Distribution characteristics of polychlorinated biphenyls in crucian carp (Carassius auratus) from major rivers in Korea

Polychlorinated biphenyls (PCBs) levels in crucian carp were determined at 20 locations along four major river systems, several small-scale rivers and a wetland in Korea. Twenty-eight congeners, ranging from tri- to hepta-CBs were detected. A gas chromatograph with a mass selective detector was used to quantify the individual PCB congeners. The objectives of this study were to investigate the levels of contamination of PCBs in freshwater fish and to observe the pattern of their distribution. The sampling locations were chosen among 31 sampling sites that are currently used as environmental residue checkpoints by the Korean Ministry of Environment. Concentrations of individual congeners ranged from not detectable (n.d.) to 0.75 ng g(-1) on a wet weight basis. The total concentrations of PCBs at each site ranged from n.d. to 5.41 ng g(-1) of wet weight. The most heavily contaminated site was the Nakdong estuary located near the Shinpyung-Janglim factory district. The PCB 153 and 138 were the principal congeners and penta- and hexa-chlorinated biphenyls comprised the main congener groups.     

Bio-reduction of arsenate using a hydrogen-based membrane biofilm reactor

Arsenate (As(V)) is a carcinogen and a significant problem in groundwater in many parts of the world. Since As(III) is generally more mobile and more toxic than As(V), the reduction of As(V) to As(III) is not a conventional treatment goal. However, reducing As(V) to As(III) may still be a means for decontamination, because As(III) can be removed from solution by precipitation or complexation with sulfide or by adsorption to Fe(II)-based solids. A promising approach for reducing oxidized contaminants is the H2-based membrane biofilm reactor (MBfR). In the case of arsenate, the MBfR allows bio-reduction of As(V) to As(III) and sulfate to sulfide, thereby giving the potential for As removal, such as by precipitation of As2S3(s) or formation of Fe(II)-based solids. When As(V) was added to a denitrifying MBfR, As(V) was reduced immediately to As(III). Decreasing the influent sulfate loading increased As(V) reduction for a fixed H2 pressure. A series of short-term experiments elaborated on how As(V) loading, nitrate and sulfate loadings, and H2 pressure controlled As(V) reduction. Lower nitrate loading and increased As(V) loading increased the extent of As(V) reduction, but increased H2 pressure did not increase As(V) reduction. As(V) reduction was sensitive to sulfate loading, with a maximum As(V)-removal percentage and flux with no addition of sulfate. As(III) could be precipitated with sulfide or adsorbed to Fe(II) solids, which was verified by scanning electron microscopy and energy dispersive X-ray analysis.     

Relation of RNA/DNA ratios to growth for the scallop Euvola (Pecten) ziczac in suspended culture

We examined the relation of RNA/DNA ratios to growth for three size groups of the tropical scallop Euvola ziczac maintained in suspended culture at 8, 21 and 34 m in depth in the Golfo de Cariaco, Venezuel. Various growth parameters indicated that production decreased with depth. This was more likely due to a decrease in seston quality with depth than to temperatures or seston abundance (which were similar at the various depths studied). The RNA/DNA ratio was correlated with the G-index of muscle growth for juveniles (r ²=0.55). A much weaker correlation was observed for the maturing scallops (r ²=0.18), probably because of the interaction between reproductive and somatic growth. In fully mature scallops, somatic growth was negligible and the RNA/DNA ratios appeared to be inversely related to the level of physiological stress of the scallops. Whereas RNA/DNA ratios are difficult to interpret for maturing E. ziczac, because an increased ratio can be due to either increased gonadal or somatic growth, they are useful in predicting growth in juveniles and physiological stress in fully mature scallops.     

Biotreatment of H2S- and NH3-containing waste gases by co-immobilized cells biofilter

Gas mixture of H2S and NH3 in this study has been the focus in the research area concerning gases generated from the animal husbandry and the anaerobic wastewater lagoons used for their treatment. A specific microflora (mixture of Thiobacillus thioparus CH11 for H2S and Nitrosomonas europaea for NH3) was immobilized with Ca-alginate and packed inside a glass column to decompose H2S and NH3. The biofilter packed with co-immobilized cells was continuously supplied with H2S and NH3 gas mixtures of various ratios, and the removal efficiency, removal kinetics, and pressure drop in the biofilter was monitored. The results showed that the efficiency remained above 95% regardless of the ratios of H2S and NH3 used. The NH3 concentration has little effect on H2S removal efficiency, however, both high NH3 and H2S concentrations significantly suppress the NH3 removal. Through product analysis, we found that controlling the inlet ratio of the H2S/NH3 could prevent the biofilter from acidification, and, therefore, enhance the operational stability. Conclusions from bioaerosol analysis and pressure drop in the biofilter suggest that the immobilized cell technique creates less environmental impact and improves pure culture operational stability. The criteria for the biofilter operation to meet the current H2S and NH3 emission standards were also established. To reach Taiwan's current ambient air standards of H2S and NH3 (0.1 and 1 ppm, respectively), the maximum inlet concentrations should not exceed 58 ppm for H2S and 164 ppm for NH3, and the residence time be kept at 72 s.     

Comparative study of H(2)O(2) and O3 effects on radiation treatment of TCE and PCE

The effects of H(2)O(2) and O(3) on the decomposition of trichloroethylene (TCE) and perchloroethylene (PCE) by gamma-rays (gamma-rays) were investigated in this work. The combined gamma-rays/O(3) process showed a synergistic effect and enhanced the removal of TCE and PCE compared with gamma-rays alone, but, the gamma-rays/H(2)O(2) process did not increase the removal. This interesting result was successfully identified by an electron paramagnetic resonance spectroscopy/spin-trapping method that can quantify hydroxyl radicals, which is directly related to the efficiency of TCE and PCE decomposition. For gamma-rays/H(2)O(2) system, there was no difference of hydroxyl radical production between gamma-rays alone and gamma-rays/H(2)O(2). This indicates gamma-rays cannot activate H(2)O(2) to produce hydroxyl radicals and this causes no increase of TCE and PCE removals. To the contrary, the production of hydroxyl radicals was obviously increased in the case of gamma-rays/O(3) process. This suggests additional hydroxyl radicals are produced from the reaction of O(3) with the irradiation products of water such as hydrated electrons, hydrogen atoms, etc. and this accelerates the removal of TCE and PCE.     

Solar photocatalytic decolorization of methylene blue in water

In this study, a photocatalytic decolorization system equipped with immobilized TiO2 and illuminated by solar light was used to remove the color of wastewater. To examine the decoloring efficiency of this system, photocatalytic decolorization of an organic dye such as methylene blue was studied as an example. The effects of light source, pH, as well as the initial concentration of dye were also investigated. It was observed that the solution of methylene blue could be almost completely decolorized by the solar light/TiO2 film process while there was about 50% color remaining with solar irradiation only. In addition, it was found that the decoloring efficiency of solution was higher with solar light irradiation than with artificial UV light irradiation, even though the artificial UV light source supplied higher UV intensity at 254 nm. The color removal rate of methylene blue with solar light irradiation was almost twice that of artificial UV light irradiation. This phenomena was mainly attributed to that some visible light range of solar light was useful for exciting the methylene blue molecules adsorbed on TiO2 film, leading to a photosensitization process undergoing and decoloring efficiency promoted. This solar-assisted photocatalytic device showed potential application for decoloring organic dyes in wastewater.     

Mechanism of effective nocardioform foam control measures for non-selector activated sludge systems.

Solids retention time (SRT), biological scum trapping and recycle, and the dynamic equilibrium between Nocardioform populations in the foam and the mixed liquor are the controlling factors in activated sludge foaming events caused by Nocardioform bacteria. For the operating modes described in this paper, a cured mixed liquor foaming condition (filament counts of approximately 10(5) intersections/g volatile suspended solids) was only achieved when SRT control, selective wasting, and polymer addition were in effect. Solids retention time control, with the SRT remaining below 1.5 days, and selective wasting will cure a severely foaming mixed liquor, but effects will only be observed after 3 or 4 months after implementation. The combined wastage of Nocardioform bacteria from selective wasting and SRT control can ensure long-term foam control to the operation of a pure-oxygen activated sludge system with foam-trapping features. An SRT of 0.3 days will result in the complete washout of Nocardioform bacteria from the activated sludge system, which can then operate at an SRT of 3 days free of Nocardioform. Polymer addition to mixed liquor is only effective for foam control when a large portion of the system biomass exists as a heavy layer of foam above the mixed liquor.