Disposal Of Coal Combustion Residues Research Articles

Physicochemical and mineral characteristics of soil materials developed naturally on two ∼ 50 years old coal combustion residue disposal sites in Croatia

Coal combustion has been one of the most dominant sources of energy for the last two centuries, generating tonnes of coal combustion residue (CCR). Rapid soil formation has been observed at old CCR disposal sites, altering the physiochemical and mineral properties of CCR, affecting contaminant release mechanisms and nutrient availability. Although ubiquitous, pedological properties of weathered CCR have been studied at only a small number of disposal sites. This study characterized two CCR landfills of similar age (∼50 years) using a range of parameters, including pH, total nitrogen and organic carbon content, major oxides (Al2O3, CaO, and SiO2), and macronutrients (Ca, K, Mg, P, and S), as well as textural and mineralogical data. In addition, specific surface area and cation exchange capacity were determined to assess particle properties, and 13C and 29Si NMR spectra were examined to characterize the organic matter and degree of polymerization of the coal ash glassy phase. Such comprehensive approach aimed to determine indicators of soil formation and to characterize the capacity of such landfills to retain water, nutrients, and contaminants. Both landfills displayed evidence of pedogenesis reflected in the pH decrease, formation of secondary minerals (such as ettringite, hydrotalcite, gypsum, and calcite), and changes in the C:N ratio. The Plaški landfill seems to have a better capacity to hold water, nutrients, and contaminants evident by higher clay content, CEC, and SSA values, possibly explaining why it developed more rapidly than Štrmac despite their similar age. The presence of montmorillonite in Plaški could be one of the main factors accelerating pedogenesis. 13C NMR spectra point to the unburned coal particles as the main origin of organic matter and 29Si NMR spectra showed higher depolymerization of a non-crystalline fraction in bare ash samples than in vegetated ash samples.

Environmental changes due to wet disposal of wastes from coal-fired heat power plant: A case study from the Tula Region, Central Russia

Long-term disposal of coal combustion residues (CCR) in the environment could change the geochemistry of soils and surface waters of adjacent territories. Aiming to evaluate the environmental impact of CCR we investigated soils and surface waters (12 and 18 sampling points, respectively) in the vicinity of the aged settling pond of the Cherepetskaya Thermal Power Plant in the Tula Region (Russia). The research reports and discusses changes in the composition of readily soluble salts in sod-podzolic soils (Retisols) as well as the content of carbonates and the distribution of potentially hazardous elements (Ni, Cr, V, Sr, Pb, Zn) in soil profiles. The mineralization of surface waters was also measured. For performing analyses, methods of HPLC, XRF, ICP-AES, and ICP-MS were used. The research revealed that the introduction of technogenic material into soils had 1.5–3 times increased the content of readily soluble salts compared to natural Retisols and changed the composition of ions. Carbonates in amounts of up to 1.9% were determined in all Retisols with introduced CCR which is never observed in natural acid soils. Differentiation in the content of V, Cr, Ni, Zn, Sr, Pb in soil profiles corresponded to leaching patterns of these elements from the CCR stated by the other researchers. Their concentrations in soils generally did not exceed the standards stated in the Russian Federation. Natural waters and waters with technogenic impact had the well-defined differentiation in the ratio of sodium and potassium in total cations. The study showed that the area of the environmental footprint of the settling pond with CCR differed in soils and surface waters. Changes in the geochemistry of surface waters were noticeable at greater distances and probably reflected the transformation of the geochemistry of groundwater. Changes in the geochemistry of soils were very local and were observed at a distance of fewer than 200 m from the settling pond.

Melt ceramics from coal ash: Constitutive product design using thermal and flow properties

New US Environmental Protection Agency regulations for the disposal of coal combustion residues (CCR) incentivize bottom-up recycling efforts, to convert them into value-added applications. This study examines producing lightweight ceramic aggregates from CCR for concrete/geotechnical applications. More specifically, we argue that industrial residues such as coal bottom ash, despite their heterogeneity and diversity, are apt feedstock materials to constitutively design melt ceramics via high temperature recycling. A lot of knowledge on the feedstock (thermal and melt flow properties) is available, because of the historical interest in (molten) coal ash properties. It is shown how thermodynamics and empirically derived models and experimental observations on the viscosity, surface tension, heat capacity, enthalpy of fusion and thermal conductivity can be used to constitutively design melt ceramics. We created a custom model for the design of spherical porous reactive aggregates (SPoRA) from two different coal bottom ashes, using NaOH as an illustrative fluxing agent. To obtain the desired aggregate design, production should occur above the solidus temperature, yet viscous flow, caused by a low viscosity of the CCR melt, should be limited. The design method developed is able to discern the influence of various design parameters on the experimentally produced ceramic aggregates. A proper match between simulations and experimentally observed object shapes was obtained, allowing to define an operating window (temperature and residence time as function of fluxing agent addition) constitutively. This work shows how the available knowledge on coal ash assists the understanding and design of novel ceramic aggregate recycling processes.

Recovery of Trace and Heavy Metals from Coal Combustion Residues for Reuse and Safe Disposal: A Review

The safe disposal of coal combustion residues (CCRs) will remain a major public issue as long as coal is used as a fuel for energy production. Both dry and wet disposal methods of CCRs create serious environmental problems. The dry disposal method creates air pollution initially, and the wet disposal method creates water pollution as a result of the presence of trace and heavy metals. These leached heavy metals from fly ash may become more hazardous when they form toxic compounds such as arsenic sulfite (As2S3) and lead nitrate (N2O6Pb). The available studies on trace and heavy metals present in CCRs cannot ensure environmentally safe utilization. In this work, a novel approach has been offered for the retrieval of trace and heavy metals from CCRs. If the proposed method becomes successful, then the recovered trace and heavy metals may become a resource and environmentally safe use of CCRs may be possible.

Ecological risk assessment for residual coal fly ash at Watts Bar Reservoir, Tennessee.

The Tennessee Valley Authority conducted a Baseline Ecological Risk Assessment (BERA) for the Kingston Fossil Plant ash release site to evaluate potential effects of residual coal ash on biota in Watts Bar Reservoir, Tennessee. The BERA was in response to a release of 4.1 million m(3) of coal ash on December 22, 2008. It used multiple lines of evidence to assess risks for 17 different ecological receptors to approximately 400000 m(3) of residual ash in the Emory and Clinch rivers. Here, we provide a brief overview of the BERA results and then focus on how the results were used to help shape risk management decisions. Those decisions included selecting monitored natural recovery for remediation of the residual ash in the Emory and Clinch rivers and designing a long-term monitoring plan that includes adaptive management principles for timely adjustment to changing conditions. This study demonstrates the importance of site-specific ecological data (e.g., tissue concentrations for food items, reproductive data, and population data) in complex ecological risk assessments. It also illustrates the value of the US Environmental Protection Agency's (USEPA) data quality objectives process in building consensus and identifying multiple uses of results. The relatively limited adverse effects of this likely worst-case scenario for ash-related exposures in a lotic environment provide important context for the USEPA's new coal combustion residue disposal rules.

Neotropical woodlice (isopoda) colonizing leaf-litter of pioneer plants in a coal residue disposal environment

The irregular disposal of coal combustion residues has adverse impacts on terrestrial ecosystems. Pioneer plants and soil invertebrates play an important role in the recovery of these areas. The goal of this study was to investigate the colonization patterns of terrestrial isopods (Oniscidea) in leaf litter of three spontaneous pioneer plants (grass - Poaceae, shrub - Euphorbiaceae, tree - Anarcadiaceae) at sites used for fly ash or boiler slag disposal. The experiment consisted of eight blocks (four per disposal site) of 12 litter bags each (four per plant species) that were randomly removed after 6, 35, 70 or 140 days of field exposure. Three isopod species were found in the litter bags: Atlantoscia floridana (van Name, 1940) (Philosciidae; n = 116), Benthana taeniata Araujo & Buckup, 1994 (Philosciidae; n = 817) and Balloniscus sellowii (Brandt, 1833) (Balloniscidae; n = 48). The isopods colonized the three leaf-litter species equally during the exposure period. However, the pattern of leaf-litter colonization by these species suggests a conflict of objectives between high quality food and shelter availability. The occurrence of A. floridana and the abundance and fecundity of B. taeniata were influenced by the residue type, indicating that the isopods have different degrees of tolerance to the characteristics of the studied sites. Considering that terrestrial isopods are abundant detritivores and stimulate the humus-forming processes, it is suggested that they could have an indirect influence on the soil restoration of this area.

Disposal of Coal Combustion Residues in Terrestrial Systems: Contamination and Risk Management

The world's ever-growing energy demand will lead to the installation of new coal-fired power plants. At least part of the coal combustion residue (CCR) generated in the coming years will be disposed of, adding to the large number of CCR disposal sites generated in the past and reinforcing the need for sound assessment and management of associated risks. Physical and chemical composition of CCR varies considerably depending on the quality of the feed coal, the combustion technology, fraction considered, and the method of disposal. Related risk pathways include (i) aerial routes, i.e., dust resuspension (Cr(VI)), emanation of radioactivity (Rn associated with U and Th series), and Hg volatilization threatening animal and human health; (ii) phytoaccumulation (B, Se, Mo, As) and plant toxicity (B) with subsequent effects on animals (e.g., Mo-induced hypocuprosis, As and Se toxicity) and humans (e.g., selenosis; food chain); and (iii) effluent discharge and percolation to groundwater and rivers (suspended solids, unfavorable pH, high Se, B, Hg, and As(III) concentrations). Recent and projected changes of CCR composition due to emerging clean coal technologies require close monitoring as the concentration of volatile elements such as Hg and Se, solubility (Hg, Cd, Cu) and volatilization (Hg, NH(3)) of some pollutants are likely to increase because of higher retention in certain fractions of CCRs and concurrent changes in pH (e.g., by mineral carbonation) and NH(3) content. These changes require additional research efforts to explore the implications for CCR quality, use, and management of risk associated with disposal sites.

Environmental risks of farmed and barren alkaline coal ash landfills in Tuzla, Bosnia and Herzegovina

The disposal of coal combustion residues (CCR) has led to a significant consumption of land in the West Balkan region. In Tuzla (Bosnia and Herzegovina) we studied previously soil-covered (farmed) and barren CCR landfills including management practises, field ageing of CCR and the transfer of trace elements into crops, wild plants and wastewaters. Soil tillage resulted in mixing of cover soil with CCR. Medicago sativa showed very low Cu:Mo ratios (1.25) which may cause hypocuprosis in ruminants. Total loads of inorganic pollutants in the CCR transport water, but not pH (∼12), were below regulatory limits of most EU countries. Arsenic concentrations in CCR transport water were <2 μg l −1 whereas reductive conditions in an abandoned landfill significantly enhanced concentrations in leachates (44 μg l −1). The opposite pattern was found for Cr likely due to large initial leaching of CrVI. Public use of landfills, including farming, should be based on a prior risk assessment due to the heterogeneity of CCR.

Ecotoxicological implications of aquatic disposal of coal combustion residues in the United States: a review.

We provide an overview of research related to environmental effects of disposal of coal combustion residues (CCR) in sites in the United States. Our focus is on aspects of CCR that have the potential to negatively influence aquatic organisms and the health of aquatic ecosystems. We identify major issues of concern, as well as areas in need of further investigation. Intentional or accidental release of CCR into aquatic systems has generally been associated with deleterious environmental effects. A large number of metals and trace elements are present in CCR, some of which are rapidly accumulated to high concentrations by aquatic organisms. Moreover, a variety of biological responses have been observed in organisms following exposure to and accumulation of CCR-related contaminants. In some vertebrates and invertebrates, CCR exposure has led to numerous histopathological, behavioral, and physiological (reproductive, energetic, and endocrinological) effects. Fish kills and extirpation of some fish species have been associated with CCR release, as have indirect effects on survival and growth of aquatic animals mediated by changes in resource abundance or quality. Recovery of CCR-impacted sites can be extremely slow due to continued cycling of contaminants within the system, even in sites that only received CCR effluents for short periods of time. The literature synthesis reveals important considerations for future investigations of CCR-impacted sites. Many studies have examined biological responses to CCR with respect to Se concentrations and accumulation because of teratogenic and reproductively toxic effects known to be associated with this element. However, the complex mixture of metals and trace elements characteristic of CCR suggests that biological assessments of many CCR-contaminated habitats should examine a variety of inorganic compounds in sediments, water, and tissues before causation can be linked to individual CCR components. Most evaluations of effects of CCR in aquatic environments have focused on lentic systems and the populations of animals occupying them. Much less is known about CCR effects in lotic systems, in which the contaminants may be transported downstream, diluted or concentrated in downstream areas, and accumulated by more transient species. Although some research has examined accumulation and effects of contaminants on terrestrial and avian species that visit CCR-impacted aquatic sites, more extensive research is also needed in this area. Effects in terrestrial or semiaquatic species range from accumulation and maternal transfer of elements to complete recruitment failure, suggesting that CCR effects need to be examined both within and outside of the aquatic habitats into which CCR is released. Requiring special attention are waterfowl and amphibians that use CCR-contaminated sites during specific seasons or life stages and are highly dependent on aquatic habitat quality during those periods. Whether accidentally discharged into natural aquatic systems or present in impoundments that attract wildlife, CCR appears to present significant risks to aquatic and semiaquatic organisms. Effects may be as subtle as changes in physiology or as drastic as extirpation of entire populations. When examined as a whole, research on responses of aquatic organisms to CCR suggests that reducing the use of disposal methods that include an aquatic slurry phase may alleviate some environmental risks associated with the waste products.

THE USE OF COAL COMBUSTION RESIDUES TO CONTROL ACID MINE DRAINAGE

The Federal Energy Technology Center of the U.S. Department of Energy is monitoring changes in water quality at three inactive mining sites where a coal combustion residue (fly ash) was injected into the spoil to control the production of acid mine drainage. Since most combustion residues are alkaline, their addition to the subsurface environment raises the pH, limiting the propagation of pyrite oxidizing bacteria and reducing the rate of acid generation. Grouts of fly ash, lime and cement, when injected underground, decrease permeability and porosity diverting water away from the pyritic material. Both mechanisms, alkaline addition and water diversion, are expected to reduce the amount of acid produced. Changes in water quality parameters (pH, acidity, anions and cations) in water samples from wells and seeps are monitored to assess the effect of CCR injection. The concentration of heavy metals in the water flowing through the sites, before and after CCR injection, is also determined. The use of underground mine sites for disposal of coal combustion residues provides a stable, low maintenance alternative to landfills, benefitting the missing and electric power industries.

Transport of heavy metals and cations in a fly ash amended soil

The potential for heavy metal contamination of groundwater in and around coal combustion residue disposal sites is one of the main areas of concern regarding proper disposal of these by-products. The use of fly ash as an amendment to agricultural soils has been investigated to explore its effects on corp growth and production. Precautions must be taken to prevent possible water contamination as a result of fly ash usage in agricultural soils. Positive correlations exist between the concentrations of either water or acid extractable B, F, Mo, and Se or acid extractable As in fly ash and those of the similar elements in effluent waters near a fly ash landfill.Solubility of fly ash in water is an important factor which determines the extent of water pollution from fly ash. This study investigates the transport of heavy metals and cations in a sandy soil amended with various rates of fly ash. 14 refs., 3 tabs.