Chemistry: analytical and immunological testing – Oxygen demand
Patent
1998-07-09
2000-09-05
Beisner, William H.
Chemistry: analytical and immunological testing
Oxygen demand
435 30, 4352871, 4352875, 435817, 422 79, G01N 3318, C12M 134
Patent
active
061141720
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention concerns a process to determine the biological oxygen demand (BOD) of sewage, whereby a sewage sample is mixed with a biologically neutral dilution water at a predetermined degree of dilution and the oxygen concentration is measured in a biological bath which changes as a result of the biological reaction of the predetermined bio-mass with the diluted sewage sample in the biological bath.
The biological oxygen demand (BOD) represents an important parameter to indicate the degree of filth in sewage, because the filth loading of sewage predominantly depends on biologically degradable substances. The common idea in the known processes to determine this degree of filth is that a bio-mass, consisting of aerobic micro-organisms usually placed on a growth surface, is nourished in a biological bath with the sewage to be evaluated or a dilution thereof. The oxygen consumption occurring as a result of the biological reaction leads to a diminishment of the oxygen concentration in the biological bath which is measured and drawn to determine the biological oxygen demand and thus the degree of filth of the sewage to be analyzed.
In a known process of the type named at the beginning (EP-B-0 049 887) which, in contrast to the previously known, time-consuming processes, brought a basic improvement and acceleration of BOD determination, a sample stream of the sewage to be evaluated was diluted before its continuous entry into the biological bath by means of the constantly measured introduction of dilution water at a predetermined degree of dilution. The oxygen concentration was measured before entry into the biological bath and after its exit from the biological bath. The average measured value was kept constant at a predetermined value by changing the degree of dilution. This degree of dilution serves to determine the biological oxygen demand. The turbulent circulation of the bio-mass in the biological bath, which is required for a satisfactory reaction speed, occurs by means of the continuous pumping in a loop of the fluid contained in the biological bath.
The device required for the conduct of this process is relatively complicated, because a regulated amount of the sample stream and the dilution water is required. Measurement of the oxygen must occur at two locations. An additional pump is required to pump the fluid out of the biological bath.
It is therefore the task of this invention to so formulate a process of the type named at the outset, that it can the performed simply, quickly and with little requirement for equipment.
SUMMARY OF THE INVENTION
The task of the invention is solved by a predetermined amount of a sewage sample being added to a biological bath filled with oxygen-saturated dilution water and intermittently mixed, so that the controlling oxygen consumption per unit of time can be measured and the biological bath can be rinsed with dilution water.
This process is intermittently performed and, after calibration of the operating conditions by means of one or more measurement cycles, results in a measured value for the biological oxygen demand in the sewage evaluated during each individual measuring cycle.
The necessary requirement for fluids limits itself in the process of this invention to one sewage sample being brought into the biological bath during each measurement cycle and the bath being rinsed with dilution water after each measurement until the content of the biological bath with respect to biologically degradable matter is so small that it can be discounted. Since the dilution water is hereby introduced in a non-proportioned manner, no pump is necessary; a mere connection to a water line will suffice. For the proportioned addition of an amount of sewage, a very simple, intermittently operating positive displacement pump will suffice. The process can therefore be performed quickly and simply with very little equipment needs, whereby a satisfactorily high degree of measurement can be achieved.
In a favored execution model of the invention it is envisio
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patent: 4314969 (1982-02-01), Arthur et al.
patent: 4350763 (1982-09-01), Suzuki et al.
patent: 4650767 (1987-03-01), Arthur
patent: 4748127 (1988-05-01), Siepmann et al.
patent: 5085759 (1992-02-01), Harker
Beisner William H.
ISCO Inc.
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