Myoung-Soo Ko

Targeted removal of trichlorophenol in water by oleic acid-coated nanoscale palladium/zero-valent iron alginate beads.

A new material was developed and evaluated for the targeted removal of trichlorophenol (TCP) from among potential interferents which are known to degrade removal activity. To achieve TCP-targeted activity, an alginate bead containing nanoscale palladium/zero-valent iron (Pd/nZVI) was coated with a highly hydrophobic oleic acid layer. The new material (Pd/nZVI-A-O) preferentially sorbed TCP from a mixture of chlorinated phenols into the oleic acid cover layer and subsequently dechlorinated it to phenol. The removal efficacy of TCP by Pd/nZVI-A-O was not affected by co-existing organic substances such as Suwannee River humic acid (SRHA), whereas the material without the oleic acid layer (Pd/nZVI-A) became less effective with increasing SRHA concentration. The inorganic substances nitrate and phosphate significantly reduced the reactivity of Pd/nZVI-A, however, Pd/nZVI-A-O showed similar TCP removal efficacies regardless of the initial inorganic ion concentrations. The influence of bicarbonate on the TCP removal efficacies of both Pd/nZVI-A and Pd/nZVI-A-O was not significant. The findings from this study suggest that Pd/nZVI-A-O, with its targeted, constant reactivity for TCP, would be effective for treating this contaminant in surface water or groundwater containing various competitive substrates.

Identification of the microbes mediating Fe reduction in a deep saline aquifer and their influence during managed aquifer recharge

In this study, indigenous microbes enabling Fe reduction under saline groundwater conditions were identified, and their potential contribution to Fe release from aquifer sediments during managed aquifer recharge (MAR) was evaluated. Sediment and groundwater samples were collected from a MAR feasibility test site in Korea, where adjacent river water will be injected into the confined aquifer. The residual groundwater had a high salinity over 26.0 psu, as well as strong reducing conditions (dissolved oxygen, DO<2.0mg/L; oxidation-reduction potential, ORP<-100 mV) with high Fe(2+) concentrations. The indigenous microbes that mediate the reduction of Fe-minerals in this deep saline aquifer were found to be Citrobacter sp. However, column experiments to simulate field operation scenarios indicated that additional Fe release would be limited during MAR, as the dominant microbial community in the sediment would shift from Citrobacter sp. to Pseudomonas sp. and Limnohabitans sp. as river water injection alters the pore water chemistry.

Acid Rain Impact on Phytoavailability of Heavy Metals in Soils

ABSTRACT Soil heavy metal contamination and acid rain effects on terrestrial ecosystems are two major environmental problems of wide concern for some countries. Acid rain leads to great releases of soil heavy metals to surrounding ecosystem due to complicated soil chemical processes, mostly cation exchange and partly dissolution of minerals. In this study, the effects of acid rain on the transfer and phytoavailability of heavy metals to crop in contaminated soil was evaluated. A pot experiment was conducted to compare plant mechanism in various pH of acid rain treatment. The soil samples were collected from the paddy field in the vicinity of Janghang smelter. The Brassica campestris ssp. Pekinensis (Chinese cabbage) was used in this experiment. Each pot including Chinese cabbages was exposed to three conditions of simulated acid rain (pH 3.0/4.5/5.6) for 42 days. The results showed that phytoavailability of heavy metals were strongly controlled by pH of acid rain and lower pH can elevate the plant uptake of heavy metals, except for Pb. This indicates that acid rain has an adverse effect on surrounding ecosystems.

Identification of refined petroleum products in contaminated soils using an identification index for GC chromatograms

Hydrocarbons found in the environment are typically characterized by gas chromatography (GC). The shape of the GC chromatogram has been used to identify the source of petroleum contamination. However, the conventional practice of simply comparing the peak patterns of source products to those of environmental samples is dependent on the subjective decisions of individual analysts. We have developed and verified a quantitative analytical method for interpreting GC chromatograms to distinguish refined petroleum products in contaminated soils. We found that chromatograms for gasoline, kerosene, and diesel could be divided into three ranges with boundaries at C6, C8, C16, and C26. In addition, the relative peak area (RPAGC) of each range, a dimensionless ratio of the peak area within each range to that of the total range (C6–C26), had a unique value for each petroleum product. An identification index for GC chromatograms (IDGC), defined as the ratio of RPAGC of C8–C16 to that of C16–C26, was able to identify diesel and kerosene sources in samples extracted from artificially contaminated soils even after weathering. Thus, the IDGC can be used to effectively distinguish between refined petroleum products in contaminated soils.

Reductive dissolution and sequestration of arsenic by microbial iron and thiosulfate reduction

Iron oxide and oxy-hydroxide are commonly used for remediation and rehabilitation of arsenic (As)-contaminated soil and water. However, the stability of As sequestered by iron oxide and oxy-hydroxide under anaerobic conditions is still uncertain. Geochemical properties influence the behavior of As; in addition, microbial activities affect the mobility of sequestered As in soil and water. Microbial-mediated iron reduction can increase the mobility of As by reductive dissolution of Fe oxide; however, microbial-mediated sulfate reduction can decrease the mobility of As by sulfide mineral precipitation. This study investigated the geomicrobial impact on the behavior of As and stability of sequestered As in iron-rich sediment under anaerobic conditions. Increase in Fe(II) concentrations in water was evidence of microbial-mediated iron reduction. Arsenic concentrations increased with Fe(II) concentration; however, the thiosulfate reduction process also induced immobilization of As through the precipitation of AsFeS. Therefore, microbial-mediated iron reduction and thiosulfate reduction have opposite influences on the mobility of As under anaerobic condition.

Identifying Type of Refined Petroleum Products in Environmental Media: Thin-Layer Chromatography (TLC) as a Quick Methodology

The ultimate goal of our study is to establish thin-layer chromatography (TLC) as a quick and simple method for identifying the type of refined petroleum products present in the environmental media. As a preliminary step, TLC chromatograms of different petroleum products, including gasoline, kerosene, and diesel, were characterized and compared. Methanol was determined as the optimum carrier solution in TLC analysis. The spherical-shaped TLC chromatogram of gasoline showed the longest migration distance, and thus the highest retardation factor (Rf) of 0.91. This was followed by that of kerosene (0.63) with an elliptical-shaped, and diesel (0.24) with an elongated trapezoid-shaped chromatogram. Rf of kerosene and diesel increased with the dilution factor, while gasoline showed a constant value. Additionally, it was observed that the TLC chromatograms of oils produced the same peak pattern with the corresponding petroleum products in gas chromatography (GC). A mixed sample of kerosene and diesel presented a triangular shaped chromatogram, underlining the need to consider the shape of chromatogram in addition to the Rf value, as an indicator of the petroleum type. The findings indicate that TLC has a huge potential to be used as a quick and reliable method for identifying the type of refined petroleum products in the environmental media.