Hun Je Jo

Toxicity identification in metal plating effluent: Implications in establishing effluent discharge limits using bioassays in Korea

Because of complexity and diversity of toxicants in effluent, chemical analysis alone gives very limited information on identifying toxic chemicals to test organisms. Toxicity identification evaluation (TIE) techniques have been widely used to identify toxicants in various samples including industrial wastewater as well as natural waters. In response to new regulation for effluent discharge in Korea, which will be effective from 2011, a necessity of studies emerges that investigates toxicity levels in industrial effluents. This work was a preliminary study examining toxicity levels in effluent from one metal plating factory using Daphnia magna (48 h immobility) and identifying toxicity-causing substances. Toxicity tests showed variability on different sampling occasions and the results of TIE methods indicated that both organic compounds and metals contributed to the observed toxicity in metal plating effluent. Further studies are necessary to help reduce effluent toxicity especially from direct dischargers, who will have to comply with the new regulation.

Combined effects of water quality parameters on mixture toxicity of copper and chromium toward Daphnia magna.

In this study, a central composite design (CCD) was employed to evaluate the combined effects of pH, hardness and dissolved organic carbon (DOC) on the toxicity of a mixture of Cu(II) and Cr(VI) toward Daphnia magna. Overall, the results showed that increases in pH, hardness and DOC concentration led to decreased mixture toxicity of Cu(II) and Cr(VI) by reducing the concentrations of toxic species such as Cu(2+) and HCrO(4)(-). In addition, empirical models for the prediction of 24-h and 48-h mortalities of D. magna were developed and validated by using three different sources of dissolved organic matter (DOM). Because the DOMs had different Cu(II)-binding capacities, the empirical models were revised using the ligand concentration of DOMs instead of the DOC concentration; however, the prediction capability of these models did not differ significantly. These results suggest that it is not likely that the chemical property of DOM is important for prediction of the mixture toxicity of Cu(II) and Cr(VI) toward D. magna when the ligand concentration of DOMs greatly exceed the Cu(II) concentration.

A toxicity monitoring study on identification and reduction of toxicants from a wastewater treatment plant.

In this study, toxicity of effluents in a wastewater treatment plant and of receiving water in an adjacent stream was periodically monitored from November 2007 to June 2008, in order to trace and reduce sources of toxicants. The results showed that toxicity of final effluent (FE) changed greatly over different sampling events, and appeared to have impacts on toxicity of downstream water with a significant correlation (r(2)=0.87, p<0.05). In particular, FE toxicity was always higher than that of secondary effluent (SE). Toxicity identification evaluation (TIE) for the FE sample collected in March 2008 showed that FE toxicity was attributed to low quality of Fenton reagent with Zn contamination used for SE treatment. Furthermore, Zn concentrations in FE samples significantly correlated with FE toxicity during the sampling period (r(2)=0.95, p<0.05). After changing the Fenton reagent to one containing low Zn, Zn concentration and toxicity of FE greatly decreased in the following months.

Enhancement of biodegradability of EDTA by gamma-ray treatment

Radiation treatment with gamma-rays was used to improve the biodegradability of EDTA that is known to be a non-biodegradable substance. The effect of metal ions and catalysts on the treatment of EDTA was studied first. The removal of EDTA was definitely decreased in the presence of metal ions such as Cr(III), Cd(II), Pb(II) and Cu(II) at doses greater than 3 kGy. The addition of a TiO2