CN112110571A - Permeable reactive barrier and repairing method - Google Patents
Permeable reactive barrier and repairing method Download PDFInfo
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- C02F1/28—Treatment of water, waste water, or sewage by sorption
- C02F1/283—Treatment of water, waste water, or sewage by sorption using coal, charred products, or inorganic mixtures containing them
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Abstract
The invention discloses a permeable reactive barrier and a repairing method thereof, belonging to the technical field of polluted soil and underground water repairing; the permeable reactive barrier comprises: the pre-reaction zone, the main reaction zone and the water outlet buffer zone are sequentially arranged along the water flow direction; the pre-reaction zone and the effluent buffer zone are filled with filler and zero-valent iron, and the main reaction zone is filled with zero-valent iron and adsorbent; monitoring holes are arranged on the main reaction zone, or monitoring holes are arranged on the pre-reaction zone, the main reaction zone and the effluent buffer zone; sampling is carried out to monitor whether passivation and blockage occur and a deactivator is added. After the reaction is carried out for a period of time, aiming at the passivation, blockage and activity reduction of zero-valent iron and the adsorbent, the invention adds the regeneration activation passivator, such as hydrogen peroxide or organic or inorganic acid salts, such as sodium oxalate, potassium chloride and the like, to react with the metal oxide and hydroxide precipitation on the surface of the zero-valent iron, thereby carrying out the passivation removal, improving the specific surface area of the material, reducing the pH value and improving the repair efficiency.
Description
Technical Field
The invention relates to the technical field of polluted soil and underground water remediation, in particular to a permeable reactive barrier and a remediation method.
Background
The site pollutants in the petrochemical industry, such as petroleum hydrocarbon, chlorohydrocarbon, inorganic heavy metals and the like, have the characteristics of complex, various and uneven pollution and the like, and the polluted underground water migrates to the downstream or the periphery along with the influence of seasons and people to form long-term and continuous pollution plume. Such contaminated plumes generally have high toxicity and low solubility, and the treatment difficulty and cost are correspondingly high. Therefore, it is urgent to develop a high-efficiency, energy-saving and in-situ sustainable remediation technology system for the pollution plume.
Permeable reactive barrier technologies (PRBs) are the most economical and efficient in-situ treatment technologies following monitoring of natural decay; the pollution feather is passively intercepted and repaired by utilizing the natural hydraulic gradient, and compared with the traditional underground water pumping treatment technology, the cost is lower in the aspects of operation and maintenance of the system. Granular zero-valent iron (ZVI) is the most widely used medium in PRBs, and more than 200 zero-valent iron permeable reactive walls (ZVIPRBs) have been used worldwide from the first field demonstration in 1994 to 2011 for the treatment of various chlorinated organics, metals and radionuclides. However, the speed of the existing PRB installation sites is relatively high, and the performance is greatly reduced within 1-5 years; the reasons are mainly medium surface passivation and pore blockage caused by corrosion of iron, and further cause reduction of medium permeability and reduction of repair efficiency. Therefore, solving the problems of medium surface passivation and pore blocking in PRBs, improving the operating efficiency is currently a major problem.
Zero-valent iron successfully treats common organic and inorganic contaminants in groundwater, such as chlorinated volatile organic compounds, petroleum hydrocarbons, chromium, and arsenic; however, the method is difficult to degrade other common pollutants or chlorinated hydrocarbon reduction degradation products, such as 1, 2-dichloroethane (1,2-DCA, also called as "dichloroethane" chloroethane "DC, dichloromethane (DCM, also called as" dichloromethane "chlorine and some chlorinated aromatic hydrocarbons), a plurality of underground waters contain mixed pollutants or intermediate products, a single material and a single technology cannot well achieve the repair target, and multi-stage deep repair needs to be carried out by adopting multi-material multi-technology combination or sequence technology.
In the process of restoring underground water by PRB (reactive resource Block), zero-valent iron is converted into Fe2+OH-is generated, so that the pH value of the water in the active iron unit increases, usually to above 9.0. The mechanism is as follows:
2Fe0+O2+2H2O22Fe2++4OH-
3Fe0→3Fe2++6e-
CH2Cl3+3H++6e-→C2H4+3Cl-
3Fe0+CH2Cl3+3H+→2Fe0+C2H4+3Cl-
it has been found that an increase in the pH of the water in the active iron unit results in the formation of potential precipitates that may passivate and coat the iron surface, reducing the reactivity and conductivity of the iron in the reaction unit and slowing the rate of degradation of the organic material.
Research shows that the front end of the PRB unit is 20-80mm, and an oxide passivation layer is easily formed to block the PRB unit. The zero valent iron reacts with water to corrode as oxides and hydroxides, and precipitates on the surface of ZVI by forming a barrier between the contaminant molecules and the surface of the medium, hindering the formation process of electron transfer and inhibiting degradation.
Disclosure of Invention
In order to solve the problems in the prior art, the invention provides a permeable reactive barrier and a repairing method thereof.
The invention discloses a permeable reactive barrier, comprising: the pre-reaction zone, the main reaction zone and the water outlet buffer zone are sequentially arranged along the water flow direction;
the pre-reaction zone and the effluent buffer zone are both filled with filler and zero-valent iron, and the main reaction zone is filled with zero-valent iron and an adsorbent;
monitoring holes are arranged on the main reaction zone, or monitoring holes are arranged on the pre-reaction zone, the main reaction zone and the water outlet buffer zone; sampling is carried out to monitor whether passivation and blockage occur and a deactivator is added.
As a further improvement of the invention, the pre-reaction zone, the main reaction zone and the water outlet buffer zone are arranged between the water inlet and the water outlet of the reaction box, and filter screens are arranged between the pre-reaction zone and the main reaction zone and between the main reaction zone and the water outlet buffer zone.
As a further improvement of the invention, the fillers of the pre-reaction zone and the effluent buffer zone are coarse sand, and the weight ratio of the coarse sand to zero-valent iron is (80-90): (10-20);
the weight ratio of the zero-valent iron to the adsorbent in the main reaction zone is (80-90): (10-20).
As a further improvement of the invention, the zero-valent iron in the pre-reaction zone is washed by 10% hydrochloric acid to remove impurities or is pre-acidified in the pre-reaction zone.
As a further improvement of the present invention, the adsorbent comprises one of activated carbon and biochar.
As a further improvement of the invention, the monitoring holes are distributed on the central lines of the pre-reaction zone, the main reaction zone and the effluent buffer zone and are used for sampling to monitor whether passivation occurs or not and adding a passivating agent to remove passivation and blockage after passivation occurs; wherein, the passivating agent comprises one or two of hydrogen peroxide, oxalic acid, citric acid, acetic acid, polyaluminium chloride and potassium chloride.
The invention also discloses a permeable reactive barrier repairing method, which comprises the following steps:
acid-washing zero-valent iron is added into the pre-reaction zone or acid is pre-added through a monitoring hole, so that the front end of the main reaction zone is prevented from being passivated and blocked;
after the main reaction zone operates for a certain period of time, sampling and monitoring are carried out through the monitoring holes, and whether passivation occurs or not is judged;
when passivation occurs, a passivating agent is added through the monitoring hole to dissolve inorganic mineral precipitates, reduce pH and react with zero-valent iron to generate active free radicals;
the repaired water is discharged or collected after reaching the standard through an effluent buffer zone.
Compared with the prior art, the invention has the beneficial effects that:
the invention carries out reduction degradation on organic chlorine, hexavalent chromium and the like through the reduction action of zero-valent iron, when the degradation efficiency is obviously reduced, through injecting hydrogen peroxide, small molecular organic acid, inorganic salt polymer and other passivators, the passivators react with the rest zero-valent iron and the passivation precipitation reaction (the main components are iron oxide and hydroxide) on the surface of the medium, the passivation and blockage of the zero-valent iron surface are relieved, and the generated hydroxyl radicals can further oxidize and degrade residual reduction dechlorination products and other composite pollutants in the water-bearing layer, such as dichloroethane, dichloroethylene, chlorohydrocarbons such as chloroethylene and the like and a small amount of petroleum hydrocarbon, thereby improving the service life of the permeable reactive barrier and the pollutant remediation efficiency.
Drawings
FIG. 1 is a schematic structural diagram of a permeable reactive barrier according to an embodiment of the present invention;
fig. 2 is a transverse cross-sectional view of fig. 1.
In the figure:
10. a reaction box; 11. a pre-reaction zone; 12. a primary reaction zone; 13. a water outlet buffer zone; 14. filtering with a screen; 15. and a monitoring hole.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, are within the scope of the present invention.
The invention is described in further detail below with reference to the attached drawing figures:
the permeable reactive barrier technology (PRB) is the most economical and effective in-situ treatment technology after monitoring natural attenuation, utilizes natural hydraulic gradient to passively capture and repair pollution plumes, and has lower cost in the aspects of operation and maintenance of a system compared with the traditional underground water pumping treatment technology. Granular zero-valent iron (ZVI) is the most commonly used medium in PRBs, and more than 200 zero-valent iron permeation reaction barriers (ZVIPRBs) have been used worldwide from first field demonstration in 1994 to 2011 for the treatment of various chlorinated organics, metals and radionuclides. However, with the operation of zero-valent iron PRB, the problems of iron aging, secondary precipitation, PRB reaction site passivation, blockage, porosity reduction and the like are easy to occur, and the service life of PRB is shortened. The service life of most PRBs is less than 10 years, while the life of the pollution plume may be as long as decades or more, and these problems limit the application of ZVIPRBs, especially, there is no large success case of single application in China. Therefore, activating and regenerating the reaction material, effectively utilizing ZVI ions, and further solving PRB blockage and improving operation efficiency are the main problems currently facing.
In order to solve the above problems, as shown in fig. 1 and 2, the present invention provides a permeable reactive barrier, which is a continuous reactive barrier structure; comprises a reaction box 10;
the reaction box 10 is of a cylindrical or square structure and is made of high borosilicate glass or polyurethane material; a filter screen 14 (preferably a stainless steel filter screen) is arranged in the reaction box 10, and the reaction box 10 is sequentially divided into a pre-reaction zone 11, a main reaction zone 12 and an effluent buffer zone 13 along the direction from a water inlet to a water outlet; when the reaction box 10 is of a square structure, the length, width and height of the reaction box can be 60cm, 40cm and 50cm, the length of the pre-reaction zone 11 is 5-10cm, the length of the main reaction zone 12 is 50-100cm, and the length of the effluent buffer zone 13 is 5-10 cm; or the ratio of the pre-reaction zone to the main reaction zone to the effluent buffer zone is 1:10-20: 1. When the reaction chamber 10 has a cylindrical structure, the diameter thereof may be 20cm and the length thereof may be 60cm, the length of the pre-reaction zone 11 is 5cm, the length of the main reaction zone 12 is 50cm, and the length of the effluent buffer zone 13 is 5 cm. Further, the above dimensions shown in the present invention are only one common reactor specification, and those skilled in the art can design the reactor according to actual requirements.
The pre-reaction zone 11 of the invention is filled with filler and zero-valent iron or filler and ferrous sulfide, the filler is coarse sand or fine sand, preferably coarse sand; the weight ratio of the filler to the zero-valent iron or ferrous sulfide is (80-90): (10-20), preferably the weight ratio of 90: 10; wherein, zero-valent iron or ferrous sulfide is cleaned by 10% hydrochloric acid to remove impurities, or 1% -10% oxalic acid and citric acid are injected through the monitoring hole 15, or about 10% pyrite is used for replacing; so as to improve the specific surface area of iron, eliminate dissolved oxygen, slow down the rate of pH rise and the like, slow down the rate of iron corrosion passivation and pore blockage, and improve the passivation and blockage at the front end of the main reaction zone 12.
The main reaction zone 12 of the invention is filled with zero-valent iron and an adsorbent, wherein the zero-valent iron is 8-50 meshes, the adsorbent comprises one of activated carbon and biochar, and the weight ratio of the zero-valent iron to the adsorbent is (80-90): (10-20), preferably the weight ratio of 90: 10. the reaction principle of the main reaction zone 12 is: sequential treatment is realized in time for chemical oxidation and dissolution after reductive dechlorination; namely, firstly, the chlorinated hydrocarbons are degraded into alkane, olefin and micromolecular chlorinated hydrocarbons by utilizing the reduction action of zero-valent iron, heavy metals are reduced, and toxic intermediate products are adsorbed and intercepted by a charcoal adsorbent; and regularly monitoring through monitoring holes 15, when the surface zero-valent iron reacts until the surface active sites are full, the surface is passivated by metal oxide and the activity is reduced, injecting 1-10% of passivating agent comprising one or two of hydrogen peroxide, oxalic acid, citric acid, acetic acid, polyaluminium chloride, potassium chloride and the like into the monitoring holes 15 arranged on the central line of the reaction zone, and H2O2With Fe in solution in the reaction zone2+Reacted and passed through Fe2+/Fe3+Circularly and continuously generate hydroxyl free radicals with stronger oxidability and activity, and continuously oxidize and degrade organic chlorine reduction products and intermediate productsPetroleum hydrocarbons in ground water, such as benzene series; simultaneous generation of H+The iron oxide reacts with the mineral deposit on the surface or in the pores of the medium, so that the mineral deposit can be effectively dissolved, and the porosity, the specific surface and the activity of the iron are increased.
Further, the zero-valent iron and the adsorbent in the main reaction zone 12 are wrapped by geotextile, the three units are separated by a permeable stainless steel filter screen, the porosity is 0.45-0.55, and the permeability can reach 1.9 multiplied by 10-4～4.5×10-4cm/s, permeability 5-6 times that of the surrounding aquifer.
The effluent buffer zone 13 is filled with filler and zero-valent iron, the filler is coarse sand or fine sand, and coarse sand is preferred; the weight ratio of the filler to the zero-valent iron is (80-90): (10-20), preferably the weight ratio of 90: 10.
According to the invention, a plurality of stages of monitoring holes 15 are designed along the underground water flow direction, namely along the central line of the reaction zone, and meanwhile, the monitoring holes 15 can also be designed in the pre-reaction zone 11 and the effluent buffer zone 13; a sealing rubber plug is arranged, and an injectable sampler is arranged in each monitoring hole, so that the sampling well can be used as a monitoring well to realize regular sampling, and can also be used as an injection well to realize regular injection of materials to remove passivation and activation agents; when the monitoring shows that the passivation and blockage affect the operation efficiency, a hydrogen peroxide oxidant system or a zero-valent iron passivator such as low-molecular organic acid, acid-reactable ions (aluminum salt and the like) and the like can be injected; wherein the deactivator is one or more of small-dose hydrogen peroxide, hydrogen peroxide/oxalic acid complex, low molecular weight organic acid such as acetic acid and oxalic acid, and inorganic salt such as aluminum sulfate, aluminum chloride and potassium chloride.
The invention provides a Permeable Reactive Barrier (PRB) repairing method based on the permeable reactive barrier, which is used for activating and regenerating a Permeable Reactive Barrier (PRB), reducing passivation and blockage and improving repairing efficiency by combining filler design, monitoring and chemical agent staged addition.
The repairing method comprises the following steps: zero-valent iron, quartz sand and biochar particles are used as reaction materials, hydrochloric ether pollutants are reduced and degraded in the same reactor, and then organic matters such as petroleum hydrocarbon, polycyclic aromatic hydrocarbon, benzene series, hydrochloric ether degradation products and the like are continuously degraded and oxidized by injecting hydrogen peroxide, hydrogen peroxide/oxalic acid complex oxidant and oxalic acid/oxalic acid. The added oxalic acid, aluminum sulfate and chloride can effectively dissolve and precipitate, remove passivation, improve passivation and blockage of reaction materials, and improve the service life and efficiency of operation.
The repairing method specifically comprises the following steps:
step 1, designing a pretreatment reaction zone, a main reaction zone and a transition zone in a reaction unit at a reaction barrier design stage, filling different material combination proportions, and optimizing a PRB operation structure; acid-washing zero-valent iron is added into the pre-reaction zone or acid is pre-added through a monitoring hole, so that the problem that the PRB water inlet end is easy to block is solved;
step 2, after a main reaction zone with zero-valent iron as a main reaction material runs for a certain period of time, sampling and monitoring through a monitoring hole to judge whether passivation occurs or not; the criteria for passivation were: the blockage degree is increased and the repair efficiency is reduced through sampling and monitoring. After passivation occurs, a passivating agent such as hydrogen peroxide, small molecular organic acid, inorganic salt and the like is injected into the main reaction zone through the monitoring hole, and the blockage and passivation problems of reaction materials can be effectively improved and the activity of iron is increased through the ways of dissolving inorganic mineral precipitates, reducing pH, reacting with zero-valent iron to generate active free radicals and the like; the repair target is achieved;
and 3, repairing complex mixed organic matters in the petrochemical site by adopting a monitoring natural attenuation technology, wherein the complex mixed organic matters comprise but are not limited to organic chlorine solvents, petroleum hydrocarbons, benzene series substances and heavy metals (chromium, arsenic, nickel and the like).
The invention has the advantages that:
after the reaction is carried out for a period of time, aiming at the passivation, blockage and activity reduction of zero-valent iron and the adsorbent, the invention adds the regeneration activation passivator, such as hydrogen peroxide or organic or inorganic acid salts, such as sodium oxalate, potassium chloride and the like, to react with the metal oxide and hydroxide precipitation on the surface of the zero-valent iron, thereby carrying out the passivation removal, improving the specific surface area of the material, reducing the pH value and improving the repair efficiency. Example 1
Example 1
The permeable reactive barrier adopted by the invention is a cylindrical reactive barrier, the diameter of which is 20cm, the length of which is 60cm, and the permeable reactive barrier flows from the pre-reaction zone 11, the main reaction zone 12 and the outlet along the water flow directionA water buffer zone 13, wherein a water inlet end and a water outlet end are respectively provided with a pre-reaction zone 11 and a water outlet buffer zone 13 which are 5cm in length, the filling material is coarse sand (1.0-5.0mm) + 10% of zero-valent iron, a main reaction zone 12 which is 50cm in length is filled with 90% of zero-valent iron and 10% of adsorbent by mass and dry weight, the zero-valent iron is fresh zero-valent iron with the purity of 99.8%, and the granularity is 1-2 mm; the adsorbent can be activated carbon, biochar or ceramsite prepared from solid waste, and the specific surface areas of the zero-valent iron and the activated carbon are respectively 0.50m2G and 750m2/g。
The invention is provided with a pump at the water inlet end to control the flow rate of polluted groundwater. Meanwhile, monitoring holes (also used as injection holes) are respectively arranged in the reaction zone, the main reaction zone and the water outlet buffer zone, the monitoring holes/injection holes are sealed by rubber, and sampling and medicament injection can be carried out through a sampling needle and an injection needle.
The permeable reactive barrier is used for treating organic chlorine solvent, hexavalent chromium and nitrobenzene, and the removal rate of organic matters reaches over 90 percent after the permeable reactive barrier is operated for 72 hours. Fe0The reactivity was not significant within the first few hours of treatment. However, the degradation coefficient is slightly reduced after the exposure time of the nitro reduction experiment allowed to be completed exceeds 1 hour; the first-order reaction kinetic constant of nitrobenzene is from 0.069h-1Reduced to 0.035h-1。
When in use, 100ml of Cr containing 2mg/L is introduced into the reaction wall6+And nitrobenzene, after 3 weeks, the zero-valent iron of the main reaction zone was almost completely covered by a passivated orange precipitate, with a maximum passivating layer concentration of 16.6 mg/g.
After the above passivation had occurred, 0.03M acetic acid (HAc), 0.015M Alum (Alum), or copper sulfate pentahydrate (CuSO) was injected through monitor hole 154·5H2O) and 0.01M potassium chloride (KCl) or ammonium chloride (NH4Cl) or sodium chloride (NaCl), the depassivation of the passivated Zero Valent Iron (ZVI) was confirmed by observation of the chemical morphology of the iron and chromium in aqueous solution and on the iron surface. Within 2-6 hours, the passivating agent can achieve 10-65% of passivating effect. Acetic acid was added and the maximum uniform depassivation rate of 61.6% was reached at the end of 6 hours. Aluminum sulfate was added as a scavenger in the same manner, and the purification was carried out for 3 hoursThe highest rate reaches 58.3 percent. Considering the depassivation conditions, the removal efficiency is the highest with acetic acid and salt mixture, the lowest with single acetic acid, other single reagent or both.
Example 2
The invention is filled with the treated sand, zero-valent iron and biochar material in a reaction wall, and the reaction wall is introduced with the mixture which is stirred uniformly and has the concentration of 100mgL-1The benzene series of (A) includes benzene (B), toluene (T), ethylbenzene (E) and xylene (X). The oxidizing agent (hydrogen peroxide, potassium persulfate, hydrogen peroxide/Fe (III)/oxalic acid) was injected through the monitoring hole and the concentrations were set to 10mM at a low concentration and 500mM at a high concentration, respectively. Mixing Fe (III) and oxalic acid (1:6) at pH7.0 for 1 hr, and adding H2O2Solution, preparation of H2O2Fe (III)/oxalic acid chelating agent.
The experiments included control group (only contaminants), charcoal adsorbent/contaminants, oxidant/contaminants and charcoal adsorbent/oxidant/contaminants, with degradation reactions at 25 ℃. In addition, the present inventors investigated the effect of hydrogen peroxide/Fe (iii)/oxalic acid on the removal of benzene series (BTEX) using a control, i.e., a contaminant containing Fe (iii)/oxalic acid) and other experiments, i.e., a contaminant containing Fe (iii)/oxalic acid/hydrogen peroxide.
The biochar adsorbent is prepared from waste biomass, wherein the raw materials comprise municipal sludge, straws, biomass shells and the like, and the biochar adsorbent is prepared by crushing the raw materials to be less than 150 mu m. Molding into small-particle spheres by a granulator, drying at the temperature of 110-120 ℃ for 48 hours, and then calcining in a muffle furnace or a rotary kiln at the temperature of 500-1000 ℃ for 30 minutes to 2 hours, wherein the higher the temperature is, the shorter the calcining time is. After cooling to room temperature, the adsorption of BTEX by the solid spent adsorbent was 54%, 64%, 62% and 65%, respectively, within a reaction time of 72 hours. When three types of oxidation systems (i.e. H) are used2O2Persulfate and H2O2Fe (iii)/oxalic acid), an increase in oxidant concentration was observed to increase BTEX removal; among these, the catalytic action of the iron oxide-containing solid adsorbent may be caused by iron oxide on the surface thereof. As potassium persulfate increases, the concentration of contaminant removed per unit of oxidant consumed increases. At H2O2The maximum degradation rate constants (K) of benzene series (BTEX) of the biochar solid waste adsorbent system in the/Fe (III)/oxalic acid are respectively 0.35, 0.37, 0.50 and 0.72h-1When 500mM H is used2O2And the BTEX adsorbed on the surface of the biochar was also degraded, indicating regeneration of the biochar adsorbent. Therefore, the injection of oxidant into permeable reaction walls packed with adsorbent may be an alternative method for adsorbing and catalytically degrading benzene series.
Only 10mM potassium Persulfate (PS) oxidation system has 50%, 41%, 20% and 24% degradation rate of benzene (B), toluene (T), ethylbenzene (E) and xylene (X) in benzene series, and the ratio of BTEX in the degradation aqueous solution of the potassium persulfate combination system (potassium persulfate/solid waste adsorbent) added with the charcoal adsorbent is increased to 96%, 81%, 53% and 61%.
Hydrogen peroxide is a commonly used oxidizing agent, commonly used for the oxidative degradation of organic matter, especially petroleum hydrocarbons. The first order kinetic degradation coefficient of the benzene series is 0.025h under the BTEX condition that only 10mM of hydrogen peroxide degrades 100mg/L-1When 10mM hydrogen peroxide is added with complexing agent of iron salt and oxalic acid, the degradation coefficient is 0.11h-1The increase is 4.36 times. 10mM H2O2The solid adsorbent system increases the BTEX removal rate. The results of the study confirmed that 10mM H of the iron complex was added2O2The system can remove more benzene series in the water solution than other systems. The removal rate increases with increasing sorbent. Thus, after a period of zero valent iron material PRB operation, zero valent iron is oxidized to Fe2+And Fe3+After the hydrogen peroxide or the hydrogen peroxide/oxalic acid is added, the generated hydroxyl free radical and complex compound accelerate and improve the removal rate of the benzene series pollutants.
The research proves that the iron complex does not influence the absorption of the benzene series on the solid waste adsorbent. The hydrogen peroxide can be catalyzed by the biochar adsorbent and the biochar and iron complex, so that the benzene series in the aqueous solution can be removed.
The above is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and various modifications and changes will occur to those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (7)
1. A permeable reactive barrier, comprising: the pre-reaction zone, the main reaction zone and the water outlet buffer zone are sequentially arranged along the water flow direction;
the pre-reaction zone and the effluent buffer zone are both filled with filler and zero-valent iron, and the main reaction zone is filled with zero-valent iron and an adsorbent;
monitoring holes are arranged on the main reaction zone, or monitoring holes are arranged on the pre-reaction zone, the main reaction zone and the water outlet buffer zone; sampling is carried out to monitor whether passivation and blockage occur and a deactivator is added.
2. A permeable reactive barrier according to claim 1, wherein the pre-reaction zone, the main reaction zone and the effluent buffer zone are disposed between the inlet and the outlet of the reaction chamber, and a filter screen is disposed between the pre-reaction zone and the main reaction zone and between the main reaction zone and the effluent buffer zone.
3. A permeable reactive barrier according to claim 1, wherein the packing of the pre-reaction zone and the effluent buffer zone is coarse sand, and the weight ratio of the coarse sand to zero-valent iron is (80-90): (10-20);
the weight ratio of the zero-valent iron to the adsorbent in the main reaction zone is (80-90): (10-20).
4. A permeable reactive barrier according to claim 1 or claim 3 wherein the zero valent iron in the pre-reaction zone is washed with 10% hydrochloric acid to remove impurities or pre-acidified in the pre-reaction zone.
5. The permeable reactive barrier of claim 1 or 3, wherein the adsorbent comprises one of activated carbon and biochar.
6. A permeable reactive barrier according to claim 1, wherein the monitoring holes are arranged on the central line of the pre-reaction zone, the main reaction zone and the effluent buffer zone for sampling to monitor whether passivation occurs and adding a passivating agent to remove passivation and blockage after passivation occurs; wherein, the passivating agent comprises one or two of hydrogen peroxide, oxalic acid, citric acid, acetic acid, polyaluminium chloride and potassium chloride.
7. A method of repairing a permeable reactive barrier according to any one of claims 1 to 6, comprising:
acid-washing zero-valent iron is added into the pre-reaction zone or acid is pre-added through a monitoring hole, so that the front end of the main reaction zone is prevented from being passivated and blocked;
after the main reaction zone operates for a certain period of time, sampling and monitoring are carried out through the monitoring holes, and whether passivation occurs or not is judged;
when passivation occurs, a passivating agent is added through the monitoring hole to dissolve inorganic mineral precipitates, reduce pH and react with zero-valent iron to generate active free radicals;
the repaired water is discharged or collected after reaching the standard through an effluent buffer zone.
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