JPS5923874B2 - Grout injection method wastewater treatment method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating wastewater in grouting methods, particularly wastewater generated during grouting methods using water glass-based chemicals.

As is well known, there are two methods for stabilizing the soil quality and preventing spring water by injecting water glass chemicals: the LW method, which involves injecting suspended or semi-suspended water glass/cement chemicals, and the other method, which does not use cement. There are solution-type injection methods, each of which stabilizes the soil and stops water depending on the properties of the soil and spring water pressure.

However, in such a grouting method, a large amount of civil engineering drainage (hereinafter referred to as grout drainage) is generated due to spring water, running water, and other civil engineering works.

This grout drainage, ranging from suspension to solution, is a big problem at construction sites.In particular, grout drainage in the water glass chemical injection method is contaminated with earth and sand, and is accompanied by the chemical, which makes it highly alkaline. This makes processing even more difficult.

For example, if the concentration of sodium silicate in wastewater is high, simply neutralizing it will result in gelation and result in a sludge with a high water content that is difficult to separate, whereas if the concentration is low, it will dissolve without gelling.

Conventionally, such grout drainage is often neutralized with sulfuric acid and separated by precipitation, but in addition to the above points, if cement particles are suspended, this is also neutralized. Not only does it require a large amount of sulfuric acid, but it also produces sludge that is difficult to separate.

In addition, this is particularly likely to occur with drainage in the LW construction method,
Depending on the wastewater, the silicic acid content in the sodium silicate becomes a colloid and a cloudy phenomenon occurs, and since this cloudiness can hardly be flocculated by the above-mentioned neutralization treatment or flocculant, it cannot be removed by normal separation operations.

The present inventors discovered the fact that the white turbidity phenomenon of grout drainage occurs when there is a certain relationship between silicate ions and divalent cations, especially Ca+, in the drainage, and that it does not occur if this relationship is removed. Based on the knowledge that neutralization treatment can also be achieved, a technology for effectively treating grout wastewater using milk of lime and carbon dioxide gas as the main chemicals has been developed and has already been filed (Japanese Patent Application No. 108195/1982).

In this method, carbon dioxide gas is introduced after adding milk of lime to the grout drainage and before separating the liquid. However, problems such as calcium carbonate depositing at the carbon dioxide gas inlet and blockage tend to occur, and the introduction of carbon dioxide gas is difficult. There were problems such as the process being inappropriate, and as a result of intensive research to further improve the process, the present invention was completed.

That is, in the present invention, when treating wastewater generated from a water glass grout injection method, milky lime slurry is added to the wastewater whose flow rate has been stably adjusted so that the pH is at least 11,
5, a step of reacting in step 5, then a step of adding a coagulant to the treated wastewater slurry to cause coagulation and sedimentation to separate solid-liquid, then a step of adding carbonated water to the separated wastewater to insolubilize excess Ca + and separating and removing it. The present invention relates to a method for treating wastewater from grout injection method, which is characterized in that the treated wastewater separated in the previous step is neutralized, and the separated sludge is concentrated and dehydrated if necessary.

Among water glass grout wastewater, wastewater that is particularly difficult to treat has an appearance that is not cloudy due to kaolin or cement particles but is cloudy overall, has a high pH, and has a large amount of settled sludge.

This kind of drainage depends on the circumstances at the site, but in many cases,
Appears during construction where a large amount of water glass is used.

The reason for this is probably that the concentration of salts that promote gelation is low relative to the dissolved amount of sodium silicate, which, together with the influence of pH in the wastewater, causes silicate ions to colloid and form fine silicate gel particles. This seems to be due to the fact that the particles do not grow until they gel.

The present invention is applicable not only to cloudy wastewater, which cannot be solved by ordinary neutralization treatment, but also to all wastewater generated by soil stabilization methods using water glass chemicals, that is, grout drainage.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A grout wastewater treatment system according to the present invention will be described below with reference to the accompanying drawings.

First, when treating grout drainage, it is necessary that the flow rate of the drainage is adjusted as stably as possible.

For this reason, it is desirable to set up a drainage pit such as the drainage regulating pond 1 at an appropriate location inside or outside the mine to send the grout drainage.

The water quality and quantity of grout drainage constantly changes depending on the grout injection method, soil quality, environment, etc. ° It is not appropriate to deal with this directly due to the diversity of conditions.

Therefore, it is desirable to buffer the grout wastewater so that the water quality and quantity of the treated wastewater can be kept as constant as possible.

Basically, the flow rate must flow through the system so that it reaches the designed value with almost 100% probability.

If the flow rate entering the system fluctuates, the following reaction time in reaction tank 2 will not be maintained and the process will proceed to the next step without any reaction occurring.
There is also a possibility that flocs may carry over from the settling tank 4.

Similarly, it is desirable for water quality to have as little fluctuation as possible.

For this reason, the drainage regulating pond 1 is provided,
It is desirable to estimate and set the pond capacity based on long-term predictions, taking into account the above reasons.

In principle, it is preferable to treat water in a highly turbid state from the viewpoint of changes in water volume load, water quality load, and formation of flocs, so clear water and turbid water should be separated in advance as much as possible.

(Thus, the wastewater to be treated is transferred from the wastewater adjustment pond 1 to the reaction tank 2 in a state where the flow rate is as stable as possible.

In this case, it is desirable that an analytical device for testing the water quality be installed in the flow path to measure the water quality of the wastewater supplied to the reaction tank 2 in advance.

Of course, there is no problem even if this channel drainage water is periodically sampled and the water quality is tested.

In this way, milk of lime slurry is added from the milk of lime storage tank 11 to the waste water whose flow rate is adjusted to be as stable as possible in the reaction tank 2, and the slurry is caused to react.

Although other calcium salts can be used in this step, milk-of-lime slurry is particularly preferred as it substantially removes silicate ions and is the best from a handling, economical and practical point of view.

Therefore, depending on the drainage and site conditions, it is also possible to use other poorly soluble calcium salts, such as slurries such as cements and calcined dolomite, which are slightly inferior but equivalent.

It is important that this reaction is carried out at a pH of at least 11.5, preferably 11.8 or higher in the waste water.

The reason for this is that if the amount is less than the above value, the amount of residual silicate ions increases, reducing the silicate ion removal effect and making it difficult to smoothly form flocs using an effective amount of flocculant.

In this step, it is necessary to generate at least global acid components such as silicate ions and colloids with Ca'' to a size that can be easily flocculated and precipitated with a flocculant in the next settling tank 4.

Milk of lime can therefore be processed with very economical consumption if added within that limit.

In other words, the amount of milk of lime added must be such that the molar ratio CaO/SiO3 to the total silicic acid content in the wastewater is at least 0.5, while the upper limit is not particularly limited and may be set based on economic conditions. However, in most cases, a range of 1 to 4 is appropriate.

The total silicic acid content in wastewater mainly means the silicic acid content of dissolved sodium silicate in the wastewater, but if colloidal silica or fine calcium silicate are present, the silicic acid content also includes them. shall mean.

Also, for the above reasons, the reaction time should be at least 20
It is necessary to maintain a residence time of about 30 minutes, preferably about 30 minutes.

In addition, when carrying out the reaction as described above, it may be difficult or unnecessary to assemble a system of the drainage regulating pond 1 and the reaction tank 2 depending on the actual situation of the construction site or the actual situation of drainage.

Therefore, in such a case, it is possible, for example, to adjust the flow rate of wastewater in the wastewater regulating pond 1 and simultaneously carry out the reaction described above, which also serves as the reaction tank 2.Also, it is possible to use a wastewater regulating tank instead of the wastewater regulating pond 1. The treatment system may be designed according to the actual situation at each site, or even a plurality of wastewater regulating ponds or wastewater regulating tanks may be provided.

The point is to buffer the fluctuating water quantity and water quality so that the above-mentioned reaction can be carried out effectively for discharged water with as stable a flow rate and water quality as possible.

Next, the treated wastewater is transferred to the settling tank 4, where it is separated into solid and liquid.

In order to perform this solid-liquid separation smoothly, it is necessary to add a flocculant, and it can be added not only in the sedimentation tank 4, but also in a step before that.

For example, if the reaction tank 2 is a multi-stage type, adding a flocculant to the latter stage and installing a flocculator 3 such as an in-tube mixer between the reaction tank 2 and the settling tank 4 will prevent the formation of coarse flocs after the reaction. Therefore, solid-liquid separation in the settling tank 4 is often performed smoothly.

In this case, in order to make the sedimentation and separation in the sedimentation tank 4 more effective, a portion of the thickened sludge from the sludge thickening tank 9 is circulated and returned to the front of the Floraculator 3, or a small amount of coagulation aid is added to promote sedimentation. It may also be added.

However, this process is not necessarily necessary, and the flora curator 3 may be provided depending on the actual situation.

In cases where the above does not apply, it is preferable that the sedimentation tank 4 doubles as a flocculation tank that requires rapid stirring after adding the flocculant, and in another embodiment, the sedimentation tank 4 may be a rapid stirring tank depending on the circumstances at the site. It can also be configured as a sedimentation basin with a

In this case, a cross-flow type sedimentation tank is superior to the conventional up-flow type sedimentation tank.

In other words, in the upflow method, the entire amount of particles with a sedimentation velocity less than the water area load (upward velocity) is carried over, whereas in the crossflow method, particles with a sedimentation velocity higher than the water area load can be removed, which is a problem in civil engineering drainage. This is particularly effective in cases where the flow rate fluctuates rapidly.

Examples of flocculants include known inorganic flocculants such as basic aluminum chloride, aluminum sulfate, iron sulfate, and iron chloride; typical organic flocculants include polyacrylamide hydrolyzate, acrylic acid and acrylamide. copolymers, etc., and one or a mixture of two or more of them is used.

Then, the treated wastewater is separated into solid and liquid into supernatant water and sludge in the settling tank 4, and the supernatant liquid of the treated wastewater is transferred to the calcium carbonate precipitation tank 5.

Here, excess Ca'' in the treated wastewater is reacted to calcium carbonate by supplying carbonated water, becomes insolubilized, and is separated and removed.

In this case, it is naturally possible to introduce CO2 gas, but since the gas inlet is often blocked by calcium carbonate precipitation, it is necessary to supply it from the liquefied CO□ tank 12 through the saturated carbonated water storage tank 13. Additionally, this reaction is most effective when carried out at a pH of around 10.
Furthermore, a flocculant may be added if necessary.

The treated wastewater is then transferred to the settling tank 7, where it is mainly subjected to solid-liquid separation from calcium carbonate.

In this case as well, the same system and apparatus as in the reaction step and solid-liquid separation step described above can be employed.

For example, solid-liquid separation can be smoothly performed by adding a flocculant after the reaction in the calcium carbonate precipitation tank 5 and transferring it to the settling tank 7 via a suitable flocculator 6 to form coarse flocs. .

Next, since the supernatant wastewater treated here is alkaline with a pH of about 10, it is neutralized in a neutralization tank 8 and is discharged as substantially harmless wastewater.

The neutralizing agent is preferably carbonated water or carbon dioxide gas, but if necessary, other acidifying agents such as sulfuric acid, hydrochloric acid, etc. may be used in aqueous solutions.

On the other hand, the separated sludge discharged from each solid-liquid separation process is dehydrated and treated by a dehydrator 10, but in order to increase this treatment capacity, it is appropriate to dehydrate it through a sludge thickening tank 9 if necessary. .

Since this sludge contains almost no harmful substances, it can simply be disposed of in a landfill at an appropriate location.

Liquid separated from the dehydrator 10, also in the sludge thickening tank 9
The separated liquid can be transferred to any of the previous treatment steps or to the neutralization tank 8, but normally it is transferred to the wastewater adjustment pond 1 as shown in the drawing.

Thus, according to the present invention, grout wastewater using water glass, which is considered difficult to treat, can be rendered harmless economically and advantageously using simple chemicals and simple operations.

In particular, silicate ions in treated wastewater are 50p as SiO□.
It is of great significance to lower it to a level below pm.

The grout drainage in the Example LW construction method is sent to the drainage regulating pond 1 and transferred to the reaction tank 2 by a pump at a flow rate of 171j/1ni1t.

By monitoring during this transfer, pH: 11.5
, turbidity: 880. Sodium silicate (Si02): 1850
It was measured as ppm.

Even if the suspended matter was separated from this wastewater, the separated liquid showed milky turbidity and had a turbidity of 150.

On the other hand, 20 g/l of slaked lime slurry is added from the lime milk storage tank 11 to the reaction tank 2 at a ratio of 0.301/rniIL and reacted at pH 11.9.

The average residence time in this reactor was 30 minutes.

Next, an appropriate amount of basic aluminum chloride solution is continuously added from the flocculant storage tank 14, and then sent to the settling tank 4 via the flocculator 3, which is an in-tube mixer.

Next, the supernatant liquid is transferred to the calcium carbonate precipitation tank 5 and the saturated carbonated water prepared from the liquefied CO□ tank 12 is supplied from the saturated carbonated water storage tank 13 to
Make H constant at 10.

Then, in the same manner, after adding a small amount of the flocculant, the flocculator 6 sends the flocculant to the settling tank 7 for solid-liquid separation.

Next, the supernatant liquid is transferred to a neutralization tank 8, where it is neutralized to pH 7.5 with carbonated water and discharged as it is.

On the other hand, the separated sludge discharged from the settling tank 4 and the settling tank T is passed through a sludge thickening tank 9 and applied to a dehydrator 10 to form a cake.

The grout wastewater thus treated has a residual 5in2:2
5 ppm, Ca - 15, and turbidity of 1.3, it was practically rendered harmless. On the other hand, the cake was completely harmless, so it was used as landfill soil at a construction site.

[Brief explanation of drawings]

The attached figure is a flowchart showing one embodiment of the grout wastewater treatment system according to the present invention. 1... Drainage adjustment pond, 2... Reaction tank, 3
... Floraculator -, 4 ... Sedimentation tank (tank), 5 ... Calcium carbonate precipitation tank, 6.
... Floraculator, 7 ... Sedimentation tank (pond), 8 ... Neutralization tank, 9 ... Sludge concentration tank, 10 ...・Dehydrator, 11...
Lime milk storage tank, 12... Liquefied CO□ tank, 13
... Saturated carbonated water storage tank, 14 ... Flocculant storage tank.

Claims (1)

[Claims] 1. When treating wastewater generated from the water glass grout injection method, a lime milk slurry is added to the wastewater whose flow rate has been adjusted stably and reacted at a pH of 11.5, and then a flocculant is added to the treated wastewater slurry. A step of adding carbonated water to the separated wastewater to cause coagulation and sedimentation for solid-liquid separation, then a step of adding carbonated water to this separated wastewater to insolubilize and separate and remove excess Ca, and then neutralizing the treated wastewater separated in the previous step. A grout injection method wastewater treatment method comprising the steps of condensing the separated sludge and then dewatering the separated sludge, if necessary.