淨水場沉澱池操作維護之成本效益分析

Abstract

本研究以兩岸淨水場實廠刮泥機運行與排泥方式結合，將運行數據運用淨現值法去進行假設情境及假設方案分析，研究收集使用金屬雙鏈條式刮泥機4座、單軌式刮泥機6座與走橋虹吸式刮泥機8座共18座淨水場沉澱池運行的操作數據，做為假設10萬噸淨水場操作因子，探討一定量之水處理淨水場沉澱池在不同系統(不同刮泥機與排泥方式)操作運行之假設情況下，分析最經濟之操作運行模式，使用因子包含沉澱池設計、建設成本、保養維護成本及營業損失，以各式刮泥機、排泥方式與污泥廢水處理之成本，進行假設5種不同方案與3種不同情境之效益分析，假設基本情境為金屬鏈條式刮泥設施15年使用壽命、單軌式刮泥設施30年使用壽命、走橋式刮泥設施20年使用壽命，排泥設施均以10年使用壽命。假設方案一：金屬鏈條式刮泥機+重力式排泥，假設方案二：金屬鏈條式刮泥機+氣昇式排泥，假設方案三：單軌式刮泥機+重力式排泥，假設方案四：單軌式刮泥機+氣昇式排泥，假設方案五：走橋虹吸式刮泥機+虹吸式排泥。情境一：假設新廠建設含土建、刮泥機、排泥、污泥處理，在該假設情境下之結果: 方案3>方案4>方案1>方案2>方案5，方案三為優選。情境2：假設新廠建設含土建、刮泥機、排泥、污泥處理，只考慮成本不考慮刮泥機年維修停水之相對效益(B2)、沉澱池排泥裝置年維修停水之相對效益(B3)與廢棄污泥耗水費之相對效益(B4)，在該假設情境下之結果:方案5>方案3>方案4>方案1>方案2，方案五為優選。情境3：假設新廠建設含土建、刮泥機、排泥、污泥處理，該情境不考慮刮泥機年維修保養費用(C2)與其年維修停水之相對效益，在該假設情境下之結果:方案3>方案4>方案1>方案2>方案5，此情境結果與情境1結果相同，情境3方案1與方案2 (金屬雙鏈條刮泥機)和方案3與方案4(單軌式刮泥機)之效益接近。此三種情境之設計為假設狀況下金屬雙鍊條式刮泥機、單軌式刮泥機及走橋虹吸式刮泥機不同條件之優勢。敏感度分析顯示在假設之狀況下情境1之最敏感因子為「廢棄污泥耗水費之相對效益」；情境2之最敏感因子為「走橋虹吸式刮泥機初設費」；情境3之最敏感因子為「金屬雙鏈條式刮泥機之初設費」。 本研究探討僅就有限數據與良多假設情境與假設條件與假設參數進行計算分析，必然有許多偏離實際現況之結果，日後相關研究或工程設計應以實際資料進行，所得結果才更具參考應用價值。本研究所探討之污泥刮泥設施種類不同，實際上每種設施均有其特色功能與應用優勢，實際工程考量應該依實際需求分析選定適宜之設施為尚。

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.