Flocculation using titanium tetrachloride (TiCl 4 ) as a coagulant is an efficient and economical application because the flocculated sludge can be recycled to produce a valuable byproduct, namely titanium dioxide (TiO 2 ) nanoparticles. However, toxicity of TiCl 4 has not yet been assessed while it is used in water treatment. The aquatic toxicity of TiCl 4 flocculation process was investigated to assess the environmental safety of the coagulant. D. magna and V. fischeri bioassays were carried out to evaluate the supernatant toxicity after TiCl 4 flocculation. Artificial wastewater, biologically treated sewage effluent and seawater were used to study the toxicity of TiCl 4 flocculation. Results showed that supernatant toxicity was very low when TiCl 4 flocculation was conducted (no observed effect concentration = 100 mg/L and lowest observed effect concentration = 150 mg/L exposed to D. magna and V. fischeri, respectively). Similarly, TiO 2 nanoparticles recovered from wastewater and seawater flocculated sludge were also found to have low toxicity. The regenerated TiO 2 nanoparticles indicated low toxicity values when compared to the commercial-TiO 2 nanoparticle, P-25.

Perchlorate is an unregulated contaminant, and recently, many cases of perchlorate contamination have been reported in the US. Unregulated contaminants (e.g. perchlorate) in drinking water are also of significant concern in Korea. We investigated perchlorate levels in tap water, river water, and sewerage water at 4 major water sources in Korea from June 2006. Tap water samples in the Nakdong River basin contained high perchlorate levels. Of the other sampling sites, one at Daegu showed the highest perchlorate level, 22.3 μg/L. The first 2 investigations of raw water sources for drinking water in the Nakdong River basin, found relatively high perchlorate concentration, 18.7–95.6 μg/L and 4.0–25.6 μg/L. The high perchlorate concentration in the Nakdong River basin was possibly derived from waste water discharged by an LCD (liquid crystal display) manufacturing factory in Gumi. The perchlorate concentration of waste water from the nearby sewerage water treatment plant was 730–1,858 μg/L. We modified the waste water treatment operation system at the LCD factory to reduce the perchlorate emissions from this source. The modified treatment system reduced the perchlorate concentration in the final effluent to 40–70 μg/L. Source reduction was successfully achieved by the modified treatment process and by using a perchlorate-free etching reagent.