KR20170088585A - Method for removing titanium oxide in sewage or wastewater - Google Patents

Abstract

The present invention relates to a method for removing titanium dioxide included in a water system comprising: a first precipitating step of introducing sewage or waste water including the titanium dioxide to a first setting pond, and precipitating soil or sand; a second precipitating step of introducing the sewage or the waste water of the first precipitating step to a second setting pond, floating a smaller matter than water, and precipitating a larger matter than the water; a step of introducing the sewage or the waste water of the second precipitating step to a bioreactor, and aerating the same; a step of introducing leakage water of the bioreactor of the aerating step to the final setting pond, precipitating sludge, and discharging supernatant; a step of absorbing the discharged supernatant to activated carbon; and/or a step of oxidizing the discharged supernatant as ozone. Particles of the titanium dioxide are aggregated by applying more than 5 mA/cm^2 current in the supernatant discharging step. An electricity aggregating process for aggregating residual pollutants of the supernatant, and titanium dioxide is performed.

Description

METHOD FOR REMOVING TITANIUM OXIDE IN SEWAGE OR WASTEWATER [0002]

The present invention relates to a method for removing titanium dioxide contained in sewage or wastewater, and more particularly, to a method for removing titanium dioxide contained in a supernatant by installing an electrocoagulation apparatus on a final settling basin.

Titanium dioxide (TiO ₂ ) is thermodynamically stable, has good whiteness and hiding power, and is widely used as a pigment for white paint such as paint, plastic, and paper. It is also widely used in the manufacture of household goods such as cosmetics, ultraviolet screening paints, fillers for tires, waveguides and non-reflecting coatings of optical devices using high refractive index, and lens additives.

However, the National Institute for Environmental Health Research (NHEERL) under the US EPA warns of the risk of nanoparticles of titanium dioxide (TiO ₂ ). Nanoparticles of titanium dioxide (TiO ₂ ), widely used in sunscreens and cosmetics, can damage nerve cells, according to a paper published in the journal Environmental Science and Technology.

Immune cells that protect mouse neurons secrete free radicals when they come in from outside. If they are exposed to titanium dioxide (TiO ₂ ) nanoparticles for more than 1 hour, they will over-secrete active oxygen, .

The toxicity of titanium dioxide (TiO ₂ ) nanoparticles is known to occur due to increased reactivity due to its large surface area.

Titanium dioxide (TiO ₂ ) nanoparticles containing this toxicity are unintentionally released during the manufacturing process, either during exposure to the workplace or during use and disposal of articles containing nanoparticles of titanium dioxide (TiO ₂ ). Occupational exposure is entrusted to my provided its own waste water treatment plant or to an external wastewater disposal service workshop to suppress the exposure of the environment, exposure by the individual consumer by flowing into the sewage treatment plant. However inhibit unintentional environmental exposure, titanium dioxide (TiO ₂ ) Contained in the final effluent is contained in a small amount even if it is properly treated in the wastewater treatment plant.

In other words, the removal efficiency of titanium dioxide (TiO ₂ ) nanoparticles is estimated to be 90 to 95% in a conventional wastewater treatment process, so 5 to 10% of the TiO ₂ nanoparticles are discharged, Moved or settled into groundwater.

On the other hand, although a method of treating wastewater using titanium dioxide (TiO ₂ ) is known, there is no technique for removing a small amount of titanium dioxide (TiO ₂ ) nanoparticles contained in wastewater.

Korean Patent Publication No. 10-2000-0067737 Korean Patent Publication No. 10-2000-0059854

It is an object of the present invention to provide a method for removing titanium dioxide which can effectively remove trace amounts of titanium dioxide (TiO ₂ ) nanoparticles contained in sewage or wastewater.

In order to accomplish the above object, the present invention provides a method of treating sewage or wastewater containing titanium dioxide, comprising the steps of: a first precipitation step of introducing soil or wastewater containing titanium dioxide into a first settling tank to deposit soil or sand; A second precipitation step in which sewage or wastewater having undergone the first precipitation step is introduced into a secondary precipitation tank to float the material having a specific gravity smaller than that of water and precipitate the material having a specific gravity larger than that of water, Or wastewater into a bioreactor to aerate the bioreactor effluent; a step of introducing the effluent of the bioreactor that has undergone the aeration step into the final clarifier to settle the sludge and discharge the supernatant; and adsorbing the discharged supernatant with activated carbon and / And a step of oxidizing the titanium dioxide by applying a current of 5 mA / cm < 2 > or more in the supernatant discharging step, To each other or aggregated particles, characterized by carrying out electric coagulation of coagulation of contaminants and titanium dioxide remaining in the supernatant.

The method for treating titanium dioxide-containing sewage or wastewater according to the present invention is characterized in that the electrocoagulation apparatus in the electrocoagulation step is installed in the vicinity of the weir of the final clarifier having a low flow rate of the supernatant.

According to the method of treating sewage or wastewater according to the present invention, an electrocoagulation process is performed on a supernatant of a final settling basin, thereby effectively removing minute amounts of titanium dioxide nanoparticles contained in sewage or wastewater .

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a flowchart showing a method for removing titanium dioxide according to the present invention. FIG.
2 is a cross-sectional view of the final settling tank equipped with an electrocoagulation device

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 for treating sewage or wastewater containing titanium dioxide (TiO ₂ ) of the present invention will be described in detail with reference to FIG. 1 attached hereto.

The method of treating sewage or wastewater containing titanium dioxide (TiO ₂ ) of the present invention is a method of treating sewage or wastewater containing titanium dioxide (TiO ₂ ) by introducing sewage or wastewater containing titanium dioxide (TiO ₂ ) into a primary settler, A second precipitation step in which sewage or wastewater having undergone the first precipitation step is flowed into a secondary precipitation tank to suspend a material having a specific gravity smaller than that of water and precipitate a material having a specific gravity greater than that of water, A step of introducing the effluent of the bioreactor having passed through the aeration step into the final settling basin to deposit the sludge and discharge the supernatant, and adsorbing the discharged supernatant to the activated carbon and / or jidoe comprises the step of oxidation with ozone, the supernatant was applied over the titanium dioxide 5㎃ / ㎠ current from the output stage (TiO ₂₎ particles caught Increase or aggregation, characterized in that the conducting electric coagulation to flocculate pollutants and titanium dioxide (TiO ₂₎ remaining in the supernatant.

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, a considerable amount of titanium dioxide (TiO ₂ ) nanoparticles contained in the inflow sewage or wastewater remains without being removed.

That is, titanium dioxide (TiO ₂ ) nanoparticles are in a colloidal state, so they are not easily precipitated by gravity, and the surface charge of the nanoparticles is close to neutrality, so that they do not bond with other species or the like.

The second settling effluent containing titanium dioxide (TiO ₂ ) nanoparticles is then introduced into the bioreactor and aerated.

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.

Next, the effluent of the bioreactor, which has been subjected to the aeration step to remove the organic matter, is introduced into the final settling basin.

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.

Here, in the step of discharging the supernatant, an electric current of 5 mA / cm 2 or more is applied to agglomerate the titanium dioxide (TiO ₂ ) particles or an electrocoagulation process in which the contaminants remaining in the supernatant and the titanium dioxide are agglomerated.

The above-described electrocoagulation process corresponds to a main feature of the present invention, and it is possible to completely remove minute amounts of titanium dioxide (TiO ₂ ) nanoparticles remaining in the supernatant through electrocoagulation.

In other words, titanium dioxide (TiO ₂₎ When performing electric coagulation to supernatant containing the nanoparticles, titanium dioxide (TiO ₂₎ nanoparticles surface is significantly more than the charge -30mV, due to this surface charge of titanium dioxide (TiO ₂ ) Coalesce with each other or bind with pollutants in the supernatant, and as a result, they are precipitated by their own weight.

Particularly, in order to more effectively remove titanium dioxide (TiO ₂ ) nanoparticles by the electrocoagulation process, an electrocoagulation apparatus can be installed in the vicinity of the precipitation tank in the present invention.

In general, in the vicinity of the settling tank, the flow rate is very low so that the fine particles are not discharged into the supernatant, and this low flow rate can easily control the charge of the TiO ₂ nanoparticles even if the current applied from the electrocoagulation device is low to be.

That is, as shown in FIG. 2, an electrocoagulation device may be provided inside or outside the fabric of the settling tank, and it is preferable to install the device at a position where the flow velocity is as low as possible.

On the other hand, the electrocoagulation process is simple in structure and easy to operate, and flocs formed by electrocoagulation are similar to those formed by chemical agglomeration and can be quickly separated by filtration. Also, TDS (Total Dissolved Solid) of treated water by electrocoagulation has an advantage that it is lower than that by chemical aggregation.

In addition, such electrocoagulation is known to be more economical when compared to biological processes because of less influence by temperature and large processing capacity per unit area. In particular, it can be applied to wastewater which is difficult to be biologically treated, such as heavy metal ions and cyanide ions, and is easily treated under normal temperature and pressure conditions and is not seasonally affected.

In addition, since the sludge generated by the electrocoagulation is composed of metal hydroxides, it has low sedimentation and dewatering ability due to low water content and is easily separated into solid and liquid. Since chemical treatment is not required, secondary pollution There is no possibility of.

The above-described electrocoagulation apparatus corresponds to a known technique, and a detailed description thereof will be omitted.

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  1>

An electrocoagulation experiment was conducted to remove titanium dioxide in the raw water containing titanium dioxide whose primary particle size is nanometer.

Filling the raw water having a concentration of 10ppm in a reaction tank an electrical reactor having a plate-like iron electrode installed, the enemy of 10 ~ 100cm / sec 10 mA / cm 2 while 10 minutes circulating the raw water by a pump so as to be movable in the range of within the reaction tank The concentration of titanium dioxide (TiO ₂ ) was measured after electrocoagulation treatment at a current density. The results are shown in Table 1.

Movement speed of enemy water Titanium Dioxide Concentration (ppm) Removal rate (%) 10 cm / min 0.07 99.3 30 cm / min 0.13 98.7 50 cm / min 0.16 98.4 80 cm / min 1.32 86.8 100 cm / min 2.63 73.7

As can be seen from Table 1, it was confirmed that the removal rate of titanium dioxide was drastically lowered as the moving speed of raw water was faster.

< Example  2>

An electrocoagulation experiment was conducted to remove titanium dioxide in the raw water containing titanium dioxide whose primary particle size is nanometer.

The raw water having a concentration of 10 ppm was filled in a reaction tank equipped with a plate type iron electrode and the concentration of titanium dioxide (TiO ₂ ) was measured after reacting for 10 minutes while varying the current applied to the electrode. The results are shown in Table 2.

Current density Titanium Dioxide Concentration (ppm) Removal rate (%) 1 mA / cm ² 3.06 69.4 3 mA / cm ² 1.52 84.8 5 mA / cm ² 0.16 98.4 8 mA / cm ² 0.09 99.1 10mA / cm ² 0.07 99.3

As can be seen from Table 2, it can be seen that the higher the current density, the higher the removal rate of titanium dioxide.

Claims (2)

A primary precipitation step of introducing sewage or wastewater containing titanium dioxide into a primary settling basin 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;
Introducing sewage or wastewater having undergone the second precipitation step into a bioreactor to aerate it;
Introducing the bioreactor effluent having passed through the aeration step into the final settling basin to deposit the sludge and discharge the supernatant; And
Adsorbing the discharged supernatant with activated carbon and / or oxidizing it with ozone,
Wherein an electric current of 5 mA / cm &lt; 2 &gt; or more is applied in the step of discharging the supernatant water to coagulate the titanium dioxide particles, or an electrocoagulation process of coagulating the contaminants remaining in the supernatant and the titanium dioxide is carried out. Or treating wastewater.
The method according to claim 1, wherein the electrocoagulation device in the electrocoagulation step is installed in the vicinity of the weir of the final clarifier having a low flow rate of the supernatant.

Images