Fly Ash Amendment Research Articles

Soil properties and turf growth on a sandy soil amended with fly ash

Field lysimeters of a sandy soil were amended to a depth of 100 mm with four rates (0, 5, 10 and 20%, wt/wt) of fly ash, and effects on soil water content, nutrient leaching, turf growth and nutrition, and uptake of trace elements by turf were assessed. Measurements were taken for 70 days for lysimeters either planted with rhizomes of Cynodon dactylon(L.) Pers., cv. `Wintergreen', or left bare. When irrigated daily, soil water content increased progressively with increasing rates of fly ash and leachate volumes were decreased by 17–52% for lysimeters containing fly ash amended soil. Fertiliser was applied equivalent to 28.4 g N m−2 and 10.3 g P m−2 for the entire 70 days (including pre-plant application). Macronutrient concentrations in leaf tissue were within levels regarded as sufficient. Total dry mass (root plus shoot) decreased when fertiliser application rates were reduced by 25%, irrespective of fly ash treatment. In `bare' lysimeters containing fly ash amended soil, cumulative leaching of NO3−, NH4+and P were 0.32–0.88 of the values in non-amended soil. When planted with turf, leaching of those nutrients was minimal (equivalent to 3% of total N applied) and leaching loses did not differ among fly ash rates. Extractable soil P levels were increased 2.5–4.5-fold in the fly ash amended zone, compared with non-amended soil. Root mass in the top 100 mm was 1.2–1.5-fold larger for turf in fly ash amended soil, compared to non-amended soil. The Se concentrations were higher in leaf tissue grown in fly ash amended soil (being at most 0.63 μg g−1), but there was no effect of fly ash amended soil on As, Ba, B, Cd, Co, Cr, Cu, Pb, Hg, Mn, Ni, Ag or Zn in leaf tissues. Thus, fly ash amendment may be a suitable management option for turf culture on sandy soils, since fly ash improved soil water holding capacity and root growth in the amended zone.

Revegetating fly ash landfills with Prosopis juliflora L.: impact of different amendments and Rhizobium inoculation

A revegetation trial was conducted to evaluate the feasibility of growing a legume species, Prosopis juliflora L., on fly ash ameliorated with combination of various organic amendments, blue-green algal biofertilizer and Rhizobium inoculation. Significant enhancements in plant biomass, photosynthetic pigments, protein content and in vivo nitrate reductase activity were found in the plants grown on ameliorated fly ash in comparison to the plants growing in unamended fly ash or garden soil. Higher growth was obtained in fly ash amended with blue-green algae (BGA) than farmyard manure or press mud (PM), a waste from sugar-processing industry, due to the greater contribution of plant nutrients, supply of fixed nitrogen and increased availability of phosphorus. Nodulation was suppressed in different amendments of fly ash with soil in a concentration–duration-dependent manner, but not with other amendments. Plants accumulated higher amounts of Fe, Mn, Cu, Zn and Cr in various fly ash amendments than in garden soil. Further, inoculation of the plant with a fly ash tolerant Rhizobium strain conferred tolerance for the plant to grow under fly ash stress conditions with more translocation of metals to the above ground parts. The results showed the potential of P. juliflora to grow in plantations on fly ash landfills and to reduce the metal contents of fly ash by bioaccumulation in its tissues.

CO 2 evolution and enzyme activities (dehydrogenase, protease and amylase) of fly ash amended soil in the presence and absence of earthworms ( Drawida willsi Michaelsen) under laboratory conditions

The CO 2 evolution and dehydrogenase, protease and amylase activities of fly ash amended soil (Orissa, India) in the presence and absence of earthworms were investigated under laboratory conditions for 2 months at 50% water-holding capacity (WHC) and 25±2 °C temperature. A toxicity test of different age groups (juvenile, immature and adult) of Drawida willsi earthworms, dominant (>80% both in number and biomass) in crop fields of India, was conducted for 14 days at different concentrations of fly ash amended soil. On the basis of the results of the toxicity test, seven concentrations of fly ash amended soil were chosen (0, 2.5, 5, 10, 15, 25 and 50%; w/w) to study the CO 2 evolution and enzyme activities in the presence and absence of D. willsi. The results demonstrated little or no inhibition of soil respiration and enzyme activities up to 2.5% fly ash amendment. With further addition of fly ash, all the above activities were significantly decreased. On the other hand, significant stimulation of soil respiration and microbial activities were observed up to 5% fly ash amendment when the soils contained earthworms. This may be due to increased microbial activity induced by substrates that are produced by the earthworms. Co-application of fly ash and earthworms at lower doses can thus be considered to stimulate soil biological activity and thereby improve nutrient cycling in acidic soil.

Chemical speciation and phytoavailability of Zn, Cu, Ni and Cd in soil amended with fly ash-stabilized sewage sludge

A sequential extraction method was used to determine chemical forms of Cu, Zn, Ni and Cd in fly ash-stabilized sludge. A loamy acid soil amended with fly ash-stabilized sludge was used to grow corn under greenhouse conditions. Sewage sludge amended with coal fly ash can reduce the availability of Cu, Zn, Ni and Cd in the sludge. Increasing fly ash amendment rate significantly reduced DTPA-extractable Cu, Zn, Ni and Cd concentrations. Percentages of Cu, Zn and Ni in residual fraction increased with an increase in fly ash amendment rates. Majority of Cu was associated with organic form, but Zn and Ni were associated with Fe–Mn oxide and residual forms. Addition of ash-amended sludge to soil significantly increased dry mass of corn. With coal fly ash amendment rate increasing, concentrations of Zn and Cu in shoot tissues of corn decreased significantly, but concentrations of Cd and Ni did not change significantly. Significant correlations were found between concentrations of Cu and Zn in corn shoot and oxide and total Cu fractions, and all chemical fractions of Zn in fly ash-stabilized sludge, respectively. Hence, ash amendment significantly reduced the availability of heavy metals by chemical modification of their chemical speciation into less available forms.

Reduced leaching of nitrate, ammonium, and phosphorus in a sandy soil by fly ash amendment

Low ionic sorption capacities and high hydraulic conductivities of sandy soils contribute to the potential for leaching of nutrients applied to these soils. Batch sorption experiments were used to examine NO3–, NH4+, and P sorption/desorption isotherms for Karrakatta sand and Kwinana fly ash. Column experiments assessed leaching of these nutrients from this sandy soil, when amended with 4 rates (0, 5, 10, and 20%, wt/wt) of fly ash. The sorption of NO3–, NH4+, and P was higher for fly ash than the sandy soil. Phosphorus sorption was greatest for unweathered fly ash, followed by weathered fly ash and then the soil; for example, sorption from a solution containing 20 mg/L P was 90%, 28%, and 14%, respectively. Desorption of P was much slower in the unweathered fly ash than weathered fly ash or the soil. Leachates collected from columns containing fly ash amended soil (5, 10, and 20%, wt/wt) generally had lower concentrations of NO3– and NH4+ than leachates from non-amended soil. Prior to adding fertiliser, the concentration of P was greater in leachate from fly ash amended soil than from the native soil, due to fly ash (weathered) itself containing 92.5 mg/kg of extractable P. However, from day 35 onwards, the concentration of P was lower in leachates from soil amended with 10% or 20% fly ash than from non-amended soil. Thus, fly ash amendment retarded NO3–, NH4+, and P leaching in the sandy soil and may therefore be a useful tool for improvement of nutrient management in sandy soils.

Soil microbial community responses to fly ash amendment as revealed by analyses of whole soils and bacterial isolates

Due to its silty texture and plant nutrient content, coal fly ash may prove a valuable amendment to coarse-textured soils. Its effects on soil chemical and physical properties in the field have been studied, but little is known regarding effects on soil microbial communities. In this study, field plots were amended with fly ash at rates of 0 or 505 Mg fly ash ha −1 and subsequently cropped to a fallow–corn–wheat rotation or continuous fescue. Twenty months later, microbial responses to the fly ash were assessed by analyzing the fatty acid composition and carbon substrate utilization potential of microbial communities and aerobic heterotrophic bacteria isolated from the field plots cropped to wheat and fescue. Differences in whole-soil fatty acid profiles from amended and non-amended soils were found. Soils amended with fly ash were enriched in fatty acid 16:1 ω5 c, and elevated quantities of 17:0 cy and 16:1 ω7 c were present in fly ash-amended soils cropped to fescue and wheat, respectively. Fatty acid profiles also were affected by cropping system. Extracts from wheat-cropped soils were enriched in 17:1 ω7 c, while those from fescue plots had greater amounts of 18:2 ω6 c and 18:1 ω9 c. Carbon substrate utilization patterns of microbial communities were affected by cropping system but not by fly ash amendment; communities from soils cropped to wheat utilized more carbon substrates than did communities from fescue-cropped soils at the soil dilution tested. Studies of bacterial isolates revealed that Arthrobacter species dominated the culturable, aerobic heterotrophic population, accounting for 25–42% of the total number of isolates recovered from the field plots. Percentages of unidentified isolates also were significant and ranged from 27 to 45% of isolate totals. Effects of fly ash on soil isolates were detected within species of Arthrobacter, with reduced numbers of A. protophormiae in soils amended with fly ash relative to non-amended soils. Overall, the structure of the culturable, aerobic heterotrophic population did not reflect that of the soil community, as fatty acids reported to be markers for Gram-positive organisms were not the major community fatty acids. Enhanced crop growth and soil texture, pH, and nutrient content as a result of fly ash amendment may explain why no detrimental effects to the microbial community were found. Instead, whole-soil fatty acid data indicates that fly ash amendment may benefit fungi and Gram-negative bacteria relative to other components of the soil microbial community.

Soil biochemical activity and growth response of rice Oryza sativa in flyash amended soil

Soil amended with different proportions of flyash, a solid waste generated from coal-fired thermal power plants, was evaluated as a soil conditioner and nutrient supplement during a field study on the growth of rice, Oryza sativa. Generally, pH and organic carbon (OC) content did not increase significantly ( P>0.05) in flyash amended soil, but significant increases ( P<0.05) in soil conductivity (32%), available phosphorus (48%) and organic matter (OM, 29%) were observed during harvest at the 20 t ha −1 flyash application rate. Amylase, invertase, dehydrogenase and protease activities, and CO 2 evolution increased in flyash amended soil over the control. The pigment (chl- a, chl- b, and carotenoid) content in rice plants did not vary significantly ( P>0.05) between different flyash amendments. Total plants biomass and aboveground biomass increased ( P<0.05) significantly (17% and 25%, respectively) at the 20 t ha −1 flyash application. However, there was a retarded growth of underground biomass. Grain and straw yield increased by 21% and 18%, respectively, at 17.5 t ha −1 flyash amendment when compared to the control. Although, a significant increase ( P<0.05) in plant biomass and grain yield in flyash amended soil is encouraging from the point of waste disposal and management, elucidation of reasons for retarded growth in underground biomass will require additional research based on long-term studies.

Impact of fly ash amendment and incorporation method on hydraulic properties of a sandy soil.

Coal fly ash has physical and chemical characteristics that makeit useful as a soil amendment, one of the more important beingthe potential to permanently improve the soil water relations ofsandy, drought-prone soils. We axemined changes in theinfiltration rate and water holding capacity of a sandy soilafter application of high rates (up to 950 Mg ha-1) of aClass F fly ash. Fly ash was applied to large field plots byeither conventional tillage (CT; moldboard plow-disk) orintensive tillage (IT; chisel plow-rotovate-disk), and tomicroplots using a rototiller. Infiltration rate (i) wasmeasured in both studies with a disk permeameter on threeoccasions over a 12-month period. Ash effects on gravimetric water content (θg) at the 0–40 cm soil depth were measuredduring a 168 hr period following a 2.5 cm rainfall event andwater release curves (33 to 500 kPa) were constructed in thelaboratory using soils from the large plots. In both studiesi was decreased by ∼80% one year after additionof fly ash and θgin ash-amended soil was higher than unamended soil throughoutthe 168 hr monitoring period. Soil water distribution variedwith tillage; the IT treatment had the highest θg increasesin the 0–20 cm depth while the CT treatment had θgincreases throughout the 0–40 cm depth. Soil water content anddistribution in ash-amended microplots were similar to ITtreatments. Fly ash amendment not only increased water holdingcapacity but also increased plant available water by 7–13% inthe 100–300 kPa range. These results suggest fly ash amendmentmay have the potential to improve crop production in excessivelydrained soils by decreasing i and increasing the amountof plant available water in the root zone.

Plant Nutrient Availability from Mixtures of Fly Ashes and Biosolids

AbstractNutrient imbalances, both deficiencies and excesses, are one reason for the poor acceptance of waste materials as fertilizer substitutes. Two greenhouse experiments were established using 24 different fly ashes with sewage sludge and poultry manure to estimate nutrient availability and imbalances to maize (Zea mays L.). The maximum maize growth attained with fly ash amendment of 80 Mg ha−1 was significantly less (50%) than a fertilized control treatment. The additional growth improvements obtained from mixtures with sewage sludge or poultry manure ranged from 30 to 49% and 30 to 71%, respectively. Organic materials applied alone achieved only 54 and 62% of the maximum potential, while growth on poultry manure mixtures was up to 94% of the best performing fertilized treatment. Results of foliage and soil analyses suggest that P and K were the main nutrient deficiencies, while B phytotoxicity and an imbalance in the K/Ca/Mg ratio also were likely causes of plant growth reduction. Fly ashes did not contribute significant P or K to correct soil and plant deficiencies, but more often exacerbated the imbalances by precipitation or adsorption of soil P. Sewage sludge mixed at 26% and poultry manure at 13% (DM) with fly ash had negligible effect on availability of phytotoxic fly ash B, but were good sources of P (both) and (poultry manure). Good agreement between plant nutrition in pot experiments and previous laboratory extraction studies implies that chemical analysis, efficient formulation and optimized application rates may overcome nutrient limitations for use of wastes as fertilizer substitutes.

Coal Fly Ash and Lime Stabilized Biosolids as an Ameliorant for Boron Deficient Acidic Soils

Previous studies have shown that a combination of coal fly ash (10% w/w) and lime (1% w/w) amendment was effective in stabilizing biosolids (ACS) by killing the pathogens and reducing heavy metal availability, and the product contained a high B content. It was, therefore, the aim of the present study to evaluate the suitability of the ACS as a B fertilizer for a degraded acid soil with B deficiency in South China. An acid and B deficient loamy soil was amended with the ACS at application rates of 6.4, 12.7, 25.5, 63.7 and 127.4 mg ha−1, which were then compared to the same soil receiving an equivalent B fertilizer application rates of 0.9, 1.4, 2.2, 4.5 and 8.4 kg ha−1, respectively. Soil hot water soluble B content and pH increased significantly with an increase in the amendment rate of the ACS mixture. Soil amended with the ACS mixture had a significantly higher dry weight yield for both cucumber and corn than the control and its counterparts of soil with B fertilizer. The highest yield was obtained in the treatment with 5% ACS mixture amendment. Boron concentrations in plant tissues increased according to the application rates of the ACS mixture and B fertilizer. Cucumber was more sensitive than corn to both B deficiency and toxicity as indicated by the insignificant effect of B fertilizer application on dry weight yields of corn. The experimental results demonstrated that the ACS mixture at an application rate of ≤ 63.7 mg ha−1 could act as a B fertilizer supplement for the acid loamy soil.

Microbial Responses to Coal Fly Ash under Field Conditions

AbstractCoal fly ash may be a valuable soil amendment because it contains plant nutrients and liming agents and has a silty texture that can improve the water‐holding capacities of sandy, drought‐prone soils. Short‐term laboratory studies have indicated that addition of unweathered fly ash to soil can stress microbial populations and their activities, but effects of fly ash addition at the field scale are not known. In this study, field plots received 0 or 505 Mg fly ash ha−1 (incorporated by conventional tillage to a depth of 40 cm) and were subsequently cropped to a fallow‐corn (Zea mays L.)‐wheat (Triticum aestivum L.) rotation or continuous fescue (Festuca arundinacea Schreb.). Twenty months later, during the wheat phase of the rotation, the plots were sampled (0–15 cm) and assayed for activity of soil enzymes (dehydrogenase, alkaline phosphatase, arylsulfatase, and denitrifying enzymes); numbers of aerobic heterotrophs, ammonium oxidizers, denitrifiers, and bradyrhizobia; and N mineralization, nitrification, and denitrification potentials. Nitrification potentials doubled in fly ash‐amended soils, and numbers of denitrifiers were 200‐fold higher in fescue‐cropped, fly ash‐amended soils relative to fescue‐cropped, non‐amended soils. No other large differences in microbial populations or activities were found. The lack of detrimental effects on microorganisms in the field was possibly due to reductions in fly ash's soluble salt and trace element concentrations with time, the mild alkalinity of the fly ash used in this study, and the positive responses of crops to fly ash amendment.

Co-composting of sewage sludge and coal fly ash: nutrient transformations

Co-composting of sewage sludge with coal fly ash was carried out for evaluating the effect of coal fly ash on nutrient transformations during sludge composting. Dewatered anaerobically-digested sewage sludge was mixed with sawdust used as a bulking agent at 2:1 (w/w), and the mixtures were amended with coal fly ash at 0, 10, 25 and 35% (w/w) and composted for 100 days. Addition of coal fly ash raised the pH of the sludge compost throughout the composting period, but significant inhibition of decomposition activity occurred only at 35% ash amendment level. Soluble organic carbon and total C decreased according to composting time, whereas total N showed an opposite trend for all treatments. Addition of coal fly ash did not affect the carbon cycle significantly except at an ash amendment level of 35%. Coal fly ash amendment caused a significant loss of NH 4N only during the thermophilic phase. Addition of coal fly ash also inhibited the nitrification process and phosphorus transformation as indicated by the lower soluble NO 3N and PO 4P contents in ash-amended sludge composts. The C/N ratios in solid and aqueous phases decreased with composting time but did not show any significant difference after 63 days of composting for all treatments indicating that ash amendment did not affect compost maturity.

Evaluation of Cocomposted Coal Fly Ash on Dynamics of Microbial Populations and Heavy Metal Uptake

Vicia faba, in a pot experiment with sandy and clayey soils under greenhouse conditions, was checked for growth response to different amendments with coal alkaline fly ash or cocomposted fly ash mixed with lignocellulosic residues. Soil microbial populations, pH and electrical conductivity as well as heavy metal uptake by plants were monitored. At rates of five and ten percent (on a dry matter basis) in both soils, neither fly ash alone nor cocomposted fly ash exerted any negative effect. Plant biomass production was not influenced in either clayey or sandy soil. Alkaline fly ash did not promote microbial growth when applied alone to the soils. However, cocomposted fly ash generally increased bacterial and actinomycetes counts in both soils. Fungi were not affected by ash. Due to the increase of soil pH by alkaline fly ash or cocomposted fly ash, plant uptake of heavy metals was depressed in the sandy soil. Heavy metal mobility did not cause change in the clayey soil where a high buffering capacity mitigated the effects of fly ash amendments.

Enzyme Activities in a Sandy Soil Amended with Sewage Sludge and Coal Fly Ash

Previous studies showed that coal fly ash could stabilize sewage sludge by reducing metal availability, but fly ash may cause an adverse effect on soil microbial activities. Therefore, an experiment was performed to evaluate the effects of amendment of soil with anaerobically digested dewatered sewage sludge, stabilised with alkaline coal fly ash, on soil enzyme activity and the implications for soil nutrient cycling. Sewage sludge was amended with 0, 5, 10, 35 and 50% w/w of fly ash, and then the ash-sludge mixtures were incubated with a sandy soil at 1:1 (v/v). Dehydrogenase activity decreased with an increase in fly ash amendment level and the time of incubation. Soil receiving 5% ash-sludge amendment had a higher dehydrogenase activity than other treatments. Soil receiving 10% ash-sludge mixture had the highest urease activity and in general, urease activity decreased with increasing incubation time. Phosphatase activity was the highest at 5% ash-sludge mixture amended soil and no general trend was observed with time. Water-soluble Zn, Mn and Cu contents were suppressed by the addition of fly ash. The present experiment indicated that addition of 10% ash-sludge mixture should have a positive benefit on the activity of soil microorganisms, N and P nutrient cycling, and reduce the availability of heavy metals.

Plasticity and Density-Moisture-Resistance Relations of Soils Amended with Fly Ash

Fly ash is a by-product of coal combustion that requires disposal worldwide. Few studies have been conducted on the potential utilization of fly ash to improve soil physical properties and workability. The objective of this study was to investigate the impact of fly ash amendments on the plasticity, water retention and penetration resistance-density-moisture relationships of three soils of sandy loam, loam and clay loam textures in order to determine the potential compaction of these soil/fly ash mixtures if they were worked at different moisture ranges. For all three soils the addition of fly ash decreased the plasticity index, but slightly increased the Proctor maximum density. This implies that fly ash amendments reduce the range of moisture within which soils are most susceptible to compaction. However, for the sandy loam and loam textured soils amended with fly ash, cultivation must be avoided at moisture contents close to field capacity since maximum densification occurs at these moisture contents. In all three soils the addition of fly ash increased water retention, especially in the sandy loam. Correlation analysis indicated significant (p≤0.05) positive correlation between critical moisture content and field capacity, critical moisture content and plastic limit, and plastic limit and field capacity. Fly ash amendments increased penetration resistance of the clay loam, but decreased penetration resistance of the sandy loam. For the loam there was an inconsistent response of penetration resistance to fly ash additions. Regression analysis indicated that penetration resistance of sandy loam/fly ash mixtures and loam/fly ash mixtures was significantly (p≤0.05) dependent on bulk density. For the clay loam/fly ash mixtures penetration resistance was significantly (p≤0.05) dependent on both bulk density and volumetric moisture content.

Fly ash influence on near-surface temperature of a clay loam soil

It has been suggested that fly ash, when applied as a soil amendment, would increase soil temperature. However, no quantitative data have been provided to support this hypothesis. This hypothesis was tested on four fly ash treatments (0, 100, 200, and 400 t ha−1) applied to clay loam soil in a randomized block design. Bi-hourly soil temperatures were measured on 3 summer days over 2 yr, and afternoon temperatures were measured on randomly selected spring days at 5-, 10-, and 20-cm depths in the four fly ash treatments. Temperatures were measured in conjunction with surface bulk density, water content, and particle size distribution which were also used to calculate thermal heat capacity. Fly ash decreased percent clay, soil water content, and soil heat capacity. Contrary to previously expected trends, fly ash amendment did not significantly increase mean daily soil temperature under dry conditions. Generalizations in the literature regarding the influence of fly ash on soil temperature, bulk density, and water-holding capacity must be considered carefully since they generally relate only to coarse to medium textured soils. Key words: Soil amendments, bulk density, reclamation, heat capacity, thermal diffusivity, thermal conductivity, volumetric water content, particle size distribution

Changes in biological parameters during co-composting of sewage sludge and coal ash residues

Coal ash residues, including fly ash (FA) and lagoon ash (LA), were co-composted with dewatered sludge for 100 days in a bench-scale composting system and biological parameters were monitored to evaluate the effect of ash residues on the composting process. Coal ash residue amendment caused a rise in alkalinity and salinity, but had no adverse effect on the population of thermophilic bacteria except for 25% FA amendment. All enzyme activities decreased with composting time. β-glucosidase and alkaline phosphatase activities were reduced with an increase in ash residue amendment, while no significant reduction was noted for urease and dehydrogenase activities after 20 days of incubation. Positive correlations were obtained among β-glucosidase, alkaline phosphatase and urease activities, while no correlation was found between thermophilic bacteria and enzyme activities. With the exception of 25% FA-amended sludge compost, addition of coal ash residues in sewage sludge is feasible and showed little effects on metabolic activity during composting process.

Implications of Fly Ash Application to Soil for Plant Growth and Feed Quality

Fly ash has shown potential as a soil amendment and a source of trace elements beneficial to plants. However, agricultural utilization of fly ash has been restricted due to variability in chemical composition, elemental toxicity, induced nutrient imbalances in plants, and inconsistent response of vegetation to fly ash amendment. Fly ash was applied to reclaimed mine soil near Edmonton, Alberta, at rates of 0, 25, 50, 100, 200, and 400 t ha−1. Total and water soluble concentrations of selected elements were determined from soil samples collected at 0 to 15 cm. Growth, development, and elemental uptake of barley (Hordeum vulgare, L., Jackson cv.), brome (Bromus inermis, Leyss), and alfalfa (Medicago sativa, L., Beaver cv.) were measured at select stages of development. Water soluble concentrations of B, Mo, Ca, Cr, K, Mg, Mo, Na, P, Se, and Sr variably increased with increasing fly ash rate. Boron concentration in plant tissue increased significantly to toxic levels with symptoms evident at early stages of barley development and increasingly severe at later stages. Toxicity symptoms were less severe for brome and alfalfa. The Cu:Mo ratio of vegetation decreased with increased fly ash rate to levels which could cause Cu deficiency in livestock. Yield of barley silage was significantly increased at intermediate rates of fly ash application, but significantly reduced at 400 t ha−1.

The Accumulation of Boron in Agropyron elongatum Grown in Coal Fly Ash and Sewage Sludge Mixture

A greenhouse pot experiment was conducted to investigate the boron (B) release capacity of coal fly ash and sewage sludge mixtures, and the accumulation of B in Agropyron elongatum after two consecutive growing seasons. Sludge was amended with fly ash at application rates of 0, 5, 10, 35, and 50% (w/w), and each mixture was then mixed with a loamy soil at either 1:1 or 1:5 (v/v). Both water soluble B (WS-B) and hot water soluble B (HWS-B) increased with increasing fly ash amendment rate. Shoot B concentrations also increased significantly according to the rate of ash amendment. The ash-sludge mixture improved plant growth with the highest total dry weight yield at 10% ash amendment rate. Boron toxicity symptoms in leaf tips were observed at 35% and 50% ash amendment rate at both soil mixing ratios. Hot water soluble B and WS-B decreased significantly after consecutive cropping of Agropyron especially at low ratio of mixure with soil i.e., 1:5 (v/v). However, soil available B contents at ≥ 35% ash application rate and 1:1 (v/v) soil mixing ratio were still excessive for normal plant growth, suggesting that deleterious effects on plant growth would be experienced in later seasons owing to the high amounts of residual B.

Pressurized fluidized bed combustion ash 2. Soil and mine spoil amendment use options

The commercial introduction of pressurized fluidized bed combustion (PFBC) has spurred evaluation of ash management options for this technology. ashes used in this study were produced in the Foster Wheeler Energia Oy's circulating PFBC pilot facility in Karhula, Finland and the American Electric Power Tidd PFBC facility in Ohio. The fly ashes contain numerous compounds, including calcite (CaCO 3), anhydrite (CaSO 4) and, in the Tidd fly ash, dolomite [CaMg(CO 3) 2], that have the potential to be a nutrient source and a soil amendment for the reclamation of acid and sodic soils (soils influenced by high levels of sodium). The objective of this research was to determine if the PFBC ash could be used as soil amendments for acid and sodic soils. The research effort consisted of three separate tests: (1) a laboratory equilibration study to determine the influence of fly ash amendments on pH and EC (electrical conductivity) of actively oxidizing, acid-forming, mine spoil material; (2) a greenhouse study to determine the influence of fly ash on plant growth; and (3) a hydraulic conductivity evaluation of sodic soils treated with the PFBC fly ash materials. The study showed that the PFBC fly ashes were effective acid spoil amendments. In a comparison with ag-lime, the fly ash reacted with the spoil at a slower rate and the final pH of the treated material was slightly lower (∼7 versus ∼8). In addition, the EC of the fly-ash-treated spoil was ∼1 mS cm −1 higher than that associated with the ag-lime-treated materials. The greenhouse study demonstrated that the fly ash was an effective amendment for the remediation of acid spoil materials. In fact, the soils amended with fly ash supported higher plant production than those amended with ag-lime. These findings are possibly due to pH and nutritional effects. The hydraulic conductivity study demonstrated that the application of fly ash to sodic soils resulted in enhanced permeability of the treated soil.