Recent toxicity information on dichloroacetic acid, one of drinking water disinfectant by-products was evaluated and the tolerable daily intake (TDI) via an oral administration was re-estimated. There are several new informations including metabolism, carcinogenicity and genotoxicity studies since the latest establishment of WHO drinking water quality guideline at 1992 was pronounced.
For general toxicity, TDI was calculated as 12.5 μg·kg^-1·d^-1 from LOAEL of 125 mg·kg^-1·d^-1, based on neurotoxicity in rats, divided by uncertainty factor of 10000. In addition to the evidence of carcinogenesis in the mouse liver, a recent chronic study demonstrated that dichloroacetic acid is also carcinogenic in the rat liver. Because there is no strong evidence for dichloroacetic acid-induced genotoxicity, TDI for carcinogenesis was considered as 3.6 μg·kg^-1·d^-1 from carcinogenic NOAEL of 3.6 mg·kg^-1·d^-1, divided by uncertainty factor of 1000. For reproductive/developmental toxicity, TDI was estimated as 104 μg·kg^-1·d^-1 from LOAEL of 31.25 mg·kg^-1·d^-1, based on testicular toxicity in rats, divided by uncertainty factor 300.

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Although pretreatment with acidified HBSS has been used to determine the viability of Cryptosporidium parvum oocysts via in-vitro excystation and/or DAPI/PI permeability assay, little information is available on the effect of pretreatment on viability. In this study, we evaluated the effect of different periods of incubation at 37°C in acidified HBSS on the viability of fresh oocysts and UV-irradiated oocysts, using both excystation assay and DAPI/PI permeability assay. The effect of incubation time on the viability of oocysts differed not only between the two assays but also between the fresh oocysts and the UV-irradiated oocysts. Appropriate preincubation time common to both fresh oocysts and UV-irradiated oocysts for maximal viability was 5 min in the excystation assay. In contrast, preincubation was found to reduce viability in the DAPI/PI permeability assay, and is therefore not recommended for this assay.

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The new method for umu test using the automatic detection device is constructed as a simple method to monitor the safety of the environmental water. This device applies the CFA (Continuous Flow Analysis) method using AutoAnalyzer II (Bran+Luebbe). After addition of samples and phosphate-buffer, the culture is incubated for 1.5 hours in the teflon tube wound in a coil in the 36°C water bath. Then β-galactosidase enzymatic reaction is acted in the teflon-tube coil. The absorbance is measured at 600nm and 420nm in the spectrophotometers with a flow cell which are controlled by Visual Basic program. AF-2, 4-NQO and 2-AA which are major mutagens were measured by both this new method and the usual manual method of umu test. The automatic detection device was more sensitive than usual method and had higher accuracy (CV = 5.5-12.1%) than usual method (CV = 11.1-14.9%). This result suggests that this automatic detection device can be used as the monitoring methods.

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In order to improve nitrogen and phosphorus removal efficiencies at low water temperature, intermittent aeration batch activated sludge process combined with biofilm process (media-added batch activated sludge process) was applied and its treatment performance was investigated for a different packing rate of string contact media with range of 0-21%. With the increase of packing rate of contact media, successful nitrification occurred. However, the dentrification efficiency decreased at the packing rate of 21%. This is because the relatively high DO concentration at the packing rate of 21% was not suitable for the denitrification condition. The optimal packing rate of media was 13% for simultaneous removal of BOD and nitrogen at 10°C.
Removal efficiencies of BOD, DTN (disoluble total nitrogen) and DTP (disoluble total phosphorus) were 90%, 31% and 20%, respectively under operating condition of 3cycle a day at 10°C. Moreover, removal efficiencies of BOD, DTN and DTP increased to 94%, 64% and 22%, respectively by combining with biofilm process. Nitrogen removal efficiency was significantly enhanced.
In spite of introduction of biofilter process, removal efficiency of phosphorus was not improved. It was observed that anaerobic phosphorous release and aerobic phosphorous uptake was significantly affected by low water temperature.
As a biological removal of phosphorus cannot be expected at low water temperature, it is necessary to consider the combination with a physical treatment method.

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The NH₄⁺ exchange capacity of natural zeolite depends on the location of extraction and on the ion contents of the waste water to be treated. The NH₄⁺ exchange capacity is determined for each zeolite and waste water sample individually in the current design method of NH₄⁺ removal equipment. Therefor, these results cannot be generally applied to other cases. In this study, the equation to obtain the design velocity of treatment through the zeolite packed cloumn by the cation exchange capacity and particle size of zeolite as well as the ammonium concentration and temperature of water was investigated. In addition, the experimental equation to show the ion exchange equilibrium from cation contents was obtained. On the basis of the investigation, the simple method to obtain the design variables was developed.

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A countercurrent extractor (204φ × 4,260mm) was designed to remove organic pollutants from aqueous solutions by supercritical carbon dioxide and the optimum operating conditions were studied and the method was subsequently evaluated. Aqueous solutions containing dissolved aromatic nitro-compounds were treated by 9.81 × 10⁶ Pa supercritical carbon dioxide at 35°C. A high removal efficiency was attained by filling up the whole space of column with the continuous aqueous phase using a differential pressure gauge to control the interface level of aqueous phase. 100 and 400 mg·l^-1 of nitrobenzene (NB) aqueous solutions were treated at space velocity (SV) of 1.5 or 4.0 h^-1. The residual ratio of NB in effluent water was not influenced by SV, but influenced by the concentration of NB in influent water and the ratio of solvent to feed (S/F value). When SV was below 4.0 h^-1, 100 and 400mg·l^-1 of NB could be removed sufficiently from the aqueous solution at 0.55 and 0.7 of S/F value, respectively. O-nitrophenol could be removed in the same order as NB, and o-nitrotoluene could be removed much more than both.

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