JP2002079262A - Equipment for flocculation and separation treatment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the consumption of a flocculant, when a suspended substance in raw water is flocculated by adding an iron or aluminum type inorganic flocculant to raw water, to reduce the use amount of the flocculant. SOLUTION: This flocculation and sedimentation or flocculation and floating separation apparatus has a stirring system, which adds the iron or aluminum type inorganic flocculant to raw water to flocculate the suspended substance in raw water, and a sludge return system, which sediments or floats flocs to separate them and returns at least a part of separated sludge to the raw water. The apparatus is provided with a means for adding a mineral acid and a cationic organic polymeric flocculant to the sludge return system not only to dissolve a metal hydroxide contained in return sludge but also to flocculate an insoluble SS-(suspended substance) other than a metal hydroxide by the cationic polymeric flocculant and subsequently supplying the acid treated and flocculated liquid to the raw water.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a facility for removing suspended substances mixed in raw water, and more particularly to an apparatus for treating a flocculated sediment with an acid to dissolve a metal hydroxide and then removing a cationic polymer flocculant. The present invention relates to a coagulation / separation treatment facility in which an acid-insoluble SS is added and returned in a coagulated state.

[0002]

2. Description of the Related Art As a conventional technique, for example, regarding a coagulation / sedimentation treatment facility, there is provided a stirring system for coagulating a suspension in raw water by adding a coagulant containing Al, and a treatment system for precipitating and collecting coagulated floc. In coagulation sedimentation processing equipment,
There is disclosed a coagulation sedimentation facility in which a sludge return system for returning a part of the settled sludge to raw water is provided, and the sludge return system is provided with an acid addition means for ionizing aluminum hydroxide.
The main features of the above-mentioned prior art are (1) the use of an aluminum-based flocculant, and (2) the amount of fresh flocculant can be reduced to some extent because aluminum ionized by acid acts as a flocculant, Sludge generation is to be reduced.

[0003]

However, the present inventor has further studied the above-mentioned prior art, and found that there are the following problems.
That is, the injection rate of the fresh aluminum-based inorganic coagulant can be reduced by about 30 to 40%, and the amount of sludge generated from the metal hydroxide does not significantly decrease. In addition, when the circulation amount of the acid-treated sludge is increased, the water quality (turbidity, chromaticity, potassium permanganate consumption) of the coagulated sedimentation treated water is deteriorated. As a result of pursuing the cause of such a phenomenon, turbid substances and organic substances (those contained in raw water removed by coagulation separation) contained in acid-treated sludge are mixed again with raw water. Therefore, it was found that the coagulant was consumed by these substances. An object of the present invention is to solve the problems pointed out in the above-mentioned conventional technology.

[0004]

The present invention has solved the above-mentioned problems by the following means. (1) A stirring system for adding an iron or aluminum-based inorganic flocculant to raw water to flocculate suspended solids in raw water, and segregating or flocculating flocculated flocs, and returning at least a part of the separated sludge to the raw water. In a coagulation sedimentation or coagulation flotation facility having a sludge return system, a mineral acid and a cationic organic polymer coagulant are added to the sludge return system to dissolve metal hydroxide contained in returned sludge. Agglomerating an insoluble SS (suspension substance) other than a metal hydroxide with a cationic polymer flocculant, and then supplying the acid-treated / aggregated liquid to the raw water. Processing equipment.

[0005]

DETAILED DESCRIPTION OF THE INVENTION The gist of the present invention is that the coagulated sediment sludge is treated with an acid to dissolve the metal hydroxide, and then a cationic polymer flocculant is added to the sludge to form an acid-insoluble suspended substance (hereinafter simply referred to as a suspended substance). This is the point that “SS” is returned in an aggregated state. On the other hand, in the conventional technology, a mineral acid (hydrochloric acid or sulfuric acid) is added to a returned sludge system, aluminum hydroxide contained in the sludge is dissolved and aluminum ionized, and this is mixed with a fresh aluminum-based flocculant ( Aluminum sulfate, PAC, etc.) is added to the raw water to agglomerate the suspended matter in the raw water, whereas in the present invention,
Mineral acids (hydrochloric acid, sulfuric acid, etc.) in precipitated sludge containing insoluble aluminum hydroxide (or iron hydroxide) and suspended particles
Is added to ionize aluminum hydroxide or iron hydroxide to metal ions, and a cationic polymer flocculant is added to flocculate SS and organic matter in the acid-treated sludge, and in this state, circulate and add to raw water In addition, by adding a fresh inorganic flocculant to flocculate the suspended solids in the raw water, it is possible to obtain flocs with remarkably large sedimentation properties and to obtain treated water with good water quality. .

[0006] A suitable pH value for dissolving the mineral acid by adding it to the iron hydroxide-containing precipitated sludge is as follows.
In the case of dissolving aluminum hydroxide-containing settled sludge, the pH is adjusted to 2-3.
It is preferred that the degree is about the same. As the cationic organic polymer flocculant, various types, for example, dimethylaminoethyl methacrylate, modified polyacrylamide Mannich, chitosan, polyvinylamidine, quaternary polyamine, polyethyleneimine, polydimethyldiallylammonium chloride and the like can be used. Particularly effective types are quaternary polyamines of low molecular weight and strong cation strength,
Polyethyleneimine, polydimethyldiallylammonium chloride, chitosan and the like can be mentioned. In addition, it goes without saying that an amphoteric polymer flocculant having both a cationic group and an anionic group may be used. Anionic or nonionic polymer flocculants have no effect.

[0007] An appropriate amount of the cationic organic polymer flocculant, ie, a polymer having a cationic group (also referred to as "cationic polymer"), is usually about 10 mg polymer per 1 g of undissolved SS in the acid-treated sludge. However, more precisely, it is desirable to determine in advance by a jar test. By returning the acid-treated sludge to the raw water, iron ions or aluminum ions contained in the acid-treated sludge again produce an effect as a flocculant, and the suspended matter contained in the acid-treated sludge becomes a cationic polymer. Since the coagulation is effectively coagulated, the inorganic coagulant is prevented from being wasted by the undissolved SS in the acid-treated sludge when returned to the raw water. As a result, a fresh inorganic flocculant, such as P
AC (polyaluminum chloride), sulfuric acid sand, second chloride
Since the amount of addition of iron and the like is reduced and flocs having good sedimentation are formed, the quality of the treated water is improved.

In the present invention, the returned sludge may be directly extracted from the coagulated sediment, but a sludge thickening tank (thickener)
When the sludge is further concentrated and returned, the sludge return flow rate can be reduced, which is more preferable.
In addition, the excess of the coagulated sediment sludge is appropriately drawn out of the system and disposed after the sludge dewatering treatment, but in the present invention, the amount of fresh aluminum or iron based coagulant added is smaller than that of the conventional method. Inevitably, the amount of excess sludge containing aluminum hydroxide or iron hydroxide as a main component is greatly reduced, and the amount of sludge requiring disposal is drastically reduced. Although the description so far has been directed to the case of coagulation sedimentation, it can be said that the same effect can be obtained in the case where a flotation separation means for adhering coagulated flocs to air bubbles and separating them is employed instead of coagulation sedimentation. Not even.

[0009] Equipment for specifically implementing the present invention will be described in detail with reference to the drawings. As shown in FIG. 1, raw water 1 is supplied to a flocculated floc forming and stirring tank 4 by a supply pipe 2. In the process of supplying the raw water 1 to the flocculated floc forming and stirring tank 4 by the supply pipe 2, the flocculant (new component) 3 and the later-described (returned sludge 16 from the non-dissolved SS flocculation tank 14 following the acid treatment stirring tank 11) 3 Ferric chloride or PAC (polyaluminum chloride) are sequentially added, and the mixture is stirred and mixed to carry out a reaction of forming flocculated flocs. A sedimentation tank 6 is disposed at the subsequent stage of the flocculation floc formation stirring tank 4, the effluent 5 from the stirring tank 4 is introduced, and the sludge is collected at the bottom of the sedimentation tank 6 by sedimentation and separation of the flocculation floc. The water 7 is introduced into a subsequent treatment system (sand filtration, activated carbon adsorption tower, etc.) not shown.

The settling sludge 8 deposited on the bottom of the settling tank 6 is
It is transferred to a sludge thickening tank (thickener) 9 for sedimentation and concentration. Condensed sludge 10 settled and concentrated in thickener 9
Is pulled out from the bottom of the thickener 9 and a part of the concentrated sludge 10 is transferred to an acid treatment stirring tank 11 provided with a pH measuring device (not shown). In the acid treatment stirring tank 11, an acid 12 such as sulfuric acid or hydrochloric acid is added, and the mixture is stirred for about 10 minutes, whereby aluminum hydroxide or iron in the sludge is dissolved, and aluminum ions or ferric ions are generated.

Next, in order to coagulate the non-dissolved SS in the concentrated sludge (mainly the suspended matter in the raw water to be subjected to the water purification treatment), the effluent 13 of the acid treatment stirred tank is transferred to the non-dissolved SS coagulation tank 14. Then, the cationic polymer flocculant 15 is added thereto and stirred for several minutes. As a result, SS not dissolved by the acid treatment aggregates to form flocs. Although the pH of the acid-treated effluent 13 is low, the cationic polymer flocculant has an acidic pH.
There is no problem because H works effectively. The acid treatment / aggregation liquid 16 is added to the raw water 1 and reused as a coagulant together with the fresh inorganic coagulant 9. Reference numeral 17 denotes the remaining sludge drawn out of the thickener 9, which is subjected to a dewatering treatment by a sludge dewatering machine 18.

[0012]

EXAMPLES The present invention will be described below in more detail with reference to examples, but the present invention is not limited by these examples.

Example 1 A test for verifying the effect of the present invention was performed on raw water at the F waterworks in Chiba Prefecture. This test was performed using a small-sized continuous test apparatus as shown in the flow chart of FIG. Table 1 shows the quality of the raw water at the F waterworks. FeCl _{3 in} raw water (injection amount: 8 mg
/ Liter), and after rapid stirring for 3 minutes and slow stirring for 10 minutes, a sedimentation device 6 with a sedimentation separation speed of 50 mm / min.
And the floc was separated by settling. After the whole amount of the settled sludge was withdrawn, and the precipitate was concentrated to an SS concentration of 2% in the settling tank 9, the pH was adjusted to 1.8 by adding sulfuric acid. After stirring for 15 minutes, the iron hydroxide was dissolved. A liquid containing iron ions and insoluble SS was obtained. 100m of condensed polyamine-based cationic polymer flocculant (Ebagrose L51; Ebara product)
g / liter was added to aggregate the SS. The operation of adding the whole amount of the liquid to the raw water to be treated for water purification was continued. As a result of continuing the operation under these conditions for 15 days, the average water quality of the coagulated sedimentation treated water is turbidity 0.8, soluble chromaticity 4.5 degrees, pH 6.0.
5. The consumption of potassium permanganate was 3.2 mg / liter.

[0014]

[Table 1]

Comparative Example 1 In Example 1, the operation was performed under the same conditions except that the cationic polymer flocculant was not added. ), The average water quality of the coagulated sedimentation treated water for 15 days is turbidity 3.
The solubility was 9 degrees, the pH was 6.8, and the consumption of potassium permanganate was 8.5 mg / liter, which was significantly inferior to Example 1. In order to obtain the same coagulation sedimentation treatment water quality as in Example 1, the injection rate of ferric chloride was set to 2
It was necessary to set it to 5 mg / liter. As a result, the amount of sludge to be disposed of outside the system of Comparative Example 1 was about three times as large as that of Example 1.

[0016]

According to the present invention, the following effects can be obtained. (1) Iron hydroxide or aluminum hydroxide in the sludge dissolves and turns into ferric ion or aluminum ion, and raw water after acid-insoluble SS in the settled sludge is aggregated by the cationic polymer flocculant Will be returned to
The inorganic coagulant is not wasted by the acid-insoluble SS. As a result, the amount of fresh flocculant for flocculating the raw water suspension is greatly reduced. (2) By the action of the cationic polymer, even at a small inorganic coagulant injection rate, the turbidity of the raw water is effectively agglomerated, a floc having very good sedimentation is formed, and the amount of sludge generated is reduced. As a result, sludge treatment and disposal is significantly streamlined. (3) As a result of reducing the amount of aluminum hydroxide or iron hydroxide in the sludge supplied to the dehydrator, the sludge dewatering property is improved and the sludge treatment cost is reduced.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an outline of a processing system according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Raw water 2 Supply pipe 3 Coagulant 4 Aggregation floc formation stirring tank 5 Effluent 6 Sedimentation tank 7 Treatment water 8 Sedimentation sludge 9 Sludge concentration tank (thickener) 10 Concentrated sludge 11 Acid treatment stirring tank 12 Acid 13 Effluent 14 Undissolved SS Coagulation tank 15 Cationic polymer coagulant 16 Acid treatment / coagulation liquid 17 Residual concentrated sludge 18 Sludge dewatering machine

 ──────────────────────────────────────────────────続 き Continued on front page F term (reference) 4D015 BA04 BA05 BA24 BA25 BB09 BB12 CA14 DA04 DA13 DB15 DB24 DB32 DC07 EA13 EA32 EA33 FA03 FA11 4D037 AA12 AB02 AB05 BA01 CA08 4D062 BA04 BA05 BA24 BA25 BB09 BB12 CA14 DB04 DB13 DB DC07 EA13 EA32 EA33 FA03 FA11

Claims (1)

[Claims] 1. A stirring system for adding an iron or aluminum-based inorganic coagulant to raw water to coagulate a suspension in the raw water;
A coagulation sedimentation or coagulation flotation facility having a sludge return system for precipitating or floating separation of flocculated flocs and returning at least a part of the separated sludge to the raw water, wherein the sludge return system has a mineral acid and a cationic organic polymer. After adding a flocculant to dissolve the metal hydroxide contained in the returned sludge and coagulating insoluble SS (suspension material) other than the metal hydroxide with a cationic polymer flocculant, the acid treatment A coagulation / separation treatment facility provided with means for supplying a coagulation liquid to the raw water;