In this study, disinfection effect of coliform group treated with ozone was analyzed for the effluent discharging from activated sludge treatment process in hospital wastewater treatment plant. Based on these results, it aims to get basic data to establish the disinfection facility in hospital wastewater treatment, suggesting affecting factors according to hydraulic retention time of the activated sludge process and design basic factors necessary to ozone disinfection. Removal efficiencies of coliform group for the effluent according to HRT such as 4hr, 8hr, 12hr were analyzed using a lab-scale activated sludge process, respectively. To decay the microorganism regulates the CT value multiplied disinfectant concentration by contact time. CT value is highly correlated with a removal efficiency of coliform group and according to increasing an injected ozone concentration, the CT value was increased.. When HRT was 4, 8, 12 hours , CT value takes place at minimum condition 50, 40, 334 mg/L-min, respectively.

The number of viable microorganism in drinking water was monitored according to storage temperature and storage period. The number of general bacteria in underground water was 10²-10^5CFU/ml and that of coliform group was decreased after 7days. The number of general bacteria in bottle water was increased until 7days but decreased after that day. Coliform group in bottle water were detected only 1 sample. The number of general bacteria in purified water was 10³-10⁴CFU/ml and 10²-10⁴CFU/ml at 8 and 25, respectively. Coliform group were not detected in purified water.

Using high voltage electric fields induced by high voltage AC (10-12 kV/cm, 20 kHz) and pulsed (20-30 kV/cm, 40 Hz) electric field generator as a semipermanent and environment-friendly disinfecting apparatus, the disinfection effect of coliform group in the effluent of sewage plant was investigated. The effects of electric field strength, treatment time, discharge area of a discharge tube, water quality factors (electric conductivity, pH and SS) on its death rate were examined. The death rate of coliform group was increased with increasing electric field strength and treatment time. For AC and pulsed electric field generator, the critical electric field strength was 6 kV/cm and 2 kV/cm, respectively, and the critical treatment time was 5 min and 2 min, respectively, regardless of electric field strength. Comparing the death rate of coliform group by AC and pulsed electric fields used in this study, its death rate was higher for the latter than the former, but did not increase linearly with increasing electric field strength. The results obtained for the effects of discharge area, electric conductivity, pH and SS on the death rate of coliform group using AC electric field (12 kV/cm, 20 kHz) were as follows: its death rate showed the trend to increase linearly with increasing discharge area; for the effect of electric conductivity, its death rate was increased with increasing electric conductivity, regardless of ionic species, increased with increasing cationic valency, but was similar between the same cationic valency; the pH 5～9 used in this study did not affect its death rate; its death rate was decreased with increasing SS concentration.