高科技產業生產需要用水，伴隨製程技術的提昇，用水水質及需求量提高，為了降低對原水的依賴，可投資回收水系統，而水資源回收及管理需要思考水質、水量與成本的關係。
本研究建立半導體廠房廢水處理與回收成本架構，藉由個案廠房水系統資料，了解水處理與回收系統的運轉模式，分析回收水的成本。水系統分純水、水處理與水回收三大系統，其成本項目有四類購置、操作、改善及排放成本。購置成本細分為系統折舊與自來水成本，操作成本細分為電力、人力、物料與維護保養，排放成本分廢水與污泥排放。
分析結果顯示，純水系統佔總成本40%，其次是水處理系統的37.5%，和水回收系統的22.5%。四類成本中操作成本最高，佔總成本的63~68%，最少的是資本折舊，只佔5%。而純水、水處理與水回收系統的運轉單價分別是18.42、21.81、8.61元/m3。
使廢水排放達到管理局的排放標準，是投資水處理系統的目的。經分析管理局的三個主要水質要求：化學需氧量、懸浮固體和氨氮濃度，其中調整懸浮固體的數值以達標準<=15mg/L，是水處理系統成本的主要花費。
經處理回收後的水，可補充廠房自來水用量，稱為可節省水量，以此算出每噸節省水需24.06元，減去自來水價的12.7元/m3，得每噸水的環境成本為11.36元。
本研究以真實案例建立的回收水架構與其成本組成，分析得出回收水單位環境成本，適用於台灣科學園區內的高科技產業，可供不同廠房參照使用。

Wastewater Treatment and Recycling Cost Framework
and Analysis for Semiconductor Plants

Keong Chi Kin
Prof. Andrew S. Chang
Department of Civil Engineering, College of Engineering

SUMMARY

Water plays an essential role for the production of the high-tech industry. As technology for semiconductor products advances, the requirements of water quality and water demand also increase. In order to reduce the dependence on raw water, water reuse and management need to take water quality, quantity, and cost into consideration.
This study establishes the cost framework of wastewater recycling for manufacturing plants. It analyzes the operations and cost data of water related systems of a case plant. The cost of recycled water comes from ultra-pure water (UPW), wastewater treatment (WWT), and water reclaim (RE) system. The percentage of the total cost for UPW, WWT and RE system are 40%, 35%, and 25%, respectively. The cost includes four aspects, which are purchase, operating, improved, and discharge expenses. Operating cost is the highest among the four cost items, which accounts for 60~68% of the total cost. In sum, the operation unit price of UPW, WWT and RE systems are $17.11, $21.77, and $8.54 per ton water, respectively.
One of the purposes of investing WWT system is to make the wastewater reach the discharge standards set by the industrial park authority. The major cost of WWT system is based on three major water quality requirements set by authority. They are chemical oxygen demand, suspended solids, and ammonia concentration, which adjust the value of suspended solids to achieve a standard <=15mg/L. As a result, reuse water cost $23.9/ton. Subtracting the price of tap water, $12.7/ton, the green cost of reuse water used in a semiconductor plant is $11.21/ton.

Keywords: water resource management, semiconductor plant, water treatment, water reclaim, cost component

INTRODUCTION

Water shortage is worsening due to the climate change caused by human beings. The annual water consumption in Taiwan is 3,950 ton per capita, which takes up 12.2% of the world average (Huang, 2013). As the industry is an important user of water resource, factories play a vital role to show positive impacts in striking a balance between water use and water protection (WBCSD, 2005). As a matter of fact, industry wastewater causes pollution as low-efficiency water use causes more wastewater. Therefore, recycling of industry water has become an important issue (Jiang, 2011).

Water reuse has long been recognized as a potential intervention strategy in addressing water scarcity (Hamoda, 2004). To encourage industry water reuse, Taiwan science park regulates the processing water reuse rate of the factories to be more than 85% (STSP, 2004).

Thus, this research focuses on studying the reasonable cost of water reuse and the relationship between water reuse and cost. This study analyzes the relationship between processing water reuse and cost in a semiconductor plant. In the study, we analyze the water balance diagram, establish its water system cost framework, collect the data from WWT and RE system, and calculate the optimal wastewater costs. Meanwhile, the cost for required discharge water is also analyzed.

MATERIALS AND METHODS

Using case study as a method, this study analyzes a semiconductor plant which is located in science park. The study reviews the literature and the cost factors of water reuse. Then, it analyzes the operation of processing water treatment and recycling system. The system data is thus collected and the staff of the manufacturing plant is interviewed in order to analyze the water reuse cost. Finally, the relationship between cost and water reuse is obtained.

This research refers to a significant amount of information, which includes four different sources of data: (1) purchase costs from interview or assumption, (2) operating costs from different fees, system record tables, water consumptions, etc., (3) improvement costs from system records, and (4) discharge costs from discharge fees paid to the science park.

RESULTS AND DISCUSSION

This study analyzes the data of a plant collected from 2010 to 2013. The WWT system of the plant in our case study includes AWD, HF, CMP, Cu-CMP, and BW system. RE system includes DIR, AWR, LSR, and CCR system.

From the costs of four years, UPW system costs 40% of the total cost, WWT system costs 35%, and RE systems cost 25%. Furthermore, UPW system’s electricity cost, WWT system’s dosing chemical cost, and RE system’s improved cost are the main affecting factors of the total water reuse cost.

The operation unit prices of UPW, WWT, and RE system are $17.11, $21.77, and $8.54 per ton water, respectively. The cost of plant spent on achieveing the discharge standard set by the authority or the internal requirements are comparable, namely 53% for authority requirements and 47% for internal recycle requirements.

One of the purposes of the processing water reuse is to supplement the amount of tap water used. Reducing the tap water use means reducing the tap water cost. In summary, the quantity of water supplement can be named as the quantity of water saved. As a result, the cost of water-saving is $23.91/ton and the green cost of recycled water is $11.21/ton. Compared with the water price of $12.7/ton, water reuse is not worthwhile. It is more economical if the plant decides to use tap water as their main water supply than to use part of the reuse water. However, water is priceless, and thus wastewater reuse is a trend to reduce the tap water need.

CONCLUSION

This study analyzes the efficiency between water reuse cost and low cost of tap water. The results of total and unit water costs of water systems are constructive. The cost framework and analysis can be used for other plants. Water reuse is related to tap water and wastewater discharge. The management of water reuse can be planned according to the results of this study.

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