DE2951707A1 - Continuous BOD determn. - by passing waste water and activated sludge through reactor and measuring change in air oxygen content - Google Patents

Abstract

Continuous determn. of the BOD of waste water is effected by passing a mixt. of the water and activated sludge through a reactor together with air and measuring the difference between the O2 concns. in the air entering and leaving the reactor. The reactor pref. comprises a series of stirrer vessels connected in parallel with a reference reactor, the latter being supplied with activated sludge and air only. The waste water and activated sludge are supplied via metering pumps. Each vessel is equipped with its own gas outlet valve so that the air from each vessel can be supplied to the analysis unit. The amts. of air entering and leaving the reactors can be measured with float-type flow meters. The reactors are pref. thermostatically controlled by a common thermostat. The process can be carried out using relatively simple, transportable equipment; results are obtained continuously with a response time of less than 2 hr, so that the process can be used for monitoring and control of water treatment facilities.

Description

DESCRIPTION

Title (technical name) of the invention Measurement method for determination the concentration of biodegradable substances in wastewater Area of application The The invention relates to a measuring device that is used for water analysis in sewage treatment plants, at water supervisory authorities and can be used in microbiological laboratories.

Purpose To assess the degradability of organic ingredients in sewage caused by microorganisms (predominantly aerobic bacteria) are measuring methods required, in which these microorganisms are included in the measuring process have to. Their metabolic activity can indicate the concentration of organic, biodegradable ingredients are closed.

To such a measuring method for the control and regulation of sewage treatment plants To make it usable, the measurement time must be less than two hours. In determining the breathability of activated sludge from biological wastewater treatment processes and in determining the reaction kinetic parameters of the degradation of organic Ingredients must also determine the metabolic activity of the microorganisms will.

Stalld of technology and criticism of known measurement methods It is known that the concentration of organic substances in the water is due to the metabolic activity can be determined by microorganisms. The metabolic activity of aerobic microorganisms can in turn be caused by the consumption of oxygen or the formation of carbon dioxide be determined.

The biochemical oxygen consumption BOD5 is the most widespread Measurement method of this type. The amount of oxygen consumed is manometric or determined by the decrease in dissolved oxygen. However, the measured value is only there after five days and can therefore not be used to regulate sewage treatment plants.

Furthermore, the amount of oxygen consumed is not just a function the metabolic activity of the microorganisms during the breakdown of organic substances, but it is also dependent on secondary processes in an unreproducible way (Wilderer, P., G. Engelmann and II. Schmenger: "Criticism of the BSB, as a pollution parameter", Das Gas- und Wasserfach (gwf) Wasser Abwasser, Volume 118 (1977) ran 8, pp. 357-564).

There are also some suggestions for short-term measurement methods been. Different devices like the Pollux-Pollumat are similar to a manometric one B5B5 measuring apparatus set up (Hartmann, L .: The plateau BOD, measurement and significance ", Umwelthygiene, Volume 5 (1974), pp. 99-102; Wilderer, P., L. Hartmann and G. Keser: The plateau BOD as a measure of the concentration of biodegradable substance ", Journal for Water and Wastewater Research, Volume 11 (1978), No. 3/4, p. 82-86; ~ Short-term BOD measurement with the Pollux-Pollumat ", publication from Pollux GmbH Ludwigshafen).

The measuring time should be shortened by a high sludge concentration. The decrease in oxygen partial pressure will be continuous as a function of time recorded. The measured value sought is reached when the curve has a maximum curvature having.

Devices of this type have the following disadvantages: the measurement takes place discontinuous, - the measured value is difficult to determine because the curvature is only little changes, - through the chemical bond of the resulting C02 the pH value, which exerts influences on the microorganisms, is lowered, - the Analysis time is shorter than 30 minutes, which means that only very easily degradable substances are taken into account - automatic devices can only be realized with high technical effort, which is usually associated with a high susceptibility to failure.

Other devices work according to the respiration method (Jübermann, 0., G. Krause and F.-J. Schulte: "Appropriate implementation of respiration measurements for the automatic control of wastewater ", Vom Wasser, Volume 34 (1967), pp. 261-280; Veits, G .: A new device for respiration measurements ", waste water technology, year 6: 9-11 (1977); Otto, G .: "Rapid determination of the degree of efficiency (BOD5 degradation) biological wastewater treatment plants ", Acta hydrochim. hydrobiol. Volume 4 (1976), Book 5, p. 491494).

The wastewater sample is inoculated with bacteria and supplied with oxygen. The decrease in the concentration of dissolved oxygen is measured with an electrode determined and recorded as a function of time. The slope of the curve is then used as a measure of the concentration of biodegradable substances.

The sample must be diluted so that the rate of oxygen consumption lies in a certain range. If the speed is too high, only easily degradable ingredients detected and the transition behavior of the measuring system can lead to additional errors. On the other hand, if the dilution is very high, the Effect of toxic substances can be weakened and thus overlooked.

OBJECT The invention is based on the object of a measuring method to develop, with the after a measurement time that is shorter than two hours, the Concentration of biodegradable substances in the water can be determined can. All the substances fed in flow through the measuring apparatus in a fully continuous manner.

The measured value is also determined continuously. The most important disruptive secondary influences are compensated.

Solution (claim 1) This task becomes inventive solved that the water to be examined - usually waste water - in a measuring cell flows and there intensively with activated sludge, which mainly consists of active microorganisms exists, and measuring air is mixed. All three streams are continuous. The oxygen concentration difference the incoming and outgoing measuring air is determined by gas analysis and is a measure for the concentration of the biodegradable constituents of the water to be examined.

Further embodiment of the invention (reproduction of the characteristic Part of the dependent claim) 2. A comparison reactor is arranged parallel to the measuring reactor, which is only traversed by activated sludge and measuring air. This will reduce oxygen consumption through endogenous respiration, disruptive influences through changing properties of the activated sludge and other secondary processes are minimized.

3. The measuring reactor is constructed in the form of a multi-stage stirrer cascade. The stirrers are designed so that there is no growth of microorganisms on the walls can train. This design has the following advantages: a) There is a high degree of conversion, which is necessary to achieve sufficient measurement accuracy is achieved.

b) If the concentration of the biodegradable ingredients changes there is only a short dead time.

4. The comparison reactor is a single or multi-stage stirred cascade educated. The influence of secondary processes, like that of endogenous respiration minimized, since the changes in the bacterial properties in the measuring cascade and in the comparative reactor tend to have the same effect and thus largely compensate.

5. All stirred reactors are provided with air outlet openings that optionally connected directly to the analysis part via a system of taps can. This also allows a) the breathability of activated sludge and b) the kinetic parameters of the degradation of the organic constituents of wastewater determine.

6. The sewage and the activated sludge are supplied via adjustable Dosing pumps. This makes it possible to change the dwell time.

7. The volume flow of the incoming measuring air is measured with flow meters certainly. This is necessary because the volume flow has a direct influence on the Has measured variable.

8. The measuring cascade and comparison reactor are in one or two Thermostating vessels that are fed by a common thermostat. Temperature fluctuations affect the measuring cascade and the comparison reactor in tend to have the same shape and thus largely compensate for each other.

9. The entire measuring device consists of several portable, fast connectable components. It is therefore possible to simply use the measuring device if necessary to be transported and quickly dismantled and assembled.

Achievable Advantages The advantages obtainable with the invention are in particular the following: - All currents flow continuously through the measuring apparatus.

There are therefore no stepping mechanisms, solenoid valves, flushing devices, Sealing mechanisms, pressure regulators, and related parts are known to be necessary cause a high susceptibility to failure.

- The response time is less than two hours, so the measuring process - together with other supplementary analytical methods - for constant monitoring and control of sewage treatment plants can be used.

- Through the parallel investigation of the microorganisms made up Activated sludge, the influence of secondary influences is minimized.

- The measuring method can still be used to carry out basic examinations to determine the breathability of microorganisms and the reaction kinetics Perform parameters of the degradation of organic constituents of the wastewater through # ~.

- Are there additional measured values for the total organic carbon content (TOC), symptoms of poisoning can be uncovered, e.g. high eoncentra; heavy metal ions occur.

- The measuring device Y1 # developed according to the measuring method can be used in three transportable housings. It is therefore possible to take measurements one after the other be carried out at various sewage treatment plants, bodies of water and in laboratories.

Description of an exemplary embodiment An exemplary embodiment of The invention is shown in Figure 1 and is described in more detail below. Included there is a subdivision into the measuring cascade, the comparison reactor and the measuring gas conditioning and analysis, as well as the mechanical structure of the measuring device.

1. Measuring cascade The wastewater to be examined is supplied by the diaphragm metering pump ? pe (9) pumped into the measuring cell, 2-die pumped. This is as a four-stage stirred tank cascade educated. The total liquid content is about 0.5 1. Each level (2,3,4 and 5) consists of one cylindrical acrylic glass container. Magnetic stirrer ensure an intensive mixing of the liquid. The metering pump (8) delivers Bacterial sludge in the first stage of the cascade. This vaccination can cause a breakdown of the organic substances contained in the wastewater are introduced by bacteria. The oxygen required by the aerobic microorganisms is supplied in the form of air. The reactor is controlled by a pressure reducer and variable area flow meter (12) supplied with compressed air from 40 1 steel bottles. In normal operating condition flows the air one after the other through all stages of the cascade and then into the sample gas conditioning and analysis part of the system.

By opening or closing the gas outlet valves accordingly However, it can also be achieved that the measuring gas is only through one, two or three Steps flows.

In the first stage, the electrode (21) and the measuring amplifier are used (22) determines the concentration of dissolved oxygen.

2. Comparison reactor In the measuring cascade, the oxygen consumption should be can be determined by the decomposition of the organic substances, i.e. by substrate breathing. However, the bacteria contained in the inoculation sludge still consume additional oxygen through endogenous respiration and through degradation of the remaining substrate in the sludge. In order to be able to eliminate these influences, a part of the metering pump (7) is used of the bacterial sludge is pumped into the comparison reactor (6). The supply of air takes place via the variable area flow meter (11).

The comparison reactor shown schematically as a square in Figure 1 is designed as a single or multi-stage stirring cascade.

The measuring cascade and the comparison reactor are located in a water bath (1), which is kept at a constant temperature by the ultra-thermostat (14).

3. Measurement grass preparation and analysis With the help of three-way cocks either the air emerging from the cascade or from the comparison reactor in the preparation and analysis section. Not each of them used Air is blown off into the environment at the taps.

Because the volume flow required for the gas analyzer is much smaller as the ventilation volume flow is, the excess air is added to the one with water filled drainage vessel (15) led into the open. The air humidity is in the cold trap (16) frozen out. The residual moisture still contained in the gas is then converted into a chemical dryer (17) retained. With the pump (10) the sample gas is over the variable area flow meter (13) to the paramagnetic oxygen analyzer (18) funded. The analyzer generates one of the oxygen concentrations in the measuring gas proportional impressed direct current. The voltage drop across a load resistor is registered by the multi-channel recorder (20). The record of concentration of the dissolved oxygen in the first stage of the cascade also takes place with the Clerk. Furthermore, an analog computer (19) is provided, which continuously the Calculation of the desired substrate concentration based on an evaluation equation performs. The compressed air can be checked using a three-way valve to check the zero point - bypassing the cascade - are fed into the analyzer. The calibration takes place with the help of calibration gases of various compositions.

4. Mechanical structure of the measuring device The individual devices of the measuring system are housed in a three-part housing with a frame made of angular steel. the Hose connections, mostly with bayonet locks, with the fittings are connected, and leave the electrical lines between the three structural units can be released in a few simple steps so that each unit can be transported separately can.

The unit 1 essentially contains the metering pumps for substrate and activated sludge, the magnetic stirrer control and a gas mixing pump for calibration of the gas analyzer.

The thermostatic bath with measuring cascade is located in unit 2 and comparison reactor, operating fittings, volume flow meter, ultra thermostat and Parts of the sample gas conditioning.

The structural unit 3 contains other parts for gas preparation, such as Cold trap with power supply unit, chemical gas dryer and a membrane filter, as well as the Gas analyzer, pressure measuring instruments, measuring amplifier for the oxygen and pH electrodes, a digital voltmeter and a 2-channel line recorder.

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Claims (9)

I 'A T s N for A N S P R U C H E learn to determine the concentration biodegradable substances in wastewater according to the BOD method, in which the Oxygen consumption measured in a wastewater sample mixed with activated sludge is, characterized in that the waste water, the activated sludge and the oxygen containing measuring air flow continuously through a measuring reactor and the oxygen concentration difference the air flowing into the measuring reactor and the air exiting from it in one Analysis part is measured. 2. The method according to claim 1, characterized in that a parallel Activated sludge and measuring air flow through comparative reactor connected to the measuring reactor is, with also the oxygen concentration difference of the entering and exiting Measuring air is measured. 3. Device for performing the method according to claim 1 and 2, characterized in that the measuring reactor consists of a multi-stage cascade, the is formed from containers provided with agitators, through which the water flows one after the other, consists. 4. Device according to claim 3, characterized in that the comparison reactor is designed as a single or multi-stage measuring cascade. 5. Device according to claim 3, characterized in that at each Container (2 to 5) an air outlet valve is provided so that the measuring air is optional can be guided from each container to the analysis part. 6. Device according to claim 3, characterized in that the feed of the wastewater and the activated sludge takes place via metering pumps (7,8,9). 7. Device according to claim 3 to 6, characterized in that for measuring the amount of incoming and outgoing measuring air, flow meters, in particular Variable area flow meters (11 to 13) are provided. 8. Device according to claim 3 to 7, characterized in that the measuring reactor (2 to 5) and the comparison reactor (6) are located in one or two thermostating vessels which are supplied by a common thermostat. 9. Device according to claim 3 to 8, characterized in that it consists of several portable, quickly connectable components.