Reverse osmosis pressure water treatment system using re-generated membrane

Abstract

The present invention relates to a reverse osmosis water treatment system comprising: a second- stage LSRRO (Low Salt Rejection RO membrane process) unit using a regenerated membrane as a reverse osmosis (RO) membrane, said regenerated membrane being obtained by subjecting a damaged membrane or a membrane which has reached the end of its service life to a physical and / or chemical treatment for reuse. The present invention comprises: an intake unit including an inlet line for seawater or organic wastewater equipped with an inlet valve, a raw water storage tank for storing the seawater or organic wastewater as raw water, and a feed pump for pressurizing the raw water at a predetermined flow rate and pressure at predetermined intervals; a pre-treatment unit including an ultrafiltration (UF) membrane or microfiltration (MF) membrane for removing fine particulate organic matter contained in the raw water to reduce the load on a downstream reverse osmosis (RO) membrane; and a first-stage RO (Reverse Osmosis) process unit to separate ionic substances included in the filtered water pre-treated by the UF or MF membrane using a reverse osmosis membrane to produce treated water and to separate the raw water into treated water and concentrated water. According to the present invention, there is an advantage in that an LSRRO system can be provided which concentrates raw water to a high concentration with lower energy consumption than conventional RO systems employing commercial membranes.

Description

[0001] REVERSE OSMOSIS PRESSURE WATER TREATMENT SYSTEM

[0002] USING RE-GENERATED MEMBRANE

[0003] FIELD OF THE INVENTION

[0004] This invention relates to a reverse osmosis water treatment system using a regenerated membrane obtained by regenerating a spent membrane. More particularly, the present invention relates to a reverse osmosis water treatment system using a regenerated membrane obtained by subjecting a membrane damaged or having reached the end of its service life in a reverse osmosis seawater desalination system to physical and chemical treatment for reuse as a reverse osmosis (RO) membrane.

[0005] BACKGROUND OF THE INVENTION

[0006] Typically, seawater desalination refers to a series of water treatment processes that remove dissolved substances, including salts, from seawater, which is normally difficult to use directly as domestic or industrial water, to produce high-purity drinking water, domestic water, industrial water, and the like. As processes used in seawater desalination plants, evaporation and reverse osmosis are the most popular. Recently the market share of seawater desalination technology using reverse osmosis, which has a lower water production cost than evaporation, is increasing. Due to the rapid development of industry in recent years, the proportion of inorganic and organic components in drinking water and sewage / wastewater has been steadily increasing with the increased use of various water resources, and various filtration technologies have been developed to purify this water. As part of these filtration technologies, membrane filtration processes are used. Generally, in water treatment for the purification of sewage / wastewater or contaminated water (hereinafter collectively referred to as "wastewater" for convenience), product water is obtained by filtering contaminants in the wastewater using a membrane.

[0007] However, these membrane filtration processes have the disadvantage of fouling over time, which degrades the performance of the membrane. Fouling refers to the accumulation of suspended solids, contained in water or substances with properties that are readily adsorbed onto the separation membrane surface, on the surface and within its pores, impeding fluid flow and reducing permeability. However, since fouling is not a deterioration of the membrane itself, but a reduction in membrane performance due to contaminants, performance can be restored by membrane cleaning. Methods for cleaning membrane foulants can be broadly divided into physical methods and chemical methods using chemical agents.

[0008] The conventional techniques of removing contaminants from the membrane is regeneration by backwashing. However, the regeneration efficiency varies depending on the backwash cycle, backwash pressure, amount of cleaning water, flow rate, etc. However, these conventional techniques have limitations in regenerating membranes fouled by a combination of physical, chemical, and biological factors, and the regeneration methods are complex and not highly efficient.

[0009] As a result, membranes used for contaminant filtration accumulate various contaminants after a certain period of use, leading to rapid degradation (a state where the quality of the filtered water degrades to the point where the membrane can no longer be used), which results in a short life span. Therefore, deteriorated membranes need to be replaced periodically. However, these membranes are often expensive, and since the used membranes have adsorbed contaminants, their disposal without treatment can cause environmental pollution.

[0010] In addition, deteriorated membranes are typically unusable for normal desalination processes and must be disposed of, resulting in a continuous generation of environmental waste. Therefore, there is a need to reuse these membranes by regenerating them through physical and chemical treatments and thereby using them to concentrate the treated water. By concentrating reverse osmosis concentrate to a high density, it is necessary to improve the treatment efficiency of sewage / wastewater and reduce the treatment cost of concentrate, while aiming to reduce the energy consumed in boiling the treated water for concentration.

[0011] Various countries around the world are establishing regulatory standards for concentrate discharges, often expressed as limits on salinity increases due to concentrate discharges, and these regulations are gradually becoming more stringent. As the need for concentrate management has become apparent, the development of related process technologies is actively underway. Concentrate treatment methods include dilution and discharge, as well as advanced concentration technologies that minimize concentrate discharge and concentrate management technologies that recover valuable resources from concentrate.

[0012] Livestock manure wastewater, which is a type of concentrate, contains various resources and is a high-value product that can be used as fertilizer. Accordingly, various methods have been developed to utilize livestock wastewater such as swine manure, and with the advancement of separation membrane filtration technology, interest in livestock wastewater resource recovery is also increasing.

[0013] Conventional treatment methods for livestock manure, livestock wastewater, or livestock washing water include various types of physicochemical unit treatment processes and biological treatment processes, which have been used in combination depending on the treatment objectives. However, most conventional treatment methods focus on the efficient purification of livestock manure, largely excluding processes for the efficient utilization of resources. Furthermore, as the discharge standards for livestock manure, livestock wastewater, or livestock washing water become more stringent, the treatment processes become more complex to meet these standards, resulting in high-cost treatment processes that are difficult to operate and maintain.

[0014] Accordingly, for the treatment of livestock manure, livestock wastewater, or treated livestock effluent, there is a demand for environmentally friendly treatment methods that utilize advanced separation membrane processes in conjunction with various aerobic or anaerobic biological treatment processes, rather than relying solely on simple purification through biological treatment. These methods facilitate recycling through the production of liquid fertilizer or discharge, among other options.

[0015] Various anaerobic digestion (AD) technologies have been developed and applied to treat organic- rich wastes such as livestock manure, sewage sludge from wastewater treatment plants, or industrial wastewater, and to recover biogas, a valuable resource for useful in human life, from this process. Anaerobic digestion, a type of filtration technology, refers to the process by which biodegradable organic matters are broken down by microorganisms under anaerobic conditions. This decomposition process primarily generates a gaseous mixture composed of methane and carbon dioxide, which may also contain trace amounts of hydrogen, hydrogen sulfide, and ammonia. This anaerobic digestion process is also intentionally utilized for purposes such as treating waste or sewage, or for the production of fuel.

[0016] The anaerobic digestion process constitutes an efficient method of treating biomass, reducing greenhouse gas emissions and generating energy, whereby organic matter is converted into biogas, while the resulting digestate is characterized by its abundance in various resources and nutrients. In particular, the solid components obtained from the anaerobic digestion process can be utilized as soil conditioners to increase the organic matter content of soil, while the liquid components can serve as fertilizers to provide essential nutrients to the soil as a substitute for chemical fertilizers.

[0017] However, while anaerobic digestion processes can be employed for the production of concentrated fertilizers, a limitation exists due to the necessity of solid-liquid separation to achieve the requisite high recovery rates. For example, Korean Patent Publication No. 10-1393712 discloses a technology for treating liquid fertilizer produced by biologically treating livestock wastewater through a membrane separation tank, an activated carbon filtration tank, and a reverse osmosis apparatus. However, this technology has the disadvantage that the equipment itself is too large and complex, resulting in reduced utility.

[0018] Prior art documents include Korean Patent Publication No. 10-1393712 (Registration Date: May 2, 2014, Title: Method and Apparatus for Treating Livestock Wastewater), and Korean Patent Publication No. 10-0355880 (Registration Date: September 26, 2002, Title: Purification Method and Apparatus for Livestock Wastewater). SUMMARY OF THE INVENTION

[0019] In view of the problems of the prior art as described above, the technical objective of the reverse osmosis water treatment system using a recycled membrane of the present invention is to provide a reverse osmosis water treatment system that can be used to solve the problems of high cost, energy consumption, and separation membrane fouling inherent in the conventional reverse osmosis (RO) process by providing a second-stage LSRRO (Low Salt Rejection Reverse Osmosis) process unit that uses a recycled membrane, which is regenerated through physical and chemical treatment of end-of-life membranes, as a reverse osmosis (RO) membrane to recover high-value-added brine / phosphorus and other valuable resources from high- concentration wastewater centered on livestock manure.

[0020] Furthermore, the technical objective of the present invention is to provide a reverse osmosis water treatment system that can reduce environmental pollution and enable cost reduction by reusing end-of-life membranes through physical and chemical treatment.

[0021] In order to solve the aforementioned technical problems, the reverse osmosis water treatment system according to the present invention comprises: an intake unit including an inlet line for seawater or organic wastewater equipped with an inlet valve, a raw water storage tank for storing seawater or organic wastewater as raw water, and a feed pump for pressurizing the raw water at a constant flow rate and pressure according to a predetermined time; a pre-treatment unit including an ultrafiltration (UF) membrane or a microfiltration (MF) membrane for removing fine particulate organic matter contained in the raw water to reduce the load on the subsequent reverse osmosis (RO) membrane; a first-stage reverse osmosis (RO) process unit that separates ionic substances contained in the filtered water pre-treated by the ultrafiltration (UF) membrane or the microfiltration (MF) membrane using a reverse osmosis (RO) membrane to produce treated water, and separates the raw water into treated water and concentrate, and a second-stage LSRRO (Low Salt Rejection Reverse Osmosis) process unit that uses a recycled membrane, which is regenerated through physical and chemical treatment of damaged or end-of-life membranes for reuse, as a reverse osmosis (RO) membrane.

[0022] A reverse osmosis water treatment system according to an embodiment of the present invention is characterized in that the second-stage LSRRO process unit removes salt contained in seawater or organic wastewater, while lowering the salt rejection rate to 50-60%, thereby highly concentrating water that would otherwise be discarded through water treatment, and lowering the operating pressure of the feed pump as the salt rejection rate decreases, allowing the concentration process to proceed with low energy consumption.

[0023] A reverse osmosis water treatment system according to an embodiment of the present invention is characterized in that it primarily concentrates raw water using a commercial membrane through the first-stage reverse osmosis (RO) process unit, and performs the recovery of valuable resources and the adjustment of treated water concentration using a regenerated membrane through the second-stage LSRRO process unit.

[0024] A reverse osmosis water treatment system according to an embodiment of the present invention is characterized in that the treated water generated through the first-stage reverse osmosis (RO) process unit is discharged, and the treated water passed through the second-stage LSRRO regenerated membrane is circulated towards the raw water direction of the first-stage reverse osmosis (RO) process to be mixed with the raw water for use, and the concentrate generated in the first-stage reverse osmosis (RO) process unit and the second-stage LSRRO process unit is highly concentrated and stored.

[0025] A reverse osmosis water treatment system according to an embodiment of the present invention is characterized by further comprising a post-treatment process unit connected downstream of the second-stage LSRRO process unit of the reverse osmosis water treatment system, wherein valuable resources contained in the raw water are recovered in an environmentally friendly manner by an MC (membrane contractor) resource recovery process.

[0026] A reverse osmosis water treatment system according to an embodiment of the present invention is characterized in that the valuable resources contained in the raw water are more than at least one of brine, or phosphorus or potassium, or ammonia.

[0027] A reverse osmosis water treatment system according to an embodiment of the present invention is characterized in that, since the osmotic pressure changes as the concentration of the raw water changes, and the operating conditions such as operating pressure change accordingly, the operating conditions of the system are set such that the concentration of the treated water in the second-stage LSRRO process and the concentration of the raw water in the first-stage reverse osmosis (RO) process are the same.

[0028] A reverse osmosis water treatment system according to an embodiment of the present invention is characterized in that it can be configured to include a first-stage reverse osmosis (RO) process unit and a second-stage LSRRO process unit, and additionally, a process unit with three or more stages by increasing the number of stages.

[0029] A reverse osmosis water treatment system according to an embodiment of the present invention is characterized in that, when the number of stages of the reverse osmosis water treatment system is further increased, the concentrate of an n-stage process unit is used as the raw water for an (n+1)-stage process unit, and the filtrate of the n-stage process unit is used as the raw water for an (n-l)-stage process unit.

[0030] According to the present invention, the reverse osmosis water treatment system using a regenerated membrane can recover valuable resources, and these resources can be used as fertilizer, thereby reducing the use of chemical fertilizers, which not only provides economic benefits but also reduces nutrient depletion and can also decrease methane emissions.

[0031] According to the reverse osmosis water treatment system of the present invention, there is an effect of reducing environmental pollution through the reuse of annually discarded membranes and securing economic feasibility through resource recycling.

[0032] Furthermore, the reverse osmosis water treatment system of the present invention can be applied not only to the concentration of anaerobic digestate but also to the concentration process of raw water in desalination and other industries, thereby having an effect that it can be utilized in processes for the production of various concentrated substances.

[0033] Furthermore, the reverse osmosis water treatment system of the present invention has an effect of providing a regenerated reverse osmosis membrane process technology capable of treating high-concentration sewage / wastewater, including livestock manure, while recovering high value- added valuable resources such as ammonia / urea solution raw materials and phosphoric acid fertilizer raw materials from the high-concentration sewage / wastewater.

[0034] Furthermore, the reverse osmosis water treatment system of the present invention has an effect of providing a reverse osmosis membrane process technology capable of concentrating digestate from livestock manure anaerobic digestion effluent, which is wastewater containing high concentrations of nitrogen and phosphorus, with low-energy, high-flux resource recovery technology, to remove nitrogen and phosphorus while simultaneously recovering valuable resources (fertilizer).

[0035] Furthermore, the reverse osmosis water treatment system of the present invention can reduce dependence on foreign countries by securing and stockpiling urea solution through nitrogen recovery for urea solution production, the entire consumption of which is currently dependent on overseas sources, and can minimize greenhouse gas emissions and energy consumption throughout the regenerated reverse osmosis membrane process. Furthermore, the reverse osmosis water treatment system of the present invention enables the efficient utilization of waste resources that would otherwise be discarded or incinerated due to the prohibition of ocean dumping of livestock manure anaerobic digestate.

[0036] Furthermore, the present invention, through this configuration, has a functional effect of providing a reverse osmosis water treatment system that allows the concentration process to proceed with lower energy consumption than conventional RO systems using commercial membranes.

[0037] BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 is a drawing illustrating a reverse osmosis water treatment system for organic wastewater concentration and valuable resource recovery according to an embodiment of the present invention; Figure 2 is a drawing illustrating a discarded membrane and a regenerated membrane created by regenerating the discarded membrane, according to an embodiment of the present invention; and

[0039] Figure 3 is a drawing illustrating a reverse osmosis water treatment system for organic wastewater concentration and valuable resource recovery according to an embodiment of the present invention.

[0040] DETAILED DESCRIPTION OF THE INVENTION

[0041] The specific structural or functional descriptions of the embodiments of the inventive concepts disclosed herein are merely illustrative for the purpose of explaining the embodiments of the inventive concepts, and the embodiments according to the inventive concepts can be implemented in various forms and are not limited to the embodiments described herein.

[0042] Given that embodiments according to the inventive concepts of the present invention may undergo various modifications and have multiple forms, embodiments are illustrated in the drawings and will be described in detail in this specification. However, this is not intended to limit the embodiments according to the concept of the present invention to specific disclosed forms, and includes all modifications, equivalents, or substitutes that fall within the spirit and technical scope of the present invention.

[0043] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by a person having ordinary skill in the art to which this invention belongs. Terms as defined in commonly used dictionaries should be interpreted to have a meaning consistent with their meaning in the context of the relevant art, and, unless expressly defined in this specification, should not be interpreted in an idealized or overly formal sense.

[0044] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0045] Referring to Figure 1 , a reverse osmosis water treatment system for organic wastewater concentration and valuable resource recovery includes an intake unit (10), a pre-treatment unit (20), a first-stage reverse osmosis (RO) process unit (30), and a second-stage LSRRO process unit (40).

[0046] First, the intake unit (10) is for the process of drawing seawater or organic wastewater, which is raw water for desalination or wastewater purification, and allows the raw water to flow into the pre-treatment process unit (20) by passing it through devices such as a strainer and a disc filter. The intake unit (10) comprises an inlet line (11) for seawater or organic wastewater equipped with an inlet valve, a raw water storage tank for storing the seawater or organic wastewater as raw water, and a feed pump for pressurizing the raw water at a constant flow rate and pressure according to a set time.

[0047] The inlet line (11) is a piping member for introducing and supplying raw water, and it is connected downstream from a raw water storage tank (12) or a supply source that stores various raw waters such as wastewater, sewage, and water supply, thereby supplying the raw water.

[0048] The feed pump (13) is installed downstream of the inlet line (11) and serves as a pumping means for pumping and injecting raw water, supplying various raw waters such as organic wastewater, sewage, and water supply to the pre-treatment unit (20) through the pumping action of the pump. The pre-treatment unit (20) is for a process to remove suspended solids, inorganic compounds, organic pollutants, and the like, which can cause fouling or damage to the reverse osmosis membrane. At this time, the suspended solids include colloids and particulate matter; the inorganic compounds include ions, manganese, calcium carbonate, calcium sulfate, silicon dioxide, and the like; and the organic pollutants include organic matter and microorganisms in seawater. Furthermore, the pre-treatment unit (20) may include at least one of a UF process (21) and an MF process (22). Generally, the UF process (21) is composed of a pressurized hollow fiber membrane and plays a pre-treatment role of removing fine particles, turbidity, organic matter, and the like contained in raw water, thereby reducing the load on the reverse osmosis membrane of the downstream first-stage reverse osmosis (RO) process unit, and it repeats forward flushing and backwashing at regular time intervals.

[0049] Water treatment using membranes has advantages over other filtration processes in that it requires less use of chemicals such as coagulants and can reduce the required site area, and is thus widely used in the overall water treatment field. A membrane is not only suitable for general filtration, which separates undissolved particles by selectively allowing certain components to pass through, but also for the separation and removal of suspended solids such as colloids and fine particles in wastewater, and refers to a membrane made of a special material capable of separating even dissolved substances or mixed gases dissolved in a liquid.

[0050] The most important aspects of a membrane are its physical strength and the amount of high quality permeate it can produce. The water quality of membrane permeate can be selected based on the pore size of the membrane, and depending on the pore size, it can be classified into microfiltration (MF) membranes, ultrafiltration (UF) membranes, nanofiltration (NF) membranes, and reverse osmosis (RO) membranes. These membranes are classified based on their performance into microfiltration membranes (MF), ultrafiltration membranes (UF), nanofiltration membranes (NF), reverse osmosis membranes (RO), ion exchange membranes (IE), electrodialysis membranes (ED), gas separation / pervaporation membranes (GAS / PV), and hemodialysis membranes (Hem dialysis), and are appropriately selected according to their intended use.

[0051] The primary removal mechanism for microfiltration (MF) and ultrafiltration (UF) is screening. MF is primarily used to remove particles and colloids, while UF is used to remove smaller colloidal particles, high molecular weight polymers, and high molecular weight organic substances. Nanofiltration (NF) and reverse osmosis (RO) remove substances based on diffusion, electrostatic properties and size. NF is primarily used to separate and remove organic materials, while RO is capable of breaking down ionic substances and is primarily used in seawater desalination and wastewater reuse.

[0052] Additionally, said pre-treatment unit (20) should select an appropriate pre-treatment process based on surrounding conditions such as treatment scale and raw water quality. It must be configured to meet the raw water quality conditions (e.g., turbidity and / or SDI) that are acceptable for the first-stage reverse osmosis (RO) membrane process unit (30). Said pre-treatment unit (20) may include pH adjusters and scale inhibitors to remove salts, such as carbonates and calcium sulfate, that cause scaling on the reverse osmosis (RO) membrane of the first-stage RO process unit (30).

[0053] In addition, said pre-treatment unit (20) can also perform treatment of organic substances and microorganisms. For instance, fouling of the reverse osmosis membrane, which refers to the phenomenon wherein contaminants adhere to the membrane surface and cause blockage, is primarily induced by organic substances and microorganisms. The organic substances may be removed by means of coagulation, sedimentation, filtration, and disinfection processes performed in the pre-treatment unit (20), and the microorganisms may be eliminated through the use of an oxidizing agent or by implementing UV disinfection.

[0054] In addition, said pre-treatment unit (20) may employ a candle filter for separating the solid phase discharged from a centrifuge, based on ultrafiltration for pig manure digestate. Furthermore, zinc, which is commonly found as a hazardous substance in pig manure and AD digestate, may be precipitated and separated through chemical pre-treatment prior to ultrafiltration.

[0055] The first-stage reverse osmosis (RO) process unit (30) refers to a process for removing salts, ions, and organic substances from seawater that has passed through the pre-treatment unit (20) by employing the principle of reverse osmosis, wherein a semipermeable membrane used in this process is referred to as a reverse osmosis membrane. For example, the reverse osmosis membrane is manufactured and used in the process in the form of a module, and the membrane module can be classified according to its structure into types such as spiral wound, hollow fiber, tubular, and flat sheet. Membrane filtration technology is a separation process that enables the substantially complete separation and removal of target substances present in raw water and sewage / wastewater, depending on the pore size and surface charge of the membrane. The membrane is a porous membrane characterized by a high pore density, and is capable of separating various substances contained in water, including organic and inorganic contaminants, parasites, and bacteria. In general, when a semipermeable membrane is placed between two solutions of different concentrations, a phenomenon occurs in which the solvent in the lower concentration solution moves toward the higher concentration solution due to the difference in osmotic pressure; this phenomenon is referred to as osmosis. Conversely, if a pressure greater than the osmotic pressure is applied to the higher concentration solution, the solvent in the higher concentration solution will pass through the semipermeable membrane and move toward the lower concentration solution; this phenomenon is called reverse osmosis.

[0056] At this time, the desalination process using reverse osmosis is referred to as a reverse osmosis process, which comprises a high-pressure pump, a reverse osmosis membrane, and an energy recovery device. The high-pressure pump serves to provide sufficient pressure such that only water in the seawater or organic wastewater can pass through the reverse osmosis membrane. In the case of the reverse osmosis process, the technique of producing freshwater by applying a pressure greater than the osmotic pressure to seawater using a reverse osmosis membrane may be defined as reverse osmosis-based seawater desalination technology.

[0057] In addition, the reverse osmosis process is widely used not only in Korea but also worldwide due to its excellent treated water quality, small land requirement, and lower freshwater production cost compared to evaporation methods. In general, reverse osmosis seawater desalination facilities are installed and operated in domestic island regions to address water shortages. In the case of seawater desalination facilities using such a reverse osmosis process, the facilities are designed and manufactured for continuous operation, without regard to variations in the amount of water produced.

[0058] More specifically, said reverse osmosis membrane is generally formed of an organic synthetic material and may, for example, be configured as a composite membrane in which a salt rejection layer is coated on a porous support layer; however, it is not limited thereto.

[0059] The second-stage LSRRO (Low Salt Rejection RO membrane process) unit (40) utilizes a regenerated membrane as a reverse osmosis (RO) membrane, wherein the regenerated membrane is obtained by subjecting a damaged or end-of-life membrane to physical and / or chemical treatment to enable its reuse.

[0060] The regenerated membrane according to an embodiment of the present invention refers to a membrane which filtration function, which has been deteriorated due to fouling caused by the blockage of the membrane or the formation of an attached layer on the membrane as solutes in the membrane supply water are retained by the membrane, is restored through physical and / or chemical treatment by separating, detaching, or decomposing the solutes, i.e., foulants attached to the membrane. Examples of foulants causing membrane fouling may include turbidity, scale, silica, metal oxides, organic matter, and microorganisms.

[0061] The membrane used in the second-stage LSRRO (Low Salt Rejection RO membrane process) unit (40) may be a damaged reverse osmosis separation membrane, and a spent reverse osmosis (RO) separation membrane module discarded from the operation of a seawater desalination plant may be utilized. For an example, raw water in the RO process of treating livestock manure with a TDS concentration of approximately 7,600 mg / L, which is obtained by treating livestock manure through a UF process, may be concentrated by approximately three times to produce treated production water through the second-stage LSRRO (Low Salt Rejection RO membrane process) unit (40) using a regenerated membrane. In conventional processes such as evaporation, a high energy consumption of about 2.5 kWh / m3, as in RO, is required to achieve a 3-fold concentration. However, according to an embodiment of the present invention, high concentration treatment of the raw water can be achieved using the second-stage LSRRO (Low Salt Rejection RO membrane process) unit (40) without additional energy consumption.

[0062] Through said second-stage LSRRO (Low Salt Rejection RO membrane process) unit (40), salts contained in seawater or organic wastewater can be removed by intentionally lowering the salt rejection rate to 40-60%, thereby allowing high concentration treatment of water that would otherwise be discarded. As the salt rejection rate decreases, the operating pressure of the feed pump can be reduced accordingly, thereby allowing the concentration process to be performed with lower energy consumption.

[0063] If the salt rejection rate is too high, the operating pressure increases, which may exceed the pressure limit of the membrane module. On the other hand, if the salt rejection rate is excessively low, the total dissolved solids (TDS) concentration of the concentrate becomes insufficient, thereby requiring an increased number of stages in the process. Therefore, the salt rejection rate is preferably maintained within a range of 40 to 60%.

[0064] In the reverse osmosis process, changes in the concentration of the raw water result in variations in osmotic pressure, which in turn affect operating conditions such as operating pressure. Therefore, in the second-stage LSRRO (Low Salt Rejection RO membrane process) unit (40), recycling of the second-stage permeates to the first-stage reverse osmosis (RO) process unit (30) is possible only when the concentration of the raw water in the first-stage unit is equal to that of the treated water from the second-stage unit. Therefore, it is necessary to redesign the operating parameters according to the characteristics of the regenerated membrane, which are different from those of conventional commercial membranes.

[0065] A reverse osmosis water treatment system according to an embodiment of the present invention may be configured to include a first-stage reverse osmosis (RO) process unit and a second-stage LSRRO process unit, and additionally, a process unit with three or more stages by increasing the number of stages.

[0066] In such a case, the concentrate obtained from the second-stage LSRRO process unit may be used as the raw water for the subsequent stage, and the filtered water obtained from the second- stage LSRRO process unit may be used as the raw water for the previous stage (the first-stage reverse osmosis (RO) process unit). Likewise, when the number of stages in the reverse osmosis water treatment system is further increased, the concentrate from the n-th stage process unit may be used as the raw water for the (n+1)-th stage process unit, and the filtered water may be used as the raw water for the (n-1)-th stage process unit. The number of stages in the reverse osmosis water treatment system according to an embodiment of the present invention may be increased until a desired concentration of the concentrate is obtained.

[0067] Hereinafter, with further reference to Figure 2, the regenerated membrane (60) used in the second-stage LSRRO process unit (40) will be described.

[0068] The regenerated membrane (60) is characterized by an RO membrane obtained by regenerating a used and discarded reverse osmosis RO separation membrane (50) having a relatively low salt rejection rate compared to a conventional used membrane and a high water permeability relative to the salt rejection rate. That is, the regenerated membrane (60) is a regenerated discarded separation membrane obtained by regenerating an end-of-life reverse osmosis membrane to be capable of adjusting water permeability and salt rejection rate according to raw water and process characteristics, and the regenerated reverse osmosis membrane obtained thereby is applied to the second-stage LSRRO process unit (40).

[0069] Globally, more than 840,000 end-of-life membranes are discarded annually, amounting to more than 14,000 tons, with the majority of these spent membranes ending up in landfills. In the case of the regenerated membrane (60), while its performance may not be comparable to that of new membrane products, it has the economic advantage of reducing the costs associated with waste disposal and new membrane production. As such, the use of regenerated reverse osmosis membranes allows for cost savings by reducing membrane installation and replacement costs, as well as the disposal costs of spent membranes, thereby ensuring economic feasibility.

[0070] Typically, a regenerated membrane refers to a membrane that has been regenerated for reuse by focusing on restoring performance through cleaning to be as close as possible to the original specifications. However, the regenerated membrane according to an embodiment of the present invention has different values from the membrane specification of a new product, and the used membrane in which changes in water permeability, salt rejection and recovery rate have occurred is cleaned by alkali / acid and other methods and then used by changing the water permeability, recovery rate and salt rejection rate of the membrane to be suitable for the current specifications of the second-stage LSRRO process unit (40).

[0071] The recovery rate of a membrane process system refers to the ratio of product water to raw water. For example, a recovery rate of 50% means that when raw water flows into the membrane at a rate of 100 m3 / hr and the product water (freshwater) from the entire system is 50%, 50 m3 / hr, the recovery rate is said to be 50%. At this time, the concentrate is also generated at 50%, 50 m3 / hr. In general, increasing the number of stages in an LSRRO reduces operating pressure and increases final concentrate concentration, but it can also increase installation costs and energy consumption costs. There is a difference between the recovery rate of a single membrane module and the recovery rate of a reverse osmosis water treatment system that includes membrane modules. That is, a reverse osmosis water treatment system can be designed according to the consumption volume by arranging multiple membranes in series, parallel, or multi-stage configurations, taking into account the recovery rate of each membrane module, the number of membrane modules, and the membrane area. However, increasing the recovery rate to 100% is practically impossible and results in high energy consumption, thereby reducing economic efficiency. Accordingly, in general, seawater desalination systems are designed with a recovery rate of approximately 40% to 60%, while systems treating low-salinity raw water such as sewage or brackish water may be designed to achieve a recovery rate of approximately 50% to 90%.

[0072] A membrane with a reduced salt rejection rate exhibits increased water permeability and recovery rate, and can be applied, through process design, to concentrate the raw water to a high concentration level for the recovery of valuable resources contained therein, and for implementation of zero liquid discharge (ZLD) or minimal liquid discharge (MLD) concepts. As described above, by applying a regenerated membrane to the reverse osmosis water treatment system of the present invention, the second-stage LSRRO process according to an embodiment of the present invention requires the design of different operating parameters from those of conventional systems using commercial membranes, due to the use of membranes modified through regeneration to suit specific applications and purposes.

[0073] A reverse osmosis water treatment system according to an embodiment of the present invention primarily concentrates raw water using a commercial membrane through the first-stage reverse osmosis (RO) process unit (30), and performs the recovery of valuable resources and the adjustment of treated water concentration using a regenerated membrane through the second- stage LSRRO process unit (40).

[0074] In addition, in the reverse osmosis water treatment system according to an embodiment of the present invention, the treated water produced through the said first-stage reverse osmosis (RO) process unit (30) is discharged, while the treated water that has passed through the regenerated membrane of the second-stage LSRRO process unit (40) is circulated toward the raw water side of the first-stage RO process unit, where it is mixed with the raw water to perform raw water blending and concentration adjustment. The concentrate generated from both the first-stage RO process unit (30) and the second-stage LSRRO process unit (40) is further concentrated and stored. In this case, since the osmotic pressure changes as the concentration of the raw water changes, and the operating conditions such as operating pressure change accordingly, the operating conditions of the system should be set such that the concentration of the treated water in the second-stage LSRRO process and the concentration of the raw water in the first-stage reverse osmosis (RO) process are the same.

[0075] Hereinafter, with additional reference to Figure 3, a reverse osmosis water treatment system for concentrating organic wastewater and recovering valuable resources, including a post-treatment process unit (70), according to an embodiment of the present invention, will be described.

[0076] The post-treatment process unit (70) refers to a process for appropriately treating the water from which salts have been removed by the first-stage reverse osmosis (RO) process unit (30) and the second-stage LSRRO process unit (40), in accordance with the intended end use. The posttreatment process unit (70) may perform processes such as removing dissolved gases such as carbon dioxide and oxygen from the water, adjusting alkalinity and pH, and disinfecting the water to prevent microbial regrowth.

[0077] In order to specialize in the recovery of resources from high concentration sewage / wastewater and wastewater containing livestock manure, the regenerated reverse osmosis membrane process system for concentrating organic wastewater and recovering valuable resources according to an embodiment of the present invention may be configured to consider the recovery of valuable resources such as brine, potassium, and phosphorus.

[0078] Representative technologies for phosphorus recovery include crystallization methods (such as the MAP method, HAP method, Heat Phos method, and acid / alkali extraction method), adsorption methods, reduction smelting methods, and carbonization methods. In addition, a nitrogen removal process using stripping and an ammonia recovery process employing an acidic solution may be utilized to achieve an ammonia recovery rate of 70-80%, and the use of nanofiltration membranes and reverse osmosis technology may further increase the ammonia recovery rate to over 90%. As described in detail above, according to the present invention, there is an advantage in that an LSRRO system capable of concentrating raw water with lower energy consumption compared to conventional RO systems using commercial membranes can be provided.

[0079] In addition, the reverse osmosis water treatment system using a regenerated membrane can recover valuable resources, and these resources can be used as fertilizer, thereby reducing the use of chemical fertilizers, which not only provides economic benefits but also reduces nutrient depletion and can also decrease methane emissions.

[0080] Furthermore, there is an effect of reducing environmental pollution through the reuse of annually discarded membranes and securing economic feasibility through resource recycling.

[0081] A novel approach was tested to enhance water recovery and concentrate organic effluents from the biogas industry. The study focused on the treatment of pig slurry digestate through a two-step membrane process involving a LSRRO system with regenerated membranes.

[0082] Digestate was pre-treated with a UF system to remove organics and suspended solids. A polymeric membrane (150 kDa, 0.33 m2) was used at lab scale. The system operated with a cross-flow velocity of 1 m / s, and an operating pressure of 1.5 bar. Permeability was measured at 20 LMH, and the conversion rate was approximately 33%.

[0083] The UF digestate, with an initial conductivity of 21.5 mS / cm, first underwent conventional reverse osmosis using commercial seawater membranes. Operating at a cross-flow velocity of 1 m / s in a flat-sheet SEPA CF cell at 25 bar, 70% of the water was recovered at this stage, producing a permeate stream below 4 mS / cm and a concentrated digestate with a conductivity of 59.4 mS / cm. In the second stage, the concentrate was further processed using a LSRRO scheme with regenerated membranes of approximately 50% salt rejection, as determined by brine test. This step operated at a cross-flow velocity of 1 m / s and 25 bar, resulting in a final concentrated digestate of 90 mS / cm and a permeate with a conductivity of 41 .8 mS / cm, recovering 60% of the initial digestate.

[0084] The results demonstrated that the two-step membrane process effectively concentrated the digestate while recovering a significant fraction of clean water, up to 88%. The use of regenerated membranes allowed further concentration at lower pressure, reducing energy consumption compared to conventional RO systems with different stages. This approach presents a viable and sustainable strategy for water reuse and resource recovery, supporting circular economy principles.

[0085] The foregoing description of the present invention is merely illustrative, and it will be understood by those skilled in the art that various modifications and changes may be made thereto without departing from the spirit or essential features of the invention.

[0086] Therefore, the embodiments described above are to be understood as illustrative and not restrictive in all aspects. By way of example, respective components described as being configured in an integrated form may be implemented in a distributed manner, and likewise, components described as being distributed may be implemented in a combined or integrated form.

[0087] The scope of the present invention is defined not by the foregoing detailed description but by the following claims. All modifications and variations derived from the meaning and scope of the claims and their equivalents are to be construed as being included within the scope of the present invention.

[0088] REFERENCES

[0089] 1 : Reverse Osmosis Water Treatment System

[0090] 10: Intake Unit

[0091] 11 : Inlet Line

[0092] 12: Raw Water Storage Tank 13: Feed Pump

[0093] 20: Pre-treatment Process Unit

[0094] 21: UF Process

[0095] 22: MF Process 30: First-Stage Reverse Osmosis (RO) Process Unit

[0096] 40: Second-Stage LSRRO Process Unit

[0097] 50: Spent Membranes

[0098] 60: Regenerated Membranes

[0099] 70: Post-treatment Process Unit

Claims

CLAIMS1. A reverse osmosis water treatment system comprising: an intake unit including: an inlet line equipped with an inlet valve for seawater or organic wastewater; a raw water storage tank for storing seawater or organic wastewater as raw water; and a feed pump for pressurizing the raw water at a constant flow rate and pressure according to a predetermined time; a pre-treatment unit including an ultrafiltration (UF) membrane or a microfiltration (MF) membrane for removing fine particulate organic matter contained in the raw water, thereby reducing the load on the downstream reverse osmosis (RO) membrane; a first-stage reverse osmosis (RO) process unit for producing treated water by separating ionic substances contained in the filtered water pretreated by the UF or MF membrane using a reverse osmosis (RO) membrane, and for separating the raw water into treated water and concentrate; and a second-stage LSRRO (Low Salt Rejection RO membrane process) unit using a regenerated membrane, which is a damaged or end-of-life RO membrane that has been regenerated through physical or chemical treatment to enable reuse, as a reverse osmosis membrane.

2. The reverse osmosis water treatment system according to Claim 1 , wherein salts contained in seawater or organic wastewater are removed through the second-stage LSRRO process unit, and a salt rejection rate is reduced to 40-60%, thereby concentrating the wastewater discharged from water treatment to a high concentration and lowering the operating pressure of the feed pump in proportion to the reduced salt rejection rate to perform the concentration process with lower energy consumption.

3. The reverse osmosis water treatment system according to Claim 1 , wherein the raw water is primarily concentrated using a commercial membrane by the first-stage reverse osmosis (RO) process unit, and recovery of valuable resources and adjustment of the concentration of the treated water are performed using a regenerated membrane through the second-stage LSRRO membrane process unit.

4. The reverse osmosis water treatment system according to Claim 1 , wherein the treated water generated through the first-stage reverse osmosis (RO) process unit is discharged, the treated water filtered through the regenerated membrane of the second-stage LSRRO process unit is recirculated toward the raw water direction of the first-stage RO process unit to be mixed with theraw water and reused, and the concentrate generated from both the first-stage RO process unit and the second-stage LSRRO process unit is highly concentrated and stored.

5. The reverse osmosis water treatment system according to Claim 1 , wherein a post-treatment process unit is additionally included, which is connected to the downstream side of the second- stage LSRRO unit of the reverse osmosis water treatment system, and recovers valuable resources contained in the raw water in an environmentally friendly manner through an MC (membrane contractor) resource recovery process.

6. The reverse osmosis water treatment system according to Claim 5, wherein the valuable resources contained in the raw water are more than at least one of brine, phosphorus or potassium, or ammonia.

7. The reverse osmosis water treatment system according to any one of Claims 1 to 6, wherein the system is configured to operate under conditions such that the concentration of the treated water from the second-stage LSRRO process is equal to the concentration of the raw water supplied to the first-stage reverse osmosis (RO) process, taking into account changes in osmotic pressure and corresponding operating conditions, such as operating pressure, due to variations in the concentration of the raw water.

8. The reverse osmosis water treatment system according to any one of Claims 1 to 7, Wherein the system may be configured to further include a third-stage or higher process unit by increasing the number of stages in addition to the first-stage reverse osmosis (RO) process unit and the second-stage LSRRO process unit.

9. The reverse osmosis water treatment system according to Claim 8, wherein, when the number of stages of the reverse osmosis water treatment system is further increased, the concentrate of an n-stage process unit is used as the raw water for an (n+1)-stage process unit, and the filtrate of the n-stage process unit is used as the raw water for an (n-l)-stage process unit.

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