Determination Of Chemical Oxygen Demand In Wastewater Study

The efficiency of catalysts ?several transitional metals, especially copper sulfate and manganese sulfate ?in COD determination was studied scientifically in this paper. In addition, two fast and practical methods, rFIA method based on stop?flow technique and a method without flux during determination, were proposed.Firstly, a method based on rFIA and stop ?flow technique was developed for the continuous determination of COD in waste water samples with the self?constructed FIA system. An acidic dichromate solution was injected into samples. After reaction in a PTFE coil at 100癈, absorbances were measured at 600nm. Glucose as a standard substance was satisfactory for a variety of wastewaters. The detection limit and precision were 5mg/L as COD and 0.82%(n=9), respectively. Chloride concentrations of ^200mg/L interfered slightly unless silver and /or mercury salts were added. COD values for various samples correlated well with those obtained by standard methods.Secondly, a method without flux was studied in order to save the time of COD determination. The results of these determinations were shown. Sometimes, the oxidation of this method was really lower than that of the standard method, but it could really save time, only several minutes per determination. At the same time, to a certain kind of samples, the correlativity could be built and the coefficient could be obtained between results of standard method and that of this method so that the determination of COD rapidly and accurately could be realized. So it was still practical.Finally, possible alternatives were sought in this paper because of the high price of silver catalyst. The alternatives investigated were (a) using no catalyst; (b) using catalyst other than Ag2SO4, for example MnSO-t, CoSO4, CuS04, and so on; (c) using reduced amounts of Ag2SO4. Thus such conclusions were drawn as follows: (1) The catalyzing efficiency of CuSO4 was lower than that of Ag2SO4, but when the demand wasn't high or samples were quite easy to be oxidized, above method could still be used practically. (2) The search for a substitute catalyst met with limited success. There was no any catalyst suitable for all kinds of samples, so different procedures should be chosen according toAbstractdifferent wastewater sources.