No abstract

The A-01 wetland treatment system (WTS) is a surface flow wetland planted with giant bulrush [Schoenoplectus californicus (C.A. Mey.) Palla] that is designed to remove Cu and other metals from the A-01 National Pollution Discharge Elimination System (NPDES) effluent at the Savannah River Site near Aiken, SC. Copper, Zn, and Pb concentrations in water were usually reduced 60 to 80% by passage through the treatment system. The Cu concentrations in the wetland sediments increased from about 4 to 205 and 796 mg kg(-1), respectively, in the organic and floc sediment layers in cell 4A over a 5-yr period. Metal concentrations were higher in the two top layers of sediment (i.e., the floc and organic layers) than in the deeper inorganic layers. Sequential extraction was used to evaluate remobilization and retention of Cu, Pb, Zn, Mn, and Fe in the wetland sediment. Metal remobilization was determined by the potentially mobile fraction (PMF) and metal retention by the recalcitrant factor (RF). The PMF values were high in the floc layer but comparatively low in the organic and inorganic layers. High RF values for Cu, Zn, and Pb in the organic and inorganic layers indicated that these metals were strongly bound in the sediment. The RF values for Mn were lower than for the other elements especially in the floc layer, indicating low retention or binding capacity. Retention of contaminants was also evaluated by distribution coefficient (Kd) values. Distribution coefficient (Kd) values were lower for Cu and Zn than for Pb, indicating a smaller exchangeable fraction for Pb.

No abstract

Soil contaminated with U was the focus of this study in order to develop in-situ, U bio-immobilization technology. We have demonstrated microbial production of a metal chelating biopolymer, pyomelanin, in U contaminated soil from the Tims Branch area of the Department of Energy (DOE) Savannah River Site (SRS) as a result of tyrosine amendments. Bacterial densities of pyomelanin producers were >106 cells/g wet soil.Pyomelanin demonstrated U chelating and mineral binding capacities at pH 4 and 7. In laboratory studies, in the presence of goethite or illite, pyomelanin enhanced U sequestration by these minerals. Tyrosine amended soils in field tests demonstrated increased U sequestration capacity following pyomelanin production up to 13 months after tyrosine treatments.

No abstract

Apatite, Ca10(PO4)6(OH,F)2, has been successfully used as a soil amendment at numerous sites to immobilize metals and radionuclides. Such sites commonly contain multiple contaminants; the impact of apatite on these contaminants is expected to vary greatly. The objective of this study was to determine the influence of apatite on nontargeted sediment contaminants. Laboratory batch experiments were conducted under oxidized (several weekly wet/dry cycles) and reduced (water-saturated) conditions with a sediment collected from a wetland contaminated with numerous metals and radionuclides. Apatite additions resulted in the significant (p < or = 0.05) reduction of porewater Cd, Co, Hg, Pb, and U concentrations. However, apatite additions also resulted in the enhanced desorption of As, Se, and Th. Increases in porewater As and Se concentrations were the result of phosphate competitive exchange and not to the release of these contaminants directly from the apatite, which contained 29 mg kg(-1) As and 0.2 mg kg(-1) Se. Apatite additions increased porewater Th and organic C concentrations under oxidized (Eh = 497 mV) but not reduced (Eh = 65 mV) conditions. In the oxidized system, the leachate from the apatite treatment had a brown coloration and contained 226 mg L(-1) organic C, as compared to 141 mg L(-1) in the unamended samples. The desorbed organic C likely contained significant quantities of Th. This conclusion was supported by (i) the observation that porewater Th partitioned to hydrophobic resins, (ii) thermodynamic calculations which predicted that essentially all porewater Th existed as organic matter complexes, and (iii) there were significant correlations (r = 0.91, n = 8, p < or = 0.01) between porewater organic C and Th concentrations. Sediment additions of zero-valent iron particles along with the apatite eliminated the enhanced desorption of As, Se, and Th observed when only apatite was added. This study underscores the importance of monitoring the influence of sediment amendments on nontarget contaminants and provides examples of how the sediment additions of apatite can effectively immobilize some contaminants while enhancing the mobility of others.

A full‐scale constructed wetland treatment system consisting of four pairs of wetland cells (3.2 ha total area) with water flowing through a pair of cells in series prior to discharge was investigated. A retention basin provided stable water flow to the system. Water retention time in the wetland system was approximately 48 hours, and the wetland cells operated at circumneutral pH. Vegetation development within the cells has been excellent. Copper removal efficiency was greater than 75 % from the start‐up of the system, while mercury efficiency improved with maturation of the treatment cells. Sampling of the water course through the wetlands conducted during the fourth year of operation validated continued performance, and assessed the fate of a larger suite of metals present in the water. Copper and mercury removal efficiencies were still very high, both in excess of 80 % removal from the water after passage through the wetland system. Mercury removal continued along the entire water course through the system, while copper was removed almost immediately upon entering the wetland cells. Lead removal from the water by the system was 83 %, zinc removal was 60 %, and nickel was generally unaffected. Organic carbon in the water was also increased by the system and reduced the bioavailability of some metals. Operation and maintenance of the system continued to be minimal, and mainly consisted of checking for growth of the vegetation and free flow of the water through the system. The system was entirely passive, relying on gravity as the power source of water flow. No reportable permit exceedances have been experienced since the wetland began treating an outfall discharge.

The use of sequestering agents for the transformation of radionuclides in low concentrations in contaminated soils/sediments offers considerable potential for longterm environmental cleanup. This study evaluated the influence of four phosphate amendments and two microbial amendments on U availability. The synchrotron X-ray fluorescence mapping of the untreated U-contaminated sediment showed that U was closely associated with Mn. All tested phosphate amendments reduced aqueous U concentration more than 90%, likely due to formation of insoluble phosphate precipitates.The addition of A. piechaudii and P. putida alone were found to reduce U concentrations 63% and 31% respectively. Uranium sorption in phosphate treatments was significantly reduced in the presence of microbes. However, increased microbial activity in the treated sediment led to reduction of phosphate effectiveness. The average U concentration in 1 M MgCl 2 extract from U amended sediment was 437 µg/kg, but in the same sediment without microbes (autoclaved sediment), the extractable U concentration was only 103 µg/kg. When the autoclaved amended sediment was treated with autoclaved biological apatite, U concentration in the 1 M MgCl 2 extract was ~0 µg/kg. Together these tests suggest that microbes may enhance U leaching and reduce phosphate amendment remedial effectiveness.