Dicke, Robert J. (ed.) / Transactions of the Wisconsin Academy of Sciences, Arts and Letters
volume XLIV (1955)
Lawton, Gerald W.
An investigation of the chemical oxygen demand determination, pp. 45-56 PDF (3.1 MB)
45AN INVESTIGATION OF THE CHEMICAL OXYGEN DEMAND DETERMINATION GERALD W. LAWTON Hydraulic and Sanitary Laboratory, Civil Engineering Department, University of Wisconsin The biochemical oxygen demand (B.O.D.) determination for evaluating the strength of domestic and industrial wastes is now used almost universally. Despite its wide acceptance it possesses the great shortcoming that five days are required for reliable data. A test that would give results in a much shorter time would of course be very desirable. Many attempts have been made to select a chemical oxygen demand (C.O.D.) test that would give the same results in a matter of hours or minutes. The difficulties encountered in such ' tests arise from the fact that chemical oxidation of organic matter follows ' different paths and stops at different points from those of biochemical oxidation. Thus the values obtained by B.O.D. and C.O.D. determinations may have a high degree of correlation but ordinarily they are not the same. Moore, Kroner, and Ruchhoft (1) as well as Ingols and Murray (2) have given brief histories of the many attempts made to develop a satisfactory C.O.D. test,. The main oxidizing agents that have been used are potassium dichromate, potassium permanganate, ceric sulfate, and iodic acid. Standard Methods for the Examination of Water and Sewage (3) at present describes an oxygen consumed test using potassium permanganate as the oxidizing agent. From recently published results (1) (2) (4) it appears that a dichromate oxidizing solution is the most reliable and is not difficult to use. Rhame (4) used potassium dichromate as the oxidizing agent in a mixture of equal parts of sulfuric and phosphoric acids. He determined the unused dichromate by means of potassium iodide, starch, and sodium thiosulfate. His method did not consider the loss of volatile materials by evaporation from the open container during boiling, and it did not use a constant mixture that would maintain a constant boiling temperature. These two conditions undoubtedly produced results that were not readily reproducible. Ingols. and Murray (2) employed the same oxidizing agent that Rhame had suggested and similarly determined the amount of unused reagent. They refined Rhame's method by refluxing in
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