제주도 소규모 하수처리시설의 대규모 하수처리시설 연계에 따른 타당성 검토

Abstract

Most of the small-sized sewage processing facilities in countryside of Jeju are located in mid-mountain areas and the facilities are getting old. As a result, sewage has been discharged to dry streams or ground. It has caused underground water pollution and its second-hand contamination. And nasty smell has been frequently reported by locals. The related organizations are making efforts to solve the problem but their measures were not fundamental. Therefore, the offices are planning to close down the small-sized sewage treatment plants and combine them with large-scaled facilities. This study examines the feasibility of connecting sewage treatment facilities. To compare the cost between keeping both of the small and large-sized plants as it currently is and running combined plants, the operation cost of existing facilities is calculated and the construction cost for combining small ones with bigger plants and operation expense of combined ones is also calculated. To examine the feasibility of the combining sewage treatment facilities, seven small-sized sewage processing plants in mid-mountain area of Jeju-si are chosen among 57 plants on Jeju island. The running cost is calculated in the case of combining the seven plants with two big plants. Firstly, the operation cost of existing facilities is calculated. But, the real expense can not be used for the study because the cost is limited to the fixed budget in reality. Therefore, the operation cost for small and large-sized sewage treatment plants is calculated theoretically through researching books. From it, the operation cost of small facilities is calculated through the arithmetical mean of three functional formulas and that of large facilities is calculated through the arithmetical mean of four functional formulas. The two big plants are based on Sequential Batch Reactor technologypopularly known as SBR technology for the treatment of sewage. To assess the running cost of them, the functional formula for maintenance cost of SBR technology is used. Each plant's maintenance cost is revised by the producer price index of 2013. Three percent, the average rate of inflation for last ten years, is applied for estimating future cost. The construction cost to connect sewer pipes is calculated and used for comparing and analyzing economic feasibility. The feasibility study shows a big burden in 2014 because sewer pipe connecting construction. But it is found that the maintenance cost will be decreased year by year, and it is expected to be economically feasible from 2071. It is analyzed that 10 billion Korean won will be saved in the year of 2100. Sewer pipe connecting construction is expected to cut operating expenses in the end and solve existing problems like non-sewage inflow from pipe-to-pipe's open joints, low concentration sewage inflow and wrongly measured operation capacity. Also it will contribute image improvement of Jeju for its clean environment.