Leaching mechanisms of Cr(VI) from chromite ore processing residue

Batch leaching tests, qualitative and quantitative x-ray powder diffraction (XRPD) analyses, and geochemical modeling were used to investigate the leaching mechanisms of Cr(VI) from chromite ore processing residue (COPR) samples obtained from an urban area in Hudson County, New Jersey. The pH of the leaching solutions was adjusted to cover a wide range between 1 and 12.5. The concentration levels for total chromium (Cr) and Cr(VI) in the leaching solutions were virtually identical for pH values >5. For pH values <5, the concentration of total Cr exceeded that of Cr(VI) with the difference between the two attributed to Cr(III). Geochemical modeling results indicated that the solubility of Cr(VI) is controlled by Cr(VI)-hydrocalumite and Cr(VI)-ettringite at pH >10.5 and by adsorption at pH <8. However, experimental results suggested that Cr(VI) solubility is controlled partially by Cr(VI)-hydrocalumite at pH >10.5 and by hydrotalcites at pH >8 in addition to adsorption of anionic chromate species onto inherently present metal oxides and hydroxides at pH <8. As pH decreased to <10, most of the Cr(VI) bearing minerals become unstable and their dissolution contributes to the increase in Cr(VI) concentration in the leachate solution. At low pH ( <1.5), Cr(III) solid phases and the oxides responsible for Cr(VI) adsorption dissolve and release Cr(III) and Cr(VI) into solution.     

Bio-reduction of N-nitrosodimethylamine (NDMA) using a hydrogen-based membrane biofilm reactor

N-Nitrosodimethylamine (NDMA) is a disinfection by-product shown to be carcinogenic, mutagenic, and teratogenic. A feasible detoxification pathway for NDMA is a three-step bio-reduction that leads to ammonia and dimethylamine. This study examines the bio-reduction of NDMA in a H2-based membrane biofilm reactor (MBfR) that also is active in nitrate and sulfate reductions. In particular, the study investigates the effects of H2 availability and the relative loadings of NDMA, nitrate, and sulfate, which potentially are competing electron acceptors. The results demonstrate that NDMA was bio-reduced to a major extent (i.e., at least 96%) in a H2-based MBfR in which the electron-equivalent fluxes from H2 oxidation were dominated by nitrate and sulfate reductions. NDMA reduction kinetics responded to NDMA concentration, H2 pressure, and the presence of competing acceptors. The most important factor controlling NDMA-reduction kinetics was the H2 availability, controlled primarily by the H2 pressure, and secondarily by competition from nitrate reduction.     

Influence of a soil enzyme on iron-cyanide complex speciation and mineral adsorption

Cyanide is commonly found as ferrocyanide [Fe(II)(CN)(6)](-4) and in the more mobile form, ferricyanide [Fe(III)(CN)(6)](-3) in contaminated soils and sediments. Although soil minerals may influence ferrocyanide speciation, and thus mobility, the possible influence of soil enzymes has not been examined. In a series of experiments conducted under a range of soil-like conditions, laccase, a phenoloxidase enzyme derived from the fungi Trametes versicolor, was found to exert a large influence on iron-cyanide speciation and mobility. In the presence of laccase, up to 93% of ferrocyanide (36-362ppm) was oxidized to ferricyanide within 4h. No significant effect of pH (3.6 and 6.2) or initial ferrocyanide concentration on the extent or rate of oxidation was found and ferrocyanide oxidation did not occur in the absence of laccase. Relative to iron-cyanide-mineral systems without laccase, ferrocyanide adsorption to aluminum hydroxide and montmorillonite decreased in the presence of laccase and was similar to or somewhat greater than that of ferricyanide without laccase. Laccase-catalyzed conversion of ferrocyanide to ferricyanide was extensive though up to 33% of the enzyme was mineral-bound. These results demonstrate that soil enzymes can play a major role in ferrocyanide speciation and mobility. Biotic soil components must be considered as highly effective oxidation catalysts that may alter the mobility of metals and metal complexes in soil. Immobilized enzymes should also be considered for use in soil metal remediation efforts.     

Comparison of the removal efficiency of endocrine disrupting compounds in pilot scale sewage treatment processes

The removal efficiency of endocrine disrupting compounds from effluents using pilot scale sewage treatment processes, including various treatment technologies, such as membrane bioreactors (MBR), nanofiltration (NF) and reverse osmosis (RO) for the purpose of water reuse, were estimated and compared. The calculated estrogenic activity, expressed in ng-EEQ/l, based on the concentration detected by GC/MS, and relative potencies for each target compound were compared to those measured using the E-screen assay. The removal efficiencies for nonylphenol, was within the range of 55-83% in effluents. High removal efficiencies of approximately >70% based on the detection limits were obtained for bisphenol A, E1, EE2 and genistein with each treatment processes, with the exception of E1 ( approximately 64%) using the MBR process. The measured EEQ values for the effluents from the MBR, NF and RO processes also indicated low estrogenic activities of 0.65, 0.23 and 0.05 ng-EEQ/l, respectively. These were markedly reduced values compared with the value of 1.2 ng-EEQ/l in influent. Consequently, the removals of EDCs in terms of the EEQ value from the biological and chemical determinations were sufficiently achieved by the treatment process applied in this study, especially in the cases of the NF and RO treatments.     

Effect of a seasonal diffuse pollution migration on natural organic matter behavior in a stratified dam reservoir

This article aims to describe the influence of diffuse pollution on the temporal and spatial characteristics of natural organic matter (NOM) in a stratified dam reservoir, the Daecheong Dam, on the basis of intensive observation results and the dynamic water quality simulation using CE-QUAL-W2. Turbidity is regarded as a comprehensive representation of allochothonous organic matter from diffuse sources in storm season because the turbidity concentration showed reasonable significance in a statistical correlation with the UV absorbance at 254 nm and total phosphorus. CE-QUAL-W2 simulation results showed good consistency with the observed data in terms of dissolved organic matter (DOM) including refractory dissolved organic carbon (RDOC) and labile DOC and also well explained the internal movement of constituents and stratification phenomenon in the reservoir. Instead turbidity and NOM were related well in the upper region of the reservoir according to flow distance, gradually as changing to dissolved form of organic matter, RDOM affected organic matter concentration of reservoir water quality compared to turbidity. To control the increase of soluble organic matters in the dam reservoir, appropriate dam water discharge gate operation provided effective measurement. Because of the gate operation let avoid the accumulation of organic matter within a dam reservoir by shorten of turbid regime retention time.     

Application of eggshell waste for the immobilization of cadmium and lead in a contaminated soil

Liming materials have been used to immobilize heavy metals in contaminated soils. However, no studies have evaluated the use of eggshell waste as a source of calcium carbonate (CaCO?) to immobilize both cadmium (Cd) and lead (Pb) in soils. This study was conducted to evaluate the effectiveness of eggshell waste on the immobilization of Cd and Pb and to determine the metal availability following various single extraction techniques. Incubation experiments were conducted by mixing 0-5% powdered eggshell waste and curing the soil (1,246 mg Pb kg?1 soil and 17 mg Cd kg?1 soil) for 30 days. Five extractants, 0.01 M calcium chloride (CaCl?), 1 M CaCl?, 0.1 M hydrochloric acid (HCl), 0.43 M acetic acid (CH?COOH), and 0.05 M ethylendiaminetetraacetic acid (EDTA), were used to determine the extractability of Cd and Pb following treatments with CaCO? and eggshell waste. Generally, the extractability of Cd and Pb in the soils decreased in response to treatments with CaCO? and eggshell waste, regardless of extractant. Using CaCl? extraction, the lowest Cd concentration was achieved upon both CaCO? and eggshell waste treatments, while the lowest Pb concentration was observed using HCl extraction. The highest amount of immobilized Cd and Pb was extracted by CH?COOH or EDTA in soils treated with CaCO? and eggshell waste, indicating that remobilization of Cd and Pb may occur under acidic conditions. Based on the findings obtained, eggshell waste can be used as an alternative to CaCO? for the immobilization of heavy metals in soils.     

Distribution and structure of heterotrophic protist communities in the northeast equatorial Pacific Ocean

The distribution and structure of heterotrophic protist communities and size-fractionated chlorophyll a were studied during the Korea Deep Ocean Study 98 (KODOS 98) research expedition (July 1998) in the northeast equatorial Pacific Ocean (5–11°N). Areas of convergence and divergence formed at the boundaries of the South Equatorial Current (SEC), North Equatorial Current (NEC), and North Equatorial Counter Current (NECC) during the expedition. Water column physicochemical characteristics significantly influenced the size structure of heterotrophic protist communities. Intense vertical mixing and high nutrient and chlorophyll a concentrations characterized SEC and NECC areas, which were affected by converging and diverging water masses, respectively. Nanophytoplankton dominated in SEC and NECC areas; both areas also had relatively high heterotrophic protist biomasses (average 743 µg C m^–2). NEC areas were characterized by a stratified vertical structure, low nutrient and chlorophyll a concentrations, and picophytoplankton dominance. The heterotrophic protist biomass in NEC areas averaged 414 µg C m^–2; nanoprotists (<20 µm) dominated the community. The nanoprotist biomass comprised 49–54% of the total heterotrophic protist biomass in SEC/NECC areas and 67–72% in NEC areas. The biomass of heterotrophic protists was higher in SEC/NECC areas than in NEC areas, but the relative importance of nanoprotists was greater in NEC areas than in SEC/NECC areas. Heterotrophic dinoflagellates were dominant components of the <20 µm and >20 µm size classes in both water columns. The biomass of heterotrophic protists significantly correlated with the net-, nano-, and picophytoplankton biomass in SEC/NECC areas and with the nano- and picophytoplankton biomass in NEC areas. Heterotrophic protists and phytoplankton also showed strong positive correlation in the study area. The size structure of the phytoplankton biomass coincided with that of heterotrophic protists; the heterotrophic protist biomass positively correlated with the protists prey source. These relationships suggest that the community structure of heterotrophic protists and the microbial food web depended on size classes within the phytoplankton biomass. Microzooplankton grazing and phytoplankton growth rates were higher in SEC/NECC areas than in NEC areas. In contrast, the potential primary production grazed by microzooplankton was relatively high in NEC areas (127.3%) compared with SEC/NECC areas (94.6%). Our results indicate that the relative importance and size structure of heterotrophic protists might vary according to two distinct water column structures.Communicated by T. Ikeda, Hakodate     

Heavy metal immobilization in soil near abandoned mines using eggshell waste and rapeseed residue

Heavy metal contamination of agricultural soils has received great concern due to potential risk to human health. Cadmium and Pb are largely released from abandoned or closed mines in Korea, resulting in soil contamination. The objective of this study was to evaluate the effects of eggshell waste in combination with the conventional nitrogen, phosphorous, and potassium fertilizer (also known as NPK fertilizer) or the rapeseed residue on immobilization of Cd and Pb in the rice paddy soil. Cadmium and Pb extractabilities were tested using two methods of (1) the toxicity characteristics leaching procedure (TCLP) and (2) the 0.1 M HCl extraction. With 5 % eggshell addition, the values of soil pH were increased from 6.33 and 6.51 to 8.15 and 8.04 in combination with NPK fertilizer and rapeseed residue, respectively, compared to no eggshell addition. The increase in soil pH may contribute to heavy metal immobilization by altering heavy metals into more stable in soils. Concentrations of TCLP-extracted Cd and Pb were reduced by up to 67.9 and 93.2 % by addition of 5 % eggshell compared to control. For 0.1 M HCl extraction method, the concentration of 0.1 M HCl-Cd in soils treated with NPK fertilizer and rapeseed residue was significantly reduced by up to 34.01 and 46.1 %, respectively, with 5 % eggshell addition compared to control. A decrease in acid phosphatase activity and an increase in alkaline phosphatase activity at high soil pH were also observed. Combined application of eggshell waste and rapeseed residue can be cost-effective and beneficial way to remediate the soil contaminated with heavy metals.     

Selective adsorption of phenanthrene dissolved in surfactant solution using activated carbon

Selective adsorption of a hazardous hydrophobic organic compound (HOC) by activated carbon as a means of recovering surfactants after a soil washing process was investigated. As a model system, phenanthrene was selected as a representative HOC and Triton X-100 as a nonionic surfactant. Three activated carbons that differed in size (Darco 20–40 (D20), 12–20 (D12) and 4–12 (D4) mesh sizes) were used in adsorption experiments. Adsorption of surfactant onto activated carbon showed a constant maximum above the critical micelle concentration, which were 0.30, 0.23, 0.15 g g⁻¹ for D20, D12, and D4, respectively. Selectivity for phenanthrene to Triton X-100 was much higher than 1 over a wide range of activated carbon doses (0–6 g l⁻¹) and initial phenanthrene concentrations (10–110 mg l⁻¹). Selectivity generally increased with decreasing particle size, increasing activated carbon dose, and decreasing initial concentration of phenanthrene. The highest selectivity was 74.9, 57.3, and 38.3 for D20, D12, and D4, respectively, at the initial conditions of 10 mg l⁻¹ phenanthrene, 5 g l⁻¹ Triton X-100 and 1 g l⁻¹ activated carbon. In the case of D20 at the same conditions, 86.5% of the initial phenanthrene was removed by sorption and 93.6% of the initial Triton X-100 remained in the solution following the selective adsorption process. The results suggest that the selective adsorption by activated carbon is a good alternative for surfactant recovery in a soil washing process.     

Influence of plant growth promoting bacteria and Cr6+ on the growth of Indian mustard

The Cr(6+) resistant plant growth promoting bacteria (PGPB), Pseudomonas sp. PsA4 and Bacillus sp. Ba32 were isolated from heavy metal contaminated soils and their plant growth promoting activity on the Indian mustard (Brassica juncea) were assessed with different concentrations of Cr(6+) in soil. Production of siderophores and the solubilization of phosphate were observed in both strains, PsA4 and Ba32. Production of IAA was only observed in strain PsA4. Inoculation of PsA4 or Ba32 promoted the growth of plants at 95.3 and 198.3 microg of Cr(6+)g(-1) soil. The maximum growth was observed in the plants inoculated with strain PsA4. Both strains, PsA4 and Ba32 did not influence the quantity of accumulation of chromium in root and shoot system. The present observations showed that the strains PsA4 and Ba32 protect the plants against the inhibitory effects of chromium, probably due to the production of IAA, siderophores and solubilization of phosphate.