their properties, including proximate and ultimate composition, energy content, thermal behaviour, composition and fusibility of the ashes was performed. The lower heating value of the biomasses ranged from 14.31 MJ kg^?1 to 29.14 MJ kg^?1, on a dry and ash free basis (daf), all presenting high volatile matter content, varying between 70.57 wt.% and 85.36 wt.% (daf) what improves the thermochemical conversion of the solids. The fouling and slagging tendency of the ashes was predicted based on the fuel ash composition and on the ash fusibility correlations proposed in the literature, which is important to the project and operation of biomass conversion systems. The potential for application of the Brazilian agroindustrial solid residues studied as alternative energy sources in thermochemical processes has been identified, especially concerning direct combustion for steam generation.     

Generation and distribution of PAHs in the process of medical waste incineration

After the deadly earthquake on May 12, 2008 in Wenchuan county of China, several different incineration approaches were used for medical waste disposal. This paper investigates the generation properties of polycyclic aromatic hydrocarbons (PAHs) during the incineration. Samples were collected from the bottom ash in an open burning slash site, surface soil at the open burning site, bottom ash from a simple incinerator, bottom ash generated from the municipal solid waste (MSW) incinerator used for medical waste disposal, and bottom ash and fly ash from an incinerator exclusively used for medical waste. The species of PAHs were analyzed, and the toxicity equivalency quantities (TEQs) of samples calculated. Analysis results indicate that the content of total PAHs in fly ash was 1.8 × 10³ times higher than that in bottom ash, and that the strongly carcinogenic PAHs with four or more rings accumulated sensitively in fly ash. The test results of samples gathered from open burning site demonstrate that Acenaphthylene (ACY), Acenaphthene (ACE), Fluorene (FLU), Phenanthrene (PHE), Anthracene (ANT) and other PAHs were inclined to migrate into surrounding environment along air and surface watershed corridors, while 4- to 6-ring PAHs accumulated more likely in soil. Being consistent with other studies, it has also been confirmed that increases in both free oxygen molecules and combustion temperatures could promote the decomposition of polycyclic PAHs. In addition, without the influence of combustion conditions, there is a positive correlation between total PCDD/Fs and total PAHs, although no such relationship has been found for TEQ.     

Assessing the environmental impact of ashes used in a landfill cover construction

Large amounts of construction materials will be needed in Europe in anticipation for capping landfills that will be closed due to the tightening up of landfill legislation. This study was conducted to assess the potential environmental impacts of using refuse derived fuel (RDF) and municipal solid waste incineration (MSWI) ashes as substitutes for natural materials in landfill cover designs. The leaching of substances from a full-scale landfill cover test area built with different fly and bottom ashes was evaluated based on laboratory tests and field monitoring. The water that drained off above the liner (drainage) and the water that percolated through the liner into the landfill (leachate) were contaminated with Cl^?, nitrogen and several trace elements (e.g., As, Cu, Mo, Ni and Se). The drainage from layers containing ash will probably require pre-treatment before discharge. The leachate quality from the ash cover is expected to have a minor influence on overall landfill leachate quality because the amounts generated from the ash covers were low, <3–30 l (m² yr)^?1. Geochemical modelling indicated that precipitation of clay minerals and other secondary compounds in the ash liner was possible within 3 years after construction, which could contribute to the retention of trace elements in the liner in the long term. Hence, from an environmental view point, the placement of ashes in layers above the liner is more critical than within the liner.     

An examination of the exothermic nature of fluidized bed combustion (FBC) residues

Circulating fluidized bed combustion (CFBC) ashes from nine operational periods at the 183 MWe CFBC boiler at Point Aconi were examined for exothermic behaviour. Bed ashes and fly ashes were investigated using a Parr 1455 solution calorimeter. Limited tests were also carried out with additional samples from Point Aconi and from the 160 MWe TVA Bubbling Fluidized Bed Combustion boiler to evaluate the effects of particle size and aging on exothermic behaviour. For the Point Aconi ashes, heat release from the bed ash ranged from 11 to 52 J/g, and the maximum heat release rates ranged from 0.06 to 0.17 J/g/s. For the fly ash heat release varied from 114 to 187 J/g and the maximum heat release rates ranged from 0.8 to 1.9 J/g/s. In the fly ash samples, 50% or more of available CaO was converted to Ca(OH)₂, while for the bed ash a third or less of the CaO was converted to Ca(OH)₂. The exothermicity of the bed ash is directly proportional to the CaO content of the ash. However, this is not true for the fly ash. The exothermic behaviour of fresh FBC ash appeared to be greatly reduced by exposure in air over a 48-h period. Another conclusion of this work is that particle size effects the exothermic behaviour.     

Remediation of Soil and Ground Water Contaminated with PAH using Heat and Fe(II)-EDTA Catalyzed Persulfate Oxidation

The feasibility of degrading 16 USEPA priority polycyclic aromatic (PAH) hydrocarbons (PAHs) with heat and Fe(II)-EDTA catalyzed persulfate oxidation was investigated in the laboratory. The experiments were conducted to determine the effects of temperature (i.e. 20 ^∘C, 30 ^∘C and 40 ^∘ C) and iron-chelate levels (i.e., 250 mg/L-, 375 mg/L- and 500 mg/L-Fe(II)) on the degradation of dissolved PAHs in aqueous systems, using a series of amber glass jars as the reactors that were placed on a shaker inside an incubator for temperature control. Each experiment was run in duplicate and had two controls (i.e., no persulfate in systems). Samples were collected after a reaction period of 144 hrs and measured for PAHs, pH and sodium persulfate levels. The extent of degradation of PAHs was determined by comparing the data for samples with the controls. The experimental results showed that persulfate oxidation under each of the tested conditions effectively degraded the 16 target PAHs. All of the targeted PAHs were degraded to below the instrument detection limits (∼4 μ/L) from a range of initial concentration (i.e., 5 μ/L for benzo(a)pyrene to 57 μ/L for Phenanthrene) within 144 hrs with 5 g/L of sodium persulfate at 20 ^∘ C, 30 ^∘C and 40 ^∘C. The data indicated that the persulfate oxidation was effective in degrading the PAHs and that external heat and iron catalysts might not be needed for the degradation of PAHs. The Fe(II)-EDTA catalyzed persulfate also effectively degraded PAHs in the study. In addition, the data on the variation of persulfate concentrations during the experiments indicated that Fe(II)-EDTA accelerated the consumption of persulfate ions. The obtained degradation data cannot be used to evaluate the influence of temperature and Fe(II) levels on the PAH degradation because the PAHs under each of the tested conditions were degraded to below the instrument detection limit within the first sampling point. However, these experiments have demonstrated the feasibility of degrading PAHs in aqueous systems with persulfate oxidation. Additional tests are being conducted to evaluate the effectiveness of treating PAHs in soils and obtaining the rate of degradation of PAHs with persulfate oxidation. Two sets of laboratory experiments were conducted to evaluate the ability of sodium persulfate in oxidizing real world PAH-contaminated soils collected from a Superfund site in Connecticut. The first set of soil sample were treated only with persulfate and to the second batch, mixture of persulfate and Fe(II)-EDTA solutions were added. The results of the second test showed that within 24 hours, 75% to 100% of the initial concentrations of seven PAH compounds detected in the soil samples were degraded by sodium persulfate mixed with FE(II)-EDTA.     

The chemical characteristics of ashes from cattle, swine and poultry manure

Animal manure is waste that contains large amounts of fertilizer resources. Incineration technology is effective in decreasing the volume of animal manure and concentrating the nutrients. In this study, the nutrient concentration and chemical compounds of several types of animal manure ash were examined to promote their recycling for agriculture. The nutrient concentration of manure ash was dependent on the reduction rate of solid materials by incineration. The phosphorus (P) and potassium (K) of cattle and layer manure were not concentrated greatly because of high silicon (Si) and calcium (Ca) concentrations, respectively. On the other hand, the P concentration of swine manure and broiler litter was increased to 10.1–12.0 % (3.6–4.6 times compared with original materials), equivalent to that of phosphate rock used as fertilizer material. The K concentration of broiler litter ash (16.1 %) was highest of all. The phosphate compounds of cattle and swine manure ashes were determined as Ca₉Fe(PO₄)₇ or Ca₉MgK(PO₄)₇. Hydroxyapatite (Ca₅(PO₄)₃(OH)) was detected in layer manure and broiler litter ashes. By acid treatment of ash, P and K availability of the fertilizer made from layer manure ash (33 % of materials) was equivalent to that of conventional chemical fertilizer.     

The significance of polynuclear aromatic hydrocarbons applied to agricultural soils in sewage sludges in the U.K.

The ubiquity of polynuclear aromatic hydrocarbons (PAHs) in sewage sludges is now well documented. Since PAHs exhibit carcinogenic/mutagenic behaviour concern has been expressed over their fate following sludge application to agricultural soils. This paper presents a resume of the behaviour of sludge applied PAHs in soils and their propensity to transfer from the soil into plant tissues. This information is used to assess the environmental significance of PAHs in sludge amended soils. Sludge PAH inputs to the U.K. environment are compared with other known sources, such as waste disposal and atmospheric deposition and the possible impact of sludge application on human exposure is considered. It is concluded that at present there is no necessity to specifically regulate PAH inputs to agricultural soils in sewage sludge.     

Sedimentary Record of Polycyclic Aromatic Hydrocarbons in the Gulf of Trieste (Northern Adriatic Sea)

To reconstruct a history of polycyclic aromatic hydrocarbon (PAH) pollution in the Gulf of Trieste, one of the largest urbanized areas in the Adriatic Sea, we analyzed three long sediment cores collected between 1996 and 1997. Concentrations of total PAHs, the sum of 16 PAH compounds and six of their methylated analogues, in all three cores show a decrease from 600–800 ng g⁻¹, at the surface, to levels below 250 ng g⁻¹ in deepest layers (down to 3 m). The same trend was shown with separate representative pyrogenic PAHs (pyrene, benzofluoranthene and phenanthrene). Using Hg as a recent geochronological tracer, we observe an increasing input of PAHs since the beginning of the 20th Century and, especially, after the Second World War coinciding with increasing industrialization and urbanization of the region. This correlation is supported by PAH ratios that are indication of combustion processes and represent a marker for anthropogenic inputs. No correlation exists between PAHs and black carbon within the core profiles, indicating two different fractions of the ‘black carbon continuum’.     

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.     

PHYSICO-CHEMICAL CHARACTERIZATION AND LEACHING OF DESULPHURIZATION COAL FLY ASH

Fly ash produced by coal combustion using two types of desulphurization process were studied: a conventional pulverized coal boiler equipped with lime injection (PCL ash), and a circulating fluidized bed combustion boiler with limestone injection (CFBC ash). The ashes were characterized completely: granulometry, morphology, mineralogy, chemical composition and behaviour to water contact. Both PCL ash and CFBC ash present similar features: fine granulometry, presence of anhydrite phase and sulphate content. However, PCL ash also shows lots of spherical particles, unlike CFBC ash, and a much higher lime content, due to the lower desulphurization rate in PC boilers. Unlike CFBC ash, most of the trace elements in PCL ash show an inverse concentration–particle size dependence. Leachates obtained from both samples are rich in soluble salts [CaSO₄and Ca(OH)₂] and arsenic and selenium are prevented from solubilizing by high lime content. In wetted PCL ash, the formation of ettringite crystals stabilizes calcium and sulphate ions. Simultaneously, arsenate, selenate and chromate anions are trapped in the crystal. CFBC ash does not really harden because the lime content is too low. However, the leached selenium concentration is cut down in wetted CFBC ash samples.     

Sustainable alkali-activated binders with municipal solid waste incineration ashes as sand or fly ash replacement

The present study investigates the feasibility of using two types of municipality solid wastes incineration ashes, namely, fly ash and bottom ash in the production of sustainable alkali-activated binder. The ashes are collected from the incineration plant and characterized to determine their particle size distribution, specific gravity, chemical composition, and heavy metals content. The ashes are then used as either fly ash or sand replacement with five replacement ratios 0%, 5%, 10%, 15%, and 20% to produce the binder. The produced binder are characterized in terms of strength, workability, density, water absorption, thermal conductivity and stability, chemical composition, and heavy metals content. The results reflect the ability of producing sustainable alkali-activated binder with small dosage of MSWI ashes as either fly ash or sand replacement without negatively affecting its strength, workability, density, and water absorption. The ashes enhance the thermal insulation capability of the binder.

     

Effect of unburned carbon on lead, zinc, and copper recovery from molten fly ash by chloride-induced volatilization

The present work focuses on investigation of the effective recovery of heavy metals from molten fly ash by applying chloride-induced volatilization. In particular, the effect of unburned carbon on the chloride-induced volatilization of lead, zinc, and copper from model and real molten fly ashes was investigated in the temperature range 873–1173 K under a N₂ atmosphere. As a result, almost 100% of lead and a significant proportion of zinc were volatilized from the real molten fly ash samples at 1173 K. In contrast, for the model fly ash, volatilization ratios of lead and zinc at 1173 K were only 85% and 25%, respectively. Further, the results of X-ray diffraction analysis suggested that PbO in molten fly ash was converted either to Pb₂OCl₂ or Pb by respective chlorination and reduction reactions. Meanwhile ZnO and CuO in the molten fly ash were reduced to Zn and Cu by reaction with unburned carbon. Subsequently, Pb, Zn, and Pb₂OCl₂ were volatilized, but Cu remained in the solid residue. Finally, the volatilization ratio of zinc increased with the addition of carbon, and more than 98% of zinc was volatilized at 1173 K from a fly ash with a carbon content of 20%.     

REVEGETATION OF WASTE FLY ASH LAGOONS II. SEEDLING TRANSPLANTS AND PLANT NUTRITION

As an alternative or in addition to direct seeding, container-grown transplants provide a means of economically and rapidly revegetating waste fly ash lagoons through the expeditious establishment of vegetation islands. Survival and growth ofEnchylaena tomentosaandNitraria billardiereitransplants were largely dependent on the size of the root volume at transplanting. Growth response of both species in fly ash increased significantly as transplant container size increased from 110 ml to 800 ml. Fly ash incorporated into the potting mix during the containerised stage of growth generally reduced plant growth and survival following eventual transplantation. Gradual hardening ofEnchylaena tomentosaseedlings to increasing concentrations of fly ash in the potting mix (25 to 50 to 75% fly ash), however, improved immediate survival following transplantation, into pure ash. Nitrogen deficiency in Port Augusta fly ash was a major nutritional limitation to growth of these two species. Growth and dry matter production responded optimally to application of N fertiliser (NH₄NO₃) at 100–150 kg N ha⁻¹. Although bicarbonate-extractable P levels in fly ash were high (over 250 mg kg⁻¹), a response ofEnchylaena tomentosato supplementary P application [Ca(H₂PO₄)₂.H₂O] at 100–200 kg P ha⁻¹was observed.N. billardiereidid not respond to supplementary P, and it was suggested that fly ash P may be selectively available to plants on a species dependent basis. No growth responses to K application (KCl) at rates of up to 400 kg K ha⁻¹were found.     

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.     

Preparation and characterization of sorbents prepared from ash (waste material) for sulfur dioxide (SO2) removal

Sorbents synthesized from various types of ash (coal fly ash, coal bottom ash, oil palm ash, and incinerator ash) for flue gas desulfurization were investigated. The sorbents were prepared by mixing the ashes with calcium oxide and calcium sulfate using the water hydration method. The effects of various sorbent preparation variables, such as the hydration period, the ratio of calcium oxide to ash, and the amount of calcium sulfate, on the Brunauer-Emmett-Teller (BET)-specific surface area of the resulting sorbent were studied using a two-level full factorial design. The surface area of the sorbents obtained range from 15.4 to 122.1m²/g. Regression models were developed to correlate the significant variables to the surface area of the sorbents. An analysis of variance (ANOVA) showed that the model was significant at a confidence level of 95%. It was found that apart from all the individual variables studied, interactions between variables also exerted a significant influence on the surface area of the sorbent. From the activity test results, it was found that sorbents prepared from coal fly ash and oil palm ash have the highest SO₂ absorption capacity. Scanning electron microscope (SEM) analysis showed that the sorbent was composed of a compound with a high structural porosity, while an X-ray diffraction spectrum showed that calcium aluminum silicate hydrate compounds are the main products of the hydration reaction.     

Effects of physicochemical factors on PAH degradation by Planomicrobium alkanoclasticum

Polycyclic aromatic hydrocarbons (PAHs) are environmental pollutants that are mutagenic, carcinogenic, and toxic to living organisms. Here, the ability and effectiveness of selected bacteria isolated from an oil‐contaminated area in biodegrading PAHs were evaluated, and the optimal conditions conducive to bacterial PAH biodegradation were determined. Of six bacterial isolates identified based on their 16S rRNA sequences, Planomicrobium alkanoclasticum could subsist on and consume nearly all hydrocarbons according to the 2,6‐dichlorophenolindophenol assay. The efficacy of this isolate at PAH biodegradation was then empirically confirmed. After 30 days of incubation, P. alkanoclasticum degraded 90.8% of the 16 PAH compounds analyzed and fully degraded eight of them. The optimum P. alkanoclasticum growth conditions were 35°C, pH 7.5, and NaNO₃ as the nitrogen source. Under these biostimulant conditions, P. alkanoclasticum degraded 91.4% of the total PAH concentration and completely decomposed seven PAHs after 15 days incubation. Hence, P. alkanoclasticum is an apt candidate for the biodegradation of PAHs and the bioremediation of sites contaminated by them.     

The biogenic content of process streams from mechanical–biological treatment plants producing solid recovered fuel. Do the manual sorting and selective dissolution determination methods correlate?

The carbon emissions trading market has created a need for standard methods for the determination of biogenic content (χ_B) in solid recovered fuels (SRF). We compare the manual sorting (MSM) and selective dissolution methods (SDM), as amended by recent research, for a range of process streams from a mechanical–biological treatment (MBT) plant. The two methods provide statistically different biogenic content values, as expressed on a dry mass basis, uncorrected for ash content. However, they correlate well (r² > 0.9) and the relative difference between them was <5% for χ_B between 21% ^w/w_d and 72% ^w/w_d (uncorrected for ash content). This range includes the average SRF biogenic content of ca. 68% ^w/w_d. Methodological improvements are discussed in light of recent studies. The repeatability of the SDM is characterised by relative standard deviations on triplicates of <2.5% for the studied population.