The purpose of this study is the development of regional multi-objective water quality management schemes considering low treatment cost, high dissolved oxygen level, and better equity among treaters. In this study, water quality simulation model QUAL2E, linear programming, mixed integer programming, and fuzzy set concept were utilized.
The JoongRyang-Cheon basin in Seoul, Korea during August, 1983 was selected as the study area. After analyzing the relationship between pollution source load and water quality effect by using QUAL2E, the optimization techniques were used to minimize the total treatment cost of the study basin.
The fuzzy set concept was applied to optimization technique for the development of multi-objective water quality management method and the acquisition of dissolved oxygen levels in the setting of zoned standard by using minimum operator and linear membership function.
The following are the results of this study:
(1) The optimal solution of the three-objective problem where the ranges of objectives were $0.8-2.5×10^9$ won for cost, 2.0-6.0 mg/1 for the dissolved oxygen level, and less than 0.65 for the difference among the treatment levels was 0.33 of degree of satisfaction, 3.3 mg/1 of dissolved oxygen, and $1.9
×10^9$ won of cost.
(2) The attainable uniform dissolved oxygen standard in JoongRyang-Cheon at August, 1983 where the potential seven treatment plants were located was 3.5 mg/1.
(3) Using the mixed integer programming, the location and the number of treatment plants could be determined in addition to the optimal treatment levels.
(4) If the several critical zones where the background dissolved oxygen level was less than 4.0 mg/1 were fuzzified, the optimal solution showed that 3.54 mg/1 of dissolved oxygen could be attained in the critical zones and 5.4 mg/1 in other zones, and the corresponding treatment cost was $0.476×10^9$ won.
(5) By using fuzzy concept, it was possible to know maximum attainable dissolved oxygen concentration at each checking point.
(6) As in the method of zoned standard, the spatial flexibility can save the unnecessary huge expenditure on the environmental control, especially in the region of higher environmental quality level.
