JPH0250800B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] This invention relates to a method for treating waste mud water. [Conventional technology] A large amount of waste mud water sometimes flows out from sites where mud water construction methods are used, but in accordance with legal regulations, such waste water must be treated by removing mud before being discharged. ing. Various methods have been used for this treatment, and typical examples include forced dehydration, solidification, and sun drying. Figure 2 is a process diagram of the conventional forced dewatering method, where 1 is waste muddy water such as bentonite, 2 is waste muddy water 1
The waste mud tank 3 for storing waste mud water 1 is a sand removal process for removing sand, gravel, etc. from the waste mud water 1, and screen roughness is separated by a mechanical separation device such as a cyclone. 4 is a flocculant treatment step, in which a flocculant is added to the waste mud water 1 from which sand, gravel, etc. have been removed in the sand removal step 3, and particles such as clay components in the waste mud water 1 are flocculated to form blocks. Generally, inorganic flocculants such as polyaluminum chloride and sulfuric acid are used, and organic flocculants include polymers such as polyacrylamide and polyvinyl alcohol. Reference numeral 5 denotes a dewatering process for waste mud water 1 containing clay components as a floc, which consists of a primary dewatering process 5a and a secondary dewatering process 5b. The primary dehydration step 5a is to dewater by a screen or sedimentation, and the secondary dehydration step 5b is to dehydrate the waste mud water 1 dehydrated in the primary dehydration step 5a by pressure dehydration using a filter press or pressure roll, centrifugal dehydration, vacuum dehydration, or Dehydration is performed by granulation and dehydration. In this way, the separated water 6 from which the solid content 8 has been removed from the waste mud water 1 is subjected to SS treatment or pH adjustment in the final step 7, and is then discharged. Furthermore, the sand, gravel 7, etc. and solid content 8 discharged from the sand removal process 3 and the dewatering process 5 are transported to a final disposal site and discarded. In addition, in the solid processing method, in the process shown in Figure 2,
In this method, a solidifying agent such as lime or cement is added to the mud dehydrated in the primary dewatering step 5a to solidify it, and then the mud is transported and disposed of in a landfill. Furthermore, in the solar drying method, a mud storage pond is set up in a remote area such as a mountainous area that is not subject to legal regulations due to environmental pollution, and the waste mud water 1 is collected, transported as it is, and stored in the mud storage pond. This method involves drying it naturally to the extent that it does not flow, and then transporting it to a final disposal site and disposing of it. [Problems to be solved by the invention] In the conventional waste mud water treatment method as described above,
In the forced dewatering method, it is necessary to select the type and amount of flocculant depending on the type and amount of mud in the waste mud water, but due to batch tests, it is necessary to experiment using many types of expensive flocculants. The losses are large in terms of time, effort and cost. Therefore, in actual driving,
A relatively versatile flocculant is added in an average amount, or the amount is adjusted by employees based on their experience. As a result, the moisture content of the dehydrated solid content 8 varies, and in dehydration equipment that uses cloth, clogging of the cloth and peeling of cake from the cloth occur, which hinders the operation and maintenance of the plant in the primary dehydration step 5a. comes out. Further, the dewatering equipment used in the secondary dewatering step 5b is complicated and expensive, and is often of a batch type, so that if a large amount of waste mud water is to be continuously treated, the equipment cost will be high. Also, in the solidification treatment method, the primary dehydration step 5a
Since the process up to this point is the same as the forced dehydration method, there are similar problems with the addition of a flocculant, and the type and amount of the solidification agent must be selected through trial and error in the same way as for the addition of a flocculant. As a result, the treatment effect varies, and if you try to operate on the safe side, you have no choice but to add an excessive amount of solidifying agent. Furthermore, since the sun drying method dehydrates water by natural drying, a large processing area is essential, but it is difficult to secure such a processing area around large cities.
For this reason, a treatment site must be located in a remote location, and the means and costs for transporting the waste mud become expensive. Conventional treatment methods have various problems as described above, and these problems directly lead to a rise in equipment costs and treatment costs, making it difficult to treat waste mud water. [Means for Solving the Problems] The wastewater treatment method according to the present invention includes a step of detecting ions in the wastewater and adding an exchangeable base other than sodium ions based on the type of the detected ions. to make the waste water alkaline,
The process consists of a step of making this alkaline waste wastewater acidic, and a dehydration step of this acidified wastewater. Further, a method for treating waste water according to another aspect of the present invention is to perform solidification treatment by adding a solidifying agent to the solid content separated from the above-described dehydration step. [Operation] In this invention, sodium ions (Na ⁺ ) of clay minerals such as montmolinite in wastewater are replaced with exchangeable bases such as calcium ions (Ca ²⁺ ) and magnesium ions (Mg ²⁺ ), and clay Large ions, calcium ions (Ca ²⁺ ) and magnesium ions (Mg ²⁺ ), enter between the unit layers of minerals, and calcium ions (Ca ²⁺ ) are bound to organic matter, which generally accounts for a large proportion in terms of volume.
It breaks the bond with alkali ions such as, making dehydration easier. In addition, in another invention of the present invention, since the clay minerals in the waste sewage are treated with acid, a part of the clay minerals dissolves, and the negative charges (SiO, ^4- ) easily reacts with the solidifying agent calcium hydroxide (Ca(OH) ₂ ), cement, etc. to form a gel, and by acid treatment, clay minerals are converted into ettringite hydrates (3CaO・Al ₂ O ₃・
Cacl ₂・12H ₂ O, 3CaO・Al ₂ O ₃・3CaSO ₄・
32H ₂ O, etc.), so it is easily solidified by solidifying agents. [Example] FIG. 1 is a process diagram showing an example of the present invention. In the figure, 1a is wastewater containing a high content of mud mainly composed of bentonite, such as waste water flowing out from a site where a muddy water construction method is used.
10 is a waste mud tank, and 11 is an ion meter attached to the waste sludge tank 10, which detects the type and amount of ions. 12 is an adjustment process, which includes an alkali treatment process 12a for the waste mud water 1a, followed by an acid treatment process 1.
It is more similar to 2b. Although this is a two-step process, it can be carried out using only one adjustment tank. Of course, each step may be performed in separate adjustment tanks. A PH meter is installed for adjustment, and the alkalinity and acidity of the waste mud water 1a are adjusted in batches according to the PH. In the alkali treatment step 12a of the adjustment step 12, the waste mud water 1a is made alkaline with a pH of about 11 using an exchangeable base other than sodium ions (Na ⁺ ), especially calcium ions (Ca ²⁺ ). Therefore, if the ions in the waste muddy water 1a in the waste sewage tank 10 are detected by the ion meter 11, and the waste sewage 1a has become alkaline due to the presence of sodium ions,
Calcium hydroxide (Ca(OH) ₂ ) is added until the pH reaches about 11 with the alkaline part removed. Calcium hydroxide (Ca(OH) ₂ ) may be added as a solid or an aqueous solution. For example, even if the amount of calcium hydroxide (Ca(OH) ₂ ) is less than 0.16 g per 1a of waste mud water, the pH is alkaline around 11. become. Additionally, cement that is alkaline and elutes calcium ions (Ca ²⁺ ) may be added.
Alternatively, waste alkali such as concrete washing water from a ready-mixed concrete factory may be used. The exchangeable base may be magnesium ion (Mg ²⁺ ) in addition to calcium ion (Ca ²⁺ ). When magnesium hydroxide (Mg(OH) ₂ ) is added, a small amount dissolves,
It elutes magnesium (Mg ²⁺ ) and becomes alkaline. Also, when dolomite plasters are added,
Both calcium ions (Ca ²⁺ ) and magnesium ions (Mg ²⁺ ) can be eluted. The waste mud water 1a that has been treated with alkali in this way is treated by adding an inorganic acid such as hydrochloric acid or sulfuric acid to the waste mud water 1a.
Make it acidic with a pH around 5 or below. From the perspective of solid-liquid separation, it is desirable to have an acidic pH of 3 or less, but the pH of the separated water 14 discharged into a river etc. from the final step 15 should be 5 to 6 according to regulations.
Therefore, it can be determined in consideration of economic efficiency such as the processing cost of the final step 15. Note that even non-genuine inorganic acids such as waste acids can be used. The acidified waste mud water 1a is then separated into solid and liquid in a solid-liquid separation step 13. As the solid-liquid separator, a screen, a settling tank, a light belt press, a filtration machine, and of course a suction dehydrator are used. Unlike the complicated, expensive equipment used in the secondary dehydration step 5a of conventional treatment methods, which can only be operated in batches, there are many equipment that can dewater continuously under light pressure, so the cost required for dewatering is low. allows stable driving. Note that the solid-liquid separator differs in the water content of the solid content 16 separated by the device. Therefore, a solid-liquid separator can be selected depending on the solid content processing method. For example, if the solid content 16 is to be disposed of in a landfill or disposed of, it is sufficient that it has been dehydrated to the extent that it can be transported to the disposal site, so it is dehydrated using heavy water dehydration equipment such as a screen or settling tank to reduce the water content to 50%. It is sufficient to separate the solid content 16 as shown below, and if further dehydration is desired, belt pressing or suction filtration with light pressure may be performed. The separated water 14 separated in the solid-liquid separation step 13 is subjected to SS treatment or pH adjustment in the final step 15, and then discharged. On the other hand, the separated solids 16 can be solidified to facilitate transportation or to reuse the solids 16. 17 has calcium hydroxide (Ca
(OH) ₂ ) is a solidification process in which a solidifying agent such as cement is added and solidified. Since the solid content 16 has been acid-treated in the acid treatment step 12b, it is easily solidified by the solidifying agent, and the solidified solid content after curing is transported to the final disposal site. Table 1 below shows the results of experiments on the above embodiment under various conditions.

[Table] (Note) ○: Good filtration property
△: Slightly poor permeability
×: Impossibility of filtration In this experiment, waste mud water containing bentonite clay was used as samples: waste mud water A with a water content of 73.1% and waste mud water B with a water content of 80.0%. Samples A and B are first made of calcium hydroxide (Ca(OH) ₂ ).
Or add _hydrochloric acid ( ^{HCl )} , aluminum sulfate (Al ₂ (SO ₄ ) ₃ ) Citric acid was added to each to make it acidic, and the quality of the acidity was tested using paper using a funnel. As a result, as shown in Table 1, the pH was 5
The filtration property will be improved if the pH is below, and the filtration property will not be improved if the pH is not lower than 3 with an organic acid such as citric acid. It has also been revealed that the filtration properties of inorganic acids vary depending on the type. Table 2 shows the water content of the solid content after dehydration of the bentonite-based clay used in the above experiment, which was subjected to alkali treatment and acid treatment, and a sample which was not treated.

〔Effect of the invention〕

As explained above, this invention allows easy solid-liquid separation of waste mud water using only alkali treatment and acid treatment. Since a forced dehydration device such as a dehydration device is not required, continuous large-scale treatment is possible, and equipment costs are also reduced. Additionally, the chemicals used in alkaline and acid treatments are significantly cheaper than the flocculants used in conventional treatments, resulting in lower material costs and lower operating costs. Furthermore, since the present invention can be carried out by measuring ions and pH, there are various effects such as enabling stable operation by feeding back the measured values. Furthermore, another aspect of the present invention is that the solid content can be easily solidified, so when a large amount of solid content is solidified and transported, it becomes possible to quickly dispose of it in terms of equipment, time, etc. Furthermore, since the solid content becomes a strong solid, it has the advantage of being able to be reused as a material.

[Brief explanation of the drawing]

FIG. 1 is a process diagram of an embodiment of the present invention, and FIG. 2 is a process diagram of a conventional waste mud water treatment method. In the figure, 10 is a waste mud tank, 11 is an ion meter,
12 is an adjustment process, 12a is an alkali treatment process, 1
2b is an acid treatment step, 13 is a solid-liquid separation step, 14 is separated water, 16 is a solid content, and 17 is a solidification treatment step.

Claims (1)

[Claims] 1. A step of detecting ions in the waste mud water; A step of making the waste mud water alkaline by adding an exchangeable base other than sodium ions based on the type of the detected ions; A method for treating waste mud water comprising the steps of: making the waste mud water acidified; and dewatering the acidified waste mud water. 2 A step of detecting ions in the waste mud water; A step of making the waste mud water alkaline by adding a compatible base other than sodium ions based on the type of ions detected above; A step of making the waste mud water made alkaline acidic and a dewatering step of the acidified waste mudwater, and the solid content separated in the dehydration step is solidified by adding a solidifying agent.