Rapid Determination of Chemical Oxygen Demand By Sulfuric-Acid Digestion and Visible Spectrometry

A rapid and simple method based on visible spectrometric procedure is proposed for the determination of COD in wastewater treatment system. It is an improvement of standard method to determine COD, i.e. determination of excess dichromate (Cr -2O + {2- } -7) by visible spectrometry at 442 nm. The absorbance value (A) of Cr -2O + {2- } -7 and the concentration of COD have linear relation by computer analogy, so COD is determined indirectly in this way. Some influencing factors, such as the refluxing time, the amount of wastewater sample and potassium dichromate, sulfuric acid concentration are investigated, respectively. The result shows that when the concentration of COD in wastewater sample is in the range of 65~(650 mg·L + {-1 }), 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 5.0%. The viability of this method is demonstrated by analyzing two kinds of synthetic wastewater and five kinds of industrial wastewater, and it proves to be a rapid and accurate method for COD determination.