RO reverse osmosis water treatment technology improvement measures
1, commonly used reverse osmosis water treatment process
2, reverse osmosis equipment in the application of the problems
Reverse osmosis desalination than other demineralization devices, such as: evaporator, electrodialysis, double bed, etc., has unique features and advantages, localization of reverse osmosis work has also been getting more attention. With the increasing application of reverse osmosis technology, problems have become increasingly serious. In recent years, the author conducted extensive research on the application of reverse osmosis water treatment devices, collecting a total of 99 sets of RO water treatment devices in various industries throughout the country, of which 76 were imported from abroad, partly domestic and partly imported There are 13 sets, a full set of equipment are made in China 10 sets. After finishing the study found that the normal use of a full set of imports was 30%; part of the domestic, part of the introduction of the normal use of equipment was 60%; full set of normal use of domestic production was 10%. The above problems are mainly due to the following reasons:
① a full set of imported equipment due to the different quality of raw water, lack of technical feasibility studies and technological changes, copying copy, not suitable for China’s actual situation. Therefore, the reverse osmosis water must be based on the quality of raw water pretreatment to meet the equipment requirements of water quality.
② Some enterprises with poor technical capabilities do not know the rational choice of the number of reverse osmosis plant membrane elements and the rational arrangement of membrane elements, resulting in the operation of some membrane elements under abnormal conditions.
③ domestic film quality but off. Film quality directly affects the quality of the salt and other impurities removal rate, the United States Dow Chemical Company Filmtec composite film, the rejection rate can be stabilized at 90%.
④ lax management. System operation, the pressure to be in the membrane can withstand the pressure range of work to prevent super-strength, overload operation, so that the membrane mechanical damage, leading to leakage. When the reverse osmosis system is running for a period of time, there is a sharp drop in water production, deteriorating water quality or pressure drop increased, indicating that the membrane needs cleaning, the machine should be converted into a clean state, the system self-cleaning, you can restore the membrane Function
3, technical improvements
3.1 mechanical filter design
The main reason for the low normal usage rate of imported equipment is that the pretreatment equipment does not combine with the poor water quality of raw water in our country. The backwashing of mechanical filter is not complete, and the upper filter cake lumps and the SDI (pollution index) increases, resulting in fouling of the membrane , Affecting system operation. RO devices generally require SDI <4 (the membrane element manufacturers have different requirements for SDI), to achieve the above requirements, the author made the following recommendations through research and practice:
3.1.1 mechanical filter selection
Combined with China’s raw water quality and equipment materials, packing situation, it is recommended to use double filter material filter. From the filtering mechanism, should be large and small, and in fact the mechanical filter is through the uppermost fine sand to intercept, so the uppermost layer of sand easily blocked, caking, head loss increased rapidly. If the top of the sand and then add particulate anthracite will increase the capacity of holding capacity, long operating cycle, the head loss increases slowly, the application of good effect in practice.
3.1.2 mechanical filter backwash
Mechanical filter due to the larger proportion of the internal filling of quartz sand, recoil is not easy, many systems are unstable operation is neglected backwash thorough, clean the process, the system set backwash devices are not up to the strength of the backwash, which Many water treatment equipment manufacturers and engineering companies exist problems. After the author and a processing equipment co., Ltd. research and practice, the use of gas and water repeatedly washed method, mechanical filter fouling backwash effect is very clear, the sand cleanliness is very clean, the performance recovery is good, the specific measures are:
① When designing the backwashing device, the backwash pump and the pipe must meet the requirements of backwash volume, and the backwashing intensity is 12-15L / (s · m2);
② using compressed air scrub filter, so that the filter surface of the sludge and other objects off, the intensity of 18 ~ 25L / (s · m2),
3.1.3 internal filler choice
Internal packing, according to the different drainage structure can choose different particle size of quartz sand, but the uppermost layer of quartz sand particle size should be 0.3mm .In the upper part of 0.5 ~ 1.0mm granular anthracite, the height of not less than 200mm.
3.2 activated carbon adsorption application
Activated carbon adsorbers have two main functions: ① adsorption of some organic matter in the water, the adsorption rate of about 60%; ② adsorption of residual chlorine in water. For direct extraction of groundwater users can cancel the activated carbon, if the hardness of the larger selection of water softeners, surface water, you must use activated carbon, because water disinfectant residual chlorine has strong oxidizing, will damage the RO membrane, according to RO System water requirements residual chlorine <0.1mg / L, so use activated carbon to adsorb residual chlorine. In addition activated carbon removal of residual chlorine is not a simple adsorption, but in its catalytic effect on the surface, so there is no adsorption of activated carbon saturation problem, but lost carbon.
3.3 coagulant choice
In the mechanical filter before adding a variety of coagulant and polymer flocculant to remove suspended solids, colloids and other impurities, but if not based on the truth of the water, blindly added, not only can not improve the water quality, on the contrary due to the pharmaceutical itself or in the pharmaceutical The impurities contained in water into the RO membrane harmful substances, many domestic pharmaceutical water treatment system, the existence of the above problems. So the choice of pharmaceuticals are very particular about. According to the characteristics of RO membrane:
① coagulant should avoid the use of aluminum salts. Aluminum salt coagulant to make the process of agglomeration easy to produce aluminum glue, into the RO surface is not easy to clean;
② should not use cationic polymer flocculant. RO membrane is anionic, cationic polymer flocculants and easy to combine with the film to form a difficult to clean the polymer membrane. If you do not attach importance to the above situation, ranging from shorten the life of the film, while some of the membrane elements scrapped. At the same time the compatibility between the agents can not be ignored, such as the selection of ST polymer flocculant should be used with ArgoAF150ul at the same time.
3.4RO system discussion
3.4.1 The importance of security filters
The main purpose of the security filter is to ensure that the RO water does not damage the membrane module. Generally, the filter pore size is selected to be 5μm. The filter is to be replaced according to the differential pressure before and after, and the pressure difference is controlled within 58.8kPa.
At present, the domestic system selects two kinds of one-time wire winding or folding filter, even if the differential pressure before and after the filter, the use of time should not be too long, because the filter easy to grow bacteria, it is recommended to use 14 ~ 15t / (h · m2) m2 filter area for the filter.)
3.4.2 Use of scale inhibitor
Reverse osmosis membrane pollution can be divided into: biological pollution, suspended solids pollution, chemical pollution, colloidal pollution, bacterial contamination. At present, most of the scale inhibitors used in the reverse osmosis system are sodium hexametaphosphate, but sodium hexametaphosphate is easily decomposed into phosphate and phosphate is the nutrient source of bacteria. Therefore, improper use can easily lead to biological contamination. In addition, sodium hexametaphosphate is not easy to dissolve, scaling itself also affect the operation of the system. I investigated several systems run well manufacturers and found that both use the British production FLOCON260 products, the product as a scale inhibitor at the same time with:
① can inhibit bacterial growth and extend the cleaning cycle;
② to prevent dissolved in the raw water and insoluble iron forming iron glue and affect the operation of the system and cause irreversible membrane pollution;
③ increased saturation threshold (LSI value up to 2.5), most of the raw water can be no acid, a small part of the raw water can also greatly reduce the acid dosing, thus reducing the reverse osmosis effluent CO2;
④ pharmaceutical ingredients stable, you can store and open a long time use. In order to ensure the normal operation of the RO system, in addition to the selection of suitable scale inhibitor varieties, the dosing amount should also be calculated according to the raw water quality. The British Argo has developed a complete set of software, which only needs to input raw water quality into the computer, Determined by the program.
3.4.3 Configuration of high flow flushing
Reverse osmosis In the process of water quality separation, the membrane surface contains many pollutants. Since the water separation direction is in a 90 ° relationship with the flow direction, part of the membrane surface contaminants can be removed by a large amount of flushing. In fact, Cleaning equipment, and imported equipment are equipped with cleaning devices. At present, I contacted some of the water treatment equipment engineering company, have developed PLC controlled flow irrigation system, the device is conducive to the extension of the life of RO membrane. [FS: PAGE]
3.4.4 chemical cleaning fluid selection
RO system in normal operation, only 3 times a year to clean, different pollution should choose different agents. China generally use citric acid and EDTA as the main ingredient, but often poor cleaning effect, and import cleaning fluid cleaning effect is obvious. As Bengbu Pharmaceutical Factory, due to serious water pollution in the Huaihe River, there are some problems in operation and management. As a result, serious fouling of the RO membrane was caused. There was no obvious effect after acid washing and caustic washing for 3 and 4 times. In view of the above situation, the author and equipment manufacturers analyzed the cause of fouling, the basic decision for the biological contamination, the bold use of a targeted chemical cleaning agent FIOCLEANMC11, the basic restoration of the original performance, and strengthen management since the operation has stable performance.
3.4.5 Reverse osmosis device design
RO device design and calculation of a complex set of calculations, the current foreign film components have been developed software, as long as the designer of raw water quality reports and the initial performance of the membrane components program, and then the quality of raw water input to the computer, the program software To verify the feasibility of the initial program, if not, issue a warning and tell which part of the design is not reasonable. In addition, designers should pay attention to the various protective measures that should be provided according to the requirements in the manual of membrane components.
3.5 mixed bed UV sterilizer and membrane filtration options
Mixed bed is the ultimate means to improve water quality, UV disinfection bacteria can kill bacteria, and then through the membrane filter to remove bacterial cadaver, these sets of designs can be used conventional products, not described here.