First, water quality requirements
Reverse osmosis as a new type of pure physical desalination process, due to the structure, material, desalination mechanism and other conditions of the reverse osmosis membrane elements, reverse osmosis equipment has higher requirements for water:
Temperature conditions between 1 and 45 °C;
The pH value must be in the range of 2 to 11;
Organic content (COD, mg/L) should be less than 1.5;
Turbidity (NTU) should be controlled below 1.0;
Silt density index (SDI value)<4.0;
Residual chlorine content <0.1mg/L(actually controlled at 0);
Iron content (mg/L): When dissolved oxygen >5mg/L, Fe<0.05;
Silica content (mg/L): SiO2<100 in concentrated water; LSI: pHb-pHs<0;
Sr, Ba and other ions are easy to form insoluble salts: Ipb<0.8Ksp.
The value of the last three items can be appropriately increased by adding scale inhibitor.
If one or several of the above indicators are not up to standard, it will have the following effects on the reverse osmosis membrane:
1. RO membrane is polluted by metal oxides;
2. Colloidal pollution;
3. RO membrane scaling;
4. Suspended matter fouling RO membrane;
5. Organic and microbial pollution, resulting in an increase in effluent COD.
This in turn has an adverse effect on the entire reverse osmosis unit:
Reduce the water yield of reverse osmosis purified water system; Reduce the water quality of reverse osmosis purified water system; Increase the operating energy consumption of reverse osmosis equipment, including raw water and electricity consumption; Increase the operating cost of water treatment, including reverse osmosis scale inhibitor, resin regeneration salt, other water treatment agents, etc.
Reverse osmosis pretreatment plays an irreplaceable role in it. When the pretreatment is not done well, the reverse osmosis inlet water quality is seriously substandard, and the time is too long, it will lead to irreversible physical and chemical damage to the reverse osmosis membrane element, and greatly shorten the service life of the reverse osmosis membrane element.
The purpose of reverse osmosis pretreatment is to solve the following problems to ensure the stable operation and service life of reverse osmosis equipment.
First, to prevent scaling on the membrane surface (including CaCO3, CaSO4, SrSO4, CaF2, SiO2, iron and aluminum oxides, etc.);
Second, to prevent the pollution and blockage of organic matter;
Third, prevent microbial fouling;
Fourth, to prevent colloidal substances and suspended solid particles fouling;
Fifth, keep the water yield of the reverse osmosis device stable.
Second, the process flow
Raw water tank
Store raw water for settling large sediment particles and other precipitable substances in the water. At the same time, the impact of unstable water pressure in the original water pipe on the water treatment system is buffered. (such as the pressure sensing response caused by the water pressure is too low or too high).
Raw water pump
Constant system water supply pressure, stable water supply.
Multimedia filter
The use of multiple filter layers of filters, the main purpose is to remove the sediment, rust, colloidal substances, suspended solids and other particles contained in the raw water in the diameter of more than 20um, can choose manual valve control or automatic controller for backwashing, forward washing and other operations. Ensure the water quality of the equipment and extend the service life of the equipment.
Activated carbon filter
The fruit shell activated carbon filter is used in the system. The activated carbon can not only adsorb electrolyte ions, but also ion exchange adsorption. Activated carbon adsorption can also reduce the oxygen consumption (COD) of potassium permanganate from 15mg/L(O2) to 2-7mg /L(O2), in addition, due to adsorption, the concentration of surface adsorption and replication increases. Therefore, it also plays a catalytic role in removing pigments, odors, a large number of biochemical organic matters, reducing the residual chlorine value of the water and pesticide pollutants and removing trihalides (THM) and other pollutants in the water. At the same time, the equipment has a self-maintenance system, and the operating cost is very low.
Ion softening system/dosing system
R/O device in order to dissolve the solid shape, the enrichment of emissions and the use of fresh water, to prevent the concentrated water side especially the last membrane module of RO device, to prevent the appearance of that the concentration volume of CaCO3, MgCO3, MgSO4, CaSO4, BaSO4, SrSO4, SiSO4 is greater than the equilibrium solubility constant deposition and crystallization precipitation from damage the deserved characters of the membrane elements, Before entering the reverse osmosis membrane component, an ion softening device or an appropriate amount of scale inhibitor should be used to prevent the crystal precipitation of carbonate, SiO2, and sulfate.
Precision filter
The use of precision filter to remove the residual suspended matter, non-curved particles and colloids etc. and other substances in the water, making the subsequent equipment such as RO system safer and more reliable operation. The filter element is 5um melt-blown filter element, the purpose is to remove the impurities greater than 5um missed by the upper filter unit. Prevent it from entering the reverse osmosis device to damage the surface of the membrane, thus damaging the desalination performance of the membrane.
Reverse osmosis system
The reverse osmosis device uses enough pressure to separate the solvent (generally water) in the solution through the reverse osmosis membrane (or semi-permeable membrane), because this process is in the opposite direction of natural osmosis, so it is called reverse osmosis. Reverse osmosis method can adapt to all kinds of raw water with salt content, especially in the water treatment project with high salt content, and can obtain good technical and economic benefits. Reverse osmosis equipment improves the desalting rate, with the characteristics of high recovery, stable operation, small footprint, easy to operate, not only removes salt, but also most of the bacteria, colloids and large molecular weight organic matter.
Ozone sterilizer/UV sterilizer (optional)
Kill bacteria produced by secondary pollution to completely ensure the sanitary index of finished water.
Raw water → raw water tank → raw water pump → multi-media filter (quartz sand filter) → activated carbon filter → soft water processor (add scale inhibitor device) → precision filter → high pressure pump → primary reverse osmosis (RO) device → ultraviolet sterilization device (ozone sterilization device) → water point
First, purified water equipment unit function
1.1 Pretreatment Equipment
The pretreatment equipment is composed of five units: raw water pressure pump, quartz sand filter, activated carbon filter, automatic water softener and fine filter.
1.1.1 Raw water pressure pump
When the raw water is tap water, the tap water pressure should be greater than the total water resistance (water pressure difference) of the quartz sand filter, activated carbon filter, automatic water softener and fine filter, and can meet the water pressure requirements of the reverse osmosis main engine, so it is necessary to set up a pressurized pump to meet the water pressure requirements.
1.1.2 Quartz sand filter
Because the turbidity of tap water is generally 3 to 5 degrees, the water also contains a small amount of suspended matter and sediment. Therefore, it is necessary to set up a quartz sand filter to reduce the turbidity of the water to no more than 1 degree to prevent blocking the reverse osmosis membrane.
1.1.3 Activated carbon filter
It mainly removes free chlorine and organic matter from water to prevent free chlorine oxidation of reverse osmosis membrane. At the same time, it can also remove the smell of water and improve the taste of drinking pure water.
1.1.4 Automatic water softener
When the process water passes through the automatic sodium ion exchanger, the cation such as Ca2+ and Mg2+ in the water exchanges ions with Na+ in the exchanger, reducing the hardness of the water and softening the water quality.
1.1.5 Fine filter
The filter is the last filter device before the tap water enters the membrane, it can effectively remove the material greater than 5μm that the sand filter and carbon filter has not removed, can stop the sand and activated carbon powder lossed from the sand filter, carbon filter, so as to effectively protect the RO membrane from pollution.
1.2 Reverse osmosis host
1.2.1 Water Intake Conditions
The reverse osmosis host shall operate under the following water intake conditions. It is very important to check if your raw water is within this limit. Failure to comply with this standard will result in permanent and irreversible contamination and damage to membrane elements.
Minimum inlet pressure: 2.8KG/CM2
Minimum inlet flow: 1.5t/h
Water temperature: 4℃ ~ 45℃
PH range: 4 ~ 9
Hardness: 17mg/L (CaCO3)
Turbidity: ≤1 degree
Total dissolved solids content: TDS<1000mg/L
Iron: <0.1mg/L
Free chlorine: <0.5mg/L
Manganese: <0.05mg/L
Organic matter: COD<1mg/L
2. Operation of purified water equipment
2.1 Startup and shutdown of pretreatment equipment and reverse osmosis host
2.1.1 Before the equipment is turned on, the operator must first be familiar with the name and function of each instrument on the electronic control panel of the reverse osmosis host, the installation position of the instrument on the panel and the circuit diagram.
2.1.2 If the equipment is powered on for the first time, the drain valve on the outlet pipe of the activated carbon filter should be opened, observe the water drain with the naked eye, and the drain valve should be closed after the water is clean and free of carbon particles. Then open the drainage valve of the lower part of the microporous membrane fine filter, and close the drainage valve when the water is clean.
2.1.3 Check whether the pre-treatment equipment and the components of the reverse osmosis host are normal, adjust the status of each valve switch, and ensure that the water is smooth during operation.
2.1.3.1 Normally open the inlet valve of the pressurized pump, slightly open the return valve of the pump bypass pipe, and the opening degree should be moderate.
2.1.3.2 Close the control valve on the sand filter bypass pipe, and open the inlet valve and outlet valve of the sand filter. At the same time close the control valve on the carbon filter bypass pipe, open the inlet valve and outlet valve on the carbon filter.
2.1.3.3 Normally open the concentrated water regulating valve of the reverse osmosis host, and adjust the throttle valve behind the high pressure pump to a moderate state.
2.1.3.4 Open the exhaust water valve at the top of the fine filter, and close the exhaust water valve after the equipment water pressure is stable.
2.1.4 Turn on all four three-phase air switches and one single-phase air switch inside the low-voltage distribution device for power supply.
2.1.5 Plug the power plug of the sand filter, carbon filter and automatic water softener into the 220 volt socket respectively, make the power on, and then adjust the controller to reach the operating state.
2.1.6 Turn the power switch on the electronic control panel of the reverse osmosis host from the OFF position to the ON position. When the power is on, the water inlet solenoid valve is opened, and the pressurized water pump and high pressure water pump are started at the same time.
2.1.7 When the power switch of the reverse osmosis host is turned on, the internal setting of the microcomputer controller will immediately open the flushing solenoid valve, and the reverse osmosis host will automatically flush. Automatic flushing is performed every time the power is turned off and started. When the power is turned off, the timing is cancelled, restored to zero, and re-timed the next time.
2.1.8 When the inlet water pressure is lower than the set value of the low pressure switch during the operation of the equipment, the low pressure switch will operate, and the internal setting of the microcomputer controller will shut down the high pressure pump of the host. When the water pressure is restored, the high pressure pump of the host starts automatically.
2.1.9 After the reverse osmosis host is finished washing, properly adjust the throttle valve at the back of the high-pressure pump, and control the inlet water pressure of the membrane shall not exceed 15kg/cm2. At the same time, adjust the concentrated water regulating valve to control the pure water flow. After meeting the above conditions, the concentrated water regulating valve and high pressure pump throttle valve are used together to adjust the recovery rate of the equipment in the appropriate range. At any time, do not completely close the concentrated water regulating valve, otherwise the pressure of the reverse osmosis host will suddenly rise, causing damage to the equipment or endangering the safety of the operator.
Three, purified water equipment maintenance
3.1 When the machine is shut down at night, the quartz sand filter and activated carbon filter can be backwashed with tap water as the raw water. Because there is a certain pressure of tap water, it can still enter the sand filter and carbon filter through the pressurized pump and the return valve.
3.2 According to the raw water quality and the operation of the equipment, the operation cycle and time of the automatic water softener can be set according to the needs of the user.
3.3 Quartz sand or activated carbon in the sand filter or carbon filter is recommended to be replaced once a year or so.
3.4 Fine filter, drain once a week, PP filter element inside the fine filter, it is recommended to replace once a month or so.
3.5 If the water production is not gradually reduced by 15% due to temperature and pressure factors, or the water quality gradually decreases beyond the standard, it indicates that the reverse osmosis membrane needs to be cleaned chemically.
3.6 During operation, some faults may occur occasionally due to various reasons. After a problem occurs, check the running records in detail to analyze the fault causes.
4. The number of daily operations should be recorded.
Operation precautions:
1) the hydrolysis of reverse osmosis membrane is easy to cause the deterioration of the performance of the reverse osmosis device, for this reason, the PH value of the water must be strictly controlled, and the PH value of the water supply is in the range of 3-11.
2) When the amount of sodium hypochlorite injected is insufficient and the free chlorine in the water supply can not be measured, there will be slime on the membrane component of the reverse osmosis device, and the pressure difference of the reverse osmosis device will increase. But for polyamide membrane, the amount of free chlorine entering the membrane module must be strictly controlled, exceeding the specified value will result in the oxidative decomposition of the membrane.
3) If the water with a FI value exceeding the standard is supplied to the reverse osmosis device as the water supply, the surface of the membrane component will be attached to dirt, so that it must be cleaned to remove dirt.
4) Excessive water supply flow will degrade the membrane component in advance, so the water supply flow cannot exceed the designed standard value. In addition, the flow of concentrated water should be avoided as far as possible less than the designed standard value, and the operation under the conditions of too small concentrated water flow will make uneven flow occurs in the pressure vessel of reverse osmosis device and fouling is precipitated on the membrane assembly due to excessive concentration.
5) The high pressure pump of the reverse osmosis device may cause the device to fail even if the operation is interrupted for a very short time.
6) Reverse osmosis inlet pressure to maintain a proper margin, otherwise due to the lack of proper compaction, the salt removal rate will be reduced.
7) When the reverse osmosis device is stopped, the water in the reverse osmosis device is replaced by low pressure feed water. This is to prevent the precipitation of silica during shutdown (due to the drop in water temperature in winter).
8) Often pay attention to the pressure difference of the security filter. The reason for the sharp rise in pressure difference is mainly the leakage of turbidity of the security filter. On the contrary, the reason for the sharp drop in pressure difference is the damage of the precision filter element, and the loosening of the fastening screws of the security filter element.
9) When the pressure difference between the inlet and outlet of the reverse osmosis device exceeds the standard, it indicates that the membrane surface has been contaminated or the water supply flow is above the design value. If the flow adjustment can not solve the pressure difference problem, the membrane surface should be cleaned.
10) In the summer, the water supply temperature is high, the water production flow is too much, and sometimes the operating pressure has to be reduced, which will lead to a decline in the water quality. To prevent this, the number of membrane components can be reduced while the operating pressure remains at a high level.
The sequence number is due to the policy
1 The reduction of the number of membrane components runs according to the designed number of membrane components
2 Low pressure operation according to the design of the reference pressure operation
3 Compaction of the membrane component occurs when operating under conditions that greatly exceed the reference pressure, the membrane component must be replaced
4 Reduction of operating temperature Run according to the design temperature of 25oC
5 Under the condition of higher recovery rate
When operating at a recovery rate of more than 75%, the amount of concentrated water is reduced, so that the concentration rate of water in the membrane module increases, resulting in a serious decline in the water quality. As the osmotic pressure of this feedwater increases, the amount of water passing through decreases. In severe cases, salt scale will precipitate on the membrane surface. Water must be produced at the design rate of recovery.
6 Metal oxides and contaminants
Attach to the membrane surface for daily low pressure flushing.
7 Differential pressure of the reverse osmosis unit in operation
Improve the operation management of pretreatment equipment and improve the water quality of reverse osmosis
Clean the membrane assembly with medicine
After normal operation of the reverse osmosis system for a period of time, the reverse osmosis membrane elements will be contaminated by suspended substances or insoluble salts that may exist in the feed water, and physical or chemical cleaning is required when the following symptoms occur:
● Under normal feed water pressure, water production is reduced by 10 ~ 15% compared with normal value;
● In order to maintain normal water production, the temperature correction constant value decreased by 10 ~ 15%;
● The quality of the produced water is reduced by 10 ~ 15%, and the salt permeability is increased by 10 ~ 15%;
● Increase the feed water pressure by 10 ~ 15%;
● The pressure difference between the sections of the system increases significantly (there may be no instrument to detect this parameter).
The cleaning unit system generally takes the following six steps:
1. Prepare a cleaning solution
The agent is added to clean water, and the preparation water must be RO product water or deionized water that has removed hardness, does not contain excessive metals and residual chlorine. Make sure the solution is thoroughly mixed even and the temperature and PH are adjusted to the desired value.
2. Input the cleaning solution at low flow
First of all, mix the cleaning liquid with the cleaning pump, and preheat the cleaning liquid at a low flow rate. The raw water in the element is then replaced with the lowest possible cleaning fluid pressure, and the pressure only needs to be enough to replace the pressure loss of the inlet water to the concentrated water, that is, the pressure must be low enough to not produce significant osmotic water production. The low pressure displacement operation minimizes the re-settling of dirt to the membrane surface, and, depending on the situation, some concentrated water is discharged to prevent dilution of the cleaning solution.
3. Cycle
When the raw water is replaced, the cleaning liquid should appear in the concentrated water pipe, so that the cleaning liquid is circulated back to the cleaning tank and the cleaning liquid temperature is kept constant.
4. Soak
Stop the operation of the cleaning pump and allow the membrane element to be completely immersed in the cleaning solution. Sometimes soaking components for 1 hour is enough, but for stubborn contaminants, it is necessary to extend the soaking time, such as soaking for 10 to 15 hours or soaking overnight. In order to maintain the temperature of the soaking process, a very low circulating flow rate can be used (about 10% of the flow rate shown in Table 1).
5. High flow pump circulation
Cycle for 30 to 60 minutes according to the flow rate listed in Table 1. The high flow rate can wash away the contaminants washed down by the cleaning solution. If the contamination is serious, please use more than 50% of the flow specified in Table 1 will help cleaning, in high flow conditions, there will be a problem of excessive pressure drop, the maximum allowable pressure drop for the single unit is 1bar(15psi), the maximum allowable pressure drop for the multi-component pressure vessel is 3.5bar(50psi), to exceed the limit.
6. Rinse
Rinse at low pressure with clean water (RO product water with removed hardness and free of metal ions such as iron and chlorine or deionized water), the cleaning solution in the rinse system can be prepared with qualified production water unless there is a corrosion problem. To prevent precipitation, the minimum flushing temperature is 20℃.
5. Conversion of purified water related units
Length: 1 inch =2.54 cm
Pressure: 0.1MPa=1kg=14.1psi
Flow rate: 1 gallon =3.785 liters
Electrical conductivity unit: μS/cm
Unit of resistivity: MΩ·CM
Conductivity =1/ resistivity
