KR19990016344A - Wastewater Treatment Method Using Reverse Osmosis and Nano Filter System - Google Patents

Abstract

The present invention is to provide a more efficient wastewater treatment method that can not only increase the recovery rate of the total permeate, but also reduce the wastewater discharge by reprocessing the concentrated water generated in the reverse osmosis system using a nano-filter system, the purpose of have.

The present invention for achieving the above object, the pretreatment step of removing particulate matter, organic components and foreign matter in the waste water; Removing the inorganic ions from the wastewater by passing the wastewater having undergone the pretreatment through a first reverse osmosis system; Passing the concentrated water excluded from the first reverse osmosis system through a nanofilter system to remove polyvalent ions in the wastewater; And it relates to a wastewater treatment method using a reverse osmosis and nano-filter system comprising the step of removing the monovalent ions in the permeated water that has passed through the nano-filter system using a secondary reverse osmosis system.

Description

Wastewater Treatment Method Using Reverse Osmosis and Nano Filter System

The present invention relates to a method for treating wastewater using reverse osmosis and nanofilter systems, and more particularly, to increase the recovery rate of wastewater by reprocessing concentrated water generated during the wastewater treatment process using a reverse osmosis system and a nanofilter system. It relates to a wastewater treatment method.

Wastewater treatment systems are discharged by treating them within legal emission limits using methods such as flocculation, sedimentation, biological treatment, and filtration. However, these effluents cannot be directly reused as industrial water due to the high content of inorganic ions that cause corrosion and scale generation of pipes. Therefore, these wastewaters are generally reused as industrial water after removing inorganic ions using a membrane method, an evaporation method, and an electrodialysis method.

Reverse osmosis is a technique for removing inorganic ions in water by using reverse osmosis. Reverse osmosis membranes have a rejection rate of about 90% or more for all ions in water. In contrast, the nanofilter method using a nanofilter membrane has a rejection ratio of about 50-80% or more for divalent or higher polyvalent ions, but a relatively low exclusion rate of 20-50% for monovalent ions.

When the influent wastewater is pressurized using a high pressure pump and then introduced into the membrane module, the wastewater is divided into permeate and membrane concentrated water. In this case, the ratio of the amount of permeated water to the inflow water is expressed as a percentage. As a representative example of wastewater treatment and reuse using separation membranes such as reverse osmosis membranes, steel wastewater treatment method by reverse osmosis membrane method (Korean Patent Publication No. 95-8371), plating wastewater treatment method and apparatus by hybrid system of reverse osmosis pressure and ferrite method (Korean patent 95-17747), method and device for treating radioactive laundry wastewater using a combination process of reverse osmosis membrane and ultrafiltration membrane (Korean Patent Publication No. 93-20489), non-discharge of wastewater by a hybrid system of chemical precipitation and precision and nanofiltration (Korean Patent Publication No. 95-11344) and the like.

However, if high concentration is used to increase the recovery rate by reverse osmosis, the inorganic ions in the wastewater precipitate as inorganic salts and form scales in the reverse osmosis membrane module, thereby rapidly decreasing the efficiency of the reverse osmosis membrane. There is a limit to recovery.

Therefore, the present inventors repeated the research and experiment to increase the recovery rate of the permeated water during the wastewater treatment, the present invention was proposed based on the results, the present invention is again nano-filter the concentrated water generated in the reverse osmosis system The purpose of the present invention is to provide a more efficient wastewater treatment method which can reduce the amount of wastewater discharged as well as increase the recovery rate of the total permeate by reprocessing using the system.

1 is a process diagram showing one example of an arrangement of devices for carrying out the method according to the invention.

The present invention for achieving the above object is a pretreatment step of removing particulate matter, organic matter and foreign matter in the waste water; Removing the inorganic ions from the wastewater by passing the wastewater having undergone the pretreatment through a first reverse osmosis system; Passing the concentrated water excluded from the first reverse osmosis system through a nanofilter system to remove polyvalent ions in the wastewater; And removing the monovalent ions from the permeated water that has passed through the nanofilter system using a secondary reverse osmosis system.

Hereinafter, the present invention will be described in more detail.

Wastewater treatment according to the present invention is subjected to a pretreatment process to remove particulate matter, organic matter and foreign matter in the wastewater.

The pretreatment can be performed by a conventional method, for example, as follows. That is, the large-diameter particulate material in the waste water is removed by the multilayer filter consisting of sand and anthrasite, and the organic matter in the waste water is removed by using the activated carbon adsorption column. Preprocessing such as removal is performed.

In the present invention, the wastewater passed through the pretreatment step is passed through a first reverse osmosis system to remove the inorganic ions in the wastewater.

The reverse osmosis membrane module of the reverse osmosis system may be generally used, but it is more preferable to use a disk-tube type module, which is a kind of plate type, which has relatively low membrane fouling and excellent membrane cleaning effect, instead of the conventional spiral module. . These modules can be applied in multiple stages, for example, by arranging seven to four in one stage, two in two stages and one in three stages to achieve a recovery rate of approximately 75% overall. It can be mentioned. At this time, the permeate is sent to the treated water storage tank and the concentrated water is sent to the primary reverse osmosis system concentrated water storage tank.

In the present invention, the concentrated water excluded from the first reverse osmosis system is passed through a nano-filter system to remove polyions in the wastewater.

High concentration concentrated water excluded from reverse osmosis system is concentrated 4 times, so it passes through nano filter system to remove polyvalent ions (Ca ⁺² , Mg ⁺² , SO ₄ ^-2 ) which are major scale causing substances in wastewater. For example, a nanofilter system may be such that 60 disk-tube modules are arranged in series. The permeate passing through the nanofilter is sent to the nanofilter permeate reservoir and the concentrated concentrate is circulated. Flows into the tank. Supersaturated inorganic salts (CaCO ₃ , CaSO ₄ ) in the sulfur tank are discharged to the outside with concentrated water in the form of crystals, and the supernatant is flowed back into the nanofilter system with the same amount of influent as the discharged nanofilter concentrate. As a result, the driving rate is about 95%.

In the present invention, the permeated water that has passed through the nanofilter system is subjected to a process of removing monovalent ions using a secondary reverse osmosis system.

The permeate which has passed through the nanofilter has a monovalent ion ^- with such a large amount because it is dissolved again by using the other secondary reverse osmosis system can be transmitted after removing the inorganic ion is transmitted through the first reverse osmosis system (Na ^+, Cl) It is sent to the treated water reservoir and combined. The secondary reverse osmosis system may be composed of a plurality of stages, it is preferable to use a two-stage configuration.

Hereinafter, the present invention will be described through examples.

Example

The effluent discharged from the wastewater treatment plant was treated in a process as shown in FIG. 1 according to the method of the present invention.

In this case, seven primary reverse osmosis membrane modules are configured in a 4: 2: 1 arrangement, and 60 nanofilter modules are configured in series. In addition, the second reverse osmosis module is composed of two stages. The module used in this embodiment is a disc-tube type product manufactured by Rochem, Germany.

After the pretreatment process (1), the inflow rate of the primary reverse osmosis system (2) was 2,800 l / min and the flow rate of the permeate was 2,100 l / min with a recovery rate of 75%. The operating pressure of the system was 30-60 bar.

The flow rate of the nanofilter system 3 was 700 l / min, the flow rate of the permeate was 665 l / min, and the recovery was 95%. The operating pressure of the system was 10-15 bar.

The inflow rate of the secondary reverse osmosis system 4 was 665 L / min and the flow rate of the permeate was 500 L / min with a recovery of 75%. The operating pressure of the system was 30-60 bar.

The operating pressure for each device, the flow rate and the recovery rate of the inflow and permeate water are shown in Table 1 below.

Driving force (bar) Flow rate (ℓ / min) % Recovery Influent Permeate Primary Reverse Osmosis System 30-60 2,800 2,100 75 Nano filter system 10-15 700 665 95 Secondary reverse osmosis system 30-60 665 500 75

Next, the water quality change of the wastewater operated under the above conditions was examined.

The electrical conductivity of the influent of the first reverse osmosis system was 3,200 ㎲ / cm and the rejection rate was 98%.

The conductivity of the nano-filtered influent was 9.500 kW / cm and the permeate had a conductivity of 7,200 kW / cm, with an exclusion rate of 24%.

The second conductivity of the reverse osmosis system was 7,200 mW / cm, and the permeate was 92 mW / cm. The rejection rate was 98%.

Table 2 shows the change in the water quality (electric conductivity) of the influent and the permeate by each device.

Conductivity (㎲ / cm) % Rejection Influent Permeate Primary Reverse Osmosis System 3,200 50 98 Nano filter system 9,500 7,200 24 Secondary reverse osmosis system 7,200 92 98

According to the method of the present invention as described above, not only can 90% or more of the waste water be recovered and reused as industrial water, but also its water quality is much better than that of general industrial water. In addition, the amount of wastewater discharged to less than 10% can minimize the capacity of after-installation equipment when the wastewater discharge technology is applied.

Claims (2)

A pretreatment step of removing particulate matter, organic matter and foreign matter from the waste water; Removing the inorganic ions in the wastewater by passing the wastewater having undergone the pretreatment through a first reverse osmosis system; Passing the concentrated water excluded from the first reverse osmosis system through a nanofilter system to remove polyvalent ions in the wastewater; And removing monovalent ions from the permeated water that has passed through the nanofilter system using a secondary reverse osmosis system. The method of claim 1, wherein the first and second reverse osmosis systems and / or modules in the nanofilter system use a disk-tube type module.