以水足跡指標建立氣候變遷情境下之再生水廠效益評估方法

Abstract

水資源的可得性在近年逐漸受到氣候變遷、用水需求增加等因素備受威脅，使得水資源短缺的問題日趨嚴重，開發非傳統水源已成為各國趨勢，其中，再生水供水不容易受氣候影響，且能將水資源循環並永續利用，是現今重要的供水來源之一。不過，再生水雖然具有 供水效益，但在處理過程中的資源使用對水資源造成之衝擊鮮少被考量；此外，再生水利用在未來氣候變遷情境下，對環境產生的潛在影響亦尚未有一套完整的評估方法。 本研究以水足跡評估方法作為基礎，結合SWAT和 TaiWAP模式進行流域水足跡模擬，並建立再生水廠建設的衝擊與效益的評估流程，選定中部大甲溪流域及臺中水湳再生水工程做為研究案例，對再生水廠進行水足跡評估，繼以流域水足跡永續性作為指標，評估再生水廠在氣候變遷情境下的供水效益。 研究結果顯示，氣候變遷所造成的降雨型態改變將會衝擊大甲溪流域的藍水、綠水與灰水資源，藍水與綠水稀缺性將會在未來情境的3-5月有明顯上升，水污染程度將會在2月大幅度上升。比較流域藍水稀缺性在不同情境下的增減量，氣候變遷造成的稀缺性增量最大達203%，而再生水所提供的減量效益最多僅有 顯示若以流域永續性的角度來看，再生水供水對藍水稀缺性減量效益很小；若以經濟效益來看，由於大甲溪流域在未來情境缺水率高，加上水湳再生水廠供水對象為產值較高的中部科學園區，經濟效益較為明顯。水湳再生水廠的水足跡盤查結果顯示，水足跡貢獻來源主要為灰水足跡，而能源為藍水足跡貢獻的主要來源；將再生水廠的水足跡與無再生水廠情境相比，在有再生水廠的情境下，每月可以減少約20萬噸的水足跡。 本研究所建立的評估方法以水足跡做為指標，能夠呈現供水設施所帶來的效益與衝擊，可作為流域水資源的管理指標，或是應用於各種供水設施的效益評估。

Reclaimed water is one of the solutions to water scarcity since it can reuse water resources and provide a stable water supply. However, water resources consumed and related impacts during wastewater treatment processes are rarely considered. Moreover, there is a lack of a complete method to evaluate the potential environmental and economic impacts of using reclaimed water, especially under climate change. This study established a framework to evaluate the water reclamation plant based on the concepts of Water Footprint Assessment methodology and the simulated data from SWAT and TaiWAP models. The method was then used to assess the water footprint of the Shuinan water reclamation plant and the benefits of the reclaimed water supply to the Dajia river basin. The results show that changes in rainfall patterns will affect the blue, green, and gray water resources of the Dajia river basin. The increment of blue water scarcity caused by climate change is up to 203%, but the reduction provided by reclaimed water is only 0.31% at most. It indicates that, from the perspective of the river basin, the supply of reclaimed water has little effect on the blue water scarcity reduction. However, from the perspective of economic benefits, the high water shortage rate in the Dajia river basin made the economic benefits more significant under climate change. The water footprint assessment results of the Shuinan water reclamation plant show that the grey water footprint is the major contribution, and energy is the main contribution to the blue water footprint. Compared to the scenario without a water reclamation plant, the water reclamation plant can reduce to about 200,000 tons of the water footprint every month. This research adopted the water footprint as an indicator to establish an assessment method for reclaimed water. The results can illustrate the benefits and impacts of water supply facilities. The indicator can further be used for water resource management or the evaluation of other water supply facilities.