JP3195495B2 - Coagulation sedimentation method and equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coagulation sedimentation method for solid-liquid separation of suspended substances contained in raw water such as river water, which is typically a treated water, in a water purification plant and the like, and an apparatus therefor. The present invention relates to a coagulation / sedimentation treatment capable of improving the effect of the coagulation / sedimentation treatment by reusing sludge recovered by coagulation / sedimentation in a coagulation / sedimentation reaction system, and more particularly to a method and an apparatus for controlling the addition of acid.

[0002]

2. Description of the Related Art As a water treatment facility for producing purified water using river water, lake water, or the like as raw water, suspended substances (S) contained in raw water are used.
To remove the S) component, an aluminum-based flocculant (eg, sulfate band, polyaluminum chloride; commonly called “PAC”) is added to flocculate the suspended substance, which is then grown into flocculated floc, Separation of the treated water and sludge by sedimentation of floc (sludge), and the separated treated water is allowed to flow out to the subsequent treatment water system. On the other hand, the separated and recovered sludge is reduced in volume by appropriate concentration, dewatered, and disposed of. Disposal type equipment has been widely used in the past.

[0003] However, it has already been pointed out that this method has a problem that although the processing operation is simple, a large amount of coagulant is used.

[0004] In order to reduce the amount of coagulant used in the above-mentioned method, the sludge separated and recovered is adjusted to a pH of about 2 and aluminum hydroxide (Al (OH)
₃ ) is dissolved and aluminum ion Al ³⁺
There is also proposed a method of recovering and recycling as a flocculant. This method is generally referred to as a regeneration band method, and is said to have the advantage of reducing the operation cost of equipment because the amount of coagulant used can be reduced by the amount reused. A large sedimentation separation tank is required to separate the supernatant, and it is necessary to add a large amount of lime to the residue to dehydrate the sedimented residue. There is a problem that it cannot always be reduced, and low turbidity raw water is hardly implemented because the effect of improving the removal rate of suspended substances cannot be realized.

[0005] Further, a regeneration band method for recycling such a flocculant, that is, a method of ionizing aluminum hydroxide having lost flocculant activity and reactivating it as a flocculant, has been further applied and developed. Instead of returning only the aluminum ions reactivated as described above to the stirring system for coagulating the substance, a method of adding an acid for ionizing aluminum hydroxide on the way while returning the sludge collected by precipitation (hereinafter referred to as “ The present applicant has proposed a "method of returning acid-added sludge" (Japanese Patent Laid-Open No. 2-157005).
This method aims to improve the flocculation of suspended solids and floc floc growth in low turbidity raw water by simultaneously returning sludge to raw water, in addition to utilizing the advantages of the above-mentioned regenerated band system by recycling flocculants. There is an advantage that can be.
That is, by adding sludge to the low turbidity raw water, the reaction of flocculation floc growth of the suspended substance is stabilized, thereby facilitating the control of the amount of the flocculant injected into the raw water, improving the quality of the treated water, and generating the water. The amount of sludge generated can be reduced, and the processability at the time of sludge disposal can be improved. Hereinafter, this method is referred to as "acid-added sludge return method" in the present invention.

[0006]

By the way, the amount of the aluminum-based flocculant is reduced by reusing it, and at the same time,
Regarding the low turbidity raw water, the inventors of the present invention have the advantage that the actual operation on an industrial scale is suitable for the "return system of acid-added sludge" proposed in JP-A-2-157005, which has the advantage of improving the flocculation floc reaction. Further research to realize
As the development proceeded, several issues to be further improved were discovered as described below.

[0007] That is, in the above-mentioned "return system of acid-added sludge", sludge is usually retained for one to several days in a system for collecting and recovering sludge in a state of being isolated from the outside air, and as a result, the sludge becomes anaerobic atmosphere. Organic acids, which are substances that cause putrefaction odor, are generated, and sulfides with strong odor are also generated by the action of sulfate-reducing bacteria to produce malodorous components, or by acid addition when returning sludge. It has been found that as a result of the decrease in the pH of the sludge, the odorous substances are liable to volatilize, generating a strong putrefaction odor. The problem of sulfide formation is
This is easily confirmed from the fact that the sludge separated and settled is black.

In addition, heavy metals such as iron and manganese contained in the returned sludge returned to the stirring system are reduced and dissolved in a reducing atmosphere in which dissolved oxygen is consumed, and ammonium ions are formed by reduction of nitrate ions. As a result of an increase in the concentration of, there was also found a problem that the facility results in an increase in the amount of chlorine added to raw water or further added to the treated water produced.

Therefore, as a proposal for solving these problems, an oxidizing means such as an aeration apparatus for maintaining the returned sludge in an aerobic microorganism growth environment at a position before the acid addition in the above-mentioned "acid-added sludge return method" is proposed. The present applicant has further proposed a new coagulation / sedimentation treatment facility which can prevent the decomposition of the odorous substances such as putrefaction odor and the reduction and dissolution of heavy metals by providing (Japanese Patent Application No. 6-73434).

[0010] The present invention relates to a novel acid-added sludge coagulation-sedimentation treatment method provided with an oxidizing means such as an aeration apparatus.
Alternatively, a new proposal for realizing the suitable operation and operation of the equipment is made. That is, the above-mentioned Japanese Patent Application No. 6-734.
When implementing the method proposed in No. 34, for example, it is assumed that the acid-added sludge is always returned and injected into the raw water in a constant amount, and the fluctuation of the amount of the flocculant required according to the fluctuation of the raw water flow rate is added to the raw water. It is also conceivable to adopt a method of adjusting the flow rate of the added aluminum-based flocculant (sulfuric acid band, polyaluminum chloride) in proportion. However, in the method in which the injection amount of the acid-added sludge is constant with respect to the fluctuating raw water flow rate, the injection amount of the acid-added sludge to the raw water is relatively fluctuated. As a result, an effect such as an increase in the pH value fluctuation amount of the treated water is caused, and the influence of this fluctuation is remarkable when the injection amount of the acid-added sludge is large.

Based on such findings, the present inventor has proposed a method of variably adjusting the return flow rate (injection amount) of the acid-added sludge with respect to the fluctuating raw water flow rate, instead of the method of keeping the return flow rate of the acid-added sludge constant. The following points were further examined as adopters.

First, for example, the flow rate of raw water flowing into a water purification plant is not constant, but fluctuates every hour every day because it is necessary to meet the demand for water purification. In addition, it is affected by long-period fluctuations depending on the season, weather, and the like. Therefore, the amount of acid-added sludge returned to reuse Al (OH) ₃ as a flocculant varies from time to time depending on the quality of raw water and the flow rate of raw water, so that at least acid is added so as not to adversely affect operation. The treatment pH value of the returned sludge added is maintained at an appropriate value so as not to adversely affect the operation, and short-term fluctuation, seasonal fluctuation,
It is necessary to cope with long-period fluctuations such as weather fluctuations.

Second, in order to maintain the pH of the returned acid-added sludge at an appropriate value, not only the amount of returned sludge, but also the fluctuation of the aluminum hydroxide content in the coagulated sludge,
It is necessary to adjust the amount of acid addition so as not to cause excess or deficiency.

Third, in industrial facilities, Al (OH) ₃
It is desired that the control for maintaining the pH value of the acid-added sludge returned to reuse the coagulant as appropriate is as simple as possible and requires few devices and measuring instruments, and When automating operation control of equipment, it is a matter to be considered that facilitation of maintenance and inspection of various detectors and devices used is regarded as important in industrial equipment.

As the third problem, particularly, the configuration of installing the pH detector in the sludge return system becomes a problem. That is, in the industrial equipment to which the present invention is applied, since there is no means for directly measuring the aluminum content contained in the returned sludge, it is necessary to confirm the ionization state of the aluminum content and to prevent the dissolution of other heavy metals. It may be necessary to measure the pH to control the amount of acid added. For this reason, if an immersion type pH detector is installed near the acid addition position or the mixing section, an acid-resistant open intermediate tank and an acid-resistant pump in the subsequent stage will be required, and strong acid sludge will be required. It is not easy to calibrate the immersed pH detector and to automatically clean the detector, which is disadvantageous particularly in automating the operation of the equipment. When an in-line type pH sensor is installed instead of the immersion type pH sensor, the pressure of sludge pumping acts on the detector. In addition to the need for ancillary equipment such as cleaning, washing in-line will cause fluctuations in the sludge return flow rate and cause deterioration in the water quality of the treatment system. There is also a problem that it is necessary to sufficiently prevent the strongly acidic sludge from scattering to the outside at the time of removal or the like.

The present invention has been made in view of these problems, and one of the objects thereof is to add an aluminum-based flocculant to be used in the above-mentioned flocculation / sedimentation treatment equipment used for producing purified water. Coagulation / sedimentation method and equipment capable of realizing reduction of the amount, reduction of equipment operation cost based on this, reduction of total amount of waste sludge, and easy operation and operation, and the equipment. Where you do it.

Another object of the present invention is to facilitate the control of the amount of coagulant to be injected into raw water, to stabilize the flocculation of flocculated floc with low turbidity raw water, to stabilize the pH of treated water, and to improve the quality of treated water. It is an object of the present invention to provide a coagulation / sedimentation treatment method provided with a control system capable of suitably realizing the above with an actual-scale facility, and a facility therefor.

Still another object of the present invention is to make the content of aluminum hydroxide in the sludge constant in the sludge recovery-reuse cycle, thereby achieving extremely simple operation control. It is to provide a processing method and its equipment.

Another object of the present invention is to provide a coagulation / sedimentation treatment facility capable of easily and safely performing calibration and washing of a pH detector installed in a sludge return system.

Still another object of the present invention is to introduce an acid-added sludge injection device into an existing coagulation and sedimentation treatment facility that is already in operation, and to make a major change in the control system of the existing equipment when introducing it. Instead, the present invention is to provide equipment that can be operated and operated by the novel control of the present invention.

[0021]

Means for Solving the Problems and Actions The coagulation / sedimentation treatment method of the present invention which achieves the above-mentioned various objects, and the features of the equipment thereof have the structure described in each of the above-mentioned claims. It is in.

One of the features of the present invention is that the sludge return flow rate is
The control is to increase or decrease according to the flow rate of raw water, and to control the acid addition at an appropriate acid addition rate according to the sludge return flow rate.

That is, the feature of the coagulation sedimentation treatment method of claim 1 is that, after the suspended substance in the raw water is coagulated by adding an aluminum coagulant, the coagulated material is separated from the treated water as sludge by sedimentation. At least a part of the sludge collected by settling is returned to the raw water, and is oxidized on the way to provide an atmosphere for growth of aerobic microorganisms, and then acid is added to the returned sludge to reuse aluminum hydroxide as a flocculant. In the coagulation sedimentation treatment method to be added, the return flow rate of the sludge is
The control is based on the result calculated from the raw water flow rate information, and the acid addition amount is controlled based on the result calculated from the sludge return flow rate information. This processing method
For example, it can be carried out using the coagulation / sedimentation treatment equipment of claim 6.

In the above description, "controlling the return of sludge based on the result calculated from the raw water flow rate information" means, for example,
The acid-added sludge injection rate setting section provided in the control device is composed of a ratio setting section that is proportional to the raw water flow rate and a bias setting section that is not proportional to the raw water flow rate. method for calculating the injection amount y ₁ for the raw water, can be used. However, the present invention is not limited to this method.

Y ₁ = a ₁ · x + b ₁ ··· (1) where y _{1 is} the return flow rate of the acid-added sludge (the amount injected into the raw water)
(Liter / h) x: raw water flow rate (m ³ / h) a ₁ : injection rate of acid-added sludge (liter-sludge / m ³ -raw water) b ₁ : fixed injection amount of acid-added sludge (liter / h) According to the equation (1), the fixed injection amount b ₁ of the bias setting unit is obtained.
And the injection amount a ₁ · of the ratio setting unit that is proportional to the raw water flow rate
and a x, injection volume y ₁ to raw acid addition sludge is calculated, the calculated result, and instructs the drive control of the pump for injecting the acid addition sludge raw water side to control the pump speed be able to. In order to accurately control the injection amount as instructed, it is of course possible to provide a general-purpose adjustment unit that performs feedback control by comparing with a sludge flow rate signal from a sludge flow rate detector. Proportion constant (injection rate a ₁ ) of the ratio setting unit that makes the injection amount of the acid-added sludge proportional to the raw water flow rate in the above equation ( ₁ )
Is not uniformly determined by the composition of the equipment and the quality of the raw water determined by the application area, but according to experiments conducted by the inventor,
It is often preferable to set the range of 0.5 to 5 [liter-sludge / m ³ -raw water].

In the above configuration, an injection pump used for returning (injecting) the acid-added sludge is a non-pulsating type fixed quantity pump capable of controlling the number of revolutions, a spiral pump and a three-way split type flow control valve in combination, and one type of sludge. A method in which the part is returned to a sludge concentration tank can be cited as a preferred example.

In the above configuration, "controlling the addition of acid based on the result calculated from the sludge return flow rate information" means, for example, Y = A ₁ .X (where Y is the addition amount of acid, and X is the addition amount of acid). According to the sludge return flow rate (injection amount), A ₁ is the acid injection rate), acid addition can be performed in proportion to the acid addition sludge return flow rate (injection amount), and the Al (OH) ₃ content rate in the sludge Is constant, the acid addition rate can be controlled as a fixed value. However, the present invention is not limited to this method.

As the acid that ionizes Al (OH) ₃ contained in the returned sludge and regenerates it into the flocculant, a mineral acid such as sulfuric acid or hydrochloric acid, preferably sulfuric acid, can be used. PH 3.0-3.5 to ionize Al (OH) ₃ and avoid dissolution of other heavy metals
Is added within the range. The inventor's experiment,
According to empirical studies, it is often preferable that the acid addition rate be in the range of ₂ to 10 [liters-H ₂ SO ₄ / m ³ sludge] when 70 wt% sulfuric acid is used.

As the acid addition pump, for example, a stroke control, a rotation speed control, or a combination of both can be used by using a pump having a quantitative property, but any pump having an accurate response to a control command can be used. There is no particular limitation as long as it is a pulse pump. Further, an acid injection amount detector may be provided to accurately control the injection amount as instructed, and a general-purpose adjusting unit for performing feedback control as compared with the acid injection amount may be provided. The detection of the raw water, the sludge return flow rate, and the acid injection rate described above is not particularly limited as long as it is a detector capable of accurately measuring the sludge flow rate, but an electromagnetic flow meter is preferably used.

A mixing section is provided downstream of the acid addition position of the sludge return system. It is sufficient that the sludge and the acid have a structure capable of sufficiently stirring and mixing, and the stirring and mixing effect may be maintained even with the minimum injection amount. For example, an agitation tank may be provided, or the agitation tank may be agitated by a method of causing meandering, swirling, and shearing flow in a pipe as shown in the following examples.

In the first or fourth aspect of the present invention, the configuration for controlling the sludge return flow rate based on the raw water flow rate information and controlling the acid addition amount based on the sludge return flow rate information is adopted for the following reasons. . That is, according to the test according to the method of the above claim 1, although not uniform for all raw water, if the sludge circulation cycle by adding the acid-added sludge to the mixing tank is repeated, even if the raw water turbidity fluctuates,
It has been found that the content of aluminum hydroxide in the sludge may not vary so much. This fact is surprising because the content of aluminum hydroxide in the settled sludge is generally considered to fluctuate not only due to seasonal fluctuations, weather fluctuations, etc. but also largely. This is probably because the sedimentation of the sludge is improved, the sludge concentration is relatively increased, and the sludge concentration is maintained at a substantially constant concentration. However, in the equipment in which the content is substantially constant as found above, the pH value of the returned sludge is generally maintained at the initial set value only by controlling the addition of the acid corresponding to the sludge return flow rate. If such a condition, that is, a condition that the content of aluminum hydroxide in the sludge does not fluctuate significantly, is satisfied, the acid addition rate is fixed and the return flow rate of the acid-added sludge is satisfied. This is extremely advantageous in terms of equipment in that extremely simple control in which the amount of acid added can be controlled in proportion to only the amount can be realized. The above “substantially constant” refers to a condition in which the variation of the aluminum hydroxide content is 20% or less, preferably 10% or less.
The adverse effect of H fluctuation does not actually pose a problem. However,
When this control method is adopted, the optimum value of the appropriate acid addition rate is determined periodically (every season, every few months, etc.) by a jar test, etc., taking into account the effects of large seasonal fluctuations, etc. It is desirable to perform the operation in order to secure the operation.

Next, the invention of claim 2 which is another feature of the present invention will be described. The feature of the present invention is that the fluctuation of the aluminum hydroxide content in the returned sludge is 20%.
%, Or when more precise control is required, a configuration is adopted in which the control of the acid addition amount is performed in consideration of pH value information. That is, when the aluminum hydroxide content in the returned sludge fluctuates, the control of the sludge return flow rate is controlled based on the result calculated from the raw water flow rate information,
It is preferable that the acid addition amount is controlled based on a result calculated from sludge return flow rate information and pH value information of the sludge after acid addition. This processing method is described in claim 6
It can be preferably carried out using the coagulation / sedimentation treatment equipment.

The reason for adopting the configuration of the second aspect of the present invention is as follows. In other words, the Al (O
H) When the ₃ content rate fluctuates, the acid addition rate (acid addition amount per unit returned sludge amount) is set to a constant value, and the acid addition amount is calculated and controlled based only on the sludge return flow rate (injection amount) information. In this method, the pH value of the acid-added sludge is inevitably changed. If Al (OH) ₃ in the sludge increases, the acid required for dissolution becomes insufficient and the pH rises. Al
If (OH) ₃ decreases, the acid required for dissolution becomes excessive and the pH drops. As described above, the fact that the pH value is too high or low relative to the appropriate value causes undesired effects such as a decrease in the recovery rate of Al (OH) _{3 in} the returned sludge and dissolution of heavy metals. Such fluctuations in the Al (OH) ₃ content in sludge often appear under the influence of relatively long-period disturbances caused by seasonal fluctuations, weather fluctuations, and the like. This is due to the fact that the injection amount of the aluminum-based flocculant is not always proportional to the turbidity of the raw water and to the change in the concentration of the sludge itself which varies depending on the properties of the settled sludge, the water temperature, and the like.

According to the second aspect of the present invention, in order to maintain the pH value of the acid-added sludge at an appropriate level, the pH of the acid-added sludge is changed by the change in the Al (OH) ₃ content in the returned sludge.
The H change was measured by a pH detector to perform the above control.

The above-mentioned "controlling the acid addition amount based on the result calculated from the sludge return amount information and the pH value information of the sludge after acid addition" means, for example, that the acid addition sludge detected by the pH detector is used. The difference between the measured pH value and the appropriate pH value is calculated by calculating the excess or deficiency of the acid to be added, and correcting the acid addition rate set value used when calculating the acid addition amount according to the sludge return flow rate. The method can be illustrated.

The present inventors have confirmed experimentally and empirically that when 70% sulfuric acid is used, the deviation from the appropriate pH is ±
± 10 ± 200 [ml-
[H ₂ SO ₄ / m ³ -sludge] is often appropriate to add or subtract from the acid addition rate set value.

When the pH value information is used to correct the acid addition amount as described above, the operation cycle is such that the sludge to which the acid is added at the corrected acid addition rate flows through the return pipe and is detected by the pH detector. Predetermined delay time (time lag) until detection
In consideration of the above, it is desirable to perform sampling with a time length equal to or longer than the delay time as a cycle. This is because the result of correction does not appear in the information sampled in a cycle shorter than the delay time. This delay time is determined by the volume of residence in the pipe from the acid addition point to the pH detector of the acid added sludge,
Calculated from sludge flow rate.

[0038] As a method for the delayed hours of operation cycle described above, the average pH after a predetermined time T _R min each reach Q _S ≧ Q _V is exemplified a method to perform correction of the above it can.

However, Q _S : integrated value of sludge flow rate Q _V : residence volume between the acid addition point and the pH detector T _R : T ₁ + T ₂ + t _C (from the time when Q _S ≧ Q _V is reached to the completion of the correction calculation) T ₁ : Sufficient time (minutes) to be longer than the delay time T ₂ : Sampling time for obtaining the average value of pH (several tens of seconds to several minutes) t _C : Calculation and correction time (ms) Further, after the operation corrected completion repeats again accumulated to reset the Q _S to zero. By such a method, the above-described appropriate correction of the acid addition rate can be performed.

In the above invention of claim 1 or 2,
The coagulant injected into the coagulant mixing tank is 100% acid-added sludge
In the long-term recovery cycle, the content of Al (OH) ₃ in the sludge gradually decreases by the amount of Al (OH) ₃ brought into the discharged dewatered sludge. Then, when the content is reduced below the content effective as a flocculant, the return and recovery effect is lost. Therefore, it is necessary to add aluminum coagulant (sulfuric acid band or polyaluminum chloride, etc.) as a coagulant directly added to the extent that the coagulant is taken out of the system as dewatered sludge. It is preferable that the content of Al (OH) ₃ therein is maintained within a predetermined range.

The amount of the acid-added sludge injected into the raw water is as shown in the above formula (1), but an aluminum-based flocculant (sulfuric acid band or polyaluminum chloride) to be directly added to the raw water.
Is given by the following equation (2).

Y ₂ = a ₂ x + b ₂ (2) where y ₂ : injection amount of aluminum-based coagulant (liter / h) x: raw water flow rate (m ³ ) a ₂ : aluminum-based coagulant injection Rate (liter-coagulant / m ³
- raw water) b _2: a fixed amount of injected aluminum-based coagulant addition (l / h), in the conventional method that does not return injected acid addition sludge for example the maximum amount y ₀ of aluminum sulfate, similarly to the above formula (2) The following expression (3) is obtained.

Y ₀ = a ₀ · x + b ₀ (3) According to the method of the present invention, the regenerated aluminum in the acid-added sludge is α · y _{1 in} terms of the sulfuric acid band based on its content, and the sulfuric acid band directly added. Since the amount is y ₂ from the above formula (2), the addition amount corresponding to the above y ₀ is given by the following formula.

Y ₀ = α · y ₁ + y ₂ = α (a ₁ · x + b
₁ ) + a ₂ .x + b ₂ where α is the H ₂ SO ₄
Therefore, the ratio of the sulfuric acid band brought in by the injected acid-added sludge to the total amount of the sulfuric acid band to be added is: (y ₁ · α / (y ₁ · α + y ₂ )) = y ₁・ Α / y ₀ =
In the present invention, it is often preferable to determine the addition rate (injection rate) of the acid-added sludge so that this value is about 0.6 to 0.9.

Incidentally, such an appropriate distribution ratio of the addition rate cannot be determined uniformly because it varies depending on the component composition ratio in the concentrated sludge. However, from the experimental and empirical findings of the present inventors, the raw water turbidity Since the component has little effect on the sludge component, the above-mentioned α is about 0.02 to 0.04. Therefore, each of the coefficients a ₁ , a ₂ , b ₁ , and b ₂ is set in the safety region (for a small value of α Addition rate), usually,
Simple control without changing the addition rate can be performed. Note that the above-mentioned safety region refers to a combination range of coefficients when the acid addition ratio is such that the pH of the acid-added sludge does not fall below a specified value.

According to the present invention, the ionic aluminum contained in the returned sludge acts together with the coagulant to which the sludge is directly added, and the injection amount of the acid-added sludge is controlled in accordance with the flow rate of the raw water. PH
The amount of acid addition is controlled so that
H can be maintained.

The aluminum content in the sludge component composition is improved as the sludge circulation cycle is repeated and the properties are improved and the properties are stabilized. This makes it possible to dynamically follow the fluctuation of the flow rate of the raw water, thereby significantly reducing the amount of coagulant to be added directly and stabilizing the water quality by generating floc having excellent sedimentation properties.

Furthermore, there is little control interaction with existing water purification equipment, and introduction and operation can be started without water interruption.

The invention of claim 7 is characterized by a preferred configuration of the piping of the sludge return system downstream of the acid addition position of the above-mentioned coagulation / sedimentation treatment equipment and the pH detector attached thereto. That is, in the case of equipment on an industrial scale, it is required that the pH detector needs to clean sludge and the like for calibration. Therefore, as in the invention of claim 6,
A terminal portion of the return pipe is formed so that the return sludge naturally falls from above with respect to a downstream terminal of the return pipe for injecting the return sludge into the mixing tank, and the terminal portion is formed between the highest point of the terminal portion and the terminal. These demands can be satisfied by installing a pH detector.

In the equipment of the present invention, a typical example of the oxidizing means used to oxidize the returned sludge so as to have an atmosphere for growing aerobic microorganisms is an aeration apparatus for aerating oxygen-containing gas. it can.

According to a tenth aspect of the present invention, the sludge return pump for returning the sludge through the return pipe is provided upstream of the acid addition position of the sludge return pipe. The advantage is that it is not necessary to use an acid-resistant sludge return pump.

[0052]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a water purification plant will be further described below with reference to the drawings.

Embodiment 1 This embodiment is for describing an embodiment corresponding to claim 1 or claim 5.

In FIG. 1, reference numeral 2 denotes a flocculating agent mixing and stirring tank, which is provided with a rotary blade type stirring device 201. Then, in the stirring tank 2, the raw water introduced from the raw water introduction pipe 1 and the flocculant (polyaluminum chloride (PAC)) injected from the flocculant storage tank 211 by the pump 212 which is a flocculant injection device are stirred and mixed. The coagulation reaction of the suspended substance contained in the raw water is performed. Caustic soda can be similarly injected into the coagulant mixing tank 2 from a caustic soda storage tank 213 by a pump 214. In the latter part of the aggregating agent mixing and stirring tank 2 of the present example, a moderately slow stirring is performed by the rotating blade type stirring device 203 to form flocculated flocculent suspended material and to further grow the flocculant. A stirring tank 202 is provided.

Reference numeral 3 denotes a sedimentation tank provided at the latter stage of the coagulant mixing and stirring tank 2, and sludge containing coagulated flocs is sedimented to the bottom by sedimentation and separation, while treated water is not shown via a filtration pond 4. From the overflow channel, the water is discharged to a downstream water purification system (not shown).

The sludge collected at the bottom of the settling tank 3 is appropriately drawn into a sludge thickening tank 6 by a sludge drawing pipe 5 and concentrated in the thickening tank 6 to a concentration suitable for returning to the raw water side as returned sludge ( For example, about 2 to 10 times). The concentrated sludge is sent to the aeration tank 7 from the bottom of the thickening tank 6 and then passed through a thickened sludge withdrawing pipe 701 by a pump 702 to form a thickened sludge treatment device 70 such as a dewatering device.
3 is provided so that the sludge is sent intermittently as appropriate so that excess sludge can be dewatered and disposed of. The aeration tank 7 is an open horizontal flow tank, and a blower (not shown) diffuses air from the bottom of the tank until the sludge sent from the concentration tank 6 is sent out by the sludge return pump 801 at the subsequent stage. 704
The aeration tank 7 is provided so as to be held in the aeration tank 7 for, for example, 24 hours by air ejected from the tank. The degree of aeration can be controlled by time as described above. However, as an industrial-scale device, the oxidation-reduction potential of sludge is monitored at the outlet of the aeration tank, and the aeration control or the sludge flow control of the aeration tank 7 is performed. It is also preferable to provide feedback so that reliable oxidation control is performed. By this aeration treatment, the organic acids, hydrogen sulfide, ammonia,
Iron, manganese, etc. are oxidized.

The concentrated sludge withdrawal pipe 701 is branched into a sludge return pipe 8 on the way, and a part of the sludge is passed through the sludge return pump 801 through the coagulant mixing and stirring tank 2.
Will be returned to you.

That is, the sludge subjected to the predetermined aeration treatment in the aeration tank 7 is added with an acid (sulfuric acid in this example) from the acid storage tank 10 on the way through the sludge return pipe 8 by the sludge return pump 801. After being sufficiently stirred on the way through the mixing section 11 provided downstream thereof to ionize the aluminum hydroxide contained in the sludge, the sludge is returned to the coagulation-mixing and stirring tank 2. As the sludge return pump 801 in this example, a non-pulsation type fixed quantity pump capable of controlling the flow rate by the number of rotations was used.

Reference numeral 101 denotes an acid addition pump for injecting the acid in the acid storage tank 10 into the sludge return pipe 8. 12 is
Acid-added sludge provided at the downstream end of return sludge pipe 8
It is a pH detector for measuring H.

Reference numeral 20 denotes a raw water flow rate detector for detecting a raw water flow rate, and reference numeral 21 denotes a sludge return flow rate detector for detecting a return sludge flow rate. These measurement information are input to an arithmetic unit 22 as input signals. It has become.

Next, the control of the return sludge flow rate y _{1 and} the control of the acid addition amount Y of the present embodiment performed based on the information measured by the raw water flow rate detector 20 and the return sludge flow rate detector 21 will be described. I do.

The computing unit 22 of this embodiment is provided with an acid-added sludge (returned sludge) injection rate setting unit 221. The setting unit 221 sets the above equation (1) [y ₁ = a ₁ · x + b ₁ ]
Fixing the injection amount of the acid added sludge corresponding to the b ₁ (l /
h) (Bias) and the injection rate of acid-added sludge (liter-sludge / m ³ -raw water) (ratio), which is a coefficient for varying the injection amount in proportion to the raw water flow rate x, are set in advance, and the raw water flow rate is detected. (1) according to the raw water flow rate information (x) from the vessel 20
Acid addition sludge (return sludge) flow y ₁ is calculated calculated according. The calculation result is output as a drive command for the sludge return pump 801, and the sludge return pump 801 is driven according to the command.

The calculator 22 has an acid addition rate setting unit 2
22 is provided, a predetermined addition rate (for example, the coefficient A _{1 of} Y = A ₁ · X described above) is set, and the sludge injection (return) flow rate information (X) from the sludge return flow rate detector 21 is used. An acid addition amount Y proportional to the sludge return flow rate is calculated and calculated, and the calculation result is output as a drive command for the acid addition pump 101, and the acid addition pump 101 is driven according to the command. As described above, the pumps 801 and 101 may be controlled to follow the command.

In this embodiment, the TU, pH, and alkalinity of raw water are detected as existing equipment, and based on these, a coagulant (PAC) addition rate and a caustic soda addition rate are respectively calculated and controlled. The operation amount of each agent is controlled by a bias setting unit for adding a fixed amount and a ratio setting unit for proportionally changing the raw water flow rate.

According to the coagulation / sedimentation treatment equipment and the control method of the present embodiment configured as described above, first, the components which hinder the water purification treatment generated in the sludge collected by coagulation / sedimentation are first removed. Since the acid is added to decompose and insolubilize by aeration treatment and then reuse the flocculant, even if the above-mentioned sludge becomes anaerobic, transfer to the anaerobic of the sludge for reuse of the flocculant The advantage is that the reuse of flocculants, which has been possible in principle in the past, can be realized ideally on industrial scale facilities without causing adverse effects such as odors. Can be

Further, the suspended substance contained in the sludge returned to the stirring tank functions as a coagulation aid by being added to the raw water, and when the raw water has a low turbidity, a conventional coagulant is added. This improves the difficulty of controlling the injection amount and also contributes to the growth of high-density flocculated flocs, thereby providing the advantage of improving the sedimentation and separation of sludge.

The amount of acid to be injected into the returned sludge for ionizing and returning Al (OH) ₃ to the raw water side is as follows:
By controlling the flow rate of returned sludge (sludge before acid addition) corresponding to the raw water flow rate, and then controlling the amount of acid addition corresponding to the flow rate of returned sludge (sludge before acid addition), the aluminum content is reduced. For acid-added sludge that is substantially constant, the amount of acid to be added can be adjusted to an appropriate value because the amount of acid to be added can be adjusted to an appropriate value, and the reuse of the aluminum flocculant by returning the sludge efficiently can be efficiently performed. It is effective in preventing harmful effects such as generation of offensive odor and increase of chlorine consumption.

Further, effects such as a reduction in the amount of coagulant used, a reduction in the total amount of waste sludge generated, a reduction in operation costs, and the like can be achieved without complicating the operation and introducing new adverse effects.

Further, the sludge return pump 801 is connected to the return pipe 8
Since the pump is disposed upstream of the acid addition position, there is an advantage that it is not necessary to use an acid-resistant pump for this pump.

Embodiment 2 This embodiment is for describing an embodiment corresponding to claim 2 or claim 6.

As shown in FIG. 2, this embodiment is characterized in that a pH detector 12 is provided at a piping terminal of a sludge return system as compared with the first embodiment, and an acid addition rate setting section 22 of an arithmetic unit 22.
2 is provided with an acid addition rate correction value calculation unit 223, and the measurement information of the pH detector 12 is converted into an acid addition rate correction value calculation unit 22.
3 is different,
Others are the same as the first embodiment. Therefore, common components are denoted by the same reference numerals as in the first embodiment, and description thereof is omitted.

In the control of this embodiment, the control of the sludge return flow rate is controlled by the calculated value calculated based on the raw water flow rate information by the bias setting section and the ratio setting section of the acid addition sludge injection rate setting section 221 of the calculator 22. This embodiment is the same as Embodiment 1 except that the control of the acid addition amount is different.

That is, the acid addition rate correction value calculator 2 of this embodiment
In 23, pH value information of the acid-added sludge injected into the coagulant mixing and stirring tank 2 detected by the pH detector 12 installed at the end of the return pipe is input, and this is used to calculate the deviation from the appropriate pH value. If so, a predetermined acid addition rate correction value Δa corresponding to this deviation is calculated, retrieved from an appropriate memory, output to the acid addition rate setting unit 222, and A representing the acid addition rate of the above-described equation (1). ₁ as (A ₁ + Δa) or (A ₁ −Δ
Correct to a). The degree of correction is not uniform according to the configuration of the equipment, the quality of raw water, and the properties of sludge, but can be determined by experiments or the like from the above-described range.

[0074] In addition to the acid addition rate correction value calculating unit 223, sludge return flow information detected by the sludge return flow detector 21 is inputted, pH from the acid addition position P ₁ of the return pipe 8
Since piping volume between the installation position P ₂ of the detector (described above retention volume) it can be known in advance from the configuration of the equipment, from these sludge return flow information and pipe volume of P ₁ to P _2,
Slightly longer than the time required until the sludge passing through the P ₁ position passes through the P ₂ position can be determined as a sampling cycle performed in the acid addition rate correction value calculation unit 223. This sampling cycle may be fixed when the sludge return flow rate does not fluctuate significantly.

Then, from the corrected acid addition rate and the sludge return flow rate information (X), an acid addition amount is calculated and calculated by Y = (A ₁ + Δa) · X, and the calculation result is used to drive the acid addition pump 101. It is output as a command, and the acid addition pump 101 is driven according to the command. The drive of the pump 101 may be controlled to follow a command, as in the first embodiment.

According to the coagulation / sedimentation treatment equipment and its control method of the present example, the same advantages as those obtained in Example 1 can be obtained, and more precisely, acid addition for effective recovery of aluminum than in Example 1 can be obtained. Appropriate amount control can be performed. Therefore, even if long-term fluctuations in raw water quality or changes in the content of aluminum in returned sludge can be achieved while operating at a raw water flow rate according to demand, aluminum can be effectively recovered, causing odor and chlorine consumption. The advantage is obtained that the coagulant can be reduced while reliably preventing an increase in the amount and the like, and the automated operation of the equipment can be realized.

Further, since the automatic correction can be performed even for a long-period change, the water quality can be stabilized for a long time.

Embodiment 3 In this embodiment shown in FIG. 3, a follow-up control section of a sludge return pump 801 and a follow-up control section of an acid addition pump 101 are added. A sludge flow controller and an acid addition flow controller are respectively provided. The second embodiment is characterized by a configuration in which it is provided, and the other configuration is the same as that of the second embodiment.

In this embodiment, by adopting the above configuration,
The advantage is obtained that the sludge can be reliably injected in response to the acid addition sludge injection amount command, and the acid can be surely added in response to the acid addition amount instruction.

Embodiment 4 This embodiment shown in FIG. 4 is a sludge return pump 801 of Embodiment 3.
Instead of using the centrifugal pump 8011 and the three-way split type flow control valve 8012, the opening degree of the valve that returns a part of the sludge from the three-way split type flow control valve 8012 to the aeration tank 7 is determined by the acid-added sludge (returned sludge). ) Return of acid-added sludge (injection) by changing according to the command from the injection rate setting unit 221
The third embodiment is characterized in that it has a configuration in which the amount is controlled, and other configurations are the same as those in the third embodiment. Therefore, the same configurations are denoted by the same reference numerals and description thereof is omitted.

In this embodiment, by adopting the above configuration,
Advantageously, a centrifugal pump with good maintainability can be used, and the variable range of the injection amount can be widened by using a control valve.

Embodiment 5 This embodiment is for describing an embodiment corresponding to claim 8.

FIG. 5 is an enlarged view of the terminal portion of the return pipe 8 for the acid-added sludge. In this figure, the main line pipe of the return pipe 8 indicated by 8 is raised vertically upward from the surface of the flocculating agent mixing and stirring tank 2 to a position at a height H, and then extends substantially horizontally at a right angle. A vertical tube portion 83 having a horizontal tube portion 81 provided at a right angle and vertically downward further has a terminal opening 82 at the lower end thereof opposed to the water surface of the flocculant mixing and stirring tank 2 at a slight interval. It is provided in. Also, the vertical pipe portion 83 of the main line pipe
An air suction vent pipe 84 for forming a siphon break is provided above.

A measuring line pipe 85 branches off from the middle of the horizontal pipe section 81 of the main line pipe, and a pH detector disposed at a position lower than the horizontal pipe section 81 via a sample inlet valve 86. An outlet pipe 89 is connected to the inlet of the pH detector 12, and an outlet pipe 89 is connected to the outlet of the pH detector 12. It is provided so that it may be parallel.

Reference numeral 87 denotes a washing water introduction pipe, and a washing water valve 88.
Is connected to the above-mentioned pH detector 12.

According to the installation configuration of the pH detector as described above, the acid-added sludge pumped to the horizontal pipe portion 81 of the main line pipe by the driving force of the sludge return pump 801 shown in the second embodiment, etc. From the horizontal pipe section 81, the mixture is poured into the flocculant mixing and stirring tank 2 by natural fall. Therefore, the sludge naturally flows into the pH detector 12 below the horizontal pipe portion 81, which is the highest point of the terminal portion of the main line pipe where the sludge naturally falls, only by switching the opening of the sample inlet valve 86. Will be. Further, by closing the sample inlet valve 86 and opening the washing water valve 88, the washing water can be automatically flowed into the pH detector, and the washing water containing the sludge can be poured into the flocculant-mixed stirring tank 2 as it is. There is an advantage that automatic cleaning of the detector can be easily realized.

Further, the following effects can be further obtained by the above configuration of this embodiment.

At the time of pH calibration, the supply of sludge to the pH detector is stopped, and calibration work can be performed after washing with washing water. Therefore, when the pH detector is removed, scattering of adhered sludge (strongly acidic) may occur. There is no fear at all, and work safety can be improved.

Since the pH of acid-added sludge can be measured at atmospheric pressure, it is easy to replenish KCl of the reference electrode.
No additional equipment such as a pressure compensator is required.

Even if the pH sensor is washed during the operation of the equipment, the amount of washing water required for washing is only the sum of the inner volume of the holder of the detector and a part of the inner volume of the measurement line pipe (approximately 1 to 1).
(2 liters / time), it is negligible as a disturbance in the water purification treatment even if it is poured into the coagulant mixing and stirring tank 2, and there is ancillary equipment for neutralizing the strong acid sludge contained in the washing water. Not required at all.

[0091] Irrespective of the calibration or washing of the pH detector, the acid-added sludge can be continuously injected into the coagulant mixing and stirring tank 2, so that the operation of the equipment is not interrupted.

As described above, the pH can be stably detected over a long period of time and can be automatically detected, which is extremely advantageous in terms of automation of equipment.

[0093]

According to the present invention, the following effects can be obtained.

According to the first and sixth aspects of the present invention, the amount of the acid-added sludge to be returned can be controlled at an appropriate injection rate in accordance with the flow rate of the raw water. is there.

[0095] Further, in a facility in which the content of aluminum hydroxide in the sludge is constant in the sludge recovery-reuse cycle, the amount of acid addition can be controlled based on the result calculated from the sludge return flow rate, so that extremely simple operation is possible. There is an effect that control can be realized.

According to the second and seventh aspects of the present invention, in addition to the above-mentioned effects, even if the appropriate acid addition rate changes with a change in the content of Al (OH) _{3 in} the sludge in a long cycle, the acidity is reduced. Add rate to pH
Correction can be made accurately by the value information, and the operation can be performed stably in the long term, and the water quality can be stabilized.

Further, the injection of the regenerative coagulant through the acid-added sludge has an effect that the coagulant used can be reduced.

According to the third aspect of the present invention, p of the acid-added sludge
By maintaining H in the range of 3.0 to 3.5, Al
There is an effect that the dissolution of heavy metals contained in the sludge can be reduced while ionizing (OH) ₃ , and the consumption of chlorine can be reduced.

According to the fifth aspect of the present invention, both the coagulant added directly to the raw water and the coagulant added via the acid-added sludge are controlled in proportion to the raw water flow rate.
It is possible to stabilize the content of Al (OH) _{3 in} the concentrated sludge for a long period of time, to stabilize the appropriate acid addition rate, and to simplify the operation.

According to the eighth aspect of the present invention, the effects (1) to (5) described in the fifth embodiment can be obtained.

According to the eleventh aspect of the present invention, it is not necessary to use an acid-resistant pump for returning the sludge, and the equipment cost can be reduced.

Further, the present invention can be applied to a coagulation / sedimentation treatment facility having no sludge return system simply by adding a piping system for returning sludge, an acid addition device, various flow meters, pumps, and the like. This has the effect.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a schematic configuration of a coagulation / sedimentation treatment facility according to a first embodiment of the present invention.

FIG. 2 is a flowchart showing a schematic configuration of a coagulation / sedimentation treatment facility according to a second embodiment of the present invention.

FIG. 3 is a flowchart showing a schematic configuration of a coagulation / sedimentation treatment facility according to a third embodiment of the present invention.

FIG. 4 is a flowchart showing a schematic configuration of a coagulation / sedimentation treatment facility according to a fourth embodiment of the present invention.

FIG. 5 is a diagram for explaining installation calibration of a pH detector according to a fifth embodiment of the present invention.

[Explanation of symbols]

1 ... raw water introduction pipe 2 ... flocculant mixing and stirring tank 3.
..Sedimentation tanks, 4 ... Filtration ponds, 5 ... Sludge extraction pipes,
6 ... sludge thickening tank, 7 ... aeration tank, 8 ... return pipe, 10 ... acid storage tank, 11 ... mixing section, 12 ...
pH detector, 20: raw water flow detector, 21: sludge return flow detector, 22: computing unit, 30: second
Arithmetic unit 101, acid addition pump 211, P
AC storage tank, 213 ... NaOH storage tank, 221 ... acid addition sludge injection rate setting unit, 222 ... acid addition rate setting unit,
223: acid addition rate correction value calculation unit, 703: dehydrator, 704: aeration device, 801: sludge return pump.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-57-4287 (JP, A) JP-A-7-328327 (JP, A) JP-A-56-168879 (JP, A) JP-A-56-168879 150481 (JP, A) JP-A-49-65052 (JP, A) JP-A-57-4299 (JP, A) JP-A-63-252599 (JP, A) JP-A-5-329498 (JP, A) (58) Field surveyed (Int.Cl. ⁷ , DB name) B01D 21/00-21/34 C02F 1/52-1/56 C02F 11/00-11/20

Claims (11)

(57) [Claims] Claims 1. After aggregating suspended matter in raw water by adding an aluminum-based flocculant, this aggregate is separated from treated water as sludge by sedimentation, and at least a part of the sludge collected by sedimentation is recovered as raw water. Agglomeration is performed so that the sludge is returned and an aerobic microorganism growth atmosphere is formed during the return, and then acid is added to the returned sludge to regenerate and reuse the aluminum hydroxide contained in the returned sludge as a coagulant. In the settling method, the sludge return flow rate is controlled based on the result calculated from the raw water flow rate information, and the acid addition amount is controlled based on the result calculated from the sludge return flow rate information. Processing method. 2. A suspended substance in raw water is aggregated by adding an aluminum-based flocculant, and this aggregate is separated from treated water as sludge by sedimentation, and at least a part of the sludge collected by sedimentation is converted into raw water. Agglomeration is performed so that the sludge is returned and an aerobic microorganism growth atmosphere is formed during the return, and then acid is added to the returned sludge to regenerate and reuse the aluminum hydroxide contained in the returned sludge as a coagulant. In the precipitation treatment method, the sludge return flow rate is controlled based on the result calculated from the raw water flow rate information, and the acid addition amount is calculated based on the sludge return flow rate information and the pH value information of the returned sludge after acid addition. A coagulation sedimentation treatment method characterized in that the coagulation sedimentation is controlled based on 3. The amount of acid added to the returned sludge according to claim 1 or 2, wherein the pH of the sludge after acid addition is 3.0.
A coagulation sedimentation method characterized in that the coagulation and sedimentation is controlled to a range of from 3.5 to 3.5 4. The pH value information of the returned sludge according to claim 2 or 3, wherein the pH value information of the returned sludge after the acid addition has a period longer than the time required for the returned sludge to pass the pH value detection position. A coagulation sedimentation method characterized by updating based on sampling results. 5. The method according to claim 1, wherein
In addition to the regenerated aluminum-based flocculant contained in the returned sludge to be injected into the raw water, the sum of the aluminum-based flocculant directly added to the raw water is added to determine the appropriate aluminum-based flocculant to be added to the raw water. A coagulation sedimentation process, wherein the addition amount is controlled based on a calculation result obtained from the raw water flow rate information so that the total amount is given and the total amount of the coagulant with respect to the raw water flow rate is an appropriate addition amount. Law. 6. A mixing tank for mixing raw water with an aluminum-based coagulant, a coagulating sedimentation tank for coagulating and sedimenting the coagulated matter containing the coagulated suspended solids and separating from treated water, and a sludge comprising the coagulated sediment. A sludge return system including a sludge return pipe for returning at least a part of the sludge to the mixing tank; an oxidizing means provided in the middle of the sludge return system to make the sludge a growth atmosphere for aerobic microorganisms; and An acid addition means provided downstream for dissolving aluminum hydroxide contained in the returned sludge, and a sludge-acid mixing section provided downstream of the acid addition means, wherein the flocculation and precipitation treatment equipment comprises: A raw water flow rate detector for detecting a raw water flow rate flowing into the mixing tank, a sludge return pump for returning sludge through the return pipe, and a sludge return flow rate detector for detecting a sludge return flow rate passing through the return pipe. And sludge return flow rate control means for controlling the driving of the sludge return pump on the basis of a result of calculation from the raw water flow rate information from the raw water flow detector,
A coagulation / sedimentation treatment facility comprising: acid addition amount control means for controlling driving of the acid addition means based on a result calculated from sludge return flow rate information from the sludge return flow rate detector. 7. A mixing tank for mixing raw water with an aluminum-based coagulant, a coagulation settling tank for coagulating and sedimenting aggregates containing coagulated suspended solids and separating from treated water, A sludge return system including a return pipe for returning at least a part of the sludge to the mixing tank, an oxidizing means provided in the middle of the sludge return system to make the sludge a growth atmosphere of aerobic microorganisms, and a downstream of the oxidizing means. A coagulation / sedimentation treatment facility provided with an acid addition means provided for dissolving aluminum hydroxide contained in the returned sludge, and a sludge-acid mixing section provided downstream of the acid addition means; A sludge return pump for detecting sludge return flow through the return pipe, a sludge return pump for returning sludge through the return pipe, and a sludge return flow detector for detecting sludge return flow through the return pipe. A pH detector provided downstream of the sludge-acid mixing section for detecting pH value information of returned sludge, and a pump for returning sludge based on a result calculated from raw water flow rate information from the raw water flow rate detector. A sludge return flow rate control means for controlling the drive; and an acid for controlling the drive of the acid addition means based on a result calculated from the sludge return flow rate information from the sludge return flow rate detector and the pH value information from the pH detector. A coagulation / sedimentation treatment facility comprising: an addition amount control means. 8. The return sludge according to claim 7, wherein a downstream end of the return pipe for injecting the return sludge into the mixing tank is formed so that the return sludge naturally falls from above, and is located below the highest point of the terminal portion. A coagulation / sedimentation treatment facility, wherein said pH detector is installed between said terminals. 9. The pH detector according to claim 7 or 8, wherein the pH detector performs sampling of the pH value information, and the returned sludge passes through a pipe from an acid addition position in the middle of the return pipe to an installation position of the pH detector. Coagulation and sedimentation treatment equipment characterized in that the treatment is carried out in a cycle longer than the time required for 10. The coagulation / sedimentation treatment facility according to claim 6, wherein the oxidizing means provided in the sludge return system is an apparatus for aerating oxygen-containing gas. 11. The coagulation method according to claim 6, wherein the sludge return pump for returning sludge through the return pipe is provided upstream of an acid addition position of the sludge return pipe. Precipitation treatment equipment.