阅读说明：本技术 基于pac滤墙包裹式膜蒸馏的放射性废水处理系统 (Radioactive wastewater treatment system based on PAC filter wall wrapping type membrane distillation ) 是由 刘畅 纪荣平 蔡玮 熊慧欣 程浩淼 于 2021-07-21 设计创作，主要内容包括：本发明公开了一种基于PAC滤墙包裹式膜蒸馏的放射性废水处理系统,包括管路依次连接的用于放置放射性废液的废液贮存池、用于将废液中的放射性元素与化学沉淀剂进行沉淀反应的沉淀池、用于对沉淀池预处理后的废液进行加热处理的膜蒸馏加热池、用于吸附、截留、固化废水中放射性物质的PAC滤墙包裹式膜蒸馏反应池、用于存储洁净水的冷侧水箱；还包括为沉淀池提供酸性条件的pH在线监测系统。本发明利用化学沉淀法预处理放射性废水,再经过PAC滤墙包裹式膜蒸馏反应器进一步吸附、截留、固化废水中的放射性物质,使得放射性废水得以高度净化并达到排放甚至回用的标准,实现放射性废水的高效减量化与净化处理,具有切实可行的实用价值和广泛的应用前景。(The invention discloses a radioactive wastewater treatment system based on PAC (poly aluminum chloride) filter wall wrapped membrane distillation, which comprises a waste liquid storage tank, a sedimentation tank, a membrane distillation heating tank, a PAC filter wall wrapped membrane distillation reaction tank and a cold side water tank, wherein the waste liquid storage tank is used for placing radioactive waste liquid, the sedimentation tank is used for carrying out precipitation reaction on radioactive elements in the waste liquid and a chemical precipitator, the membrane distillation heating tank is used for heating the waste liquid pretreated by the sedimentation tank, the PAC filter wall wrapped membrane distillation reaction tank is used for adsorbing, intercepting and solidifying radioactive substances in the waste water, and the cold side water tank is used for storing the cold side water; the system also comprises a pH on-line monitoring system for providing acidic conditions for the sedimentation tank. The invention utilizes the chemical precipitation method to pretreat the radioactive wastewater, and then the radioactive wastewater is further adsorbed, intercepted and solidified by the PAC filter wall wrapped membrane distillation reactor, so that the radioactive wastewater can be highly purified and reaches the standard of discharge and even reuse, the high-efficiency reduction and purification treatment of the radioactive wastewater are realized, and the invention has practical and practical value and wide application prospect.)

1. A radioactive wastewater treatment system based on PAC filter wall wrapped membrane distillation is characterized by comprising a waste liquid storage tank, a sedimentation tank, a membrane distillation heating tank, a PAC filter wall wrapped membrane distillation reaction tank and a cold side water tank, wherein the waste liquid storage tank is used for placing radioactive waste liquid, the sedimentation tank is used for carrying out precipitation reaction on radioactive elements in the waste liquid and a chemical precipitator, the membrane distillation heating tank is used for heating the waste liquid pretreated by the sedimentation tank, the PAC filter wall wrapped membrane distillation reaction tank is used for adsorbing, intercepting and solidifying radioactive substances in the waste water, and the cold side water tank is used for storing the water; the system also comprises a pH on-line monitoring system for providing acidic conditions for the sedimentation tank.

2. The radioactive waste water treatment system based on PAC (programmable automation controller) filter wall wrapped membrane distillation according to claim 1, wherein 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 from a water inlet of the reaction tank to the inside of the PAC filter wall wrapped membrane distillation 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; and penetrating water vapor of the membrane distillation membrane module is conveyed to a penetrating fluid cooling device from a water outlet of the membrane module through a vacuum pump, and cooled liquid water is conveyed to a cold side water tank.

3. The PAC filter wall wrapped membrane distillation based radioactive waste treatment system of claim 2, wherein the temperature of the permeate cooling apparatus 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 the penetrating fluid storage tank through a cold side water pump to be stored; and an outlet water quality online monitoring system is arranged in the cold side water tank and used for monitoring the water quality change of the penetrating fluid 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 membrane replacement of the membrane distillation membrane component in the PAC filter wall wrapped type membrane distillation reaction tank according to the monitoring data of the outlet water quality online monitoring system.

4. The radioactive wastewater treatment system based on PAC (polyaluminium chloride) filter wall wrapped membrane distillation according to claim 2 or 3, wherein the three-dimensional adsorption-reaction filter wall uses powdered activated carbon PAC as a filter wall supporting material, the biological treatment agent comprises bacillus, penicillium and yeast, the bacillus, the penicillium and the yeast are loaded in the PAC filter wall material, and the radioactive substances in the waste liquid are subjected to physical adsorption-biological adsorption treatment to fix the radioactive substances in the waste liquid from a liquid phase to a solid phase.

5. The radioactive wastewater treatment system based on PAC (PAC) filter wall wrapped membrane distillation as claimed in claim 2 or 3, wherein the membrane distillation membrane component is prepared from a polytetrafluoroethylene hydrophobic base membrane and diatomite, and the preparation method of the distillation membrane comprises the following steps:

step 1, preparation of diatomite slurry: weighing 30-40g of diatomite, adding the diatomite into 200mL of ethanol solution, fully mixing, adding 3.5g of sodium hexametaphosphate dispersant, ultrasonically dispersing for 30-40min, adding 5-8% of polyvinylidene fluoride (PVDF) serving as a cross-linking agent in percentage by mass, and stirring in a water bath environment at 65 ℃ for 1-2h to obtain diatomite coating slurry;

step 2, defoaming: performing vacuum defoaming treatment on the diatomite slurry prepared in the step (1) for 20-30min, and transferring the diatomite slurry into a material pouring device to obtain a diatomite coating;

step 3, coating of diatomite coating: placing Polytetrafluoroethylene (PTFE) as a hydrophobic base film on a coating machine, setting the thickness of the conductive coating to be 300-600 mu m, and uniformly coating the diatomite coating prepared in the step (2) on the hydrophobic surface of the PTFE by means of the coating machine;

step 4, standing and drying: and standing and curing the hydrophobic distillation membrane coated with the diatomite coating for 15-25min, and drying in a vacuum drying oven at 55-65 ℃ for 24h to obtain the diatomite-loaded distillation membrane.

6. The PAC filter wall wrapped membrane distillation based radioactive waste treatment system of claim 5, wherein the membrane distillation membrane module has a membrane pore size of 0.1 to 0.4 μm.

7. The radioactive wastewater treatment system based on PAC (programmable automation controller) filter wall wrapped membrane distillation according to claim 1, wherein the sedimentation tank is used for removing part of radioactive substances in wastewater through sedimentation, the water temperature is controlled to be 30 +/-5 ℃, the pH value is set to be 3-5, and the retention time of the sedimentation tank is 40-60 min.

8. The radioactive wastewater treatment system based on PAC (programmable automation controller) filter wall wrapped membrane distillation according to claim 1, wherein a mud scraper and a mud discharge pipe are arranged at the bottom of the sedimentation tank, the mud scraper is used for periodically scraping chemical sludge deposited at the bottom of the sedimentation tank, the chemical sludge is transported to the outside of the sedimentation tank through the mud discharge pipe and a mud discharge pump, and after being dehydrated through freezing, melting and vacuum filtration treatment, the chemical sludge is solidified by using cement; the sedimentation tank is internally provided with a pH on-line monitoring system for controlling the extraction of a pH adjusting buffer solution and adding the pH adjusting buffer solution into the sedimentation tank, adjusting the pH value of wastewater in the sedimentation tank, and is also internally provided with a micropore aeration device for full contact reaction of a chemical precipitator in the sedimentation tank and radioactive elements in the wastewater, the aeration intensity of the micropore aeration device is controlled by an air pump, a rotor flow meter monitors the aeration quantity value in real time, the aeration period is controlled by a computer, the aeration period is set to be 8 hours, and the single aeration time is 20-30 minutes; the dosing barrel is communicated with the interior of the sedimentation tank through a second dosing pump and provides chemical precipitation agents for the sedimentation tank.

9. The radioactive wastewater treatment system based on PAC (programmable automation controller) filter wall wrapped membrane distillation according to claim 8, wherein the dosing barrel is used for storing a pre-configured ferric ferrocyanide precipitator and an active silica coagulant aid, the ferric ferrocyanide chemical precipitator is periodically dosed to the sedimentation tank through a second dosing pump, the dosing period and the dosing amount of the ferric ferrocyanide chemical precipitator are controlled by the computer, and the dosing period is set to 8 hours.

10. The radioactive wastewater treatment system based on PAC (programmable automation controller) filter wall wrapped membrane distillation of claim 1, wherein a heat collector heats the membrane distillation heating tank, the heat collector is connected with a solar energy absorption device for providing heat energy, a temperature sensor is arranged in the membrane distillation heating tank, and the water temperature is controlled to be 70 +/-5 ℃.

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

Radioactive wastewater refers to various wastewater discharged in nuclear power plants, nuclear fuel pretreatment, spent fuel aftertreatment and radioisotope application processes, and the types, concentrations, acidity, other chemical components and the like of radioactive nuclides contained in different wastewater are greatly different. Radioactive waste water, after entering the environment, causes water and soil pollution and may enter the human body through various routes, causing harm to the environment and human beings.

At present, methods for treating radioactive wastewater generated by a nuclear power plant mainly include 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 hydroxides, carbonates, phosphates and the like and transfers and concentrates the insoluble precipitates into sludge, and is suitable for low-level wastewater with low purification requirements. However, the method has high 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 the radioactive sludge generated after treatment is large (usually 1-5% of the original water quantity), and secondary pollution is easily caused in subsequent dehydration reduction. In addition, when the formed radioactive sludge is immobilized by cement, the mechanical properties of the cement are easily damaged by the radioactive sludge, so that the immobilization effect is reduced, and secondary pollution is easily caused.

The ion exchange method is to exchange radioactive elements existing in an ion state in the wastewater to a polymer net rack of an ion exchanger for enrichment and concentration, although the removal rate is high, 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 at present also has certain difficulty.

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 although the decontamination factor and the concentration factor are high, the energy consumption is high and the operation cost is high.

The membrane separation method is to separate and concentrate radioactive elements by means of a selective permeable membrane and taking pressure difference, temperature difference or potential difference as power, and the like, has good purification effect, but has higher construction and operation cost, and does not realize large-scale industrial application at present.

The adsorption method is to transfer radioactive elements to a solid phase by using an adsorbent for enrichment and concentration, and commonly used adsorbents include activated carbon, zeolite, montmorillonite and the like, but the adsorbents are greatly influenced by the pH value of wastewater, the adsorption effect is unstable, the solidification effect of the formed radioactive adsorbent in immobilization treatment is not good, and the radioactive elements are easy to release to form secondary pollution.

The membrane distillation technology is a novel membrane separation technology combining membrane separation and distillation technology, a hydrophobic microporous filter membrane is used as a medium, under the action of steam pressure difference on two sides of the membrane, moisture in feed liquid penetrates through membrane holes in a steam form to enter a cold side, and non-volatile components are intercepted on a hot side of the hydrophobic membrane, so that the aim of separating or purifying a mixture is fulfilled. Compared with the traditional thermal desalination process, the membrane distillation technology does not need to heat the feed liquid to the boiling point, only needs to maintain proper temperature difference at two sides of the membrane, can utilize low-grade waste heat, solar energy and other cheap energy sources, obviously reduces energy consumption and can better prevent scaling. Compared with the reverse osmosis technology, the membrane distillation process is almost carried out under normal pressure, the equipment is simple, the operation is convenient, and the membrane distillation process is one of the most promising seawater desalination and sewage and wastewater advanced treatment processes in the 21 st century. In addition, the membrane distillation has strong treatment and recovery capacity on the strong brine, is the only desalination method which can separate 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 the recycling of resources, and can effectively solve the pollution load caused by the discharge of concentrated liquid to the water environment; meanwhile, the membrane distillation product has good water quality, is the method with the highest retention rate in the existing membrane method desalination technology, has the retention rate of 100 percent under the condition that the membrane is not soaked, and has huge commercial potential in the field of ultrapure water preparation. However, membrane fouling, especially salt crystallization fouling, is a major obstacle that hinders the popularization and application of membrane distillation technology at present.

Disclosure of Invention

The purpose of the invention is as follows: the invention aims to provide a radioactive wastewater treatment system based on PAC filter wall wrapping type membrane distillation, aiming at the defects in the prior art, the removal rate of radioactive elements such as cobalt (Co), uranium (U) and the like in radioactive wastewater reaches more than 99.5%, the removal rate of metal ions such as Fe, Mn and the like reaches more than 99.9%, the high purification of water quality is realized, and the near zero emission treatment, the high efficiency reduction and the energy consumption reduction of the radioactive wastewater are realized.

The technical scheme is as follows: a radioactive wastewater treatment system based on PAC filter wall wrapped membrane distillation comprises a waste liquid storage tank, a sedimentation tank, a membrane distillation heating tank, a PAC filter wall wrapped membrane distillation reaction tank and a cold side water tank, wherein the waste liquid storage tank is used for placing radioactive waste liquid, the sedimentation tank is used for carrying out precipitation reaction on radioactive elements in the waste liquid and a chemical precipitator, the membrane distillation heating tank is used for heating the waste liquid pretreated by the sedimentation tank, the PAC filter wall wrapped membrane distillation reaction tank is used for adsorbing, intercepting and solidifying radioactive substances in the waste water, and the cold side water tank is used for storing clean water; the system also comprises a pH on-line 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 type membrane distillation reaction tank, hot waste liquid of the membrane distillation heating tank is conveyed from a water inlet of the reaction tank to the interior of the PAC filter wall wrapped type membrane distillation 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 by a hot side circulating pump; and penetrating water vapor of the membrane distillation membrane module is conveyed to a penetrating fluid cooling device from a water outlet of the membrane module through a vacuum pump, and cooled liquid water is conveyed to a cold side water tank.

Preferably, the temperature of the penetrating fluid 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 the penetrating fluid storage tank through a cold side water pump to be stored; and an outlet water quality online monitoring system is arranged in the cold side water tank and used for monitoring the water quality change of the penetrating fluid 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 membrane replacement of the membrane distillation membrane component in the PAC filter wall wrapped type membrane distillation reaction tank according to the monitoring data of the outlet water quality online monitoring system.

Preferably, the three-dimensional adsorption-reaction filter wall uses powdered activated carbon PAC as a filter wall supporting material, the biological treatment agent comprises bacillus, penicillium and yeast, the biological treatment agent is loaded in the PAC filter wall material, and the physical adsorption-biological adsorption treatment is carried out on the radioactive substances in the waste liquid, so that the radioactive substances in the waste liquid are fixed from a liquid phase to a solid phase.

Preferably, the membrane distillation membrane component is prepared from a polytetrafluoroethylene hydrophobic base membrane and diatomite, and the preparation method of the distillation membrane comprises the following steps:

step 1, preparation of diatomite slurry: weighing 30-40g of diatomite, adding the diatomite into 200mL of ethanol solution, fully mixing, adding 3.5g of sodium hexametaphosphate dispersant, ultrasonically dispersing for 30-40min, adding 5-8% of polyvinylidene fluoride (PVDF) serving as a cross-linking agent in percentage by mass, and stirring in a water bath environment at 65 ℃ for 1-2h to obtain diatomite coating slurry;

step 2, defoaming: performing vacuum defoaming treatment on the diatomite slurry prepared in the step (1) for 20-30min, and transferring the diatomite slurry into a material pouring device to obtain a diatomite coating;

step 3, coating of diatomite coating: placing Polytetrafluoroethylene (PTFE) as a hydrophobic base film on a coating machine, setting the thickness of the conductive coating to be 300-600 mu m, and uniformly coating the diatomite coating prepared in the step (2) on the hydrophobic surface of the PTFE by means of the coating machine;

step 4, standing and drying: and standing and curing the hydrophobic distillation membrane coated with the diatomite coating for 15-25min, and drying in a vacuum drying oven at 55-65 ℃ for 24h to obtain the diatomite-loaded distillation membrane.

Preferably, the membrane distillation membrane module has a membrane pore size of 0.1-0.4 μm.

Preferably, the sedimentation tank is used for removing part of radioactive substances in the wastewater through sedimentation, the water temperature is controlled at 30 +/-5 ℃, the pH value is set to be 3-5, and the retention time of the sedimentation tank is 40-60 min.

Preferably, the bottom of the sedimentation tank is provided with a mud scraper and a mud discharge pipe, the mud scraper is used for periodically scraping chemical sludge deposited at the bottom of the sedimentation tank, the chemical sludge is transported to the outside of the sedimentation tank through the mud discharge pipe and a mud discharge pump, and the chemical sludge is solidified by using cement after being dehydrated through freezing, melting and vacuum filtration; the sedimentation tank is internally provided with a pH on-line monitoring system for controlling the extraction of a pH adjusting buffer solution and adding the pH adjusting buffer solution into the sedimentation tank, adjusting the pH value of wastewater in the sedimentation tank, and is also internally provided with a micropore aeration device for full contact reaction of a chemical precipitator in the sedimentation tank and radioactive elements in the wastewater, the aeration intensity of the micropore aeration device is controlled by an air pump, a rotor flow meter monitors the aeration quantity value in real time, the aeration period is controlled by a computer, the aeration period is set to be 8 hours, and the single aeration time is 20-30 minutes; the dosing barrel is communicated with the interior of the sedimentation tank through a second dosing pump and provides chemical precipitation agents for the sedimentation tank.

Preferably, the dosing barrel is used for storing a pre-configured ferric ferrocyanide precipitator and an active silica coagulant aid, the ferric ferrocyanide chemical precipitator is periodically dosed to the sedimentation tank through a second dosing pump, the dosing period and the dosing amount of the ferric ferrocyanide chemical precipitator are controlled by the computer, and the dosing period is set as 8 hours.

Preferably, the heat collector heats a membrane distillation heating pool, the heat collector is connected with a solar energy absorption device providing heat energy, a temperature sensor is arranged in the membrane distillation heating pool, and the water temperature is controlled to be 70 +/-5 ℃.

Has the advantages that: compared with the prior art, the invention has the following remarkable advantages:

according to the invention, radioactive wastewater is pretreated by using 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 the radioactive elements and metal ions in the wastewater are further adsorbed, intercepted and solidified through the PAC filter wall wrapped membrane distillation reactor process, so that the metal ions and the radioactive elements in the radioactive wastewater are efficiently intercepted and adsorbed and removed, the effluent quality is highly purified, the efficient reduction and near zero emission treatment of the radioactive wastewater are realized, and the problem of secondary pollution caused by the discharge of membrane filtration concentrate to the environment is avoided; meanwhile, the chemical precipitation treatment and PAC filter wall wrapped membrane distillation treatment process efficiently transfer radioactive substances in the waste liquid from a liquid phase to a solid phase, so that the storage space of radioactive waste water is effectively reduced; through the liquid level control system, the temperature sensor, the pH on-line control system, the chemical precipitant on-line feeding system, the micropore aeration system and the real-time sludge scraping system, the reaction condition is controlled in the optimal range, the removal effect of radioactive elements and metal ions is further improved, 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, and saves the operation cost by utilizing the clean energy of solar energy; meanwhile, the introduction of chemical precipitation agents, PAC filter wall materials and diatomite efficiently adsorbs and removes radioactive elements in the waste liquid, effectively relieves the pollution trend of the distillation membrane, prolongs the service life of the distillation membrane and reduces the operation cost caused by membrane cleaning/membrane replacement.

Drawings

FIG. 1 is a schematic process flow diagram of the present invention;

FIG. 2 is a structural diagram of a PAC filter wall wrapped membrane distillation reaction tank in the invention;

FIG. 3 is a cross-sectional view of a PAC filter wall wrapped membrane distillation reaction tank in the invention;

in the figure: a waste liquid storage tank 1, a sedimentation tank 2, a membrane distillation heating tank 3, a PAC filter wall wrapped membrane distillation reaction tank 4, a penetrating fluid cooling device 5, a cold side water tank 6, a penetrating fluid storage tank 7, a first sewage pump 8, a second sewage pump 9, a second dosing pump 10, a dosing barrel 11, a pH adjusting acid liquid tank 12, a pH adjusting alkali liquid tank 13, a first gate valve 14, a second gate valve 15, a first dosing pump 16, a pH signal control system 17, a pH sensor 18, a pH probe 19, a mud scraper 20, a mud discharge pipe 21, a mud discharge pump 22, a micropore aeration device 23, a rotor flow meter 24, an air pump 25, a third sewage pump 26, a solar energy absorption device 27, a heat collector 28, a temperature sensor 29, a fourth sewage pump 30, a circulating pump 31, a vacuum pump 32, a cold side water pump 33, an effluent online monitoring system 34, a computer 35, a PAC adsorption-reaction filter wall 401, a membrane distillation module 402, A concrete shell 403, a reaction tank water inlet 404, a reaction tank water outlet 405 and a membrane module water outlet 406.

Detailed Description

The technical scheme of the invention is further explained by combining the attached 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 pool by using a first sewage pump for temporary storage.

(2) Adjusting the pH value in the 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 adjusted within a range of 3-5, and the precipitation reaction of radioactive elements and a chemical precipitator in the waste liquid under an acidic condition is realized.

(3) Adding chemical agents: preparing ferric ferrocyanide precipitator and active silica coagulant aid with proper concentrations in advance, storing in a dosing barrel, controlling the opening and closing of a second dosing pump through a computer program, and setting the dosing period of chemical agents to be 8 h.

(4) Aeration treatment in 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 an air pump and the flow of the air pump are controlled by a computer program, a microporous aeration device in the sedimentation tank is arranged for periodic aeration, the aeration period is set to be 8 hours, the single aeration time is 20-30min, and a rotor flow meter monitors the aeration amount in real time.

(5) Sludge scraping at the bottom of the sedimentation tank: the opening and closing of the mud scraper in the sedimentation tank are controlled by a computer program, the mud discharging period is set to be 12 hours, chemical precipitated mud scraped by the mud scraper is conveyed to the outside of the sedimentation tank through a mud discharging pipe and a mud discharging pump, 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: introducing the radioactive wastewater in the waste liquid storage tank into a sedimentation tank for pre-sedimentation treatment, fully contacting and reacting the radioactive elements in the waste liquid with a chemical precipitator to generate precipitates, and removing the radioactive substances in the waste liquid from the waste liquid in the form of chemical precipitation sludge, wherein the pre-treatment time of the sedimentation tank is 40-60 min.

(7) Heating wastewater: and conveying the waste liquid pretreated by the sedimentation tank into a membrane distillation heating tank for heating treatment.

(8) PAC filter wall wrapped membrane distillation separation treatment: after heating treatment, the pretreated waste liquid is introduced into a PAC filter wall wrapped type membrane distillation reaction tank by a fourth sewage pump, metal ions and radioactive elements in the waste liquid are efficiently adsorbed and intercepted to the PAC filter wall material and a diatomite coating layer of a distillation membrane surface by utilizing a self-made high-performance permeable reaction filter wall material and a diatomite loaded distillation membrane in the PAC filter wall wrapped type membrane distillation process, so that the purposes of adsorption, interception and solidification of the radioactive elements are achieved, and the membrane pollution trend of the distillation membrane is relieved at the same time; and water vapor in the hot waste liquid enters the permeation side of the membrane distillation membrane component through the distillation membrane holes, is condensed into liquid clean water through the vacuum pump and the penetrating fluid cooling device, and is temporarily stored in the cold side water tank.

(9) Preparing a high-performance permeable reactive filter wall: the PAC is loaded in the PAC filter wall material by taking powdered activated carbon PAC as a filter wall supporting material and taking microbial thalli such as bacillus, penicillium, yeast and the like as a biological treatment agent, and the physical adsorption-biological adsorption treatment is carried out on radioactive substances in the waste liquid.

(10) Preparation of a diatomite-loaded distillation membrane: selecting polytetrafluoroethylene as a substrate hydrophobic membrane, selecting diatomite as a surface adsorption coating, mixing the diatomite, a dispersing agent and ethanol in proportion, performing ultrasonic pre-dispersion treatment to obtain diatomite coating slurry, adding a proper amount of adhesive, placing the mixture in a water bath kettle, stirring the mixture in a water bath, performing vacuum defoaming 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 the polytetrafluoroethylene, standing, curing and performing vacuum drying to obtain the excellent diatomite-loaded distillation membrane. The preparation method of the diatomite-loaded distillation membrane comprises the following steps:

step 1, preparation of diatomite slurry: weighing 30-40g of diatomite, adding the diatomite into 200mL of ethanol solution, fully mixing, adding 3.5g of sodium hexametaphosphate dispersant, ultrasonically dispersing for 30-40min, adding 5-8% of polyvinylidene fluoride (PVDF) serving as a cross-linking agent in percentage by mass, and stirring in a water bath environment at 65 ℃ for 1-2h to obtain diatomite coating slurry;

step 2, defoaming: performing vacuum defoaming treatment on the diatomite slurry prepared in the step (1) for 20-30min, and transferring the diatomite slurry into a material pouring device to obtain a diatomite coating;

step 3, coating of diatomite coating: placing Polytetrafluoroethylene (PTFE) as a hydrophobic base film on a coating machine, setting the thickness of the conductive coating to be 300-600 mu m, and uniformly coating the diatomite coating prepared in the step (2) on the hydrophobic surface of the PTFE by means of the coating machine;

step 4, standing and drying: and standing and curing the hydrophobic distillation membrane coated with the diatomite coating for 15-25min, and drying in a vacuum drying oven at 55-65 ℃ for 24h to obtain the diatomite-loaded distillation membrane.

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 at 30 +/-5 ℃, setting the pH value to be 3-5, and keeping the sedimentation tank for 40-60 min; a liquid level controller, a pH online control system, a temperature sensor, a chemical precipitation agent online feeding system, an online mud scraping system and an aeration device online control system are arranged in the sedimentation tank; the temperature sensor is arranged in the membrane distillation heating pool, and the heat collector in the membrane distillation heating pool is connected to the solar absorption device, so that the recycling of clean energy is realized, the energy consumption is obviously reduced, and the operation cost is saved; a water quality online monitoring system and a liquid level controller are arranged in the cold side water tank, and the replacement of the PAC filter wall wrapped type membrane distillation internal three-dimensional adsorption-reaction filter wall and the cleaning or replacement frequency of the membrane distillation membrane component are controlled by a computer; the membrane aperture of the membrane component is 0.1-0.4 μm, and a PTFE membrane with higher hydrophobicity is selected as a substrate material; the temperature of the penetrating fluid cooling device is controlled at 10 +/-5 ℃.

Example 1

As shown in fig. 1 and 2, a radioactive wastewater treatment system based on a PAC filter wall wrapped 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 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 wrapped membrane distillation reaction tank 4 is condensed into liquid clean water by 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 penetrating fluid storage tank 7 through a cold side water pump 33 for storage and standby; the sedimentation tank 2 is connected with 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 a connecting pipeline of the sedimentation tank 2; the first gate valve 14, the second gate valve 15 and the first dosing pump 16 are in control connection with a pH signal control system 17 and a computer 35; the sedimentation tank 2 consists of a micropore aeration device 23, a rotor flow meter 24, an air pump 25, a mud scraping device 20, a mud discharge pipe 21, a mud discharge pump 22, a dosing barrel 11, a second dosing pump 10, a pH sensor 18 and a pH probe 19.

Firstly, the radioactive wastewater is conveyed to the waste liquid storage tank 1 by the first sewage pump 8 for temporary storage. The waste water stored in the waste liquid storage tank is transported to the sedimentation tank 2 through a second sewage pump 9 for pretreatment. The chemical precipitator 11 is added, the mud scraper 20 is opened and closed, and the microporous aerator 23 is opened and closed under the control of a computer program.

Before operation, enough acid liquid 30% hydrochloric acid and alkali liquid 30% sodium hydroxide are prepared and stored in an acid tank 12 and an alkali tank 13 of a pH adjusting tank respectively, and then the pH of the radioactive wastewater in the settling tank 2 is adjusted within a range of 3-5 by 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 a pH on-line monitoring sensor 19 in the settling tank 2. 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 feeding pump 16 to be opened, and after the acid liquid is absorbed from the acid tank 12 of the pH adjusting tank to adjust the pH of the waste water to be within the range of 3-5, the computer program controls the first gate valve 14 and the first feeding pump 16 to be closed.

And (3) preparing enough 10% ferric ferrocyanide solution and 3% active silica coagulant aid solution in advance, placing the solutions in a dosing barrel 11, controlling a second dosing pump 10 to be periodically opened and closed through a computer program, and conveying a chemical precipitator into the sedimentation tank 2, wherein the dosing period is set to be 8 hours.

After the pH value of the waste liquid in the sedimentation tank is adjusted, the opening of the microporous aeration device 23 and the air pump 25 is controlled by a computer program, the aeration is carried out for 20-30min, the closing of the microporous aeration device 23 and the air pump 25 is controlled by the computer program, and the aeration period is set to 8 h; after the aeration is finished, the chemical precipitation reagent in the sedimentation tank 2 and the radioactive elements in the waste liquid form precipitates which are gradually settled to the bottom of the sedimentation tank 2; the chemical sludge deposited at the bottom is periodically scraped by the sludge scraping device 20 at the bottom of the sedimentation tank 2 and is transported to the outside of the sedimentation tank 2 through the sludge discharge pipe 21 and the sludge discharge pipe 22, the sludge discharge period of the sludge scraping device is controlled by a computer program to be 12h, and the chemical sludge discharged from the sedimentation tank 2 is dehydrated through the freezing-melting-vacuum filtration treatment process and then is solidified by using cement.

After the chemical precipitation pretreatment is finished, the supernatant liquid pretreated in the sedimentation tank 2 is introduced into the membrane distillation heating tank 3 by a third sewage pump 26 for heating treatment. The heat in the heating pool 3 is provided by solar energy, and the solar energy absorption device 27, the heat collector 28 and the temperature sensor 29 in the pool are connected, so that the purpose of heating the waste liquid is achieved. The embodiment adopts the temperature difference control heat collection principle, when the solar heat source absorption device 27 absorbs solar radiation, 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 out an instruction, cold water in the central water heater is input into the heat collector 28, and the water returns to the membrane distillation heating pool 3 after being heated, 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 a set temperature range of 70 +/-5 ℃, starting the fourth sewage pump 30, conveying the hot waste liquid in the membrane distillation heating pool 3 to the PAC filter wall wrapped membrane distillation reaction pool 4, further adsorbing and intercepting to remove radioactive elements and metal ions in the waste liquid, conveying the hot waste liquid from the water inlet 404 of the reaction pool to the interior of the reaction pool 4, and returning the hot waste liquid from the water outlet 405 of the reaction pool to the membrane distillation heating pool 3 through the hot side 31; as shown in fig. 3, the three-dimensional adsorption-reaction filter wall 401 in the reaction tank 4 physically and biologically adsorbs the radioactive elements in the waste liquid, so as to fix the radioactive elements in the waste liquid in the PAC reaction filter wall 401; meanwhile, the diatomite loaded on the membrane surface of the membrane distillation membrane module 402 further adsorbs radioactive substances, and performs membrane distillation membrane separation and interception treatment on the radioactive substances and metal ions, so as to efficiently remove substances such as radioactive elements and metal ions in the waste liquid. The permeable water vapor on the cold side of the PAC filter wall wrapped membrane distillation reaction tank 4 is conveyed to a permeable fluid cooling device 5 from a membrane component water outlet 406 through a vacuum pump 32, the permeable water vapor is condensed into liquid water after being treated by the permeable fluid cooling device 5 and is conveyed to a cold side water tank 6, and the temperature of the permeable fluid cooling device 5 is controlled to be 10 +/-5 ℃; in the embodiment, a hydrophobic PTFE membrane with a pore diameter of 0.1-0.4 μm is selected as a base membrane to prepare the excellent diatomite-loaded distillation membrane 402.

In order to control the reduction and treatment effect of the combined process of the PAC filter wall wrapped type membrane distillation reactor on radioactive wastewater in the optimal range, a liquid level control system, a temperature sensor, a pH online control system, a chemical precipitant online adding system, a micropore 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 online monitoring system 34 is arranged in the cold side water tank 6, water quality data are transmitted to a computer 35 in real time, the computer 35 is used for controlling the replacement of the three-dimensional adsorption-reaction filter wall 401 and the membrane cleaning and the membrane replacement of the membrane distillation membrane component 402 in the PAC filter wall wrapped type membrane distillation reaction tank 4 according to the monitoring data of the effluent water quality online monitoring system 34, 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 adopted to treat the medium-level radioactive wastewater generated by a certain nuclear power station.

(1) Introducing the medium level radioactive wastewater generated by the nuclear power station into a sedimentation tank 2 for chemical sedimentation pretreatment, adjusting the pH of the waste liquid in the tank to be about 4, and controlling the water temperature to be about 30 ℃;

(2) aerating in the sedimentation tank 2 for 20min, standing for 40min, precipitating, introducing the supernatant in the sedimentation tank 2 into the membrane distillation heating tank 3 for heating treatment, and controlling the water temperature at about 70 ℃;

(3) after the temperature of the waste liquid in the membrane distillation heating tank 3 rises to 70 ℃, the hot waste liquid is conveyed to the PAC filter wall wrapped membrane distillation reaction tank 4 by a fourth sewage pump 30 for further adsorption-interception removal treatment;

(4) the hot side of the PAC filter wall wrapped 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 permeating water vapor at the cold side is conveyed to the permeating liquid cooling device 5 through the vacuum pump 32 and condensed into liquid water, and the temperature of the permeating liquid cooling device 5 is controlled to be about 10 ℃; the membrane distillation module 402 in the reaction tank 4 uses a hydrophobic PTFE membrane with a pore size of 0.22 μm as a base membrane.

Operating according to the above method, the radioactive waste liquid produced by the nuclear power station has a total activity of about 5X 10⁷Bq/L, detected to contain Co²⁺、Fe³⁺、Mn²⁺、UO₂ ²⁺、Sr²⁺、Ba²⁺Plasma with initial pH value of about 2.0, purifying the Co of the effluent after the treatment of the combined technology of PAC filter wall wrapped membrane distillation reactor²⁺The removal rate reaches 99.9 percent, and UO₂ ²⁺The removal rate reaches 99.8 percent, and Fe³⁺The removal rate reaches 99.9 percent, and Mn is removed²⁺The removal rate reaches 99.9 percent, Sr²⁺The removal rate reaches 99.5 percent, and Ba is added²⁺The removal rate reaches 99.4 percent, and the total activity of the radioactivity of the effluent<1Bq/L, meets the relevant requirements of the national comprehensive sewage discharge standard GB 8978-.

The embodiments of the present invention are not described in detail, but are known in the art, and can be implemented by referring to the known techniques.