化學需氧量為水質監測之一項重要指標，指水中有機物在氧化劑及催化劑作用下分解所需的氧量。水中化學需氧量愈大，表示有機物含量愈高，水質污染愈嚴重。傳統偵測廢水中化學需氧量的方法為重鉻酸鉀迴流法及密閉式迴流滴定法，此法不僅所需之試劑量大，實驗操作時間長，且會產生大量含汞的毒性廢液。 本研究室歷年曾發表以密閉式微波消化法快速偵測水中化學需氧量之研究。本研究係繼續改進微波消化法，微波消化裝置，從進樣、微波消化、冷卻至偵測系統，已初步建立並完成測試。實驗係將樣品與試劑之混合液，以蠕動幫浦注入設置於微波爐內腔之鐵氟龍管中，並以鐵氟龍襯裏控制閥形成密閉系統。經微波氧化反應完成後，將微波氧化之樣品流經冷卻裝置之環形管迅速冷卻，連接至接收瓶中，經由0.45μm PVDF 之注射式過濾頭過濾後，再連接至分光光度計內光徑10 mm 之穿流式樣品槽，以偵測600 nm之溶液吸光度。最後，再比對COD 標準品所製備之檢量線，以測定出水中之化學需氧量。 實驗結果顯示，微波最佳化條件為功率570 W﹔時間23秒；0.5 mL 0.141 M之硝酸銀溶液，3 mL 0.55 %之硫酸銀溶液，0.75 mL 0.0417 M之重鉻酸鉀溶液, 2 mL之水樣。當COD濃度在0~500 mg/L時，偵測所得之檢量線皆有良好的線性關係。並分別對KHP溶液、草酸鈉溶液、葡萄糖溶液及APG盲樣進行測試，結果精密度與準確度皆在6 %內。 對於含氯鹽水樣之測試，不添加抑制劑的情況下，利用硫酸銀溶液可以抑制2600 mg/L之氯鹽。若添加硝酸銀溶液以抑制氯鹽之干擾，結果顯示，以最佳化之實驗條件，添加0.5 mL 0.141 M之硝酸銀溶液可以有效抑制4700 mg/L之氯鹽。真實水樣之測試方面，以四家工廠廢水作為測試對象，分別以微波消化法及密閉式迴流滴定法測定，二者試驗所得之相對差異皆在10 %之內，證明此一微波消化法之可信度及適用性。 A simple method for determination of chemical oxygen demand using microwave digestion in wastewater is proposed. Chemical oxygen demand (COD) is a widely used parameter used to measure water quality, as well as to control the treatment process. It is one of the important index in water monitoring. This parameter is defined as the amount of oxygen required for, or equivalent to, the oxidation of all chemically oxidizable matter in water. The traditional method for COD determination consists of oxidizing the organic matter of the sample, is done by adding a known amount of oxidant, refluxing at high temperature on open containers and titrating the excess oxidant. However, the method require the time-consuming process of heating samples to achieve more complete oxidation. It also consume some expensive(Ag2SO4) and toxic(HgSO4) chemicals.
Therefore the goal of this study is to develop continuous and rapid determination of COD by microware digestion. In this system, the absorbance of Cr3+ generated during sample oxidation is measured at 600 nm, Chemical oxygen demand can be obtained in just 23 second. The optimal experimental condition are: 0.5 mL 0.141 M silver nitrate solution; 3 mL 0.55 % sulfuric acid solution; 0.75 mL 0.0417 M potassium dichromate solution and 2 mL sample. The calibration graph is liner in the range of 0~500 mg/L. The interference of Cl- can be removed up to be moved up to 4700mg/L. The method has a good precision and accuracy for KHP solution , glucose solution and sodium oxalate solution. There is results for a COD certified reference materials were in good agreement with the certified COD value. The viability of this method is demonstrated by analyzing four kinds of industrial wastewater, and the results obtained by using the method presented exhibit good agreement with those given by the standard method of COD determination, and the relative error is less than 10 %.
