JP2930594B2 - Coagulation settling equipment - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a coagulation-sedimentation facility for solid-liquid separation of suspended substances in raw water by a coagulation-sedimentation method, and more particularly to a coagulation-sedimentation reaction of sludge recovered by coagulation-sedimentation. By reusing in the system of
The present invention relates to a coagulation / sedimentation facility having improved effects of coagulation / sedimentation.

(Background of the Invention and Prior Art) Generally, in water purification treatment, an aluminum-based flocculant is added to raw water introduced into a treatment facility to coagulate suspended substances contained in the raw water, and a coagulation sedimentation tank is used. A typical method of growing and flocculating flocculated floc, and collecting and treating the precipitated sludge is known. In such water purification treatment, it is generally required to realize sufficient removal of suspended substances contained in raw water and to reduce the cost of equipment operation. Conventionally, various devices have been proposed.

One of these concerns the reuse of flocculants. That is, the sludge generated by coagulating and sedimenting suspended matter in raw water contains a coagulant added to raw water in the form of, for example, aluminum hydroxide. It is beneficial to reuse it as a flocculant. This method is generally called a reproduction band method, and has been actually implemented conventionally. The content of the regeneration band method is that the sludge collected by precipitation is transferred to a sludge treatment facility, and the pH of the sludge is adjusted to about 2 by adding a strong acid such as sulfuric acid or hydrochloric acid, so that the aluminum hydroxide Al contained in the sludge is removed. (OH) ₃ is dissolved, a supernatant containing the dissolved aluminum is taken out, and aluminum ion Al ³⁺ is recovered from the supernatant and reused as a flocculant. The use has a feature that a new amount of the coagulant used is reduced and a total amount of the sludge to be treated is reduced.

Also, apart from the reuse of the flocculant as described above, improvements for the purpose of improving the flocculant effect have also been proposed, for example, adding a suspended substance such as kaolin or bentonite as a flocculant with the flocculant, There is also known a method of improving the balance between the flocculant and the substance to be flocculated to improve the flocculation reaction.
This method is considered to be effective for raw water having low turbidity and for removing chromaticity.

Among these methods, the above-mentioned regenerated band method has an advantage that the amount of newly added flocculant can be greatly reduced, but the amount of aluminum contained in the supernatant depends on the amount and quality of the flocculated sludge. Therefore, there is a problem that it is difficult to control the injection amount to make the agglomeration reaction suitable. In addition, since the pH is set to about 2 as described above in order to increase the recovery rate of aluminum, other iron contained in the sludge There is also a problem that heavy metals such as are dissolved in a large amount, and the heavy metals gradually accumulate in accordance with the number of times of reusing the flocculant.

On the other hand, the above-mentioned method of adding kaolin or bentonite as a coagulation aid to improve the coagulation reaction has an effect of coagulation and sedimentation of raw water having low turbidity due to water quality, ineffective coagulation reaction or poor sedimentation of coagulated floc. However, these kaolins and bentonite are discharged as a part of the sludge, so that the amount of waste increases, resulting in an increase in the cost of water purification treatment.

(Problems to be Solved by the Invention) The present invention solves the various problems described above, and reduces the amount of coagulant injected for coagulation and sedimentation as much as possible in performing water purification treatment, thereby achieving economical treatment. It is an object of the present invention to provide a coagulation / sedimentation treatment facility capable of improving the coagulation reaction and the sedimentation of coagulated floc, thereby realizing a good sedimentation treatment.

Another object of the present invention is particularly effective in improving coagulation sedimentation for raw water of low turbidity, thereby reducing the amount of coagulant added, and reducing the amount of coagulants such as kaolin and bentonite described above. It is an object of the present invention to provide a coagulation / sedimentation treatment facility characterized in that the amount of addition can be reduced or omitted, and an increase in the amount of sludge generated due to the addition of a coagulant or a coagulation aid can be prevented. In recent years, the reduction of the amount of generated sludge has become one of the important technical issues from the viewpoint of pollution prevention. In disposal of excess sludge as industrial waste after dehydration treatment, aluminum hydroxide contained in the sludge Although the amount greatly affects the difficulty of the treatment, the realization of the purpose of reducing the amount of the coagulant added can facilitate the treatment.

Still another object of the present invention is to provide a coagulation / sedimentation treatment facility which does not cause any adverse effects due to accumulation of heavy metals.

Another object of the present invention is to provide a coagulation sedimentation treatment facility that can suitably cope with a case where river water or lake water whose water quality tends to fluctuate due to seasonal or weather conditions is used as a water source. That is, river water or lake water is often used as a water source in coagulation and sedimentation treatment such as water supply, but such water sources are generally characterized by low turbidity but increased water due to rainfall or snow melting. Is known to increase turbidity. In this case, when the turbidity increases, a good flocculation precipitate is observed by adding an appropriate flocculant, but when the turbidity is low, a flocculent floc with poor sedimentation due to poor balance between the flocculant and the flocculant in the raw water is generated. There is a problem that the quality of treated water deteriorates. In such a case, in the present invention, it is possible to provide a coagulation / sedimentation treatment facility which does not need to add a large amount of the above-mentioned suspended substances such as kaolin and bentonite as coagulation aids.

(Means for Solving the Problems) A feature of the present invention made to realize the above various objects is that sludge containing both insoluble aluminum hydroxide and a suspended substance that is a substance to be agglomerated is used. One feature is that the suspended solids in the raw water are returned to (or before or after) a stirring system for coagulating the suspended matter in the raw water by the addition of a coagulant containing Al. The return of the sludge may be partial or full, or the return amount may be appropriately changed and controlled in consideration of seasonal variation, weather, and the like.

Generally, it is often appropriate to provide a stirring system for adding a flocculant to the raw water as a flocculant mixing tank provided with a stirring means. Further, it is not always necessary to clearly distinguish the stirring system from the system that performs the coagulation reaction, and the point is that the sludge is returned before the system that performs the coagulation reaction in the coagulation / sedimentation treatment facility, thereby achieving the object of the present invention. .

Another feature of the present invention resides in that a mineral acid such as hydrochloric acid is added to the returned sludge to ionize aluminum hydroxide contained therein. The amount of acid to be added may be such that the aluminum hydroxide contained in the sludge is ionized into Al ³⁺ or aluminum polyion, etc., and then added under the condition that this acts as a coagulant. Is adjusted to pH 3 to 4 so as to dissolve about 30 to 80% of the aluminum hydroxide. When the amount of the acid added is increased, the dissolution ratio of aluminum hydroxide is increased, but there is a problem that heavy metals are also dissolved.

By returning such sludge, the dissolved aluminum component and undissolved aluminum component contained in the sludge returned to the stirring system (or before and after) have the effect as a flocculant again, and the suspended substances contained in the sludge Becomes a coagulated substance, which contributes to coagulation and precipitation in excess of the coagulated substance contained in the raw water. As a result, compared with the conventional coagulation sedimentation method, the amount of the coagulation sedimentation agent to be added can be reduced and the flocculant having good sedimentation can be formed.

The above-mentioned coagulation-sedimentation treatment equipment for performing the treatment of water purification according to the present invention for returning sludge containing ionized aluminum and suspended substances, when the raw water is low-turbidity raw water having a turbidity of 10 degrees or less. Demonstrates an excellent effect on the treatment of
That is, when targeting such low turbidity raw water, in the conventional method, it was common to add about 5 ppm of kaolin or bentonite which is a clay mineral as a coagulation aid, but according to the treatment equipment of the present invention. External addition of such a coagulation aid is substantially unnecessary or can be greatly reduced,
Also, compared to the conventional method for adding low-turbidity raw water to which 20 to 50 ppm of a coagulant such as a sulfuric acid band or polyaluminum chloride is required, the equipment of the present invention substantially eliminates this, or It can be reduced to at most about 10 ppm.

In the present invention, the sludge to be coagulated / precipitated and returned may be returned directly from the coagulation / precipitation tank. However, returning the sludge after further concentrating it to about 1 to 10% in the sludge concentration tank reduces the return amount. Is desirable. In the sludge return, a sludge storage tank may be provided in the middle of the return system.In this case, the sludge is drawn out intermittently from the sludge concentration tank and the like, and the sludge return and injection into the stirring system etc. is continuously performed. There are advantages that can be done.

The excess of the coagulated / precipitated sludge may be appropriately extracted, treated by a known method, and disposed as industrial waste. In the equipment of the present invention, although the amount of suspended substances and the like circulating in the system by returning sludge is increased, it is not necessary to reduce the amount of coagulant to be added or the amount of substance to be coagulated.
There is also an advantage that the amount to be disposed of as excess sludge is reduced.

(Function) The present invention has the above-described structure, whereby the ionic aluminum contained in the returned sludge acts as a coagulant, and a coexisting suspended substance becomes a substance to be coagulated. The coagulation sedimentation treatment is performed by also taking in the coagulated substances contained in the coagulation, and as a result, the amount of coagulant injected is significantly reduced and flocculants having good sedimentation properties are formed as compared with the conventional coagulation sedimentation method. .

(Examples) Hereinafter, the present invention will be described based on examples shown in the drawings.

In this figure, reference numeral 2 denotes a flocculant mixing / stirring tank, which stirs and mixes raw water introduced from the raw water introduction pipe 1 with a flocculant injected from a flocculant storage tank 13 by a flocculant injection device 12 such as a pump. Allow the coagulation reaction to take place.

A flocculating sedimentation tank 3 is disposed downstream of the flocculant mixing and stirring tank 2, and collects sludge at the bottom of the flocculating tank 3 by the growth and sedimentation of flocculated floc. Not discharged to the downstream treated water system.

The sludge collected at the bottom of the coagulation / precipitation tank is appropriately drawn out to the coagulation sludge concentration tank 5 by the coagulation sludge drawing pipe 4, and the sludge is further concentrated about 10 times. And from the bottom of the flocculation sludge concentration tank 5, by appropriately intermittently Okudoro aggregation sludge processor 14 through the concentrated aggregate sludge drawn pipe 6 ₁ Concentration coagulation sludge Okudoro pump _71, can be discarded surplus sludge together it has manner, sludge return system the concentrated sludge is connected so as to be returned to the flocculant mixing stirring tank 2 through concentrated aggregation sludge drawn pipe 6 ₂ are provided by the enriched flocculation sludge Okudoro pump 7 ₂ .

In the middle of this sludge return system, a branch path from an acid injection pump 8 for adding an acid from an acid storage tank 9 is connected. Downstream of the junction of this branch path, a stirrer 10 is arranged to appropriately stir the added acid and sludge, and a pH meter 11 for detecting the pH of the sludge due to the acid addition is provided. The sludge return system is equipped.

According to the coagulation / sedimentation treatment equipment having the above-described configuration, aluminum hydroxide contained in the sludge collected by coagulation / precipitation can be dissolved and ionized with an acid and reused as a coagulant for raw water. The suspended substance contained in the sludge is returned to the coagulation mixing tank so that the balance between the coagulant and the substance to be coagulated can be adjusted. Conventionally, kaolin or bentonite was added as a substance to be agglomerated for the purpose of preventing the formation of bad agglomeration flocs.However, in the present invention, there is an advantage that the addition of such kaolin becomes unnecessary. is there.

From such characteristics, the apparatus of the present invention is particularly effective as a coagulation / sedimentation treatment facility for water having relatively low turbidity, and the balance between the coagulant and the substance to be coagulated can be easily determined by the amount of returned sludge. Therefore, its usefulness is extremely large when the water source is a water system in which the water quality is likely to change due to weather and seasonal fluctuations.

(Effects of the Invention) According to the present invention, the following effects are obtained.

To produce flocculated floc with low sedimentation in low turbidity water while reducing or eliminating flocculants such as kaolin and bentonite, which were conventionally added to improve flocculation. And the quality of the treated water does not deteriorate.

Since the flocculant in the sludge is re-coagulated, the amount of the flocculant used is greatly reduced.

As a result of the decrease in the amount of the coagulant used, the amount of aluminum hydroxide generated by the injection of the coagulant decreases, and the total amount of coagulated sludge decreases.

As a result of reducing the content of aluminum hydroxide in the coagulated sludge, the dewatering property in the sludge is improved and the sludge treatment cost is reduced.

[Brief description of the drawings]

The drawing is a diagram showing an example of the configuration outline of the water purification equipment according to the present invention. DESCRIPTION OF SYMBOLS 1 ... Raw water introduction pipe 2 ... Coagulant mixing and stirring tank 3 ... Coagulation sedimentation tank 4 ... Coagulation sludge extraction pipe 5 ... Coagulation sludge concentration tank 6 ₁ , 6 ₂ ... Concentrated coagulation sludge extraction pipe 7 ₁ , 7 ₂ … Concentrated flocculated sludge pump 8… Acid injection pump 9… Acid storage tank 10… Agitator 11… pH meter 12… Coagulant injection device 13… Coagulant storage tank 14 …… Aggregated sludge treatment equipment 15 …… Treatment water

Continuation of the front page (72) Inventor Hiroyuki Hirokawa 5-6-16 Hongo, Bunkyo-ku, Tokyo Organo Corporation (56) References JP-A-56-168879 (JP, A) JP-A-56-150481 ( JP, A) (58) Field surveyed (Int. Cl. ⁶ , DB name) B01D 21/24 C02F 1/52 C02F 1/00

Claims (3)

(57) [Claims] A stirring system for adding a coagulant containing Al to low-turbidity raw water having a turbidity of 10 degrees or less to coagulate suspended substances in the raw water, Wherein the sludge collected by the treatment system for sedimentation and recovery of the sludge is subjected to at least a part of the stirring system or the stirring system. A sludge return system for returning to the path through which raw water is introduced into the system, and a sludge disposal system for disposing excess sludge are provided. In the middle of the sludge return system, Al (OH) contained in returned sludge is provided. _3. A coagulation / sedimentation treatment facility for treating water purification, wherein an acid addition means for ionizing ₃ is provided. 2. A stirring system for coagulating the suspended substance and a coagulant mixing tank for adding and stirring a coagulant to the raw water to be introduced, and returning returned sludge to the coagulant mixing tank. A coagulation / sedimentation treatment facility for treating water purification according to claim 1. 3. The coagulated sedimentation treatment equipment according to claim 1 or 2, wherein the means for adding acid to the returned sludge adjusts the returned sludge to have a pH of 3-4. .