JP4471112B2 - Method for coagulating and dewatering muddy water - Google Patents

Description

  The present invention relates to a turbid water coagulation dehydration method, and more particularly, to a coagulation dehydration method with reduced dehydration time for muddy water such as construction wastewater.

  Conventionally, in coagulation treatment of turbid water such as construction wastewater, an inorganic coagulant and an organic coagulant are used alone or in combination, and fine particles are condensed or flocked (for example, Patent Document 1). reference).

The flocs subjected to the agglomeration treatment are effective in removing separated water because of their fast sedimentation properties. In recent years, however, it has been common to further perform mechanical dehydration treatment on the sedimented flocs. In the agglomeration treatment, the addition amount of the flocculant and the stirring conditions for floc generation are generally set according to the suspension concentration and pH of the suspended wastewater, the amount of organic matter, and the like.
JP 2000-185204 A

  However, in this agglomeration treatment, flocs added with a polymer flocculant as an organic flocculant have extremely poor dehydration properties in mechanical dehydration treatment, and require long-time dehydration or high pressure dehydration. There was a problem that it was necessary to increase the size of the dehydrator.

  For this reason, attempts have been made to improve the dehydrator and use dehydration aids to efficiently agglomerate and dehydrate the turbid water. The law was not reached.

  An object of the present invention is to provide a turbid water coagulation dehydration method in which the moisture content of a dehydrated cake is low, the dewaterability of flocs is improved, and the dehydration time is shortened.

To solve this problem,
The invention according to claim 1 includes construction wastewater, industrial wastewater, suspended water containing inorganic / organic sludge, washed contaminated soil containing harmful substances, and suspended water containing fine particles adsorbed with harmful substances, After adding the inorganic flocculant A to any muddy water and stirring and mixing, add the organic flocculant B to the muddy water and stirring slowly to produce floc L. Agent C is added and stirred and mixed, and the floc L is decomposed or broken, and then the organic flocculant D is added thereto, and the floc M is generated by gently stirring to dehydrate the floc M. A method for coagulating and dewatering turbid water to produce a dehydrated cake, wherein the stirring and mixing are performed at a speed of 100 to 5000 rpm, the slow stirring is performed at a speed of 10 to 500 rpm, and both are stirred so as to ensure a residence time of 30 seconds or more The inorganic flocculant A, , And E, characterized in that the at least one selected from the group consisting of aluminum sulfate, polyaluminum chloride, iron salts, the organic aggregating agent B, D, and F, to polyacrylamide or polyacrylic acid The turbid water coagulation dehydration method.

The invention according to claim 2 further includes adding an inorganic flocculant E to the floc M, stirring and mixing, decomposing or destroying the floc M, and further adding an organic flocculant F thereto. slow stirring to produce a floc N, the flock N dehydrated, a turbid water flocculation dehydration method according to claim 1 to produce a dewatered cake.

  According to the turbid water flocculation and dehydration treatment method of the present invention, the conventional flocculating and dewatering treatment is repeated by repeating the addition of the inorganic flocculating agent and stirring and mixing the organic flocculating agent and slow stirring twice or more. Since the flocs that have been coarse in the addition of 1 time are decomposed or destroyed and become non-hydrophilic, the dehydration property (water drainability) of the flocs in the dehydration treatment is improved, and the dehydration time can be significantly shortened.

  Hereinafter, an example of an embodiment of a turbid water coagulation dehydration method according to the present invention will be described with reference to the drawings.

  FIG. 1 is a process diagram according to an embodiment of the muddy water coagulation dehydration method of the present invention. In the turbid water coagulation dehydration method of this embodiment, after adding the inorganic flocculant A to the turbid water and stirring and mixing, the organic flocculant B is added thereto, and the floc L is generated by gently stirring. An inorganic flocculant C is added to the floc L and mixed with stirring. After the floc L is decomposed or destroyed, an organic flocculant D is added thereto, and the floc L is stirred slowly to produce floc M. Flock M is dehydrated to produce a dehydrated cake.

  The target turbid water includes construction wastewater, industrial wastewater, suspended water containing inorganic and organic sludge, suspended water containing mud that adsorbs harmful substances by washing contaminated soil containing harmful substances. Etc. The turbid water generally contains fine particles having a particle diameter of 75 μm or less that do not settle in water.

  Examples of the inorganic flocculant A that is first added to the muddy water include aluminum salts and iron salts. As such an aluminum salt, for example, aluminum sulfate (sulfuric acid band), polyaluminum chloride (PAC), aluminum chloride and the like are suitable.

  Moreover, ferrous chloride, ferric chloride, ferrous sulfate, ferric sulfate, polyiron sulfate, etc. are used as the iron salt. Among these, at least one selected from the group consisting of aluminum sulfate, polyaluminum chloride, and iron salt is preferable. One or two or more of these inorganic flocculants are appropriately selected according to the purpose and used.

  The amount of the inorganic flocculant A added is preferably 10 to 5000 ppm, more preferably 100 to 1000 ppm with respect to the turbid water, although it depends on the nature of the turbid water. By making the addition amount of the inorganic flocculant A appropriate, single particles in muddy water can be made into a flock shape in which several particles are bonded.

  The inorganic flocculant A is added to the turbid water and mixed with stirring. A known stirring and mixing device can be used for the stirring and mixing. It is preferable to ensure a residence time of 30 seconds or more for the stirring and mixing time. By ensuring a residence time of 30 seconds or longer, an agglomeration reaction in which the fine particles are electrically neutralized can be sufficiently performed. Further, the stirring and mixing speed is preferably 100 to 5000 rpm, and more preferably 300 to 3000 rpm.

  Next, the organic flocculant B is added thereto. Examples of the organic flocculant B to be added include polymer flocculants. Among these, polyacrylamide or polyacrylic acid is preferable. Moreover, it is preferable that it is 1-500 ppm with respect to muddy water, and, as for the addition amount of the organic type flocculant B, it is more preferable that it is 3-300 ppm. By making the addition amount of the organic coagulant B appropriate, it is possible to obtain a hydrous floc L that is coarsened by wrapping a solid with a polymer.

  After the organic flocculant B is added, floc L is produced by gentle stirring. The stirring and mixing after adding the organic flocculant B is slower than the speed during stirring and mixing when the inorganic flocculant A is added, and is preferably 10 to 500 rpm, and is preferably 10 to 100 rpm. Is more preferable. By carrying out the slow stirring, the division of flocs due to mechanical cutting is reduced, the floc L is coarsened, and the sedimentation speed can be increased. Moreover, it is preferable that the slow stirring time secures a residence time of 30 seconds or more.

  In the conventional method, the generated floc L is dehydrated as it is to complete the process. In the present embodiment, the dehydration process is not performed here, and the inorganic flocculant C is added to the floc L to perform stirring and mixing. As the inorganic flocculant C to be added, the flocculants exemplified in the inorganic flocculant A can be used.

  Moreover, it is preferable that the addition amount of the inorganic coagulant C is equal to or less than the addition amount of the inorganic coagulant A. In addition, for stirring and mixing, the same apparatus as that used for adding the inorganic flocculant A can be used, and the stirring and mixing time and speed are preferably the same.

  Once the inorganic flocculant C is added to the floc L that has been generated, the floc L is cut and broken by agitation, the polymer polymer shrinks and becomes non-hydrophilic, so the water contained in the floc L is released. Flock L means that organic flocculant B is added to a group of fine particles brought into contact by condensation or electrical neutralization by addition of inorganic flocculant A, and the polymer of organic flocculant B causes the fine particle group and water to be mixed simultaneously. Wrapped into coarse flocs. When the inorganic flocculant C is added to the floc L, the coarse floc polymer is decomposed and reduced to release water, and the floc becomes finer.

  Although dehydration can be performed in this state, the decomposition product of floc L is fluid and difficult to remove as a solid such as a dewatered cake. It is necessary to carry out at 1.5 times higher than the above.

  In this embodiment, dehydration is not performed here, and the process proceeds to the next step. That is, the organic flocculant D is added to the decomposition product of floc L, and the floc M is generated by stirring gently. As the organic flocculant D to be added, the flocculants exemplified in the organic flocculant B can be used. Moreover, the addition amount of the organic coagulant D may be less than the addition amount of the organic coagulant B, or may be the same or more.

  In addition, the same apparatus as that used for the addition of the organic coagulant B can be used for the agitation and mixing, and the agitation and mixing time and speed are preferably the same. When the floc L is once decomposed and re-agglomerated, excess water is also desorbed, so that the moisture content of the floc M can be lowered than that of the floc L.

  Next, the floc M is dehydrated to produce a dehydrated cake. For the dehydration treatment, a known dehydrator such as a belt press, a filter press, or a vacuum dehydrator can be used. Since the floc M has improved dewaterability compared to the floc L, the processing capacity of the dehydrator can be improved by 1.5 times or more, and the dewatering time can be shortened by about 50%. In addition, a dehydrated cake having a reduced moisture content can be obtained.

  In the turbid water coagulation dehydration treatment method of the present invention, since the coagulant is added twice, the amount of the coagulant used is 1.5 times or more compared with the conventional method, but the processing capacity of the dehydrator is improved and the dehydration time is increased. Therefore, the total cost of flocculation / dehydration can be reduced by 30 to 50% compared to the conventional case.

  In this embodiment, the floc M produced by adding the organic flocculant D is dehydrated, but the floc M is further added with an inorganic flocculant E and mixed with stirring to decompose or disassemble the floc M. After the destruction, an organic flocculant F may be further added thereto, and the floc N may be generated by stirring gently to generate a dehydrated cake by dehydrating the floc N.

  In this case, as the inorganic flocculant E, the flocculants exemplified in the above-mentioned inorganic flocculant C can be used, and the addition amount can be the same as the addition amount of the inorganic flocculant C. In addition, the organic flocculant F can be the same flocculant as mentioned in the organic flocculant D, and the addition amount can be the same as the addition amount of the organic flocculant D.

  By adding the flocculant three times as described above, the dewaterability of floc N can be further improved.

  Hereinafter, the present invention will be described in more detail by way of examples. The present invention is not limited to the following examples.

[Example 1]
The contaminated soil containing harmful substances is washed, and 500 ppm of polyaluminum chloride (abbreviated as “PAC”), an inorganic flocculant A, is added to suspended water containing fine particles adsorbed with harmful substances. The mixture was stirred and mixed at 200 rpm for 1 minute with a mold stirrer (three-one motor). To this was added 5 ppm of PA-331 (Kurita Co., Ltd.), an organic flocculant B, and the mixture was gently stirred at 20 rpm for 0.5 minutes to produce floc L.

  To this floc L, 250 ppm of PAC, which is an inorganic flocculant C, was further added, and the mixture was stirred and mixed for 1 minute at 200 rpm with the above apparatus, and the floc L was broken. To this, 10 ppm of PA-331, an organic flocculant D, was added and gently stirred at 20 rpm for 0.5 minutes to produce floc M. The amount of these flocculants added is shown in Table 1.

  The Flock M was dehydrated with a Nutsche vacuum dehydrator to obtain about 20 g of dehydrated cake. The relationship between the amount of dehydration (ml) and the dehydration time (seconds) at this time was measured and is shown in FIG. FIG. 2 is a graph plotting the relationship between the amount of dehydration and the dehydration time in the dehydration process of Flock M.

[Example 2]
A floc M was generated in the same manner as in Example 1 except that the addition amount of the organic coagulant D was changed to 20 ppm, and the dehydration amount (ml) and the dehydration time (seconds). And the relationship was measured. The amount of flocculant added is shown in Table 1, and the results are shown in FIG.

[Example 3]
Add 1000 ppm of inorganic flocculant A, 20 ppm of organic flocculant B, 250 ppm of inorganic flocculant C, and 10 ppm of organic flocculant D to produce floc M in the same manner as in Example 1. The relationship between volume (ml) and dehydration time (seconds) was measured. The amount of flocculant added is shown in Table 1, and the results are shown in FIG.

[Comparative Example 1]
Add 500 ppm of PAC as inorganic flocculant A to the same amount of suspended water as in Example 1, stir and mix at 200 rpm for 1 minute with a propeller-type stirrer, and add 5 ppm of PA-331 as organic flocculant B Then, floc L was produced by gentle stirring at 20 rpm for 0.5 minutes, and this was dehydrated in the same manner as in Example 1. The amount of flocculant added is shown in Table 1, and the relationship between the amount of dehydration (ml) and the time of dehydration (seconds) in the dehydration treatment of floc L is shown in FIG.

[Comparative Example 2]
Flock L was generated in the same manner as in Comparative Example 1 except that 750 ppm of inorganic flocculant A and 10 ppm of organic flocculant B were added, and the relationship between dewatering amount (ml) and dewatering time (seconds) was measured. did. The amount of flocculant added is shown in Table 1, and the results are shown in FIG.

  From the results shown in FIG. 2, it took 171 seconds for Comparative Example 1 and 200 seconds for Comparative Example 2 to reach 180 ml, but it took 24 seconds for Example 1, 83 seconds for Example 2, and Example 3 In Example 1, the dehydration rate was 7 to 8 times that of Comparative Examples 1 and 2, and in Examples 2 to 3 was 1.7 to 2.4 times that of Comparative Examples 1 and 2. I understood it.

  From the above results, it was confirmed that according to the turbid water coagulation dehydration method of the present invention, the dewaterability in the floc dewatering process was improved and the dehydration time could be shortened by 1.5 times or more.

It is process drawing which concerns on one Embodiment of the aggregation dehydration processing method of the muddy water of this invention. It is the graph which plotted the relationship between the dehydration amount and the dehydration time in the dehydration process of the flock in Examples 1-3 and Comparative Examples 1-2.

Claims (2)

Wastewater from construction works, industrial wastewater, suspended water containing inorganic and organic sludge, washed contaminated soil containing harmful substances, suspended water containing particulates adsorbed with harmful substances , inorganic to any muddy water After adding the system flocculant A and stirring and mixing,
Add organic flocculant B to this and stir gently to produce floc L,
After adding the inorganic flocculant C to the floc L and stirring and mixing it, the floc L is decomposed or destroyed,
Add organic flocculant D to this and stir slowly to produce floc M,
A muddy water coagulation dehydration method for dehydrating the floc M to produce a dehydrated cake,
The stirring and mixing is performed at a speed of 100 to 5000 rpm, the slow stirring is performed at a speed of 10 to 500 rpm, and both are stirred so as to ensure a residence time of 30 seconds or more.
The inorganic flocculants A, C, and E are at least one selected from the group consisting of aluminum sulfate, polyaluminum chloride, and iron salt,
The organic flocculants B, D, and F are polyacrylamide or polyacrylic acid . After the floc M is generated, an inorganic flocculant E is further added and mixed by stirring to decompose or destroy the floc M.
To this, an organic flocculant F is further added, and the floc N is generated by gently stirring,
The method for coagulating and dewatering muddy water according to claim 1, wherein the floc N is dehydrated to produce a dehydrated cake .

Images