GB2071633A

GB2071633A - Waste Water Treating Apparatus

Info

Publication number: GB2071633A
Application number: GB8106361A
Authority: GB
Original assignee: Kubota Corp
Current assignee: Kubota Corp
Priority date: 1980-03-07
Filing date: 1981-02-27
Publication date: 1981-09-23
Also published as: GB2071633B; DE3108629A1; DE3108629C2

Abstract

A waste water treating apparatus comprises an inner tube and an outer tube disposed around the inner tube extending to a considerable depth. The inner and outer tubes are communicated with each other at the bottom portion, whereby the inner and outer tubes form a downward and upward flow chamber, respectively, of a waste water including circulated water. The waste water that flows from the downward flow chamber to the upward flow chamber is circulated to the downward flow chamber by means of a pump. In circulation of the waste water by the pump, an oxygen containing gas is simultaneously supplied to the waste water. An apparatus for monitoring the concentration of oxygen or carbon dioxide in an exhaust gas is provided at an outlet of the upward flow chamber. The oxygen containing gas being supplied is controlled to a predetermined optimum flow rate in response to the monitored concentration.

Description

SPECIFICATION Waste Water Treating Apparatus Background of the Invention Field of the Invention The present invention relates to a waste water treating apparatus by circulating mixed liquor by means of a pump while supplying an oxygen containing gas into the waste water. More specifically, the present invention relates to a waste water treating apparatus adapted for automatically adjusting an oxygen containing gas being supplied as a function of an organic loading contained in the waste water.

Description of the Prior Art Generally a waste water treating apparatus is adapted to dissolve an oxygen containing gas into a waste water and an activated sludge to change the carbon of an organic material contained in the waste water to carbon dioxide, whereby the same is discharged into the atmosphere in a harmless form. Accordingly, the oxygen or the oxygen containing gas being supplied need be increased as an organic material contained in the waste water is increased, as a matter of course. The microorganisms contained in the activated sludge makes use of the oxygen containing gas fully dissolved in the water to convert the carbon contained in the waste water to carbon dioxide.

Accordingly, one concern in a waste water treating apparatus is how effectively oxygen containing gas is dissolved in the water. However, when an aeration tank is not so deep, say 4 m, the air or oxygen containing gas supplied into the water comes upward within approximately ten seconds and a time period of contact of the water with oxygen containing gas is very short, with the result that the amount of oxygen being dissolved into the water is accordingly small. Therefore, in the case of an increased amount of an organic material contained in the waste water, a sufficient amount of oxygen containing gas enough to decompose the same cannot be supplied. On the other hand, the fact that the amount of oxygen containing gas being dissolved in a water is proportional to the pressure being applied to the water is known as Henry's law.Therefore, for the purpose of increasing the pressure, an approach may be considered in which the depth of an aeration tank is considerably increased and in fact a waste water treating apparatus of a deep well type of say 100 m deep has been proposed and put into practical use. The solubility of oxygen containing gas in waste water can be enhanced by decreasing the diameter of bubbles being supplied into the waste water, inasmuch as the interfacial area between the oxygen containing bubbles and the water is increased. For example, in the case of an aeration tank of a deep well type, such as of 100 m depth, the pressure is increased at the bottom area approximately ten times that of an aeration tank of a usual depth and accordingly oxygen containing gas of as much as 1 1 times the usual amount is dissolved.In addition, since an oxygen containing gas such as an air is supplied by blowing into a supplied waste water, the oxygen bubbles become very small due to a turbulent flow effect. For example, in the case where the waste water is caused to flow downward at the flow rate of 1 second, a turbulent flow effect occurs so that the bubbles become extremely fine. As the bubbles become fine, a time period of contact between the waste water and the bubbles is prolonged and accordingly solubility of oxygen containing gas is enhanced. Thus, it has been well-known that in order to enhance solubility of oxygen containing gas into a water it is better to increase the pressure, to decrease the diameter of the bubbles entered into the water and to prolong a time period of contact between the waste water and the bubbles.

A search of the prior art conducted by the inventors indicates that United States Patent No.

3,476,366 issued November 4, 1969 to Owen E.

Brooks et al is of interest to the present invention, which discloses a gas liquid transfer apparatus of such as a chemical reactor having an inner tube serving as a mixed liquor downward flow chamber and an outer tube serving as a mixed liquor upward flow chamber, which are adapted such that the water is circulated from the upward flow chamber to the downward flow chamber. A gas is continually supplied to a liquid being processed. United States Patent No. 3,804,255 issued April 1 6, 1 974 to Richard E. Speece is also of interest, which also basically discloses an apparatus adapted for circulating a water using a pump while a gas is supplied into the water, as disclosed in the above referenced United States Patent No. 3,476,366, although the United States Patent No. 3,804,255 is mainly aimed at processing of a waste water.However, any of these United States Patents fail to teach or suggest anything about changing of a supply amount of a gas in association with an organic loading of the water being treated.

On the other hand, an article entitled "HYPOLIMNION AERATION" authored by R. E.

Speece, appearing in JAWWA (Journal American Water Works Association) January 1971 vol. 63, pages 6 to 9 discloses an apparatus aimed at aeration in a deep layer in a dam. The apparatus employs both circulation of a water by means of a pump and a deep well aimed at enhancement of solubility of oxygen containing gas due to an increased pressure. However, the apparatus neither contemplates changing of a supply amount of an oxygen containing gas in association with an organic loading in a deep layer.

As described in the foregoing, although the prior art discloses circulation of a water by means of a pump while an oxygen containing gas is supplied into a water, any of the prior art fails to contemplate changing of a supply flow rate of an oxygen containing gas in accordance with variation of an organic loading in a waste water (i.e. a water flow rate x an organic concentration).

Accordingly, in case of an excess of an organic loading, a amount of oxygen containing gas runs short, whereas in case of a small of an organic loading an amount of oxygen containing gas becomes excessive. In the former case, decomposition of an organic material becomes insufficient, whereas in the latter case aeration becomes too much, which makes solid-liquid separation difficult. Thus either causes an undesired phenomenon. Conventionally, the flow rate of a water by means of a pump and the flow rate of an oxygen containing gas have been preset to a predetermined flow rate in consideration of the maximum treatment loading of a waste water treating apparatus. Accordingly, an oxygen containing gas is supplied more than actually required without regard to an organic loading and a power cost for supply of a gas becomes high and uneconomical.Furthermore, if and when a state of a drastically decreased amount of an organic loading continues for a long period of time, a dissolved oxygen becomes excessive, to cause autolysis of an activated sludge, resulting in incapability of continual running or a problem in restarting the next normal running.

Summary of the Invention The inventive waste water treating apparatus comprises a downward flow chamber disposed extending in the depth direction and allowing for a flow of a waste water, an upward flow chamber disposed adjacent to the downward flow chamber extending in the depth direction and allowing for an upward flow of the waste water being supplied through the downward flow chamber and circulation means for circulating the waste water from the upward flow chamber to the downward flow chamber. Gas supply means is provided in the downward flow chamber for supplying an oxygen containing gas so that an oxygen containing gas may be allowed to blow into a waste water being supplied to the downward flow chamber. Information associated with an organic loading contained in a waste water being treated is provided.A supply flow rate of the oxygen containing gas is controlled in response to the organic loading associated information thus provided, whereby a supply flow rate of the oxygen containing gas suited for the organic loading is supplied.

In a preferred embodiment of the present invention, means is provided for monitoring the concentration of carbon dioxide gas contained in an exhaust gas discharged from the upward flow chamber for the purpose of providing the organic loading associated information. In this case, the organic loading associated information is represented by the concentration of carbon dioxide gas. Alternatively, means may be provided for monitoring the concentration of oxygen gas contained in the exhaust gas discharged from the upward flow chamber, for the purpose of providing the organic loading associated information. In this case, the organic loading associated information is represented by the concentration of oxygen gas.

In a more preferred embodiment of the present invention, the flow rate of the mixed liquor pumped up by the circulation means to be circulated to the downward flow chamber is set to a predetermined value. Then it is determined whether the flow rate of the oxygen containing gas being supplied has exceeded a flow rate of the oxygen containing gas corresponding to the above described predetermined amount of the water being circulated. In the case where the flow rate of the oxygen containing gas corresponding to the predetermined flow rate of mixed liquor being circulated is exceeded, the circulation means is controlled to attain a flow rate of the mixed liquor being circulated exceeding the above described predetermined flow rate of the mixed liquor.

In still a further preferred embodiment of the present invention, the amount of the organic loading contained in the waste water being treated is directly monitored. A required flow rate of oxygen containing gas being supplied is evaluated responsive to the monitored output in accordance with a predetermined functional relation between the organic loading amount and a required flow rate of oxygen containing gas being supplied corresponding thereto. Such functional relation is stored in storage means. The above described oxygen containing gas supply flow rate control means is adapted to control the oxygen containing gas supply flow rate upon comparison of a supply flow rate of the oxygen containing gas in the preceding control cycle and the information obtained from the above described associated information providing means for each control cycle.

Accordingly, a principal object of the present invention is to provide a waste water treating apparatus for controlling a flow rate of an oxygen containing gas being supplied in association with variation of an organic loading in a waste water.

Another object of the present invention is to provide a waste water treating apparatus adapted for controlling a flow rate of an oxygen containing gas being supplied in association with variation of an organic loading in a waste water, wherein upon determination that a required flow rate of oxygen containing gas exceeds a flow rate of oxygen containing gas corresponding to a predetermined flow rate of the mixed liquor being circulated the predetermined flow rate of the mixed liquor bring circulated is increased.

These objects and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.

Brief Description of the Drawings Fig. 1 is a view schematically showing the structural features of a waste water treating apparatus of the prior art and the characteristic features of the present invention: Fig. 2 is a graph showing a relation between a required flow rate of oxygen containing gas being supplied and an amount of an organic loading for explaining the principle of the present invention; Fig. 3 is a flow diagram for depicting a controlling operation for determining the flow rate of an oxygen containing gas being supplied in association with variation of the organic loading; Fig. 4 is a flow diagram for depicting a controlling operation of the flow rate of an oxygen containing gas and flow rate of the mixed liquor being circulated in association with variation of the organic loading;; Fig. 5 is a graph for explaining the principle of another embodiment of the present invention; Fig. 6 is a flow diagram for depicting a controlling operation in accordance with the Fig.

5 principle; Fig. 7 is a hardware implementation of the inventive control scheme; Fig. 8 is a view showing an outline of a modification of an oxygen containing gas supply means for use in the inventive waste water treating apparatus; Fig. 9 is a sectional view of a major portion of a mixing portion of the Fig. 8 oxygen containing gas supply means; and Fig.10 is a sectional view taken along the line IX-IX in Fig. 9.

Description of the Preferred Embodiments Fig. 1 is a view showing an outline of the structural features of a waste water treating apparatus of the prior art and a control scheme in accordance with the present invention employed therein. The waste water treating apparatus shown comprises a waste water treating apparatus of a deep well type using a pump circulation system. A water treating apparatus of this type comprises an inner tube 2 forming a downward flow chamber A of a waste water being supplied, and an outer tube 4 forming an upward flow chamber B disposed to enclose the above described inner tube 2 in the depth direction, these tubes being buried to extend underground to the depth of say 100 m. The inner tube 2 and the outer tube 4 are communicated with each other at the bottom portion.The outer tube 4 is coupled at the upper portion thereof to a tank or a tub 6 having the width larger than that of the outer tube in the lateral direction. The inner tube 2 is formed to extend through the tank 6 up to above the tank. A pump 8 of a variable capacity type is coupled to the bottom of the tank 6, so that a flow chamber C is formed through the pump 8 to the downward flow chamber A formed by the inner tube 2. As a result the water brought upward through the upward flow chamber B is pumped up by the variable capacity type pump 8 and is circulated through the flow chamber C to the downward flow chamber A. On the other hand, a supply tube 10 of a water being treated, i.e. a waste water of such as city sewage is coupled to the entrance of the inner tube 2 or the tank 6. The waste water is supplied through the supply tube 10 to the inner tube 2 or the tank 6.

In the case where a waste water including an activated sludge flows between the inner tube 2 and the outer tube 4, a head is formed due to resistance and a difference of gas hold up of two tubes and hence a head of as large as 0.5 to 7 m is formed between the downward flow chamber A and the upward flow chamber B. Therefore, a waste water of such as city sewage being supplied to the downward flow chamber A is circulated through the downward flow chamber A and the upward flow chamber B. If necessary, the circulation flow rate of the mixed liquor can be changed in accordance with adjustment of the above described head by changing the flow rate of the mixed liquor being pumped up to the downward flow chamber A by means of the variable capacity type pump 8. This will be described in more detail subsequently.

Furthermore, a nozzle 12 is provided at the upper portion of the downward flow chamber A.

The nozzle 12 is coupled to a blower 16 of a variable capacity type through a gas supply flow chamber 14 for an oxygen containing gas. The oxygen containing gas is supplied through the gas supply flow chamber 14 and the nozzle 12 into a waste water when the variable capacity type blower 16 is energized. The oxygen containing gas being supplied is dissolved into the mixed liquor, whereby carbon in an organic material contained in the waste water is converted into carbon dioxide. As described previously, the water treating apparatus of the embodiment shown comprises a waste water treating apparatus of a deep well type having the depth of say 100 m wherein a head as large as 0.5 to 7 m is formed between the downward flow chamber A and the upward flow chamber B.Therefore, the pressure at the bottom portion of the inner tube 2 and the outer tube 4 is extremely high and accordingly the oxygen containing gas being supplied to the waste water is better dissolved. In addition, as the oxygen containing gas is brought into the water through the blower 16 and the nozzle 12 and a turbulent flow is caused depending on a flow rate of the mixed liquor being circulated by the pump 8, the bubbles of the gas being applied to the water become extremely fine. As a result, a time period of the gas being in contact with the waste water is prolonged and solution of oxygen into the waste water is much expedited.

A separator 18 is provided adjacent the tank 6, so that the mixed liquor is separated into an activated sludge and a purified water as treated.

The purified water is fed to an after-treatment apparatus 20, while the activated sludge is scraped up into a sludge pit 34 by means of a sludge scraper 33. The sludge is fed through a return pipe 24 to the downward flow chamber A by means of a returning pump 22, while the waste sludge is fed to a waste sludge aftertreatment apparatus 26.

The feature of the present invention resides in changing the flow rate of an oxygen containing gas being supplied to a waste water by means of the blower 16 in association with the amount of an organic loading of a waste water being treated.

To that end, the apparatus comprises means 28 for monitoring the amount of an organic loading, and a control mechanism 100 responsive to the output monitored by the monitoring means 28 for evaluating an oxygen supply flow rate suited for the monitored amount of the organic loading. The control mechanism 100 is adapted to evaluate a required supply f Jw rate of the oxygen containing gas to control a flow rate control mechanism 16a provided in the variable capacity type blower 16 as a function of the evaluated value and to provide a control signal to a pumped up mixed liquor controlling mechanism 8a provided in the variable capacitance type pump 8. A relation between the organic loading amount monitoring means 28 and the control mechanism 100 which constitutes the essential feature of the present invention will be described in detail in the following.

Fig. 2 is a graph for depicting the basic principle of a control in accordance with the feature of the present invention. Generally, it has been known that a relation between an organic loading amount x and a required supply flow rate A of oxygen containing gas is linear. in other words, the relation is expressed by the following formula: A=ax where a is a constant determineable by a waste water being treated. Therefore, assuming that the organic loading amount is xO, a required supply flow rate Ao of oxygen containing gas is expressed as axO. Theoretically, a required supply flow rate of oxygen containing gas should be evaluated with accuracy in accordance with the above described functional relation.In actuality, however, a supply flow rate of oxygen containing gas is controlled with sone controlling range in controlling the oxygen containing gas supply flow rate using an actual apparatus and to that end a given allowance range is usually determined in a required supply flow rate of oxygen containing gas. Assuming that such allowance range with respect to an ideal value is c, the overall allowance range is defined by two straight lines defined by A=ax+c and A=ax-c, with the line defined by A=ax at the center thereof.

Accordingly, by monitoring with accuracy an organic loading contained in a waste water being treated, it is possible to control a required supply flow rate of oxygen containing gas in a fine manner. In order to directly monitor the amount of an organic loading, for example, an ultraviolet photo meter may be employed to monitor variation of the light beam which is transmitted through the waste water. By storing in advance the above described function A=ax shown in Fig.

2, a required supply flow rate of oxygen containing gas can be evaulated or can be read out in accordance with the organic loading amount monitored by monitoring the light intensity using the above described ultraviolet photo meter.

Fig. 3 is a flow diagram achieving the above described basic principle shown in Fig. 2. Now referring to the Fig. 3 flow diagram, the basic principle of the present invention will be described in more detail. Before entering into the detailed description, let it be assumed that a supply flow rate of oxygen containing gas being presently supplied by the variable capacity type blower 16 (Fig. 1) is Ap. The oxygen containing gas supply flow rate Ap is a flow rate evaluated by an arithmetic operation in the preceding cycle. As a matter of course, the present oxygen containing gas supply flow rate Ap may be a value obtained by actually measuring a supply flow rate of oxygen containing gas directly supplied from the blower 16. Based on the above described assumption, the principle is described in detail in the following.

(1) In the case where a supply flow rate of oxygen containing gas is too large.

First at the step S1 an organic loading amount contained in a waste water being treated is monitored by means of an ultraviolet photo meter.

Let it be assumed that the monitored value is xO.

Then at the step S2 a required oxygen containing gas supply flow rate Ao is calculated from the function A=ax stored in advance in a memory, such as a read only memory. At the step S3 a supply amount Ap stored in a storage for storing the current oxygen containing gas supply flow rate is read out. The supply flow rate Ap being read out may be a value determined in the preceding cycle or a value obtained by directly monitoring a supply amount of an oxygen containing gas being presently supplied and temporarily stored in a storage. At the step S4 it is determined whether a value obtained by subtracting the required oxygen containing gas supply flow rate Ao evaluated at the step S2 from the current oxygen containing gas supply flow rate Ap exceeds an allowance range c.Since it has been assumed that the current oxygen containing gas supply flow rate is too large, the difference (Ap AO) is larger than the allowance range c and therefore the program proceeds to the following step S5. At the step S5 the supply flow rate of the oxygen containing gas being supplied through the variable capacity blower 16 is reduced by one rank. After the oxygen containing gas supply flow rate is reduced by one rank, at the following step S6 the information stored in the current oxygen containing gas supply flow rate storage is cleared and a new oxygen containing gas flow rate determined at the step S5 is stored as Ap. Thus one control cycle of a required oxygen containing gas flow rate is achieved. The above described control cycle is repeated until the current oxygen containing gas supply flow rate comes to fall in a proper corresponding range. Each time the above described control cycle is repeated, the current oxygen containing gas supply flow rate Ap is decreased and at a given cycle the difference (Ap-A,) comes to be smaller than the allowance range c at the step S4. Accordingly, the program proceeds this time to the step S7. At the step S7 it is determined whether the difference (A0-Ap) is larger than the allowance range c. If and when the current oxygen containing gas supply flow rate is within the allowance range c shown in Fig.

2, the difference (A,-Ap) is smaller than the allowance range c. Therefore, decision at the step S7 is NO and the program proceeds to the start of the next cycle. Thus, the oxygen containing gas supply flow rate is controlled to become a proper oxygen containing gas supply flow rate corresponding to a monitored organic loading amount.

(2) In the case where the current oxygen containing gas supply flow rate is too small.

The program proceeds from the step 81 to the step S4 in the same manner as described in the above assumed case (1). However, since it has been assumed that the current oxygen containing gas supply flow rate is too small, at the step S4 it is determined that the difference (Ap~Ao) is smaller than the allowance range c. As a result, the program proceeds to the following step S7. At the step S7, contrary to the step S4, it is determined whether the difference (A,-Ap) is larger than the allowance range c. Since the current oxygen containing gas supply flow rate is small; the decision at the step S7 is YES.

Accordingly, at the step S8 the oxygen containing gas supply flow rate through the variable capacity blower 16 is increased by one rank. Then at the following step S9 the same operation as the previously described step S6 is performed. More specifically, the information stored is the storage for storing the current oxygen containing gas supply flow rate is cleared and the new determined information Ap is stored. Thus one control cycle is performed. Each time the above described control cycle is repeated, the oxygen containing gas supply flow rate is increased by one rank, so that the current oxygen containing gas supply flow rate Ap is decreased. As a result, at the step S7 of a given control cycle the difference (A,-Ap) becomes smaller than the allowance range c.This means that the current oxygen containing gas supply flow rate is controlled to fall within the allowance range c shown in Fig. 2.

(3) In the case where the current oxygen containing gas supply flow rate just falls in the allowance range of the required oxygen containing gas supply flow rate Ao corresponding to the monitored organic loading amount.

In such a case, as is apparent from the foregoing description in conjunction with the above assumed cases (1) and (2), the cycles preceding to the routine of the steps S1, S2, S3, S4 and S7 is repeated.

From the foregoing description in conjunction with the Fig. 3 flow diagram, a control to a required oxygen containing gas supply flow rate corresponding to an organic loading amount shown in Fig. 2 would be appreciated. According to the basic principle of the present invention, even in the case where the organic loading amount becomes very small and ultimately to zero, a required oxygen containing gas supply flow rate can be controlled accordingly to even zero by bringing the blower to a stop.

In the case of the above described fundamental structure of the present invention described with reference to Figs. 2 and 3, flow rate of mixed liquor circulated by the variable capacity pump 8 to the downward flow chamber A was set to a predetermined relatively large flow rate W. In other words, in the foregoing description, the circulation flow rate was set to a relatively large value W without taking into particular consideration a relation between a supply flow rate of an oxygen containing gas being supplied to the downward flow chamber and a flow rate of mixed liquor being circulated by the pump.

However, generally a relation between the oxygen containing gas supply flow rate A and the circulation flow rate should be preferably selected such that a gas/liquid ratio (A"'W or A/A+W) may be smaller than 0.2 and more preferably to be smaller than 0.16. The reason is that if and when the gas/liquid ratio is larger than the above described value the so-called clogging phenomenon occurs in the flow chamber which makes it impossible to provide a stabilized mixture of gas and liquid in circulation of the mixed liquor. In order to avoid such situation, one approach may be employed in which the circulation flow rate is controlled on a stepwise basis in association with the required oxygen containing gas supply flow rate taking into consideration the above described gas/liquid ratio.Therefore, referring again to Fig. 2, the principle of controlling the circulation flow rate will be described. First the initial circulation flow rate is assumed to be W1 and the range up to the oxygen containing gas supply flow rate A for achieving the gas/liquid ratio A/A+AW1=0.16 is set to the above described initial circulation flow rate W1. If and when the gas/liquid ratio A/A+W1 exceeds 0.16, the circulation flow rate is increased by one rank to be set to W2. A change of the circulation flow rate from W1 to W2 may be achieved by directly controlling the variable capacity type pump 8. Alternatively, such change may be achieved by providing a plurality of pumps 8 and by controllably changing the number of the variable capacity type pumps in accordance with variation of the required oxygen containing gas supply flow rate.Thus, taking into consideration the gas/liquid ratio, the circulation flow rate can be increased or decreased on a stepwise basis by evaluating the gas/liquid ratio at each control cycle.

Fig. 4 is a flow diagram for depicting a control manner of controlling both the oxygen containing gas supply flow rate and the circulation flow rate as described with reference to Fig. 2. Basically, the steps S1 to S9 for determining the required oxygen containing gas supply flow rate are the same as those described in conjunction with Fig.

3.

(1) In the case where the oxygen containing gas supply flow rate A is presently excessive with respect to the monitored organic loading amount x0 (Fig. 2).

In such a case the circulation flow rate so far supplied in accordance with the previous control is W3, as seen from Fig. 2. Now, referring to Fig.

4, description will be made of how the oxygen containing gas supply flow rate is decreased while the circulation flow rate is decreased in such condition. Since currently the oxygen containing gas supply flow rate is excessive, as assumed previously, the program is in succession executed from the step S1 to the step S6 in accordance with the foregoing description made in conjunction with the above assumed case (1) with reference to Fig. 3. After the step S6, at the step 811 the present circulation flow rate Was stored is read out from the storage. In the above described case, the current circulation flow rate W is W3. Then at the step 512 the gas/liquid ratio A/A+W is evaluated and determination is made whether the evaluated value is smaller than 0.06.

Although in the above described example the circulation flow rate W is W3, as described previously, the oxygen containing gas supply flow rate A has been decreased by one rank previously at the step S6 from An to Ano. As for the value Ano decreased by one rank, the gas/liquid ratio Aa#Aa0+W3 is smaller than 0.06. Accordingly, it follows that the program proceeds from the step S12 to the step S13. At the step S13 the circulation flow rate W is decreased by one rank to become W2. Then at the step S14 the previous circulation flow rate W3 stored in the storage is cleared and the new determined circulation flow rate W2 is stored in the storage.After the circulation flow rate is thus decreased by one rank and the new information is stored, again the program proceeds to the steps S11 and S12, whereupon the same operation is repeated. It is to be noted that, in such a case, at the step 812 this time the circulation flow rate W is W2 and therefore the oxygen containing gas supply flow rate A is Aoe As a result, the gas/liquid ratio A0#Aa0+W2 becomes larger than 0.06 and therefore decision at the step S12 becomes NO, whereby one control cycle is ended. After the oxygen containing gas supply flow rate is thus decreased by one rank, the circulation flow rate corresponding to the decreased oxygen containing gas supply flow rate is set.If and when in the following control cycle the oxygen containing gas supply flow rate is further decreased by one rank, the circulation flow rate corresponding thereto is readily determined through repetition of the above described operation.

(2) In the case where the current oxygen containing gas supply flow rate is a value A which is smaller than the allowance range of the required oxygen containing gas supply flow rate required for the organic loading amount xO.

In such a case, the control cycle described in conjunction with the assumed case (2) with reference to Fig. 3 is performed at the steps 81, S2, S3, S4, S7, S8 and S9. After the step S9, the current circulation flow rate W stored in the storage is read out in the same manner as at the previously described step 811. As seen from Fig.

2, the current circulation flow rate is W1. Then at the step 816 the gas/liquid ratio A/AsW is evaluated and determination is made whether the evaluated value is smaller than 0.16. It is assumed that the oxygen containing gas supply flow rate has been increased by one rank at the - step S8 and as a result the oxygen containing gas supply flow rate has been increased by one rank at the step S8 and as a result the oxygen containing gasbiupply flow rate A O has come to fall in the required allowance range. Accordingly, it follows that A/A+W=A JA o+W1. As is clear from the'positional relation' shown in Fig. 2, this value is larger than 0.16.Accordingly, the program proceeds from the step 816 to the step 81 7. At the step 81 7 the circulation flow rate W is increased by one rank. More specifically, the circulation flow rate is controlled to become W2.

Then at the step 818 the previous circulation flow rate W1 stored in the storage is cleared and the new circulation flow rate W2 is stored therein.

Thereafter at the steps 815 and 816 the same operation is repeated and, when the gas/liquid ratio A(A+W becomes smaller than 0.16, for the first time one control cycle is ended.

It goes without saying that in the case where the present oxygen containing gas supply flow rate is within a proper allowance range with respect to the organic loading amount x0 one control cycle is ended after the program proceeds through the steps S1, S2, S3, S4 and S7.

Fig. 5 is a graph depicting the basic principle of another embodiment of the present invention. In the case of the Fig. 2 embodiment the organic loading amount was directly monitored and the required oxygen containing gas supply flow rate corresponding thereto was directly evaluated, whereas in the case of the Fig. 5 embodiment the organic loading amount was not directly monitored but the organic loading amount was indirectly monitored by monitoring the oxygen concentration or the carbon dioxide concentration of the exhaust gas discharged from the upward flow chamber B, inasmuch as the oxygen concentration or the carbon dioxide concentration of the exhaust gas is closely associated with the organic loading amount and hence such concentration may be used as information associated with the organic loading in evaluating a required oxygen containing gas supply flow rate.

To that end, the organic loading amount monitoring means 28 comprises an oxygen gas analyzer 28 in Fig. The tank 6 is provided with a lid 30 at the top portion thereof to enclose the same thereby to maintain the exhaust gas discharged from the upward flow chamber. While the exhaust gas discharged through the pipe 32 to the lid 30 at the top portion of the tank 6 is discharged to the atmosphere, a portion thereof is fed to the oxygen gas analyzer 28. Thus, the oxygen gas analyzer 28 monitors the concentration of the oxygen gas contained in the exhaust gas discharged through the upward flow chamber B. In the case where the concentration of the carbon dioxide gas contained in the exhaust gas is to be monitored, a carbon dioxide gas analyzer is employed in place of the oxygen gas analyzer 28, as is needless to say.

The Fig. 5 graph also shows, basically in the same manner as that in Fig. 2, the required oxygen containing gas supply flow rate in the ordinate and the organic loading amount in the abscissa. A functional relation of a straight line L1 is established to represent a function of a required oxygen containing gas supply flow rate with respect to an organic loading amount. However, in the case of the embodiment in description, the organic loading amount is not directly monitored but the oxygen concentration of the exhaust gas is used as a parameter. Variation of the oxygen concentration of the exhaust gas is indicated in the rotational direction about the origin point of the graph.The straight line L2 shows the maximum allowance value of the oxygen concentration in the exhaust gas, say the oxygen concentration of 1 5% in the exhaust gas, whereas the straight line L3 shows the minimum allowance value of the oxygen concentration in the exhaust gas, say the oxygen concentration of 5% in the exhaust gas. Thus, the system is controlled such that a required oxygen containing gas supply flow rate with respect to an organic loading amount may fall in the region as hatched defined between the straight lines L2 and L3. In order to describe in more detail, it is assumed that the current oxygen containing gas supply flow rate is Al. In such a situation the oxygen concentration in the exhaust gas discharged through the upward flow chamber is monitored.It is assumed that the oxygen concentration in the exhaust gas is a value smaller than the minimum allowance value. Assuming that a straight line with respect to the value smaller than the minimum allowance value of the oxygen concentration in the exhaust gas is L5, the intersection A between the line in parallel with the abscissa representing the oxygen containing gas supply flow rate Al and the above described straight line L5 is a point representing a relation between the current oxygen containing gas supply flow rate and the organic loading amount.

Since the point A is outside the allowance range, as shown in Fig. 5, it is necessary to increase the oxygen containing gas supply flow rate from Al to A2 by one rank, so that the oxygen containing gas supply flow rate may be increased to fall within the allowance range of the point A0. As for the relation of the circulation flow rate, the same as described in conjunction with Fig. 2 applies.

Since in the above described case the oxygen containing gas supply flow rate is within the range of the circulation flow rate W2 even if the oxygen containing gas supply flow rate is increased by one rank, it is not necessary to control the circulation flow rate. However, assuming that the current oxygen containing gas supply flow rate is A2 and the oxygen concentration in the exhaust gas is smaller than the minimum allowance value, say the oxygen concentration of the exhaust gas is that represented by the straight line L5, then the state of the current oxygen containing gas supply flow rate and the organic loading amount is represented by the point B. In this case as well, the oxygen containing gas supply flow rate need be increased by one rank from A2 to A3 in the same manner as described in conjunction with the point A.However, in this case the relation of the gas'liquid ratio comes not to meet the requirement as the oxygen containing gas supply flow rate is increased, which means that the circulation flow rate also need be increased by one rank from W2 to W3, as seen from Fig. 5.

Now as regards a relation between the organic loading amount and the oxygen containing gas supply flow rate, consider a case where the current oxygen containing gas supply flow rate is too large. In the case where the oxygen containing gas supply flow rate is too large, accordingly the oxygen concentration in the exhaust gas discharged from the upward flow chamber becomes larger than a predetermined maximum allowance value, say 15%.Now assuming that the present oxygen containing gas supply flow rate is A3 and the oxygen concentration in the exhaust gas at that time is that represented by the straight line L4, for example, then the state at that time of the oxygen containing gas supply flow rate and the organic loading amount is represented by the intersection C between the line in parallel with the abscissa representing the oxygen containing gas supply flow rate A3 and the straight line L4. Accordingly, in such a case the oxygen containing gas supply flow rate need be decreased by one rank from A3 to A2 to reach the point CO in the allowance range. At that time the circulation flow rate need also be decreased simultaneously from W3 to W2.In the case of the point D, however, only the oxygen containing gas supply flow rate need be decreased by one rank, while the circulation flow rate may be maintained, as is appreciated from Fig. 5.

Fig. 6 is a flow diagram achieving the basic principle described in conjunction with Fig. 5. For facility of understanding, the specific values and symbols employed in describing the Fig. 5 are employed in the following description as a specific example.

(1) In the case where the current state is the point A.

In such a state, as described previously, the control which need be made is to increase the oxygen containing gas supply flow rate by one rank. First at the step S31 the oxygen concentration in the exhaust gas is monitored. At the step S32 the monitored oxygen containing gas concentration in the exhaust gas is temporarily stored in the storage as 02. At the step S33 the difference between the monitored value O2 and the maximum allowance concentration 02MAY stored in advance in the storage is evaluated and it is determined whether the evaluated value is plus or minus. Since the point A is on the line L5 which is smaller than the minimum allowance line L3, as seen from Fig. 5, the above described difference is minus as a matter of course. Accordingly, the program proceeds to the following step S34.At the step S34 the difference between the monitored oxygen concentration O2 and the minimum allowance concentration 02MIN and it is determined whether the difference is plus or minus. Since the monitored concentration O2 in the exhaust gas is on the above described line L5, again the above described difference is minus.

Accordingly, the program proceeds to the step S35. At the step S35 the oxygen containing gas supply flow rate is increased by one rank from Al to A2. At the step S36 the current oxygen containing gas supply flow rate stored in the storage storing the oxygen containing gas supply flow rate is cleared, i.e. in this case the oxygen containing gas supply flow rate Al is cleared, and the new oxygen containing gas supply flow rate A2 is stored. Thereafter at the step S37 the current circulation flow rate W is read out. As is clear from Fig. 5, the current circulation flow rate isW2.

At the following step S38 the gas/liquid ratio A/A+W is evaluated and it is determined whether the evaluated value is smaller than 0.16. In the above described case, A/A+W=A2/A2+W2 and, as is clear from Fig. 5, the same is smaller than 0.16. Accordingly, the program returns from the step S38 to the step S31 for the purpose of the following control cycle. Thus, in one control cycle control is made such that the point A becomes the point Ao within the allowance range.

(2) In the case where the current state is represented by the point B.

In this case the oxygen containing gas supply flow rate need be increased by one rank and the circulation flow rate need also be increased by one rank. The operation until the oxygen containing gas supply flow rate is increased by one rank is performed in the same manner as described in the above described case (1) while the program proceeds from the step S31 to the step S38. The calculation A/(A+W) achieved at the step 338 is A3/(A3+W2) in this particular case. Since the evaluated value is clearly larger than 0.16, the decision at the step S38 is NO.

Accordingly, the program proceeds to the step S39 and at the step S39 the circulation flow rate is increased by one rank from W2 to W3.

Thereafter at the step S40 the circulation flow rate W so far stored in the storage, in this particular case the circulation flow rate W2, is cleared and the new set circulation flow rate W3 is stored in the storage. Thereafter the program returns again to the step S37 and the current circulation flow rate W is read out. Since the current circulation flow rate W has been renewed at the previous step S40 from W2 to W3, the currently read out circulation flow rate W becomes W3. Then at the step S38 this time A"(A+W)=A3/(A3+W3) and as a matter of course the evaluated value at that time becomes smaller than 0.16 and therefore the decision becomes YES. Thus the oxygen containing gas supply flow rate and the circulation flow rate required therefor are controlled.

(3) In the case where the current state is the point C.

In such a case, the current oxygen containing gas supply flow rate is too large. The operation at the steps S31, S32 and S33 is the same as those described in conjunction with the above described case (1). At the step S33 the difference ( 2~ 02MiX) becomes positive this time, because the monitored value of the oxygen concentration in the exhaust gas is on the straight line L4 showing a value larger than the straight line L2 representing 02may Accordingly, the program proceeds from the step S33 to the step S41. At the step S41 the current oxygen containing gas supply flow rate is decreased by one rank from A3 to A2 and at the step S42 the oxygen containing gas supply flow rate A3 so far stored in the storage is cleared and the new set oxygen containing gas supply flow rate A2 is stored in the storage.At the step S43 the current circulation flow rate W is read out. In the particular case, the current circulation flow rate is W3. At the step S44 the gas/liquid ratio A/A+W is evaluated and in this particular case A/'A+W=A2/(A2+W3) and it is determined whether the same is smaller than 0.06. Since the circulation flow rate remains W3 whereas the oxygen containing gas supply flow rate has been decreased from A3 to A2, the evaluated value is smaller than 0.06 as a matter of course. Accordingly, the program proceeds to the following step S45 and at the step S45 the circulation flow rate W is decreased by one rank from W3 to W2. At the step S46 the circulation flow rate W3 so far stored in the storage is cleared and the new set circulation flow rate W2 is stored in the storage.Thereafter the program returns to the step S43 and again the current circulation flow rate is read out from the storage.

Since the new set circulation flow rate W2 has been stored at the step S46, the current read out circulation flow rate W is W2. Accordingly at the following step S44 the gas/liquid ratio A/A+W becomes A2/(A2+W2) and, since this value is larger than 0.06 as a matter of course, the decision at the step S44 becomes NO. Thus, the required oxygen containing gas supply flow rate is decreased by one rank, while the circulation flow rate is also decreased by one rank.

(4) In the case where the current state is the point D.

In this case the same operation is performed at the steps S31, S32, S33, S41, S42, S43 and S44 as in the above described case (3). Since at the S44 the gas/liquid ratio A/A+W becomes A3/A3+W3, the evaluated value becomes larger than 0.06 as a matter of course and hence the decision at the step S44 becomes NO. Thus, in this particular case, only the oxygen containing gas supply flow rate is decreased by one rank.

(5) In the case where the current state is the point El.

This particular case means a case where the monitored value of the oxygen concentration in the exhaust gas is extremely low and accordingly control can not follow such situation by simply increasing the oxygen containing gas supply flow rate by one rank. In this case, basically the operation at the steps described in conjunction with the above described cases (1) and (2) is repeated, as is readily understood. In the case of increasing from the point El to the point E2, the oxygen containing gas supply flow rate is increased by one rank while the circulation flow rate is also increased by one rank in accordance with the operation described in conjunction with the above described case (2).Then in the following cycle, an increasing operation is performed from the point E2 to the point E3 and in this case only the oxygen containing gas supply flow rate is increased by one rank in accordance with the operation described in conjunction with the above described case (1). Then an increasing operation from the point E3 to the point E4 is also performed in the same manner as described in the above described case (1). Thus, after the three control cycles are repeated, the oxygen containing gas supply flow rate.and the circulation flow rate required for the organic loading amount are determined.

Although the Fig. 6 embodiment adopted a sequence wherein the oxygen concentration in the exhaust gas is first monitored and then the required oxygen containing gas supply flow rate and the circulation flow rate are controlled with the oxygen concentration as a reference, alternatively the carbon dioxide concentration in the exhaust gas may be monitored and the required oxygen containing gas supply flow rate and the circulation flow rate may be controlled base thereon, as described previously. In such a case, at the step S31 the carbon dioxide concentration is monitored in place of monitoring of the oxygen concentration and accordingly at the step S32 the carbon dioxide concentration CO2 is stored. At the step S33 (CO2~CO2MíN) < O is determined.At the step S34 (C 2~CO2MAX) > O is determined. It goes without saying that CO2MIN and CO2MAx denote the minimum allowance concentration and the maximum allowance concentration, respectively. Since the oxygen concentration and the carbon dioxide concentration in the exhaust gas are inverse proportional to each other, in the case where the carbon dioxide concentration is monitored, the relation at the steps S33 and S34 shown in Fig. 6 has been reversed.

Fig. 7 is a block diagram showing a hardware implementation for achieving the inventive control. Basically, the inventive system comprises a central processing unit 110, a first read only memory 1 20 for storing a predetermined program, such as shown in Figs. 3, 4 and 6, a second read only memory 130 for storing a function as shown in Fig. 2 set in advance for evaluating a required oxygen containing gas supply flow rate from a monitored value of an organic loading amount, a random access memory 140 for storing monitored data, and an input/output port 150.The information monitored by the monitoring means 200 for monitoring the information associated with the organic loading amount, such as the information of the carbon dioxide concentration in the exhaust gas or the information of the oxygen concentration in the exhaust gas or the information of the organic loading amount; information of the current oxygen containing gas supply flow rate monitored from the monitoring means 210 for monitoring the oxygen containing gas supply flow rate; and the information of the current circulation flow rate monitored by the circulation flow rate monitoring means 220 of the circulation waste water circulated by the pump from the upward flow chamber to the downward flow chamber are transferred through the input/output interface 1 60 and the data bus 170 for communication with the read only memories 120 and 130, the random access memory 140 and the input/output port 150. A control bus 180 and an address bus 190 are provided between the central processing unit 110, the read only memories 120 and 130, the random access memory 140 and the input/output port 150. More specifically, the random access memory 140 is used as a storage for storing the data being transferred.For example, in the case where the oxygen concentration in the exhaust gas is monitored, the information of the monitored oxygen concentration is transferred through the input/output interface 160, the input/output port 150 and the data bus 170 to the random access memory 140 and is stored therein. The central processing unit 110 makes a series of processing operations in accordance with a program stored in the read only memory 120.The new set oxygen containing gas supply flow rate and circulation flow rate obtained by calculation by the central processing unit 110 in accordance with the program stored in the read only memory 120 are transferred through the data bus 170 to the random access memory 140 and stored therein and are also transferred through the data bus 170, the input/output port 150 and the input/output interface 160 to the oxygen containing gas supply flow rate control apparatus 230 and the circulation flow rate control apparatus 240.

Meanwhile, referring to the Fig. 4 program, for example, the steps in which the current oxygen containing gas supply flow rate and the current circulation flow rate are seen. These pieces of information may be those provided from the oxygen containing gas supply flow rate monitoring means 210 and the circulation flow rate monitoring means 220 and stored in the random access memory but usually such oxygen containing gas supply flow rate and the circulation flow rate are those determined in the preceding control cycle and therefore the oxygen containing gas supply flow rate and the circulation flow rate determined in the preceding control cycle may be stored in the random access memory 140 and read out as necessary.

Fig. 8 is a view schematically showing the overall outline of a modification of a supply means of an oxygen containing gas for use in the inventive waste water treating apparatus. As described previously, for the purpose of improving solution of an oxygen gas into a waste water being treated, it is better to make more fine the bubbles of an oxygen containing gas being supplied into a water. The Fig. 8 embodiment comprises an improvement for making such bubbles fine. As seen, the fundamental structure of the Fig. 8 embodiment is substantially the same as that shown in Fig. 1. Accordingly, the same reference characters as those in Fig. 1 have been used to denote like portions in Fig. 8.The Fig. 8 modification comprises a screw 50 provided in the vicinity in the lower portion of an exit 12a of a nozzle 12 so as to be rotatable and so as to cause a jet flow in the downward direction into the mixed liquor. The bubbles of an oxygen containing gas being supplied from the nozzle 12 are forcedly mixed by the above described screw 50 to be made fine, while the same are forced downward as a downward circulation flow.

Figs. 9 and 10 show different modifications of the Fig. 8 forced mixing portion. In these modifications, a hollow shaft 60 is rotatably provided and a bottomed cylindrical member 61 having the diameter larger than that of the hollow shaft is coupled to the lower end of the hollow shaft 60. Screw blades 62 are provided spaced apart in the peripheral direction of the cylindrical member 61. Discharge ports 12a are provided positioned adjacent downward in the rotational direction of the respective blades 62. The supply pipe 14 for supplying an oxygen containing gas and the above described hollow shaft 60 are coupled to be communicated by means of a rotary joint 63. Accordingly, the oxygen containing gas supplied from the compressor through the supply tube 14 is brought through the rotary joint 63 and the hollow shaft 60 to the discharge ports 12a of the nozzle 12.The gas as discharged through the discharge ports 12a are forced to be changed to fine bubbles by means of the screw blades 62 positioned downward in the rotational direction.

With such structure, a negative pressure atmosphere is provided due to rotation of the screw blades 12 in supplying the oxygen containing gas and therefore the water pressure from the water being treated with respect to the respective discharge ports 12a is decreased and accordingly the gas supply pressure and thus the driving power of the compressor 16 may be decreased. It would be readily understood to those skilled in the art that for the purpose of making fine the bubbles of the oxygen containing gas in the water various types of modified structures other than the above described screws 50 and the screw blade 62 may be employed.

Thus, according to the embodiments shown in Figs. 8 to 10, the bubbles of the oxygen containing gas being supplied to the mixed liquor can be made fine and therefore buoyancy of the supplied gas can be decreased and a driving power for supply of the gas can also be decreased while a downward flow of bubbles together with the mixed liquor can be preferably caused. In addition, since the bubbles are fine, the oxygen gas can be preferably dissolved under pressure.

Furthermore, since the buoyancy of the supplied gas can be suppressed, growth of the bubbles generated in the vicinity of the inner surface at the upper end of the downward flow chamber A is prevented from being assisted by the supplied gas. Accordingly, the bubbles are prevented from growing into an air block, which is liable to be split to cause leakage of the waste water being treated.

It is pointed out that the foregoing description is only by way of example and various types of modifications can be made without departing from the spirit of the present invention. For example, the oxygen containing ratio may be monitored by gas analysis for the purpose of detecting an oxygen containing ratio in the exhaust gas. Furthermore, although in the above described embodiment the value evaluated by the control mechanism 100 is utilized as an amount of the oxygen containing gas being supplied from the variable capacity type blower or the compressor 16 through the gas supply tube 14 to the water being treated, the supply amount may be actually monitored directly from the gas supply tube 14.

Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims.

Claims

1. A waste water treating apparatus for treating a waste water including an organic material, comprising: a downward flow chamber disposed to extend in the depth direction for allowing for a downward flow of a mixed liquor comprising said waste water being treated and an activated sludge, an upward flow chamber disposed in the depth direction outside and adjacent to said downward flow chamber for allowing for an upward flow of said mixed liquor being supplied through said downward flow chamber, circulation means for circulating said mixed liquor through said upward flow chamber and said downward flow chamber by raising said mixed liquor from said upward flow chamber to said downward flow chamber, gas supply means for supplying an oxygen containing gas into said downward flow chamber, organic loading associated information providing means operatively coupled to at least one of said upward flow chamber and the downward flow chamber for providing information associated with an organic loading of said waste water being supplied, and control means responsive to said information from said organic loading associated information providing means for controlling a supply amount of said oxygen containing gas from said oxygen containing gas supply means.

2. A waste water treating apparatus in accordance with claim 1, wherein: said organic loading associated information providing means comprises organic loading amount monitoring means for directly monitoring an organic loading amount of said waste water, and said organic loading associated information comprises information representing said organic loading amount.

3. A waste water treating apparatus in accordance with claim 2, wherein: said organic loading amount monitoring means comprises an ultraviolet photo meter.

4. A waste water treating apparatus in accordance with claim 12, wherein said bubble fine making means is formed Indeisendently of said oxygen containing gas supply path.

1

5. A waste water treating apparatus substantially as herein described with reiZerace to the accompanying drawings.

4. A waste water treating apparatus in accordance with claim 2, wherein said oxygen containing gas supply flow rate controlling means comprises: first storage means for storing a predetermined functional relation between the organic loading amount of said waste water and a required oxygen containing gas supply flow rate corresponding thereto, withdrawing means responsive to said monitored output from said organic loading amount monitoring means for withdrawning oxygen containing gas supply flow rate information corresponding to said monitored output from said functional relation stored in said first storage means, monitoring means for monitoring the oxygen containing gas supply flow rate being presently supplied by said oxygen containing gas supply means, comparing means for comparing said oxygen containing gas supply flow rate information withdrawn by said oxygen containing gas supply flow rate information withdrawing means and said current supply flow rate information monitored by said supply flow rate monitoring means, and controlling means responsive to the output of said comparing means for controlling said oxygen containing gas supply flow rate from said oxygen containing gas supply means to fall within a predetermined allowance supply flow rate range.

5. A waste water treating apparatus in accordance with any one of the preceding claims 1 to 4, wherein the circulation flow rate of said mixed liquor being circulated by said circulation means has been set to a predetermined flow rate, and which further comprises: determining means for determining that the oxygen containing gas supply flow rate being supplied from said oxygen containing gas supply means has exceeded a predetermined oxygen containing gas supply flow rate corresponding to said predetermined circulation flow rate, and controlling means responsive to the output of said determining means for controlling said circulation means so that the circulation flow rate may exceed said predetermined circulation flow rate of said circulation means.

6. A waste water treating apparatus in accordance with claim 5, wherein said determining means is adapted to determine that said predetermined flow rate is exceeded by directly monitoring the oxygen containing gas being supplied from said oxygen containing gas supply means to said downward flow chamber.

7. A waste water treating apparatus in accordance with claim 5, wherein said determining means comprises: second storage means for storing reference value information representing a predetermined value of said oxygen containing gas corresponding to said predetermined circulation flow rate, and comparing means for comparing said reference value information stored in said second storage means and required oxygen containing gas supply flow rate information withdrawn from said oxygen containing gas supply flow rate controlling means.

8. A waste water treating apparatus in accordance with claim 1 , wherein said organic loading amount associated information withdrawing means comprises carbon dioxide gas concentration monitoring means for monitoring the concentration of carbon dioxide gas contained in said exhaust gas discharged from said upward flow chamber, and said organic loading amount associated information comprises information representing said concentration of carbon dioxide.

9. A waste water treating apparatus in accordance with claim 8, wherein said oxygen containing gas supply flow rate controlling means comprises: determining means for determining whether said concentration of carbon dioxide gas monitored by said carbon dioxide gas concentration monitoring means is between a predetermined maximum allowance value and a predetermined minimum allowance value contained in said exhaust gas, and controlling means responsive to the output of said determining means for controlling said oxygen containing gas supply flow rate from said oxygen containing gas supply means to fall within a predetermined allowance supply flow rate range.

10. A waste water treating apparatus in accordance with claim 1, wherein said organic loading amount associated information withdrawing means comprises oxygen gas concentration monitoring means for monitoring the concentration of an oxygen gas contained in said exhaust gas discharged from said upward flow chamber, and said organic loading amount associated information comprises information representing the concentration of said oxygen gas.

11. A waste water treating apparatus in accordance with claim 10, wherein said oxygen containing gas supply flow rate controlling means comprises: determining means for determining whsi:hts, said concentration of carbon dioxide gas monitored by said carbon dioxide gas concentration monitoring means is between a predetermined maximum allowance value and predetermined minimum allowance value contained in said exhaust gas, and controlling means responsive to the output of said determining means for controlling said oxygen containing gas supply flow rate from said oxygen containing gas supply means to fall within a ,aredeLeri-nined allowance supply flow rate range.

12. A waste water treating apparatus in accordance with claim 1, wherein said oxygen containing gas supply means comprises an oxygen containing gas supply chamber and, which further comprises bubble fine making means provided in the vicinity of the outlet of said oxygen containing gas supply path for making fine said bubbles in said mixed liquor.

1 3. A waste water treating apparatus in accordance with claim 12, wherein said bubble fine making means also consti..uves said oxygen containing gas supply path.