An automated instrument for monitoring oxygen demand in polluted waters

An automated instrument is described which measures the oxygen demand of th e organic content of a fluid based on oxidation by hydrogen peroxide with U V light. Residual hydrogen peroxide remaining after oxidation of the organi c compounds is determined by gas liberated From H2O2 decomposition by catal ase, measured by a low flow gas meter. Oxygen produced by the internal chai n reaction of H2O2 with hydroxyl free radicals is also measured and since t he amount of peroxide added is known, the amount of peroxide used to oxidis e the organic compounds can be calculated. A linear relationship between or ganic strength (measured as COD or BOD) and the output of the instrument wa s obtained for dilutions of raw sewage (25-150 mg l(-1) COD and undetectabl e to 54 mg l(-1) BOD), a synthetic sewage (100-1400 mg l(-1) COD and 68-952 mg l(-1) BOD) and effluents from a creamery (50-600 mg l(-1) COD) and pota to processing factory (50-350 mg l(-1) GOD). The instrument is fully automa ted in the present version giving one sample measurement every 55 min and c ould be used on-line as the basis of a control strategy for wastewater trea tment plants. The instrument is robust, with relatively low capital cost an d cost of ownership. (C) 1999 Elsevier Science Ltd. All rights reserved.