Self-cleaning filtration method for water treatment

Abstract

The application discloses a kind of self-cleaning filtration methods for water treatment, belong to gushing spring water treatment technical field;Including pretreatment, filtration adsorption treatment and disinfection treatment;Pretreatment stage, after centrifugal separation, gushing is added with the composite functional agent containing modified polyaspartic acid, modified glucosamine hydrochloride etc., and is filtered by microfiltration screen;Filtering adsorption treatment stage, after mixing pretreatment effluent with modified silicon dioxide-polyepoxysuccinic acid compound self-cleaning agent, into PVDF-TiO2 Compound modified ultrafiltration membrane module, membrane effluent is treated by nHAP-activated carbon composite adsorption column;Disinfection treatment stage, food-grade sodium hypochlorite is added to the advanced treatment water, and after disinfection, active carbon adsorption tank is handled to obtain treated gushing spring.The application can solve the problem that high turbidity and high calcium scale composite layer of karst rainy season gushing spring is difficult to remove, humic acid-calcium complex is difficult to adsorb, and high drug-resistant bacteria is difficult to disinfect.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of gushing spring water treatment, and particularly relates to a self-cleaning filtration method for water treatment. BACKGROUND

[0002] China is one of the countries with the widest distribution and richest types of karst landforms in the world, covering many regions such as Southwest China, South China and Northwest China; among them, the central and southern part of the Yungui Plateau (Qian South State, Anshun City, Yunnan Qujing City, Sichuan Southwest (Luzhou Xuyong County, Yibin Xingwen County, Liangshan State Leibo County) is the most typical and concentrated core area of karst landform development. Compared with ordinary mountain spring water in non-karst areas in Southwest China (such as mountain spring water in Yacheng District, Ya'an, Sichuan, and Yiliang County, Kunming, Yunnan), the gushing spring in this area has the following three unique characteristics, which is also a problem that the prior art cannot solve:

[0003] First, the problem of forming high turbidity, high calcium and high alkalinity, and stubborn scale composite water quality:

[0004] Ordinary mountain spring water has stable turbidity all year round (≤50 NTU, with a maximum of 30 NTU in the rainy season), calcium concentration of 40-80 mg / L, and pH value of 6.8-7.3 (neutral), without obvious scale formation.

[0005] However, due to limestone corrosion in the above-mentioned karst areas, the calcium ion concentration of gushing spring water reaches 120-250 mg / L (2-3 times that of ordinary mountain spring water) or even higher, and the pH value is 8.2-9.3 (alkaline). When the ambient temperature rises in summer, calcium bicarbonate decomposes rapidly into calcium carbonate precipitate, forming dense scale particles. Combined with the mud and microorganisms in the high-turbidity water (the turbidity suddenly rises to 150-300 NTU due to the rainwater washing the fissure mud and humus in the rainy season, far exceeding the turbidity range of ordinary mountain spring water), the scale-mud composite layer is formed, which has a hardness much higher than the density of the mud layer of ordinary mountain spring water. Conventional backwashing process can only remove part of the loose mud on the surface, and cannot strip the internal dense scale, which seriously affects the filter membrane flux and treatment efficiency.

[0006] Second, the problem of producing humic acid-calcium complex:

[0007] The ordinary mountain spring water is mainly free humic acid, and the concentration is less than or equal to 2 mg / L, and the adsorption rate of the conventional activated carbon is more than 85%. The karst spring in the above area: the precipitation in the rainy season washes the surface vegetation residues (shrubs, ferns and fallen leaves), and the humic acid generated by the decomposition of the residues penetrates into the spring with the rainwater. Due to the existence of high-concentration calcium ions in the water, the humic acid will form a stable humic acid-calcium complex with the calcium ions. The complex has a compact structure, and the adsorption rate of the conventional activated carbon is much lower than that of the free humic acid in the ordinary mountain spring water, which leads to the difficulty in effectively removing the organic matter, and the residual humic acid will react with the reagent in the subsequent disinfection process, thereby increasing the risk of generating disinfection by-products.

[0008] Thirdly, the problem of producing high drug-resistant bacteria:

[0009] The bacteria in the ordinary mountain spring water do not have a special protective layer, and the conventional sodium hypochlorite disinfection (dosing amount: 0.5-1.0 mg / L) can achieve a killing rate of more than 99%.

[0010] However, the karst cave in the above area is dark and humid, and the cell membranes of the alkali-resistant bacteria (such as bacillus and pseudomonas) growing in the cave will form a “calcium salt protective layer”, which can isolate the conventional disinfectant. The killing rate of the conventional sodium hypochlorite (0.5-1.0 mg / L) on the alkali-resistant bacteria is less than 60%, and the disinfection is not complete.

[0011] Therefore, it is extremely important to provide a filtering method which can effectively solve the problems of the composite water quality removal, the humic acid-calcium complex adsorption and the high drug-resistant bacteria disinfection. SUMMARY

[0012] The purpose of the present application is to provide a self-cleaning filtering method for water treatment, which effectively solves the problems of the composite water quality of the karst spring in the rainy season, such as high turbidity, high calcium, humic acid-calcium complex and high drug-resistant bacteria, through a whole-process technology of pretreatment, filtration and adsorption and disinfection treatment.

[0013] The purpose of the present application is achieved by the following technical solutions:

[0014] S1. Pretreatment:

[0015] S11. After the intermittent spring in the rainy season in the karst area is separated by a vortex centrifugal separator, a pretreated spring is obtained; wherein the calcium concentration of the intermittent spring in the rainy season in the karst area is greater than or equal to 120 mg / L, the turbidity is greater than or equal to 120 NTU, and the total humic acid concentration is greater than or equal to 1.8 mg / L (including humic acid-calcium complex and free humic acid);

[0016] S12. A composite functional agent is added to the pretreated spring, and after sufficient stirring, a composite flocculation body is obtained;

[0017] The composite functional agent comprises the following components:

[0018] Modified polyaspartic acid: polyaspartic acid modified by aminopropyl triethoxysilane (APTES);

[0019] Modified glucosamine hydrochloride: glucosamine hydrochloride coated by food-grade chitosan;

[0020] Modified nano-montmorillonite: nano-montmorillonite modified by aluminum ion impregnation;

[0021] pH buffer;

[0022] S13. The composite floc is filtered through a 0.08-0.12 μm microfiltration screen to obtain pretreated effluent;

[0023] S2. Filtration and adsorption treatment:

[0024] S21. The pretreated effluent is mixed with modified silica-polyepoxysuccinic acid (modified nSiO2-PESA) self-cleaning agent, and then introduced into a PVDF-TiO2 composite modified ultrafiltration membrane module; when the pressure difference between the inlet and outlet of the membrane is > 0.03-0.04 MPa, self-cleaning is started; the modified silica is silica modified by sodium dodecyl benzene sulfonate (SDBS) and hydroxypropyl methyl cellulose in sequence (in the modified nSiO2-PESA self-cleaning agent, anionic modified nSiO2 and cationic modified nano-montmorillonite can form a stable cooperative isolation layer through charge attraction, avoiding competition with modified nano-montmorillonite adsorption, forming a continuous hydrophilic isolation layer on the membrane surface, reducing the membrane pollution rate, and ensuring long-term stable operation of the membrane module);

[0025] S22. The membrane effluent is treated by nHAP-activated carbon composite adsorption column to obtain deeply treated water;

[0026] S3. Disinfection treatment:

[0027] Food-grade sodium hypochlorite is added to the deeply treated water for disinfection, and the dosage is 0.45-1 mg / L; after disinfection, the activated carbon adsorption tank is treated to obtain treated gushing spring.

[0028] As some embodiments of the present application, in the composite functional agent, the mass ratio of some components is modified polyaspartic acid: modified glucosamine hydrochloride: modified nano-montmorillonite = (1.8-2.2): (0.9-1.1): (0.9-1.1).

[0029] As some embodiments of the present application, in the PVDF-TiO2 composite modified ultrafiltration membrane module, the membrane pore size is 0.005-0.009 μm. This pore size can retain humic acid-calcium complexes in the pretreated water body that have not been adsorbed, while allowing water molecules to pass through normally.

[0030] As some embodiments of the present application, the calcium concentration electrode is used to monitor the calcium concentration in the deep treated water, and the calcium concentration is adjusted by adding 10wt% calcium chloride solution; when the calcium concentration is <14mg / L, the calcium chloride solution dosage is >0.08mL / L; when the calcium concentration is 14-16mg / L, the calcium chloride solution dosage is 0.04-0.08mL / L; when the calcium concentration is ≥16mg / L, no calcium chloride solution needs to be added, so that the calcium concentration of the water before disinfection is stabilized at 16-25mg / L.

[0031] In actual implementation, the calcium complexing ability of the modified polyaspartic acid is strong, and excessive complexing can lead to too low calcium concentration before disinfection, which reduces the stability of sodium hypochlorite, and the residual chlorine cannot meet the requirements of the pipe network terminal. The present scheme realizes precise compensation of calcium concentration by calcium concentration electrode and calcium addition, maintains the stability of sodium hypochlorite, ensures that the residual chlorine after disinfection meets the standard requirements, and avoids disinfection failure caused by low calcium environment.

[0032] As some embodiments of the present application, when the turbidity of the intermittent spring in the rainy season in the karst region is >350NTU, polyacrylamide (CPAM) is added to the pretreated spring; at the same time, a sedimentation tank is added before the microfiltration screen.

[0033] When the turbidity of the spring increases, a large amount of silt will wrap the components of the composite functional agent, causing the dispersion of the flocs and the blockage of the microfiltration screen, so that the turbidity of the pretreated effluent exceeds the standard.

[0034] By adding CPAM and adding a sedimentation tank, CPAM enhances the floc formation effect, the sedimentation tank removes a large amount of coarse flocs in advance, reduces the filtration resistance of the microfiltration screen, and ensures that the turbidity of the pretreated effluent meets the standard under extreme turbidity.

[0035] As some embodiments of the present application, before adding the composite functional agent, modified attapulgite is added first, and the modified attapulgite is iron ion modified attapulgite.

[0036] The karst spring in southwest China often contains heavy metal ions due to the dissolution of minerals in the karst cave. By adding iron ion modified attapulgite before adding the composite functional agent, the iron ion sites of the attapulgite can preferentially adsorb heavy metals, and the heavy metal concentration of the effluent can meet the standard with the composite flocs being trapped.

[0037] In actual implementation, the modified palygorskite and the CPAM are directly combined due to strong charge attraction to form a modified palygorskite-CPAM complex, which leads to the decrease of the heavy metal adsorption capacity of the modified palygorskite and the flocculation strengthening effect of the CPAM. Based on this, as some implementable manners of the present application, the modified palygorskite is further modified by polyethylene glycol 4000; the polyethylene glycol 4000 forms a hydrogen bond with the surface hydroxyl group of the modified palygorskite through the hydroxyl group, coats part of the negative potential sites, so that the zeta potential of the modified palygorskite decreases, and the charge attraction force of the cationic CPAM is significantly weakened; at the same time, the long chain structure of the PEG4000 can form a steric hindrance on the surface of the modified palygorskite, avoiding the agglomeration of the modified palygorskite due to the Ca 2+ Bridge effect occurs agglomeration.

[0038] The modified palygorskite, the CPAM and the composite functional agent are sequentially added to the pretreated gushing spring; the modified palygorskite is added first, and then the surface iron ions form ion exchange and adsorption complexation with heavy metal ions (such as Pb 2+ ) to form a modified palygorskite-heavy metal complex. The complex is further reduced due to the adsorption of heavy metals and the charge repulsion of the cationic CPAM, further reducing the adsorption of the two; the CPAM is added after the modified palygorskite, at this time there is no large amount of free heavy metal competition in the water body, the CPAM can directly combine with the mud and the modified nano montmorillonite to form a preliminary flocculation, and the settling velocity is improved; finally, the composite functional agent is added, which can complex residual Ca 2+ , humic acid-calcium complex, etc., and the modified palygorskite-heavy metal complex and the CPAM formed in the early stage are synergized to form a multi-layer composite flocculation for effective subsequent filtration.

[0039] A 10-15cm thick modified quartz sand filter layer is added between the sedimentation tank and the microfiltration screen; the modified quartz sand is aluminum ion impregnated quartz sand; the particle size of the modified quartz sand is 0.5-1mm; after the quartz sand is modified by aluminum ion impregnation, it can assist the cationic CPAM to connect the negatively charged small particles (such as the modified palygorskite-heavy metal complex that has not settled) in the water to form larger flocculation for interception, so as to reduce the total amount of pollutants entering the membrane module.

[0040] As some implementable manners of the present application, food-grade polyglycerol fatty acid ester is added to the composite functional agent.

[0041] In actual implementation, the modified polyaspartic acid is in long-term contact with the PVDF membrane, which is easy to react with the membrane surface to cause the aging of the membrane wire; at the same time, the modified palygorskite and the modified nSiO2 are easy to agglomerate in a high calcium environment, affecting the heavy metal adsorption and the membrane protection effect.

[0042] In the scheme, the food-grade polyglycerol fatty acid ester contains an amphiphilic structure, the hydrophobic segment is combined with the surface of the PVDF membrane to form a temporary protective layer, and the amino group of the modified polyaspartic acid is blocked from reacting with the fluorine atoms on the surface of the membrane; at the same time, the hydrophilic segment is adsorbed on the surface of the modified attapulgite and the modified nSiO2, and the dispersibility of the modified attapulgite and the modified nSiO2 in a high-calcium environment is enhanced through the steric hindrance effect, thereby avoiding agglomeration.

[0043] As some embodiments of the present application, the activated carbon adsorption tank is filled with double-layer fillers, the lower layer is coconut shell activated carbon with a particle size of 0.8-1.2 mm, and the upper layer is activated carbon with a particle size of 0.4-1.2 mm.

[0044] In the scheme, the lower layer of coconut shell activated carbon adsorbs macromolecular disinfection by-products, and the upper layer of activated carbon adsorbs small molecular pollutants, thereby improving the disinfection by-product removal effect.

[0045] Compared with the prior art, the present application has the following beneficial effects:

[0046] The present application provides a whole-process technology of pretreatment, filtration and adsorption, and disinfection treatment according to the characteristics of high turbidity, high calcium, humic acid-calcium complex, and high drug-resistant bacteria of Karst rain-season gushing springs, effectively solves the problems of difficult removal of high-turbidity high-calcium water scale composite layer, difficult adsorption of humic acid-calcium complex, and difficult disinfection of high drug-resistant bacteria mentioned in the background art, guarantees that the effluent water quality meets the standards, and provides an efficient and feasible technical solution for Karst region gushing spring water treatment in the southwest.

[0047] The specific solution idea is as follows:

[0048] Firstly, the problem of difficult removal of high-turbidity high-calcium water scale composite layer is solved:

[0049] In the pretreatment stage, the Karst region rain-season intermittent gushing spring is subjected to vortex centrifugal separation of particles with a size of 4-6 microns or more, so as to reduce the subsequent treatment load; then a composite functional agent is added to the pretreated gushing spring, the modified polyaspartic acid in the composite functional agent forms a complex with calcium ions, the amino groups of the modified polyaspartic acid form hydrogen bonds with the hydroxyl groups on the surface of the modified nanometer montmorillonite, and the aluminum ions on the surface of the modified nanometer montmorillonite form coordination bonds with the carboxyl groups of the modified polyaspartic acid, so as to guide the modified nanometer montmorillonite to be adsorbed on the surface of the modified polyaspartic acid-calcium complex in a directional manner, and form a modified polyaspartic acid-calcium-modified nanometer montmorillonite composite carrier, which simultaneously adsorbs humic acid and wraps alkali-resistant bacteria and silt particles, and after filtration through a microfiltration screen, the turbidity of the pretreated effluent is significantly reduced.

[0050] The residual modified nano-montmorillonite and modified nSiO2-PESA in the pretreated effluent form a synergistic isolation layer, realizing the cross-stage cooperation of pretreatment and filtration: the modified nano-montmorillonite continues to adsorb trace pollutants in water, the modified nSiO2 enhances the hydrophilicity of the membrane surface, and the PESA further chelates residual calcium ions, all of which work together to reduce the attachment of scale-bacteria on the membrane surface.

[0051] Secondly, the problem of adsorption difficulty of humic acid-calcium complex is solved:

[0052] The carboxyl group of the modified polyaspartic acid has a stronger complexing ability with Ca 2+ than humic acid, and can competitively capture Ca 2+ in the humic acid-calcium complex, realizing preliminary complex breaking; the chitosan coating layer of the modified glucosamine hydrochloride slowly swells and releases the core material; the core material is further converted into glucosamine derivatives in weakly alkaline water, assisting the modified polyaspartic acid in strengthening the complex breaking effect and releasing free humic acid, and at the same time, the modified nano-montmorillonite captures the humic acid. However, due to the limited complex breaking efficiency of the composite functional agent, when the subsequent membrane effluent is treated by the nHAP-activated carbon composite adsorption column, the nHAP replaces Ca 2+ in the residual complex through ion exchange, ensuring that the free humic acid is deeply adsorbed by the activated carbon.

[0053] After the pretreated effluent enters the PVDF-TiO2 composite modified ultrafiltration membrane module, the synergistic isolation layer of the residual modified nano-montmorillonite and modified nSiO2-PESA further intercepts trace amounts of unadsorbed humic acid-calcium complex; the membrane effluent is treated by the nHAP-activated carbon composite adsorption column, the nHAP replaces calcium ions in the residual complex, and the activated carbon deeply adsorbs free humic acid, finally deeply reducing the concentration of humic acid in the water, solving the problem of poor adsorption effect of conventional adsorption process on humic acid-calcium complex.

[0054] Thirdly, the problem of difficult killing of high drug-resistant bacteria is solved:

[0055] The modified glucosamine hydrochloride derivative released by the slow degradation of the chitosan coating layer penetrates the calcium salt protective layer of alkali-resistant bacteria and forms a synergistic adsorption site with the modified nano-montmorillonite, improving the removal effect of alkali-resistant bacteria; the modified nano-montmorillonite maintains dispersibility under the action of the buffer, fully wrapping the alkali-resistant bacteria in water, and reducing the subsequent treatment load.

[0056] The residual modified nano montmorillonite in the pretreated effluent and the modified nSiO2-PESA synergistic isolation layer adsorb bacteria attached to the membrane surface and reduce the breeding of bacteria in the membrane module; 0.45-1 mg / L of food-grade sodium hypochlorite (conventional reagent and conventional dosage) is added to the deep treatment water, and the sodium hypochlorite directly acts on the alkali-resistant bacteria inside the calcium salt protection layer, and the killing effect is remarkable, and no coliform bacteria are detected; after disinfection, the activated carbon adsorption tank is treated to remove disinfection by-products and ensure the safety of the effluent. DETAILED DESCRIPTION

[0057] Example 1

[0058] S1. Pretreatment:

[0059] S11: Take 100 L of Karst spring (taken from the Karst region of Qian Nan in Guizhou, calcium concentration 180 mg / L, pH 8.8, turbidity 220 NTU, Pb 2+ Concentration is 0.03 mg / L, total humic acid concentration is 2.5 mg / L (of which humic acid-calcium complex concentration is 1.75 mg / L, and free humic acid concentration is 0.75 mg), introduce 10 L into the pretreatment tank, start the vortex centrifugal device (this is the prior art), the vortex flow guides the river sand with particle size ≥4-6 μm to deposit, after standing for 15 min, the supernatant (pretreated spring) is introduced into the treatment tank;

[0060] S12: First, add modified attapulgite (dosing amount 0.6 mg / L) to the pretreated spring in the treatment tank, stir at 120 r / min for 6 min; then add a composite functional agent (the first component is added in an amount of 0.35 mg / L; the second component is added in an amount to control the pH value of the spring to 7.8-8.7), continue to stir at 130 r / min for 22 min to form a composite floc.

[0061] S13: The composite floc is filtered through a 0.1 μm microfiltration screen, and the pretreated effluent is collected.

[0062] S2. Filtration and adsorption treatment:

[0063] S21: Add modified nSiO2-PESA self-cleaning agent (0.04 mg / L in solid form) to the pretreated effluent, stir uniformly, and then pass into the PVDF-TiO2 membrane module (membrane area 0.1 m², membrane pore size 0.008 μm), cross-flow filtration (speed 0.5 m / s, pressure 0.14 MPa); when the membrane inlet and outlet pressure difference >0.35 MPa, start self-cleaning.

[0064] The self-cleaning is realized through an automatic control system, and the control system comprises a pressure sensor, a PLC controller, an electromagnetic valve and a cleaning pump. The pressure sensor is installed in the water inlet and outlet pipes of the membrane module respectively, and collects pressure signals in real time and transmits them to the PLC controller. When the calculated pressure difference between the inlet and outlet of the membrane is greater than 0.035 MPa, the PLC controller triggers the electromagnetic valve (corresponding to the pure water backflushing pipeline, the pretreated water extraction pipeline and the normal filtration pipeline) and the cleaning pump (corresponding to the pure water supply and the pretreated water extraction) according to a preset logic, and sequentially performs the steps of hydraulic backflushing, functional agent enhanced cleaning and pure water final washing. After the cleaning is completed, the state of the electromagnetic valve is automatically switched and the cleaning pump is stopped, and the cross-flow filtration operation is restored.

[0065] The self-cleaning specifically comprises the following three steps:

[0066] The first step is hydraulic backflushing: pure water is used, the pressure is 0.2 MPa, and the time is 12 s, so as to strip loose pollutants from the surface of the membrane.

[0067] The second step is functional agent enhanced cleaning: the membrane outlet water filtered through a 0.22 μm precision filter is extracted, a composite functional agent mother liquor is added at a volume ratio of 100:1, and after uniform stirring, the membrane module is washed in a reverse flushing manner at a pressure of 0.18 MPa, and the time is 30 s. The modified polyaspartic acid in the composite functional agent mother liquor can dissolve small water scale, and the modified glucosamine hydrochloride derivative can assist in dispersing residual pollutants.

[0068] The preparation method of the composite functional agent mother liquor is as follows: the composite functional agent is dissolved in the membrane outlet water at a mass-volume ratio of 1:10 (g / mL), stirred for 30 min, filtered through a 0.02 μm precision filter, and the composite functional agent mother liquor is obtained.

[0069] The third step is pure water final washing: pure water is used for backflushing again, the pressure is 0.15 MPa, and the time is 15 s, so as to wash away the residual pretreated water impurities on the surface of the membrane and complete the self-cleaning.

[0070] The pure water used for self-cleaning needs to meet the "Drinking Water Health Standards", the conductivity is ≤10 μS / cm, and the turbidity is ≤0.5 NTU, so as to avoid secondary pollution of the membrane module caused by impurities in the cleaning water.

[0071] S22: The membrane outlet water is introduced into an nHAP-activated carbon composite adsorption column

nHAP (nano-hydroxyapatite, particle size 50-100 nm) and coconut activated carbon are filled at a mass ratio of 1:2, the filling height is 1.5 m, and the filtration speed is 6 m / h

[0072] The calcium concentration of the deep treated water was detected by a calcium concentration electrode (detection value 15 mg / L), and a 0.06 mL / L 10 wt% calcium chloride solution was added to the metering pump to compensate the calcium concentration to 20 mg / L.

[0073] S3. Disinfection treatment:

[0074] The food-grade sodium hypochlorite solution (1 mg / L of sodium hypochlorite solid) was added to the compensated deep treated water, and stirred for 30 min; after disinfection, the activated carbon adsorption tank was passed in 【0.8-1.2 mm coconut shell activated carbon (particle size 0.8-1.2 mm, iodine adsorption value≥1000 mg / g) in the lower layer, 0.4-1.2 mm coal activated carbon in the upper layer, height ratio 2:1, filter speed 10 m / h】to collect the treated gushing spring.

[0075] In the above examples, the preparation method of the related reagent materials is as follows:

[0076] (1) Modified polyaspartic acid: take 100 g of food-grade polyaspartic acid (solid content≥40%), add 500 mL of deionized water, and stir until completely dissolved; add 8 g of APTES to the solution, and stir at 60°C for 3 h; after the reaction is completed, vacuum drying (60°C, vacuum degree -0.09 MPa) to constant weight, and crushing through a 100 mesh sieve to obtain modified polyaspartic acid.

[0077] (2) Modified glucosamine hydrochloride: take 50 g of food-grade glucosamine hydrochloride, add 200 mL of deionized water, and stir until dissolved; take another 20 g of food-grade chitosan (degree of deacetylation≥90%), add 100 mL of 1 wt% acetic acid solution, and stir until dissolved; slowly pour the chitosan solution into the glucosamine hydrochloride solution, and stir at 30°C for 2 h; after the reaction, spray drying (inlet air temperature 120°C, outlet air temperature 60°C) to obtain modified glucosamine hydrochloride.

[0078] (3) Modified nano-montmorillonite: take 50 g of nano-montmorillonite (particle size 50-100 nm), add 500 mL of 0.1 mol / L aluminum chloride solution, and stir at 50°C for 2 h; filter and wash with deionized water until there is no chloride ion in the filtrate; vacuum drying (80°C, vacuum degree -0.09 MPa) to constant weight, and crushing through a 200 mesh sieve to obtain modified nano-montmorillonite.

[0079] (4) Composite functional agent (consisting of a first component and a second component): take modified polyaspartic acid, modified glucosamine hydrochloride, and modified nanometer montmorillonite in a mass ratio of 2:1:1, mix uniformly to obtain the first component; the second component is a pH buffer (food-grade sodium citrate: food-grade sodium dihydrogen phosphate = 1:2 in mass ratio). It can control the pH value of the gushing spring within 7.8-8.7.

[0080] (5) Modified silicon dioxide:

[0081] ① SDBS (anionic) modification: take 50g of silicon dioxide (particle size 8-22nm), add 500mL of 0.02mol / L SDBS solution, stir at 60℃ for 2h, filter, wash, and vacuum dry (80℃, vacuum degree -0.09MPa) to constant weight to obtain SDBS modified nSiO2.

[0082] ② HPMC modification: add 500mL of 0.5wt% HPMC aqueous solution to the above SDBS modified nSiO2, stir at 50℃ for 1h; spray dry (inlet temperature 120℃, outlet temperature 60℃) to obtain HPMC-SDBS complex modified nSiO2.

[0083] (6) Modified nSiO2-PESA compound self-cleaning agent: take 20g of modified nSiO2 and 60g of PESA (solid content ≥40%), add 200mL of deionized water, ultrasonic dispersion for 30min (power 300W) to obtain a uniform compound self-cleaning agent.

[0084] (7) PVDF-TiO2 composite modified ultrafiltration membrane:

[0085] ① Casting solution preparation: take 15g of PVDF powder (molecular weight 500,000, food grade), add 80g of N,N-dimethylacetamide, stir to dissolve completely at 50℃; add 5g of TiO2 nanoparticles (particle size 20-30nm, anatase type), ultrasonic dispersion for 30min, then stir for 2h to obtain a uniform casting solution.

[0086] ② Membrane preparation: uniformly coat the casting solution on a clean glass substrate (wet film thickness 200μm), place in air for 5min; immerse in a 25℃ deionized water coagulation bath for 24h; after taking out, wash with deionized water, vacuum dry (50℃, vacuum degree -0.09MPa) to constant weight to obtain a PVDF-TiO2 composite modified ultrafiltration membrane.

[0087] (8) Modified attapulgite:

[0088] ① Iron ion modification: take 100 g of attapulgite (particle size 100-200 mesh), add 1000 mL of 0.2 mol / L ferric chloride solution, and stir and soak at 60°C for 2 h; filter and wash with deionized water until the filtrate is free of iron ions; vacuum dry (80°C, vacuum degree -0.09 MPa) to constant weight to obtain iron ion modified attapulgite.

[0089] ② PEG4000 modification: take 50 g of iron ion modified attapulgite, add 500 mL of 0.1% PEG4000 aqueous solution, and stir at 50°C for 1 h; filter and vacuum dry (60°C, vacuum degree -0.09 MPa) to constant weight to obtain PEG4000-iron ion composite modified attapulgite.

[0090] Example 2

[0091] Compared with Example 1, the following adjustments are made:

[0092] Yongquan water quality: calcium concentration 250 mg / L, pH 9.2, turbidity 300 NTU, Pb 2+ concentration 0.032 mg / L.

[0093] Composite functional agent: the first component is added at a dosage of 0.45 mg / L, and the second component is added at a dosage to control the pH value of Yongquan to 7.8-8.7.

[0094] Modified attapulgite: dosage 0.7 mg / L.

[0095] Modified nSiO2-PESA: dosage 0.05 mg / L.

[0096] PVDF-TiO2 membrane: cross-flow speed 0.6 m / s.

[0097] Calcium concentration compensation: the calcium concentration of the deep treatment water is detected to be 18 mg / L, and no calcium chloride needs to be added.

[0098] The remaining parameters and steps not mentioned are the same as in Example 1.

[0099] Example 3

[0100] On the basis of Example 1, 0.05 wt% food-grade polyglycerol fatty acid ester is additionally added to the composite functional agent, and the mixture is added after being uniformly mixed.

[0101] The remaining parameters and steps are the same as in Example 1.

[0102] Example 4

[0103] Compared with Example 3, the following adjustments are made:

[0104] Spring water quality: turbidity 400 NTU (add silt to the spring of Example 3 to adjust).

[0105] Food-grade CPAM was added to the treatment tank at a dosage of 0.03 mg / L.

[0106] A slanted tube sedimentation tank (inclined at 60° and with a residence time of 18 min) was added before the treatment tank and the microfiltration screen; a 12 cm thick modified quartz sand filter layer (particle size 0.5-1 mm) was added between the sedimentation tank and the microfiltration screen.

[0107] The preparation method of the modified quartz sand was as follows: 100 g of quartz sand (particle size 0.5-1 mm) was taken, 500 mL of 0.1 mol / L aluminum sulfate solution was added, and stirring and immersion were carried out at 50°C for 2 h; filtration was performed, and the product was washed with deionized water for 3 times and dried at 105°C to constant weight to obtain aluminum ion modified quartz sand.

[0108] After the above adjustment, the specific operation of S12 was as follows:

[0109] First, modified attapulgite (dosage 0.6 mg / L) was added and stirred for 6 min, then CPAM (molecular weight 3-5 million) was added and stirred for 3 min, and then the mixture was allowed to stand for 5 min, and finally a composite functional agent containing food-grade polyglycerol fatty acid ester (polyglycerol-6 stearate, HLB value 9-11) (dosage 0.3 mg / L) was added and stirred for 28 min; the composite flocs first entered the slanted tube sedimentation tank for sedimentation, and then passed through the modified quartz sand filter layer and the 0.1 μm microfiltration screen for filtration to obtain the pretreated effluent.

[0110] The remaining parameters and steps were the same as in Example 3.

[0111] It should be noted that the reagents used in the above examples were all food-grade if available.

[0112] The residual amount of food-grade polyglycerol fatty acid ester in the final treatment of the spring in Examples 1-4 was <0.05 mg / L; the total number of bacteria was ≤50 CFU / mL; and no coliform bacteria or heat-resistant coliform bacteria were detected.

[0113] Comparative Example 1

[0114] In Comparative Example 1, the modified polyaspartic acid in the composite functional agent was replaced by unmodified polyaspartic acid, the modified glucosamine hydrochloride was replaced by unmodified glucosamine hydrochloride, and the modified nanometer montmorillonite was replaced by unmodified nanometer montmorillonite.

[0115] The remaining parameters and steps were the same as in Example 1.

[0116] Comparative Example 2

[0117] On the basis of example 1, no modified nSiO2-PESA self-cleaning agent is added, and the remaining parameters and steps are the same as in example 1.

[0118] Comparative example 3

[0119] Compared with example 1, the membrane effluent directly enters the calcium concentration compensation link without passing through the nHAP-activated carbon composite adsorption column, and the remaining parameters and steps are the same as in example 1.

[0120] Comparative example 4

[0121] Compared with example 1, no modified nano montmorillonite is added to the composite functional agent, and the remaining parameters and steps are the same as in example 1.

[0122] Comparative example 5

[0123] Compared with example 4, the order of adding materials is adjusted: first add CPAM (cationic, molecular weight 3-5 million) and stir for 3 min, then add modified attapulgite (addition amount 0.6 mg / L) and stir for 6 min, and finally add the composite functional agent containing food-grade polyglycerol fatty acid ester (addition amount 0.4 mg / L) and stir for 28 min; the composite flocs first enter the inclined tube sedimentation tank for sedimentation, then pass through the modified quartz sand filter layer and the 0.1 μm microfiltration screen for filtration to obtain the pretreated effluent.

[0124] The remaining parameters and steps are the same as in example 4.

[0125] Experimental example

[0126] Take the pretreated effluent in examples 1-4 and comparative examples 1-5 and the final treatment gushing spring, detect its turbidity (determined by a portable turbidity meter), calcium concentration (EDTA complexometric titration method), humic acid concentration

ultraviolet spectrophotometry (wavelength 254 nm)

【plate count method: take 10 mL of water sample, gradient dilution (10 -3 -10 -5 times) is carried out, then take 0.1 mL of the diluent and spread it on LB culture medium, cultivate at 37℃ for 24 h, and count the number of bacteria; the initial bacterial concentration is 10 6 -10 7 CFU / mL, the kill rate = (initial bacterial number - residual bacterial number) / initial bacterial number × 100%, membrane flux attenuation rate

membrane flux detector records the initial flux and the flux after 30 days of operation, and calculates the attenuation rate (attenuation rate = (initial flux - 30-day flux) / initial flux × 100%)

[0127] Table 1:

[0128]

[0129] Note: "-" in Table 1 means that the relevant experiment is not carried out.

[0130] From Table 1, it can be seen that the treatment effect of Examples 1-4 is better than that of Comparative Examples 1-5. After treatment of Examples 1-4, the turbidity is ≤1.5 NTU, humic acid is ≤0.07 mg / L (of which humic acid-calcium complex is ≤0.02 mg / L), alkali-resistant bacteria killing rate is ≥99.2%, Pb 2+ ≤0.008 mg / L, chloroform is ≤25.7 μg / L, and membrane flux attenuation rate is ≤11.1%, which is better than that of the comparative examples, fully embodying the effectiveness of the process of the application on karst rain season gushing spring water treatment.

[0131] In Comparative Example 1, the unmodified polyaspartic acid lacks amino groups grafted by APTES, and cannot form stable complexes with calcium, nor can it guide the directional adsorption of nano-montmorillonite, resulting in a sharp decrease in calcium complexing rate and loose flocs; the surface of the unmodified nano-montmorillonite is not modified with aluminum ions, and the adsorption sites are few and easy to agglomerate, making it difficult to capture humic acid and alkali-resistant bacteria; the chitosan coating layer of unmodified glucosamine hydrochloride degrades out of control, and cannot continuously release the derivative products that break the protective layer.

[0132] In Comparative Example 2, after the modified nSiO2-PESA is missing, the membrane surface loses the hydrophilic isolation layer and calcium chelation protection: on the one hand, the hydrophilicity of the membrane surface decreases, and pollutants are easy to adhere and form a dense scale layer; on the other hand, without PESA continuously chelating residual calcium, calcium is easy to form scale in the membrane pore channel. Although pretreatment can still remove part of the pollutants, the membrane fouling rate increases significantly, and the membrane flux attenuation rate increases significantly.

[0133] In Comparative Example 3, nHAP can replace calcium in the humic acid-calcium complex to release free humic acid for activated carbon adsorption, and after the missing, it is difficult to remove humic acid in depth.

[0134] In Comparative Example 4, after the modified nano-montmorillonite is missing, the "polyaspartic acid-calcium" complex formed by the modified polyaspartic acid lacks carrier support, the floc particle size is small, and the settling property is poor, the turbidity of the pretreatment effluent increases; at the same time, the silicon hydroxyl group of the montmorillonite and the derivative products of glucosamine hydrochloride form a synergistic adsorption site, the humic acid adsorption effect decreases, and part of the pollutants enter the membrane module with the water flow, resulting in an increase in the membrane flux attenuation rate.

[0135] In Comparative Example 5, CPAM (positive) is added first, and then the modified attapulgite (which is still weakly negatively charged after modification by PEG4000) is added, which causes partial electrostatic adsorption between them, resulting in the modified attapulgite being unable to fully adsorb heavy metals.

Claims

1. A self-cleaning filtration method for water treatment, characterized in that, Includes the following steps: S1. Preprocessing: S11. The intermittent springs in the karst region during the rainy season are separated by vortex centrifugation to obtain pretreated springs; wherein, the intermittent springs in the karst region during the rainy season have a calcium concentration ≥120mg / L, a turbidity ≥120NTU, and a total humic acid concentration ≥1.8mg / L. S12. Add the composite functional agent to the pretreated spring and stir thoroughly to obtain composite flocs; The composite functional agent comprises the following components: Modified polyaspartic acid: obtained by modifying polyaspartic acid with aminopropyltriethoxysilane; Modified glucosamine hydrochloride: obtained by coating glucosamine hydrochloride with food-grade chitosan; Modified nano-montmorillonite: obtained by modifying nano-montmorillonite through aluminum ion impregnation; pH buffer; S13. Filter the composite flocs through a 0.08-0.12μm microfiltration screen to obtain pretreated effluent; S2. Filtration and adsorption treatment: S21. Mix the pretreated effluent with a modified silica-polyepoxysuccinic acid compound self-cleaning agent, and then pass it through a PVDF-TiO2 composite modified ultrafiltration membrane module; start self-cleaning when the pressure difference between the membrane inlet and outlet is >0.03-0.04MPa; The modified silica is obtained by modifying silica successively with sodium dodecylbenzenesulfonate and hydroxypropyl methylcellulose; S22. The membrane effluent is treated by an nHAP-activated carbon composite adsorption column to obtain deeply treated water; S3. Disinfection treatment: Food-grade sodium hypochlorite is added to the deeply treated water for disinfection at a dosage of 0.45-1 mg / L; after disinfection, the water is treated by activated carbon adsorption tank to obtain treated spring water.

2. The self-cleaning filtration method for water treatment according to claim 1, characterized in that, In the composite functional agent, the mass ratio of some components is: modified polyaspartic acid: modified glucosamine hydrochloride: modified nano montmorillonite = (1.8-2.2): (0.9-1.1): (0.9-1.1).

3. The self-cleaning filtration method for water treatment according to claim 1, characterized in that, In the PVDF-TiO2 composite modified ultrafiltration membrane module, the membrane pore size is 0.005-0.009μm.

4. The self-cleaning filtration method for water treatment according to claim 1, characterized in that, The calcium concentration in the deep-treated water was monitored using a calcium concentration electrode, and the calcium concentration was adjusted by adding 10wt% calcium chloride solution. When the calcium concentration was <14mg / L, the amount of calcium chloride solution added was >0.08mL / L; when the calcium concentration was 14-16mg / L, the amount of calcium chloride solution added was 0.04-0.08mL / L; when the calcium concentration was ≥16mg / L, no addition was required, so that the calcium concentration of the water before disinfection was stabilized at 16-25mg / L.

5. The self-cleaning filtration method for water treatment according to claim 1, characterized in that, When the turbidity of intermittent springs in the karst region during the rainy season exceeds 350 NTU, polyacrylamide is added to the treatment tank; at the same time, a sedimentation tank is added before the microfiltration screen.

6. A self-cleaning filtration method for water treatment according to claim 1 or 5, characterized in that, Before adding the composite functional agent, modified attapulgite is added first. The modified attapulgite is attapulgite modified with iron ions.

7. A self-cleaning filtration method for water treatment according to claim 6, characterized in that, The modified attapulgite was further modified with polyethylene glycol 4000; Modified attapulgite, polyacrylamide, and composite functional agent are added to the pretreated spring in a specific order. A 10-15cm thick modified quartz sand filter layer is added between the sedimentation tank and the microfiltration screen; the modified quartz sand is aluminum ion impregnated quartz sand; the particle size of the modified quartz sand is 0.5-1mm.

8. A self-cleaning filtration method for water treatment according to claim 1 or 7, characterized in that, Food-grade polyglycerol fatty acid esters are added to the compound functional agent.

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