KR0153722B1 - Method of waste water treatment using chemical precipitation microfiltration nanofilteration hybrid system - Google Patents

Abstract

Wastewater comprising passing the wastewater through a neutralization device and a chemical precipitation treatment device, passing the effluent from the chemical precipitation treatment device to a microfiltration device, and passing the effluent from the microfiltration device to a nanofiltration device. In the treatment method, a wastewater treatment method that removes components that interfere with wastewater reuse from wastewater containing high concentrations of inorganic ions prevents flux reduction due to membrane contamination, improves the water quality of the treated water, and increases the washing cycle. It is an efficient, economical and simple zero discharge system with the advantages.

Description

[Name of invention]

Wastewater Treatment Method Using Chemical Sedimentation-Microfiltration-Nanofiltration System

[Background of invention]

[Field of Invention]

The present invention relates to a method for removing wastewater reuse barriers, and more particularly, to a wastewater treatment method using a chemical precipitation microfiltration and nanofiltration complex system for removing wastewater reuse barriers from wastewater to reuse treated water. It is about.

[Prior art]

Wastewater of harmful substances used in various industrial fields of industrialization, especially wastewater in the glass industry, is a strongly acidic wastewater containing a large amount of fluorine and heavy metals, and if discharged as it is, serious environmental problems are raised. In addition, even when neutralizing or diluting to some extent to lower the residual concentration of harmful components and then discharge the treated water, these components are concentrated in the soil or increase the pollution of water resources, which in turn will be harmful to the human body. Therefore, wastewater discharge thresholds in environmental legislation for these components are becoming increasingly stringent.

However, no matter how stringent the wastewater discharge standard is, the method of discharge may cause the above-mentioned soil concentration or water quality deterioration. Therefore, this is not a fundamental measure to solve the environmental pollution problem. The primary way to prevent environmental pollution is to recycle the treated water after proper treatment using a zero discharge system without discharging the wastewater. In particular, wastewater neutralized and chemically precipitated by slaked lime has been mostly discharged after dilution to meet water quality standards. However, this is not a way to reduce the total amount of pollutants released to the outside. In order to solve this problem, instead of discharging the chemically settled wastewater, it is necessary to develop a technology that prevents the discharge of pollutants to the outside by reducing the use of industrial water by reusing the treated wastewater as process water. Do.

However, the wastewater after the chemical precipitation treatment has a high degree of supersaturation of the inorganic salts, so when used as process water, sediment accumulates in pipes and tanks. It is also unsuitable for the use of chemically precipitated waste water as product wash water due to the degradation of the product by evaporation residues. Therefore, in order to reuse such wastewater as process water, it is necessary to lower the concentration of the waste-disturbing components.

Various methods such as ion exchange, electrodialysis and reverse osmosis have been used to reduce the concentration of components and the like. When the chemically treated wastewater is injected into the above-mentioned devices, the solids (TDS) content in the influent to be subjected to the chemical precipitation treatment is so high that the device is overloaded so that the water quality of the treated water is deteriorated and its performance is deteriorated. As a result, additional equipment is required, which increases the complexity and cost of the process.

Nano-filtration method (Nanofiltration) is added to the water pressure as the radius that it separates out of a material that can not pass through the membrane by to escape from the water through the membrane technique is not less than 10 ^-9 m almost any material can be separated from the water have. In other words, the nanofiltration method is a separation technology that improves the reverse osmosis method that can filter almost any substance other than water, and thus has a high treatment capacity even at low pressure, thereby reducing energy cost and device cost. The nanofiltration membrane has a high removal rate for the divalent ions that cause deposit formation, compared to the removal rate for other ions. No overload Therefore, since the water quality of the wastewater treated by nanofiltration is very good and no additional treatment is required, the process is simplified and effective, and the treatment efficiency is stable because it does not depend greatly on the variation of the load.

However, in the conventional ion removal technology using nanofiltration membranes, the problem of flux reduction due to membrane contamination was serious. Low fluxes are critical to the economics of the process, as the capacity to process per unit time is small. Continuous recycling of the concentrate into the nanofiltration system in order to obtain the maximum amount of filtrate from a certain amount of influent has led to a further reduction in flux, which has been a major obstacle to the practical use of the process.

U.S. Patent 4,994,882 and U.S. Patent 4,981,594 describe a zero discharge-free system by nanofiltration. In the hybrid membrane seperation systems of U.S. Patent No. 4,994,882, reverse osmosis, nanofiltration, membrane distillation and permeation evaporation can be used as separation techniques of organic solvents to separate organic solvents and solutes. One of the processes such as pervaporation and one of the solute separation processes, a permeation method, a supported liquid membrane, a coupled transport membrane, and a membrane contactor were combined.

The waste water purification system of US Pat. No. 4,981,594 combines sand filtration, sterilization and nanofiltration to treat wastewater from a cooling tower. However, in this system, since the nanofiltration method is directly re-injected into the module, there is a problem of reducing flux due to membrane contamination. In order to solve this flux reduction problem, an antiscalent was added. However, when this sediment generating inhibitor acts on a zero discharge system, it accumulates in the wastewater and has a fatal drawback that reduces the efficiency of the chemical precipitation step.

In addition, both of the above systems are intended to separate volatile organic solvents and solutes, and are not techniques for removing supersaturated salts and solid components, which are reusable interference components in the wastewater. In addition, none of these systems combines microfiltration and nanofiltration as in the present invention, and does not play a role of improving the water quality by lowering the ion concentration in the filtered water, due to chemical precipitation reaction on the surface of the nanofiltration membrane. There is no function to prevent flux reduction.

[Summary of invention]

The present inventors have proposed a chemical precipitation-microfiltration-nanofiltration combination system as a simple and effective wastewater-free-reuse technique.

It is an object of the present invention to significantly simplify the process of producing process water from wastewater by removing supersaturated salts and solids, which are components that prevent the wastewater from being reused as process water, from chemically treated wastewater, and to provide high quality industrial water for a short time. It is to provide a wastewater discharge-free reuse technology that can be obtained.

Another object is to provide a zero discharge-reuse technique that prevents flux reduction due to membrane fouling using a microfiltration-nanofiltration combination system that is superior to methods using precipitate generation inhibitors to prevent deposit formation.

In order to achieve the above object, the present invention is to pass the waste water through the neutralization device and / or chemical precipitation treatment device, the effluent from the chemical precipitation treatment device through the microfiltration device, A wastewater treatment method comprising a step of passing effluent through a nanofiltration device, and provides a wastewater treatment method for removing a component that prevents wastewater reuse from wastewater containing a high concentration of inorganic ions.

And a first means for neutralizing and / or chemically precipitating the waste water, a second means for microfiltration of the effluent from the first means, and a third means for nanofiltration of the effluent from the second means. It provides a precipitation-microfiltration-nanofiltration complex system.

The nanofiltration device of the present invention includes a polymer membrane having a high divalent ion removal rate and an operating pressure of 5 to 20 atm, and the module of the membrane is preferably flat or spiral.

The microfiltration device of the present invention preferably includes a polymer membrane or cartridge filter having a pore size of 0.2 to 50 µm.

[Brief Description of Drawings]

1 is a schematic diagram of a complex system according to the present invention.

2 is a graph showing the flux of the wastewater treated according to the first embodiment of the present invention using a concentration factor.

3 is a graph showing the flux of the wastewater treated according to the second embodiment of the present invention using a concentration factor.

Detailed description of the invention

In the present invention, instead of re-injecting the concentrated water directly into the nanofiltration device without microfiltration, it is circulated by injecting into the nanofiltration device after an intermediate treatment through microfiltration. Therefore, the flux reduction due to the membrane contamination is prevented, the water quality of the treated water is improved, and the washing cycle of the membrane is increased, thereby greatly improving the efficiency and economic efficiency of the nanofiltration process.

The pore size of the cartridge filter or polymer membrane used for microfiltration is 0.2 to 50 µm depending on the quality of the concentrated water.

In order to improve the efficiency of the nanofiltration membrane, the operating pressure of the nanofiltration membrane for maintaining the high value of the filtration water is preferably 5 to 20 atm, and the module of the nanofiltration membrane is preferably flat or spiral.

The following examples further illustrate the invention but do not limit the scope of the invention.

Example 1

In Doosan Glass Co., Ltd., Gwangju, Gyeonggi-do, wastewater generated during the surface polishing process of crystal glass was passed through the neutralization and chemical precipitation apparatus 1 of FIG. 1, and the effluent water from the chemical precipitation apparatus 1 was After passing through the microfiltration apparatus 2, the elution water from the microfiltration apparatus 2 was then injected into the nanofiltration apparatus 3 of FIG. The flow rate on the membrane surface was 1.9 m / sec, the operating pressure was 10 atm, and the temperature was 30 deg. The module of the nanofiltration film used a flat plate type. The pore size of the cartridge filter used was 0.45 mu m.

Comparative Example 1

Wastewater was treated in the same manner as in Example 1 except that the nanofiltration method was not used.

In order to find the optimum operating conditions, the flux was measured while changing the transmembrane pressure, and the water quality of the permeate and the retentate was analyzed.

The results of measuring the concentration and removal rate of ions in the influent and filtered water treated by Example 1 according to the present invention are shown in Table 1 below. Ion concentration in Table 1 was measured by ion chromatography (device name: DIONEX Series 4500i), and the removal rate (%) was calculated by the following equation.

2 shows the flux of Example 1 and Comparative Example 1 using the concentration factor. As shown in FIG. 2, the flux of Comparative Example 1 decreases very rapidly while the flux of Example 1 according to the present invention decreases very gently. As shown in Table 1, the removal rate of divalent ions is at least 97%, and the removal rate of total dissolved solids is at least 80%.

Example 2

The wastewater was treated in the same manner as in Example 1 except that the flow rate of the membrane surface was 0.6 m / sec and the module of the nanofiltration membrane was helical.

Comparative Example 2

Wastewater was treated in the same manner as in Example 2 except that the nanofiltration method was not used.

3 shows the flux of Example 2 and Comparative Example 2 using the concentration factor. As shown in FIG. 3, the flux of Comparative Example 2 decreases sharply while the flux of Example 2 decreases very slowly.

The pore size of the cartridge filter or microfiltration membrane used in the intermediate treatment of the concentrated water is appropriately 0.2 to 50 µm depending on the quality of the concentrated water, and the flux of the concentrated water is 40 L under operating conditions of 10 atm and 25 to 30 ° C. A maximum effect was obtained at / m 2 / h or more.

In conclusion, the way to obtain the maximum amount of filtered water from a certain amount of influent is to recycle the concentrated water into the nanofiltration device. However, this method of recycling of the concentrated water causes fouling of the membrane, leading to flux reduction and water quality deterioration. In order to prevent flux reduction and water quality deterioration due to membrane contamination generated when recycling the concentrated water according to the prior art, the present inventors nanotreated the concentrated water after the intermediate treatment of the concentrated water through the microfiltration method in the present invention. The technique of reinjecting into the device was used.

The present invention is a non-discharge recirculation system that can obtain a high quality treated water irrespective of time and process load changes, and the present invention can produce the process water in a simple process because no steps such as flocculation and precipitation are necessary. Thus, the site and manpower are greatly reduced, and the control and operation of the process is simplified.

The technology for removing wastewater-free-reuse interfering components by the chemical precipitation-microfiltration-nanofiltration combination system of the present invention is to re-use the highly concentrated inorganic wastewater containing a large amount of fluorine and heavy metals after neutralization and chemical precipitation treatment. Can be used for In particular, it is effective when the wastewater generated in the surface treatment process of the glass industry and the electronics industry is desired to be discharge-free.

Claims (6)

Passing the waste water through the neutralization device and / or the chemical precipitation treatment device; Passing the effluent from the chemical precipitation treatment device through a microfiltration device; Passing the effluent from the microfiltration device through a nanofiltration device; A wastewater treatment method comprising a step, the wastewater treatment method of removing a component that prevents wastewater reuse from wastewater containing a high concentration of inorganic ions. The method of claim 1, wherein the nanofiltration device comprises a polymer membrane having a high divalent ion removal rate, an operating pressure of 5 to 20 atmospheres, and the module of the membrane being flat or spiral. The method of claim 1, wherein the microfiltration device has a polymer membrane or cartridge filter having a pore size of 0.2 to 50 µm. First means for neutralizing and / or chemically precipitation the wastewater; Second means for micro filtration of effluent from said first means; Third means for nanofiltration of effluent from the second means; Chemical precipitation-microfiltration-nanofiltration complex system comprising. 5. A composite system according to claim 4, wherein the third means comprises a polymer membrane having a high divalent ion removal rate and an operating pressure of 5 to 20 atm, and the module of the membrane is flat or spiral. The complex system according to claim 4, wherein the second means is a polymer membrane or a cartridge filter having a pore size of 0.2 to 50 µm.