Bon-Jun Koo

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.

Characterization of Organic Acids Recovered from Rhizosphere of Corn Grown on Biosolids‐Treated Medium

Abstract Organic acid production by plants and microorganisms was quantified in sand media amended with biosolids in the presence and absence of corn (Zea mays L.) in a sand‐culture hydroponic medium. Total quantities of organic acids were greatest in treatments containing both plants and biosolids, with lesser amounts in treatments with plants alone, biosolids‐treated media alone, and a nutrient solution–irrigated blank medium. Biosolids enhanced organic acid production in the rhizosphere and influenced the composition of organic acid mixtures. Only lactic, acetic, butyric, and oxalic acids were detected in media without plants. When the medium was planted, additional organic acids were recovered including tartaric, maleic, succinic, valeric, glutaric, pyruvic, and propionic. Lactic, acetic, and butyric acids were predominant in solutions recovered from the planted media and collectively accounted for 0.65 to 0.75 of the COO− mole fraction. Oxalic, maleic, and tartaric acids were the second most abundant and varied from 0.05 to 0.1 of the mole fraction, followed by succinic, valeric, glutaric, propionic, and pyruvic acids, comprising ≤0.05 of the mole fraction. Plant growth stage had no effect on relative proportions of organic acids but did influence the total quantities of organic acids recovered. Biosolids sources did not have a significant effect on either the quantity or composition of organic acids in any media. The predominance of organic acids that are microbial fermentation products suggests that the carbon contained in root exudates and biosolid amendments was transformed into a mixture of various fermentation products that accumulated in the rhizosphere solution and sand medium as a result of microbial growth and activity.

A root exudates based approach to assess the long-term phytoavailability of metals in biosolids-amended soils

Organic acids present in the rhizosphere of growing plants are widely recognized to be responsible for dissolving the solid phase metals in the soil and making them available for plant absorption. We proposed a root exudates-based model to assess the long-term phytoavailability of metals in biosolids-amended soils. The phytoavailability of biosolids-borne metals was defined in terms of a capacity factor and an intensity factor. The plant available metal pool, C(0) (capacity factor, mgkg(-1)), can be estimated by fitting the successive organic acids extraction data to an exponential decay kinetic equation. The field metal removal rate, k (intensity factor, yr(-1)), can be estimated from the successive extraction-based metal release rate through an effective annual organic acid production in the rhizosphere which was found to be characteristic of plant species. The protocol was successfully used to assess the long-term phytoavailability of metals in biosolids-amended soil from two biosolids land application sites.

Availability and Plant Uptake of Biosolid-Borne Metals

Metal uptake by different plant species was quantified in sand media amended with biosolids in a sand-culture hydroponic medium. In a previous paper (Koo et al. 2006), we concluded that total quantities of organic acids were greatest in treatments containing both plants and biosolids, with lesser amounts in treatments with plants alone, biosolids-treated media alone, and a nutrient solution-irrigated blank medium. Biosolids enhanced organic acid production in the rhizosphere. The purpose of this study was to evaluate how organic acids in root exudates affect the absorption of metals by selected plants. We found that the concentrations of metals in the plant tissue grown on biosolids-treated medium were always higher than that from the standard medium, irrespective of species and cultivar. The amount of metal transferred from the biosolids-treated medium to the plant varied with the metal element, following the order: Cd > Ni = Zn > Cu > Pb > Cr. Interspecies and cultivar differences in metal uptake were trivial compared to differences induced by the treatment. The metal uptake decreased with the growth period, and the kinetics of metal uptake, as indicated by accumulation in corn shoots, were essentially a first order during the initial 4 weeks of growth, especially for Cd and Zn.

Biogeochemistry of phosphorus, iron, and trace elements in soils as influenced by soil-plant-microbial interactions.

Publisher Summary The rhizosphere, a thin layer of soil adjacent to roots of living plants, is a chemically complex and microbiologically dynamic segment of the soil. At any given time, it accounts for a small fraction of the bulk soil in the root zone. All the surface soils, at one time or another, may be under the influence of roots. The rhizosphere receives exudates from roots, supports a dense and diverse population of microorganisms, and its chemistry is affected by the organic substances exuded by plant roots and by metabolites produced from microbial degradation of the organic substrates. The extraction of nutrients such as potassium ions by plants often initiates the weathering of primary minerals to secondary minerals. The biogeochemical activities in the rhizosphere have profound influence on evolution of soils. They induce dissolution of not readily soluble plant nutrients and potentially toxic elements and accelerate the weathering of clay minerals affecting the soil ability to accommodate plant nutrients and to attenuate toxic elements.

Phytoavailability of Trace Elements from a Landfill Containing Coal Combustion Waste

The 488-D Ash Basin (488-DAB) is an unlined, earthen landfill on the U.S. Department of Energy’s Savannah River Site, SC that contains approximately one million tons of coal combustion wastes (CCWs). Pyrite that is co-mingled with the CCWs has undergone oxidation and formed sulfuric acid, which has dissolved metals and trace elements in the CCWs and facilitated their mobility. The acid leachate contributes to ground-water deterioration in the area and threatens biota on, and adjacent to, the landfill. A study was undertaken to examine CCWs and vegetation on the 488-DAB to assess the potential for phytoavailability of these elements and to determine if a secondary contamination source exist. Results indicated that trace element concentrations of the CCWs were higher than those of native soils in the area. Mean pH (1.79 ± 0.75) and As concentrations (64.7 ± 43.0 mg kg−1) for the CCWs were in the range of critical plant toxicity. Sequential extractions of the CCWs indicated that Mn, Zn, Ni, and Cr were organically bound and in exchangeable fractions in the material and likely phytoavailable, while Pb and Se were tightly bound in the crystalline and acid extractable (residual) fractions. The fractionation patterns for Al, As, Cd and Fe were very similar with most bound to the poorly crystalline fraction, which suggest that their solubilities are likely controlled by a common precipitate or mineral in the CCWs. Tissue analysis indicated that Mn and Zn were accumulated by species growing on the 488-DAB, as predicted. However, Ni and Cr were not accumulated at levels above that of the CCWs. Uptake of Se and Cd in tissue was observed at levels over that of the CCWs in several species, but not all. Given these conditions, results suggest that periodic monitoring of plant species growing on the 488-DAB should continue to ensure that toxicity and secondary contaminant problems do not arise.

Evaluation of Bahiagrass (Paspalum notatum) as a Vegetative Cover for a Landfill Containing Coal Combustion Waste

A vegetative cover is a remedial technique utilized on landfills and waste sites for soil stabilization and for the physical and/or chemical immobilization of contaminants. Many herbaceous plants, primarily grasses, exhibit rapid growth, are moderately resistance to environmental stress, and are therefore often used as cover crops in environmental restoration and remediation projects. Use of bahiagrass (Paspalum notatum) was examined as a potential cover species and phytostabilizer on an unlined landfill (488-D Ash Basin, 488-DAB) containing approximately one million Mg of coal combustion wastes (CCWs) at the U.S. Department of Energy’s Savannah River Site (SRS) in South Carolina. Use of soil amendments and treatments to relieve physical limitations at the site (compaction) and promote vegetation success were implemented and assessed. The influence of these treatments on metal uptake by bahiagrass was also evaluated. Results indicated that the survival of bahiagrass growing in plots treated with a surface amendment (15 cm layer of material applied over the CCWs) was the highest in those containing a topsoil cover and followed the order: topsoil > biosolid > ash > apatite > control. Ripping of the landfill prior to planting also resulted in increased survival for the bahiagrass. Significant differences with respect to survival and metal uptake were not observed in plots that were inoculated with vesicular-arbuscular mycorrhizae (VAM) over those not inoculated. However, significant differences (p < 0.05) were observed in plant tissue concentrations of Al, Cr, Fe, Ni, and Zn in plots treated with ash over those of the topsoil and biosolid treatments. Results indicated that the use of soil amendments and subsurface (physical) treatments were essential for plant survival and that periodic monitoring of plant species should be continued to ensure that metal toxicity and secondary contaminant problems do not arise with time.

SOIL AMENDMENTS PROMOTE VEGETATION ESTABLISHMENT AND CONTROL ACIDITY IN COAL COMBUSTION WASTE

The effects of adding various soil amendments and a pyrite oxidation inhibitor to aid in the establishment of vegetation and to reduce acid drainage (AD) from coal fly ash and coal reject (FA + CR*) were assessed in an outdoor mesocosm study. Preliminary greenhouse experiments and field observations at the U.S. Department of Energy’s Savannah River Site (SRS) indicated that plants would not survive in this material without altering its physical and chemical characteristics. Samples of mixed FA + CR were obtained from a field site at the SRS. The following treatments were used: Biosolid only (Treatment A), Biosolid + Surfactant (Treatment B), Topsoil + Surfactant (Treatment C), and Biosolid + Topsoil + Surfactant (Treatment D). Leaching was induced due to inadequate rainfall. Loblolly pine seedlings (Pinus taeda) inoculated with ectomycorrhizal fungi — Pisolithus tinctorius (Pt) and Scleroderma cepa (Sc) — were transplanted into each mesocosm tank. Soil solution samplers were installed in each unit at 15 and 41 cm depths. Samples were taken periodically and measured for pH, EC, and other parameters.

Dissolution of Metals from Biosolid-Treated Soils by Organic Acid Mixtures

Results for the solubilization of metals from biosolid- (BSL-) treated soils by simulated organic acid-based synthetic root exudates (OA mixtures) of differing composition and concentrations are presented. This study used two BSL-treated Romona soils and a BSL-free Romona soil control that were collected from experimental plots of a long-term BSL land application experiment. Results indicate that the solubility of metals in a BSL-treated soil with 0.01 and 0.1 M OA mixtures was significantly higher than that of 0.001 M concentrations. Differences in composition of OAs caused by BSL treatment and the length of growing periods did not affect the solubility of metals. There were no significant differences in organic composition and metals extracted for plants grown at 2, 4, 8, 12, and 16 weeks. The amount of metals extracted tended to decrease with the increase of the pH. Results of metal dissolution kinetics indicate two-stage metal dissolution. A rapid dissolution of metals occurred in the first 15 minutes. For Cd, Cu, Ni, and Zn, approximately 60–70% of the metals were released in the first 15 minutes while the initial releases for Cr and Pb were approximately 30% of the total. It was then followed by a slow but steady release of additional metals over 48 hours.

488-D Ash Basin Vegetative Cover Treatibility Study

The 488-D Ash Basin is an unlined containment basin that received ash and coal reject material from the operation of a powerhouse at the USDOEs Savannah River Site, SC. They pyretic nature of the coal rejects has resulted in the formation of acidic drainage (AD), which has contributed to groundwater deterioration and threatens biota in down gradient wetlands. Establishment of a vegetative cover was examined as a remedial alternative for reducing AD generation within this system by enhanced utilization of rainwater and subsequent non-point source water pollution control. The low nutrient content, high acidity, and high salinity of the basin material, however, was deleterious to plant survivability. As such, studies to identify suitable plant species and potential adaptations, and pretreatment techniques in the form of amendments, tilling, and/or chemical stabilization were needed. A randomized block design consisting of three subsurface treatments (blocks) and five duplicated surface amendments (treatments) was developed. One hundred inoculated pine trees were planted on each plot. Herbaceous species were also planted on half of the plots in duplicated 1-m2 beds. After two growing seasons, deep ripping, subsurface amendments and surface covers were shown to be essential for the successful establishment of vegetation on the basin. This is the final report of the study.