KR20170042015A - Method for removing zinc oxide in water using phosphate and iron salt - Google Patents

Abstract

The present invention relates to a method of removing zinc oxide contained in water, comprising the following steps of: primarily settling soil or sand by introducing sewage or wastewater containing zinc oxide into a primary settling basin; floating a material having a weight less than water and secondarily settling a material having a weight greater than the water by introducing the sewage or wastewater that has passed through the step of primarily settling into a secondary settling basin to stay the same; measuring a concentration of the zinc oxide of the sewage or wastewater that has passed through the step of secondarily settling, and injecting phosphate thereto; introducing the sewage or wastewater to which the phosphate is injected into a bioreactor, and aerating the same; measuring a concentration of the phosphate of the sewage or wastewater that has passed through the step of aeration, and adding iron salt thereto; introducing the sewage or wastewater to which the iron salt is added into a final settling basin to settle sludge and to discharge supernatant; and performing an activated carbon adsorption process and/or an ozone oxidation process on the discharged supernatant.

Description

METHOD FOR REMOVING ZINC OXIDE IN WATER USING PHOSPHATE AND IRON SALT BACKGROUND OF THE INVENTION 1. Field of the Invention [0001]

The present invention relates to a method for removing zinc oxide contained in a water system, and more particularly, to a method for removing zinc oxide contained in sewage or wastewater by injecting a phosphate and an iron-based coagulant.

Nanomaterials are raw materials that are unintentionally released into the environment during exposure to the workplace in the manufacturing process or in the process of using and disposing of nanomaterials containing nanomaterials, which causes unintentional environmental pollution.

Such nanomaterials include zinc oxide (ZnO), which is widely used in various industrial fields, and wastewater or sewage containing zinc oxide (ZnO) can be treated with zinc oxide (ZnO) Can not be completely removed.

In other words, since zinc oxide tends to be easily ionized in a liquid phase, it can not be completely removed by a conventional wastewater treatment process, and thus is released even in a small amount in discharged water of the wastewater treatment plant.

Although attempts have been made to develop a new coagulant to completely remove zinc oxide (ZnO) contained in such water, zinc oxide (ZnO) which can not be sufficiently removed due to excellent water solubility, Is exposed to the problem of accumulating in the organism and causing secondary pollution.

Korean Patent Registration No. 1993-0000095 Korean Patent Registration No. 10-1386599

It is an object of the present invention to provide a method for removing zinc oxide that can effectively remove a small amount of zinc oxide nanomaterials contained in water.

In order to accomplish the above object, the present invention provides a method for removing zinc oxide contained in wastewater using phosphate and iron salts, comprising: a first precipitation step in which sewage or wastewater containing zinc oxide is introduced into a first settling tank to deposit soil or sand; A second precipitation step in which sewage or wastewater having undergone the primary precipitation step is flowed into a secondary settler so that a material having a specific gravity smaller than water is suspended and a material having a specific gravity larger than that of water is precipitated; Measuring the concentration of zinc oxide in the sewage or wastewater through the secondary precipitation step and injecting phosphate; Introducing the phosphate-infused sewage or wastewater into the bioreactor and aeration; Measuring the phosphate concentration of the sewage or wastewater through the aeration step and adding the iron salt; Introducing the iron salt-added sewage or wastewater into the final settling basin, thereby precipitating the sludge and discharging the supernatant; And performing the activated carbon adsorption process and / or the ozone oxidation process on the discharged supernatant.

In the method of treating sewage or wastewater containing zinc oxide according to the present invention, in the step of injecting phosphate, zinc oxide of the sewage or wastewater subjected to the second precipitation step is reacted with the injected phosphate The stirring step and the precipitation step are further carried out.

Further, the method of treating sewage or wastewater containing zinc oxide according to the present invention further comprises the step of taking out zinc phosphate hydrate (Zn ₃ (PO ₄ ) ₂ .H ₂ O) precipitated by reaction with the phosphate, to the outside .

Further, the method for treating sewage or wastewater containing zinc oxide of the present invention is characterized in that the phosphate is disodium hydrogen phosphate (Na ₂ HPO ₄ ).

Further, in the method of treating sewage or wastewater containing zinc oxide of the present invention, the injection concentration of the phosphate is 0.05 to 1 M.

According to the zinc oxide removal method of the present invention, water soluble zinc oxide can be insolubilized and removed by injecting phosphate, so that the removal efficiency of zinc oxide can be increased compared with the conventional method of treating wastewater.

In addition, according to the zinc oxide removal method of the present invention, the remaining phosphorus component has the effect of suppressing eutrophication because the coagulant is added to remove it.

In addition, according to the zinc oxide removal method of the present invention, since the iron salt flocculant for removing phosphorus is added after the microbial aeration step, there is no need for a separate flocculant for the separation of iron phosphate which is an aggregation product, Can be effective.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a flowchart showing a zinc oxide removal method of the present invention. FIG.
FIG. 2 is a photograph showing the sedimentation reaction results of zinc oxide and sodium phosphate ((a) at the start of the reaction and (b) after standing for 8 hours after completion of the reaction).
3 is an image obtained by transmission electron microscopy analysis of a precipitated zinc compound.

Hereinafter, preferred embodiments of the present invention will be described in detail so that those skilled in the art can easily carry out the present invention. The embodiments of the present invention can be modified into various other forms, and the scope of the present invention is not limited to the embodiments described below.

Hereinafter, a method of removing zinc oxide contained in wastewater using phosphate and iron salts of the present invention will be described in detail with reference to FIG. 1 attached hereto.

The method for treating sewage or wastewater containing zinc oxide according to the present invention comprises a first precipitation step in which sewage or wastewater containing zinc oxide is introduced into a primary settler so as to deposit soil or sand, Or the wastewater is introduced into the secondary settling tank, the material having a specific gravity smaller than that of the water is floated, and the material having a specific gravity larger than that of the water is settled; a step of injecting phosphate into the sewage or wastewater having passed through the secondary settling step A step of introducing the phosphate-infused sewage or wastewater into the bioreactor to aerate the effluent, adding an iron salt to the sewage or wastewater through the aeration step, introducing the iron salt-added sewage or wastewater into the final settling basin, And discharging the supernatant; and performing the activated carbon adsorption process and / or the ozone oxidation process on the discharged supernatant. The.

The first precipitation step is a step of introducing into the first settling basin (sedimentation bed) in order to precipitate and remove a relatively heavy material such as soil or sand that has entered through a sewage line. That is, it is possible to prevent dead space by depositing sediments which may be caused in the subsequent process and the sludge disposal process by previously removing the sludge and contaminants contained in the inflow sewage or wastewater, Thereby preventing breakdown and piping closure.

The sewage or wastewater from which the soil or sand has been removed is introduced into the secondary settling tank to carry out the second settling step. In the secondary precipitation step, SS (Suspended Solid) is removed and the biological oxygen demand (BOD) caused by the suspended solids (SSO) is removed together, And to increase the treatment efficiency.

That is, the second settling step is a step of removing floating solids by gravitational sedimentation through a secondary settling facility, which is intended to reduce the load of the biological treatment process, reduce the facility capacity of the subsequent treatment facility, and reduce the operating cost stably .

In the second precipitation step, about 30% of the biological oxygen demand (BOD) and about 35% of the suspended solid (SS) can be removed by retaining the sewage or the wastewater for about 3 to 4 hours.

However, even if the first precipitation step and the second precipitation step are carried out, zinc oxide contained in the influent sewage or wastewater is not removed and most of it remains as it is.

In other words, when zinc oxide (ZnO) ionizes in water, some ions exist as ZnOH ⁺ or Zn (OH) ₂ , but most of them are present in the form of Zn ^{2 +} ion and are removed in the first precipitation and second precipitation Do not.

On the other hand, when ionized zinc oxide (ZnO) is present in the liquid phase, the presence of phosphate ion (PO ₄ ^3- ) generates a zinc phosphate reaction (Zn ₃ (PO ₄ ) ₂ ) The shape can also be adjusted. That is, when the pH of the reaction is adjusted to 6, the size of the reactant particles can be further increased. When the pH is 8, only zinc oxide is coated with the reaction product of zinc phosphate.

The resulting zinc phosphate reactant (Zn ₃ (PO ₄ ) ₂ ) precipitates in the form of agglomerates or hydrates, so that the zinc oxide nanomaterial can be completely removed by separating the supernatant except for the precipitate.

Therefore, in order to remove ionized zinc (Zn ²⁺ ) contained in sewage or wastewater subjected to the primary and secondary precipitation steps, in the present invention, a step of injecting phosphate into the sewage or wastewater through the secondary precipitation step Is performed.

Here, the phosphate preferably includes disodium hydrogen phosphate (Na ₂ HPO ₄ ), but is not limited thereto.

Further, after the phosphate is added to the zinc oxide, a stirring step may be further performed so that the injected phosphate and the zinc ion (Zn ^{2 +} ) react well, and a precipitating step is further added to separate the aggregate or hydrate It is possible.

Next, a step of introducing the phosphate-infused sewage or wastewater into the bioreactor to aeration is performed.

In the aeration step, an aerobic microorganism adsorbs and decomposes organic matter, nitrogen, and phosphorus contained in the inflow sewage to form floc having good sedimentation, and is sedimented and separated from sludge and treated water in the final sedimentation basin.

That is, in the aeration step, the effluent that has undergone the second precipitation step through the aeration tank is aeration together with the microorganism, thereby decomposing and removing the organic matter by the metabolic action of the microorganism.

On the other hand, unreacted phosphate remains in the excessively charged phosphate for the purpose of removing ionized zinc (Zn ^{2 +} ), and if such phosphate is discharged as it is, it may cause a secondary problem, that is, .

Green algae, which means phytoplankton green algae and cyanobacteria, is a phenomenon that changes water color to green, and organic matter such as domestic sewage, industrial wastewater, livestock excrement etc. is introduced and nutrients such as nitrogen and phosphorus are increased in water . This green algae phenomenon reduces the amount of dissolved oxygen in water without shutting off sunlight and adding dissolved oxygen to the water. This causes fish and aquatic creatures to die and smell, and the ecosystem of the water is destroyed, There are many problems in terms of enemy.

In order to prevent the above-mentioned green algae phenomenon, since the inflow of nitrogen and phosphorus into the river water system must be suppressed to the utmost, the emission allowance standards of nitrogen and phosphorus are being strengthened.

Thus the present invention has a step of one phosphate injection for the purpose of removing the phosphorus, and the ionized zinc (Zn ^{2 +)} is contained in the incoming sewage injected into the flocculant prevent flow into the river water removing phosphate may be further provided with .

That is, the concentration of phosphate contained in the aeration tank effluent can be measured periodically, and the amount of coagulant to be injected can be determined according to the measured result.

The iron salt coagulant is preferably ferrous sulfate (FeSO ₄ ), ferric sulfate (Fe ₂ (SO ₄ ) ₃ ) or ferric chloride (FeCl ₃ .6H ₂ O).

When the above-mentioned iron salt is injected and stirred, the phosphate reacts with the iron salt to form iron phosphate (FePO ₄ .nH ₂ O), and the iron phosphate (FePO ₄ .nH ₂ O) Separation is easy.

Particularly, the reason why the coagulation step of removing phosphate by injecting iron salt is carried out after the aeration step in the bioreactor is because the microorganisms in the bioreactor need only take in phosphorus for the phosphate remaining after ingesting phosphorus, Can be minimized. In addition, iron phosphate (FePO ₄ .nH ₂ O), which is a reactant of iron salt and phosphate, is removed at the final precipitation step to be described later, so that a separate precipitate is not required.

Next, sewage or wastewater to which the iron salt is added is introduced into the final settling basin, and the sludge is settled and the supernatant is discharged.

The purpose of the sewage or wastewater flowing into the final sedimentation basin is to obtain the purified effluent by solid-liquid separation of the activated sludge and treated water produced during the aeration step in the bioreactor.

Thus, the microorganisms and the sewage are separated by solid-liquid separation through the final settling basin, and the supernatant is discharged. The settled sludge is returned to a partial aeration tank to maintain the microorganism concentration, and the remaining sludge is treated through the sludge treatment facility.

As described above, since the iron phosphate (FePO ₄ .nH ₂ O) formed by reacting with the iron salt flocculant injected for the purpose of removing phosphate can be removed together in the final sedimentation tank, the advantage of maximizing the efficiency of the process have.

On the other hand, an advanced treatment process can be further performed to completely remove trace organic substances contained in the discharged water of the final clarifier.

Typical examples of the above-described advanced treatment processes include an ozone oxidation process and an activated carbon adsorption process.

The ozone oxidation process is a treatment method of decomposing and purifying organics by using the strong oxidizing power of ozone. It removes organic matter by using two pathways that are directly oxidized by ozone and oxidized by OH radical generated in ozone decomposition process It will be done.

The adsorption process using activated carbon is a process for adsorbing organic substances by using activated carbon in which numerous pores have been formed, or for taking microorganisms in activated carbon to remove organic substances.

In addition to the above-described ozone oxidation process and activated carbon adsorption process, a number of advanced processes such as a Fenton oxidation process, a photocatalytic oxidation process, a separation membrane filtration process, and the like can be applied. Therefore, detailed description will be omitted.

Hereinafter, the present invention will be described in detail with reference to examples.

Example  One. Disodium hydrogen phosphate (Na ₂ HPO ₄ )of  Sedimentation reaction of zinc oxide used

An aqueous solution of about 1 M concentration was prepared using sodium phosphate dibasic as the disodium hydrogenphosphate precursor.

In order to determine the optimum conditions for sedimentation, 5 ml of aqueous solution of disodium hydrogen phosphate (0.1 M, 0.2 M, and 0.5 M) was injected into 5 ml of zinc oxide (100 ppm), followed by compounding and sedimentation reaction at room temperature for 1 hour.

Fig. 2 is a photograph showing the results of sedimentation reaction of zinc oxide and sodium phosphate. Fig. 2 (a) is a photograph taken at the start of the reaction, and Fig. 2 (b) is a photograph taken after being left for 8 hours after completion of the reaction. The reaction vessel was prepared by adding 5 ml of the previously prepared sodium phosphate aqueous solution so as to have the concentrations of (1) 0.05M, (2) 0.10M, and (3) 0.25M. As can be seen from FIG. 2, the solution was comparatively opaque when the added phosphate concentration was low (once solution), but the solution containing zinc oxide became transparent as soon as the phosphate was added at a higher concentration . Also, in FIG. 2 (b), although the image is transparent, it is confirmed that a transparent zinc compound is deposited under the glass container. This is because zinc phosphate, which is a reactant, is present in a hydrate form (Zn ₃ (PO ₄ ) ₂ .H ₂ O) and appears transparent.

Example  2. Precipitated Zinc phosphate  Transmission electron microscopy analysis of compounds

Transmission electron microscopy (TEM, JEOL, JEM-2010) analysis was performed to determine the shape and size of precipitated zinc compounds after phosphate injection into aqueous zinc oxide solution. The optimal concentration for removal of zinc deposits was determined as phosphate concentration of 0.002M per 1ppm of zinc oxide of the same volume. The analytical sample was prepared by adding 5mL of phosphate to 5mL zinc oxide and 0.2M concentration of zinc oxide.

As can be seen from FIG. 3, precipitated zinc phosphate (Zn ₃ (PO ₄ ) ₂ ) produced large sized compounds and exhibited aggregated sol form. In addition, it was confirmed that zinc oxide particles in the aqueous solution were surely separated by generating precipitated particles in micrometer units.

Example  3. Aqueous phase  Zinc oxide ( ZnO ) Removability  analysis

In order to confirm the possibility of removal of the zinc oxide material in the aqueous solution by the precipitation reaction of zinc oxide according to Example 1, 5 ml of 0.2 M sodium phosphate was injected into 5 ml of zinc oxide aqueous solution of 100 ppm, which is the condition of Example 2 Zeta potential, pH, zinc concentration in the supernatant, initial coagulation rate, sedimentation rate, etc. were measured and the results are shown in Table 1.

Sample ZnO 100 ppm ZnO + Na ₂ HPO ₄ Zeta (mV) 42.26 0.51 pH 7.95 10.03 Concentration (ppm) > 100 0.147 HDD (nm) 65-70 sediments Initial aggregation rate (m ³ / sec) 5.589E-28 not measurable Sedimentation rate (탆 / min) 44 8,014 Removal efficiency (%) - 99.99

As can be seen from Table 1, the surface charge shows positive (+) value of about 42 mV before the reaction but shows almost zero at the time of the phosphate treatment, indicating that there is no ionic substance having charge in the solution have. The concentration of zinc oxide in the supernatant was 100 ppm before the addition of the phosphate, but it was lowered to 0.147 ppm after the addition of the phosphate, and almost 100% of the zinc oxide was removed.

Claims (5)

A first precipitation step in which sewage or wastewater containing zinc oxide is introduced into a primary settling column to deposit soil or sand;
A second precipitation step in which sewage or wastewater having undergone the primary precipitation step is flowed into a secondary settler so that a material having a specific gravity smaller than water is suspended and a material having a specific gravity larger than that of water is precipitated;
Measuring the concentration of zinc oxide in the sewage or wastewater through the secondary precipitation step and injecting phosphate;
Introducing the phosphate-infused sewage or wastewater into the bioreactor and aeration;
Measuring the phosphate concentration of the sewage or wastewater through the aeration step and adding the iron salt;
Introducing the iron salt-added sewage or wastewater into the final settling basin, thereby precipitating the sludge and discharging the supernatant; And
Characterized in that said discharged supernatant is subjected to an activated carbon adsorption process and / or an ozone oxidation process.
2. The method of claim 1, wherein in the step of injecting the phosphate, the step of stirring and the step of precipitating are further performed so that the zinc oxide of the sewage or wastewater that has undergone the second precipitation step reacts with the injected phosphate. A method for treating sewage or wastewater containing zinc oxide.
The method according to claim 2, further comprising the step of discharging the zinc phosphate hydrate (Zn ₃ (PO ₄ ) ₂ .H ₂ O) precipitated by reaction with the phosphate to the outside, How to treat wastewater.
The method of claim 3, wherein the phosphate is disodium hydrogen phosphate (Na ₂ HPO ₄ ).
5. The method of treating sewage or wastewater according to claim 4, wherein the concentration of the phosphate is 0.05 to 1M.

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