JP2008188548A - Method for suppressing generation of sludge in aerobic wastewater treatment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for suppressing the generation of sludge in an aerobic wastewater treatment which can suppress the generation of excess sludge. <P>SOLUTION: The method comprises the step of blowing air or oxygen into an aeration tank 10 so that a dissolved oxygen concentration (DO) in wastewater in the aeration tank 10 may reach 5 mg/L or higher, detecting the dissolved oxygen concentration (DO) and also adjusting the dissolved oxygen concentration (DO) so that an activated sludge concentration (X) in the wastewater in the aeration tank 10 may reach not more than a set value when the wastewater containing an organic substance is introduced into the aeration tank 10 and its wastewater is subjected to the aerobic treatment by activated sludge. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to aerobic wastewater treatment for aeration of industrial wastewater and domestic wastewater, and more particularly to a method for suppressing sludge generation in aerobic wastewater treatment that can suppress the generation of activated sludge.

  When the wastewater is purified aerobically, about half of the pollutants (organic matter) in the wastewater is decomposed into carbon dioxide and water, while the other half is used for sludge (microorganism) growth. In the activated sludge method, which is a typical example of the aerobic treatment, it is necessary to keep the sludge concentration constant. Generally, the grown sludge is drawn out of the system and subjected to treatment such as dehydration, incineration, and landfill. Also, in some plants, there is a method in which the sludge that has been grown is liquefied under high temperature and high pressure and then returned to activated sludge for treatment.

  In general methods, sludge disposal costs raise running costs and have problems such as tight landfill sites. The method of high-temperature and high-pressure treatment is an unstable process and is under development.

  In general, in order to increase the treatment capacity by activated sludge, pure oxygen is blown or air is used as a pressurized tank in order to increase the dissolved oxygen concentration in the aerated tank as shown in Patent Documents 1 to 3. It has been proposed to infuse.

JP 54-81660 A JP-A-56-100695 JP 2002-23957 A

  However, even if the dissolved oxygen concentration is simply increased in order to increase the aerobic treatment capacity, there is a problem that the amount of activated sludge generated increases accordingly.

  That is, if the dissolved oxygen concentration is increased, the activated sludge becomes more active and the activated sludge grows. This is also related to the BOD concentration of the wastewater flowing into the aeration tank. For example, if the BOD concentration is low, the dissolved sludge is dissolved. Even if the oxygen concentration is increased, the sludge concentration in the aeration tank decreases, and conversely, if the BOD concentration is high, the sludge concentration increases, and excess sludge is generated accordingly. It is difficult to maintain an appropriate dissolved oxygen concentration in the air tank.

  Even if the sludge concentration and dissolved oxygen concentration in the aeration tank are maintained properly, the BOD concentration of the raw water flowing into the aeration tank always fluctuates, so the appropriate operating conditions also fluctuate. End up.

  Thus, the technique which maintains the dissolved oxygen concentration in an aeration tank appropriately is suppressed, suppressing the excess sludge discharged | emitted from an aeration tank.

  Then, the objective of this invention is providing the suppression method of the sludge generation | occurrence | production in the aerobic waste water treatment which can suppress generation | occurrence | production of excess sludge when solving the said subject and performing aerobic waste water treatment.

  In order to achieve the above object, the invention of claim 1 is directed to the introduction of wastewater containing organic matter into an aeration tank, and when the wastewater is aerobically treated with activated sludge, dissolved in the wastewater in the aeration tank. Air or oxygen is blown into the aeration tank so that the oxygen concentration is 5 mg / L or more, the dissolved oxygen concentration is detected, and dissolved so that the activated sludge concentration in the aeration tank is below the set value. This is a method for suppressing sludge generation in aerobic wastewater treatment, characterized by adjusting the oxygen concentration.

  The invention of claim 2 is such that b / a when the conversion rate of BOD sludge is a and the self-decomposition rate coefficient of sludge is b is the wastewater treatment amount, the volume of the aeration tank, the BOD concentration of the wastewater to be introduced, While calculating from the sludge concentration in the tank and the BOD concentration in the aeration tank, the b / a based on the dissolved oxygen concentration is calculated based on the b / a data obtained from these, and the inside of the aeration tank is calculated. The sludge generation is detected in the aerobic wastewater treatment according to claim 1, wherein the sludge concentration is detected, b / a at which the sludge concentration is not more than a set value is obtained, and the dissolved oxygen concentration is controlled to be the b / a. Is the law.

  The invention of claim 3 is the method for suppressing sludge generation in the aerobic wastewater treatment according to claim 2, wherein the dissolved oxygen concentration is controlled so that the b / a is 0.15 or more.

  The invention of claim 4 controls oxygen concentration by mixing pure oxygen or oxygen-enriched air into a gas such as air so that the amount of gas blown from the aeration tube in the aeration tank is constant. The method for suppressing the generation of sludge in the aerobic wastewater treatment according to any one of the above.

  In the invention of claim 5, the aeration tank is of a pressurized type, the compressed air is supplied from the aeration pipe, the gas discharged from the aeration tank is mixed with the compressed air, and the amount of gas blown from the aeration pipe is constant. The method for suppressing the generation of sludge in the aerobic wastewater treatment according to any one of claims 1 to 3, wherein the oxygen concentration is controlled while being controlled.

  According to the present invention, by adjusting the dissolved oxygen concentration so that the activated sludge concentration of the wastewater in the aeration tank is equal to or lower than the set value, an excellent effect that excess sludge can be suppressed is exhibited. is there.

  A preferred embodiment of the present invention will be described below in detail with reference to the accompanying drawings.

  First, the standard activated sludge method will be described with reference to FIG.

  Wastewater (waste water) containing organic substances is introduced into the aeration tank 10 from the drainage line 11, and air or oxygen 17 is supplied from the aeration pipe 12 provided at the bottom of the aeration tank 10, and aerobic treatment is performed. The treated water after the aeration is introduced into the sedimentation tank 14 from the line 13, where it is separated into solid and liquid, and the supernatant is discharged from the treated water line 15 as treated water.

  The activated sludge that has settled at the bottom of the settling tank 14 is returned to the aeration tank 10 via the return line 15 as a partially returned sludge, and the remainder is discharged from the sludge line 16 as surplus sludge.

  The amount of sludge generated in this standard activated sludge method will be described.

The wastewater treatment amount is F [m ³ / d], the inflow raw water BOD concentration is S ₀ [mg / L], the volume of the aeration tank 10 is V [m ³ ], and the sludge concentration (MLSS) is X [mg / L]. L], the BOD concentration in the aeration tank is S [mg / L], the dissolved oxygen concentration is DO [mg / L], the concentration rate in the sedimentation tank is c, the sludge return rate is α, the excess sludge discharge rate F _ex Is [m ³ / d],
The amount of surplus sludge (F _ex cX) generated is
F _ex cX = aF (S ₀ −S) −bXV
However,
a: BOD sludge conversion rate (= Y _{X / S} )
b: Self-decomposition rate coefficient of sludge.

Here, in the system without sludge extraction,
F _ex cX = aF (S ₀ −S) −bXV = 0 (1)
From the two terms on the right side of Equation (1), the sludge self-decomposition rate coefficient b is
b = (1 / X) (F / V) (S ₀ −S) a (2)
When the parameter indicating sludge generation is b / a,
b / a = (1 / X) (F / V) (S ₀ −S) (3)
It becomes.

Here, when an aerobic treatment is performed by blowing air and pure oxygen into an aeration tank,
Air Pure oxygen Dissolved oxygen concentration (DO) [mg / L] 2 19
Raw water (inflow) BOD concentration S ₀ [mg / L] 250 250
BOD removal rate [%] 93.6 92.4
BOD concentration in treated water S [mg / L] 16 19
Aeration tank volume V [L] 3 6
Processing amount F [L / d] 6 6
Sludge concentration (MLSS) X [mg / L] 3,500 2,000
And
From the equation (3), b / a is 0.13 when the dissolved oxygen concentration DO = 2 in which air is drawn in, and 0.23 when DO = 19 where pure oxygen is blown in.

The BOD sludge conversion rate a of general activated sludge is constant at a = 0.5 to 0.8, and the parameter b / a indicating sludge generation when air is blown and when pure oxygen is blown is Assuming that the conversion rate is minimum and a = 0.5,
For air, b / a = 0.0065
For pure oxygen, b / a = 0.115
Also, assuming that the conversion rate is maximum and a = 0.8,
For air, b / a = 0.104
For pure oxygen, b / a = 0.184
Thus, it can be seen that the dissolved oxygen concentration (DO) affects the sludge generation parameters.

  The above equation (3) includes parameters of the volume V of the aeration tank, the BOD concentration S of the treated water, and the sludge concentration (MLSS) X, and both the sludge concentration X and the dissolved oxygen concentration (DO) change. , B / a is difficult to obtain.

  Therefore, the table below and FIG. 4 show the results of obtaining b / a from the following data (1) to (4) in which the sludge concentration (MLSS) X and the dissolved oxygen concentration (DO) are stable.

DO MLSS Raw water BOD BOD removal rate b / a
(1) 4.0 2500 250 85 0.17
(2) 10.0 2000 300 85 0.255
(3) 30.0 1600 400 95 0.475
(4) 18.0 1500 350 90 0.42
It can be seen from this table and FIG. 4 that when the dissolved oxygen concentration (DO) is increased, the sludge concentration (MLSS) is decreased and the BOD removal rate is constant or increased. However, from FIG. 4, even if the dissolved oxygen concentration is increased from 20 [mg / L] to 30 [mg / L], the sludge concentration (MLSS) does not change. This is relative to the BOD concentration of the wastewater (raw water). Even if the dissolved oxygen concentration is excessively increased, the removal rate is constant or increased, but oxygen or the like is wasted and the running cost is increased.

Next, based on the data (1) to (4), the change in b / a with respect to the dissolved oxygen concentration (DO) is approximated by the Michaelis-Mainte equation.
b / a = (b / a) _max * {DO / ( _{Kb / a} + DO) (4)
It becomes.

However, (b / a) _max is the maximum value of b / a at the maximum dissolved oxygen concentration of waste water, and K _{b / a} is the saturation constant of dissolved oxygen.

FIG. 5 shows the result of taking the inverse of DO and b / a in the above data (1) to (4) and plotting it (line weaver plot). From FIG. 5, DO ⁻¹ is expressed as x, b. / A ^-1 is y, y = 17.422 + 1.661
The approximate expression is obtained.

Based on this, when (b / a) _max and K _{b / a} are obtained,
(B / a) _max is 0.602, and K _{b / a} is 10.49.

  FIG. 6 shows the DO and b / a calculation results obtained by the approximate expression (4) and the DO and b / a values of the data (1) to (4).

  In FIG. 6, a portion indicated by a dotted region R is a control region performed by a general activated sludge method by air blowing. In the present invention, outside this region, that is, b / a is 0.00. It was found that if the dissolved oxygen concentration (DO) is 5 [mg / L] or more at 15 or more and is operated at an appropriate dissolved oxygen concentration, aerobic treatment can be performed while suppressing excess activated sludge.

In actual control, first, the standard activated sludge method shown in FIG. 1 is used so that the dissolved oxygen concentration (DO) is 5 [mg / L] or more, and the average BOD concentration of the raw water (drainage) to be treated. In accordance with S ₀ , the sludge concentration (MLSS) X ₀ in the aeration tank 10 is set, and based on this, the supply amount of air or oxygen is set to perform the aerobic treatment.

  In this aerobic treatment, the dissolved oxygen meter 20 is installed in the aeration tank 10 to detect the dissolved oxygen concentration (DO), and the value of b / a shown in FIG. 6 from the detected dissolved oxygen concentration (DO). Ask for.

The b / a value obtained from FIG. 6 is a value obtained from the actual dissolved oxygen concentration (DO) by the above equation (4), and this b / a value is expressed by the above equation (3). If substituted, the sludge concentration X (MLSS) is obtained, and conversely, the BOD concentration S ₀ flowing into the aeration tank 10 and the BOD concentration S of the treated water are obtained, and the sludge concentration X (MLSS) is further sampled. If measured directly or with an optical measuring instrument, a / b can be obtained from equation (3).

  Therefore, if the sludge concentration X is obtained based on the equation (3) based on the value of b / a obtained by the equation (4), and this is compared with the actually measured sludge concentration, the sludge concentration The surplus is known, and conversely, the value of a / b is calculated from the actually measured sludge concentration X by the equation (3), and the dissolved oxygen concentration (DO) is calculated by the equation (4) based on the value. If it asks for, it will know the excess and deficiency of oxygen concentration.

Thus, the dissolved oxygen concentration (DO), the actual measured sludge concentration X data, in the above (3), (4), by obtaining a / b and the sludge concentration, respectively, with respect to the sludge concentration X ₀ set Thus, it is possible to determine whether the sludge concentration X in the aeration tank 10 is appropriate, and according to the measured sludge concentration X, the dissolved oxygen concentration (DO) at which the b / a value is appropriate can be obtained. Thus, by controlling the oxygen supply amount so that the inside of the flash tank 10 has an appropriate dissolved oxygen concentration, an operation in which the generation of excess sludge is suppressed can be performed.

  Thus, the present invention focuses on the ability to limit the growth amount of microorganisms by culturing microorganisms under conditions of high dissolved oxygen concentration (DO) and increasing the ratio of autolysis to growth. It has been found that if operation is performed with a high dissolved oxygen concentration, the generation of excess sludge can be suppressed.

  That is, the present invention detects a dissolved oxygen concentration (DO), obtains b / a by the DO, and attains a high BOD removal rate by setting an appropriate oxygen concentration according to the measured sludge concentration (MLSS). Generation | occurrence | production of the excess activated sludge can be suppressed, maintaining.

  In general, the activated sludge method does not reduce the microbial activity even if the dissolved oxygen is increased, so it is possible to reduce the amount of excess sludge generated while maintaining the treatment performance, and there is no need for conventional treatment equipment such as a sedimentation tank. The running cost can be reduced.

  In an aerobic treatment facility, since the dissolved oxygen concentration can be increased only by about 4 mg / L when air is blown, pure oxygen or oxygen-enriched air is used to increase the dissolved oxygen concentration (DO). Alternatively, there is a method in which the entire equipment is a pressure vessel, a pressure type, and compressed air is blown.

  In the present invention, by supplying oxygen or pressurizing it, the dissolved oxygen concentration is controlled to an appropriate dissolved oxygen concentration in the range of 5 to 40 [mg / L], thereby reducing the activity of microorganisms. Therefore, it is possible to prepare an environment incapable of breeding, thereby suppressing the generation of excess sludge.

  Next, an example of the apparatus of the present invention will be described with reference to FIGS.

  FIG. 2 shows a normal pressure type apparatus configuration, in which a drain line 11 is connected to the bottom of the upper open type aeration tank 10 and a treated water line 15 is connected to the top.

  The flash tank 10 is directly filled with activated sludge so as to have a predetermined sludge concentration according to the organic matter in the wastewater to be treated, or filled with activated sludge supported on a carrier.

  An aeration tube 12 is installed at the bottom of the aeration tank 10, an inner cylinder 21 for air lift is provided in the aeration tank 10, and a reverse funnel-shaped gas collecting member 22 is installed on the upper part of the inner cylinder 21. . As a result, the wastewater containing organic matter from the drainage line 11 rises in the inner cylinder 21 by pure oxygen and oxygen-enriched air blown from the aeration pipe 12, and oxygen is collected from the gas collecting member 22. The air is exhausted from the air tank 10.

  On the other hand, the waste water containing the organic matter and the activated sludge is reversed as shown by the arrow 24 in the gas collecting member 22, flows down to the outer periphery of the inner cylinder 21, and flows again to the inner cylinder 21 for circulation. In addition, the liquid component that has risen together with oxygen from the gas collecting member 22 overflows from the upper end of the gas collecting member 22, where the solid content settles as indicated by the arrow 25 and is separated into solid and liquid, and is inverted as indicated by the arrow 24. It is circulated again in the inner cylinder 21 together with the liquid that has become the downward flow. The treated water that has been subjected to solid-liquid separation is drained from the treated water line 15.

  In the apparatus shown in FIG. 2, a dissolved oxygen meter 20 is provided above the liquid surface of the aeration tank 10 serving as a solid-liquid separation unit, and this detected value is connected to an oxygen supply line 26 for supplying oxygen to the aeration tube 12. Input to the control device 27.

  The oxygen supply control device 27 controls the amount of oxygen blown from the aeration tube 12 so that the dissolved oxygen concentration input from the dissolved oxygen concentration meter 20 is appropriate. In this case, the oxygen supply control device 27 makes the amount of oxygen blown from the aeration tube 12 constant and changes the oxygen concentration mixed in the gas in order to make the internal circulation amount of the liquid by the inner cylinder 21 constant. To control. Specifically, pure oxygen or oxygen-enriched air is mixed with air so that the oxygen concentration becomes a predetermined value, or although not shown in the figure, the aeration tank 10 is a sealed type, and the aeration tank 10 A gas containing carbon dioxide or the like exhausted from the gas may be returned to the oxygen supply control device 27, and oxygen may be mixed with the gas.

  As described above, the oxygen supply control device 27 receives the detected values of the BOD concentration of the raw water from the drain line 11, the sludge concentration in the aeration tank 10, and the BOD concentration of the treated water discharged from the treated water line 15. The optimal oxygen concentration is set based on these, and the BOD removal rate is suppressed while surplus sludge is suppressed by blowing from the aeration pipe 12 so that the inside of the aeration tank 10 has the set dissolved oxygen concentration. High aerobic treatment can be performed.

  FIG. 3 shows the aeration tank 30 as a pressurized type, and the internal structure in the aeration tank 30 is the same except that the aeration tank 30 is formed of a pressure vessel. An inner cylinder 21 and a gas collecting member 22 are similarly installed inside, and a dissolved oxygen concentration meter 20 is provided.

  In this example, the oxygen supply control device 37 supplies the compressed air to the aeration tube 12 so as to increase the dissolved oxygen concentration of the waste water in the aeration tank 10, and the amount of liquid circulation by the inner cylinder 21. In order to keep the pressure constant, the pressure in the aeration tank 30 is made constant by returning a part of the gas exhausted from the aeration tank 30 from the return line 32 to the oxygen supply control device 37 via the blower 33. The amount of dissolved oxygen can be controlled as it is.

  Normally, by blowing compressed air of about 5 atm into the aeration tank 30 and keeping the pressure in the aeration tank 30 at the compressed air pressure, the dissolved oxygen concentration is 40 mg / L at the maximum at a water temperature of 20 ° C. It is possible to control the dissolved oxygen concentration in the range of 5 to 40 mg / L by mixing the gas from the return line 32.

  In this example, unlike FIG. 2, since compressed air is blown compared to blowing pure oxygen, the running cost can be reduced.

In this invention, it is a figure which shows the balance sheet for demonstrating sludge generation | occurrence | production in an aeration tank. It is a figure which shows the example of an apparatus which implements the method of this invention. It is a figure which shows the other example of an apparatus which enforces the method of this invention. In this invention, it is a figure which shows the result of the dissolved oxygen density | concentration when carrying out an aerobic process, the sludge density | concentration in an aeration tank, and a BOD removal rate. FIG. 5 is a diagram for creating an approximate expression for obtaining b / a by the dissolved oxygen concentration from the result of FIG. 4. In this invention, it is the figure which showed the relationship between dissolved oxygen concentration and b / a from the result of FIG. 4, and the approximate expression of FIG.

Explanation of symbols

10 Aeration tank 11 Drainage line 12 Aeration pipe

Claims (5)

  When introducing wastewater containing organic substances into the aeration tank and aerobic treatment of the wastewater with activated sludge, the aeration tank is set so that the dissolved oxygen concentration in the wastewater in the aeration tank is 5 mg / L or more. Aerobic wastewater treatment characterized by injecting air or oxygen into the interior and detecting the dissolved oxygen concentration and adjusting the dissolved oxygen concentration so that the activated sludge concentration of the wastewater in the aeration tank is lower than the set value Of sludge generation in Japan.   B / a, where BOD sludge conversion rate is a and sludge self-decomposition rate coefficient is b, wastewater treatment volume, aeration tank volume, BOD concentration of wastewater to be introduced, sludge concentration in the aeration tank, Calculate from the BOD concentration in the aeration tank, calculate b / a based on the dissolved oxygen concentration based on the b / a data obtained from these, and detect the sludge concentration in the aeration tank. The method for suppressing sludge generation in aerobic wastewater treatment according to claim 1, wherein the b / a at which the sludge concentration is not more than a set value is obtained, and the dissolved oxygen concentration is controlled so as to be b / a.   The method for suppressing sludge generation in aerobic wastewater treatment according to claim 2, wherein the dissolved oxygen concentration is controlled so that the b / a is 0.15 or more.   4. The oxygen concentration according to claim 1, wherein the oxygen concentration is controlled by mixing pure oxygen or oxygen-enriched air into a gas such as air so that the amount of gas blown from the aeration tube in the aeration tank is constant. Suppression method of sludge generation in aerobic wastewater treatment.   The aeration tank is a pressurized type, supplying compressed air from the aeration pipe, mixing the gas discharged from the aeration tank with the compressed air, and controlling the amount of gas blown from the aeration pipe to be constant The method for suppressing sludge generation in aerobic wastewater treatment according to any one of claims 1 to 3, wherein the concentration is controlled.

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