DE2214963A1 - DEVICE FOR DETERMINING THE BIOCHEMICAL OXYGEN REQUIREMENTS OF POLLUTED WATER - Google Patents

Description

469Ü Herne, 6000 Munich 23,

Freiligrathstrasse 19 -. , I «« DU Rahr Eisenacher Strasse 17

P.O. Box 140 U I ρ I. - I Π g. Π. Π. D d Π Γ Pat. Beizler

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IOWA State University Research

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Device for determining the biochemical oxygen demand of contaminated water

The invention relates to improvements in an electrolytic Method for determining the biochemical oxygen demand ■ of contaminated water and in particular a device for this. The electrolytic method that sometimes also called the Clark method, for the continuous determination of the oxygen uptake of a larger one inhomogeneous biological, sample was first described in an article by J.W. Clark in 1959 as the Engineering Experimental Station Bulletin No. 11 published by New Mexico State University. The principle described concerned the

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Maintaining the pressure in a closed vessel containing the sample by topping up or topping up or replacing the oxygen consumed by the metabolism with the electrolysis of thin acid. _{The CO 2 produced} during metabolism was absorbed with potassium hydroxide. The internal pressure of the cell was monitored by a device capable of sensing a pressure drop to operate a power source for the electrolytic cell. A direct current was fed to the electrolytic cell, and the duty cycle of the power source, which was measured on an hour meter, formed a measure of the oxygen consumed by the sample.

After Faraday'sehen a Faraday law is to _T number of ampere-seconds, which is required to an electrochemical equivalent weight of a substance dissolved. For example, in the case of water, a Faraday produces 8,000 mg of oxygen on the positive electrode per 96.485 ampere-seconds. With a constant current, time is therefore a direct measure of Op generation.

Improvements to this technique were described in an article published in the journal Analytical Chemistry, vol. yi , page 784 (May, 1965) and entitled "An Improved Apparatus for Biochemical Oxygen Demand", which authors are JC Young, W. Garner and JW Clark.

The electrical construction of the power source used in this earlier model was unsatisfactory. There was no steering and control of the

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electricity used for electrolysis., and frequent of Manual adjustments and corrections were necessary. . The fact is that fluctuations in the generated amount of oxygen occur as a result of changes in the mains voltage, changes in the electrolytic concentration due to evaporation from the cell, Changes in electrolytic concentration from the electrolytic conversion of water to hydrogen and Oxygen here and there as a result of differences in processing new electrolyte solutions. Frequent readjustments of the units were therefore necessary in order to maintain a constant To maintain electricity. Despite these sources of error, the biochemical oxygen demand of samples could exist from raw wastewater and synthetic waste with a composition or degree of enrichment that is different that of raw wastewater can be measured more precisely,

it
than possible with other available methods

An article of the methods is a review of the development of the manometric for determination of biochemical oxygen demand and the title "The Determination of Biochemical Oxygen Demand by Respirometric Methods", author HAC Montgomery, ^a ifurde in the journal "Water Research", Pergamon Press, (I967) vol. 1, pages 63I-662. "

The present invention also provides improvements in the electrolytic method of determining biochemical Oxygen requirements first described by Clark and was further developed later, as mentioned above. The improvements relate to the construction the electrolytic cell and the overall system that

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has a regulated power source. The cell includes a substantially cylindrical outer wall, one with the outer wall has a coaxial cylindrical partition which has an opening so that the electrolyte is free can flow on both sides of the cylindrical partition. A central tube is inside the partition is provided and extends into a region above the surface or the level of the electrolyte. A cap with a frusto-conical body and a circular top splash is on top of the placed on the cylindrical partition of the electrolytic cell. Three electrodes extend through the Splash, namely a sensing electrode for detection the height of the electrolyte level, a common or negative DC electrode and a positive DC current electrode.

With regard to the structural features of the new system, it should be emphasized that the diameter of the circular Flange of the cell cap is approximately equal to the outer diameter of the outer cylindrical wall of the cell. When the cap is placed on the cylindrical partition in a sealing connection therewith, is located the circular flange is slightly above the outer cylindrical wall of the cell, at a distance from two to three mm to create an annular opening that communicates with the part of the electrolyte in that the DC negative electrode is immersed. Thus, the narrow annular opening allows the escape Hydrogen and still brings the evaporation of the electrolyte to a minimum.

In addition, there is an opening in the upper seat or passport

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part of the inner cylindrical wall of the cell (above the electrolyte) is provided, and in the frustoconical A corresponding opening is located on the wall of the cell cap. When these two openings are aligned, the interior of the reaction vessel receiving the sample is in communication with the atmosphere via the central tube of the cell to control the pressure inside the reaction vessel to match that of the atmosphere as a reference or starting point.

Further improvements according to the invention in the overall combination result from the use of a regulated direct current source in order to ensure that a constant current always flows when the direct current electrodes are switched on, so that an operating hours counter or a timer which is only activated when the regulated direct current source is switched on takes a very precise measurement of the O2 consumed. As is known, the amount of oxygen generated is a linear function of the time integral of the current. When using the new energy supply system, the current for the electrolysis is kept within a deviation range of 1 % of the desired value for changes of + $ 0% in the electrolyte composition and for changes of + ± 0% in the mains voltage.

A manually operated selector switch is provided to set the magnitude of the current so that the magnitude of the current times the elapsed time is a measure of the oxygen consumed. The sensing electrode provided for the electrolyte level in _; the cell is connected to a relay. .When the level of the electrolyte in the space between the cylindrical partition and the outer wall

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sinks below a predetermined level (caused by a Decrease in the C ^ pressure in the reaction vessel), switches the relay switches on the current-regulated energy supply to the direct current electrodes and also actuates the Operating hours meter. The DC negative electrode serves as a common lead for the system. Through this it also forms one of the alternating current sensing electrodes, which eliminates the need for an additional electrode.

Other features and advantages of the present invention will be apparent to those skilled in the art those skilled in the art from the following description of a preferred embodiment with reference to FIG Drawings in which the same reference characters always refer to the same parts in different views.

FIG. 1 is a plan view showing the improved electrolytic cell, partially shown in FIG Sectional view, in connection with the representation of a Control cabinet j

Figure 2 is an exploded perspective view of the improved electrolytic cell, in part in sectional view;

Figure 3 is a circuit diagram of the control portion of the system.

In FIGS. 1 and 2, the reference number denotes a reaction vessel as a whole. At 11 there is an electrolytic Cell designated and the reference numeral 12 denotes

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draws the cabinet for the energy and control unit. The reaction vessel Io is a glass container, preferably made of Pyrex, with a cylindrical side wall 13 and an upper open neck 14. The ones marked I5 The designated sample is contained in the reaction vessel Io, and an air space 16 is above the surface of the sample 15 within the reaction vessel Io. A magnetic stirrer, shown schematically at S. is arranged inside the reaction vessel Io.

The neck 14 of the reaction vessel Io takes an extension piece or insert, which is designated as a whole by the reference numeral 17, the insert 17 is also preferably made of Pyrex glass.

The insert 17 includes an upper, tapered sleeve 18, the outer surface of which is in sealing engagement with the inner, upwardly flared surface of the neck 14. A tubular container 19 with a closed bottom extends downward from the sleeve 18. The container I9 contains a quantity of potassium hydroxide solution 2o to absorb the CO ₂ generated by the metabolism of the microorganisms in the sample. A wick 21 made of glass wool is located in the solution 2o and extends beyond its upper mirror. First and second openings 2J and 24 (FIG. 2) are formed in the wall of the insert 17 in the area of the upper end of the container 19 and are in communication with the air space 16 of the reaction vessel 10. The openings 2j5 and 24 allow the CO ₂ developed by the sample to enter the container 19 of the insert I7 and through the

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retained potassium hydroxide solution is absorbed. As can be clearly seen from the following description, the openings 2; and 24 also allows O ₂ from the electrolytic cell to enter the air space 16, where it is absorbed and consumed by the sample. Both the outer and inner surfaces of the glass sleeve 18 are ground to create an airtight connection with the inner surface of the neck 14 and the electrolytic cell 11 to provide. The inner surface of the neck 14 is also ground.

The electrolytic cell 11 shown in FIGS. 1 and 2 comprises a cylindrical outer wall 26, a cylindrical intermediate wall 27 coaxial with the outer wall 26 and a central tube 28 which runs coaxially with respect to the walls 26 and 27. An outer annular space which is formed by the cylindrical walls 26 and 27 is denoted by 29a. The inner annular space between the wall 27 and the tube 28 is denoted by 29b. The lower part of the wall 26 is drawn inwards and narrows in the direction of the intermediate wall 27 to which it is connected. The bottom of the tube 28 is widened to merge with the inner surface of the wall 27.

From the lower part of the outer wall 26, an inwardly narrowing fitting piece J> o with an outer ground surface for insertion into the sleeve 18 of the insert piece 17 projects downwards. The outer surface of the fitting piece 3o narrows accordingly, as can be seen from FIG. An opening 51 is provided in the vicinity of the bottom of the cylindrical partition 27, so that the annular space 29a with the annular

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shaped space 29b communicates. An electrolyte 55 is in both of these 'annular spaces and can move freely through the opening 5I. A preferred type of electrolyte is a 0.5 to 0.5 normal solution of sulfuric acid. The upper part of the partition 27 tapers to a narrowed dimension at the upper end, around a conical seat surface 27a for receiving a cap designated as a whole as 55, which is also preferably made of Pyrex glass. An opening 54 is in the conical part 27a the intermediate wall 27 is formed.

The cap 55 has a frustoconical mount 57 to be placed on the correspondingly tapering part 27a of the intermediate wall 27. The inner surface of the socket 57 is also ground, as is the outer surface of the tapering part 27a of the intermediate wall 27, in order to enable an airtight connection. The cap 55 also has an upper circular flange 58 that forms part with the socket 57. The flange 58 has three openings 59 *. 4o and 4l to accommodate three separate electrodes, as will be described below. The outer diameter of the circular flange 58 is approximately equal to the outer diameter of the cylindrical outer wall 26. When the cap 55 is fully fitted onto the intermediate wall 27, an annular space, designated 44, remains between the lower surface of the flange 58 and the upper edge of the outer wall 26 exist. The annular space 44 is preferably about 2 to 5 mm · This annular opening allows the escape of hydrogen which is formed during the electrolysis of the electrolyte ~ ^ J>, and yet reduces the evaporation of the electrolyte and this has proved advantageous

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for a long-term accurate operation of the cell, as is normally aimed at.

The socket .37 of the cap 35 has an opening 57a, which can optionally be brought into alignment with the opening 34 of the seat 27a of the intermediate wall 27 or into a position that covers this opening and seals it by rotating the cap 35. When the cap 35 is placed on the cell 11, as shown in FIG. 1, a chamber designated by 47 in FIG. 1 is created. The chamber 47 is formed by the tapered part 27 a of the intermediate wall 27 and by the cap 35. The chamber 47 communicates with the upper air space 16 of the reaction vessel Io via the tube 28, the adapter 3o of the cell 11 and via the openings 23 and 24 of the insert I7. When the openings 34 and 37a are in alignment; are together, the chamber 47 is also through the annular space 44 with the atmosphere in communication to equalize the pressure prevailing in the chamber to that of the atmosphere and to bring the level of the electrolyte within the annular inner space 29b to the same height the electrolyte has in the annular space 29a. When the cap 35 is rotated so that the openings 34 and 37a are not in alignment with one another, the chamber 47 and the air space 16 are sealed off from the atmosphere. _{When O 2 is then} consumed by the sample as a result of metabolism and CO _{2 is released} into the chamber 16, the COp 'is brought through the openings 23 and 24 into the interior of the tubular container 19, where it is absorbed by the potassium hydroxide 2o creating a slight vacuum. This reduced pressure is transferred to the chamber 47 * around the electrolyte in the inner annulus 29b

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to bring a greater height or a higher mirror, whereby the mirror of the in the outer annular space 29a contained electrolytes is lowered.

A first sense electrode 50 extends through the opening 39 in circular flange 38 and is there attached by means of an epoxy adhesive. The electrode 50 extends to a predetermined height within the outer annular space 29a of the cell 11 and is located normally in contact with the electrolyte. When the COo in the headspace 16 is absorbed by the potassium hydroxide solution, as already described., the level of the electrolyte in the outer annular space falls and the contact with the sensing electrode 50 is interrupted. When this contact break occurs, it becomes a direct current, as will be explained in detail later led to the electrodes 52 and 53, which are in corresponding openings 4o and 4l of the circular flange 38 are added and fixed there with epoxy and sealed. The electrodes 50, 52 and. 55 'are preferably made made of platinum. - '■ "-,

The electrode 52 extends through the chamber 47 into the electrolyte contained in the inner annular space 29b. The electrode 53 is in contact with the electrolyte 33 in the outer annular space 29a, as can be seen from FIG. 1. Therefore, when the electrolyte 33 breaks contact with the sensing or mirror monitoring electrode 50, indicating a reduced pressure in the chamber 47, the electrolytic process is initiated. O _{2 is} generated at the positive electrode 52 in order to increase the pressure within the chamber 47 and at the same time _{to replenish the supply of O 2} in the air space 16. Hydrogen becomes at the negative electrode 53

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and via the annular gap 44 released the atmosphere. This process continues until the pressure inside chamber 47 rises above the level of the electrolyte in the inner annulus 29b, thereby increasing the level of electrolyte in the outer Annular space 29a is caused so as to make contact with the electrode po. When the contact reaches the electrolysis is stopped, this keeps the level of the electrolyte within a narrow range held, whereby the Og pressure within the air space 16 is kept substantially constant. Corresponding Pig. 3 are power lines ρό and 57 through a usual AC power source, not shown, fed at 60 Hz. A fuse 58 and a main switch 59 are in of line 56. The primary coil of a first transformer 60 is connected by lines 56 and 57 to the Power source connected, and a secondary coil of the transformer 6o feeds a double rectifier bridge, indicated at 61 for generating a DC output voltage. A capacitor 62 filters this DC voltage, and this is connected to a current-regulated power supply via a manual switch 65 or energy supply applied, which is bordered by the dashed line 64. Because it is intended a multitude To test samples simultaneously, it is preferred that only one voltage source carrying direct current is present is and that this. Voltage is applied to a separate current regulated power supply for each operating cell will. The positive potential of the bridge output is connected to the collector of an NPN transistor Ql, whose base with the negative terminal (which forms the earth, also called the common system) of the Bridge circuit via a Zener diode Z is connected. A current path is between the collector and the base

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of the transistor Ql is provided through a resistor 65 to bias the Zener diode Z and to provide a path for the base current for the transistor Ql. The emitter of the transistor Q1 is connected via a resistor 06 to the emitter of a PNP transistor Q2. The collector of transistor Q2 is connected to the moving contact of contacts 67a of a two-position relay. The normally open terminal of contacts 67a is connected to a reactive load resistor 68. The other side of the resistor 68 is connected to the common system. The normally closed contacts 67a are in series with a plug-in socket 69 and an ammeter 70 connected to the positive electrode of ^a ^ 52nd The electrode 53 is connected to the common system and serves as a negative Gleiehstrom.ffirelectrode when the electrolyte in the annular space 29a is below the predetermined level, that is, when it is not in contact with the sensing electrode 5o. The electrode 5j5 also serves as a common line for the AC power source, as will be described below.

The base of transistor Q2 is with the emitter of a second PNP transistor QJ, whose collector is in common connection with the collector of the transistor Q2. Therefore, the transistors Q2 and Q2 form Q3 a Darlington amplifier. A resistor 7oa is between the emitter of the transistor Ql and the base of the transistor Qjü> connected. The resistor 7oa acts in conjunction with a second resistor as Voltage divider for the voltage at the input of the Darlington amplifier to hold at a chosen constant value. The second branch of the voltage divider includes a selected one Resistance value to the output current of the

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To determine regulator circuit 64. This means that four separate resistance branches are provided, which can be selected by a switch 71, the movable arm of which is directly connected to the common system and which has four fixed contacts labeled I-IV. In particular, a first variable resistor 73 is connected in series with a fixed resistor 7 ^ between the base of transistor Q3 and a fixed contact I of switch 71. A second variable resistor 75 is connected in series with a fixed resistor Jo between the base of the transistor Q3 and a fixed contact II of the switch 71. A third variable resistor 77 is connected in series with a fixed resistor to position III of the switch 71, and a fourth variable resistor 79 is connected in series with a fixed resistor 80 to the fixed contact IV of the switch 71. Each of these variable resistors 73 * 75 * 77 and 79 allows a fine adjustment of the output current to a predetermined value. Once an initial schedule has been made, these settings are usually not changed afterwards.

When the current regulator is in operation, the Zener diode Z maintains a constant voltage at the base of the transistor Ql upright. Since the transistor Ql is biased in the active area, its base-emitter connection is forward biased so that the voltage at the emitter of transistor Ql in all areas of the current im is essentially constant. Therefore, the first stage of the current regulator takes the DC output of the bridge circuit 61, which fluctuates with the line voltage, and brings it to a lower but constant value regardless of changes in the network amounting to + lo $

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Care. Thereby, the voltage at the voltage divider holds including the resistor 7oa and one of the selected and connected to the switch ¹ Jl branch, a constant, but · selectable voltage at the base of the transistor Q5 upright. As long as transistors 0, 2 and Q3 are in the active region, the total collector current depends on the base current, which is determined by the voltage across resistor 7oa and emitter resistor 66. When the load changes, it causes the voltage to change Resistor 66 changes and adjusts the base current of transistors Q2 and Q3 to keep the load current at a constant value. The total resistance of the branches of switch Jl connected to positions I-IV becomes progressively smaller in order to increase the voltage across resistor 7oa when the movable contact of switch ^ l is moved to a higher position. Therefore, the output current from the collectors ″ of the transistors Q2 and QJ is essentially independent of the load value within the range of the arrangement. For example, a constant load current can be achieved with changes in the range of + 5 % in the electrolyte composition and with changes of + Io % in the supply network.

The primary coil of a transformer 84 is connected to the Power lines 56 and 57 connected, and the secondary coil of the transformer 84 is between the common System and the coil of a relay 67 placed. The other end of the coil of relay 67 is directly connected to the sensing electrode 5o. Connected. The previously described Contacts 67a 'are actuated by relay 67, i.e. when the coil of relay 67 is not energized. the Contacts 67a connect the output of the current regulator directly to the positive electrode 52 via the plug-in

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socket 69 and the ammeter 7o. On the other hand, when the coil of relay 67 is energized, oil contacts 57a, indicating that the level of electrolyte in annulus 29a is at least as high as predetermined, connect the output of the current regulator circuit directly to a dummy load (Resistor 08) so that the current control circuit is always in operation and, for the purpose of greater accuracy, operates at a stabilized equilibrium temperature. The relay 67 is. provided with a second set of contacts 67b, and these contacts are connected in series to a switch 85 for connecting the power lines 56, 57 to a timer or hour meter 86. The contacts 67b are normally closed. Therefore, not only is the current regulator connected to the electrode 52 when the level of the electrolyte falls below a predetermined level, thereby stopping the energization of the relay's r-coil, but also the operating hours counter 86 begins to count the time measure up. An indicator lamp 87 is connected between power line 57 and the junction of switch 85 and contacts 86b, and when illuminated it means that the current control circuit and the hour meter circuit are energized. Switch numerals 63 and 85 each indicate, on one side, a single two-pole switch.

As can be seen from Fig. 1, the setting or Selection device for the ammeter 7o (here it can are a simple multiplication factor) marked 90 on the front panel of the cabinet and is the scale for the operating hours counter 86 is shown at 91. The button for the selector switch 71 is designated by 92, and the shaft of the switch and the

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Switch 85 of the operating hours counter circuit carries the reference numeral 9 ^. The indicator lamp 87 is also

specified. . .

After describing a preferred embodiment • example of the improved system for determining the biochemical oxygen demand. by electrolysis is it can be seen that the operation of the system is made more precise through the use of a regulated and very accurate DC power supply that is only effective between the two electrolysis electrodes 52 and 53 is when the level of the electrolyte is below a predetermined level, thereby reducing a Pressure inside the reaction vessel containing the sample is displayed. The output current of the Regulated power supply is insensitive to changes or fluctuations in the supply network and in the electrolyte composition. In addition, one of the electrodes causing the electrolysis is used, namely the electrode 53, as a common system and is used in connection with the sensing electrode 50 to to determine the level of the electrolyte inside the cell. When the level of the electrolyte is at least as high as it corresponds to a predetermined height (this depends on the end of the electrode 50 ab) in the outer annulus 29a, the electrodes 50 and 53 receive current from an alternating current source. Against it the electrodes 52 and 53 are fed by a regulated direct current source during the electrolysis process. The setup of the "system" is facilitated by the presence of the openings which are aligned with one another 3 ^ and 37a in the cylindrical partition 27 and the cap 35 * to reduce the pressure inside the reaction vessel Io before the device is started up

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to adapt to the atmosphere. It should be noted that the circular patch 38 of the cap 35 * which has essentially the same diameter as the outer wall 26 of the electrolytic cell 11 and is arranged therefrom by a small distance of the order of 2-3 mm, the evaporation of the electrolyte solution 33 very strongly limited while simultaneously allowing the escape of the resulting at the electrode ^ hydrogen gas. In addition, access to the interior of the cell 11 for cleaning and maintenance purposes is greatly facilitated by the fact that the electrodes are attached to the cap 35.

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Claims (2)

22H963 Αϊ Claims lj device for determining the biochemical oxygen demand of contaminated water, geke η η ζ eich η et by a reaction vessel (Io) ,, which contains a sample (15) and with a neck (14) and an air space (16) above the sample "(15) next to the neck (14), a cell (H) / which is received in the neck (14) and an outer wall (26), an intermediate wall (27) and a central tube (28) to form a first and a second space (29a, 29b) between the outer wall (26) and the partition (27) and the tube (28) for receiving an electrolyte (33), the partition (27) having an opening (Jl) has below the level of the electrolyte (33) for a connection of the first and the second space (29a) or (29b) with one another, a sensing electrode (5o) which normally touches the electrolyte (33) in the first space (29a), positive and negative electrodes (52, 53) in the first and second spaces (29a and 29b, respectively), immersed in the electrolyte (35) » a direct current source (61) for exciting the positive and negative electrodes (52 or 53) depending on the interruption of the contact of the electrolyte (33) with the sensing electrode (5ο) _Λ a cap (35) * which is received on the partition (27) and cooperates with this to form a chamber (47) above the electrolyte (33) in the second space (29b), the chamber (47) with the air space (16) in the reaction vessel (Io), the tube (28) is in communication, the arrangement - 19 309840/0660 a second opening (3 ² O in the partition (27) above the level of the electrolyte (33) and the arrangement of a third opening (37a) in the cap (35) for an optionally aligned position with said second opening (3 ² O the partition (2j) , when the said second opening (3 ² O of the partition (27) and the said opening (37a) of the cap (35) are aligned with each other, the air space (Ib) of the reaction vessel (Io) with the atmosphere communicates in order to equalize the pressure contained therein with that of the atmosphere. 2. Device according to claim 1, characterized in that that the direct current source has a rectifier (61), the electrical energy from a AC power source receives and generates a DC voltage, as well as a separator, which the output voltage of said rectifier (61) for generating a constant direct current voltage independently of Absorbs fluctuations in the named alternating current source, and a control circuit (64) for generating a constant current as a function of the output voltage of said disconnecting device, wherein an operating hours counter (86) which is switched on when said Voltage is applied, the amount of biochemical oxygen demand of the sample. - 2o - 3098 k 0/0660 Blank