CN113628775B - Radioactive wastewater treatment system based on PAC filter wall wrapped membrane distillation - Google Patents
Radioactive wastewater treatment system based on PAC filter wall wrapped membrane distillation Download PDFInfo
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- CN113628775B CN113628775B CN202110823983.9A CN202110823983A CN113628775B CN 113628775 B CN113628775 B CN 113628775B CN 202110823983 A CN202110823983 A CN 202110823983A CN 113628775 B CN113628775 B CN 113628775B
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- G21F—PROTECTION AGAINST X-RADIATION, GAMMA RADIATION, CORPUSCULAR RADIATION OR PARTICLE BOMBARDMENT; TREATING RADIOACTIVELY CONTAMINATED MATERIAL; DECONTAMINATION ARRANGEMENTS THEREFOR
- G21F9/00—Treating radioactively contaminated material; Decontamination arrangements therefor
- G21F9/04—Treating liquids
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- G—PHYSICS
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- G21F—PROTECTION AGAINST X-RADIATION, GAMMA RADIATION, CORPUSCULAR RADIATION OR PARTICLE BOMBARDMENT; TREATING RADIOACTIVELY CONTAMINATED MATERIAL; DECONTAMINATION ARRANGEMENTS THEREFOR
- G21F9/00—Treating radioactively contaminated material; Decontamination arrangements therefor
- G21F9/04—Treating liquids
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- G—PHYSICS
- G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
- G21F—PROTECTION AGAINST X-RADIATION, GAMMA RADIATION, CORPUSCULAR RADIATION OR PARTICLE BOMBARDMENT; TREATING RADIOACTIVELY CONTAMINATED MATERIAL; DECONTAMINATION ARRANGEMENTS THEREFOR
- G21F9/00—Treating radioactively contaminated material; Decontamination arrangements therefor
- G21F9/04—Treating liquids
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Abstract
The invention discloses a radioactive wastewater treatment system based on PAC (programmable logic controller) filter wall wrapped membrane distillation, which comprises a waste liquid storage tank for placing radioactive waste liquid, a sedimentation tank for carrying out sedimentation reaction on radioactive elements in the waste liquid and a chemical sedimentation agent, a membrane distillation heating tank for carrying out heating treatment on the waste liquid pretreated by the sedimentation tank, a PAC filter wall wrapped membrane distillation reaction tank for adsorbing, intercepting and solidifying radioactive substances in the wastewater, and a cold side water tank for storing clean water, wherein the waste liquid storage tank is sequentially connected with pipelines; the system also comprises an online pH monitoring system for providing acidic conditions for the sedimentation tank. The method for preparing the radioactive wastewater by using the chemical precipitation method and the PAC filter wall wrapped membrane distillation reactor to further adsorb, retain and solidify the radioactive substances in the wastewater, so that the radioactive wastewater can be highly purified and reach the standard of discharge and even reuse, the efficient reduction and purification treatment of the radioactive wastewater are realized, and the method has practical and practical values and wide application prospects.
Description
Technical Field
The invention relates to the field of radioactive wastewater treatment, in particular to a radioactive wastewater treatment system based on PAC filter wall wrapped membrane distillation.
Background
The radioactive wastewater refers to various wastewater discharged in the processes of nuclear power plants, nuclear fuel pretreatment, spent fuel post-treatment and radioisotope application, and the types and the concentrations of radionuclides, acidity, other chemical components and the like contained in different wastewater are quite different. The radioactive wastewater is polluted by water and soil after entering the environment and can enter human bodies through various ways, thereby causing harm to the environment and the human bodies.
At present, the method for treating the radioactive wastewater generated by the nuclear power station mainly comprises a chemical precipitation method, an ion exchange method, an evaporation concentration method, a membrane separation method, an adsorption method and the like.
The chemical precipitation method mainly converts radioactive elements into insoluble precipitates such as hydroxide, carbonate, phosphate and the like, and transfers the insoluble precipitates to concentrate the insoluble precipitates into sludge, and is suitable for low-level wastewater with low purification requirements. However, the method has higher requirement on the pH value of the wastewater in the treatment process, the treatment effect is obviously influenced by impurities contained in the wastewater, the quality of radioactive sludge generated after the treatment is larger (usually 1-5% of the original water amount), and secondary pollution is easy to cause in the subsequent dehydration decrement. In addition, when the formed radioactive sludge is immobilized by adopting cement, the radioactive sludge is easy to damage the mechanical property of the cement, thereby reducing the immobilization effect and easily forming secondary pollution.
The ion exchange method is to exchange the radioactive elements existing in the ion state in the wastewater to the polymer net frame of the ion exchanger for enrichment and concentration, and has higher removal rate, but the operation is relatively complex, the operation cost is high, in addition, the ion exchanger needs to be frequently regenerated when the wastewater with high salt content is treated, and the treatment of the radioactive ion exchanger formed after the treatment is difficult to a certain extent at present.
The evaporation concentration method is to evaporate and condense water by heating so as to separate the water from the radioactive elements which are difficult to volatilize, and the decontamination coefficient and the concentration coefficient are high, but the energy consumption is high and the operation cost is high.
The membrane separation method is to separate and concentrate radioactive elements by using a selective permeable membrane and taking pressure difference, temperature difference or potential difference as power, has good purification effect, but has higher construction and operation cost, and has not been applied to large-scale industrialization at present.
The adsorption method is to transfer the radioactive element to the solid phase for enrichment and concentration by using adsorbents, and the common adsorbents comprise active carbon, zeolite, montmorillonite and the like, however, the adsorbents are greatly influenced by the pH value of wastewater, the adsorption effect is unstable, and the solidification effect is poor when the formed radioactive adsorbent is subjected to the immobilization treatment, and the radioactive element is easy to release to form secondary pollution.
The membrane distillation technology is a novel membrane separation technology combining membrane separation and distillation technology, and takes a hydrophobic microporous filter membrane as a medium, under the action of vapor pressure difference on two sides of the membrane, moisture in feed liquid penetrates through the membrane pores in a vapor form to enter a cold side, and non-volatile components are trapped on a hot side of the hydrophobic membrane, so that the purpose of separating or purifying a mixture is realized. Compared with the traditional thermal desalting process, the membrane distillation technology does not need to heat the feed liquid to the boiling point, only needs to maintain the proper temperature difference at the two sides of the membrane, can utilize low-grade waste heat, solar energy and other cheap energy sources, obviously reduces the energy consumption and can better prevent scaling. Compared with the reverse osmosis technology, the membrane distillation process is almost carried out under normal pressure, and the device is simple and convenient to operate, and is one of the most promising sea water desalination and sewage and wastewater advanced treatment processes in the 21 st century. In addition, the membrane distillation has strong capability of treating and recycling strong brine, is the only desalting method capable of separating out easily-crystallized substances contained in the strong brine through concentration and crystallization, is obviously superior to the reverse osmosis technology, has important significance on recycling resources, and can effectively solve the pollution load caused by the discharge of concentrated solution to the water environment; meanwhile, the water quality of the membrane distillation product is good, the method is the method with the highest rejection rate in the currently known membrane method desalination technology, the rejection rate can reach 100% under the condition that the membrane is not soaked, and the method has great commercial potential in the field of ultrapure water preparation. But membrane pollution, especially salt crystallization pollution, is a major obstacle currently preventing the popularization and application of membrane distillation technology.
Disclosure of Invention
The invention aims to: aiming at the defects existing in the prior art, the invention provides a radioactive wastewater treatment system based on PAC filter wall wrapped membrane distillation, which has the advantages that the removal rate of cobalt (Co), uranium (U) and other radioactive elements in radioactive wastewater reaches over 99.5 percent, the removal rate of Fe, mn and other metal ions reaches over 99.9 percent, the high purification of water quality is realized, and the near zero emission treatment, the high-efficiency reduction and the energy consumption of the radioactive wastewater are realized.
The technical scheme is as follows: a radioactive wastewater treatment system based on PAC (programmable logic controller) filter wall wrapped type membrane distillation comprises a wastewater storage tank for placing radioactive wastewater, a sedimentation tank for carrying out sedimentation reaction on radioactive elements in the wastewater and a chemical sedimentation agent, a membrane distillation heating tank for carrying out heating treatment on the wastewater pretreated by the sedimentation tank, a PAC filter wall wrapped type membrane distillation reaction tank for adsorbing, intercepting and solidifying the radioactive substances in the wastewater, and a cold side water tank for storing clean water, wherein the wastewater storage tank is sequentially connected with pipelines; the system also comprises an online pH monitoring system for providing acidic conditions for the sedimentation tank.
Preferably, a three-dimensional adsorption-reaction filter wall and a membrane distillation membrane component are sequentially arranged in a concrete shell of the PAC filter wall wrapped membrane distillation reaction tank, hot waste liquid of the membrane distillation heating tank is conveyed to the inside of the PAC filter wall wrapped membrane distillation reaction tank from a water inlet of the reaction tank through a fourth sewage pump, and the waste liquid flows back to the membrane distillation heating tank from a water outlet of the reaction tank through a hot side circulating pump; the permeated water vapor of the membrane distillation membrane assembly is conveyed to the permeate liquid cooling device from the water outlet of the membrane assembly through a vacuum pump, and the cooled liquid water is conveyed to a cold side water tank.
Preferably, the temperature of the permeate cooling device is controlled at 10+/-5 ℃; a liquid level control system is arranged in the cold side water tank, and clean water exceeding a set water level in the cold side water tank is conveyed to a permeate storage tank for storage through a cold side water pump; the cold-side water tank is internally provided with an effluent water quality on-line monitoring system which is used for monitoring the water quality change of the permeate liquid in real time and transmitting data to a computer in real time, and the computer is used for controlling the replacement of the three-dimensional adsorption-reaction filter wall and the membrane cleaning and the membrane replacement of the membrane distillation membrane component in the PAC filter wall wrapped membrane distillation reaction tank according to the monitoring data of the effluent water quality on-line monitoring system.
Preferably, the three-dimensional adsorption-reaction filter wall uses powdered activated carbon PAC as a filter wall supporting material, and the biological treatment agent comprises bacillus, penicillium and yeast, is loaded in the PAC filter wall material, and performs physical adsorption-biological adsorption treatment on radioactive substances in the waste liquid to fix the radioactive substances in the waste liquid from a liquid phase to a solid phase.
Preferably, the membrane distillation membrane component is prepared from a polytetrafluoroethylene hydrophobic substrate membrane and diatomite, and the preparation method of the distillation membrane comprises the following steps:
step 2, defoaming: the diatomite slurry prepared in the step 1 is subjected to vacuum defoaming treatment for 20-30min and then is transferred into a pouring device, and then the diatomite coating is obtained;
step 3, diatomite coating: taking polytetrafluoroethylene PTFE as a hydrophobic substrate film, placing the hydrophobic substrate film on a film coating machine, setting the thickness of a conductive coating to be 300-600 mu m, and uniformly coating the diatomite coating prepared in the step 2 on the hydrophobic surface of PTFE by the film coating machine;
and 4, standing and drying: and standing and solidifying the hydrophobic distillation film coated with the diatomite coating for 15-25min, and drying the hydrophobic distillation film in a vacuum drying oven at 55-65 ℃ for 24h to obtain the diatomite-loaded distillation film.
Preferably, the membrane pore size of the membrane distillation membrane module is 0.1-0.4 μm.
Preferably, the sedimentation tank is used for removing part of radioactive substances in the wastewater by sedimentation, the water temperature is controlled to be 30+/-5 ℃, the pH is set to be 3-5, and the retention time of the sedimentation tank is 40-60min.
Preferably, the bottom of the sedimentation tank is provided with a mud scraper and a mud discharging pipe, the mud scraper is used for periodically scraping chemical mud deposited at the bottom of the sedimentation tank, the chemical mud is transported to the outside of the sedimentation tank through the mud discharging pipe and the mud discharging pump, and is dehydrated through freezing, melting and vacuum filtration treatment and then solidified by cement; the sedimentation tank is internally provided with a pH on-line monitoring system for controlling and extracting pH adjusting buffer solution and adding the pH adjusting buffer solution into the sedimentation tank, the sedimentation tank is internally provided with a microporous aeration device for fully contacting and reacting chemical precipitants in the sedimentation tank with radioactive elements in waste liquid, the aeration intensity of the microporous aeration device is controlled by an air pump, a rotor flowmeter monitors the aeration quantity value in real time, the aeration period is controlled by a computer, the aeration period is set to 8 hours, and the single aeration duration is 20-30 minutes; the dosing barrel is communicated with the interior of the sedimentation tank through a second dosing pump, and the dosing barrel provides chemical sedimentation agents for the sedimentation tank.
Preferably, the dosing barrel is used for storing the pre-configured ferric ferrocyanide precipitant and the active silicon dioxide coagulant aid, the ferric ferrocyanide chemical precipitant is periodically dosed to the sedimentation tank through the second dosing pump, and the dosing period and the dosing amount of the ferric ferrocyanide chemical precipitant are controlled by the computer, wherein the dosing period is set to be 8 hours.
Preferably, the heat collector is a membrane distillation heating pool for heating, the heat collector is connected with a solar energy absorbing device for providing heat energy, a temperature sensor is arranged in the membrane distillation heating pool, and the water temperature is controlled to be 70+/-5 ℃.
The beneficial effects are that: compared with the prior art, the invention has the following remarkable advantages:
the method is characterized in that radioactive wastewater is pretreated by a chemical precipitation method, radioactive elements in the wastewater are efficiently removed, radioactive substances in the wastewater are discharged from a liquid phase in the form of chemical precipitation sludge, and then the radioactive elements and metal ions in the wastewater are further adsorbed, intercepted and solidified by a PAC filter wall wrapping type membrane distillation reactor, so that the metal ions and the radioactive elements in the radioactive wastewater are efficiently intercepted and adsorbed, the effluent water quality is highly purified, the efficient reduction and near zero emission treatment of the radioactive wastewater are realized, and the problem of secondary pollution to the environment caused by the discharge of membrane filtration concentrate is avoided; meanwhile, the radioactive substances in the waste liquid are efficiently transferred from the liquid phase to the solid phase in the chemical precipitation treatment and PAC filter wall wrapping type membrane distillation treatment processes, so that the storage space of radioactive waste water is effectively reduced; the reaction conditions are controlled in the optimal range through the liquid level control system, the temperature sensor, the pH on-line control system, the chemical precipitant on-line feeding system, the microporous aeration system and the real-time mud scraping system, so that the removal effect of radioactive elements and metal ions is further improved, and meanwhile, the full-automatic control of the whole process is realized, and a large amount of manpower is saved. The system has novel structure, small occupied area and convenient maintenance, utilizes the solar energy, namely clean energy, and saves the operation cost; meanwhile, due to the introduction of chemical precipitation agents, PAC filter wall materials and diatomite, radioactive elements in the waste liquid are efficiently adsorbed and removed, the pollution trend of the distillation membrane is effectively relieved, the service life of the distillation membrane is prolonged, and the operation cost caused by membrane cleaning/membrane replacement is reduced.
Drawings
FIG. 1 is a schematic illustration of a process flow of the present invention;
FIG. 2 is a diagram of the PAC filter wall wrapped membrane distillation reaction tank according to the present invention;
FIG. 3 is a cross-sectional view of a PAC filter wall wrapped membrane distillation reaction tank in the present invention;
in the figure: the waste liquid storage tank 1, the sedimentation tank 2, the membrane distillation heating tank 3, the PAC filter wall wrapped membrane distillation reaction tank 4, the permeate cooling device 5, the cold side water tank 6, the permeate storage tank 7, the first sewage pump 8, the second sewage pump 9, the second dosing pump 10, the dosing barrel 11, the pH adjusting acid liquid tank 12, the pH adjusting alkali liquid tank 13, the first gate valve 14, the second gate valve 15, the first feeding pump 16, the pH signal control system 17, the pH sensor 18, the pH probe 19, the mud scraper 20, the mud discharging pipe 21, the mud discharging pump 22, the microporous aeration device 23, the rotor flowmeter 24, the air pump 25, the third sewage pump 26, the solar absorbing device 27, the heat collector 28, the temperature sensor 29, the fourth sewage pump 30, the hot side circulating pump 31, the vacuum pump 32, the cold side water pump 33, the effluent online monitoring system 34, the computer 35, the PAC three-dimensional adsorption-reaction wall 401, the membrane distillation membrane module 402, the concrete housing 403, the reaction tank water inlet 404, the reaction tank water outlet 405 and the membrane module water outlet 406.
Detailed Description
The technical scheme of the invention is further described below with reference to the accompanying drawings.
As shown in fig. 1, the invention is realized by the following technical scheme:
(1) Pre-storing waste liquid: and conveying the radioactive waste liquid to a waste liquid storage tank by using a first sewage pump for temporary storage.
(2) Regulating pH in a sedimentation tank: the pH value of the waste liquid in the sedimentation tank is monitored in real time by utilizing a pH online monitoring system, and the opening and closing of the first feeding pump, the first gate valve and the second gate valve are controlled by a computer program, so that the pH value in the sedimentation tank is regulated to be within the range of 3-5, and the sedimentation reaction of radioactive elements in the waste liquid and a chemical precipitator under an acidic condition is realized.
(3) Adding chemical agents: ferric ferrocyanide precipitant and active silica coagulant aid with proper concentrations are prepared in advance, the ferric ferrocyanide precipitant and the active silica coagulant aid are stored in a dosing barrel, the second dosing pump is controlled to be opened and closed through a computer program, and the chemical agent dosing period is set to be 8 hours.
(4) Aeration treatment of a sedimentation tank: in order to promote the full contact reaction of radioactive substances and chemical precipitants in the sedimentation tank, the opening and closing of the air pump and the flow of the air pump are controlled by a computer program, a microporous aeration device in the sedimentation tank is set for periodic aeration, the aeration period is set to 8h, the single aeration duration is 20-30min, and the aeration quantity is monitored by a rotameter in real time.
(5) Mud is scraped to sedimentation tank bottom: the start and stop of a mud scraper in the sedimentation tank are controlled by a computer program, the mud discharge period is set to be 12 hours, and chemical sediment mud scraped by the mud scraper is conveyed to the outside of the sedimentation tank through a mud discharge pipe and a mud discharge pump, and then the subsequent freezing-melting-vacuum filtration dehydration treatment is carried out, and the solidification treatment is carried out by utilizing cement.
(6) Chemical precipitation pretreatment: and (3) introducing the radioactive wastewater in the waste liquid storage tank into a sedimentation tank for pre-sedimentation treatment, fully contacting and reacting radioactive elements in the waste liquid with a chemical precipitator to generate precipitate, and removing radioactive substances in the waste liquid from the waste liquid in the form of chemical precipitation sludge, wherein the pretreatment time of the sedimentation tank is 40-60min.
(7) Heating the wastewater: and conveying the waste liquid pretreated by the sedimentation tank into a membrane distillation heating tank for heating treatment.
(8) PAC filter wall wrapping type membrane distillation separation treatment: after heating treatment, introducing the pretreated waste liquid into a PAC filter wall wrapping type membrane distillation reaction tank by a fourth sewage pump, wherein the PAC filter wall wrapping type membrane distillation process utilizes self-made high-performance permeable reaction filter wall materials and diatomite to load a distillation membrane, and efficiently adsorbs and entraps metal ions and radioactive elements in the waste liquid into the PAC filter wall materials and diatomite coating layers on the surface of the distillation membrane so as to achieve the purposes of adsorbing, entrapping and solidifying the radioactive elements and simultaneously slow down the membrane pollution trend of the distillation membrane; the water vapor in the hot waste liquid enters the permeation side of the membrane distillation membrane component through the distillation membrane hole, is condensed into liquid clean water through the vacuum pump and the permeate liquid cooling device, and is temporarily stored in the cold side water tank.
(9) Preparation of high-performance permeable reaction filter wall: the powder activated carbon PAC is used as a filter wall supporting material, and microbial thalli such as bacillus, penicillium, yeast and the like are used as biological treatment agents and are loaded in the PAC filter wall material to carry out physical adsorption-biological adsorption treatment on radioactive substances in the waste liquid.
(10) Preparation of diatomite loaded distillation membrane: selecting polytetrafluoroethylene as a substrate hydrophobic film, selecting diatomite as a surface adsorption coating, mixing diatomite, a dispersing agent and ethanol according to a proportion, carrying out ultrasonic pre-dispersing treatment to obtain diatomite coating slurry, adding a proper amount of adhesive, placing the diatomite coating slurry in a water bath kettle, stirring the mixture in a water bath, carrying out vacuum defoamation treatment for 20min, transferring the mixture to a material pouring device, setting a proper coating thickness, uniformly coating the diatomite coating slurry on the surface of polytetrafluoroethylene, standing, solidifying and carrying out vacuum drying to obtain the excellent diatomite-loaded distillation film. The preparation method of the diatomite loaded distillation membrane comprises the following steps:
step 2, defoaming: the diatomite slurry prepared in the step 1 is subjected to vacuum defoaming treatment for 20-30min and then is transferred into a pouring device, and then the diatomite coating is obtained;
step 3, diatomite coating: taking polytetrafluoroethylene PTFE as a hydrophobic substrate film, placing the hydrophobic substrate film on a film coating machine, setting the thickness of a conductive coating to be 300-600 mu m, and uniformly coating the diatomite coating prepared in the step 2 on the hydrophobic surface of PTFE by the film coating machine;
and 4, standing and drying: and standing and solidifying the hydrophobic distillation film coated with the diatomite coating for 15-25min, and drying the hydrophobic distillation film in a vacuum drying oven at 55-65 ℃ for 24h to obtain the diatomite-loaded distillation film.
Preferably, the temperature of the wastewater in the membrane distillation heating pool is controlled to be 70+/-5 ℃; controlling the water temperature of the sedimentation tank to be 30+/-5 ℃, setting the pH value to be 3-5, and controlling the residence time of the sedimentation tank to be 40-60min; the sedimentation tank is internally provided with a liquid level controller, a pH on-line control system, a temperature sensor, a chemical sedimentation agent on-line feeding system, an on-line mud scraping system and an aeration device on-line control system; a temperature sensor is arranged in the membrane distillation heating pool, and a heat collector in the membrane distillation heating pool is connected to the solar energy absorbing device, so that clean energy is reused, energy consumption is obviously reduced, and running cost is saved; the cold side water tank is internally provided with a water quality on-line monitoring system and a liquid level controller, and the replacement of the three-dimensional adsorption-reaction filter wall and the cleaning or replacement frequency of the membrane distillation membrane component in the PAC filter wall wrapped membrane distillation are controlled by a computer; the membrane pore diameter of the membrane component is 0.1-0.4 mu m, and a PTFE membrane with higher hydrophobicity is selected as a base material; the temperature of the permeate cooling device is controlled to be 10+/-5 ℃.
Example 1
As shown in fig. 1 and 2, a radioactive wastewater treatment system based on a PAC (programmable logic controller) filter wall wrapped type membrane distillation reaction tank comprises a wastewater storage tank 1, a sedimentation tank 2, a membrane distillation heating tank 3, a PAC filter wall wrapped type membrane distillation reaction tank 4, a cold side water tank 6 and a permeate storage tank 7 which are connected in sequence; a second sewage pump 9 is arranged on a connecting pipeline between the wastewater storage tank 1 and the sedimentation tank 2; the sedimentation tank 2, the membrane distillation heating tank 3 and the PAC filter wall wrapped membrane distillation reaction tank 4 form a circulating system through connecting pipelines, and a third sewage pump 26, a fourth sewage pump 30 and a hot side circulating pump 31 are arranged on the connecting pipelines of the circulating system; the penetrating fluid generated by the PAC filter wall wrapping type membrane distillation reaction tank 4 is condensed into liquid clean water through a vacuum pump 32 and a penetrating fluid cooling device 5 and is conveyed to a cold side water tank 6; clean water in the cold-side water tank 6 is conveyed to the permeate storage tank 7 through the cold-side water pump 33 to be stored for standby; the sedimentation tank 2 is connected with the pH adjusting tanks 12 and 13, and a first feeding pump 16, a first gate valve 14 and a second gate valve 15 are arranged on the connecting pipelines of the sedimentation tank; the first gate valve 14, the second gate valve 15 and the first dosing pump 16 are in control connection by a pH signal control system 17 and a computer 35; the sedimentation tank 2 is composed of a microporous aeration device 23, a rotameter 24, an air pump 25, a mud scraping device 20, a mud discharging pipe 21, a mud discharging pump 22, a dosing barrel 11, a second dosing pump 10, a pH sensor 18 and a pH probe 19.
Firstly, radioactive wastewater is transported into the waste liquid storage tank 1 for temporary storage by the first sewage pump 8. The waste water stored in the waste liquid storage tank is transported to the sedimentation tank 2 for pretreatment by the second sewage pump 9. The chemical precipitant 11 is added, the mud scraping device 20 is opened and closed, and the microporous aeration device 23 is opened and closed under the control of a computer program.
Before operation, preparing enough acid liquor of 30% hydrochloric acid and alkali liquor of 30% sodium hydroxide, respectively storing the acid liquor in an acid tank 12 and the alkali tank 13 of a pH regulating tank, then controlling the opening and closing of a first feeding pump 16, a first gate valve 14 and a second gate valve 15 through a computer program according to an online pH monitoring sensor 19 in the sedimentation tank 2, and regulating the pH of radioactive wastewater in the sedimentation tank 2 to be in a range of 3-5. When the pH on-line monitoring sensor 19 shows that the pH of the waste liquid in the tank is higher than 5, the computer program controls the first gate valve 14 and the first dosing pump 16 to be opened, and after the pH of the waste water is adjusted to be 3-5 by sucking acid liquor from the acid tank 12 of the pH adjusting tank, the computer program controls the first gate valve 14 and the first dosing pump 16 to be closed.
Sufficient 10% ferric ferrocyanide solution and 3% active silicon dioxide coagulant aid solution are prepared in advance, are placed in a dosing barrel 11, a second dosing pump 10 is controlled to be periodically opened and closed through a computer program, chemical precipitant is conveyed into a sedimentation tank 2, and the dosing period is set to be 8 hours.
After the pH of the waste liquid in the sedimentation tank is regulated, the micro-pore aeration device 23 and the air pump 25 are controlled to be opened by a computer program, and after aeration is carried out for 20-30min, the micro-pore aeration device 23 and the air pump 25 are controlled to be closed by the computer program, and the aeration period is set to be 8h; after aeration is finished, the chemical precipitation agent in the sedimentation tank 2 and radioactive elements in the waste liquid form precipitates and gradually settle to the bottom of the sedimentation tank 2; the mud scraping device 20 at the bottom of the sedimentation tank 2 scrapes chemical mud deposited at the bottom regularly, the chemical mud is transported to the outside of the sedimentation tank 2 through the mud discharging pipe 21 and the mud discharging pipe 22, the mud discharging period of the mud scraping device is controlled to be 12 hours by a computer program, and the chemical sediment discharged from the sedimentation tank 2 is dehydrated through the freezing-melting-vacuum filtration treatment process and then solidified through cement.
After the chemical precipitation pretreatment is finished, the supernatant fluid pretreated by the precipitation tank 2 is led into the membrane distillation heating tank 3 by the third sewage pump 26 for heating treatment. The heat in the heating tank 3 is provided by solar energy, and the solar energy absorbing device 27, the heat collector 28 and the temperature sensor 29 in the tank are connected, so that the purpose of heating the waste liquid is achieved. In this embodiment, the temperature difference control heat collection principle is adopted, when the solar heat source absorber 27 absorbs solar radiation and the temperature of the heat collection tube rises to reach the set value of the temperature difference delta T between the heat collector 28 and the membrane distillation heating pool 3, the monitoring system sends a command, cold water in the central water heater is input into the heat collector 28, and the water is heated and then returns to the membrane distillation heating pool 3, so that the temperature of waste liquid in the pool reaches the set temperature, and the water temperature in the membrane distillation heating pool 3 is controlled to be 70+/-5 ℃.
According to the temperature sensor 29 in the membrane distillation heating pool 3, after the temperature of the waste liquid in the pool reaches the set temperature range of 70+/-5 ℃, starting a fourth sewage pump 30, conveying the hot waste liquid in the membrane distillation heating pool 3 into the PAC filter wall wrapped membrane distillation reaction pool 4, further adsorbing and intercepting and removing radioactive elements and metal ions in the waste liquid, conveying the hot waste liquid into the reaction pool 4 from a reaction pool water inlet 404, and refluxing the hot waste liquid to the membrane distillation heating pool 3 from a reaction pool water outlet 405 by a hot side circulating pump 31; as shown in fig. 3, the three-dimensional adsorption-reaction filter 401 in the reaction tank 4 performs physical adsorption and biological adsorption treatment on the radioactive elements in the waste liquid, and fixes the radioactive elements in the waste liquid in the PAC reaction filter 401; meanwhile, diatomite loaded on the membrane surface of the membrane distillation membrane component 402 is used for further adsorbing and treating radioactive substances, and performing membrane distillation membrane separation interception treatment on the radioactive substances and metal ions, so that substances such as radioactive elements and metal ions in the waste liquid are removed efficiently. The permeation water vapor at the cold side of the PAC filter wall wrapping type membrane distillation reaction tank 4 is conveyed to the permeate cooling device 5 from a membrane assembly water outlet 406 through a vacuum pump 32, the permeation water vapor treated by the permeate cooling device 5 is condensed into liquid water and is conveyed to a cold side water tank 6, and the temperature of the permeate cooling device 5 is controlled to be 10+/-5 ℃; in this example, a hydrophobic PTFE membrane having a pore size in the range of 0.1 to 0.4 μm was used as a base membrane to prepare an excellent diatomaceous earth-supported distillation membrane 402.
In order to control the reduction and treatment effect of the PAC filter wall wrapped type membrane distillation reactor on radioactive wastewater within an optimal range, a liquid level control system, a temperature sensor, a pH on-line control system, a chemical precipitant on-line feeding system, a microporous aeration system and a real-time mud scraping system are arranged in the sedimentation tank 2, a temperature sensor is arranged in the membrane distillation heating tank 3, an effluent water quality on-line monitoring system 34 is arranged in the cold side water tank 6, water quality data are transmitted to a computer 35 in real time, and the computer 35 is used for controlling the replacement of the three-dimensional adsorption-reaction filter wall 401 and the membrane cleaning and membrane replacement of the membrane distillation membrane module 402 in the PAC filter wall wrapped type membrane distillation reaction tank 4 according to the monitoring data of the effluent water quality on-line monitoring system 34, so that the full-automatic control of the whole process is realized, and a large amount of manpower is saved.
Example 2
The device and the process are used for treating the medium-level radioactive wastewater generated by a nuclear power station.
(1) Introducing medium-level radioactive wastewater generated by a nuclear power station into a sedimentation tank 2 for chemical sedimentation pretreatment, regulating the pH of waste liquid in the tank to be about 4, and controlling the water temperature to be about 30 ℃;
(2) Aerating in a sedimentation tank 2 for 20min, standing for sedimentation for 40min, and introducing supernatant of the sedimentation tank 2 into a membrane distillation heating tank 3 for heating treatment after sedimentation, wherein the water temperature is controlled to be about 70 ℃;
(3) After the temperature of the waste liquid in the membrane distillation heating pool 3 rises to 70 ℃, conveying the hot waste liquid into the PAC filter wall wrapped membrane distillation reaction pool 4 through a fourth sewage pump 30 for further adsorption-interception removal treatment;
(4) The hot side of the PAC filter wall wrapped type membrane distillation reaction tank 4 and the membrane distillation heating tank 3 form a circulating system through a fourth sewage pump 30 and a hot side circulating pump 31; the permeate water vapor on the cold side is conveyed to the permeate cooling device 5 through the vacuum pump 32 and condensed into liquid water, and the temperature of the permeate cooling device 5 is controlled to be about 10 ℃; the membrane distillation membrane module 402 in the reaction tank 4 uses a hydrophobic PTFE membrane having a pore size of 0.22 μm as a base membrane.
Operating according to the method, the total activity of the radioactive waste liquid generated by the nuclear power station is about 5 multiplied by 10 7 Bq/L, detected to contain Co 2+ 、Fe 3+ 、Mn 2+ 、UO 2 2+ 、Sr 2+ 、Ba 2+ Plasma with initial pH value of about 2.0 is treated by PAC filter wall wrapped membrane distillation reactor technology, and Co of water is purified 2+ The removal rate reaches 99.9%, UO 2 2+ The removal rate reaches 99.8 percent, fe 3+ The removal rate reaches 99.9 percent, mn 2+ The removal rate reaches 99.9 percent, sr 2+ The removal rate reaches 99.5 percent, ba 2+ The removal rate reaches 99.4 percent, and the total activity of the water outlet radioactivity<1Bq/L meets the related requirements of national integrated sewage discharge standard GB 8978-1996.
In the embodiments of the present invention, the descriptions not related to the embodiments are known in the art, and may be implemented with reference to the known art.
Claims (6)
1. The radioactive wastewater treatment system based on PAC filter wall wrapped membrane distillation is characterized by comprising a waste liquid storage tank for placing radioactive waste liquid, a sedimentation tank for carrying out sedimentation reaction on radioactive elements in the waste liquid and a chemical sedimentation agent, a membrane distillation heating tank for carrying out heating treatment on the waste liquid pretreated by the sedimentation tank, a PAC filter wall wrapped membrane distillation reaction tank for adsorbing, intercepting and solidifying radioactive substances in the waste water and a cold side water tank for storing clean water, wherein the waste liquid storage tank is sequentially connected through pipelines; the system also comprises a pH on-line monitoring system for providing an acidic condition for the sedimentation tank;
a three-dimensional adsorption-reaction filter wall and a membrane distillation membrane component are sequentially arranged in a concrete shell of the PAC filter wall wrapped membrane distillation reaction tank, hot waste liquid of the membrane distillation heating tank is conveyed to the inside of the PAC filter wall wrapped membrane distillation reaction tank from a water inlet of the reaction tank through a fourth sewage pump, and the waste liquid flows back to the membrane distillation heating tank from a water outlet of the reaction tank through a hot side circulating pump; the permeation water vapor of the membrane distillation membrane assembly is conveyed to a permeation liquid cooling device from a water outlet of the membrane assembly through a vacuum pump, and the cooled liquid water is conveyed to a cold side water tank;
the temperature of the permeate cooling device is controlled to be 10+/-5 ℃; a liquid level control system is arranged in the cold side water tank, and clean water exceeding a set water level in the cold side water tank is conveyed to a permeate storage tank for storage through a cold side water pump; the cold-side water tank is internally provided with an effluent water quality online monitoring system which is used for monitoring the water quality change of the permeate in real time and transmitting data to a computer in real time, and the computer is used for controlling the replacement of the three-dimensional adsorption-reaction filter wall and the membrane cleaning and the membrane replacement of the membrane distillation membrane component in the PAC filter wall wrapped membrane distillation reaction tank according to the monitoring data of the effluent water quality online monitoring system;
the three-dimensional adsorption-reaction filter wall uses powdered activated carbon PAC as a filter wall supporting material, a biological treatment agent comprises bacillus, penicillium and yeast, the biological treatment agent is loaded in the PAC filter wall material, physical adsorption-biological adsorption treatment is carried out on radioactive substances in the waste liquid, and the radioactive substances in the waste liquid are fixed from a liquid phase to a solid phase;
the membrane distillation membrane component is prepared from a polytetrafluoroethylene hydrophobic substrate membrane and diatomite, and the preparation method of the distillation membrane comprises the following steps:
step 1, diatomite slurry preparation: weighing 30-40g of diatomite, adding the diatomite into 200mL of ethanol solution, fully mixing, adding 3.5g of sodium hexametaphosphate dispersant, performing ultrasonic dispersion for 30-40min, adding a cross-linking agent polyvinylidene fluoride PVDF according to the mass percent of 5-8%, and placing the mixture in a water bath environment at 65 ℃ for stirring for 1-2h to obtain diatomite coating slurry;
step 2, defoaming: the diatomite slurry prepared in the step 1 is subjected to vacuum defoaming treatment for 20-30min and then is transferred into a pouring device, and then the diatomite coating is obtained;
step 3, diatomite coating: taking polytetrafluoroethylene PTFE as a hydrophobic substrate film, placing the hydrophobic substrate film on a film coating machine, setting the thickness of a conductive coating to be 300-600 mu m, and uniformly coating the diatomite coating prepared in the step 2 on the hydrophobic surface of PTFE by the film coating machine;
and 4, standing and drying: and standing and solidifying the hydrophobic distillation film coated with the diatomite coating for 15-25min, and drying the hydrophobic distillation film in a vacuum drying oven at 55-65 ℃ for 24h to obtain the diatomite-loaded distillation film.
2. The PAC filter wall wrapping type membrane distillation based radioactive wastewater treatment system of claim 1, wherein the membrane pore size of the membrane distillation membrane module is 0.1-0.4 μm.
3. The radioactive wastewater treatment system based on PAC filter wall wrapped membrane distillation according to claim 1, wherein the sedimentation tank is used for removing part of radioactive substances in wastewater by sedimentation, the water temperature is controlled to be 30+/-5 ℃, the pH is set to be 3-5, and the retention time of the sedimentation tank is 40-60min.
4. The radioactive wastewater treatment system based on PAC filter wall wrapped membrane distillation according to claim 1, wherein a mud scraper and a mud discharging pipe are arranged at the bottom of the sedimentation tank, the mud scraper is used for periodically scraping chemical mud deposited at the bottom of the sedimentation tank, the chemical mud is transported to the outside of the sedimentation tank through the mud discharging pipe and a mud discharging pump, and after the chemical mud is dehydrated through freezing, thawing and vacuum filtration treatment, the chemical mud is solidified by cement; the sedimentation tank is internally provided with a pH on-line monitoring system which is used for controlling and extracting pH adjusting buffer solution and adding the pH adjusting buffer solution into the sedimentation tank, the sedimentation tank is internally provided with a microporous aeration device which is used for fully contacting and reacting chemical precipitants in the sedimentation tank with radioactive elements in waste liquid, the aeration intensity of the microporous aeration device is controlled by an air pump, the value of the aeration quantity is monitored by a rotor flowmeter in real time, the aeration period is controlled by a computer, the aeration period is set to 8 hours, and the single aeration duration is 20-30 minutes; the dosing barrel is communicated with the interior of the sedimentation tank through a second dosing pump, and the dosing barrel provides chemical sedimentation agents for the sedimentation tank.
5. The radioactive wastewater treatment system based on PAC filter wall wrapping type membrane distillation according to claim 4, wherein the dosing barrel is used for storing the pre-configured ferric ferrocyanide precipitant and the active silica coagulant aid, the ferric ferrocyanide chemical precipitant is periodically dosed to the sedimentation tank through the second dosing pump, and the dosing period and the dosing amount of the ferric ferrocyanide chemical precipitant are controlled by the computer, and the dosing period is set to 8 hours.
6. The radioactive wastewater treatment system based on PAC (programmable logic controller) filter wall wrapped type membrane distillation according to claim 1, wherein a heat collector is used for heating the membrane distillation heating pool, the heat collector is connected with a solar energy absorbing device for providing heat energy, a temperature sensor is arranged in the membrane distillation heating pool, and the water temperature is controlled to be 70+/-5 ℃.
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