Chemistry: analytical and immunological testing – Oxygen demand
Patent
1987-10-15
1991-05-21
Warden, Robert J.
Chemistry: analytical and immunological testing
Oxygen demand
422 681, 422 79, 436136, 436138, G01N 3318, G01N 33483
Patent
active
050174967
DESCRIPTION:
BRIEF SUMMARY
As is known, oxygen-consuming biochemical reactions such as substrate oxidation, nitrification, and formation and degradation of cell material and reserve substances take place in an active sludge suspension. These reactions result in an overall oxygen consumption of the suspension and the rate at which said oxygen consumption takes place is therefore a good measure of the biological activity of the sludge. The rate, expressed in mass of oxygen per unit volume and unit time is termed respiration rate.
For the purpose of biological waste water purification it is of importance to be able to measure the respiration rate of active sludge. This can be illustrated by a few examples: Thus, an optimum matching of the aeration to the oxygen consumption makes it possible, on the one hand, to save energy costs for the aeration and, on the other hand, to match the effluent quality to the standards imposed thereon. reactor in which partial flows of influent and return sludge are combined is an indication that the influent has an acutely toxic effect on the active sludge. This observation may then result in actions which prevent process breakdown. environmentally extraneous substances in active sludge, measurement of the respiration rate will provide important information. of measuring the respiration rate which preferably can be used on line with a view to automation.
Methods of measurement known from the state of the art are the methods using the manometric principle, i.e. based on the measurement of the volume of oxygen consumed. Since the introduction of the manometric respiration measurement, various methods have been conceived for improving said measurement. The most well-known embodiment is the Warburg one (Jenkins, D., 1960, "The use of manometric methods in the study of sewage and trade wastes" in: Waste Treatment, Pergamon Press, New York), in which the volume of gas is kept constant. General disadvantages of the manometric methods are: considerable experience, and
After the introduction of the amperometric oxygen concentration measurement by means of the Clarck cell (Mancy K. H., Okun D., and Reilley C. N., 1962, "A galvanic cell oxygen analyser"; J. Electroanal. Chem., 4, 65-92), the manometric methods have been superseded by the electrochemical respiration measurements. These are based on measuring the concentration of dissolved oxygen in an active sludge suspension. The measurement of the oxygen concentration is relatively simple and lends itself to on-line applications. It is possible to correct for the effects of temperature and pressure fluctuations in a relatively simple manner. A distinction can broadly be made between two methods: the batchwise or "closed" respiration measurement and the continuous or "open" respiration measurement.
Batchwise methods are the most used. In this case, the respiration rate is determined by measuring the rate of decrease of the oxygen content in a sludge sample after switching off the aeration and sealing it off from the atmosphere (Stack, V. T., 1970, "Method and apparatus for measuring rate of consumption of dissolved gas in a liquid"; U.S. Pat. No. 3,510,406, and Pagge, U., and Gunthner W., 1981, "The BASF toximeter--a helpful instrument to control and monitor biological waste water treatment plants"; Wat. Sci. Tech., 13, 233-238). However, said method has the disadvantage that continuous measurements are not possible.
In an open respirometer aeration takes place. An equilibrium is established between the supply and the consumption of oxygen. If the oxygen supply coefficient (Kla) is known, the respiration rate can be calculated directly from the measured oxygen concentration (Farkas, 1969, "Method for measuring aerobic decomposition activity of activated sludge in an open system"--Advances in Water Pollution Research, 4th Int. Conf. Prague, April 21-25, 1969 (edited by Jenkins) Pergamon Press, London, Dec. 4, 1969, pages 309-317, 319-327; Holmberg U. and Olsson G., 1985, "Simultaneous estimation of oxygen transfer rate and respiration rate"; Modelling and control of
REFERENCES:
patent: 3731522 (1973-05-01), Mikesell
patent: 3813325 (1974-05-01), Merrell et al.
Klapwijk Abraham
Spanjers Henricus L. F. M.
Ecotechniek B.V.
Johnston Jill
Warden Robert J.
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