都市住宅地區下水의 汚染과 處理法에 關한 硏究

Abstract

[한글]

[영문]

A lack of sanitary disposal of sewage is one of the neglected public health problems in rapidly growing cities in Korea. The purpose of this study was to measure the extent of pollution by sewage in a residential area of Seoul City and to compare the effectiveness of several methods of treatment.

The study area chosen was a residential area (20.7 km**2) in the vicinity of Yonsei University in which about 31,000 inhabitants reside and 14, 000 students of the University and 1,500 patients of the University Medical Center attend the

institutions per day in an average.

The sewage samples for this study ware collected at four different points of the four sewage lines in the area; namely "point 1" for sewage mainly from Yonsei University Campus; "point 2" for the outflow from the Medical Center's septic tank;

"point 3" for the combination of above two branch stream, and "point 4" for the predominantly domestic sewage from the residential area. The survey was conducted in three different seasons; summer (June 15 to July 15, 1966), early winter

(November 2 to December 5, 1966) and spring (March 20 to April 20, 1967).

The salient findings are as follows:

1. At point 3, which sewage represents point 1 and 2, it was found that a relatively higher level of pollution was prevalent in summer season than in other seasons. The average level of pollution in summer was 123.5 ppm in chloride ion, 418.0 ppm in BOD, 26.0×10**5/ml in general count of bacteria and 168.6×10**5 in MPN of coliform group organisms.

The probability exceeding over 300 ppm of BOD of the sewage in this point were 76% in a.m. and 50% in p.m. respectively in summer season, and showed 0.688 f**3/sec, 1,711 ton/day in average flow in early winter.

These levels of pollution at point 3 indicated that the extent of its pollution is far less than that of the residential areas.

2. At point 4, where the sewage is predominantly from the residential areas, it was found that the highest average value was 465.3 ppm in chloride ion, 556.4 ppm in BOD, 1,160×10**5/ml in general count of bacteria and 1,460×10**5 in MPN of coliform group organisms during gummer season.

Seventyfotr per cent of the samples collected in both morning and afternoon in summer season exceeded 300 ppm in BOD. The flow rate of the sewage of this point was in an average 1.56 f**3/sec. or 3,814.4 ton/day in the early winter season.

The above data at point 4 indicated that the sewage from the residential area was heavily polluted in comparison with other sewage studied.

3. Total flow of the sewage in the whole study area was 159.6 litter/capita/day in an average. Population equivalent of BOD was 34,649 persons. This means the discharge of BOD per capita per day in the study area was 0.116 lb. It was almost the same level as found in domestic sewage in the United States of America where

excreta is being directly discharged into the sewage system.

This BOD value is high when we consider that most of the residents in this area use the privy without flushing toilet. Then, such a high value of BOD is mainly due to the rapid exhausion of DO(dissalved oxygen) by disposing a large amount of

domestic refuse in the open sewerage system with lees flow of waste water in residential areas, where water supply is far less than in developed countries.

4. While the level of pollution used to reach a peak in the afternoon in the U.S.A., it was noticed that there are two peaks in the level of pollution in this study; one in the morning and another in the afternoon. This may be related to the direct discharge of waste and refuse from home cooking into the open sewerage system in the study area.

5. In this comparative study of three kinds of sewage treatment methods, it was found that a method of sedimentation process reduced the pollution 65.2% in COD, 100% in suspended solid, 52% of BOD during 24 hours, and 50.5% of coliform group organisms in MPN during 29 hours respectively.

6. By the dispersed growth aeration process, the level of pollution was significantly lowered, by reducing 82.2% and 92.9% in BOD during 24 hours and 48 hours respectively. 74.2% of coliform group organisms was also eliminated during 29 hours by this treatment.

7. By the trickling filter process with double filtration, the level of pollution was diminished, by reducing 47.5% in BOD. 59.0% of coliform group organisms was also eliminated by this method. This indicated that this process is less effective than other methods in reducing the level of pollution, while it has some advantage by saving the time of treatment.

8. Taking into account the above results from the three treatment methods, we consider that the sedimentation process followed by trickling filter process or the same process after the aeration treatment is to be recommended for effective treatment of sewage in residential areas. It is also recommended that all open sewerage should be covered in order to further prevent the pollution of sewage.

9. This study clearly indicates that there is need of sanitary treatment of sewage now being discharged into the open sewerage system, in order to protect the quality of river water which is a common source of public water supply in the urban area.