A Seasonal Assessment of the Impact of Coal Fly Ash Disposal on the River Yamuna,Delhi, II. Biology

The impact of fly ash on the biology of the Yamuna River, Delhi, was studied. Effluents come from a 200 MW capacity I.P. thermal power station. Seasonal variations in the biological features in the non-impacted (Y-1) and the impacted (Y-2) segments of the river receiving fly ash effluents were studied. 60 genera of phytoplankton including 29 Chlorophyceae, 19 Bacillariophyceae, 8 Cyanobacteria, and 4 Euglenophyceae were recorded. Phytoplankton diversity was reduced at the impacted site in comparison to the non-impacted site of the river and substantial changes in the composition of various groups inhabiting these areas were observed. Zooplankton were also reduced at Y-2 compared to Y-1, especially rotifers and protozoans, while copepods and nauplii larvae were not affected to the same degree. Species diversity was not significantly different at Y-2 and Y-1 but similarity index varied from low to high between the two stations. Thus, not only was the density, number of genera and diversity reduced, even the generic composition of the plankton was markedly affected in the impacted waters. The observed perturbations could be due to sedimentation of ash particles, pH or elevated metal or salt concentration. A change in the concentration of one or more constituents disturbs the relationship between biota and could be the possible cause of reduced densities in the impacted waters.     

Boron availability to plants from coal combustion by-products

Agronomic use of coal combustion by-products is often associated with boron (B) excess in amended soils and subsequently in plants. A greenhouse study with corn (Zea mays L.) as test plant was conducted to determine safe application rates of five fly ashes and one flue gas desulfurization gypsum (FDG). All by-products increased soil and corn tissue B concentration, in some cases above toxicity levels which are 5 mg hot water soluble B (hwsB) kg^?1 soil and 100 mg B kg^?1 in corn tissue. Acceptable application rates varied from 4 to 100 Mg ha^? for different by-products. Leaching and weathering of a high B fly ash under ponding conditions decreased its B content and that of corn grown in fly ash amended soil, while leaching of the same fly ash under laboratory conditions increased fly ash B availability to corn in comparison to the fresh fly ash. Hot water soluble B in fly ash or FDG amended soil correlated very well with corn tissue B. Hot water soluble B in fly ash amended soil could be predicted based on soil pH and B solubility in ash at different pH values but not so in the case of FDG. Another greenhouse study was conducted to compare the influence of FDG and Ca(OH)₂ on B concentration in spinach (Spinacia oleracea L.) leaves grown in soil amended with the high B fly ash. The Ca(OH)₂ significantly decreased tissue B content, while FDG did not affect B uptake from fly ash amended soil.     

Studies on the Phase Mineralogy and Leaching Characteristics of Coal Fly Ash

The phase mineralogy and leaching characteristics of some Indian coal fly ashes were studied to assess their safe disposal in abandoned coal mines. Since, fly ash contains a number of toxic trace elements, the leaching of fly ash was tested using strong acid/alkali solutions and distilled water under different conditions (solid-liquid ratio, leaching time, pH) in the temperature range of 30-100 °C. It was found that the concentration of various metals in leachates depends on their chemical nature, association with mineral phases of ash and follows the almost similar concentration profile to that of iron, especially in acidic medium. The distribution of toxic trace elements in fly ash and their leachability were found to depend on the amount of unburnt carbon and iron in fly ash. In alkaline medium, leaching of iron and toxic trace elements (except As) from fly ash was very negligible. Hence, alkali treatment of coal fly ash is desirable for its safe use in refilling of coal mines.     

Dual Inoculation of Arbuscular Mycorrhizal and Phosphate Solubilizing Fungi Contributes in Sustainable Maintenance of Plant Health in Fly Ash Ponds

Fly ash is one of the residues produced during combustion of coal, and its disposal is a major environmental concern throughout coal-based power-generated counties. Deficiencies of essential nutrients, low soil microbial activity, and high-soluble salt concentrations of trace elements are some of the concerns for reclamation of fly ash ponds. The effect of fly-ash-adapted arbuscular mycorrhizal (AM) fungi and phosphate solubilizing fungus Aspergillus tubingensis was studied on the growth, nutrient, and metal uptake of bamboo (Dendrocalamus strictus) plants grown in fly ash. Co-inoculation of these fungi significantly increased the P (150%), K (67%), Ca (106%), and Mg (180%) in shoot tissues compared control plants. The Al and Fe content were significantly reduced (50% and 60%, respectively) due to the presence of AM fungi and A. tubingensis. The physicochemical and biochemical properties of fly ash were improved compared to those of individual inoculation and control. The results showed that combination of AM fungi and A. tubingensis elicited a synergetic effect by increasing plant growth and uptake of nutrients with reducing metal translocation.     

Uptake of multielements by corn from fly ash-compost amended soil

Fly ash was collected from a coal-fired power plant in and near the U.S. Department of Energy Savannah River Site to study the feasibility of the application of fly ash compost mixture to soils for the availability and uptake of various elements by corn (Zea mays L.). The crop was grown in potted Ogeechee sandy loam soil using eight treatments: soil alone, soil amended with 15% compost, and soil amended with 2, 5, 10, 15, 20 and 25% of fly ash-amended compost. It was observed that 20–25% fly ash and compost soil ratio treatments generally increased plant growth and the yield. The plant uptake of K, Mn, and Cu increased with increasing percentages (2–25%) of fly ash+compost: soil ratios. The total content of K in plants was positively correlated with the dry matter yield of corn. This study indicates that the application of fly ash blended with compost to soil is beneficial to corn production without causing any deleterious effects on plant growth and plant composition.     

Physico-chemical characterization of water extracts of different coal fly ashes and fly ash-amended composts

The pH, conductivity and the concentration of 15 selected elements were measured in the water extracts of five coal fly ash samples collected from Savannah River Site (SRS) and one from South Carolina Electric and Gas (SCE & G) power plant. This work was intended to study the differences in the physico-chemical properties of SRS fly ash samples relative to those of a reference sample (SCE & G) and to make fly ash-amended composts for agricultural use. Similar analyses were also performed in water extracts of a commercial organic manure, ‘Gotta Grow’, that was composted with one of the fly ash samples (SRS 484-D) in different proportions. Our results show that fly ash samples used in this study differ considerably in pH, conductivity, and elemental composition and that transition metals appear to bind more tightly on smaller particles than on larger ones. The elementally rich manure, ‘Gotta Grow’, is not suitable to study the effects of fly ash on the elemental release from fly ash-amended composts. Low grade or home-made organic composts are being investigated as possible choice for making ly ash-amended composts.     

Effect of Flue Gas Treatment on the Solubility and Fractionation of Different Metals in Fly Ash of Powder River Basin Coal

Studies were conducted to examine the effect of flue gas carbon dioxide (CO₂) on solubility and availability of different metals in fly ash of Powder River Basin (PRB) coal, Wyoming, USA. Initial fly ash (control) was alkaline and contains large amounts of water-soluble and exchangeable metals. Reaction of flue gas CO₂ with alkaline fly ash resulted in the formation of carbonates which minimized the solubility of metals. Results for metal fractionation studies also supported this fact. The present study also suggested that most of the water-soluble and exchangeable metals present in the control (untreated) fly ash samples decreased in the flue gas-treated samples. This may be due to the transfer of the above two forms to more resistant forms like carbonate bound (CBD), oxide bound (OXD), and residual (RS). Geochemical modeling (Visual MINTEQ) of water solubility data suggested that the saturation index (SI) values of dolomite (CaMg(CO₃)₂) and calcite (CaCO₃) were oversaturated, which has potential to mineralize atmospheric CO₂ and thereby reduce leaching of toxic metals from fly ash. Results from this study also showed that the reaction of flue gas CO₂ with alkaline fly ash not only control the solubility of toxic metals but also form carbonate minerals which have the potential to fix CO₂.     

The practice of leaching boron and soluble salts from fly ash-amended soils

The leachability of B and salts from two fly ash-amended soils was conducted in a column leaching experiment. Fly ash was applied to the surface 3 cm of a Baywood (acid) sand and an Arizo (calcareous) sandy, loam at 5% by weight; the columns were continously leached with Colorado River water at two different pH's. Boron from fly ash was solubilized more readily in the Baywood than in the Arizo soil. Addition of fly ash increased B levels in the leachates from 0.25 to 2.35 μg ml^?1 (Baywood) and 0.93 μg ml^?1 (Arizo). Acidified leaching water had no significant effect on B leaching patterns but resulted in leaching higher soluble salts. Approximately 348 and 161 cm of water for the Arizo and the Baywood soils respectively, would be required to reduce the B concentration below a critical limit for B sensitive crops. It is suggested that crops planted when fly ash is applied for disposal/recycling on land should be both salt and B tolerant.     

Increasing magnetic susceptibility of the suspended particles in Yangtze River and possible contribution of fly ash

The magnetic properties of soil have been increasingly applied as a rapid and economic way to monitor environment pollution. Sediments from a growing islet in the lower reach of Yangtze River as well as the suspended particles in the surrounding river water were used to identify anthropogenic influence on the magnetic susceptibility (MS) of the Yangtze River sediment. Results show that newly deposited sediments in 2004 have significantly higher MS (~ 150 × 10⁻⁸ m³ kg⁻¹) on average than that of the ancient deposit (~ 50 × 10⁻⁸ m³ kg^− 1). Scanning electron microscope (SEM) of the extracted magnetic particles from newly deposited sediments and fly ash samples indicates large contribution of fly ash for the samples with elevated MS. Dependence of MS on grain size is evident, which enable calculation of the MS of suspended particles from river sediment. A value of 32 × 10⁻⁸ m³ kg^− 1is inferred for the suspended particles in ancient Yangtze River. The records from 2004 to 2010 indicate progressive increase in the MS of the suspended particles in Yangtze River from 67 to 96 × 10⁻⁸ m³ kg^− 1, which is much higher than that of the ancient. Mass balance calculation based on the increasing MS suggests that at least 7% of the fly ash produced within the catchment of Yangtze River was released into the environment.     

The use of coal fly ash in sodic soil reclamation

An experiment was conducted for two years in northwest India to explore the feasibility of using coal fly ash for reclamation of waterlogged sodic soils and its resultant effects on plant growth in padi–wheat rotation. The initial pH, electrical conductivity, exchangeable sodium percentage and sodium adsorption ratio of the experimental soil were 9.07, 3.87 dS m⁻¹, 26.0 and 4.77 (me l)^−1/2, respectively. The fly ash obtained from electrostatic precipitators of thermal power plant had a pH of 5.89 and electrical conductivity of 0.88 dS m⁻¹. The treatments comprised of fly ash levels of 0.0, 1.5, 3.0, 4.5, 6.0 and 7.5 per cent, used alone as well as in combination with 100, 80, 60, 40, 20 and 10 per cent gypsum requirement of the soil, respectively. There was a slight reduction in soil pH while electrical conductivity of the soil decreased significantly with fly ash as measured after padi and wheat crops. The sodium adsorption ratio of the soil decreased with increasing fly ash levels, while gypsum treatments considerably added to its favourable effects. Fly ash application increased the available elemental status of N, K, Ca, Mg, S, Fe, Mn, B, Mo, Al, Pb, Ni, Co, but decreased Na, P and Zn in the soil. An application of fly ash to the soil also increased the concentrations of above elements except Na, P and Zn in the seeds and straw of padi and wheat crops. The available as well as elemental concentrations in the plants was maximum in the 0 per cent fly ash + 100 per cent gypsum requirement treatment except Na and heavy elements like Ni, Co, Cr. The treatment effects were greater in the fly ash + gypsum requirement combinations as compared to fly ash alone. Saturated hydraulic conductivity and soil water retention generally improved with the addition of fly ash while bulk density decreased. Application of fly ash up to 4.5 per cent level increased the straw and grain yield of padi and wheat crops significantly in both years. The results indicated that for reclaiming sodic soils of the southwest Punjab, gypsum could possibly be substituted up to 40 per cent of the gypsum requirement with 3.0 per cent acidic fly ash. Copyright © 2003 John Wiley & Sons, Ltd.     

Effects of fly ash on microbial C02 evolution from an agricultural soil

Unweathered, acidic fly ash from a coal-fired power plant was applied to alfalfa meal-amended agricultural soil at levels equivalent to 0, 100, 400, and 700 tonne ha^?1. Amended soils were placed in respirometer jars and monitored for C0₂-C evolution over a 37-day period. Fly ash applications of 400 and 700 tonne ha^?1 reduced C0₂-C production significantly compared to 0 and 100 tonne ha^?1 treatments. Carbon dioxide-carbon from all treatments was considerably greater than that from soil treated with 1000 ppm CdCl₂. The results suggest that soil heterotrophic microbial activity may be impacted minimally by relatively low levels of fly ash application, but may be inhibited by higher levels of fly ash. Several metals were present at potentially toxic levels in the fly ash employed and may have accounted for the inhibition of CO₂ C evolution. The availability of some of these metals was indicated in companion plant uptake experiments.     

Formulation of Environmentally Sound Waste Mixtures for Land Application

Major impediments to the land application of coal combustion byproducts (fly ash) for crop fertilization have been the presence of heavy metals and their relatively low and imbalanced essential nutrient concentration. Although nutrient deficiencies, in particular N, P, and K, may be readily augmented by adding organic wastes such as sewage sludge and animal manure, the indiscriminate application of mixtures to crops can cause excessive soil alkalinity, imbalanced nutrition (P, Mg), phytotoxicities (B, Mn, ammonia, nitrite), and unspecified contamination of the food chain by elements such as As. In this study, nutrient availability data and linear programming (LP) were used to solve these problems by formulating fly ash-biosolid triple mixtures which complied with both plant and soil fertilization requirements, and met existing U.S.A. environmental regulations for total As application in sewage sludge (EPA-503). Thirteen different fly ash samples were LP-formulated with sewage sludge, poultry manure, CaCO₃, and KCl to yield 13 unique mixtures, which were then evaluated in greenhouse pot experiments. Results indicated that normal growth and balanced nutrition of sorghum (Sorghumbicolor L.) and soybean (Glycine max (L.) Merr.) crops were achieved in all mixtures, comparable to a balanced fertilizer reference treatment, and significantly better than the untreated control. Phytotoxic levels of B, NH₃, NO₂ ^-, overliming problems, and excessive As levels which were previously encountered from indiscriminate use of these waste materials, were all well controlled by LP-formulated mixtures. Most fly ash quantities in mixtures were limited by either available B (< 4 kg ha^-1) or total As (< 2 kg ha^-1) restrictions during formulation, while the most alkaline fly ash was limited by its high calcium carbonate equivalence (CCE = 53.9%). These results confirmed that fly ash land application should not be at arbitrary fixed rates, but should be variable, depending on the soil, crop, and particularly the fly ash chemistry.     

Evaluation of fly ash as a soil amendment for the Atlantic Coastal Plain: I. Soil hydraulic properties and elemental leaching

A major limitation to crop yields in the Atlantic Coastal Plain is drought stress caused by the low moisture-holding capacities of the coarse-textured soils common to the area. Because coal fly ash is comprised primarily of silt and clay-sized particles, it has the potential, if applied at high enough rates, to permanently change soil texture and increase moisture holding capacity. A series of soil column studies were conducted to evaluate the effects of high rates of fly ash on soil hydraulic properties and elemental leaching of trace metals and boron. Fly ash from two Delaware power plants (EM=Edgemoor and IR=Indian River) was incorporated in a Hammonton loamy sand (fine-loamy, siliceous, mesic, Typic Hapludults) at six rates (0, 5, 10, 20, 30, and 40%, by weight). The effect of fly ash on soil moisture holding capacity, hydraulic conductivity, and wetting front velocity was determined. Leachates from columns amended with 30% fly ash were analyzed for B, Cd, Ni, Pb, Cu, and Zn. Soil moisture holding capacity was increased from 12% in the soil alone to 25% in the soil amended with 30% fly ash. Boron and soluble salts leached rapidly from ash amended soils while only trace quantities of Cd, Ni, Pb, Cu, and Zn were detected in column leachates.     

Reduction in CO2 emission from normal and saline soils amended with coal fly ash

Purpose

Fly ash can reduce CO₂ emission from soils via biochemical (i.e., inhibition of microbial activity) and physicochemical (i.e., carbonation) mechanisms. This study investigated the effects of fly ash amendment on biochemical and physicochemical reduction in CO₂ emission from normal and saline soils.

Materials and methods

The physicochemical mechanisms of reduction in CO₂ emission by fly ash were estimated in a batch experiment with carbonate solution as a CO₂ source by the scanning electron microscope (SEM) and inductively coupled plasma analyses. Biochemical mechanisms of reduction in CO₂ emission by fly ash were investigated in a 3-day laboratory incubation experiment with normal and saline soils in the absence and presence of fly ash. Finally, the effects of fly ash amendment at a variety rate from 2 to 15?% (w/w) on CO₂ emission from normal and saline soils in the presence of additional organic carbon source (glucose) were investigated through a 15-day laboratory incubation study.

Results and discussion

In the batch experiment with carbonate solution, both the SEM image of fly ash and changes in soluble Ca and Mg concentrations during reaction with carbonate suggested that the formation of CaCO₃ and MgCO₃ via carbonation was the principal physicochemical mechanism of carbonate removal by fly ash. In the 3-day incubation study conducted to examine biochemical mechanisms of reduction in CO₂ emission by fly ash, microbial respiration of saline soil was inhibited (P?<?0.05) by fly ash due to high pH, salinity, and boron concentration of fly ash; meanwhile, for normal soil, there was no inhibitory effect of fly ash on microbial respiration. In the 15-day incubation with glucose, fly ash application at a variety rates from 2 to 15?% (w/w) reduced CO₂ emission by 3.6 to 21.4?% for normal and by 19.8 to 30.3?% for saline soil compared to the control without fly ash. For saline soil, the reduction in CO₂ emission was attributed primarily to inhibition of microbial respiration by fly ash; however, for normal soil in which suppression of microbial respiration by fly ash was not apparent, carbonation was believed to play an important role in reduction of CO₂ emission.

Conclusions

Therefore, fly ash may be helpful in reducing CO₂ emission from normal soils via carbonation. For saline soil, however, fly ash needs to be carefully considered as a soil amendment to reduce CO₂ emission as it can inhibit soil microbial activities and thus degrade soil quality.     

Microbial activities in forest soils exposed to chronic depositions from a lignite power plant

Atmospheric emissions of fly ash and SO₂ from lignite-fired power plants strongly affect large forest areas in Germany. The impact of different deposition loads on the microbial biomass and enzyme activities was studied at three forest sites (Picea abies (L.) Karst.) along an emission gradient of 3, 6, and 15 km downwind of a coal-fired power plant (sites Ia, II, and III, respectively), representing high, moderate and low emission rates. An additional site (site Ib) at a distance of 3 km from the power plant was chosen to study the influence of forest type on microbial parameters in coniferous forest soils under fly ash and SO₂ emissions. Soil microbial biomass C and N, CO₂ evolved and activities of l-asparaginase, l-glutaminase, β -glucosidase, acid phosphatase and arylsulfatase (expressed on dry soil and organic C basis) were determined in the forest floor (L, Of and Oh horizon) and mineral top soil (0-10 cm). The emission-induced increases in ferromagnetic susceptibility, soil pH, concentrations of mobile (NH₄NO₃ extractable) Cd, Cr, and Ni, effective cation exchange capacity and base saturation in the humus layer along the 15 km long transect significantly (P<0.05) reflected the effect of past depositions of alkaline fly ash. Soil microbial and biochemical parameters were significantly (P<0.05) affected by chronic fly ash depositions. The effect of forest type (i.e. comparison of sites Ia and Ib) on the studied parameters was generally dominated by the deposition effect. Alkaline depositions significantly (P<0.05) decreased the microbial biomass C and N, microbial biomass C-to-N ratios and microbial biomass C-to-organic C ratios. Microbial respiration, metabolic quotient (qCO₂) and the activities of l-asparaginase, l-glutaminase, β-glucosidase, acid phosphatase and arylsulfatase were increased by long-term depositions from the power plants. Acid phosphatase had the highest specific (enzyme activities expressed per unit organic C) activity values among the enzymes studied and arylsulfatase the lowest. The responses of the microbial biomass and soil respiration data to different atmospheric deposition loads were mainly controlled by the content of organic C and cation exchange capacity, while those of enzyme activities were governed by the soil pH and concentrations of mobile heavy metals. We concluded that chronic fly ash depositions decrease litter decomposition by influencing specific microbial and enzymatic processes in forest soils.     

Long‐term supply and uptake by plants of elements from coal fly ash

Abstract

To assess the mineral composition of plants growing in pure fly ash, grasses growing on lysimeters filled with alkaline, neutral, or acid fly ash were sampled several times in a 6‐year period. The samples were analyzed for elements essential for plants and animals as well as non‐essential, but environmentally significant, trace elements. Grasses were also sampled from ash dumps that were 20 and 30 years old. Fly ash is not a proper source of plant macronutrients N, P, and K. Plant growth on the alkaline fly ash can be influenced for some time by the high salinity of that ash. Grasses growing on unweathered fly ash were found to be high in Al, B, Co, Fe, Mo, Ni, Pb, and Se. Concentrations of several elements declined in time but levels of B, Fe, Mo, and Ni were still elevated in grasses on both fly ash dumps. All concentrations, except Al, were lower than toxicity levels for plants as found in literature. In plants growing on fresh fly ash concentrations of Mo, Pb, and Se can exceed the maximum tolerable levels for domestic animals. On weathered fly ashes (ash dumps) the Mo, Pb, and Se concentrations in grasses were below the maximum tolerable levels. Effects on animals by Mo in weathered ash may not be excluded because Mo concentrations can be high enough to induce Cu deficiency. Animals that feed on plants grown on fly ash could suffer from Ca, Mg, Na, and P deficiency.     

Promotion of mycorrhiza formation and growth of willows by the bacterial strain <Emphasis Type="Italic">Sphingomonas</Emphasis> sp. 23L on fly ash

Re-vegetation of fly ash, the principal by-product of coal fired power stations, is hampered by its unfavourable chemical and physical properties for plant growth. In the present study, we evaluated the use of inoculation with a mycorrhiza-associated bacterial strain (Sphingomonas sp. 23L) to promote mycorrhiza formation and plant growth of three willow clones (Salix spp.) on fly ash from an over-burdened dump in a pot experiment. The high pH_H2O (8.7) and low nitrogen content (N_t = 0.1 g kg⁻¹) in combination with hydrophobicity of the particle surfaces caused low plant growth. Inoculation of the willows with Sphingomonas sp. 23L improved the nitrogen uptake by plants, increased plant growth and stimulated formation of ectomycorrhizae with an autochthonous Geopora sp. strain on all three willow clones. The ectomycorrhiza formed by the Geopora sp. was morphologically and anatomically described. The inoculation significantly increased the shoot growth of two Salix viminalis clones and the root growth of a S. viminalis x caprea hybrid clone. We conclude that inoculation with mycorrhiza promoting bacterial strains might be a suitable approach to support mycorrhiza formation with autochtonous site-adapted ectomycorrhizal fungi in fly ash and thereby to improve re-vegetation of fly ash landfills with willows.     

Reaction of CO2 with clean coal technology ash to reduce trace element mobility

The combustion of coal in power plants generates solids (e.g., fly ash, bottom ash) and flue gas (e.g., SO _x , CO₂). New Clean Air Act mandated reduction of SO _x emissions from coal burning power plants. As a result, a variety of Clean Coal Technologies (CCT) are implemented to comply with these amendments. However, most of the CCT processes transfer environmentally sensitive elements (e.g., As, Cd, Pb, Se) from flue gas to CCT ash. The objective of this study was to determine the effect of a pressurized CO₂ treatment on the chemistry of CCT ash. Three CCT ash samples, produced from lime injection, atmospheric fluidized bed combustion, and sodium carbonate injection processes were reacted under different CO₂ pressure treatment conditions. Treated and untreated samples were subjected to various experiments including, X-ray diffraction (XRD) analysis, calcium carbonate solubility studies, and trace element extraction studies. Factors influencing the efficiency of a CO₂ treatment for CCT ash samples include combustion process, moisture, CO₂ concentration, and pressure. The CO₂ pressure treatment resulted in the precipitation of calcite in CCT ash samples, and thus lowered the pH and the concentration of extractable trace elements (e.g., Cd, Pb, Cr, As, Se). Furthermore, we found that CO₂ pressure treatment was more effective for lime injection and atmospheric fluidized bed combustion processed samples than for sodium carbonate injection processed samples.     

Weathered Fly Ash Does Not Affect Soil And Biosolid Carbon Mineralization

Fly ash and biosolid wastes can be mixed and applied to soil as a means of disposal. A significant decline in soil respiration following waste application indicates restricted activities of functional microbial populations. Weathering decreases salinity and neutralizes alkalinity in fly ash, but there is little information on the effects of unweathered fly ash and biosolid mixtures on soil carbon (C) mineralization. The objective of this study was to determine the effects of a weathered fly ash–limestone scrubber residue (LSR) mixed with an aerobically digested biosolid on soil respiration in a laboratory incubation study. Biosolids significantly increased carbon dioxide (CO₂) production (p < 0.05), but up to 6.75% (w/w) fly ash did not. Mean total C mineralization was 770 mg CO₂‐C kg^?1 soil in the control and 3,810 mg CO₂‐C kg^?1 soil in the 6.75% (w/w) biosolid treatment. Fly ash with neutral pH and low salinity appears unlikely to affect soil and biosolid C mineralization.     

Effects of High Rates of Coal Fly Ash on Soil,Turfgrass, and Groundwater Quality

A field study (1993–1996) assessed the effects of applying unusually high rates of coal fly ash as a soil additive forthe turf culture of centipedegrass (Eremochloa ophiroides).In addition, the quality of the soil and the underlying groundwater was evaluated. A Latin Square plot design was employed to include 0 (control, no ash applied), 280, 560, and 1120 Mg ha^-1 (mega gram ha^-1, i.e., tonne ha^-1)application rates of unweathered precipitator fly ash. The onceapplied fly ash was rototilled and allowed to weather for 8 months before seeding. Ash application significantly increasedthe concentrations in plant tissue of B, Mo, As, Be, Se, and Bawhile also significantly reducing the concentrations of Mg, Mn,and Zn. The other elements measured (i.e., N, K, Ca, Cu, Fe, Ag,Cd, Cr, Hg, Ni, Pb, Sb, Tl, Na, and Al) were not affected. Of these elements Mg, Cu, and Mo concentrations in plant tissue increased with time while B and Se decreased temporally. The diminution of B and Na appears to be related to the leaching ofsoluble salts from ash-treated soils. Of all the elements measured, only Mn produced significant correlation (p = 0.0001) between the tissue and soil extractable concentrations. Ash treatment elevated the soil pH to as high as 6.45 with theenhanced effect occurring primarily in the 0–15 cm depth. Soilsalinity increased with the application rate with the largestincreases occurring in the initial year of application. However,by the second year, most of the soluble salts had already leachedfrom the treatment zone into deeper depths, and by the fourthyear, these salts had completely disappeared from the profile.The chemical composition of the underlying groundwater was notadversely impacted by the ash application. Plant tissue and groundwater data however, indicate that much higher rates of fly ash can be used on this type of land use where the plant species is tolerant of soil salinity and does not appear tobioaccumulate potentially toxic trace elements.