利用生命週期評估探討五種移除水中硝酸鹽之環境友善技術

Abstract

硝酸鹽為自然界常見之污染物，主要是由農業過度施肥滲透土壤造成地下水污染，硝酸鹽一旦被攝取進人體會在體內還原成亞硝酸鹽，阻礙血液輸送氧氣的能力，嚴重時恐會引發休克。近年來利用化學脫硝與催化脫硝程序去除水中硝酸鹽之新興技術已被證實是有效率且經濟性的處理方式，然而因處理程序中添加部分貴金屬並製備奈米級材料等，致使此類處理技術是否反而替環境帶來負面衝擊成為眾所關切之議題，故本研究之目的是以生命週期評估(Life Cycle Assessment, LCA)結合層級分析法(Analytic Hierarchy Process, AHP)建立一套環境友善性評價系統，針對五種去除水中硝酸鹽之技術進行盤查，比較處理程序間之環境友善度差異。五種技術分別為：鈀銅批載氧化鈦奈米管(Pd-Cu/TNTs)、鈀銅批載二氧化鈦之加氫系統(H2 + Pd-Cu/TiO2)、鈀銅批載二氧化鈦(Pd-Cu/TiO2)、鈀批載零價鋅(Pd/Zn0)、鈀銅批載零價鐵(Pd-Cu/Fe0)。 本研究利用生命週期評估軟體SimaPro7.1與層級分析法軟體Expert Choice來建立環境友善性評價系統，首先利用Eco-indicator 99做為衝擊評估模式進行生命週期評估，以量化研究案例對環境面之衝擊；接續建立環境友善評價系統之指標，並將總經濟成本與環境衝擊面給予1:1之等權重，再以層級分析法決定環境衝擊面之細部指標權重，即得環境友善評價系統。 研究結果顯示：(1)鈀金屬與電力耗損為貢獻環境衝擊之主要原因；(2)環境友善評價系統之權重，總經濟成本為50%，環境衝擊面為50%，其下之權重為：生態毒性(9.4 %) > 石化燃料(8.9 %) > 致癌物(5.6 %) > 輻射(4.5 %) > 土地利用(4.3 %) > 臭氧層破壞(3.2 %) = 氣候變遷(3.2 %) > 礦物(3.0 %) > 可吸入性有機物(2.9 %) = 酸化與優養化(2.9 %) > 可吸入性無機物(2.2 %)；(3)考量去除相同量之硝酸鹽、去除能力、投入原物料與能源耗損造成環境之衝擊、污染物排放對環境之衝擊、經濟成本等多準則評估下，以Pd-Cu/TiO2做為催化脫硝之技術最為環境友善。本研究所建立的環境廢污處理技術之環境友善性評估雖為實驗室規模，但可了解新興處理技術在物質使用、能源投入、二次污染、經濟成本等多面向之衝擊，故做為未來實務上選用之參考。

Nitrate, one of common contamination in nature, is widespread due to over-fertilization in agriculture. Once taken into the body, nitrates are converted into nitrites, which can interfere with the oxygen-carrying capacity of the blood. It will lead to severe shock at the worst. In recent years, catalytic reduction processes applied in the removal of nitrate in water has been proved to be an effective and economical treatment. However, some of the noble metal and nanomaterials will be used in the processes, the potential risks and impacts to the environment with catalytic reduction processes associated are viewed critically. In this study, the main purpose is to establish evaluation system of environmentally friendly by life cycle assessment (LCA) and analytic hierarchy process (AHP). With this objective a life cycle assessment has been used as a tool for the assessment of the environmental impact of five environmentally friendly processes for the removal of nitrates from water : (1)Pd-Cu/TNTs, (2)H2 + Pd-Cu/TiO2 , (3)Pd-Cu/TiO2 , (4)Pd/Zn0 , (5)Pd-Cu/Fe0. The inventoried data has been classified considering the potential environmental impacts categories included in the Eco-indicator 99 method of SimaPro 7.1. Evaluation system of environmentally friendly considers the economic and life cycle environmental effects of process, giving these equal weighting. On the other hand, the Expert Choice has been used as an AHP tool to decide the weighting factors of environmental impacts. Among the five cases considered, Pd-Cu/TiO2 treatment proved to have the lowest environmental impact in all the evaluation system of environmentally friendly due to the lower palladium and electricity consumptions. On the other hand, the weighting factors of environmental impacts were : ecotoxicity (9.4 %) > fossil fuels (8.9 %) > carcinogens (5.6 %) > radiation (4.5 %) > land use (4.3 %) > ozone layer (3.2 %) = climate change (3.2 %) > minerals (3.0%) > respiratory organics (2.9 %) = acidification / eutrophication (2.9 %) > respiratory inorganics (2.2 %). Although the evaluation system of environmentally friendly of the removal of nitrate from water was focused on five bench-scale treatments, it will be valuable on site in the future.