| 摘要: | 硝酸鹽(Nitrate)是一般自然水中常見污染物，污染來源多為農業化學肥料之使用、動物家禽糞便或是工業排放未經處理之廢水。受硝酸鹽污染之水體流入環境中，會產生地下水污染問題。然而，水中若含有過量硝酸鹽，使水中藻類過度生長繁殖，造成水中溶氧量降低，導致水中動植物無法存活以及生物多樣性下降。若是人類攝入過量硝酸鹽，經過口腔和腸胃道會轉化為亞硝酸鹽。而在高溫或是酸性環境下，亞硝酸鹽和胺類物質結合，則會轉化為N-亞硝胺，已經有相關文獻顯示N-亞硝胺會導致腸胃道異常以及增加罹患癌症的風險。
我國能源的發展型態多以火力發電為主。在2018年，臺中市政府於臺中火力發電廠廢水排放口檢測硝酸鹽氮濃度，結果檢測結果超過我國放流水標準達1.68倍。在能源產生過程中所衍生之環境污染是必須關注的問題。
去除水中硝酸鹽之研究方法甚多，但其各有限制，如不適用於水質複雜、物化特性不明確和經濟成本高。本研究使用雙極系統，搭配電化學還原法(Electrochemical reduction)，利用陽極氧化且陰極還原的電解反應，將硝酸鹽於陰極還原為穩定之中間產物亞硝酸鹽，最終再還原為氨氮或是氮氣。為了探討水中其他污染物是否會影響硝酸鹽去除效果，在批次實驗當中添加硼酸作為可能污染物。另外，還會研究其他實驗參數，探討影響硝酸鹽去除率之可能因素。
與相關文獻比較，本研究雙極電化學系統使用鋁極板，此電化學系統反應表面積大、電流密度低、所需實驗反應時間短。研究結果顯示，隨著極板數量或電流強度或極板有效反應表面積增加，硝酸鹽氮去除率隨之增加；而初始硝酸鹽濃度、可能污染物(硼酸)以及對應離子(Counter ion)對於硝酸鹽氮去除率沒有影響。根據化學反應動力學，硝酸鹽氮去除率符合一階動力反應(First-Order reactions)。
Nitrate is common contaminant in wastewater, primarily originating from the use of agricultural chemical fertilizers, animal feces, or untreated industrial wastewater. When water contaminated with nitrate flows into the environment, it can lead to groundwater pollution issues. Moreover, excessive levels of nitrate in water can lead to overgrowth of plankton and algae, causing a reduction in dissolved oxygen levels, thereby hindering the survival of aquatic organisms and leading to a decline in biological diversity. Human ingestion of excessive nitrate can lead to the formation of nitrite in the oral and gastrointestinal tracts. In high temperature or acidic condition, nitrite combines with amine compounds to form N-nitrosamines. Relevant literature indicates that N-nitrosamines can lead to gastrointestinal abnormalities and increase the risk of cancer.
In Taiwan, the primary mode of energy generation is thermal power generation. In 2018, the Taichung City Government detected nitrate nitrogen concentrations exceeding national discharge standards by 1.68 times at the wastewater discharge outlet of the Taichung thermal power plant. Environmental pollution resulting from the energy generation process is a crucial issue that requires attention.
Relevant literature indicates that there are numerous methods available for removing nitrate from water; however, each method has its limitations, such as high cost or inapplicability to water with complex physicochemical characteristics. This study employs a bipolar electrochemical system coupled with electrochemical reduction, utilizing electrolytic reactions where nitrate undergoes oxidation at the anode and reduction at the cathode. This process leads to the reduction of nitrate to nitrite at the cathode, ultimately further reduced to either ammonia or nitrogen gas. In batch experiments, boric acid is added as a potential contaminant to investigate its potential impact on nitrate removal. Additionally, other experimental parameters will be studied to explore factors influencing nitrate removal efficiency.
In this study, a bipolar electrochemical system utilizing aluminum electrode was employed. This system features a high reaction surface area, low current density, and a short experimental reaction time. The research findings indicate that the nitrate nitrogen (NO3－-N) removal rate increases with the number of aluminum electrode, the current intensity, and the effective reaction surface area of the aluminum electrode. Conversely, the initial nitrate concentration, potential contaminants (boric acid), and counter ion did not significantly impact the nitrate nitrogen (NO3－-N) removal rates. Based on chemical reaction kinetics, the nitrate nitrogen removal rate follows first-order reaction kinetics. |
