The Cost Benefit Analysis on Sedimentation Operation and Maintenance of Water Purification Plants

• Main Authors: HSIU-YU YEN, 顏秀羽
• Other Authors: Cheng-Fang Lin
• Format: Others
• Language: zh-TW
• Published: 2015
• Online Access: http://ndltd.ncl.edu.tw/handle/11468527886489686627

碩士 === 國立臺灣大學 === 環境工程學研究所 === 103 === In this research, net present value (NPV) method was adopted to analyze the different cases of combining the different scrapers with removal ways of sludge based on the current situation in Taiwan and China water purification plant. Next, the operation data of 4 metallic double-chain scrapers (MDCS), 6 monorail-type scrapers (MS), and 8 siphon-type scrapers (SS) were collected by questionnaires.Then, that operation data would be used in a 100,000 CMD capacity of water purification plant which was assumed in this study in order to discuss the most economic operation ways of clarifiers and the considered parameters including functional the design of clarifiers, the cost of construction, the cost of maintainance, operating deficit, and any kinds of cost of scrapers, removal ways of sludge, and wastewater treatment. Furthermore, there were 5 different cases with 3 kinds of scenarios in this study and the basic assumption listed as followed: 1) the life time of MDCS was set in 15 years, 2) the life time of MS was set in 30 years, 3) the life time of sS was set in 20 years, 4) the life time of all kinds of sludge removal devices was set in 10 years. 5 different cases were mentioned below: 1) MDCS combines with gravity-type of sludge removal system(GSRS), 2) MDCS combines with airlifting-type of sludge removal system(ASRS), 3) MS combines with GSRS, 4) MS combines with ASRS, 5) SS combines with siphon-type of sludge removal system (SSRS). The definition and the result of 3 kinds of scenarios were interpreted as followed: 1) The scenario 1 was supposed as a new water purification plant construction considering the civil, scrapers, ways of sludge removal, and sludge treatment and the corresponding result showed that the order of optimal combination was case 3, case 4, case 1, case 2, and case 5, which conveys that the case 3 was the best option. 2) The scenario 2 was as same as scenario 1 without considering the relative benefit of considered parameters; that is, the scenario 2 focused on the cost only and the result showed that the order of optimal combination was case 5, case 3, case 4, case 1, and case 2, which conveys that the case 5 was the best option. 3) The scenario 3 also considered the new water purification plant construction while without considering the yearly maintainance of scapers and its relative benefit. Under such scenario, the optimized order awared to case 3, case 4, case 1, case 2, and case 5 whose result was as same as the result of scenario 1 while in scenario 3, the NPV result of case 1 and case 2 were closed to case 3 and case 4. Under these 3 scenarios, the advantage of different scrapers can be shown up. The sensitivity results showed that the most sensitive factor in scenario 1 was “the relative benefit of wasted sludge treatment”; the most sensitive factor in scenario 2 was “the initial investment/cost of siphon-type scrapers (SS)”, and the most sensitive factor in scenario 3 was “the initial investment/cost of metallic double-chain scrapers (MDCS)”. In summary, lots of data, scenarios, assumed condition, and parameters were used and being analyzed in this research, which may be contrary to the current situation. For the futher research and study, more actual and specific data should needed to be collected; so that, the research result could have more credibility for reference or application. And each kinds of scrapers discussed in this study owned its merits and characteristics, so it is proper to choose based on the real facts and need on the engineering projects.