以實驗室模擬氣候變遷對水質及消毒副產物生成影響之研究

Abstract

水資源是很容易受到氣候變遷影響的自然資源。極端氣候事件（例如：洪水與乾旱）的發生頻率與強度的增加，以及環境溫度的上升都被認為是氣候變遷所造成的結果。這些極端氣候事件可能會對表面水體水質以及下游的飲用水處理造成威脅。 近幾十年來，已經有許多研究發現水中溶解性有機物質(Dissolved organic matter, DOM)的濃度有上升的趨勢，許多氣候相關因子被認為是導致這些DOM濃度變化的可能原因，其中又以溫度以及降雨型態的改變尤其受到關注。 以往研究指出DOM是消毒副產物(Disinfection by-products, DBPs)的重要前趨物質，在飲用水處理的過程中，這些濃度增加的DOM與不同的消毒劑反應之後，可能會導致不同毒性及致癌性的DBPs濃度上升。本篇研究的目的在了解在不同的氣候模擬條件下，DOM與DBPs生成的特性與濃度變化。實驗室模擬的氣候條件包含溫度、乾旱、降雨強度、海平面上升以及酸沉降。在實驗室模擬結束後，也進行消毒副產物生成潛能 (DBP formation potentials, DBPFPs)實驗來了解氣候變遷對於水質與DBPs生成的影響。 經過十次不同模擬試驗之後，本研究結果顯示總溶解性有機碳 (Dissolved organic carbon, DOC) 與含碳的消毒副產物 (C-DBPFP) 的濃度會隨著溫度的增加而增加。在評估海平面上升對於水質的影響、也就是溴離子存在於土壤有機質回溶的過程時，含溴的三鹵甲烷 (Br-THMFP) 濃度也會增加。此外，酸沉降在不同的氣候條件下對於水質會有正反兩面的影響。土壤基質以及土地利用的改變也會影響DOM的濃度以及之後DBPs的生成。 降雨模擬的結果顯示極端降雨會在降雨初期造成水質的惡化。大量的DOM會從土壤中被淋洗出來，導致DBPs產生一個高峰值。若極端降雨發生在一個長期乾旱之後，伴隨著乾旱回溶的循環效應 (drought-rewetting cycle effects)，水質惡化的情形可能會更加嚴重。

Water resource is one of the essential natural resources which are vulnerable to climate change. Increased frequency and severity of extreme weather events (i.e. floods and droughts) combined with elevated temperature are considered as the consequences of climate change. These extreme weather events will cause potential threats to the surface water quality and the downstream drinking water productions. Many studies have found that the concentrations of dissolved organic matter (DOM) have increased in surface waters over the past decades. Studies also indicated that DOM is an important precursor of various disinfection by-products (DBPs). Several climate-related factors are considered as the potential drivers of DOM changes, especially temperatures and rainfall patterns. The rising DOM, after reactions with various disinfectants, may results in the increasing concentrations of DBPs with different toxicities or carcinogenesis during water treatment processes. The objective of this study is to characterize the DOM and DBPs formation under different simulated weather conditions. The effects of temperature, drought, rainfall intensity, sea level rising, and acid deposition were considered in the laboratory simulated systems. After simulated treatments, the DBP formation potentials (DBPFPs) were measured to assess the impacts of climate change on DBPs formation and drinking water quality. After ten various laboratory simulations, it was found that there is an increasing trend on dissolved organic carbon (DOC) and C-DBPFP levels with increasing temperature and dry scenarios. Br-THMFP levels were increased when bromide was presented during rewetting processes that represents the impact of sea level rise on drinking water quality. As a comparison, when bromide was presented before chlorination, only the proportion of Br-DBPFP increased. Besides, acid deposition had a two-side effect under different weather conditions. Also, the matrix of soil sources and change of the land uses may influence the DOM concentrations and the following DBPs formation. The results of the rainfall simulations suggested that the deterioration of the water quality was observed in the beginning period of extreme rainfalls. Abundant DOM was flushed out from the soil, and led to a high peak of DBPFPs. If the rainfall was happened after a long drought, accompanying with the drought-rewetting cycle effects, the situation would become much more severe.