Immersed UF membrane desalination pretreatment process

Abstract

The invention discloses a membrane desalination pretreatment process of an immersed UF. The membrane desalination pretreatment process of the immersed UF comprises the following steps: S1, feeding system incoming water into a homogeneous regulation tank; s2, the effluent of the homogeneous regulation tank enters a high-density tank 1 #, and a chemical group 1 is put into the high-density tank 1 # to remove hardness of the tank water. According to the membrane desalination pretreatment process of the immersed UF, provided by the invention, the membrane desalination pretreatment process of the high-density clarification tank and the immersed UF is adopted, so that high-salinity wastewater can be pretreated, normal and stable operation of a subsequent membrane system and the quality and stability of evaporative crystallization of saltpeter are ensured, and the multiple immersed UF membrane tanks which are designed in parallel are used, so that the operation efficiency is improved. Compared with sand filtration, carbon filtration and pressure type ultrafiltration devices, the immersed UF membrane pool has the advantages of less maintenance points, low investment, low operation cost, reduction of the investment and operation cost, pollution blockage resistance and high suspended matter impact resistance.

Description

Technical Field

[0001] The invention relates to the technical field of wastewater treatment, and in particular to an immersion UF membrane desalination pretreatment process. Background Art

[0002] Industrial wastewater refers to wastewater and waste liquid discharged during the production process, which contains industrial production materials, intermediate products, by-products and pollutants generated during the production process. It is an important cause of environmental pollution, especially water pollution. Although the treatment of industrial wastewater began as early as the end of the 19th century, due to the complex composition and variable nature of many industrial wastewaters, there are still some technical problems that have not been completely solved.

[0003] After pretreatment, concentration, evaporation and salt separation crystallization, high-salt wastewater produces sodium chloride and sodium sulfate salts respectively, and the discharged high-concentration mother liquor is dried into impurities. "Clarification + filtration + ultrafiltration + ion exchange deep hardness removal" is a very mature pretreatment process. Most crystallization and salt separation projects use this pretreatment solution to remove impurities such as silicon, suspended matter, calcium and magnesium hardness, and heavy metals. The inlet water of the reverse osmosis membrane group device is usually selected according to the clarified water production and the combined water volume. Sand filtration, carbon filtration and pressure ultrafiltration devices are usually selected.

[0004] However, sand filtration, carbon filtration and pressure ultrafiltration devices have the following disadvantages:

[0005] ①Pressure ultrafiltration was first used in the pretreatment of chemical water, but when it was extended to recycled water and high-salt wastewater, many phenomena of inapplicability appeared;

[0006] ② In internal pressure ultrafiltration, pollutants are trapped in the inner pores of the membrane fibers and are most difficult to discharge from the membrane elements;

[0007] ③ In external pressure ultrafiltration, pollutants are trapped between the outer surface of the membrane fiber and the membrane shell, and it is also very difficult to discharge them from the membrane element.

[0008] Therefore, it is necessary to provide a submerged UF membrane desalination pretreatment process to solve the above technical problems. Summary of the invention

[0009] In view of the above situation, in order to overcome the defects of the prior art, the present invention provides an immersed UF membrane desalination pretreatment process that is resistant to fouling and high suspended matter impact.

[0010] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0011] The membrane desalination pretreatment process of immersed UF includes the following steps: S1: the system water enters the homogenization regulating tank to remove Ca2+ and Mg2+ in the water; S2: the effluent of the homogenization regulating tank enters the high-density tank 1#, and a pair of reagents are added to the high-density tank 1# to remove the hardness of the pool water; S3: the effluent of the high-density tank 1# enters the high-density tank 2#, and a pair of reagents are added to the high-density tank 2# to remove silicon from the pool water; S4: the effluent of the high-density tank 2# goes to the high-strength membrane tank, which is an immersed UF membrane tank, and the number is multiple, and multiple immersed The submerged UF membrane pools are arranged in parallel, and the total capacity of multiple submerged UF membrane pools is greater than 1.5 times the design capacity. When a single submerged UF membrane pool is overhauled, it will not affect the normal operation of the entire system; S5: the effluent from the high-intensity membrane pool is sent to the two-stage weak acid cation bed; S6: the effluent from the two-stage weak acid cation bed is sent to the medium and high pressure membrane device; S7: the concentrated water from the medium and high pressure membrane device is sent to the ozone + activated carbon device; S8: the effluent from the ozone + activated carbon device is sent to the ultra-high pressure membrane device; S9: the concentrated water from the ultra-high pressure membrane device is sent to the concentrated water feed tank.

[0012] Preferably, reagents are added into the homogenization regulating tank to remove Ca2+, Mg2+ and heavy metals.

[0013] Preferably, the reagent group 1 includes PAC, PAM, lime soda and NaOH.

[0014] Preferably, the second drug group includes PAC, PAM and sodium aluminate.

[0015] Preferably, the backwash drainage of the two-stage weak acid cation bed is returned to the homogenization regulating tank.

[0016] Preferably, the backwash drainage of the ozone + activated carbon device is returned to the homogenization regulating tank.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] The present invention adopts a membrane desalination pretreatment process of high-density clarification tank + immersed UF, which can pretreat high-salt wastewater, ensure the normal and stable operation of the subsequent membrane system and the quality and stability of evaporated crystallized saltpeter, and use multiple immersed UF membrane pools designed in parallel to reduce the impact of maintenance on water treatment efficiency. Compared with sand filtration, carbon filtration and pressure ultrafiltration devices, the immersed UF membrane pool has fewer maintenance points, low investment, and low operating costs, thus reducing investment and operating costs, and is resistant to fouling and blockage, and resistant to the impact of high suspended matter. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a process flow chart of the present invention;

[0020] Figure 2 It is the principle diagram of the high-strength membrane pool in the present invention. DETAILED DESCRIPTION

[0021] The present invention is further described below in conjunction with the accompanying drawings and embodiments. The embodiments of the present invention include but are not limited to the following embodiments.

[0022] like Figure 1-2 As shown, the membrane desalination pretreatment process of the submerged UF provided by the present invention includes the following steps: S1: the water from the system enters the homogenization regulating tank to remove Ca2+ and Mg2+ in the water; S2: the effluent from the homogenization regulating tank enters the high-density tank 1#, and a pair of reagents are added into the high-density tank 1# to remove the hardness of the pool water; S3: the effluent from the high-density tank 1# enters the high-density tank 2#, and a pair of reagents are added into the high-density tank 2# to remove silicon from the pool water; S4: the effluent from the high-density tank 2# is sent to the high-strength membrane tank, which is a submerged UF membrane tank, and the number is multiple, and the multiple submerged UF membrane tanks are arranged in parallel, and the total capacity of the multiple submerged UF membrane tanks is greater than 1.5 times the design capacity, and the single submerged UF membrane tank is overhauled. It will not affect the normal operation of the entire system; S5: the effluent from the high-intensity membrane pool is sent to the two-stage weak acid cation bed; S6: the effluent from the two-stage weak acid cation bed is sent to the medium and high pressure membrane device; S7: the concentrated water from the medium and high pressure membrane device is sent to the ozone + activated carbon device; S8: the effluent from the ozone + activated carbon device is sent to the ultra-high pressure membrane device; S9: the concentrated water from the ultra-high pressure membrane device is sent to the concentrated water feed tank. After the above steps, Ca2+, Mg2+, silicon, suspended matter, heavy metals, part of fluorine and part of organic matter in the high-salt system water are removed to ensure the normal and stable operation of the subsequent membrane system and the quality and stability of the evaporated crystallized salt and nitrate. Multiple submerged UF membrane pools designed in parallel are used to reduce the impact of maintenance on water treatment efficiency.

[0023] 1) Silicon removal

[0024] The desiliconization process uses commonly used chemicals and electrocoagulation. The comparison of the two desiliconization processes is shown in Table 1.

[0025] Table 1 Comparison of silicon removal methods

[0026]

[0027]

[0028] The comparison shows that the effect of electrocoagulation silicon removal technology is not very ideal and has many problems; chemical silicon removal has a better effect on silicon dioxide removal and can adapt to more complex water quality. Therefore, this application uses a traditional stable clarifier and adds magnesium and sodium aluminate for chemical silicon removal.

[0029] 2) Remove suspended matter

[0030] At present, the water treatment structures that are widely used to remove suspended solids and other impurities are mainly mechanical stirring clarifiers and high-density clarifiers. A comparison of the two facilities is shown in Table 2.

[0031] Table 2 Comparison of suspended solids removal structures

[0032]

[0033]

[0034] Through a multi-factor comparison of the two structures, combined with the domestic operation and operation examples of high-salt wastewater, the quality characteristics of high-salt wastewater in this application and a large amount of high-salt concentrated water engineering practice, the high-density clarifier is more suitable for the treatment of complex high-salt wastewater, so the high-density clarifier is selected as the main process facility for pre-treatment to remove hardness, silicon and some impurities.

[0035] 3) Filter

[0036] The influent of the reverse osmosis membrane group device is usually based on the clarified water output. The combined water volume usually selects sand filtration, carbon filtration and pressure ultrafiltration devices or uses submerged ultrafiltration as pretreatment.

[0037] (1) Comparison between sand filtration + pressure ultrafiltration and submerged ultrafiltration

[0038] ① There are misunderstandings about the selection of ultrafiltration: pressure ultrafiltration was first used in the pretreatment of chemical water, and many phenomena of inapplicability appeared when it was extended to recycled water and high-salt wastewater;

[0039] ② In internal pressure ultrafiltration, pollutants are trapped in the inner pores of the membrane fibers and are most difficult to discharge from the membrane elements;

[0040] ③ In external pressure ultrafiltration, pollutants are trapped between the outer surface of the membrane fiber and the membrane shell, and it is also very difficult to discharge the membrane element;

[0041] ④ Immersed ultrafiltration, since there is no membrane shell, the trapped pollutants are very easy to shake out of the membrane box from the outer surface of the membrane fibers; plus the driving force is the negative pressure formed by the suction from the middle of the membrane fibers by an ordinary centrifugal pump, the operating flux is designed to be half of the external pressure type, the water output is good, and the protection for subsequent reverse osmosis is the best;

[0042] ⑤ Comparing the three versions of the design specifications DL / T5068-1996, DL / T5068-2006, and DL / T5068-2014, it can be seen that the requirements for the inlet water of pressure ultrafiltration are getting higher and higher. This shows that pressure ultrafiltration can only accept water with very low turbidity. When the turbidity cannot be guaranteed, it is necessary to add two units of medium filter (when the water volume is large, choose V-type filter tank) + self-cleaning filter as pretreatment of pressure ultrafiltration to ensure the operation of pressure ultrafiltration. At the same time, it also shows that the medium filter before pressure ultrafiltration is very important. Many projects do not use porous plates for multi-media, and the operation effect of multi-media is very poor, which seriously affects the protection of ultrafiltration. Therefore, the current trend is: in the reuse of reclaimed water and crystallization and salt separation, more and more submerged ultrafiltration is used instead of pressure ultrafiltration.

[0043] ⑥ Characteristics of submerged ultrafiltration technology:

[0044] Remove part of COD.

[0045] Resistant to higher suspended solids.

[0046] Resistant to higher sludge concentrations.

[0047] Very good at removing colloid.

[0048] The water recovery rate is as high as ≥95%, and the backwash drainage is still in the high-strength membrane pool.

[0049] Strong impact resistance and easy operation and management.

[0050] It is suitable for use in water reuse treatment and high-salinity wastewater before reverse osmosis systems.

[0051] The technical analysis and comparison of pressure ultrafiltration and immersion ultrafiltration is shown in Table 3, and the filtration process analysis and comparison is shown in Table 4. Table 3 Comparison of pressure ultrafiltration and immersion ultrafiltration technology analysis

[0052]

[0053] Table 4 Filtration process analysis comparison table

[0054]

[0055]

[0056]

[0057] The submerged UF membrane pools are connected to the system in parallel, and multiple submerged UF membrane pools are used synchronously. The water inlet and outlet speeds of each submerged UF membrane pool are regulated according to the load, and multiple submerged UF membrane pools are maintained in a rotational maintenance manner, which can further reduce the impact of maintenance shutdowns on the wastewater treatment capacity of the entire system.

[0058] After comparing the three schemes, the membrane desalination pretreatment process of high-density clarification tank + submerged UF is adopted. Chemicals are added to the clarification tank to remove Ca2+, Mg2+ and heavy metals. After filtering through the high-intensity membrane pool, it enters the ozone + activated carbon filter to remove some organic matter, and then enters the ion exchange section to deeply remove Ca2+ and Mg2+. The concentration of Ca2+ and Mg2+ in the ion exchange regeneration liquid is relatively high. This water flows back to the regulating tank in front of the high-density pool and is de-hardened again through the high-density pool.

[0059] By adopting the membrane desalination pretreatment process of high-density clarification tank + immersed UF, high-salt wastewater can be pretreated to ensure the normal and stable operation of the subsequent membrane system and the quality and stability of evaporated crystallized saltpeter. The use of multiple immersed UF membrane pools designed in parallel can reduce the impact of maintenance on water treatment efficiency. Compared with sand filtration, carbon filtration and pressure ultrafiltration devices, immersed UF membrane pools have fewer maintenance points, low investment, and low operating costs, which reduces investment and operating costs, and are resistant to fouling and high suspended matter impact.

[0060] The above embodiment is only one of the preferred implementation modes of the present invention and should not be used to limit the protection scope of the present invention. Any changes or modifications that are made to the main design concept and spirit of the present invention and have no substantive significance, and the technical problems they solve are still consistent with the present invention, should be included in the protection scope of the present invention.

Claims

1. A membrane desalination pretreatment process for submerged UF, characterized in that: The following steps are involved: S1: The system water enters the homogenization regulating tank; S2: The effluent from the homogenizing regulating pool enters the high-density pool 1#, and a pair of reagents are added into the high-density pool 1# to remove the hardness of the pool water; S3: The effluent from high-density pool 1# enters high-density pool 2#, and a second reagent group is added into high-density pool 2# to remove silicon from the pool water; S4: The effluent from high-density pool 2# is sent to the high-strength membrane pool. The high-strength membrane pool is an immersed UF membrane pool, and there are multiple immersed UF membrane pools, which are set in parallel; S5: The effluent from the high-strength membrane pool is sent to the two-stage weak acid cation bed; S6: The effluent from the two-stage weak acid cation bed is sent to the medium and high pressure membrane devices; S7: The concentrated water from the medium and high pressure membrane devices is sent to the ozone + activated carbon device; S8: The effluent from the ozone + activated carbon device is sent to the ultra-high pressure membrane device; S9: The ultra-high pressure membrane device discharges concentrated water to the concentrated water feed tank.

2. The membrane desalination pretreatment process of an immersed UF according to claim 1 is characterized in that: Add reagents into the homogenization regulating tank to remove Ca2+, Mg2+ and heavy metals.

3. The membrane desalination pretreatment process of an immersed UF according to claim 1 is characterized in that: The reagent group 1 includes PAC, PAM, lime soda and NaOH.

4. The membrane desalination pretreatment process of an immersed UF according to claim 1 is characterized in that: The second pharmaceutical composition comprises PAC, PAM and sodium aluminate.

5. The membrane desalination pretreatment process of an immersed UF according to claim 1 is characterized in that: The backwash drainage of the two-stage weak acid cation bed is returned to the homogenization regulating tank.

6. The membrane desalination pretreatment process of an immersed UF according to claim 1 is characterized in that: The backwash drainage of the ozone + activated carbon device is returned to the homogenization regulating tank.

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