Analysis on the Performance Evaluation of a High-Speed Filtering Apparatus for the Treatment of Combined Sewer Overflows (CSOs)

Abstract

In this study, the generation characteristics of the Combined Sewer Overflows (CSOs) that occur in urban areas were investigated. In addition, performance evaluation of the CSO treatment efficiency was conducted through the field application of a high-speed filtering apparatus using a fibrous filter medium for the treatment of the CSOs that occurred in an urban area. The study site, a city located in Seoul, South Korea, was one that included the typical residential and commercial districts. The daily average flow rate of the Eungbong drainage area, which was the study site, was 92.5 m 3 /hr during the dry season, and the daily average flow rate ranged from 70.2 to 129.2 m 3 /hr, indicating a wide daily-average-flow-rate range. The highest flow rate was shown at around 9 a.m. on weekdays and at around 11 a.m. on weekends. The average influent concentrations that occurred during the dry season were 19.0 mg/L (BOD), 15.9 mg/L (COD), 10.9 mg/L (SS), 33.9 mg/L (TN), and 0.5mg/L (TP), and the hourly concentration ranges turned out to be 4.1~43.5 mg/L (BOD), 9.5~26.8 mg/L (COD), 3.6~33.0 mg/L (SS), 25.5~52.2 mg/L (TN), and 0.4~0.9 mg/L (TP). The results of the field application of a high-speed filtering apparatus using a fibrous filter medium showed that the average treatment efficiency of SS was 63.7% during the dry season. The average treatment efficiency of SS during rainfall was 84.2% (1 st ), 88.0% (2 nd ), 87.5% (3 rd ), 85.8% (4 th ), 75.8% (5 th ), 75.5% (6 th ), and 90.3% (7 th ), and exhibiting more than 80% treatment efficiency. In the case of organic contaminants like BOD, however, low treatment efficiency (less than 30%) appeared. Judging from the above results, it is difficult to expect a treatment effect if the influent concentration is less than 30 mg/L in the case of an organic material when the high-speed filtering apparatus is applied to the site, and even in the case of an influent concentration of more than 30 mg/L, the treatment efficiency is about 30% on average. The treatment effect of the particulate material (SS) remained quite high, however, without significant restrictions on the filtering liner velocity and influent concentration. The results of the analysis of the characteristics of the CSOs in urban areas and of the application of a highspeed filtering apparatus using a fibrous filter medium are expected to be utilized as basic data for management alternatives to reduce rainfall runoff loads with respect to overflows that occur during rainfall.