Chemical cleaning solution for reverse osmosis unit

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1. Overview After long-term operation of reverse osmosis, the desalination rate, water production, pressure difference, etc. will gradually decrease. Insoluble salts, bacteria, and biofilm dirt will be deposited in the membrane, which must be cleaned and removed in time, otherwise it will have a greater impact on the operation of the device. This plan is specially formulated. 2. General principles 1. Flushing conditions Cleaning should be carried out when one of the following situations occurs: ① Under normal pressure, if the product water flow rate drops to 10~15% of the normal value. ② In order to maintain normal product water flow, the temperature-corrected feed water pressure is increased by 10 to 15%. ③ Product water quality is reduced by 10~15% ； The salt permeability increases by 10~15%. ④ The operating pressure increases by 10~15%. ⑤ The pressure difference between each RO section increases significantly. 2 Preparation work 2.1 The chemical cleaning work of reverse osmosis is carried out after the replacement of the first membrane of the reverse osmosis section. 2.2 The chemicals required for chemical cleaning have been prepared. Including NaOH, hydrochloric acid, EDTA-4Na.CH 3〈CH2〕11SO3Na, etc. At the same time, pH test paper needs to be prepared. 2.3 The reverse osmosis and previous devices must have operational capabilities to provide power and water source during cleaning. 2.4 Stop the reverse osmosis system to be cleaned, close the high-pressure pump outlet valve, and close the manual valve into the reverse osmosis. 2.5 The cleaning water tank reaches the specified water level 3. Safety preparations for reverse osmosis chemical cleaning 3.1 Personal safety protective equipment Prepare a hard hat, acid and alkali resistant gloves, and an acid and alkali resistant protective mask. Anti-acid and alkali waistband, warning signs, signs and warning lines 3.2 Technicians, safety officers, and persons in charge of reverse osmosis chemical cleaning projects organize relevant personnel to inspect the equipment required for the operation before operation. Carry out careful inspection of tools and equipment to ensure safe and reliable use of machinery and equipment 4 Overview of chemical cleaning 4.1 RO membrane module contamination symptoms and treatment methods: See Table 1. RO membrane module pollution symptoms and treatment methods. Table 1. General characteristics of pollutants. Treatment methods 1. Calcium deposits (calcium carbonate and calcium phosphate, generally occur in the second stage of the system). The desalination rate is significantly reduced. The pressure drop of the system is increased. The water production of the system is slightly reduced. Clean the system with solution 1#. 2. Oxides (iron, nickel, copper, etc.). The desalination rate is significantly reduced. The pressure drop of the system is significantly increased. The water production of the system is significantly reduced. Clean the system with solution 1#. 3. Various colloids (iron, organic matter and silica colloids) The desalination rate dropped significantly and the system pressure drop gradually increased. The system water production gradually decreased. Use solution 2# to clean the system. 4. Calcium sulfate (generally occurs in the second section of the system). The desalination rate is significantly reduced. The system pressure drop is slightly or moderately increased. The system water production is slightly reduced. Clean the system with solution 2#. 5. The organic matter deposition desalination rate may reduce the system pressure drop. Gradually increase the system water production and gradually decrease. Use solution 2# to clean the system. When the pollution is serious, use solution 3# to clean the system. 6. Bacterial contamination. The desalination rate may decrease. The system pressure drop will increase significantly. The system water production will significantly decrease. Select one of the three solutions according to the possible pollution types. 4.2 RO membrane element cleaning solution formula RO membrane element cleaning solution formula table 2 Ingredients of cleaning fluid: Adding amount when preparing 500 liters of solution. pH adjustment 1# Citric acid reverse osmosis product water (no free chlorine) 10.16 kg 500 liters Use ammonia to adjust PH to 3.0 2# Sodium tripolyphosphate EDTA tetrasodium salt reverse osmosis product water (no free chlorine) 10.16 kg 4.2 kg 500 liters Use sulfuric acid to adjust PH to 10.0 3# Sodium tripolyphosphate Sodium dodecyl benzene sulfonate reverse osmosis product water (no free chlorine) 10.16 kg 1.28 kg 500 liters Adjust PH to 10.0 with sulfuric acid Cleaning fluid suitable for different pollutants (%, weight ratio) Table 3 Recommended cleaning fluid for main pollutants Remarks Inorganic salt precipitate 0.2% hydrochloric acid 0.5% phosphoric acid 2.0% citric acid 2.0% MCT103 HCL H3PO4 C3H4(OH)(CO2H3) American ARGO Company Metal oxide pollution 0.5% phosphoric acid 1.0% sodium dithionite 2.0% citric acid 2.0% MCT103 H3PO4 Na2S2O4 American ARGO Company inorganic colloidal sediment 0.1% sodium hydroxide: 30℃ 0.025 sodium lauryl sulfate + 0.1% sodium hydroxide 2.0% MCT511 NaOH Na-DDS+ NaOH American ARGO company microbial colloidal pollutant 0.1% sodium hydroxide: 30℃ 0.1% EDTA sodium salt powder + 0.1% sodium hydroxide 2.0% MCT511 NaOH Na-EDTA+ NaOH American ARGO Company organic pollution 0.05% sodium lauryl sulfate + 0.1% sodium hydroxide 0.1% sodium tripphosphate (STP) + 1.0% EDTA sodium salt powder 2.0% MCT511 Na-DDS+ NaOH Na5P3O10 +Na-EDTA American ARGO company's silica gel contaminates 0.1% sodium hydroxide: 30℃ 0.1% EDTA sodium salt powder + 0.1% sodium hydroxide 2.0% MCT511 NaOH Na-EDTA+ NaOH American ARGO company’s drug list for preventing biological contamination Table 4 Drug name Usage concentration remarks Sodium hypochlorite -0.1ppm Due to the oxidation of the reverse osmosis membrane, caution should be used when using transition metal elements such as iron. Sodium bisulfite -0.1ppm should not be used. Food-grade products should be used, the safest hydrogen peroxide/peracetic acid -0.2%. In order to maintain the maximum sterilization effect and the performance and life of the membrane, the PH value should be controlled at around 3. Keep the temperature below 25°C to maintain the salt transmission rate of the membrane. It should not be used when there are transition metal elements such as iron. It is best to use it after cleaning organic and inorganic substances. Peracetic acid -0.2% should not be used after cleaning organic and inorganic substances when there are transition metal elements such as iron. Formaldehyde 0.5-3.0% This product has certain toxicity and is not recommended for use, especially when using reverse osmosis to produce drinking water or purified water. In addition, the new film must be used 24 hours before use. If the system is out of service for a long time, consider using 1% mixed solution as a protective solution. Isothiazoline (Rohm&Haas) 15-25mg/L can be used as a fungicide for long-term storage. MCT882 (ARGO) 0.2% has a storage period of 6 months and is non-toxic. 3. Chemical cleaning method of RO membrane element 3. Valve action sequence 1. Cleaning section: The flushing valve, the first-stage cleaning water outlet and the second-stage water inlet valve (at this time are used as the first-stage water outlet), the first- and second-stage cleaning switching valves, and the cleaning water production valve are opened, and the other valves are closed. 2. Clean the second stage: The second-stage water inlet main gate valve, the cleaning first-stage water outlet and the second-stage water inlet valve (used as water inlet at this time), the cleaning water production valve, and the second-stage concentrated water valve. The remaining valves are closed. 3. Clean one and two sections at the same time: The flushing valve, cleaning product water valve, and second-stage concentrated water valve are closed, and the other valves are closed. 4. Clean the container: The second-stage water inlet main gate valve, the first- and second-stage cleaning switching valves, and the other valves are closed. General steps for cleaning reverse osmosis membrane elements: 1. Rinse the reverse osmosis membrane element. Use a pump to pump clean, free chlorine-free reverse osmosis product water from the cleaning tank (or corresponding water source) into the pressure pipe and discharge it for a few minutes. 2. Prepare cleaning fluid. Use clean product water to prepare cleaning fluid in the cleaning tank according to the conditions in Table 2. 3. Clean the reverse osmosis membrane element and circulate the cleaning fluid in the pressure tube for 1 hour or according to the preset time value. For 8-inch pressure pipe, the flow rate is 135 to 150 liters/minute (35 to 40 gallons/minute), and for 4-inch pressure pipe, the flow rate is 35 to 40 liters/minute (9 to 10 gallons/minute). 4. Rinse the cleaning tank. After the cleaning is completed, drain and rinse the cleaning tank, and then fill the cleaning tank with clean product water for the next step of flushing. 5. Rinse the reverse osmosis membrane element again. Use a pump to pump clean, free chlorine-free product water from the cleaning tank (or corresponding water source) into the pressure pipe and discharge it for a few minutes. 6. Put the reverse osmosis system into operation. After flushing the reverse osmosis system, put the reverse osmosis system into operation with the product water discharge valve open until the product water is clean, no foam or no cleaning agent (usually 15 to 30 minutes). Open the product water valve and close the product water discharge valve. At this time, the reverse osmosis system enters normal operation. 4. Precautions 1. During the cleaning process, be sure to pay attention to the correct switching of the valve to prevent back pressure from being generated in the RO. Once back pressure is generated, the reverse osmosis membrane will be irreparably damaged. It is required that during the cleaning process, attention must be paid to the pressure gauge readings on each pressure pipeline to ensure that the pressure is within the control range. 2. Observe the chemical solution after each cleaning step and make a record. 3. The unused chemical solution must be properly placed. Do not place it randomly to cause unnecessary accidents. 4. After cleaning, replace the cleaning water tank to avoid contaminating the produced water during normal operation. 5. According to the production water situation, the cleaning time can be adjusted appropriately.