城市水系統之動態生命週期評估—以金門為例

A tracking dynamic life cycle assessment tool for water treatment facilities in Kinmen islands, Taiwan

許桓瑜(Huan-Yu Shiu)

指導教授 ： 闕蓓德

國立臺灣大學/工學院/環境工程學研究所/博士(2021年)

https://doi.org/10.6342/NTU202104534

摘要

生命週期評估 (Life Cycle Assessment, LCA) 是常見的環境衝擊評估方法，用來量化產品於原料開採、製程、使用及廢棄階段對環境的影響。傳統的LCA著重於產品的環境衝擊比較、環境衝擊熱點分析，以供決策者改善建議。然而對於長壽命設施之使用會隨著時間變化，傳統LCA缺乏時間因子，無法呈現隨時間而異的盤查分析及相對應之衝擊變化，因此本研究導入考量時間之動態生命週期評估方法(Dynamic Life Cycle Assessment, DLCA)，量化具有長期使用年限特徵之城市水系統，分析供水及污水處理的環境衝擊。相較於傳統LCA，DLCA記錄時間軸上城市水系統操作之能源與資源使用狀態，追蹤環境衝擊變化。本研究以金門縣水系統為案例，以DLCA方法評估各個水處理設施之長期衝擊動態變化，在技術進步、節水、能源政策、政治風險等情境下，城市水服務之衝擊變化，比傳統LCA更可看到設施環境衝擊變化之趨勢。
　　傳統LCA的衝擊評估結果指出，衝擊最高為紅山淨水場(標準化數值2.18E-11)，一般來說衝擊最高為海水淡化(標準化數值2.41E-12)，其次為再生水(標準化數值2.75E-13)、淨水(標準化數值2.39E-13)，最低是境外引水(標準化數值1.88E-14)，但這之中，紅山淨水廠能源效率和基礎建設使用率都低，使紅山淨水場的衝擊為所有設施中最高。傳統LCA結果於多個水處理設施中低估或高估了衝擊，主要原因可能來自於傳統LCA方法，挑選某一年做為評估基準，而該年度代表了設施壽命的水處理衝擊結果。
　　DLCA分析了城市水系統隨時間變動時對環境衝擊的影響，並展示不同水處理設施每1m3衝擊變化趨勢，淨水廠衝擊與供水量穩定度有關，而污水處理處理水量逐年增加，其處理效率上升使衝擊經攤提而降低。DLCA計算城市水系統服務1m3水之動態的衝擊變化結果，基礎情境境外引水為主要供水水源，平均環境衝擊之標準化值為4.16E-13；水再生技術發展情境之平均標準化數值為4.39E-13，相較於基礎情境，增加水處理設備使衝擊增加22%，但是可以為工業提供了更高品質的再生水；節水情境中，設定每人每日用水量降低10%，平均環境衝擊之標準化值為4.16E-13，儘管節水可以降低能源與藥品等資源使用量，但是此供水量降低使供水設施的使用效率並且改變了城市水處理設施的服務比率，相較於基礎情境每噸水增加了0.4%衝擊，若計算壽命總衝擊時則是衝擊最低的情境；能源政策情境對整體結果相較於基礎情境小於0.1%，在能源衝擊的管理上，優先考慮降低能源耗用；考慮金門面對政治風險而無法使用境外引水的情況下，政治風險情境之平均標準化衝擊數值為7.03E-13，儘管2019年污水廠擴建，提高再生水使用在此情境中些微降低衝擊，但隨著逐年增加之用水需求，對於海水淡化的依賴越高。整體而言，DLCA提供了時間維度的環境衝擊結果，使衝擊量化可以隨著不同時間給予實際狀態之評估結果，發展為具有長期時間維度之衝擊管理工具。

關鍵字

動態生命週期評估 ； 城市水資源系統 ； 能源組合衝擊 ； 技術發展衝擊 ； 時間變化

並列摘要

Life cycle assessment (LCA) is a common methodology for evaluating the environmental impact of a product, process, or service during the raw material, manufacturing, use and disposal stages. The conventional LCA focuses on the comparison and hotspot analysis of environmental impact, but it lacks a time factor to present time-varying inventory analysis for long-life facilities. Therefore, this study develops a dynamic life cycle assessment method with a time factor to quantify the urban water system with long-term use characteristics. Compared with conventional LCA, DLCA can record the usage of material, chemicals, energy, etc., for the urban water system and track the change of the environmental impacts. To demonstrate the effect of DLCA, the urban water system of Kinmen islands is the case study in this research. The DLCA provides the trend of impact changes for urban water services in the scenarios of technological advancement, water conservation, energy policy, and political risk.
　In this study, the normalized environmental impact values of all water treatment facilities were first analyzed by conventional LCA. Generally, the highest impact is desalination (2.41E-12), followed by reclaimed water (2.75E-13), potable water (2.39E-13), and the lowest is imported water (1.88E-14). But among these, the Hongshan potable water treatment plant (PWTP) with low energy efficiency and infrastructure usage, making the highest impact (2.18E-11). Compared to the DLCA results, the conventional LCA results underestimate the impact in multiple water treatment facilities. The reason for this is that the conventional LCA method selects a year as the basis for evaluation, and that year represents the impact results for the life of the facility.
The DLCA further analyzes the impact of urban water service (in 1 m3) and shows the trend of impact changes in all water treatment facilities. The results show that the impact of PWTP is related to the stability of water supply, and the impact of wastewater treatment plant is reduced by the wastewater increasing (meaning that the treatment efficiency is higher). The dynamic normalized environmental impact values for urban water service in the scenarios are basic scenario (S0: 4.16E-13), technological advancement (S1: 4.39E-13), water conservation (S2: 4.16E-13), energy policy (S3: 4.16E-13), and political risk (S4: 7.03E-13). Compared to the S0, although the addition of capacitive deionization (CDI) increases the impact (22%) in S1, it can provide industry with higher quality reclaimed water. Although the water saving of S2 reduce the use of resources (energy and chemicals), this reduction in water supply reduces the efficiency of water facilities and changes the service rate between urban water treatment facilities. Compared to the S0, the impact of per m3 urban water service increases by 0.4%. When evaluating the total life cycle impact, S2 is the lowest impact scenario. The result of energy policy scenario (S3) are reduced by less than 0.1% compared to the S0, and the results suggest that reducing energy consumption may be more effective than changing the energy structure. Political risk scenario (S4) has the highest impact. Even though the expansion of wastewater plants in 2019 and the increased use of reclaimed water slightly reduces the impact in this scenario, the reliance on desalination increases as water demand increases each year. Overall, DLCA provides environmental impact results in a time dimension. The impact assessment can be further developed into a management tool with a time dimension by giving the actual state assessment results over time.

並列關鍵字

Dynamic life cycle assessment ； Urban water system ； Environmental impact of energy structure ； Environmental impact of technology development ； Temporal variation

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