Technical note: Vetiver can grow on coal fly ash without DNA damage

Fly ash is a by-product of coal-fired electricity generation plants. The prevalent practice of disposal is as slurry of ash and water to open lands or ash ponds located near power plants and this has lain to waste thousands of hectares all over the world. Wind and leaching are often the causes of off-site contamination from fly ash dumpsites. Vetiver (Vetiveria zizanioides) grown on fly ash for three months showed massive, mesh-like growth of roots which could have a phytostabilizing effect. The plant achieved this without any damage to its nuclear DNA as shown by comet assay done on the root nuclei, which implies the long-term survival of the plant on the remediation site. Also, when Vetiver is used for phytoremediation of coal fly ash, its shoots can be safely grazed by animals as very little of heavy metals in fly ash were found to be translocated to the shoots. These features make planting of Vetiver a practical and environmentally compatible method for restoration of fly ash dumpsites. Lack of DNA damage in Vetiver has been compared to that in a sensitive plant i.e. Allium cepa. Our results suggested that apart from traditional end-points viz. growth parameters like root length, shoot length and dry weight, comet assay could also be included in a battery of tests for initial, rapid and effective selection of plants for restoration and phytoremediation of polluted sites.     

Characteristics of boron accumulation by fly ash application in paddy soil

Fly ash has a high content of plant available silicate which is strongly needed for rice cultivation in Korea. One concern for plants grown on soils amended with fly ash is boron (B) toxicity because most of the fresh fly ash contains considerable B. This study was conducted in paddy soil to determine B uptake by rice and characteristics of B accumulation in soil after fly ash application (0, 40, 80, and 120 Mg fly ash ha⁻¹). In all fly ash treatments, B content in rice leaves and available B in soil at all growing stage were higher than those of control, but were not exceeded a toxicity levels. Boron occluded in amorphous Fe and Al oxides comprised ca. 20–39% of total B and was not affected by fly ash application. Most of the B was accumulated by fly ash application as a residual B which is plant-unavailable form, comprised >60% of the total B in soil. Thus, fly ash can be a good soil amendment for rice production without B toxicity.     

Boron toxicity

Whilst of lesser prevalence than B deficient soils, B-rich soils are important, causing B toxicity in the field and decreased crop yields in different regions of the world. The highest naturally occurring concentrations of soil B are in soils derived from marine evaporites and marine argillaceous sediment. In addition, various anthropogenic sources of excess B may increase soil B to levels toxic for plants. The most important source is irrigation water, but others include wastes from surface mining, fly ash, and industrial chemicals. Ameliorating high-B soils is extremely difficult. A commonly used method of reclaiming high B soils is to extensively leach with low B water. Though used successfully, leaching may not be a permanent solution and causes difficulties with the disposal of the leachates. Other amelioration methods include the use of soil amendments (e.g. lime, gypsum) and the planting of plant genotypes that are tolerant of high external B concentrations. Although there are various methods available to determine the levels of B in soils, soil analysis can provide little more than a general risk assessment for B toxicity. Similarly, diagnosing B toxicity in plants, either by visible symptoms or tissue analysis has limited applicability. Thus at present, neither soil nor plant analysis can be recommended to precisely predict the growth of plants on high soil B. Recent physiological and genetic studies have provided some understanding of genetic variation in the response of plants to high concentrations of B. Moreover, these studies have facilitated the breeding of tolerant genotypes for cultivation on high B soils. Considerable genetic variation in response to high B has been identified in a wide range of plant species, most of which share a similar tolerance mechanism – reduced uptake of B in both shoots and roots. The tolerance mechanism appears to be under the control of several major additive genes, and specific chromosomal locations have been identified for the genes in some species. Considerable success has been achieved in breeding for tolerance to B toxicity, a process that is greatly aided by the ease with which genotypic variation for this characteristic can be assessed and the range of methods available to screen breeding populations.     

Fly ash effect on improving soil properties and rice productivity in Korean paddy soils

Paddy soils in Korea generally require the addition of Si to enhance rice productivity. Coal combustion fly ash, which has a high available Si content and alkaline pH, was selected as a potential source of Si in this study. Two field experiments were carried out to evaluate rice (Oryza sativa) productivity in silt loam and loamy sand soils to which 0, 40, 80, and 120 Mg ha(-1) of fly ash were added with 2 Mg ha(-1) Si as a control. Fly ash increased the soil pH and available Si and P contents of both soils. The amount of available B increased to a maximum of 2.57 mg kg(-1), and the B content of the rice plants increased to a maximum of 52-53 mg kg(-1) following the addition of 120 Mg ha(-1) fly ash. The rice plants did not show toxicity effects. The highest rice yields were achieved following the addition of around 90 Mg ha(-1) fly ash. The application of fly ash increased Si, P and K uptake by the rice plants, but did not result in an excessive uptake of heavy metals in the submerged paddy soil. In conclusion, fly ash could be a good supplement to other inorganic soil amendments to improve the nutrient balance in paddy soils.     

The uptake of cadmium,lead and selenium by barley and cabbage grown on soils amended with refuse incinerator fly ash

Summary Barley and cabbage plants grown in the greenhouse on soils amended with refuse incinerator fly ash contained significantly elevated levels of Cd, Pb and Se, with Cd uptake being greatest in both plant species. Cabbage grown on 20% ash amended soil contained 146 times more Cd than controls. Cadmium and Se appeared to be less available in a successive barley crop after overwintering the pots of soil outside, but elemental concentrations still remained elevated. Comparisons with data from other studies indicated that Cd availability was greater from refuse fly ash than from sewage sludge.     

Leachant pH effects on the leachability of metals from fly ash

The leachability of metals from fly ash produced by a coal‐fired electric plant and a municipal waste incinerator under acidic conditions was experimentally investigated. The results of these column‐leaching experiments show that a decrease in the pH of the leachant favors the extraction of metal ions from solid particles of both coal combustion fly ash and municipal waste incinerator fly ash. The significant increase in the extraction of cadmium, chromium, zinc, lead, mercury, and silver ions from the ash is attributed to the instability of the mineral phases that contain these metals under acidic conditions.     

Effect of Ash Pond Soil and Amendments on the Growth and Arbuscular Mycorrhizal Colonization of Allium cepa and Germination of Arachis hypogaea,Lycopersicon esculentum,and Vigna mungo Seeds

The effect of fly ash pond soil on the growth and yield of onion (Allium cepa var. microaggregatum) plants grown in pots was investigated. The fly ash pond soil was amended with combinations of red soil and press mud, a waste product from sugar mills. Water-holding capacity of ash pond soil amended with press mud increased; however, addition of press mud delayed onion bulb development. Onion bulb germination took place rapidly in ash pond soil; however, subsequent bulb development declined. The addition of red soil and press mud increased the growth and yield of onion plants. In all the soils and amendments, onion plant roots were colonized by native arbuscular mycorrhizal species. Both vesicles and arbuscules were present in the roots. Colonization was low in ash pond soil but increased with the addition of red soil. Effect of fly ash pond soil on germination of groundnut (Arachis hypogaea), tomato (Lycopersicon esculentum), and black gram (Vigna mungo) seeds was evaluated and compared with red soil in the laboratory. Ash pond soil increased the germination of tomato seeds but did not affect the germination of groundnut and black gram seeds.     

Variability over time in the mutagenicity of ashes from municipal solid-waste incinerators

Incineration of municipal solid waste as an alternative to its disposal in landfills has advantages such as volume reduction and generation of energy. However, both air emissions and the residual ash may pose environmental and human health hazards. The Ames mutagenicity assay was used to determine the mutagenicity of fly and bottom ash from two incinerators over time. This assay is an alternative to costly and time-consuming chemical analyses and is more realistic for the assessment of the best disposition of the ash i.e. whether it could pose a risk to handlers of the ash, whether it can be used in cement or as a fertilizer or whether it should be relegated to a landfill. The mutagenic potency of fly and bottom ash on a per g weight basis of material is similar. Furthermore, the variability over time in mutagenicity indicates that constant monitoring of incineration products and byproducts is essential.     

Environmental hazard assessment of coal ash disposal at the proposed Rampal power plant

A proposed coal-fired power plant at Rampal, Bangladesh will produce over 38 million tons of ash during 60 years of operation at 90% electric load generation capacity. The ash disposal pond would be full in twelve years even if half of all fly ash is used in concrete and brick production, leaving at least 20 million tons of ash with a disposal plan that is limited to surface impoundment and unlined fills, which are known to cause groundwater and surface water pollution. At Rampal, probable storm tides of 7.4 meters would breach the ash pond walls during the operational life of the coal plant, potentially resulting in catastrophic failure and massive spills of ash. Seasonal monsoon flooding would cause the ash pond itself to overflow, releasing huge volumes of contaminated water. Ash disposal for the proposed coal-fired power plant at Rampal, Bangladesh, would release toxic heavy metals into the waterways of the Sundarbans Delta and Bay of Bengal, which is a World Heritage Site and includes globally important mangroves, endangered aquatic species, and a fishery that feeds hundreds of thousands of poor people. The economic damage cost of the Rampal Plant could exceed $US 100 million dollars per year.     

Biological treatment of waste with high ash content using a hydrolytically assisted extended aeration process

In previous reports from this laboratory it has been shown that the extended aeration process for biological treatment of organically laden municipal and/or industrial waste could be successfully employed for concurrent purification and sludge disposal. Also results using a modified process in which autodigestion was aided and controlled by periodic partial hydrolysis of small portions of the recycle sludge showed that operational control was feasible. There was some question regarding the success of such a process if the original waste contained a large portion of inorganic solids. Accordingly, a 1½ year pilot plant study was made using a waste (hydrolyzed trickling filter sludge) of exceptionally high ash content (50–60%). It was found that the ash content of activated sludge grown on this substrate did not continually increase nor did the high ash content of the waste interfere in any way with the efficiency of removal of organic matter. In general it exceeded 90 percent. Also a highly nitrified effluent was produced. A variety of analyses were performed: COD, BOD, TOC, suspended solids, NH₃-N, organic-N, NO₃-N, etc. Interrelationships between these important monitoring parameters for assessing plant performance offered useful insight into operational control for hydrolytically assisted extended aeration processes.     

Recovery of value added products from rice husk ash to explore an economic way for recycle and reuse of agricultural waste

Rice husk ash (RHA) is the major by-product left after the burning of rice husk, which is profusely present throughout the process of the rice milling. The burnt rice husk, as RHA, in turn causes more environmental pollution and its disposal becomes a difficult problem, hence requiring serious attention from the scientific community regarding its disposal and proper reuse if possible. The major economic reason for recycling the ash is the value added products which can be generated from it. The focus is on the use of RHA as adsorbent and subsequent silica production owing to the fact that the ash is mainly composed of carbon and silica. As regards other potential applications of ash, research is still going on and some of the products, which are under development phase, have also been brought to limelight in this review. This literature review provides an effective scheme to utilize RHA and discussed process pathway for economically valuable products to provide a solution to the problem associated with its proper disposal through superior recycle of this agriculture waste.     

Characterization of thermal power-plant fly ash for agronomic purposes and to identify pollution hazards

Ash samples were collected from a dumping site (fly ash) and an electrostatic precipitator (ESP ash) of a 440 MW thermal power plant for characterization. Analysis of ash samples showed that the major matrix elements in fly ash were Si and Al, together with significant percentages of K, Fe, Ca and Mg. Some of the biologically-toxic elements, Ni, Cr, Pb, B and Mo, were also present in substantial amounts. Ash collected directly from electrostatic precipitator (ESP ash) was finer in texture, lower in pH and generally richer in nutrients than the ash collected from dumping sites (fly ash). The saturation moisture percentages of both the ashes were higher, but the bulk density was lower, than the normal cultivated soils. Calcium was the dominant cation of the exchange complex, followed by Mg²⁺, Na⁺ and K⁺. Contents of available sulphur were quite high. Among DTPA extractable micronutrients, only iron was present in significant amounts, but the contents of hazardous constituents were very low. Compositions of watersoluble constituents of both the ashes were substantially affected by water: fly ash ratio and decreased with dilution. The rate of release of sodium was found to be much less than calcium and magnesium.     

Chemical,microbial and physical properties of manufactured soils produced by co-composting municipal green waste with coal fly ash

Increasing proportions of coal fly ash were co-composted with municipal green waste to produce manufactured soil for landscaping use. Only the 100% green waste treatment reached a thermophilic composting phase (?50 °C) which lasted for 6 days. The 25% and 50% ash treatments reached 36–38 °C over the same period while little or no self-heating occurred in the 75% and 100% ash treatments. Composted green waste had a low bulk density and high total and macro-porosity. Addition of 25% ash to green waste resulted in a 75% increase in available water holding capacity. As the proportions of added ash in the composts increased, the organic C, soluble C, microbial biomass C, basal respiration and activities of β-glucosidase, L-asparaginase, alkali phosphatase and arylsulphatase enzymes in the composted products all decreased. It could be concluded that addition of fly ash to green waste at a proportion higher than 25% did not improve the quality parameters of manufactured soil.     

Growth and physiological response of lemongrass (Cymbopogon citratus (D.C.) Stapf.) under different levels of fly ash-amended soil

Revegetation with metal tolerant plants for management of fly ash deposits is an important environmental perspective nowadays. Growth performance, photosynthesis, and antioxidant defense of lemongrass (Cymbopogon citratus (D.C.) Stapf.) were evaluated under various combination of fly ash amended with garden soil in order to assess its fly ash tolerance potential. Under low level of fly ash (25%) amended soil, the plant growth parameters such as shoot, root, and total plant biomass as well as metal tolerance index were increased compared to the control plants grown on garden soil, followed by decline under higher concentration of fly ash (50%, 75% and 100%). In addition, leaf photosynthetic rate, stomatal conductance, and photosystem (PS) II activity were not significantly changed under low level of fly ash (25%) amended soil compared to the garden soil but these parameters were significantly decreased further with increase of fly ash concentrations. Furthermore, increase of activities of some antioxidant enzymes such as superoxide dismutase, ascorbate peroxidase, and guaiacol peroxidase over control were noticed in lemongrass under all fly ash treatments. Taken together, the study suggests that lemongrass can be used for phytoremediation of fly ash at 25% amended soil.     

Natural revegetation of coal fly ash in a highly saline disposal lagoon in Hong Kong

Question: What is the relationship of the naturally colonizing vegetation and substrate characteristics in fly ash lagoons? Location: West lagoon, Deep Bay, a 13‐ha coastal lagoon in Hong Kong in subtropical Southeast Asia. Methods: Vegetation establishment was examined in a coal fly ash lagoon two years after its abandonment to investigate the distribution of vegetation in relationship to the chemical properties of the fly ash in the lagoon. A greenhouse experiment assessed the limits imposed on plant growth in fly ash. Results: The fly ash was saline, slightly alkaline and very poor in organic matter and nitrogen. Ash from bare and vegetated areas differed significantly in their salinity and extractable concentrations of inorganic nitrogen and various metals. Bare ash had a significantly higher conductivity and extractable sodium, aluminum, manganese, potassium, and lead. In total 11 plant species that belonged to seven families were found growing on the fly ash; all species except the shrub Tamarix chinensis were herbaceous. Using discriminant analysis, the most important factors in distinguishing bare and vegetated ashes were conductivity and sodium. Cluster analysis of bare samples gave two distinct groups, one from the periphery of the lagoon, which had lower sodium, conductivity, organic carbon, potassium and copper, and the other from a second group that contained ashes from the central region of the lagoon. Results of the greenhouse experiment showed that the inhibition of plant growth was significantly correlated with the presence of soluble toxic elements in ash. Conclusion: Toxicity and salinity seem to be the major limiting factors to plant establishment in fly ash, and these factors must be ameliorated for the successful reclamation of these fly ash lagoons.     

A life cycle comparison of disposal and beneficial use of coal combustion products in Florida

Background, aim, and scope  Beneficial use of coal combustion products (CCPs) in industrial or construction operations has the potential to minimize environmental and human health impacts that would otherwise be associated with disposal of CCPs in the life cycle of coal used for electricity generation. To assess opportunities for reducing impacts associated with four CCP materials considered in this study, fly ash, bottom ash, boiler slag, and flue gas desulfurization (FGD) material, this paper reports results of expanding a life cycle inventory of raw material and emissions (part 1 of this series of papers) by performing life cycle impact assessment on five scenarios of CCP management. Materials and methods  SimaPro 5.1 software (PRé Consultants) was used to calculate comparative environmental impacts of all scenarios using CML2001 and Environmental Design of Industrial Products 1997 midpoint impact assessment methods and Heirarchist and Individualist levels of the Eco-indicator 99 end point method. Trends were compared for global and local environmental and human health impact categories of global warming, acidification, smog formation, human toxicity, and ecotoxicity. Results  In each impact category, beneficial use of fly ash, bottom ash, and FGD material resulted in a reduced impact compared to disposal of these materials. The extent to which beneficial use reduced impacts depended on several factors, including the impact category in consideration, the magnitude of potentially avoided impacts associated with producing raw materials that CCPs replace, and the potential impact of CCP disposal methods. Global warming impacts were reduced by the substitution of fly ash for Portland cement in concrete production, as production of Portland cement generates large quantities of CO₂. However, for categories of global warming, smog formation, and acidification, impact reductions from CCP beneficial use are small, less than 6%, as these impacts were attributable, in greater part, to upstream processes of coal mining, transportation, and combustion. Human toxicity and ecotoxicity categories showed larger but more varied reductions, from 0% to 50%, caused by diverting CCPs from landfills and surface impoundments. Discussion  When comparing beneficial use scenarios, the four impact assessment methods used showed similar trends in categories of global warming, acidification, and smog formation. However, results diverged for human toxicity and ecotoxicity categories due to the lack of consensus among methods in classification and characterization of impacts from heavy metal release. Similarly, when assessing sensitivity of these results to changes in assumptions or system boundaries, human toxicity and ecotoxicity categories were most susceptible to change, while other impact categories had more robust results. Conclusions  Impact assessment results showed that beneficial use of CCPs presented opportunities for reduced environmental impacts in the life cycle of coal combusted for electricity generation, as compared to the baseline scenario of 100% CCP disposal, although the impact reductions varied depending on the CCPs used, the ultimate beneficial use, and the impact category in consideration. Recommendations and perspectives  As regulators and electric utilities increasingly consider viability and economics of the use of CCPs in various applications, this study provides a first-basis study of selected beneficial use alternatives. With these initial results, future studies should be directed towards beneficial uses that promise significant economic and environmental savings, such as use of fly ash in concrete, to quantify the currently unknown risk of these applications.     

Soybean growth on fly ashamended strip mine spoils

Summary The use of fly ash as an amendment for strip mine soils has been studied under field conditions. Spoils ranging in pH from 4.0–6.0 were tested. The addition of fly ash in all cases was effective as an acid soil neutralizer and substantially enhanced the growth and development of all experimental plants. The parameters used in growth analyses were plant height, dry weight, root/shoot ratios, nodulation, pod production, and nitrogen fixing capacity for legumes. re]19761004     

Population dynamics of houseflies,Musca domestica,on experimentally accumulated refuse

The population dynamics of the housefly, Musca domestica, on patchy and unstable habitats consisting of refuse was investigated at a waste disposal site by using sticky flypaper and mark-release-recapture technique (Jolly-Seber 's method). The newly disposed garbage was favorable for breeding of the flies for about one month after being disposed, while a mixture of garbage and ash from incinerated refuse was less favorable. On the garbage under favorable conditions, the rates of population increase was 1.25–2.82 per day, and approximately 1300–1500 flies were produced per square meter within the available period of one month. The rapid decrease in the fly density was observed just after the appearance of high density peaks. The mark-release-recapture study suggested that this rapid decrease would be mainly due to the density-dependent emigration of adult flies from the patchy habitats. The emigration was also activated when the time after garbage disposition became long.     

Growth response of two grasses and a legume on coal fly ash amended strip mine spoils

The use of fly ash as an amendment for strip mine soils was studied under field conditions. Three plant species—Agrostis tenuis var. Highlander,Festuca arundinacea, andLespedeza cuneata—were grown in strip mine plots. Half of the plots were treated with an equivalent of 70 metric tons per hectare of coal fly ash and half were untreated. Biomass production ranged from 5 to 30 times higher in fly ash treated plots compared to untreated plots. No toxic effects to the plants were observed.     

Amendments promote the development of Lolium perenne in soils affected by historical copper smelting operations

The Puchuncaví valley, central Chile, has been exposed to aerial emissions from a copper smelter. Nowadays, soils in the surroundings are sparsely-vegetated, acidic, and metal-contaminated, and their remediation is needed to reduce environmental risks. We assessed effectiveness of lime, fly ash, compost, and iron grit as amendments to immobilize Cu in soils and promote plant growth. Amended soils were cultivated with Lolium perenne for 60 days under controlled conditions. Total dissolved Cu and Cu2+ activity in the soil solution, ryegrass biomass, and Cu accumulation in plant tissues were measured. Addition of lime and fly ash decreased Cu concentrations and Cu2+ activity in the soil solution, increased plant biomass, and reduced shoot Cu concentration below 22 mg kg(-1) (the phytotoxicity threshold for the species). The most effective amendment with respect to the shoot biomass yield was a combination of lime and compost. Water content of the substrate and the K accumulation were positively correlated with the compost application rate. Compost combined with iron grit decreased dissolved Cu concentrations during the period of highest solubility, i.e., during the first 60 days after the compost application. However, iron grit incorporation into soils amended with lime and compost decreased the shoot biomass of ryegrass.