半導體產業使用再生水之永續性評估：不同情境的水足跡比較分析

Abstract

臺灣有著顯著的豐枯水期，加上陡峭地形及短而湍急的河川，造成水資源不足的問題，當中以南部缺水問題更為嚴重。近年，再生水廠在各政府部門的推動下陸續落成，受限於法規的規範，再生水主要以非食品業、藥品業的工業用途為主。而半導體產業為耗水且需要高品質水源的產業，缺水危機會對其帶來一定風險，從而影響臺灣經濟。隨著水處理技術的成熟，以再生水作為半導體產業水源的做法漸趨普及，產業耗水性的特質有望能提高工業部門的再生水應用。透過工業用水減量，則可調動更多水源供其他用水部門使用，有助於緩解水資源短缺。

本研究目的是通過水足跡分析，瞭解運用民生污水產製之再生水供應半導體用水對於緩解水資源短缺的效率，並分析水回收中的各個處理過程對環境的衝擊。研究以高雄的一個再生水廠作為實際案例，根據 ISO 14046 標準方法進行水足跡分析，並聚焦於半導體產業使用再生水及自來水的水足跡差異，分析符合半導體產業水質標準的 1 立方米水的水足跡。水足跡分為三個部分呈現，包括間接用水、直接用水及用水減量。為反映再生水廠對區域性水壓力的影響，本研究套用了針對臺灣水域建立的水資源耗用特徵因數，以瞭解各情境取水量的變化對特定集水區的不同用水部門帶來的潛在的最大衝擊或效益。

研究結果顯示，以再生水為水源情境下的間接用水比自來水更高，再生水供水的水足跡主要貢獻來源為用藥（54.23%）及用電（45.33%）。然而再生水供水在運用民生污水的情況下，彌補了再生水與自來水供水因水回收率所致的直接用水差異，因此再生水供水的直接用水稍微比自來水供水低。另外，再生水供水情境緩解了作為自來水廠取水源高屏溪的用水壓力。綜合以上，因間接用水沒有特定取水來源，再生水廠的緩解效率主要參考直接用水的衝擊及用水減量的效率。以集水區水源出發，再生水廠水源，即阿公店溪，取水量會增加；而自來水廠水源，即高屏溪，取水量則會減少。與不同集水區的特徵因數相乘後可見，無論從哪一個部門調配水源，再生水廠所改變的取水量對生態用水造成的剝削或緩解都是最顯著的。除生態部門，阿公店溪的唯一用水標的是家庭公共用水，若需從阿公店溪調配水作再生水廠之水源，勢必要影響家庭公共用水，因此再生水廠所需用水主要對家庭公共用水造成潛在競爭壓力。若需從高屏溪調配水作淨水廠之水源，比較分別從各部門調動水源，各用水標的潛在競爭壓力從大至小順序為：工業、農業、公共。

本研究使用水足跡分析評估運用民生用水產製之再生水供應半導體用水對於區域水資源的效益，提供水壓力影響數據，以瞭解再生水廠在不同集水區造成的水資源競爭改變，可供集水區可用水管理參考。

Taiwan has distinct wet and dry seasons, with its steep relief and short, rapid river flow, which results in a water shortage crisis. More water reclamation plants are gradually constructed, however, under the restriction by law regulation, the application of reclaimed water is mainly limited to industrial uses other than food and pharmaceutical industries. Meanwhile, as a water-consuming industry with high water quality requirements, the semiconductor industry faces certain risks under water shortage, which may affect the economy of Taiwan. As water treatment technology gets more mature, the application of reclaimed water for semiconductor uses also becoming more common. The water-consuming characteristic of this industry is expected to increase reclaimed water usage in the industrial sector. By reducing water consumption in the industrial sector, more water can be freed up for other water-use sectors, alleviating water scarcity.

Through water footprint assessment, this study aims to understand the efficiency of utilizing reclaimed water produced with municipal wastewater to supply semiconductor uses in alleviating water shortage and to analyze the environmental impact of each treatment process in water reclamation. QT Water Reclamation Plant is chosen as a case study, a water footprint assessment is conducted based on the ISO14046 LCA approach, with a focus on the water consumption difference between reclaimed water and tap water as the water source for semiconductor water uses, to examine the water footprint of producing 1 m³ of water that meets the water quality demand of the semiconductor industry. The water footprint is classified into 3 parts, indirect water consumption, direct water consumption, and the water consumption reduction under the presence of a water reclamation plant. To reflect the impact of the water reclamation plant on regional water stress, a characterization factor for consumptive water use developed based on conditions in Taiwan is applied to understand the greatest potential water competition pressure brought to different water-use sectors in corresponding watersheds.

The results of this study show, that indirect water consumption in scenarios with reclaimed water as the source is higher than tap water. The major contribution of the water footprint of reclaimed water sourcing is from chemical addition (54.23%) and electricity consumption (45.33%). Under the effect of the introduction of municipal wastewater, the direct water consumption difference between supplying reclaimed water and tap water due to water recovery rates is narrowed. Therefore, the direct water consumption of reclaimed water is slightly lower than tap water. The water reclamation plant can also relieve the water stress of the Gaoping River, the source of tap water production.

As there is no specific source of water withdrawal for indirect water consumption, the mitigation efficiency of the water reclamation plant mainly refers to the impact of direct water consumption and water consumption reduction by the plant. In terms of watersheds, water withdrawal from the Agongdian River would increase, while from the Gaoping River would reduce. No matter from which sector the water is diverted, the changes in water demand impact the water stress of the ecosystem, which brings the most significant impact on this sector. Apart from the ecosystem sector, as the domestic sector is the only water user of the Agongdian River, the water reclamation plant mainly creates potential competitive pressure on this sector as water has to be diverted for the water demand of the plant. The potential competitive pressure on each sector in the Gaoping River is in the descending order of industry, agriculture, and domestic.

This study uses water footprint analysis to evaluate the benefits of utilizing reclaimed water from municipal wastewater to supply semiconductor-use water to regional water availability. The impact on water stress is quantified, to understand the changes in competitive pressure by the water reclamation plant on certain watersheds, which can be used as a reference for water management on the regional water availability.