Mass balance of arsenic and antimony in municipal waste incinerators

The arsenic and antimony balance in two municipal waste incinerators was investigated. Initially, the production rates of ash and wet scrubber effluent were estimated. Then the arsenic and antimony in the ash and wet scrubber effluent were determined, which gave an estimate of the elemental balance. The total amounts of arsenic and antimony in the municipal waste were 0.9 g/t and 30–44 g/t, respectively. The distributions to fly ash were 45–47% and 33–74% for arsenic and antimony, respectively. The distribution mechanisms of arsenic and antimony are discussed from the viewpoints of their thermodynamics as well as their initial valencies, which greatly affect their behaviour. Received: July 2, 1998 / Accepted: February 27, 1999     

In situ remediation of arsenic in contaminated soils

In situ chemical fixation represents a promising and potentially cost‐effective treatment alternative for metal‐contaminated soils. This article presents the findings of the use of iron‐bearing soil amendments to reduce the leachability and bioaccessibility of arsenic in soils impacted by stack fallout from a zinc smelter. The focus of this investigation was to reduce the lead bioaccessibility of the soils through addition with phosphorus‐bearing amendments. However, as phosphorus addition was expected to increase arsenic mobility, the fixation strategy also incorporated use of iron‐bearing amendments to offset or reverse these effects. The findings of this investigation demonstrated that inclusion of iron‐bearing chemicals in the amendment formulation reduced arsenic leachability and bioaccessibility without compromising amendment effectiveness for reducing lead bioaccessibility. These results suggest that in situ chemical fixation has the potential to be an effective strategy for treatment of the impacted soils. © 2003 Wiley Periodicals, Inc.     

Fluoride sorption by treated fly ash: kinetic and isotherm studies

High fluoride levels in drinking water have become a critical health hazard. In the present study, the performance of magnesia-loaded fly ash adsorption in the removal of fluoride from aqueous solution was investigated in a batch study. The effect of contact time, dosage, pH, temperature and agitation speed was studied at different values. The maximum removal efficiency was 88 % at 150 min. The effective dose of adsorbent was found to be 2.5 g/l. The optimum pH was found to be at pH 4. Kinetic studies and isotherm studies were also performed to understand the ability of the adsorbents. The monolayer adsorption capacity determined from the Langmuir adsorption equation was found to be 11.61 mg/g. The kinetic measurements suggested the involvement of pseudo-second-order kinetics in adsorption and were controlled by a particle diffusion process. Overall, the results of this study suggest that magnesia-loaded fly ash is an environmentally friendly, efficient and low-cost adsorbent, useful for the removal of fluoride from aqueous solution.     

Fate and behavior of selected heavy metals with mercury mass distribution in a fluidized bed sewage sludge incinerator

In this paper, emission and distribution behavior of six heavy metals (As, Cd, Cr, Ni, Pb, and Hg), particulate matter and mass distribution of mercury within the different streams of a fluidized bed sewage sludge incinerator are presented. At the inlet of air pollution control devices (APCDs); Cd, Cr, Ni and Pb were mainly enriched in coarse particles; comparatively As content was higher in fine particles (<PM_2.5). The concentration of heavy metals in total particulate matter and PM_2.5, at the inlet of APCDs, were in the order of Cr > Ni > Pb > As > Cd. Mercury was almost always distributed in flue gas. Metals, other than mercury, were efficiently removed in APCDs and their concentrations in bottom ash, with fly ash being higher, whereas for that in wastewater, then waste sand was lesser. Overall mercury removal efficiency of APCDs was 98.6 %. More than 83.3 % of mercury was speciated into oxidized form at the inlet of APCDs, attributed by higher chlorine content in sludge. Mercury was mainly distributed in wastewater (78.4 %), wastewater from a spray dry reactor (16.8 %), fly ash in a hopper (3.4 %) and flue gas (1.4 %). This result is one of the first for data to be obtained; more experiments are required to control emission from such sources.     

Effects of fly ash addition on physical properties of porous clay-fly ash composites via polymeric replica technique

The porous composites of clay and fly ash have the potential to be used in many fields, such as catalyst support and gas adsorbents. In this study, various ratios of fly ash (1–2) with different percentage of suspension (50–70 wt%) were applied to produce porous clay-fly ash composites via polymeric replica technique. Fabrication process starts by mixing clay and fly ash in distilled water to form slurry. The process is followed by fully immersing polymer sponge in slurry. The excess slurry is then removed through squeezing. Finally, the sponge coated with slurry is sintered at 500 and 1250 °C for 1 h. It is found that the compressive strength of porous composites improves significantly (0.178–1.28 MPa) when the amount of clay-fly ash suspension mixture (50–70 wt%) increases. The compressive strength of porous composites is mainly attributed to the mullite, quartz and amorphous phase formations. These results are supported by X-ray diffraction analysis. On the other hand, increase in the amount of suspension reduces the apparent density (from 2.44 to 2.32 g/cm³) and porosity (from 97 to 85 %). The reduction in apparent density is believed to be caused by the presence of high fly ash content in porous composites. The melted fly ash cenospheres have closed the internal pores and increased density of samples. Higher suspension level not only reduces porosity, but also increases close pores of the porous composites. The results are justified through the observation from the structures of porous clay-fly ash composites.     

Trace chemical partitioning in construction and demolition debris fines: process and market implications

Construction and demolition debris (CDD) fines, a residue generated from mechanized CDD recycling, can often be beneficially reused. Concentrations of chemicals of potential concern in CDD fines should be evaluated prior to being reintroduced into the environment to assess risk and make informed decisions about appropriate reuse opportunities. The distribution of trace chemicals in CDD fines as a function of particle size was measured to evaluate if concentrations in the bulk material can be reduced by removing certain particle size ranges through screening. Chemicals of potential concern, including arsenic, lead, sulfate and polycyclic aromatic hydrocarbons (PAH), were characterized in four different size fractions (19–4.8 mm, 4.8–0.84 mm, 0.84–0.3 mm, < 0.3 mm) of CDD fine samples collected from 12 US CDD recycling facilities throughout the US. Results revealed that aluminum, arsenic and chromium concentrations were distributed evenly throughout all four size fractions. As for the remaining chemicals, most samples had lower concentrations in the 19–4.8 mm size range. In some samples and for certain chemicals, removal of the finer size fractions reduced overall concentrations in CDD fines, suggesting that additional processing may be worth further investigation.     

The adsorption characteristics of heavy metals by various particle sizes of MSWI bottom ash

The incineration rate of municipal solid waste (MSW) has been increased because of difficulty in securing a proper disposal site for MSW in Korea. The advantage of incineration is reduction of the volume of waste; however, significant amounts of bottom ash and fly ash were generated in the incineration process. Their treatment has attracted growing interest because of the potential toxicity of hazardous heavy metals. Generally, heavy metals are less released from bottom ash than from fly ash. In this study the adsorption characteristics of heavy metals were investigated using various particle sizes of MSWI bottom ash. Since bottom ash has a broad particle size distribution, it was sieved to size classes of +20, -20, -48, -80, -100 mesh. Cation exchange capacity (CEC) was analyzed by the ammonium acetate method to evaluate the potential as an adsorbent. The CEC values and surface areas increase as the range of particle size becomes finer. The adsorption experiment was conducted using synthetic (Cu and Ni) and plating rinse water as a function of reaction time (10-180 min), liquid/solid ratio (2-100) and particle size (+20 to -100 mesh), respectively. The adsorption rate increased with decreasing particle size and with increasing liquid/solid ratio; however, the removal efficiency of Cu was higher than that of Ni. In the case of plating rinse water, the adsorption rate decreased sharply at high liquid/solid ratio, and it showed over 80% of adsorption rates for Cu and Ni at an initial pH of 3.     

The potential of SO2 for reducing corrosion in WtE plants

Due to the high-temperature boiler corrosion induced by chloride-rich fly ash deposits, steam generation in today’s Waste-to-Energy (WtE) plants is typically designed only for 40 bar/400 °C as an economic compromise between acceptable corrosion rate and maximum power generation. The high-corrosive metal chlorides in the fly ash can react with SO₂ forming low-corrosive sulfates. The sulfation efficiency is enhanced by high SO₂ levels and sufficient residence time of the flue gas at high-temperatures (700–900 °C). The fly ash sulfation was tested in full scale in a Swedish WtE plant by applying the economic sulfur recirculation method. Probes of several alloys (16Mo3, Inconel 625, Sanicro 28) were exposed for 1000 h at controlled material temperatures in the superheater position, at normal and during sulfating operation respectively. Analyses of the fly ash showed that the molar Cl/S was decreased to values well below 1 and the corresponding corrosion rates of the individual material samples were less than half when sulfur recirculation was in operation. These positive findings demonstrate that the sulfur recirculation process has high potential for low-corrosive high-temperature steam generation (T ≈ 500 °C) and improved electricity production. Further steam superheating can be realized by staged superheating using small amounts of secondary fuel.     

A study of disposed fly ash from landfill to replace Portland cement

The landfills of fly ash are the problem of all power plants because this disposed fly ash is not used in any work. This research studies the potential of using disposed fly ashes which have disposal time of 6-24 months from the landfill of Mae Moh power plants in Thailand to replace Portland cement type I. Median particle sizes of disposed fly ashes between 55.4 and 99.3 microm were ground to reduce the sizes to about 7.1-8.4 microm. Both original and ground disposed fly ashes were investigated on physical and chemical properties. Compressive strengths of disposed fly ash mortars were determined when Portland cement type I was replaced by disposed fly ashes at the rate of 10%, 20%, and 30% by weight of cementitious material (Portland cement type I and disposed fly ash). The results presented that most particles of original disposed fly ashes were solid and sphere with some irregular shape while those of ground disposed fly ashes were solid and irregular shape. CaO and LOI contents of disposed fly ashes with different disposal times had high variation. The compressive strengths of original disposed fly ash mortars were low but those of ground disposed fly ash mortars at the age of 7 days were higher than 75% of the standard mortar and increased to be higher than 100% after 60 days. From the results, it could be concluded that ground disposed fly ashes were excellent pozzolanic materials and could be used as a partial replacement of cement in concrete, even though they were exposed to the weather for 24 months.     

Optimizing Cr(VI) adsorption on activated carbon produced from heavy oil fly ash

In order to explore the beneficial utilization of heavy oil fly ash (HOFA) generated in the power plants, the present study is intended to optimize the chromium(VI) [Cr(VI)] adsorption on activated carbon produced from HOFA. The raw HOFA obtained from a power plant was washed by nitric/hydrochloric acid and activated at 800 °C with a holding time of 60 min to produce fly ash activated carbon (FAC). Phosphoric acid was used as a chemical agent to improve the surface characteristics of the HOFA during the activation process. Batch adsorption experiments were employed to evaluate the effects of different parameters such as initial Cr(VI) concentration, pH, and FAC dose on the removal of Cr(VI) from aqueous solution. A total of 17 adsorption experimental runs were carried out employing the detailed conditions followed the response surface methodology based on the Box–Behnken design. The results indicate that developed FAC has the potential for removing Cr(VI) from wastewater. Under the test conditions, a maximum of 91.51 % Cr(VI) removal efficiency was achieved.     

New technology and application of brick making with coal fly ash

China has ranked first in the coal fly ash emission in the world. The multipurpose use of the fly ash from power plant waste is always an important topic for the Chinese environmental protection, which has drawn the concern of the government, scientific research departments, manufacturing enterprises and industry experts. This paper introduces an experimental research on how to recycle fly ash effectively, a kind of new technology of making bricks by which fly ash content could be amounted to 50–80 %. The article introduces raw materials of fly ash brick, production process and key control points. It introduces how to change the technical parameters of the existing brick-making mechanical device, optimize the parameters combination and improve the device performance. High-content fly ash bricks are manufactured, which selects wet fly ash from power plants, adding aggregate with reasonable ratio and additives with reasonable dosage, and do the experimental research on manufactured products for properties, production technology and selection about technology parameters of production equipment. All indexes of strength grade, freezing-thawing resisting, and other standards of the studied bricks reached the national standards for building materials industry.     

Evaluation on the applicability of dry processed bottom ash as lightweight aggregate for construction fields

Currently, wet bottom ash is not sufficiently utilized due to its content of unburned coal, chloride and moisture. In contrast, bottom ash discharged from the recently introduced dry process spends a longer time on the clinker conveyer in the lower part of the boiler and consequently contains a significantly smaller amount of unburned coal. Consequently, it has high potential for use as a lightweight aggregate for construction material because of properties such as high porosity, low unburned coal content, non-chloride, and non-moisture. However, it is not frequently used for construction because the ash particle has a flat and thin shape, coarse surface and unfavorable structural strength. Against this backdrop, this study has conducted a range of experiments to identify the shapes, structure, density, absorption, percentage of floating particles, unit volume weight, solid volume, characteristics of air bubbles and micro pores, crushing strength of bottom ash, and the following results were observed. Though the dry bottom ash has sharp and angular edges, its flat and thin shapes lead to vulnerable structures. Dry bottom ash of the size of 0.6 mm or larger has 50–60 % of the total pore rate and 30–50 % of the closed pore rate. Considering these qualities, by removing the relatively fragile surface parts and making the particles more globular, dry bottom ash can be used as a lightweight aggregate for construction field having outstanding performance in terms of light weight and insulation.     

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.     

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.     

Physical containment of municipal solid waste incineration bottom ash by accelerated carbonation

Accelerated carbonation of municipal solid waste incineration residues is effective for immobilizing heavy metals. In this study, the contribution of the physical containment by carbonation to immobilization of some heavy metals was examined by some leaching tests and SEM–EDS analysis of untreated, carbonated, and milled bottom ash after carbonation that was crushed with a mortar to a mean particle size of approximately 1 μm. The surface of carbonated bottom ash particles on SEM images seemed mostly coated, while there were uneven micro-spaces on the surface of the untreated bottom ash. Results of Japan Leaching Test No. 18 (JLT18) for soil pollution showed that milling carbonated bottom ash increased the pH and EC. The leaching concentration of each element tended to be high for untreated samples, and was decreased by carbonation. However, after the milling of carbonated samples, the leaching concentration became high again. The immobilization effect of each element was weakened by milling. The ratio of physical containment effect to immobilization effects by accelerated carbonation was calculated using the results of JLT18. The ratio for each element was as follows: Pb: 13.9–69.0 %, Cu: 12.0–49.1 %, Cr: 24.1–99.7 %, Zn: 20.0–33.3 %, and Ca: 28.9–63.4 %.     

Possibility of using waste tire rubber and fly ash with Portland cement as construction materials

The growing amount of waste rubber produced from used tires has resulted in an environmental problem. Recycling waste tires has been widely studied for the last 20 years in applications such as asphalt pavement, waterproofing systems and membrane liners. The aim of this study is to evaluate the feasibility of utilizing fly ash and rubber waste with Portland cement as a composite material for masonry applications. Class C fly ash and waste automobile tires in three different sizes were used with Portland cement. Compressive and flexural strength, dry unit weight and water absorption tests were performed on the composite specimens containing waste tire rubber. The compressive strength decreased by increasing the rubber content while increased by increasing the fly ash content for all curing periods. This trend is slightly influenced by particle size. For flexural strength, the specimens with waste tire rubber showed higher values than the control mix probably due to the effect of rubber fibers. The dry unit weight of all specimens decreased with increasing rubber content, which can be explained by the low specific gravity of rubber particles. Water absorption decreased slightly with the increase in rubber particles size. These composite materials containing 10% Portland cement, 70% and 60% fly ash and 20% and 30% tire rubber particles have sufficient strength for masonry applications.     

The effect of the addition of fly ash to municipal digested sludge on its electroosmotic dewatering

Effective handling of municipal digested sludge requires that the product cake have low water content. To this end, we investigated the change in sludge dewaterability after the addition of fly ash to municipal digested sludge, dewatering of which is difficult because of its high organic content. The performance of the dewatering is compared with that of electroosmotic dewatering (EDW) and conventional mechanical dewatering (CMD). Fly ash classified by sieving to the size of 25–75 μm and >75 μm is added to the municipal digested sludge by 10, 20, and 50 wt% by wet base. When adding fly ash particles to municipal digested sludge, dewatering efficiency improved with smaller fly ash particle size and with increase in the amount. When sludge was dewatered using an electroosmotic dewatering method, the dewatering efficiency is improved about 40% by adding fly ash of 25–75 μm particle size with 20 wt% when compared with conventional mechanical dewatering method without adding the fly ash. It is concluded that fly ash particles rich in inorganic material are helpful in the dewatering process when added to municipal digested sludge and EDW is more effective than CDW.     

Characterization of PCDD/Fs and heavy metals from MSW incineration plant in Harbin

The characterization of PCDD/Fs and heavy metals in the flue gas and fly ash of Harbin municipal solid waste (MSW) incineration plant, located in the northeast of China, was investigated in this study. The MSW was treated in a twin internal fluidized (TIF) bed incinerator. The results indicate that the emission of PCDD/Fs into the environment is 0.02 ng I-TEQ/m3 and the level of PCDD/Fs in the fabric filter fly ash is 0.7982 ng I-TEQ/g. The leachability levels of Pb, Cd and Hg in the fly ash are below the limits of environmental protection standard in China. However, the contents of Cu, Zn, and Hg are high in the fly ash. This suggests that the fly ash is a hazardous waste that requires special treatment and disposal. The practice of more than four years of operation shows that the TIF bed incinerator is very suitable and practical for China.     

Synergistic Effect of Oil Palm Based Pozzolanic Materials/Oil Palm Waste on Polyester Hybrid Composite

This research work aims to investigate the synergistic effect of pozzolanic materials such as oil palm ash (OPA) and oil palm empty fruit bunch (OPEFB) on the developed hybrid polymer composites. The OPEFB and OPA fillers of different particle sizes (250, 150, and 75 µm) were mixed at OPEFB:OPA ratios of (0:100; 20:80; 40:60; 60:40; 80:20 and 100:0) and incorporated into an unsaturated polyester resin. Furthermore, both mechanical and morphological properties of the composites were analyzed and it was found that tensile, flexural, and impact properties were significantly improved at OPEFB:OPA of 75 µm particle size hybridization of the polymer. The increase of OPEFB to OPA filler ratio up to 80:20 significantly improved the tensile properties of the composites while 40:60 ratio of 75 µm gave the optimum filler ratio to obtain the highest flexural and impact properties of the composites among all studied samples. Scanning electron micrograph images showed strong particle dispersion of the embedded fillers with resin which explained the excellent mechanical strength enhancement of the composite.     

Environmental impact of fly ash utilization in roadway embankments

The leaching potential of heavy metals from a roadway embankment constructed of fly ash and soil mixture was studied. Leaching of eight environmentally concerned metals Ag, As, Ba, Cd, Cr, Hg, Pb, and Se from the fly ash–soil mixtures was examined through batch leaching test and column leaching test. The batch leaching test results showed that the fly ash meets the local regulatory standards for beneficial use of nonhazardous wastes. The column leach test revealed that only Ba, Cr, and Se were detectable in the effluents. The peak concentration of Ba in the effluents was much lower than the US EPA Primary Drinking Water Regulations’ maximum contaminant level (MCL). The peak concentrations of Cr and Se exceeded the MCLs only in the initial flush stage and quickly decreased to below the MCLs. Results of this study suggest a great potential for fly ash to be used in roadway embankments to enhance their mechanical properties, reduce the use of soil, and avoid the disposal of fly ash as waste.