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    Home > Technical Information

    RO reverse osmosis water treatment technology and equipment maintenance troubleshooting

    Source: Author: Time: 2016-07-27 Views: Times

    The standard process flow is as follows:

    Well water (tap water) → raw water tank → raw water pump → sand filter → activated carbon filter → fully automatic softened water equipment → security filter → ultrafiltration → reverse osmosis host → pure water tank → ozone sterilizer → centralized water collection point.

    1.Original water tank

    The device prevents the booster pump from directly drawing water from the pipe network to damage the booster pump or affect the normal operation of the system due to insufficient flow and unstable pressure. The original water tank has a built-in stainless steel float ball valve and a liquid level sensor. Large equipment must be equipped with a water inlet electric disc valve.

    1) The function of the floating ball valve is to control the amount of raw water intake, and to replenish water in time when the system is running.

    2) The liquid level sensor has a middle water level and a low water level, which is used to control the start and stop of the booster pump; the booster pump can automatically start when the water tank level is above the middle water level; The pump stops automatically.

    2. Raw water pump

    In order to ensure that the flow and pressure of the system's water supply are constant, the system's raw water booster pump uses a maintenance-free mechanical seal pump with high efficiency, low noise, and stable and reliable performance. The original water pump is automatically started and stopped by the water level of the original water tank.

    3.Add coagulant device

    Coagulation——Using coagulants such as iron salts, aluminum salts, and polymers, large particles of sediment are formed by flocculation and bridging with impurities in water, and then removed by other equipment, such as clarification and filtration.

    Add proper amount of coagulant to effectively coagulate the colloids and organic impurities in the water, so that the above substances can generate large particles of sediment or floc by flocculation and bridging, and then filtered through pretreatment to improve the filtering effect of pretreatment. The SDI (pollution index) is ≤5. If the SDI value of the incoming water is too large, a coagulant should be added.

    Common coagulants are: aluminum sulfate, polyaluminum chloride, ferrous sulfate, ferric chloride, etc.

    Commonly used coagulant aids are: calcium oxide, calcium hydroxide, polyacrylic acid amine, sodium carbonate, etc.

    Control: Start synchronously with the original water pump.

    4, pre-processing (also known as pre-processing)

    Currently we have three types of pre-treatment filters: stainless steel filters, glass steel filters and carbon steel lined rubber filters. The pretreatment filtration is divided into three parts: multi-media filtration, iron and manganese removal device, activated carbon filtration and softening filtration; multi-way valve can be used to automatically control the filter material in the filter tank by back washing and positive washing according to the set time. ; Or select manual operation control.

    Before the water is refined, a preliminary treatment is performed in advance, so as to obtain good results and improve the water quality during the water refining. Water in nature has a large amount of impurities, such as sediment, clay, organic matter, microorganisms, mechanical impurities, etc. The existence of these impurities seriously affects the water quality and treatment effect of refined water, so some impurities must be reduced or Removal, which requires pretreatment.

    1) Multi-media filter (also known as mechanical filter)

    Multi-media filters are mainly used to remove suspended matter, sediment and particulate impurities in water.

    The main fillers are: quartz sand, anthracite, fiber ball, etc.

    2) Iron removal filter

    The requirement of iron ions in the water of RO: Fe2 + ≤0.1mg / L. Sometimes it can be relaxed to ≤1mg / L to save costs.

    Its main filler is: natural manganese sand.

    Iron removal principle: Oxidation method is used to oxidize low-priced iron ions and low-manganese ions in water to high-priced iron ions and high-manganese.

    3) Activated carbon filter

    The activated carbon filter contains granular water-purifying activated carbon, which mainly removes macromolecular organics, colloids, odors, residual chlorine and other impurities in the water. Its strong absorption capacity can remove more than 90% on average. The residual chlorine is a strong oxidant, which has an oxidizing effect on the RO membrane, and must be limited to ≤0.1 mg / L.

    There are three types of activated carbon: round bar charcoal, amorphous shell charcoal and coconut shell charcoal.

    4) Cationic resin softener

    Principle of sodium ion exchange softening treatment: The raw water is passed through a sodium-type cation exchange resin to exchange the hardness components Ca2 + and Mg2 + in the water with the Na2 + ions in the resin, thereby adsorbing Ca2 + and Mg2 + in the water and softening the water.

    Function: It is of positive significance to prevent scaling on the surface of reverse osmosis membrane and improve the working life and treatment effect of reverse osmosis. Therefore, a softener is configured in the system. When the total hardness is less than 200mg / LCaCO3, no softener is required. The best control method is automatic control.

    5.Add antiscalant device


    1. Enclose the colloidal particles with anionic or non-ionic polymers to stabilize them in a dispersed state. Such agents are called dispersants. Such as: phosphate

    2. Turn metal ions into a chelating ion or complex ion, which inhibits them from combining with anions to produce a precipitate. Such agents are called chelating agents and complexing agents. Example: EDTA

    3. Use the aggregation and bridging action of polymer coagulant to form colloidal particles into alum flowers and suspend them in water. Such as: polyacrylamide.

    The main function of the device is to prevent the scaling of the reverse osmosis membrane, and the metering pump is used to add the medicine, the dosage is accurate and the stability of the equipment is good.

    Commonly used scale inhibitors are: sodium hexametaphosphate, organic phosphate, polypropylene.

    Control: High-pressure pumps of the same stage are started synchronously.

    6. Fine filter (also known as security filter)

    This device is mainly used for fine filtration of the water in the reverse osmosis system, the purpose is to reduce or eliminate the filter material particles leaked out of the pretreatment equipment for final protection, to ensure that the water that finally enters the reverse osmosis system meets the requirements.

    Filtration accuracy: generally 10um, 5um, 1um

    Fine filters are available in two types (blue filter) ABS and stainless steel; blue filters are 10-inch and 20-inch; stainless steel filters are 10-inch, 20-inch, 30-inch and 40-inch 5-core, 7-core, 10-core, There are 16 specifications of 20 cores.

    7.Voltage control switch

    Control the start and stop of the high-pressure pump to prevent the high-pressure pump from running under conditions of water shortage and water supply, and to guide the damage of the high-pressure pump.

    Generally, the high-pressure pump can start automatically when the inlet water pressure is more than 1kg, and it stops automatically when it is less than 0.5kg.

    8.High pressure pump

    Apply constant osmotic pressure to the reverse osmosis system.

    Control: Automatic start and stop are controlled by the original water tank water level, pressure switch, regeneration micro switch, and pure water tank water level.

    9.Water inlet solenoid valve

    The main function of the device is: when the pure water tank is full of water or the automatic head is backwashed and regenerated, the system automatically controls the electromagnetic shutdown so that the system automatically stops running.


    Ultrafiltration is a pressurized membrane separation technology, that is, under a certain pressure, small molecule solutes and solvents are passed through a special membrane with a certain pore size, so that macromolecular solutes are impermeable and left on one side of the membrane, so that large The molecular material was partially purified. The principle of ultrafiltration is also a membrane separation process principle. Ultrafiltration uses a pressure-active membrane to trap colloids, particles, and relatively high molecular weight substances in water under the influence of external driving force (pressure), and water and small solute particles penetrate The separation process through a membrane.

    Materials with molecular weights ranging from 3 10000 to 1 10000 can be retained through micropore screening on the membrane surface. When the treated water passes through the membrane surface at a certain flow rate by the effect of external pressure, water molecules and solutes with a molecular weight of less than 300-500 pass through the membrane, and particles and macromolecules larger than the membrane pores are trapped due to sieving. Thereby the water is purified.

    That is, when water passes through the ultrafiltration membrane, most of the colloidal silicon contained in the water can be removed, and at the same time, a large amount of organic matter can be removed. The principle of ultrafiltration is not complicated. During the ultrafiltration process, as the trapped impurities continue to accumulate on the membrane surface, a concentration polarization phenomenon will occur. When the solute concentration on the membrane surface reaches a certain limit, a gel layer is formed, which drastically reduces the water permeability of the membrane. This makes the application of ultrafiltration limited to some extent. For this reason, research is needed through experiments to determine the optimal process and operating conditions, to minimize the effects of concentration polarization, and to make ultrafiltration a reliable pretreatment method for reverse osmosis.

    The key to ultrafiltration technology is the membrane. There are various types and specifications of the membrane, which can be selected according to the needs of the work. Early films were isotropic, uniform films, that is, microporous films commonly used today, and their pore diameters were usually 0.05 mm and 0.025 mm. In recent years, some anisotropic asymmetric ultrafiltration membranes have been produced. One type of anisotropic diffusion membrane consists of a very thin, porous "skin layer" with a certain pore size (about 0.1 mm to 1.0 mm). And a relatively thick (about 1mm) layer which is more permeable and is used as a support "sponge layer".

    The skin layer determines the selectivity of the membrane, while the sponge layer adds mechanical strength. Because the skin layer is very thin, it is highly efficient, has good permeability, large flow rate, and is not easily blocked by solutes, resulting in a decrease in flow rate. Commonly used membranes are generally made of acetate or nitrocellulose or a mixture of both. In recent years, in order to meet the needs of sterilization in the pharmaceutical and food industries, non-fibrous anisotropic membranes have been developed, such as polysulfone membranes, polysulfoneamide membranes, and polyacrylonitrile membranes.

    This membrane is stable at pH 1 to 14 and can work normally at 90 C. Ultrafiltration membranes are usually relatively stable and can be used continuously for 1 to 2 years if used properly. Not used for the time being, it can be immersed in 1% formaldehyde solution or 0.2% NaN3 for storage. The basic performance indicators of ultrafiltration membranes are: water flux [cm3 / (cm2? H)]; retention rate (expressed as a percentage%); chemical and physical stability (including mechanical strength), etc.

    11. Reverse osmosis device (RO membrane technology)

    1) Working principle:

    Permeation ---- When a semi-permeable membrane is used to separate two solutions of different concentrations, the solvent in the dilute solution will penetrate the semi-permeable membrane into the concentrated solution. Reverse osmosis is a scientific method to reverse its natural osmosis process.When an external pressure is applied to the concentrated solution side that is greater than the osmotic pressure, the solvent will reverse its original osmosis direction and enter the dilute membrane from the concentrated solution side through the semipermeable membrane. In solution.

    2) Water inlet requirements: turbidity ≤ 2 degrees, water temperature: 5-35 C, SDI ≤ 5Fe ≤ 0.1 mg / L

    PH: 4-11 residual chlorine ≤ 0.1 mg / L

    3) The system can use the most advanced membrane elements in the world, its single membrane has a desalination rate of ≥99%, and a system desalination rate of 97-99%, and can effectively remove suspended matter, organic colloids, organic matter, bacteria, viruses, In order to ensure the stable performance and long-term operation of the RO device, impurities such as heat sources have been set up with a timing automatic flushing device.

    4) The RO working pressures currently used in China are: ultra-low pressure membrane ---- 7-10kg, low-pressure membrane ----- 15kg, high-pressure membrane ---- 55kg.

    5) Film material:

    6) Maintenance and cleaning of reverse osmosis membrane:

    Maintenance: With the widespread application of water purification equipment in the water treatment industry, reverse osmosis membranes have gradually been valued. The cost of reverse osmosis membrane is one of the most concerned issues for consumers. Good maintenance helps to extend the life of reverse osmosis membrane. New reverse osmosis membrane elements are usually impregnated with 1% NaHSO3 and 18% glycerol in water and stored in sealed plastic bags. In the case that the plastic bag is not broken, it will not affect the life and performance of the reverse osmosis membrane after being stored for about 1 year. When the plastic bag is opened, it should be used as soon as possible to prevent the NaHSO3 from oxidizing in the air and adversely affecting the components. Therefore, the film should be opened as much as possible before use.

    After the equipment is tested, we use two methods to protect the reverse osmosis membrane. Run the machine for two days (15 to 24 hours), and then use 2% formaldehyde solution for maintenance; or run 2 to 6 hours, use 1% NaHSO3 solution to maintain the reverse osmosis membrane (the air in the equipment pipeline should be exhausted To ensure that the equipment does not leak, close all inlet and outlet valves). Satisfactory results can be obtained with both methods. The first method is more expensive and is used when it is idle for a long time. The second method is used to maintain the reverse osmosis membrane when it is idle for a short time.

    Cleaning: The general steps for cleaning reverse osmosis membrane elements are:

    (1) Use a pump to drive clean, free chlorine-free reverse osmosis product water into the pressure vessel from the cleaning tank (or the corresponding water source) and discharge it for several minutes.

    (2) Prepare the cleaning solution in the cleaning box with clean product water. (3) Circulate the cleaning liquid in the pressure container for 1 hour or a preset time.

    (4) After the cleaning is completed, drain the cleaning tank and rinse it, and then fill the cleaning tank with clean product water for the next flushing.

    (5) Pump the clean, free chlorine-free product water into the pressure vessel from the cleaning tank (or the corresponding water source) and discharge it for several minutes.

    (6) After flushing the reverse osmosis system, run the reverse osmosis system with the product water discharge valve open until the product water is clean, foam-free, or detergent-free (usually 15-30 minutes).

    7) Common brand film codes:

    Toray: TM series means low-pressure high-flux membrane, working pressure 16kg

    Dow: BW30-4040 means brackish water desalination membrane --- diameter 4 inches, length 40 inches, working pressure 15kg

    TW30-4040 means ordinary municipal water film --- 4 inches in diameter and 40 inches in length, working pressure 10kg

    BW30-400 means brackish water desalination membrane --- effective area 400 square feet, working pressure 15kg

    SW30 series represents seawater desalination membrane, working pressure 55kg

    Hyde Energy: ESPA series means ultra-low pressure large flux membrane, working pressure is 10kg, of which ESPA4 is 7kg

    CPA series means brackish water desalination membrane, working pressure 15kg

    SWC series means seawater desalination membrane, working pressure 55kg

    Sehan: BE4040 (8040) -BE series indicate high desalination membrane, working pressure 15kg

    BE4040 (8040) -BL series means ultra-low pressure and large flux membrane, working pressure is 10kg

    TMG series means ultra-low pressure and large flux membrane, working pressure 7.5kg

    12. First-grade pure water intermediate tank (also called intermediate water tank)

    The role of the intermediate water tank is to control the operation and stop of the booster pump, the primary high-pressure pump and the secondary high-pressure pump, and to ensure the water supply to the secondary high-pressure pump, to prevent the secondary high-pressure pump from running in the absence of water, and to guide the secondary high-pressure pump. damage.

    The middle water tank has three water levels: high, middle and low. When the water tank is at a low water level, the secondary high-pressure pump automatically stops running until the water in the water tank reaches or exceeds the middle water level. The booster pump and the first-stage high-pressure pump automatically start water production when the water level in the water tank is lower than the middle water level. When the water level is high, the booster pump and the first-stage high-pressure pump stop automatically.

    13.Secondary alkali adding device

    Such as setting the device to add an appropriate amount of NaOH (sodium hydroxide), carbon dioxide and a single molecule through the RO membrane chemical reaction to generate molecular groups, better removal of secondary ions, thereby improving the effect of secondary water production. Generally, the conductivity of secondary water production can reach below 2us / cm ?, and properly adjusted can reach below 1us / cm ?.

    Control: Start synchronously with the secondary high-pressure pump.

    14.Ozone fresh-keeping device

    Sterilization mechanism: The structure of the microbial membrane is destroyed by oxidation to achieve the sterilization effect. Ozone first acts on the cell membrane, causing damage to the membrane constituents and causing metabolic disorders. Ozone continues to penetrate and penetrate the membrane, destroying the lipoproteins and lipopolysaccharides in the membrane, changing the permeability of the cells, leading to cell lysis and death. Ozone-inactivated viruses are thought to be oxidized directly to destroy their RNA or DNA.

    The ozone fresh-keeping device includes two parts, an ozone machine and an ozone mixer. The ozone mixer fully mixes ozone produced by the ozone mechanism with the finished water, and plays a role of sterilizing and keeping fresh the bacteria remaining in the finished water.

    Ozone machine is equipped with: 3 grams of ozone machine for each ton of finished water. Ozone machine specifications are 3, 5, 6, 10, 15, 20, 25, 32, 40, 50, 60, 80 g / set.

    15. Secondary pure water tank (finished water tank)

    Used to store product water.

    There are three water levels in the water tank: high, middle and low; when the water level of the water tank is low, the pure water pump automatically stops water supply, and it can automatically start and resume water supply until the water in the water tank reaches or exceeds the middle water level; The secondary high-pressure pump automatically starts water production when the secondary high-pressure pump stops automatically when the water tank is high.

    If there are special sterilization requirements, an immersion ultraviolet sterilization device can be installed in the water tank.

    16.Pure water pump

    Automatic delivery of pure water for water points.

    Control: Automatic start and stop of the pure water tank.

    17.Ultraviolet sterilization device

    Principle: As the light energy emitted by ultraviolet rays is absorbed by the organism, it causes changes in the cells themselves, especially the nucleic acids in the cells, which absorbs ultraviolet rays between 240-260nm much, causing changes in genetic factors in the nucleic acids, causing their functions to be destroyed. Loss of fertility.

    When the microorganisms that have lost the ability to reproduce are irradiated with ultraviolet light, the organism swells, causing the material in the organism to begin to flow out until necrosis, which leads to the death of the bacteria, thereby playing a role of sterilization and preservation.

    This device is mostly used in industrial water treatment, while drinking pure water is rarely used.

    18.Post precision filter

    The device is used as the last step for the final treatment of the product water, mainly removing fine particles and bacterial debris.

    The filter element has a foldable microporous element and a titanium alloy element. The foldable element is not resistant to ozone and has a short life span. Ozone water has a great oxidizing effect on the foldable element. Prevent the microporous filter element from polluting the finished water after being oxidized. Filtration accuracy is 0.22-1u. Titanium alloy filter has the characteristics of long ozone-resistant life, and the filtering range is 0.45u--1u.


    The system can be connected by UPVC pipe or stainless steel pipe. UPVC pipe fittings have been recognized by customers for their quality for many years of application; strong acid and alkali resistance and aging resistance. The high-pressure part of the equipment above the 2m? / H level 2 is connected by stainless steel pipes.


    The system is divided into manual and fully automatic modes. The automatic control system uses PLC (programmable controller) as the central control element, and realizes the automatic operation of the system through the combination of multi-point multi-channel water level sensors and dynamic pressure controllers. Manual operation can be used for installation, commissioning, maintenance, or in case of failure of an automated system.

    RO reverse osmosis purified water equipment maintenance troubleshooting, 10 major problems you must know!

    The switch is on, but the device does not start

    ①Electrical circuit failure, such as broken insurance, electric wires fall off

    ② The thermal protection element is not reset after protection

    ③ Undervoltage in waterway, check insurance, check wiring everywhere

    ② Thermal protection element reset

    ③ Check the waterway and ensure the water supply pressure

    After starting the equipment, the water inlet solenoid valve does not open

    ① Wiring off

    ② Internal mechanical failure of solenoid valve

    ③ The solenoid valve coil is broken. ① Check the wiring.

    ②Removing the solenoid valve for maintenance

    ③ Repair or replace the coil

    Pump runs but fails to reach rated pressure and flow

    ① Reverse pump

    ② The security filter element is dirty

    ③ There is air in the pump

    ④Flush solenoid valve is open, ①Reconnect

    ②Clean or replace the filter element ③Exclude the air in the pump

    When the system pressure rises, the pump makes a lot of noise

    ① Insufficient raw water flow

    ② Raw water flow is unstable

    ③Check the original water pump and pipeline

    ④ Inspect the original water pump and pipeline, and check whether the pipeline is leaking

    Solenoid valve does not close after flushing

    ① Solenoid valve control element and circuit failure

    ② Solenoid valve mechanical failure

    ③ Check or replace components and wiring

    ④Remove the solenoid valve, repair or replace

    Under-voltage shutdown

    ① Insufficient raw water supply ② Blockage of security filter element

    ③ Improper pressure adjustment and under pressure during automatic flushing

    ① Check whether the raw water pump and pre-treatment system are working ② Clean and replace the filter element

    ③Adjust the system pressure to the best state, and keep the pressure after filtration above 20psi

    Concentrated water pressure does not reach rated value

    ① Pipeline leakage

    ② The flushing solenoid valves are not all closed

    ③Recycling system leaks

    ① Inspect and repair pipelines

    ② Check and replace the flush solenoid valve

    ③ Check and repair the recovery system

    The pressure is enough, but the pressure is not displayed properly

    ① Foreign objects in the pressure gauge hose are blocked

    ② There is air in the hose

    ③ Pressure gauge failure

    ① Check and clear the pipeline

    ② Exclude air

    ③ Replace the pressure gauge

    Poor water quality

    ① Membrane fouling and scaling

    ② Sealing failure of membrane joint head

    ① Chemical cleaning according to technical requirements

    ② Replace O-ring

    ③ Replace the film

    Yield decline

    ① Membrane fouling and scaling, chemical cleaning according to technical requirements

    ② Water temperature changes are recalculated to determine the water production according to the actual water temperature.


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