JPS5939196B2 - Method for recycling flocculant in flocculation treatment of dyeing wastewater - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a method for recycling a flocculant when purifying wastewater by adding a flocculant to dyeing wastewater, and particularly provides a method for efficiently recovering the flocculant. .

Conventionally, as a method for purifying dyeing wastewater, a flocculant such as polyaluminum chloride or sulfuric acid bread soil is added to the dyeing wastewater to coagulate the pollutant particles in the wastewater, causing them to settle or float and be removed as sludge. method is commonly adopted.

According to this method, a large amount of sludge is generated, which is either incinerated and disposed of or simply dumped, but it is expensive to process and has considerable problems such as securing a dumping site.

Furthermore, since the flocculant is simply discarded, the cost is considerably high.

Therefore, the present invention effectively utilizes these sludges,
This provides an effective method for regenerating it as a flocculant.

That is, in the present invention, when an inorganic flocculant is added to dyeing wastewater for flocculation treatment, the concentration of the sulfuric acid aqueous solution in the sludge-sulfuric acid mixture is 40% for the sludge obtained by the flocculation treatment.
A basic invention of a method for regenerating a flocculant in flocculation treatment of dyeing wastewater, which is characterized by adding sulfuric acid to dissolve it so that the concentration is less than %, diluting with water, filtering, and using the filtrate as a regenerated flocculant. That is.

Although the present invention can be applied to any dyeing wastewater, it can be most effectively applied to synthetic fiber dyeing wastewater or pre-dyed dyeing wastewater of synthetic fibers.

The present invention will be explained in detail below based on the flow sheet shown in FIG.

Dyeing wastewater that has undergone scouring, dyeing or finishing processes is sent to a flocculation treatment tank, and an appropriate amount of an inorganic flocculant such as sulfuric acid bread clay or polyaluminum chloride is added from a flocculant storage tank.

By appropriately adjusting the pH, for example, the aluminum-based flocculant reacts with the alkaline content in the water, producing aluminum hydroxide flocs, which neutralizes the negative charge of pollutant particles in the wastewater and binds the particles. At the same time, it adsorbs this and forms large flocs, producing sludge.

Next, this sludge is dehydrated using, for example, a centrifugal dehydrator.

Dehydration is carried out to make the water content unevenly contained in the sludge uniform, and in the next step, sulfuric acid It is effective when dissolved in

There is no need to provide a special dewatering process if the sludge is naturally dehydrated at the stage of transfer to the next process.

The sludge after the dehydration treatment is directly put into a reaction tank without going through processes such as heating and drying, combustion, etc., and an arbitrary amount of sulfuric acid is added from the sulfuric acid tank.

It is preferable to use concentrated sulfuric acid with a H2SO4 content of 95% or more, but commercially available cabin sulfuric acid with a H2SO4 content of about 60% or tower acid with a H2SO4 content of about 80% can also be used.

In the present invention, the following experiment was conducted in order to determine the optimum amount of sulfuric acid added to the sludge.

That is, the sludge obtained by the coagulation treatment of dyeing wastewater was dehydrated by 30% by weight to make the water content of the sludge 90% by weight, an arbitrary amount of 98% concentrated sulfuric acid was added to this dehydrated sludge 50f, and after stirring, it was left for 30 minutes. Next, the sludge was diluted 50 times with water, filtered, and the dissolved state of the sludge was examined.
4 cc of the filtrate was taken to confirm the flocculation effect in 200 cc of dyeing waste water.

Regarding the evaluation of the agglomeration effect, the case where polyaluminum chloride was used was given as a comparative example.

The results of the above experiment are shown in Table 1.

As is clear from Table 1, the amount of concentrated sulfuric acid added is 5 to 10c.
c addition (addition of 9 to 18? in H2S04 equivalent weight, concentration of sulfuric acid aqueous solution in sludge-sulfuric acid mixture 16.6% to 28%,
4%) has a small amount of filtration residue (and excellent flocculation effect), and addition of excessive concentrated sulfuric acid conversely reduces both the dissolution effect and the flocculation effect.

From these experimental results and confirmation results in the actual process, it has been found that the appropriate amount of sulfuric acid to be added is that the concentration of sulfuric acid aqueous solution in the sludge-sulfuric acid mixture is 40% or less, and that 15 to 30% is particularly good. Understood.

As described above, in the present invention, an appropriate amount of sulfuric acid is added to the sludge.

Next, after adding sulfuric acid, the mixture of sludge and sulfuric acid is reacted by stirring and left for about 30 minutes.

The sulfuric acid is diluted with the water contained in the sludge and becomes dilute sulfuric acid depending on the amount of sulfuric acid added, and as an acid it dissolves the aluminum hydroxide contained in the sludge, and the heat generated during dilution promotes the dissolution.

The reaction at this time is It is indicated by.

After being left for about 30 minutes, the mixed solution of sludge and sulfuric acid is sent to a dilution tank and diluted about 50 times with water from the water tank.

For dilution, a reaction tank may also serve as a dilution tank without providing a special dilution tank.

This dilution completely dissolves the aluminum hydroxide,
The flocculant is completely recovered as an aqueous solution of aluminum sulfate.

Furthermore, dilution makes it easier to filter in the next step, and the filtration rate can be increased.

After dilution, the aluminum sulfate aqueous solution is recovered as a regenerated flocculant by filtration in a filtration tank and sent to a flocculant storage tank to be used as a flocculant.

Sludge that is not dissolved by sulfuric acid is separated as a filtration residue in a filtration tank, neutralized by adding sodium hydroxide, and filtered, and the filtrate is drained.

The amount of surplus sludge remaining at the end is minute compared to the initial sludge, and there is almost no problem in dumping it.

In addition, this surplus sludge can be heated and dried and used as an adsorbent for advanced treatment of dyeing wastewater, allowing all of the discharged sludge to be recycled.

As described above, in the present invention, the sludge obtained from the coagulation treatment of dyeing wastewater can be efficiently recovered as a regenerated coagulant, and the processing cost is drastically reduced, and the amount of discarded sludge is almost eliminated, thereby reducing secondary pollution. Prevented.

Embodiments of the present invention will be described below with reference to FIG.

Example A flocculation treatment was carried out by adding 11,000 pp of polyaluminum chloride to the dyeing wastewater after dyeing a polyester synthetic fiber yarn in the form of a package with a disperse dye.

The sludge produced by the coagulation process was dehydrated by 30% by weight using a centrifugal dehydrator (not shown) to bring the water content to 90%.

Take 1000 kg of this dehydrated sludge, crush it as small as possible, and charge it into the mixing reaction tank 1 from arrow A.

Next, the automatic valve 3 opens, and after a few seconds the sulfuric acid transfer pump 4
operates and mixes 98% concentrated sulfuric acid from sulfuric acid tank 2 into reaction tank 1.
A fixed amount of 1001 (calculated as H2S04 equivalent weight 180 kg and specific gravity 1.84) is sent to.

The concentration of sulfuric acid aqueous solution in the sludge-sulfuric acid mixture is 16.6%
becomes.

After the transfer, the automatic valve 3 is closed and the sulfuric acid transfer pump 4 is stopped at the same time.

In addition, in advance, fill the dilution tank 8 with dilution water using the automatic valve 10, and close the automatic valve 10 when the water level reaches a certain level using the floatless switch FLS water level gauge H.

Immediately after the sulfuric acid transfer pump 4 is stopped, the processing liquid circulation transfer pump 5 and automatic valve 6 are opened, and the sulfuric acid solution is circulated to dissolve the sludge.

After dissolving by circulating for 30 minutes, automatic valve 6 is closed and automatic valve 7 is opened.

At this time, check whether the floatless switch FLS is working.

The entire mixed treatment liquid in the mixing reaction tank 1 is transferred to the dilution tank 8 via an automatic valve 7, and after the transfer is completed, the treatment liquid transfer pump 5 is stopped.

Next, the automatic valve 7 is closed, and the diluted liquid is stirred by the stirrer 9 in the dilution tank 8.

After stirring for a certain period of time, the stirrer 9 is stopped, the diluent transfer pump 12 is started, and after a few seconds the automatic valve 13.1 is turned on.
6 is opened, and the entire amount of the filtrate is transferred to the processing liquid storage tank 18 via the filtration tank 14 below the dilution tank 8.

After the entire amount has been transferred, the automatic valve 16 is closed and the diluent transfer pump 12 is stopped.

Since the dilution tank 8 and the filter tank 14 are contaminated with an acidic solution due to sulfuric acid and sludge, this is neutralized and washed, and boiler blow water is effectively used at this time.

Boiler blow water has a pH of 10 to 10.5 because it is used for washing water inside the boiler, and is convenient for neutralizing and washing.

That is, after the entire amount of treated liquid is discharged from the dilution tank 8, the blow water stored in the boiler blow water tank 23 is transferred from the boiler (not shown) through the piping 24 to the dilution tank 8 by the operation of the blow water transfer pump 22. Send it in.

The blow water is detected by the water level gauge of the floatless switch FLS in the dilution tank 8, the blow water transfer pump 22 is stopped, and the post-dilution transfer pump 12 and the agitator 9 are activated.

At the same time, the automatic valve 15 is opened to circulate and clean the dilution tank 8 and the filtration device 14.

During circulation cleaning, a PHIC, which is a pH controller, is operated to measure the pH, and if the pH is below the neutralization point, the blow water transfer pump 22 is operated to supply blow water up to the neutralization point.

When PRIC indicates the neutralization point, the blow water transfer pump 22
stops, the automatic valve 11 opens to spray water to clean the inside of the dilution tank 8, and the automatic valve 17 is opened to drain water into the drainage tank 21.

After watering for a certain period of time, the automatic valve 11 is closed.

After draining, all circuits are restored and the odor is removed from the filtration tank 1.
The filtration residue accumulated in the bag filter installed in 4 is taken out along with the filter, heated and dried, and used as an adsorbent.

A required amount of the aluminum sulfate aqueous solution stored in the treatment liquid storage tank 18 is transferred to the dyeing wastewater coagulation treatment device 20 by the chemical injection pump 19 and used as a regenerated coagulant.

Regarding the obtained sludge made of the recycled flocculant, the above example is repeated to collect the recycled flocculant many times.

Here, in order to confirm the effect of the regenerated flocculant, the above example was repeated three times and the effect of each regenerated flocculant was checked, and the results shown in Table 2 were obtained.

As a result, it was confirmed that the present invention can be used as a regenerated flocculant without the need to add any flocculant by repeating the experiment up to three times.

After the third time, the treatment effect slightly decreases, so the treatment effect can be maintained by adding a small amount of new flocculant.

BOD of dyeing wastewater treated with recovered coagulant,
The COD values were all well below the wastewater standards, and there were no other problems with the wastewater standards.

As described above, according to the present invention, most of the flocculant in the sludge can be recovered as regenerated flocculant, and no new flocculant is required or only a small amount is added, which greatly reduces processing costs. reduced to

Furthermore, since almost all of the sludge can be used effectively, the problem of secondary pollution, such as where it is dumped, can be solved.

[Brief explanation of drawings]

FIG. 1 shows a flow sheet of the present invention. FIG. 2 is a process diagram showing an example of a specific apparatus of the present invention. A... Dehydrated sludge, 1... Mixing reaction tank, 2... Sulfuric acid tank, 8... Dilution tank, 1
4...filter tank, 18...processing liquid storage tank,
23...Boiler blow tank.

Claims (1)

[Scope of Claims] 1. When adding an inorganic flocculant to dyeing wastewater for flocculation treatment, sulfuric acid is added to the sludge obtained by the flocculation treatment so that the concentration of the sulfuric acid aqueous solution in the sludge-sulfuric acid mixture is 40% or less. 1. A method for regenerating a flocculant in flocculation treatment of dyeing wastewater, which comprises adding and dissolving, further diluting with water, filtering, and using the filtrate as a regenerated flocculant. 2 The concentration of sulfuric acid aqueous solution in the sludge-sulfuric acid mixture is 15~
A method for regenerating a flocculant in a flocculant treatment for dyeing wastewater according to claim 1, characterized in that sludge is dissolved by adding sulfuric acid to a concentration of 30%.