A new ecological nano-iron dynamic membrane interface assembly and its enhanced arsenic removal method

Abstract

A new ecological nano-iron dynamic membrane interface assembly and its enhanced arsenic removal method, which belongs to the field of drinking water treatment technology. The method of the present invention utilizes the in-situ coagulation, synergistic oxidation and membrane filtration of the Fe(II) / Cl2 system to simultaneously realize the in-situ modification of the membrane and the deep removal of arsenic. The specific method is completed by the following steps: 1. Add chlorine oxidant and divalent iron salt to the arsenic-containing raw water at the same time, and introduce the raw water into the membrane pool after tubular mixing; 2. Stir the raw water in the membrane pool by aeration, mechanical stirring or hydraulic mixing to fully mix the raw water in the membrane pool; 3. After the membrane pool is running, the membrane after the new ecological nano-iron dynamic interface assembly and the water with arsenic removed are obtained. The present invention requires few facilities, is easy to operate, has low maintenance and operation costs, and has strong arsenic removal capacity. It is a new and efficient arsenic removal method.

Description

Technical Field

[0001] The invention belongs to the technical field of drinking water treatment, and specifically relates to a new ecological nano-iron dynamic membrane interface assembly and an enhanced arsenic removal method thereof. Background Art

[0002] The main problems facing the world in the field of water supply today include two major areas: water resources and drinking water health. According to statistics, about 663 million people in the world face drinking water safety issues. As a pollutant, arsenic will greatly endanger drinking water safety at low concentrations of its single substance and compounds. Arsenic is mainly distributed in the earth's crust, air, water, soil and sediments. my country's current "Sanitary Standard for Drinking Water" (GB 5749-2022) stipulates that the arsenic content in drinking water shall not exceed 10μg / L. Under normal circumstances, arsenic exists in four valence states: -3 (arsenide), 0 (metallic arsenic), +3 (arsenite), and +5 (arsenate). Among them, trivalent arsenic and pentavalent arsenic are the main forms of arsenic in water. With the rapid development of my country's economy and the improvement of living standards, people's requirements for the quality of life are getting higher and higher, and they pay more attention to the safety of drinking water. With the promulgation and implementation of the new drinking water hygiene standards, more convenient and efficient water treatment technologies are now needed to improve the quality of water supply and ensure the safety and quality of residents' drinking water.

[0003] At present, the main methods for arsenic removal include adsorption, electrocoagulation, and ion exchange. Among them, the adsorption method has problems such as low arsenic removal rate, frequent regeneration of adsorbents, and large amounts of waste liquid discharge. Although the electrocoagulation method has a high arsenic removal rate, the investment cost is relatively high compared to other methods, which is not conducive to large-scale promotion. The ion exchange method has a high arsenic removal rate, but the corresponding investment cost is also high, and the regeneration operation of ion exchange resin is complicated, and a large amount of waste liquid is discharged. Studies have found that the As(III) removal rate is extremely low when the coagulation process is used alone; the removal rate of As(III) is still low when the oxidation-coagulation process is used to oxidize As(III) to As(V), and increasing the amount of coagulant added will result in too large floc particle size and small specific surface area, which is not conducive to further adsorption of arsenic. Pre-oxidation-coagulation-membrane filtration has a good arsenic removal effect, but the membrane is seriously polluted after long-term operation, requiring chemical cleaning, which increases the operating cost. In addition, arsenic-containing surface water or groundwater often also contains other heavy metals, such as manganese, arsenic, thallium, molybdenum, lead, etc. How to remove arsenic from water at low cost, stably and deeply is still a major problem in current drinking water treatment. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a new ecological nano-iron dynamic film interface assembly and enhanced arsenic removal method thereof.

[0005] A novel ecological nano-iron dynamic membrane interface assembly and enhanced arsenic removal method thereof, characterized in that the method utilizes the in-situ coagulation, synergistic oxidation and membrane filtration of the Fe(II) / Cl2 system to simultaneously achieve in-situ modification of the membrane and deep removal of arsenic. The specific method is completed by the following steps:

[0006] 1. Chlorine oxidant and divalent iron salt are added to the arsenic-containing raw water at the same time, and the raw water is introduced into the membrane pool after tubular mixing;

[0007] 2. Stir the raw water in the membrane pool by aeration, mechanical stirring or hydraulic mixing to fully mix the raw water in the membrane pool;

[0008] 3. After the membrane pool is running, the water produced is a membrane assembled with a new ecological nano-iron dynamic interface and water free of arsenic.

[0009] The beneficial effects of the present invention are:

[0010] 1. In addition to heavy metals such as arsenic, raw water may also contain pollutants such as particulate matter, macromolecular organic matter, and algae. These background pollutants will not only affect the coagulation effect, but also aggravate membrane pollution, resulting in a decrease in membrane flux after long-term operation. Although the arsenic removal effect of the traditional pre-oxidation-coagulation / precipitation-membrane filtration process can meet the water quality requirements, the flux decays seriously after long-term operation, making it difficult to meet the water production needs of actual applications. The backwashing frequency is high, which increases the operating cost. The present invention proposes a new ecological nano-iron dynamic membrane interface assembly and an enhanced arsenic removal method thereof. The iron floccules generated in situ by the Fe(II) / Cl2 system are looser, have more adsorption sites, are more likely to adsorb negatively charged arsenic oxygen anions, and produce chlorine free radical active species, and the coagulation effect is better than that of the traditional trivalent iron salt coagulation system. In addition, the required coagulation time is shorter, and micro-flocs can be directly formed in the membrane pool. The new ecological nano-iron oxides generated by the Fe(II) / Cl2 system have significant hydrophilic properties. The system reacts and self-assembles on the membrane surface to produce a hydrophilic layer, which improves the anti-pollution effect of the membrane and ensures the water production effect when the filter membrane is actually used.

[0011] 2. The present invention requires few facilities, is easy to operate, has low maintenance and operation costs, and has strong arsenic removal capabilities. It is a new and efficient arsenic removal method. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 A schematic diagram of a novel ecological nano-iron dynamic membrane interface assembly and an enhanced arsenic removal method thereof in the present invention;

[0013] Figure 2 This is the effect of different quenchers on the arsenic removal effect of the system;

[0014] Figure 3The morphology comparison diagram of flocs, the left figure is a TEM image of flocs in the membrane pool after the hydraulic retention time in step 2 of comparative example 1 is over, and the right figure is a TEM image of flocs in the membrane pool after the hydraulic retention time in step 2 of embodiment 1 is over;

[0015] Figure 4 This is a SEM image of the membrane after the new ecological nano-iron dynamic interface assembly obtained after the membrane pool is running in Example 1. DETAILED DESCRIPTION

[0016] Specific implementation method 1: A new ecological nano-iron dynamic membrane interface assembly and enhanced arsenic removal method, characterized in that the method utilizes the in-situ coagulation, synergistic oxidation and membrane filtration of the Fe(II) / Cl2 system to simultaneously achieve in-situ modification of the membrane and deep removal of arsenic. The specific method is completed by the following steps:

[0017] 1. Chlorine oxidant and divalent iron salt are added to the arsenic-containing raw water at the same time, and the raw water is introduced into the membrane pool after tubular mixing;

[0018] 2. Stir the raw water in the membrane pool by aeration, mechanical stirring or hydraulic mixing to fully mix the raw water in the membrane pool;

[0019] 3. After the membrane pool is running, the water produced is a membrane assembled with a new ecological nano-iron dynamic interface and water free of arsenic.

[0020] Specific implementation method 2: This implementation method is different from specific implementation method 1 in that the chlorine oxidant in step 1 is sodium hypochlorite, calcium hypochlorite or liquid chlorine. The other steps are the same as those in specific implementation method 1.

[0021] Specific implementation method 3: This implementation method is different from specific implementation method 1 or 2 in that the divalent iron salt in step 1 is ferrous sulfate or ferrous chloride. The other steps are the same as those in specific implementation method 1 or 2.

[0022] Specific embodiment 4: The difference between this embodiment and specific embodiments 1 to 3 is that in step 1, when the arsenic concentration in the arsenic-containing raw water does not exceed 0.2 mg / L, the Fe in the divalent iron salt 2+ The dosage is 3 mg / L. The other steps are the same as those in the first to third embodiments.

[0023] Specific embodiment 5: The difference between this embodiment and specific embodiments 1 to 4 is that in step 1, when the arsenic concentration in the arsenic-containing raw water is 0.2 mg / L to 0.5 mg / L, the Fe in the divalent iron salt 2+ The dosage of the addition amount is 5 mg / L. The other steps are the same as those in the specific implementation modes 1 to 4.

[0024] Specific embodiment 6: This embodiment differs from specific embodiments 1 to 5 in that: in step 1, when the arsenic concentration in the arsenic-containing raw water does not exceed 0.2 mg / L, the dosage of the chlorine element in the chlorine oxidant is 1 mg / L. The other steps are the same as those of specific embodiments 1 to 5.

[0025] Specific embodiment 7: This embodiment differs from specific embodiments 1 to 6 in that: in step 1, when the arsenic concentration in the arsenic-containing raw water is 0.2 mg / L to 0.5 mg / L, the dosage of the chlorine element in the chlorine oxidant is 2 mg / L. The other steps are the same as those of specific embodiments 1 to 6.

[0026] Specific embodiment 8: This embodiment differs from specific embodiments 1 to 7 in that the time of tubular mixing in step 1 is 0.1 min to 2 min. The other steps are the same as those of specific embodiments 1 to 7.

[0027] Specific embodiment 9: This embodiment differs from specific embodiments 1 to 8 in that the hydraulic retention time of the membrane pool described in step 2 is 5 to 60 minutes. The other steps are the same as those of specific embodiments 1 to 8.

[0028] Specific embodiment 10: This embodiment differs from specific embodiments 1 to 9 in that the filter membrane used in the membrane pool described in step 2 is an ultrafiltration membrane or a microfiltration membrane; the water head of the membrane filtration is 0.1m to 2m. The other steps are the same as specific embodiments 1 to 9.

[0029] The following examples are used to verify the beneficial effects of the present invention:

[0030] Example 1: A novel ecological nano-iron dynamic membrane interface assembly and enhanced arsenic removal method utilizes the in-situ coagulation, synergistic oxidation and membrane filtration of the Fe(II) / Cl2 system to achieve deep arsenic removal. The specific method is completed by the following steps:

[0031] 1. Add arsenic to the Songhua River as raw water, add sodium hypochlorite and ferrous sulfate to the arsenic-containing raw water at the same time, and then introduce the raw water into the membrane pool after tubular mixing;

[0032] The arsenic content in the arsenic-containing raw water described in step 1 is 0.2 mg / L, the dosage of ferrous sulfate is 3 mg / L, and the dosage of sodium hypochlorite is 1 mg / L;

[0033] The time of the tubular mixing described in step 1 is 6 seconds;

[0034] Second, the membrane pool disturbs the water body by bottom aeration to fully mix the sodium hypochlorite and ferrous sulfate;

[0035] The hydraulic retention time of the membrane pool described in step 2 is 30 min;

[0036] The intensity of aeration described in step 2 is 5m 3 / (m 2 h);

[0037] The membrane in the membrane pool in step 2 is a polyethersulfone hollow fiber membrane with a molecular weight cutoff of 100 kDa, an effective water head of 80 cm, and an effective filtration area of ​​2 m 2 The ultrafiltration device is backwashed with clean water for 1 minute every 2 hours of operation, and the sludge is discharged for 1 minute. It can be operated continuously for 24 hours.

[0038] 3. After the membrane pool is running, the water is discharged to obtain the membrane after the new ecological nano-iron dynamic interface assembly and the water after the arsenic is removed;

[0039] Comparative Example 1: The method for removing arsenic by pre-oxidation-coagulation-membrane filtration is specifically completed according to the following steps:

[0040] 1. Add arsenic to the Songhua River as raw water, add sodium hypochlorite and ferric chloride to the arsenic-containing raw water at the same time, and then introduce the raw water into the membrane pool after tubular mixing;

[0041] The arsenic content in the arsenic-containing raw water described in step 1 is 0.2 mg / L, the dosage of ferric chloride is 3 mg / L, and the dosage of sodium hypochlorite is 1 mg / L;

[0042] The time of the tubular mixing described in step 1 is 6 seconds;

[0043] Second, the membrane pool disturbs the water body by bottom aeration to fully mix the sodium hypochlorite and ferrous sulfate;

[0044] The hydraulic retention time of the membrane pool described in step 2 is 30 min;

[0045] The intensity of aeration described in step 2 is 5m 3 / (m 2 h);

[0046] The membrane in the membrane pool in step 2 is a polyethersulfone hollow fiber membrane with a molecular weight cutoff of 100 kDa, an effective water head of 80 cm, and an effective filtration area of ​​2 m 2 The ultrafiltration device is backwashed with clean water for 1 minute every 2 hours of operation, and the sludge is discharged for 1 minute. It can be operated continuously for 24 hours.

[0047] 3. After membrane filtration, water free of arsenic is obtained.

[0048] Figure 1 A schematic diagram of a novel ecological nano-iron dynamic membrane interface assembly and its enhanced arsenic removal method in the present invention;

[0049] The test results show that in Example 1 of the present invention, when the arsenic content in the raw water is 0.2 mg / L, the dosage of ferrous sulfate is 3 mg / L, and the dosage of sodium hypochlorite is 1 mg / L, neither arsenic nor iron is detected in the effluent, and the arsenic removal effect is excellent; the arsenic concentration of the effluent of Comparative Example 1 of traditional pre-oxidation-coagulation-membrane filtration fluctuates in the range of 6 to 15 μg / L, there is a risk of excessive arsenic in the effluent, and iron in the effluent is not detected.

[0050] Example 2: Investigating the effect of quencher on arsenic removal effect of the system:

[0051] 1. Add arsenic to the Songhua River as raw water, add quencher, sodium hypochlorite and ferrous sulfate to the arsenic-containing raw water at the same time, and then introduce the raw water into the membrane pool after tubular mixing;

[0052] The quenching agents described in step 1 are nitrobenzene, tert-butyl alcohol and benzoic acid;

[0053] The concentration of the quencher described in step 1 is 5 mmol / L;

[0054] The arsenic content in the arsenic-containing raw water described in step 1 is 0.2 mg / L, the dosage of ferrous sulfate is 3 mg / L, and the dosage of sodium hypochlorite is 1 mg / L;

[0055] The time of the tubular mixing described in step 1 is 6 seconds;

[0056] Second, the membrane pool disturbs the water body by bottom aeration to fully mix the sodium hypochlorite and ferrous sulfate;

[0057] The hydraulic retention time of the membrane pool described in step 2 is 30 min;

[0058] The intensity of aeration described in step 2 is 5m 3 / (m 2 h);

[0059] The membrane in the membrane pool in step 2 is a polyethersulfone hollow fiber membrane with a molecular weight cutoff of 100 kDa, an effective water head of 80 cm, and an effective filtration area of ​​2 m 2 The ultrafiltration device is backwashed with clean water for 1 minute every 2 hours of operation, and the sludge is discharged for 1 minute. It can be operated continuously for 24 hours.

[0060] 3. After membrane filtration, water free of arsenic is obtained.

[0061] Figure 2 This is the effect of different quenchers on the arsenic removal effect of the system;

[0062] The study of Example 2 found that benzoic acid has a significant inhibitory effect on the arsenic removal effect of the system, indicating that chlorine free radicals are produced in the system and have a significant impact on the coagulation and arsenic removal effects of the system. Chlorine free radicals, as active species, can enhance the oxidation of organic matter and heavy metals in water and improve the coagulation effect. This is a major difference between the new ecological iron in-situ coagulation and the traditional coagulation system.

[0063] Figure 3 The morphology comparison diagram of flocs, the left figure is the TEM image of flocs in the membrane pool after the hydraulic retention time in step 2 of comparative example 1 is over, and the right figure is the TEM image of flocs in the membrane pool after the hydraulic retention time in step 2 of embodiment 1 is over.

[0064] from Figure 3 It can be seen that the flocs of the new ecological iron system in Example 1 of the present invention are smaller and looser.

[0065] The tests of Example 1 and Comparative Example 1 were run continuously for 15 days. The specific flux of the traditional pre-oxidation-coagulation-membrane filtration Comparative Example 1 dropped to 0.43, while the specific flux of the new ecological iron in-situ coagulation-membrane filtration Example 1 was 0.79. This shows that compared with the traditional coagulation system, the new ecological iron in-situ coagulation of the present invention can slow down membrane pollution, reduce water production costs, and has higher practical promotion and application value.

[0066] Figure 4 This is a SEM image of the membrane after the new ecological nano-iron dynamic interface assembly obtained after the membrane pool is running in Example 1.

[0067] from Figure 4 It can be seen that nano-iron oxides with a particle size of 10 to 20 nm are evenly distributed on the membrane surface, with a loose and porous structure and fewer large particles of organic pollutants on the surface, indicating that the dynamic generation and assembly of new ecological nano-iron on the membrane surface can greatly reduce membrane pollution.

Claims

1. A new ecological nano-iron dynamic membrane interface assembly and enhanced arsenic removal method, characterized in that The method utilizes the in-situ coagulation, synergistic oxidation and membrane filtration of the Fe(II) / Cl2 system to simultaneously achieve in-situ modification of the membrane and deep removal of arsenic. After the membrane pool is in operation, nano-iron oxides with a particle size of 10 to 20 nm are evenly distributed on the membrane surface. The structure is loose and porous, and there are fewer large particles of organic pollutants on the surface. After continuous operation for 15 days, the specific flux is 0.79, which improves the anti-pollution effect of the membrane; neither arsenic nor iron is detected in the effluent. The method is specifically completed according to the following steps:

1. Add arsenic to the Songhua River as raw water, add sodium hypochlorite and ferrous sulfate to the arsenic-containing raw water at the same time, and then introduce the raw water into the membrane pool after tubular mixing; The arsenic content in the arsenic-containing raw water described in step 1 is 0.2 mg / L, the dosage of ferrous sulfate is 3 mg / L, and the dosage of sodium hypochlorite is 1 mg / L; The time of the tubular mixing described in step 1 is 6 seconds; Second, the membrane pool disturbs the water body by bottom aeration to fully mix the sodium hypochlorite and ferrous sulfate; The hydraulic retention time of the membrane pool described in step 2 is 30 min; The aeration intensity described in step 2 is 5m 3 / (m 2 h); The membrane in the membrane pool in step 2 is a polyethersulfone hollow fiber membrane with a molecular weight cutoff of 100 kDa, an effective water head of 80 cm, and an effective filtration area of ​​2 m 2 The ultrafiltration device is backwashed with clean water for 1 minute every 2 hours of operation, and the sludge is discharged for 1 minute. It can be operated continuously for 24 hours.

3. After the membrane pool is running, the water produced is a membrane assembled with a new ecological nano-iron dynamic interface and water free of arsenic.

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