RO reverse osmosis desalination purified water equipment

Reverse osmosis water treatment equipment, as a special equipment for purified water filtration production, utilizes the selective permeation principle of reverse osmosis membrane. Through the high-pressure pump of the equipment, a certain pressure is applied to the raw water passing through the reverse osmosis membrane, allowing water molecules in the raw water to permeate through the membrane and dialyze out, while other inorganic salts, microorganisms, and organic matter cannot pass through the membrane due to the retention characteristics of the reverse osmosis membrane for these substances, thus obtaining pure ion-free water.

Reverse osmosis (RO) is an important part of membrane separation technology. Under the action of pressure higher than the osmotic pressure of the solution, substances that cannot pass through the semi-permeable membrane are separated from the water.

Because the pore size of the reverse osmosis membrane is very small (only about 10A), it can effectively remove dissolved salts, colloids, microorganisms, organic matter, etc., in the water (removal rate as high as 97-98%).

It has the advantages of good water quality, low energy consumption, no pollution, simple process, and easy operation. It has become the most energy-efficient and convenient technology for seawater and brackish water desalination, as well as pure water preparation.

It is now widely used in many industries such as medicine, electronics, chemicals, food, and seawater desalination.

The RO system should adopt an automatic control operation mode according to the water level of the primary demineralization water tank and the system water production. If startup, shutdown, or system switching is required, it should be manually switched after confirmation by the operating personnel. The control of the RO system and the control of the entire chemical water treatment equipment are both realized through the control system (PLC) in the control room. We select imported membrane components with high water permeability, high desalination rate, good chemical stability, good anti-pollution performance, and good mechanical strength according to the raw water quality. Based on the water source quality and the SDI value of the feed water, we propose the maximum membrane flux, recovery rate, and maximum feed water membrane area of the membrane module. The level and section arrangement and combination of the membrane module are determined by factors such as the influent water quality, recovery rate, and water production.

RO is currently the most advanced and practical desalination equipment at home and abroad. This system uses reverse osmosis membranes from Dow Chemical Company. It can remove organic matter, bacteria, and viruses. This membrane can operate in an ultra-low pressure working environment, thus achieving energy saving and reducing equipment investment and operating costs. It achieves the optimal combination of water permeability and desalination, so Dow membranes are widely used in the world, and their technical performance and product quality are highly praised by users.

 

Top 10 troubleshooting issues for RO reverse osmosis purified water equipment!

The switch is on, but the equipment does not start.

① Electrical circuit failure, such as a blown fuse or loose wire

② Thermal protection component is protected and not reset

③ Low voltage in the water system; check the fuse and wiring.

② Reset the thermal protection component

③ Check the water system and ensure sufficient water pressure.

After the equipment starts, the water inlet solenoid valve does not open.

① Loose wiring

② Internal mechanical failure of the solenoid valve

③ Solenoid valve coil failure ① Check the wiring

② Disassemble and repair the solenoid valve

③ Repair or replace the coil

The pump is running, but the rated pressure and flow rate are not reached.

① Pump reversal

② Security filter cartridge is dirty

③ Air in the pump

④ Flushing solenoid valve is open; ① Rewire

② Clean or replace the filter cartridge ③ Remove air from the pump ④ Adjust the pressure after the flushing is complete

The pump is noisy when the system pressure increases.

① Insufficient raw water flow

② Unstable raw water flow

③ Check the raw water pump and piping

④ Check the raw water pump and piping; check for leaks in the piping

The solenoid valve does not close after flushing.

① Failure of the solenoid valve control components and wiring

② Mechanical failure of the solenoid valve

③ Check or replace components and wiring

④ Disassemble the solenoid valve, repair or replace

Undervoltage shutdown

① Insufficient raw water supply ② Security filter cartridge is clogged

③ Improper pressure adjustment; undervoltage during automatic flushing

① Check if the raw water pump and pretreatment system are working ② Clean or replace the filter cartridge

③ Adjust the system pressure to the optimal state, maintaining the post-filtration pressure above 20 psi

Concentrate water pressure does not reach the rated value.

① Pipeline leakage

② Flushing solenoid valve is not fully closed

③ Recovery system leakage

① Check and repair the pipeline

② Check and replace the flushing solenoid valve

③ Check and repair the recovery system

Sufficient pressure, but the pressure display is inaccurate.

① Foreign object blockage in the pressure gauge hose

② Air in the hose

③ Pressure gauge malfunction

① Check and clear the pipeline

② Remove air

③ Replace the pressure gauge

Water quality deteriorates.

① Membrane fouling, scaling

② Membrane head seal aging and failure

① Chemical cleaning according to technical requirements

②Replace the O-ring

③Replace the membrane

Production decline

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

②Recalculate and determine the water production according to the actual water temperature

 

RO Reverse Osmosis Pure Water Equipment Process Description

The RO reverse osmosis pure water equipment combines the advantages of drinking pure water technology. With its cabinet-style design, it is very convenient to maintain. It also uses a reverse osmosis program controller for control, ensuring smooth equipment operation and simple operation. Control operation only requires one switch, greatly improving the operational stability of the equipment. So, what is the operation process of the RO reverse osmosis pure water equipment? This article will provide a detailed explanation.

1. Pretreatment:

The raw water undergoes pretreatment to improve the water quality and meet the requirements, reducing and delaying membrane pollution and extending its lifespan. It mainly deals with microorganisms, bacteria, colloids, organic matter, heavy metal ions, solid particles, and free chlorine in the incoming water to meet the requirements of the reverse osmosis device's incoming water and ensure the long-term stable operation of the reverse osmosis device. It consists of a sand filter, a carbon filter, a water softener, and a security filter.

Quartz sand filter: Filters out mud, impurities, and suspended solids in the water, reducing the SDI (Silt Density Index) value of the raw water.

Activated carbon filter: Has a dual role, adsorption and filtration. It removes chemical organic matter, heavy metals, chroma, odor, and residual chlorine from tap water, improving taste.

Resin water softener: Through sodium-type cation exchange resin exchange treatment, it removes scaling ions such as calcium and magnesium from the raw water, removing the hardness of the raw water.

Precision (security) filter: 5-micron PPF filter cartridge, intercepts objects larger than 5 microns, extending the life of the membrane.

2. Reverse osmosis device:

The reverse osmosis device can remove organic matter (such as trihalomethane intermediates, colloids, suspended solids, microorganisms, bacteria, algae, mold, etc.), heat sources, and viruses from the water. After the fluid undergoes deep separation treatment by the reverse osmosis RO membrane main unit after the first three stages of pretreatment, the water beneficial to human health passes through, and the water not beneficial to human health is excluded, with a desalination rate of 98%, producing pure water that enters the pure water tank. Depending on the specific situation, membrane filtration is divided into one or two stages of reverse osmosis treatment.

A good system design can ensure that the entire system does not need to replace membrane components within 3 years (service life is related to the water source quality). The online conductivity meter dynamically displays the water quality status of the purified water production at any time. The high-pressure pump provides the working pressure for the membrane permeate water. Maintain the water production rate. This water treatment system is a first-stage reverse osmosis.

3. Control system:

This system changes the output signals of the inlet valve, high-pressure pump, and flushing valve according to the changes in input signals such as high pressure, low pressure, liquid level, reset, and switch, achieving automatic control of a standard RO system and realizing pressure protection, liquid level control, and power-on/full water/automatic flushing functions.

 

Why does the service life of the RO reverse osmosis membrane in pure water equipment shorten?

Reasons for the shortened service life of the RO reverse osmosis membrane

The pore size of the RO reverse osmosis membrane is as small as the nanometer level (1 nanometer = 10*-9 meters). Under a certain pressure, water molecules can pass through the RO membrane, while inorganic salts, heavy metal ions, organic matter, colloids, bacteria, and viruses in the source water cannot pass through the RO membrane, thus strictly separating the permeable pure water from the impermeable concentrated water.

In the civilian sector, RO reverse osmosis membranes are mostly used in water purifiers as one of the filtration devices for water purification. They play the most crucial role in the filtration of tap water into purified water. RO membranes can effectively remove calcium, magnesium, bacteria, organic matter, inorganic matter, metal ions, and radioactive substances from water. The water purified by this device is crystal clear and sweet and mellow. This device is suitable for household and business units such as hotels, hospitals, and other enterprises and institutions for drinking water use.

The conductivity of pure water after general tap water is filtered through an RO membrane is 5μs/cm (the conductivity of the water after RO membrane filtration = the conductivity of the incoming water × desalination rate. Generally, imported reverse osmosis membranes can achieve a desalination rate of more than 99%, and the operation can guarantee more than 97% within 5 years. For those with higher requirements for the conductivity of the effluent, two-stage reverse osmosis can be used, and after simple treatment, the water conductivity can be less than 1μs/cm), which meets the national laboratory's third-grade water standard. After further filtration by an atomic-level ion exchange column cycle, the resistivity of the effluent can reach 18.2M.cm, exceeding the national laboratory's first-grade water standard (GB6682—92).

 

Reasons for the shortened service life of RO

1. Improper operation of the reverse osmosis equipment causes damage to the membrane performance

Residual gas in the reverse osmosis equipment operating under high pressure forms a water hammer that can damage the reverse osmosis membrane.

There are usually two situations:

A. When the equipment is drained and restarted, the gas is not completely exhausted before rapid pressurization operation. The remaining air should be exhausted at a pressure of 2-4 bar before gradually increasing the pressure.

B. When the joint between the pretreatment equipment and the high-pressure pump is not well sealed or leaks (especially the microfiltration device and the subsequent pipeline leakage), when the pretreatment water supply is insufficient, such as microfiltration blockage, due to the vacuum, some air will be sucked in at the poorly sealed place. The microfiltration device should be cleaned or replaced to ensure that the pipeline does not leak. In short, the pressure should be gradually increased when there are no bubbles in the flow meter, and if bubbles are found during operation, the pressure should be gradually reduced to check the cause.

2. Incorrect method of shutting down the reverse osmosis equipment

A. Rapid depressurization without thorough rinsing when shutting down. Because the concentration of inorganic salts on the membrane concentrate side is higher than that of the raw water, it is easy to scale and pollute the membrane.

B. Rinsing with pretreated water containing added chemical reagents. Because water containing chemical reagents may cause membrane pollution during equipment shutdown.

When the reverse osmosis equipment is ready to be shut down, the addition of chemical reagents should be stopped, the pressure should be gradually reduced to about 3 bar, and the equipment should be rinsed with pretreated water for 10 minutes until the TDS of the concentrated water is very close to the TDS of the raw water.

3. Poor disinfection and maintenance of reverse osmosis equipment leading to microbial contamination

This is a common problem in the use of composite polyamide membranes, because polyamide membranes have poor resistance to residual chlorine. In use, disinfectants such as chlorine are not added correctly, and users do not pay enough attention to microbial prevention, easily leading to microbial contamination. Currently, many manufacturers' pure water microbial levels exceed standards, which is caused by poor disinfection and maintenance.

This is mainly manifested in: at the time of leaving the factory, the RO equipment did not use disinfectant maintenance; after the equipment was installed, the entire pipeline and pretreatment equipment were not disinfected; intermittent operation did not adopt disinfection and maintenance measures; the pretreatment equipment and reverse osmosis equipment were not disinfected regularly; the maintenance solution failed or the concentration was insufficient.

4. Poor monitoring of residual chlorine in reverse osmosis equipment

1. If the chemical dosing pump fails, the chemical solution fails, or the activated carbon is saturated, the membrane is damaged due to residual chlorine.

2. Membrane performance damage caused by untimely cleaning and incorrect cleaning methods.

During the use of the equipment, in addition to the normal attenuation of performance, the attenuation of equipment performance caused by pollution is more serious. Common pollution mainly includes chemical scaling, organic matter and colloid pollution, and microbial pollution. Different pollutions show different symptoms. Different membrane companies have some differences in the symptoms of membrane pollution they propose.

In the project, we found that the duration of pollution is different, and the symptoms are also different. For example: when the membrane is contaminated with calcium carbonate scale, the pollution time is one week, mainly manifested as a rapid decrease in desalination rate, a slow increase in pressure difference, and no significant change in water production. Cleaning with citric acid can fully restore performance. The pollution time is one year (a certain pure water machine), the salt flux increased from the initial 2mg/L to 37mg/L (raw water is 140mg/L～160mg/L), the water production decreased from 230L/h to 50L/h, and after cleaning with citric acid, the salt flux decreased to 7mg/L, and the water production increased to 210L/h.

Furthermore, pollution is often not single, and its symptoms are also different, making pollution identification more difficult.

To identify the type of pollution, the raw water quality, design parameters, pollution index, operation records, equipment performance changes, and microbial indicators should be comprehensively judged:

(1) Colloid pollution: When colloid pollution occurs, it is usually accompanied by the following two characteristics:

A. The microfiltration filter in the pretreatment is blocked very quickly, especially the pressure difference increases very quickly.

B. The SDI value is usually above 2.5.

(2) Microbial pollution: When microbial pollution occurs, the bacterial count in both the permeate water and concentrate water of the RO equipment is relatively high, and maintenance and disinfection have not been carried out according to the requirements.

(3) Calcium scaling: It can be judged according to the raw water quality and design parameters. For carbonate-type water, if the recovery rate is 75%, and scale inhibitors are added during design, the LSI of the concentrate should be less than 1; if no scale inhibitors are added, the LSI of the concentrate should be less than zero, and calcium scaling will generally not occur.

(4) A 1/4-inch PVC plastic tube can be inserted into the component to test the performance changes of different parts of the component.

(5) Judge the type of pollution based on the changes in equipment performance.

(6) Acid washing (such as citric acid, dilute HNO3) can be used. The type of calcium scaling can be judged based on the cleaning effect and cleaning solution, and further confirmed by analyzing the components of the cleaning solution.

(7) Chemical analysis of the cleaning solution: Take raw water, original cleaning solution, and cleaning solution samples for analysis.

After determining the type of pollution, the cleaning method in Table 1 can be used, and then disinfected and used. When the type of pollution cannot be determined, the cleaning (3) + disinfection + 0.1% HCl (pH=3) steps are usually used for cleaning.

Preventing membrane damage and maintenance

1. Preventing membrane damage

New reverse osmosis membrane elements are usually immersed in a 1% NaHSO3 and 18% glycerol aqueous solution and stored in a sealed plastic bag. If the plastic bag is not broken, storage for about one year will not affect its life and performance. When the plastic bag is opened, it should be used as soon as possible to avoid adverse effects on the components due to the oxidation of NaHSO3 in the air. Therefore, the membrane should be opened before use as much as possible.

After the reverse osmosis equipment is tested, we have used two methods to protect the membrane. The equipment is tested and run for two days (15～24h), and then maintained with a 2% formaldehyde solution; or after running for 2～6h, it is maintained with a 1% NaHSO3 aqueous solution (the air in the equipment pipeline should be drained, ensuring that the equipment does not leak, and closing all inlet and outlet valves). Both methods can achieve satisfactory results. The first method is more expensive and is used when the idle time is long, while the second method is used when the idle time is shorter.

2. Maintenance

After a period of normal operation, the membrane elements will be contaminated by suspended matter or insoluble matter that may be present in the feed water. Under standard conditions, when the system performance drops by 10%, or obvious scaling or clogging occurs, cleaning should be carried out in time. Regular water flushing and chemical cleaning can restore the performance of the membrane elements and extend the service life of the membrane elements.

During short-term shutdown of the system, the system should be flushed every 5 days, and the valves should be closed after flushing to prevent scaling and blockage.

For long-term shutdown of the system (more than 30 days), add a 1% sodium bisulfite solution to prevent bacterial growth.