KR20070049560A - Wastewater treatment device and wastewater treatment method - Google Patents

Abstract

(Task) After the biological treatment of the water to be treated, when the flocculating agent is added to remove the soluble or suspended substances containing the cells or biological metabolites in the biological treatment water, the flocculating agent is reduced after the addition amount of the flocculant is reduced. Good treated water is obtained.

(Solution means) A bioreactor 1 for biologically treating the water to be treated, agglomeration reaction tanks 2A and 2B for adding a coagulant to the biological treatment water flowing out of the bioreactor 1 and performing a coagulation reaction, The wastewater treatment apparatus provided with the pressure flotation separation tank 3 which solid-separates the flocculation process water which flows out from the flocculation reaction tank 2B. The aeration means is formed in the agglomeration reaction tank 2A, the cohesiveness is increased by stirring by aeration, and the pressure flotation separation property at the rear end is improved.

Description

WASTEWATER TREATMENT DEVICE AND WASTEWATER TREATMENT METHOD}

1 is a system diagram showing an embodiment of a wastewater treatment apparatus of the present invention.

2 is a system diagram showing another embodiment of the wastewater treatment apparatus of the present invention.

3 is a system diagram showing another embodiment of the wastewater treatment apparatus of the present invention.

4 is a system diagram showing another embodiment of the wastewater treatment apparatus of the present invention.

5 is a system diagram showing another embodiment of the wastewater treatment apparatus of the present invention.

<Explanation of symbols for main parts of drawing>

1: biological reactor

2: flocculation tank

2A: first flocculation tank

2B: second flocculation tank

2C: 3rd flocculation tank

3: pressurized flotation tank

4: filtration device

5: RO membrane separation device

6: activated carbon tower

The present invention relates to a wastewater treatment apparatus and a wastewater treatment method, and in particular, after biotreatment of the water to be treated, a flocculant is added to remove soluble substances or suspending substances containing cells or biological metabolites in the biological treatment water. The present invention relates to a wastewater treatment apparatus and a wastewater treatment method for obtaining good treated water after reducing the amount of the flocculant added.

As the treatment method of organic wastewater, the biological treatment method is widely adopted. In addition, in order to remove contaminants such as suspended substances and soluble substances in biologically treated water, or to recover water in the case of a large amount of wastewater, to coagulate the biologically treated water, or further, to treat the membrane after the agglomerated treatment. It is done.

For example, Japanese Laid-Open Patent Publication No. 2005-238152 discloses that the organic matter-containing water is biotreated, a flocculant is added to the biologically treated water to coagulate, the coagulated water is solid-liquid separated, and the separated water is filtered by a filtration device. A method of membrane separation treatment is again described in a reverse osmosis membrane separation apparatus. In this method, the floating separation device is also described as the solid-liquid separation means. The pressurized flotation separation tank as the solid-liquid separation means has an advantage that the installation space may be smaller than that of the precipitation tank.

Since the flocculant (inorganic flocculant) added when flocculating biological treatment water for promoting flocculation action is an element directly connected to the running cost, the addition amount is desired to be reduced. However, in the flocculation treatment of the biological treatment water, it is dissolved. Aggregation of organics (S-TOC), in particular biological metabolites, is difficult and usually requires a large amount of flocculant.

In particular, in recent years, the recycling of water resources is important, and the recovery of wastewater is made. However, in order to highly purify the water discharged as wastewater to a level that can be reused after biological treatment, a large amount of flocculant is required. For this reason, the addition amount reduction of the flocculant in the flocculation process of biological treatment water is a big subject.

Moreover, although the method of using a coagulant | flocculation adjuvant together is proposed as a method of reducing the addition amount of a coagulant, since the cost for adding an adjuvant is high, a present method is required which is a simpler and cheaper method.

The present invention solves the above-mentioned conventional problems and, after biological treatment of the water to be treated, a flocculant is added to remove the soluble or suspended substances containing the cells or biological metabolites in the biological treatment water. At this time, an object of the present invention is to provide a wastewater treatment apparatus and a wastewater treatment method capable of obtaining good treated water after reducing the addition amount of the flocculant.

MEANS TO SOLVE THE PROBLEM As a result of earnestly examining about the said subject, when agglomerating the microbial cells, biological metabolites, etc. after a biological treatment, the present inventors perform air aeration at the time of stirring in an agglomeration reaction tank, and then pressurize and float the flocculation process water. It was found that the amount of the flocculant added can be reduced by doing so. In addition, it was found that the quality of the treated water was further improved by adjusting the water in the aggregation reaction system to a more optimal pH range and using an oxidant in combination.

This invention is achieved based on this knowledge, and makes the following a summary.

[1] a solid solution of a biological reaction tank for biologically treating the water to be treated, an agglomeration reaction tank for adding a coagulant to the biological treatment water flowing out of the biological reaction tank, and performing an agglomeration reaction, and an agglomeration treated water flowing out from the agglomeration reaction tank A waste water treatment apparatus provided with a pressure floating separation tank for separating, wherein the aeration means is formed in the agglomeration reaction tank.

[2] The wastewater treatment apparatus according to [1], further comprising a pH adjuster addition means for adjusting the pH of the water in the aggregation reaction tank to 3 to 6.

[3] The wastewater treatment apparatus according to [1] or [2], further comprising an oxidizing agent adding means for adding an oxidizing agent to the agglomeration reaction tank.

[4] The drainage treatment device according to any one of [1] to [3], further comprising a filtration device for solid-liquid separation of the pressurized floatation water flowing out from the pressurized floatation separation tank.

[5] a bioreaction process for biologically treating the water to be treated, an agglomeration reaction step for adding a coagulant to a biological treatment water flowing out of the bioreaction step and performing a coagulation reaction, and a coagulation flowing out of the coagulation reaction step A wastewater treatment method comprising a pressure flotation separation process for solid-liquid separation of treated water, wherein the flocculation reaction in the flocculation reaction step is performed under aeration.

[6] The wastewater treatment method according to [5], wherein a pH adjuster is added to the water in the flocculation reaction step to adjust the pH of the water to 3 to 6.

[7] The wastewater treatment method according to [5] or [6], wherein an oxidizing agent is added to water in the flocculation reaction step.

[8] The wastewater treatment method according to any one of [5] to [7], further comprising a filtration step for solid-liquid separation of the pressurized flotation separation water flowing out from the pressurized flotation separation step.

Details of the mechanism of action of such effects according to the present invention are not disclosed, but are considered as follows.

In the water after biological treatment, there are cells and dissolved polymer organic substances (eg, proteins) that are dispersed and present in water, but particularly in the apparatus combining agglomeration treatment and filtration, it has a great influence on the filtered water quality. Is considered to be a protein. As with the foam seen in biological treatment tanks, some of the proteins have affinity with air. In the present invention, when the air is aerated in a state in which the protein is charged neutralized and coarsened by the inorganic flocculant, the coarse protein is considered to be in a state where the coarse protein is entangled with bubbles. As a result, when liquid-liquid separation is carried out by the pressure flotation method at the rear end of the aggregation reaction tank, it is considered that fine bubbles are further entangled and the separability is improved.

In particular, in the iron-based coagulant, trivalent iron is effective for coagulation in the weakly acidic to weakly alkaline region. However, even when a ferric chloride (trivalent iron) -based coagulant is used, Iron is present. Therefore, when aeration is carried out in the aggregation reaction tank, such divalent iron is oxidized to become trivalent iron effective for aggregation. In addition, the addition of an oxidizing agent such as hypochlorous acid to the flocculation tank further increases the oxidizing effect (claims 3 and 7 in the claims). In addition, since most of proteins have an isoelectric point in the weakly acidic region, it is thought that the dissociation of water is eliminated as the pH is in the acidic region (for example, pH 3 to 6) and the aggregation effect is increased. 2, 6).

By this mechanism, according to the present invention, treated water of high quality is obtained with a small amount of flocculant added,

(1) Reduction of the flocculant cost by reducing the addition amount of the flocculant, and also the reduction of the neutralizer cost and the sludge treatment cost can be aimed at.

(2) The installation space can be reduced by improving the pressure floating separation of the flocculation floc and thereby improving the water passage speed of the pressure floating separation tank.

(3) Improvement of the post-treatment efficiency by reducing the amount of flocculant added and improving the water quality of the separated water by pressure flotation separation, that is, when the filtration device is installed at the rear end, the backwashing frequency of the filtration device is reduced again. If a reverse osmosis (RO) membrane separation device is provided at the rear end, efficient water recovery and reuse can be performed under the effect of preventing fouling of the RO membrane.

Best Mode for Carrying Out the Invention

EMBODIMENT OF THE INVENTION Below, embodiment of the wastewater processing apparatus and wastewater processing method of this invention is described in detail.

[Drainage]

In the present invention, the wastewater to be treated may be an organic matter-containing wastewater which is usually biologically treated, and is not particularly limited. Examples thereof include electronic industry wastewater, chemical plant wastewater and food plant wastewater. For example, in the electronic component manufacturing process, various organic wastewaters are generated in a developing process, a peeling process, an etching process, a cleaning process, etc., and furthermore, it is desired to recover the wastewater, purify it to a pure level, and reuse it. Drainage is suitable as the wastewater to be treated in the present invention.

Examples of such organic wastewater include organic wastewater containing isopropyl alcohol, ethyl alcohol, organic wastewater containing monoethanolamine (MEA), tetramethylammonium hydroxide (TMAH), organic wastewater containing ammonia nitrogen, Organic wastewater containing organic sulfur compounds, such as dimethyl sulfoxide (DMSO), is mentioned.

[Biological treatment]

As a biological reaction tank for biological treatment of waste water, what is necessary is just what is excellent in the decomposition efficiency of an organic substance, and the biological reaction tank of a known aerobic or anaerobic biological treatment system can be used. For example, a flotation system for holding the activated sludge in a suspended state in the tank, a biofilm system for attaching the retained sludge to the carrier and the like can be employed. In addition, the biofilm system may be any microbial floor system such as fixed floor, flow floor, or expanded floor, and any activated carbon, various plastic carriers, sponge carriers, or the like may be used as the carrier.

In the floating system, solid-liquid separation means for separating the activated sludge from the treated water is required, and solid-liquid separation means such as a precipitation tank and a membrane separation device are formed at the rear of the biological treatment reactor. Alternatively, such solid-liquid separation means can be omitted in order to maintain active sludge in the biological treatment reactor.

As a carrier, a sponge carrier is preferable, and if it is a sponge carrier, microorganisms can be maintained at high concentration. Although it does not specifically limit as a sponge raw material, An ester type polyurethane is preferable. Although there is no restriction | limiting in particular also as an addition amount of a support | carrier, Usually, it is preferable to set it as about 10 to 50% by the apparent capacity of the support | carrier with respect to the crude capacity of a biological reactor.

As an aerobic bioreactor in which organic matter is decomposed microorganisms in an aerobic state, an aeration tank provided with oxygen gas supply means such as an acid pipe or an aerator for supplying oxygen (air) in the tank can be used. Can be.

On the other hand, as an anaerobic biological reaction tank which decomposes organic matter microorganisms in an anaerobic state, an anaerobic tank holding a carrier or granular sludge can be used.

The bioreactor may be a breakfast of an aerobic bioreactor or an anaerobic bioreactor, may be a multi-tank of an aerobic bioreactor and / or an anaerobic bioreactor, or may form a partition wall in the bath at a single breakfast.

[Aggregation processing]

In the present invention, a flocculant is added to the biologically treated water during the flocculation treatment of the biologically treated water obtained by biologically treating the wastewater in a biological reaction tank, and agitation is performed by aeration.

<Coagulation tank>

Only one set may be sufficient as the aggregation reaction tank (henceforth a "coagulation tank") used for aggregation processing, and what formed two or more layers of aggregation tanks in multiple stages may be sufficient as it.

The flocculation treatment plant is generally composed of a rapid agitation tank for sufficiently bringing the flocculent into contact with the water to be treated and a slow agitation tank for growing the flocculation flocs. It is preferable to perform stirring by the aeration which concerns on this invention in a rapid stirring tank, and to stabilize stable growth of a floc by stirring which does not use aeration in the following slow stirring tank. Therefore, when forming two or more sets of flocculation tanks in multiple stages, it is preferable to make an agglomeration tank of a front end into an air aeration tank, and to make a agitation tank of a rear stage into a mechanical stirring tank.

There is no restriction | limiting in particular in the amount of air aeration in an air aeration tank, What is necessary is just enough to be sufficient that a flocculant is fully stirred. This air aeration tank may use mechanical stirring together.

<Coagulant>

Examples of the coagulant used in the coagulation treatment include iron coagulants such as ferric chloride and iron polysulfate, and aluminum coagulants such as aluminum sulfate, aluminum chloride, and polyaluminum chloride. Iron coagulants are preferred in terms of coagulation effects. These inorganic flocculants may be used individually by 1 type, and may use 2 or more types together.

The amount of the inorganic flocculant added also depends on the properties and water quality of the biologically treated water, but it is usually preferably about 50 to 300 mg / L.

In addition, the use of an organic flocculant and a flotation aid in combination may improve the water quality of the flocculated water and improve the pressure flotation separation property in some cases. In this case, an organic flocculant may be added at the front end of an inorganic flocculant addition process, may be added at a later stage, and may be added to the addition process of an inorganic flocculant.

Although the addition amount of an organic flocculant changes also with the water quality of biologically-treated water and the use form of an organic flocculant, it is preferable to set it as about 1-10 mg / L normally.

<pH adjustment>

It is preferable that pH at the time of agglomeration processing is pH 3-6 in the flocculation tank which performs aeration stirring, and it can improve the coagulation process effect by adjusting to pH acidic region in this way. In particular, when an iron-based flocculant is used, mixing by aeration agitation at pH 5.5 or less is effective. When an aluminum-based flocculant is used, it is effective to mix it at pH 5.5 or less by aeration agitation and then adjust it to pH 6.0 or more again. .

When the flocculation treatment plant is composed of two or more flocculation tanks, the pH is adjusted to 3 to 6 in at least one of the flocculation tanks which perform aeration agitation, and the other flocculation tanks are adjusted to pH 3-6 depending on the drainage properties and the type of flocculating agent applied. You may adjust to pH other than this.

pH adjustment, an alkali such as hydrochloric acid (HCl), sulfuric acid (H ₂ SO ₄₎ or an acid such as, sodium hydroxide (NaOH) is suitably used.

<Oxidizer>

As described above, it is preferable to add an oxidizing agent in the flocculation treatment step, whereby a better flocculation treatment result can be obtained.

As the oxidizing agent, one kind or two or more kinds such as sodium hypochlorite (NaClO) and sodium persulfate can be used, and the amount of addition depends on the water quality of the biologically treated water and the conditions of flocculation treatment, but usually 1 to 10 mg / l. It is preferable to make it to an extent.

[Pressure Injury Separation]

The flocculated water is then subjected to pressure flotation separation, and the resulting flocculated floc is separated into solid-liquid.

A normal pressure flotation separation tank can be used for this pressure flotation separation.

In the present invention, thereby improving the separation of the pressing portion can coagulation treatability by carrying out aeration in the flocculation treatment, the water passage of the LV pressure during floatation of water passing LV 4~7 hr in the conventional pressurized floatation treatment ^{- 1} 10~20 hr ^- can increase to ^1, an improvement in treatment efficiency, and thus to achieve reduction of the installation space due to the size reduction of the device.

[percolation]

It is preferable that the separated water obtained by pressure flotation separation is again filtered by a filtration apparatus. As this filtration apparatus, a membrane filter using membranes such as a packed bed filter filled with a filter medium such as sand and anthracite, a microfiltration (MF) membrane, an ultrafiltration (UF) membrane, or the like can be used.

According to the present invention, in order to improve the pressure flotation separation property by performing aeration during the flocculation treatment, the pressure flotation separation water of good water quality can be obtained, thereby preventing clogging of the filtration device and reducing the frequency of backwashing of the filtration device. As a result, the processing efficiency can be improved.

[RO membrane treatment]

The pressure flotation separation water or the filtration treated water obtained by filtration thereof may be passed through the RO membrane separation device again to treat the RO membrane, and high purity water can be obtained by deionization treatment by the RO membrane treatment.

In this case, prior to the RO membrane treatment, in order to remove the residual SS in the pressurized flotation separation water, it is preferable to pass the pressurized flotation separation water through the filtration device described above and perform the filtration treatment. However, you may process RO membrane directly by pressurized floating separation water.

As the RO membrane separation device, any conventional device can be used.

In the present invention, a good pressure flotation separation water can be obtained with a small amount of inorganic flocculant addition, and the filtration treated water has a low FI value and can be supplied to the RO membrane separation device. The fall of the membrane flux can be suppressed, and treated water (permeate) can be obtained stably for a long time.

In addition, the FI value is used as an index for judging whether the water quality of the feed water to the RO membrane separation device when water is passed through the RO membrane separation device and deionized is suitable for the RO membrane treatment. Although the amount of dissolved organic matter and SS in water is generally equivalent, when the RO membrane treatment is performed, the membrane flux may be lowered or not at an early stage. In such a case, a difference occurs in the FI value of the RO water supply.

As described in the water quality evaluation in the examples described later, the FI value is operated by measuring the time required for passing a sample water through a membrane filter having a predetermined pore size and filtering a predetermined amount. It can obtain | require from time and the required time after water passage for a predetermined time, and it is used to determine whether it is the water quality which is easy to produce a membrane contamination, a film blockage, or it is the water quality which is hard to produce. Generally, even if the water quality of FI value 5 or less is acceptable as RO water supply, it is generally desired to be the water quality of FI value 4 or less. Therefore, in the present invention, it is preferable that the biological treatment water is subjected to the flocculation treatment and the pressure flotation separation treatment, and preferably filtered again to obtain water having a FI value of 4 or less, which is RO membrane treated.

[Other processing]

Moreover, in this invention, you may use other processes of that excepting the above at the rear end of a pressure flotation separation tank. For example, in order to remove residual soluble organic matter, you may install an activated carbon tower and perform the adsorption process with activated carbon.

In this case, the activated carbon column is the rear end of the filtration device, and is preferably formed at the front end of the RO membrane separation device.

[Processing Unit]

An example of the wastewater treatment apparatus of this invention is demonstrated below with reference to drawings.

1 to 5 are schematic diagrams showing an example of the wastewater treatment apparatus of the present invention, where 1 is a bioreactor, 2, 2A, 2B, and 2C are flocculation tanks, 3 is a pressure flotation separator, 4 is a filtration device, and 5 is RO. Membrane separation apparatus, 6 represents an activated carbon tower.

In the wastewater treatment apparatus of FIG. 1, after the wastewater is biologically treated in the biological reactor 1, in the first flocculation tank 2A in which the aeration means is formed, an inorganic flocculant (for example, an iron-based flocculant), an oxidizing agent and After the acid is added and coagulated under the conditions of pH 3 to 6 under rapid stirring, it is introduced into the second coagulation tank 2B provided with the stirrer, and the organic coagulant and the alkali are added to coagulate the mixture under slow stirring under the conditions of pH 5 to 8. Then, the flocculated treated water is separated by pressure flotation in the pressure flotation separation tank 3, and the separation water is filtered again by the filtration device 4, and the filtered water is taken out as the treated water.

The apparatus shown in FIG. 2 is provided with the RO membrane separation apparatus 5 further at the rear end of the filtration apparatus 4 in FIG. 1, and the filtration treated water obtained similarly to the apparatus of FIG. 1 is RO membrane separation again. After deionization in the apparatus 5, it is taken out as treated water.

In the apparatus of FIG. 3, in the apparatus of FIG. 2, an activated carbon tower 6 is provided between the filtration device 4 and the RO membrane separation device 5, and the inorganic coagulant ( For example, an aluminum flocculant) and an oxidizing agent and an acid or an alkali are added, and only an acid or an alkali is added in the second flocculation tank 2B, and the flocculation treatment, the pressure flotation separation treatment, as in the case of FIG. The filtered water is further deionized in the RO membrane separation device 5 after the residual soluble organics are removed from the activated carbon tower 6 and taken out as treated water.

In the apparatus shown in FIG. 4, in the apparatus of FIG. 2, in the flocculation tank 2 which has only one flocculation tank and provided the aeration means, an inorganic flocculant, an oxidizing agent, an acid, or an alkali was added, and pH weakly acidic. After the flocculation treatment is carried out under the conditions, the pressure flotation separation treatment is carried out in the pressure flotation separation tank 3, followed by filtration treatment and RO membrane separation treatment, and the treated water is taken out.

In the apparatus shown in FIG. 5, in the apparatus of FIG. 1, three flocculation tanks are used, and the biologically treated water is added with an organic flocculant and an acid or an alkali in the first flocculation tank 2A in which mechanical agitation means is formed. The flocculation process is carried out under the conditions of ˜7, and then an inorganic flocculant, an oxidizing agent, an acid or an alkali is added under the aeration stirring in the second flocculation tank 2B, and the flocculation treatment is performed under the conditions of pH 3 to 6, and again the third flocculation tank ( In 2C), acid or alkali is added under mechanical agitation to coagulate the mixture under conditions of pH 6 to 8, and the flocculated treated water is subjected to a pressure flotation separation treatment, followed by filtration to take out the treated water.

In addition, the apparatus shown in FIGS. 1-5 is an example of the wastewater processing apparatus of this invention, This invention is not limited to the method shown at all, As mentioned above, in the coagulation tank and the downstream process apparatus, many other Various aspects can be employed.

Example

An Example and a comparative example are given to the following, and this invention is demonstrated more concretely.

Examples 1-4

By the apparatus shown in FIG. 1, the organic wastewater was processed in accordance with the present invention. The quality and the operating conditions of the treated organic wastewater, the biological reaction tank and the flocculation tank used were as follows, and the treatment was performed at a throughput of 2400 L / day.

The FI value computed as follows from the filtration time at the time of the water quality evaluation of the treated water at this time, extracting the separated water of a pressurized floating separation tank, and filtering it to the 0.45 micrometer filter on 2.1 kg / cm <2> of press conditions, and a filtration apparatus. The filtration duration of (filtering duration until the filtration device occludes and requires backwashing) is evaluated, and the results are shown in Table 1.

In addition, as described above, the water passage standard for the RO membrane separation device is FI value 4 or less, and it is preferable that treated water having a FI value 4 or less is obtained.

FI = {(1-T ₀ / T ₁₅ ) / T ₁₅ } 10O

T ₀ : Time required for initial 500㏄ filtration (sec)

T ₁₅ : Time required for filtration of 50O㏄ after 15 minutes of filtration duration (sec)

[Organic drainage water quality]

BOD: 1000 mg / l

[Biological reaction tank]

Tank Capacity: 2400ℓ

Aeration amount: 20Oℓ / min

Carrier: Add 50% of the crude volume to the apparent volume of 3 mm long sponge

[First flocculation tank]

Tank Capacity: 50ℓ

Inorganic coagulant: 38% by weight of chloride 2 20O㎎ / ℓ (FeCl ₃ equivalent amount) was added an aqueous solution of iron

Oxidizer: Addition of Sodium Hypochlorite in Table 1

PH in bath: as shown in Table 1 (adjusted by addition of HCl or NaCl)

Air Aeration Rate: 20ℓ / min

[2nd flocculation tank]

Tank Capacity: 50ℓ

Organic flocculant: Add 0.5 mg / l polyacrylamide partial hydrolyzate

PH in bath: as shown in Table 1 (adjusted by addition of HCl or NaOH)

Stirrer: Paddle stirring of flat blade 40mm × 200mm, 60rpm

[Pressure Floating Septic Tank]

Jaw: Cylindrical floating separator with a diameter of 130 mm

Pressurized water ratio: 30%

Passage LV: 10m / hr

[Filtration device]

Filtration method: gravity two-layer filtration

Filtration LV: 5.6m / hr

Comparative Example 1

In Example 1, it processed similarly except having made the stirring means of a 1st flocculation tank into the paddle stirring similar to the 2nd flocculation tank instead of air aeration, and the processing result is shown in Table 1.

Comparative Example 2

In Comparative Example 1, the treatment was performed in the same manner as in Table 1 except that the amount of the inorganic flocculant addition in the first flocculation tank was increased as shown in Table 1, and the treatment results are shown in Table 1.

From Table 1 the following is clear.

That is, in the comparative example 1 which carried out mechanical stirring in the 1st flocculation tank, FI value of treated water is high and the water quality of treated water falls. Moreover, the filtration duration is also short compared with Examples 1-4. In Comparative Example 2, in which the amount of the inorganic flocculant was increased, the FI value was improved but not sufficient. Furthermore, since the formation of the flocculation floc and the affinity with the foam of the floc were insufficient, the filtration flotation was poor. The duration is very short.

In contrast, in Examples 1 to 4 where air aeration was carried out in the first flocculation tank, good results were obtained. In particular, when an oxidizing agent was added (Example 3), the pH of the first flocculation tank was changed to an acidic region. In the case (Examples 1 and 2), favorable results were obtained.

Example 5

In Example 1, the addition amount was set to 250 mg / L using PAC (polyaluminum chloride) as the inorganic flocculant added to the first flocculation tank, and the pHs of the first flocculation tank and the second flocculation tank were shown. Processing was performed similarly except having set it as the value shown in 2, and the processing result is shown in Table 2.

Comparative Example 3

In Example 5, the same treatment was performed except that the stirring means of the first flocculation tank was not the air aeration but the same paddle stirring as the second flocculation tank, and the treatment results are shown in Table 2.

From Table 2, even when PAC is used as an inorganic flocculant, it turns out that the effect of this invention by air aeration is acquired. In contrast with Example 5 and Comparative Example 3, Example 5 is better than Comparative Example 3 in the FI value, and the filtration duration is longer than that of Comparative Example 3.

Although it is difficult to agglomerate soluble substances or suspending substances containing cells and biological metabolites in biologically treated water, especially biological metabolites, and in the past, a large amount of flocculant is required, according to the present invention, the biologically treated water is aggregated. In the treatment, the cohesiveness and the solid-liquid separation can be improved by treating the agitation during the coagulation treatment by aeration (usually air) and combining the flocculation floc separation with the pressure flotation separation. Thereby, reduction of the addition amount of a flocculant can be aimed at and favorable treated water can be obtained.

Claims (8)

A biological reactor for biologically treating the water to be treated, An agglomeration reaction tank which adds a coagulant to the biological treatment water flowing out of the biological reaction tank and performs an agglomeration reaction, In the wastewater treatment apparatus provided with the pressure flotation separation tank which solid-separates the flocculation process water which flows out from this flocculation reaction tank, An aeration means is formed in the agglomeration reaction tank. The method of claim 1, And a pH adjuster adding means for adjusting the pH of the water in the flocculation reactor to 3 to 6. The method according to claim 1 or 2, And an oxidizing agent adding means for adding an oxidizing agent to the agglomeration reaction tank. The method according to any one of claims 1 to 3, And a filtration device for solid-liquid separation of the pressurized flotation separation water flowing out from the pressurized flotation separation tank. A biological reaction process for biologically treating the water to be treated, A coagulation reaction step of adding a coagulant to the biological treatment water flowing out of the bioreaction step to perform a coagulation reaction, In the wastewater treatment method provided with the pressure flotation separation process of carrying out the solid-liquid separation of the flocculation process water which flows out from the flocculation reaction process, The wastewater treatment method characterized by performing the aggregation reaction in the said aggregation reaction process under aeration. The method of claim 5, A pH adjuster is added to the water of the said flocculation reaction process, and the pH of this water is adjusted to 3-6, The wastewater processing method characterized by the above-mentioned. The method according to claim 5 or 6, An oxidizing agent is added to the water of the flocculation reaction step. The method according to any one of claims 5 to 7, And a filtration step for solid-liquid separation of the pressurized flotation separation water flowing out from the pressurized flotation separation process.

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