| Summary: | 碩士 === 淡江大學 === 水資源及環境工程學系 === 89 === Ⅰ. Determination of the Chemical Oxygen Demand (COD) in
Wastewater by Mercury-free Microwave Digestion
The traditional method for the determination of chemical oxygen demand (COD) in wastewater is mainly to digest the organics by open reflux method and the potassium dichromate as oxidant. This process is not only time-consuming but also produces a large amount of toxic waste . The silver nitrate solution instead of mercury sulfate for removal the chloride interference in determination of COD using microwave method has been studied in our laboratory. The conditions for optimized microwave digestion were microwave power 700 W, reaction time 5 min, silver nitrate solution 2 mL (0.0705M), potassium dichromate solution 2 mL (0.0417M), silver sulfate solution 7 mL (0.55%), sample volume 5 mL. The results of this method were in good agreement with the conventional reflux method in industrial wastewaters and certified reference material (CRM). The goals of this study are to investigate the relationship between microwave power and sample size as well as number of reaction vessels.
The results showed that the microwave power was increased with decreaseing the reaction time. The 1640 joule was applied to digest the sample (1ml) completely. Neither AgNO3 nor HgSO4 was used for sample containing chlroide concentration of 1000 mg/L with the normal microwave digestion. The AgNO3 solution was needed if the concentration of chloride was more than 1000mg/L. A simple method for the continuous and rapid determination of the COD by flow injection with spectrophotometry was proposed and tested. The potassium hydrogen phthalate (KHP) has been used as standard to check method performance and the average recovery of KHP is 105 % with standard deviation (S.D.) 2.12 (n=5).
Ⅱ.The Elution Behavior of Polychlorinated Biphenyls (PCBs)
Congeners in Different Chromatographic Column
The lack of confirmation of the analytes in environmental gas chromatography that uses the traditional one-column, one-detector system often raises questions as to the validity of the data. The elution pattarns of six pairs of PCB congeners were analyzed by gas chromatography (GC) with two different capillary columns (DB-5 and DB-17) and confirmed by GC-mass spectrometry. The results indicated that the elution orders of 12 PCBs congeners in DB-5 column were reverse except one pair (PCB-170 and PCB-199) in DB-17 column. The reason might be that the 50% phenyl coated on the stationary in DB-17 column can be interacted with PCBs.
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