抄録
In order to investigate the condition of disinfection devices, the study was made at 75 domestic wastewater treatment plants about the relation between residual chlorine and the numbers of microorganisms in the chlorinated effluents, the change of bacteria flora during chlorination, and the factors necessary to detect the residual chlorine. The means for the chlorinated effluents were 1.5×102 CFU/ml of fecal coliforms, 5.8×102 CFU/ml of total coliforms, and 5.1 × 104 CFU/ml of standard plate count bacteria. The means of the bacteria removal rate during the disinfection process were 69.6% for fecal coliforms, 79.8% for total coliforms, and 90.3% for standard plate count bacteria, respectively. When free residual chlorine was over 0.1mg/l, fecal coliforms and total coliforms were practically non-detectable. As for total coliforms in the chlorinated effluents, 34.7% of the surveyed plants were under 30 CFU/ml, but 5.3% were over 3.0×103 CFU/ml which exceeds the effluent standard value.
In the secondary effluent in which standard plate count bacteria were 1.4×104 CFU/ml, besides Enterobacteriaceae, Alcaligenes sp., Flavobacterium sp., Moraxella sp., and Pseudomonas sp. were detected. But in the chlorinated effluent in which free residual chlorine was 1.5mg/l, only Bacillus sp. was detected. The important factors controlling the detection of free residual chlorine were the presence of a flow equalization tank, the presence of a disinfection device to maintain a sufficient water depth, and the NH4-N concentration in the inflow.
