CN112143505A - Cadmium-polluted soil and underground water repairing agent and method for repairing cadmium-polluted soil and underground water by using same - Google Patents
Cadmium-polluted soil and underground water repairing agent and method for repairing cadmium-polluted soil and underground water by using same Download PDFInfo
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Abstract
The invention discloses a cadmium-polluted soil and underground water repairing agent and a repairing method thereof. The repairing agent comprises zero-valent iron powder and hydrogen autotrophic denitrifying bacteria. The method comprises the following steps: and adding zero-valent iron powder, hydrogen autotrophic denitrifying bacteria and nitrate into the cadmium-polluted soil and underground water, and repairing under the anaerobic environment at normal temperature. The hydrogen autotrophic denitrifying bacteria take hydrogen released by the reaction of zero-valent iron and water as an electron donor to perform denitrification, promote the corrosion of the zero-valent iron and generate high-activity iron minerals on the surface of the zero-valent iron, so that the zero-valent iron can adsorb and fix a large amount of cadmium ions. The repairing method effectively solves the difficulty that zero-valent iron cannot directly generate oxidation-reduction reaction with cadmium to cause the corrosion limitation of the zero-valent iron, and can greatly reduce the migration capacity and bioavailability of the cadmium in soil and underground water. The method has the characteristics of stable repairing effect, low cost, small influence on the environment and the like, and is suitable for repairing cadmium-polluted soil and underground water.
Description
Technical Field
The invention belongs to the technical field of soil and underground water environment remediation, and particularly relates to a cadmium-polluted soil and underground water remediation agent and a remediation method for cadmium-polluted soil and underground water by using the same.
Background
Cadmium is used as an important chemical raw material and widely applied to industries such as metal processing, battery manufacturing, electroplating, dyes and the like. Under natural conditions, cadmium often coexists with lead and zinc to form lead-zinc ores, and in industrial production such as ore sintering, metal smelting and the like, a large amount of cadmium enters soil and underground water environment due to leakage in the production process, unreasonable discharge of wastewater, cadmium-containing waste residues seepage and the like, so that increasingly serious cadmium pollution is caused. Cadmium has a biological enrichment effect and can be accumulated and transferred through a food chain, and excessive cadmium ingested by a human body can damage organs such as liver, lung, kidney and the like, and meanwhile, cadmium has a carcinogenic effect. Therefore, how to solve the problem of cadmium pollution in the environment becomes one of important research contents in the field of environmental remediation nowadays. Cadmium is generally present as a water-soluble positive divalent ion (Cd) in soil and groundwater environments2+) Exist, by means of hydrodynamic diffusion conditionsHas strong migration capability. Therefore, in the remediation of cadmium-polluted soil and underground water, people mainly block the effective migration of cadmium in the environment through two ways and reduce the bioavailability of cadmium, thereby realizing the remediation of the cadmium-polluted environment. The first is to directly remove cadmium from polluted soil and groundwater, such as extraction method, electric power restoration method and the like. The other approach is to fix free cadmium in soil and underground water by adding a repairing agent, so that the migration capacity and the bioavailability of the cadmium in the environment are reduced, and the method comprises an adsorption method, a precipitation method and the like.
Zero-valent iron, which is an economical, easily available and environmentally friendly material, has attracted extensive attention of researchers in the field of environmental remediation, and its use for immobilizing heavy metals in soil and groundwater is a new technology that has rapidly developed in recent years. The reaction of zero-valent iron with water and oxygen can produce iron oxides with strong adsorption capacity, such as Fe2O3、Fe3O4FeOOH and the like, can effectively adsorb and fix Cd in soil and groundwater2+Forming a stable complex, according to the following reaction formula:
≡FeO-+Cd2+→≡FeOCd+
≡FeO-+Cd2+→≡FeOCdOH。
relevant research shows that the zero-valent iron and the oxide thereof have Cd2+The removal process of (a) is an interface control reaction which occurs at active sites on a solid surface, and thus the removal efficiency of cadmium depends on the degree of corrosion of the zero-valent iron surface, the number of active sites, and the amount of iron oxide produced. However, since soil and groundwater are often anaerobic, zero-valent iron is difficult to react with oxygen to cause oxidation corrosion, and the oxidation-reduction potential of cadmium (Cd/Cd)2+-0.40V) and oxidation-reduction potential of iron (Fe/Fe)2+(-0.44V), zero-valent iron and Cd2+Oxidation-reduction reaction is difficult to occur between the iron oxide and the iron oxide, so that zero-valent iron corrosion is hindered and the amount of generated iron oxide is very limited; in addition, under abiotic conditions, zero-valent iron can corrode its surfaceA dense passivation layer tends to form, causing the etch process to terminate, further impeding electron transport. The research shows that zero-valent iron has influence on the form and effectiveness of heavy metal cadmium in beach soil [ J]Jiangsu agricultural science, 2017,45(18): 249-251), the soil cadmium pollution remediation is carried out by simply using zero-valent iron as a remediation agent, even if the addition amount of the zero-valent iron reaches 40g/kg, the removal rate of quick-acting cadmium in soil can only reach 60%, the utilization efficiency of the zero-valent iron is extremely low, and only 0.2mg of Cd is used2+/g Fe0. Therefore, in the actual operation of repairing cadmium contaminated soil and groundwater by using zero-valent iron, problems such as the corrosion of zero-valent iron is hindered, and the cadmium removal efficiency is low often exist.
Cadmium-tolerant microorganisms widely exist in cadmium-polluted soil and underground water environments, play an important role in chemical substance circulation of the soil and the underground water environments, and have important significance in applying the microorganisms to a cadmium-polluted remediation system. Another interesting property of zero-valent iron is that it can react with water under anaerobic conditions and release hydrogen gas in surface crevices, according to the following equation:
Fe0+2H2O→Fe2++2OH-+H2↑
thereby inducing the hydrogen autotrophic microorganisms such as denitrifying bacteria widely existing in the environment to react with H on the surface2Being an electron donor, NO3 -Is an electron acceptor, and carbonate is a carbon source for metabolic growth. Therefore, the cadmium polluted soil and underground water can be repaired through a synergistic system formed by the zero-valent iron and the hydrogen autotrophic denitrifying bacteria. On the one hand, from the reaction kinetics point of view, zero-valent iron corrodes the released H2Can promote the continuous corrosion of zero-valent iron and the generation of Fe when being consumed by the hydrogen autotrophic denitrifying bacteria in time2+Thereby overcoming zero-valent iron and Cd2+The slow corrosion of zero-valent iron caused by difficult oxidation-reduction reaction; on the other hand, to obtain more H2The hydrogen autotrophic denitrifying bacteria can release various extracellular polymeric substances, and Fe is treated by the extracellular polymeric substances2+The complexation of the iron can reduce the generation of a passivation layer on the surface of zero-valent iron and induce Fe2+Gradually, graduallyActive secondary minerals such as green rust, magnetite, lepidocrocite and the like are generated, and compared with the iron oxide generated by zero-valent iron corrosion under the non-biological condition, the active minerals have higher specific surface area, more active reaction sites, stronger electron transfer capacity and the like, and the adsorption and fixation of Cd by the zero-valent iron can be greatly improved2+The ability of (c); in addition, zero-valent iron corrosion and denitrification processes release OH continuously-The alkaline environment is favorable for Cd2+With OH-Precipitation occurs, further reducing the migratory capacity and bioavailability of cadmium.
In conclusion, the hydrogen autotrophic denitrifying bacteria and the zero-valent iron are combined to form the soil and underground water cadmium pollution cooperative repair system, so that the unique physical and chemical properties of the zero-valent iron are fully exerted, the repair system has biochemical reaction characteristics, the problems of slow self corrosion, poor cadmium removal effect and the like of the zero-valent iron in the process of independently repairing cadmium polluted soil and underground water can be effectively solved, and the theoretical guiding significance and the practical application value for repairing the cadmium polluted soil and underground water are achieved.
Disclosure of Invention
In order to overcome the defects in the prior art, the invention aims to provide a cadmium-polluted soil and underground water repairing agent and a method for repairing the cadmium-polluted soil and underground water by using the cadmium-polluted soil and underground water repairing agent.
The invention provides a cadmium polluted soil and underground water repairing agent and a repairing method thereof, aiming at the problems of slow corrosion, low cadmium removing efficiency and the like of zero-valent iron in repairing cadmium polluted soil and underground water. The repairing agent is prepared by mixing zero-valent iron powder and hydrogen autotrophic denitrifying bacteria in proportion, and in the repairing process of cadmium polluted soil and underground water, microorganisms react with water to release H by using zero-valent iron under the anaerobic condition2Being an electron donor, NO3 -For the metabolic growth of electron acceptors, by continuous consumption of H2Promoting the corrosion reaction of the zero-valent iron and keeping the surface active sites of the zero-valent iron updated; meanwhile, extracellular polymers of various microorganisms can induce Fe released by zero-valent iron corrosion2+Active secondary minerals are generated, and zero-valent iron adsorption and Cd fixation are greatly improved2+OfForce.
The purpose of the invention is realized by at least one of the following technical solutions.
The invention provides a cadmium contaminated soil and underground water repairing agent which comprises zero-valent iron powder, a hydrogen autotrophic denitrifying bacteria suspension and nitrate with the concentration of 62-248mg/L, wherein the concentration of the hydrogen autotrophic denitrifying bacteria suspension is 1-4 g/L.
The hydrogen autotrophic denitrifying bacteria can be obtained by screening and domesticating municipal sludge.
The hydrogen autotrophic denitrifying bacteria take hydrogen as an electron donor and nitrate as an electron acceptor to carry out metabolic activity.
Further, the grain size of the zero-valent iron powder is 0.1-1mm, and the iron content is more than 97%; the zero-valent iron powder is cleaned with an acidic substance to remove surface oxides before use.
Further, the domestication of the hydrogen autotrophic denitrifying bacteria by using domesticated strains comprises:
screening denitrifying bacteria from sludge, and domesticating the strains in an anaerobic reactor by using hydrogen as a main electron donor and adopting a cadmium concentration gradient method; during domestication, the sludge concentration is 5-20g/L, the glucose concentration is 50-150mg/L, the cadmium concentration is 1-10mg/L, the nitrate concentration is 62-248mg/L, the hydraulic retention time of the anaerobic reactor is 20-30h, and when the consumption rate of the nitrate in the liquid of the anaerobic reactor is stable to reach more than 95%, the domesticated hydrogen autotrophic denitrifying bacteria are obtained. After the domesticated hydrogen autotrophic denitrifying bacteria are washed by clear water, the hydrogen autotrophic denitrifying bacteria are centrifugally concentrated and are prepared into bacterial suspension with the microbial concentration of 1-4g/L by deoxygenated water. The domesticated hydrogen autotrophic denitrifying bacteria are fully mixed with zero-valent iron powder 2-5 days before use, and the concentration of nitrate in the solution is maintained to be 62-248 mg/L.
Preferably, the hydraulic retention time of the anaerobic reactor is 24 h.
Further, in the anaerobic reactor, the cadmium concentration is gradually increased from 1-10mg/L, and is gradually increased once every 40-50h, and the cadmium concentration is gradually increased by 0.5-1.5mg/L each time until the cadmium concentration is 10 mg/L; the gas atmosphere of the anaerobic reactor is nitrogen, hydrogen and dioxygenA mixed atmosphere of carbonized carbon; the volume ratio of the nitrogen to the hydrogen to the carbon dioxide is as follows: n is a radical of2：H2：CO2＝85％：10％：5％。
Preferably, in the anaerobic reactor, the cadmium concentration is gradually increased from 1-10mg/L, and is gradually increased once every 48 hours until the cadmium concentration is 10mg/L, wherein the cadmium concentration is gradually increased by 1mg/L each time.
Further, when the repairing agent is used for soil repair, the dosage of the zero-valent iron powder is 1-10g/kg (relative to the dosage of soil to be repaired), and the dosage of the hydrogen autotrophic denitrifying bacteria suspension is 50-200mg/kg (relative to the dosage of soil to be repaired).
Further, when the repairing agent is used for groundwater repair, the addition amount of the zero-valent iron is 1-500g/L (relative to the amount of groundwater to be repaired), and the addition amount of the bacterial suspension is 50-400mg/L (relative to the amount of groundwater to be repaired).
The invention provides a method for repairing cadmium-polluted soil or underground water by using the cadmium-polluted soil and underground water repairing agent, which comprises ex-situ repairing and in-situ repairing;
the ectopic repair comprises: taking a cadmium-polluted soil or underground water sample to be repaired, adding a cadmium-polluted soil and underground water repairing agent (a repairing agent prepared from zero-valent iron powder and bacterial suspension) to obtain a mixture, and then placing the mixture in an anaerobic reactor for ectopic repairing treatment (repairing in a normal-temperature anaerobic environment);
when the sample to be repaired is cadmium contaminated soil, the in-situ repair comprises the following steps: the cadmium-polluted soil and underground water remediation agent is sprayed to cadmium-polluted soil to be remedied in a rotating mode, and then in-situ remediation treatment is carried out in an anaerobic environment (remediation is carried out in a normal-temperature anaerobic environment);
when the sample to be repaired is cadmium-polluted underground water, the in-situ repair comprises the following steps: the cadmium-polluted soil and groundwater remediation agent are uniformly mixed with quartz sand, then the mixture is filled into a permeable reactive barrier, the permeable reactive barrier is contacted with groundwater, and then in-situ remediation treatment is carried out in an anaerobic environment.
Further, the particle size of the cadmium-polluted soil is 0.1-3mm, the water content is 50-65%, and the cadmium concentration is 1-15 mg/kg; the cadmium concentration in the cadmium-polluted underground water is 1-10 mg/L.
Further, the time of the ex-situ repair treatment and the time of the in-situ repair treatment are both 5-15d, and the temperature of the ex-situ repair treatment and the temperature of the in-situ repair treatment are 25-35 ℃; the volume ratio of the cadmium-polluted soil and groundwater remediation agent to the quartz sand is 0.5-1.5: 1.
preferably, the volume ratio of the cadmium-polluted soil and groundwater remediation agent to the quartz sand is 1: 1.
further, the pH value of the cadmium polluted soil and the cadmium polluted groundwater is 5.0-8.0; the concentration of nitrate in the cadmium polluted soil and the cadmium polluted underground water is 62-248 mg/L.
Compared with the prior art, the invention has the following advantages and beneficial effects:
(1) the invention uses the method of combining the zero-valent iron and the hydrogen autotrophic denitrifying bacteria to repair the cadmium polluted soil and underground water, skillfully utilizes the characteristic that the zero-valent iron reacts with water to generate hydrogen under the anaerobic condition, and overcomes the defects of zero-valent iron and Cd2+Because the oxidation-reduction potentials are similar, the oxidation-reduction reaction is difficult to occur, so that the problem of slow corrosion of zero-valent iron is caused; due to the zero-valent iron pair Cd2+The removal process of (a) is an interface control reaction, so that high efficiency corrosion will enhance the zero-valent iron to Cd2+The effective adsorption of the method solves the problem of poor cadmium pollution removal effect when the zero-valent iron is used alone.
(2) Autotrophic denitrifying bacteria promote zero-valent iron corrosion and induce Fe released by zero-valent iron corrosion through secreting extracellular polymer2+Generating active secondary minerals such as green rust, magnetite, lepidocrocite and the like, further promoting the adsorption of zero-valent iron and the fixation of Cd2+The ability of the cell to perform. And OH is continuously released in zero-valent iron corrosion and denitrification processes-Is favorable to Cd2+With OH-Precipitation occurs. Through the synergistic effect of the zero-valent iron and the autotrophic denitrifying bacteria, the remediation effect of cadmium contaminated soil and polluted underground water can be greatly improved while the remediation cost and the environmental influence are lower.
Drawings
FIG. 1 shows X-ray diffraction patterns (XRD) of the respective systems before and after the reaction.
FIG. 2 shows zero-valent iron (unreacted Fe)0) Scanning Electron Micrograph (SEM) before reaction.
FIG. 3 shows zero-valent iron (Fe)0) Scanning Electron Micrographs (SEM) after the reaction.
FIG. 4 shows the zero-valent iron and the microorganism (Fe)0+ microorganisms) after reaction Scanning Electron Microscopy (SEM).
FIGS. 5 and 6 show the nitrate-mediated reaction of zero-valent iron with microorganisms (Fe)0+ microorganism + NO3 -) Scanning Electron Micrographs (SEM) after the reaction.
FIG. 7 is a graph comparing the effect of groundwater cadmium removal.
FIG. 8 is a graph comparing the removal of cadmium from soil.
FIG. 9 is a graph comparing the effect of different nitrate concentrations on the synergistic system.
FIG. 10 is a graph comparing the effect of different pH on synergistic systems.
Detailed Description
The following examples are presented to further illustrate the practice of the invention, but the practice and protection of the invention is not limited thereto. It is noted that the processes described below, if not specifically described in detail, are all realizable or understandable by those skilled in the art with reference to the prior art. The reagents or apparatus used are not indicated to the manufacturer, and are considered to be conventional products available by commercial purchase.
Example 1
A cadmium contaminated soil and groundwater remediation agent and a remediation method thereof comprise the following steps:
2kg of municipal sludge is collected, the concentration of the sludge is adjusted to 10-20g/L by clear water, and 1g/L of glucose and 2g/L of sodium nitrate are added. The supernatant was replaced daily and 1g/L glucose and 2g/L sodium nitrate were added. After 14 days, the sludge is transferred to an anaerobic incubator with the proportion of N2：H2：CO285%: 10%: 5% mixed gas, and culturing the sludge under the conditions that the nitrate concentration is 2g/L and the temperature is 25 ℃. After six months of culture, separating the sludge and the culture solution by a centrifugal methodTaking sludge with the thickness of 1/3 in the middle of a sludge layer as inoculated sludge to perform acclimatization and propagation in an anaerobic reactor, wherein the inoculated concentration of the sludge is 10g/L, clear water, 20g/L zero-valent iron powder (with the particle size of 0.15mm), 50mg/L glucose, 85mg/L dipotassium hydrogen phosphate, 150mg/L ammonium chloride, 50mg/L calcium chloride, 150mg/L magnesium sulfate, 500mg/L sodium bicarbonate, copper chloride, manganese chloride, cobalt chloride, nickel chloride, zinc sulfate and ammonium molybdate are respectively 0.5mg/L, and 124mg/L nitrate (in NO form) is added at the same time3 -Measured) and adopts the cadmium concentration (in Cd)2+Metering) a gradient method (1-10mg/L) to domesticate the strains, gradually increasing the cadmium concentration from 1-10mg/L in sequence, gradually increasing the cadmium concentration once every 48h, and gradually increasing the cadmium concentration by 1mg/L each time until the cadmium concentration is 10 mg/L; setting the hydraulic retention time to be 24h, and considering that the acclimation of the required dominant bacteria is finished when the consumption rate of the nitrate in the effluent of the reactor is stably over 95 percent. After the strains obtained by domestication are washed by clear water, the strains are centrifugally concentrated and are prepared into bacterial suspension with the microbial concentration of 1g/L by using deoxygenated water. And 3d before use, fully mixing the powder with zero-valent iron, maintaining the concentration of nitrate in the solution to be 124mg/L, and fully attaching and growing the strains on the surface of the zero-valent iron to prepare the repairing agent.
Preparing 250mL of cadmium-polluted underground water simulation sample by using deoxidized water in an anaerobic reactor, wherein Cd is2+Concentration of 10mg/L, NO3 -N concentration of 28mg/L, pH adjustment of 7.0, addition of a repairing agent containing zero-valent iron and microorganisms (wherein the content of zero-valent iron in the sample is 1g/L and the content of microorganisms in the sample is 50mg/L), evacuation of the reactor air with nitrogen gas, and subsequent sealing at 25 ℃ for reaction for 5 d. Taking 5mL of water sample from the reactor at 0d, 0.5d, 1d, 2d, 3d, 4d and 5d after the reaction is started, filtering the water sample by a 0.22 mu m filter membrane and determining Cd2+The concentration of (c).
Collecting and preparing Cd2+500g of cadmium-contaminated soil with the concentration of 10mg/kg is placed in an anaerobic reactor, the pH of the soil is adjusted to 7.0, NO is added3 -N concentration of 28mg/kg, soil water content of 60% by weight adjusted with water, restoration agent containing zero-valent iron and microorganism (wherein the content of zero-valent iron in the sample is 1g/kg, and the content of microorganism in the sample is 50mg/kg) was added, and usedAfter the nitrogen gas is discharged from the air in the reactor, the reactor is sealed and placed at 25 ℃ for reaction for 5 d. Respectively taking 10g of soil sample out of the reactor at 0d, 0.5d, 1d, 2d, 3d, 4d and 5d after the reaction starts, adding a certain amount of deionized water, centrifuging for 10min at the rotating speed of 4000rpm, filtering the supernatant through a 0.22 mu m filter membrane, and measuring the Cd of the supernatant2+And (4) concentration.
5 reaction systems are set for the cadmium pollution remediation process: (1) a blank system, a treatment system comprising only the reaction substrate; (2) zero-valent iron system (Fe)0) A treatment system comprising only zero-valent iron and a reaction substrate; (3) a microbial system, a treatment system comprising only microbes and a reaction substrate; (4) a zero-valent iron + microbial system comprising a treatment system of zero-valent iron, microbes and a nitrate-free reaction substrate; (5) a nitrate-mediated zero-valent iron + microorganism synergistic system, which comprises a zero-valent iron, a microorganism and a reaction substrate treatment system. After the experiment, Fe0System, Fe0+ microbial System and Fe0+ microorganism + NO3 -The residue in the reactor of the system was frozen in a-80 ℃ freezer for 12h and then quickly placed in a freeze-dryer for drying for 48 h. The dried mixture was taken out in an anaerobic glove box (N)2：H295: 5) the iron powder particles after reaction are separated by using a magnet and ground, and meanwhile, the zero-valent iron powder before reaction is collected under the same operation condition, and is analyzed by using an X-ray diffractometer and a scanning electron microscope to investigate the change situation of the surface appearance and the structure, and the results are shown in fig. 1, fig. 2, fig. 3, fig. 4, fig. 5 and fig. 6. As can be seen from the scanning electron microscope images of the surfaces of the iron powder particles after the reaction, the surface structure of the iron powder particles of the synergistic system (fig. 5 and 6) mediated by the nitrate is obviously changed compared with other systems in the repair process, and the corrosion degree is more obvious; meanwhile, XRD analysis (figure 1) shows that more lepidocrocite, magnetite, patina and other iron minerals exist in the synergistic system, which indicates that more active secondary minerals are generated on the surface of the zero-valent iron under the synergistic action of denitrifying bacteria.
The effect of each reaction system on cadmium removal in groundwater samples is shown in fig. 7. As can be seen from FIG. 7, during the reaction time of 5d, the nitrate-mediated synergistic system: (Fe0+ microorganism + NO3 -) For Cd2+The removal rate of the iron is up to 86.2 percent, and the iron is respectively a zero-valent iron system (Fe)0) And 4.9 times and 4.1 times of microbial system (microbe), which is zero-valent iron + microbial system (Fe)0+ microorganism) 1.6 times. Nitrate mediated synergistic system (Fe) in soil samples0+ microorganism + NO3 -) The removal capability of cadmium is also greatly improved, and as shown in figure 8, the nitrate-mediated synergistic system is used for removing Cd in soil2+The removal rate of (a) is 79.2%, which is significantly higher than that of a zero-valent iron system (11.1%), a microbial system (21.2%) and a zero-valent iron + microbial system (53.5%).
On one hand, the synergistic effect of the zero-valent iron and the autotrophic denitrifying bacteria effectively solves the problems that the corrosion of the zero-valent iron is hindered under the non-biological condition, a passivation layer hinders the reaction and the like, on the other hand, the hydrogen generated by the corrosion of the zero-valent iron under the anaerobic condition is consumed at an accelerated speed under the denitrification effect of the hydrogen autotrophic denitrifying bacteria, the electron transfer efficiency is greatly improved, and the corrosion of the zero-valent iron is further promoted. Therefore, the autotrophic denitrifying bacteria under the mediation of nitrate can effectively improve the corrosion degree of zero-valent iron and treat Cd in cadmium-polluted soil and groundwater2+Has obvious adsorption and fixation effects.
Example 2
A cadmium contaminated soil and groundwater remediation agent and a remediation method thereof comprise the following steps:
the preparation of the repair agent is described in example 1.
Preparing 250mL of cadmium-polluted underground water sample by using deoxidized water in an anaerobic reactor, wherein Cd is2+Concentration of 10mg/L, NO3 -N concentrations of 0, 7, 14, 28, and 56mg/L, respectively, adjusting pH to 7.0, adding a repairing agent containing zero-valent iron and microorganisms (wherein the content of zero-valent iron in the sample is 1g/L, and the content of microorganisms in the sample is 50mg/L), evacuating the interior of the reactor with nitrogen gas, and then hermetically holding at 25 ℃ for reaction for 5 d. At 0d, 0.5d, 1d, 2d, 3d, 4d and 5d after the reaction is started, respectively taking 5mL of water sample from the reactor, filtering the water sample by a 0.22 mu m filter membrane, and determining Cd2+Is rich inAnd (4) degree.
The remediation of cadmium contamination by a nitrate-mediated zero-valent iron + microbial synergistic system at different nitrate concentrations is shown in fig. 9. It can be seen that when the concentration of nitrate nitrogen in the system is increased from 0 to 28mg/L, the system is cooperated with Cd2+The removal capacity of the method is improved by 60.5 percent, which shows that the hydrogen autotrophic nitrate reduction process dominates the removal effect of the synergistic system on cadmium pollution, and the synergistic effect of microorganisms effectively promotes zero-valent iron to control Cd2+Adsorption and immobilization; when the concentration of nitrate and nitrogen is further increased to 56mg/L, the dominant factor determining the cadmium pollution removal effect of the synergistic system is not the concentration of nitrate any more, so that Cd2+The removal rate of (a) only slightly increases. Therefore, the nitrate existing in the underground water plays a key role in the remediation of cadmium pollution by the synergistic system of the zero-valent iron and the autotrophic denitrifying bacteria.
Example 3
A cadmium contaminated soil and groundwater remediation agent and a remediation method thereof comprise the following steps:
the preparation of the repair agent is described in example 1.
Preparing 250mL of cadmium-polluted underground water sample by using deoxidized water in an anaerobic reactor, wherein Cd is2+Concentration of 10mg/L, NO3 -N concentration of 28mg/L, pH adjustment of 5.0, 6.0, 7.0, 8.0, respectively, addition of a repair agent containing zero-valent iron and microorganisms (wherein the content of zero-valent iron in the sample is 1g/L and the content of microorganisms in the sample is 50mg/L), evacuation of the reactor air with nitrogen gas, and subsequent sealing at 25 ℃ for reaction for 5 days. Taking 5mL of water sample from the reactor at 0d, 0.5d, 1d, 2d, 3d, 4d and 5d after the reaction is started, filtering the water sample by a 0.22 mu m filter membrane and determining Cd2+The concentration of (c).
The remediation effect of the nitrate-mediated zero-valent iron + microbial synergistic system on cadmium contamination at different pH values is shown in FIG. 10. It can be seen that the removal effect of the synergistic system on cadmium pollution reaches over 75 percent in a wider pH range, and Cd is reduced from 8 to 52+The removal rate of the catalyst is gradually improved and can reach 99.8 percent at most. When the pH is low, a large amount of H is present in the solution+The passivation layer on the surface of the zero-valent iron is dissolved, the physical barrier which hinders the reaction is broken, the update of the reaction sites on the surface of the zero-valent iron is accelerated, and the removal effect of cadmium pollution is obviously improved; while at higher pH, the activity of the microorganism is inhibited to some extent, but at a pH higher than the zero charge point of the surface of zero-valent ironzpcThe zero-valent iron particles can be negatively charged and can adsorb a part of positively charged Cd2+Ion, simultaneous Cd under alkaline conditions2+Tends to precipitate on the surface of zero-valent iron, so that a part of Cd can be still precipitated by the synergistic system2+Adsorbing and fixing. Therefore, the synergistic system can still maintain better cadmium pollution remediation capability in a wider pH range and has better impact resistance.
Example 4
A cadmium contaminated soil and groundwater remediation agent and a remediation method thereof comprise the following steps:
the preparation of the repair agent is described in example 1.
Preparing 250mL of cadmium-polluted underground water sample by using deoxidized water in an anaerobic reactor, wherein Cd is2+Concentration of 10mg/L, NO3 -N concentration of 28mg/L, pH adjustment of 7.0, addition of a repairing agent containing zero-valent iron and microorganisms (wherein the content of zero-valent iron in the sample is 1, 4, 10g/L, respectively, and the content of microorganisms in the sample is 50mg/L), evacuation of the reactor air with nitrogen gas, and subsequent sealing at 25 ℃ for 5 days. After the reaction, 5mL of water sample is taken from the reactor, filtered by a 0.22 mu m filter membrane and then Cd is measured2+The concentration of (c).
The effect of the nitrate-mediated zero-valent iron + microbial synergistic system on cadmium removal under different zero-valent iron dosages is shown in table 1. As can be seen from the data in Table 1, Cd increases the proportion of zero-valent iron in the repairing agent added2+The removal rate is further improved, but because the content of other elements in the synergistic system cannot be increased in time, the microbial biomass in the system is a limiting factor at the moment, and part of zero-valent iron cannot solve the problem of corrosion resistance in time, so that the Cd in a short time2+The removal rate is improved to a limited extent, and the unit mass in the system is at the same timeZero valent iron pair Cd2+The removal amount of (A) is reduced, and the utilization rate of the repairing agent is low.
Table 1 removal of cadmium by synergistic system at different zero-valent iron dosages
Example 5
A cadmium contaminated soil and groundwater remediation agent and a remediation method thereof comprise the following steps:
the preparation of the repair agent is described in example 1.
Preparing 250mL of cadmium-polluted underground water sample by using deoxidized water in a reactor, wherein Cd is2+Concentration of 10mg/L, NO3 -N concentration of 28mg/L, pH adjustment of 7.0, addition of a repairing agent containing zero-valent iron and microorganisms, respectively (wherein the content of zero-valent iron in the sample is 1g/L, and the content of microorganisms in the sample is 50, 100, 200, 400mg/L, respectively), evacuation of the reactor air with nitrogen gas, and subsequent sealing at 25 ℃ for reaction for 5 days. After the reaction, 5mL of water sample is taken from the reactor, filtered by a 0.22 mu m filter membrane and then Cd is measured2+The concentration of (c).
The cadmium removal effect of the nitrate-mediated zero-valent iron + microorganism synergistic system at different microorganism addition concentrations is shown in table 2. When the content of the microorganism in the added repairing agent is increased, Cd is generated under the synergistic action of the microorganism and zero-valent iron2+The removal rate of (A) is improved to a certain extent. However, when the concentration of the microorganism is too high, since the amount of the zero-valent iron is a limiting factor, although the content of the microorganism is increased in multiples and the utilization rate of the zero-valent iron is further improved, the improvement of the effect of removing cadmium is limited.
TABLE 2 Effect of microbial concentration on cadmium removal in synergistic systems
The above examples are only preferred embodiments of the present invention, which are intended to be illustrative and not limiting, and those skilled in the art should understand that they can make various changes, substitutions and alterations without departing from the spirit and scope of the invention.
Claims (10)
1. The cadmium-polluted soil and underground water restoration agent is characterized by comprising zero-valent iron powder, hydrogen autotrophic denitrifying bacteria suspension and nitrate with the concentration of 62-248mg/L, wherein the concentration of the hydrogen autotrophic denitrifying bacteria suspension is 1-4 g/L.
2. The cadmium-contaminated soil and groundwater remediation agent of claim 1, wherein the zero valent iron powder has a particle size of 0.1-1mm, and an iron content of greater than 97%; the zero-valent iron powder is cleaned with an acidic substance to remove surface oxides before use.
3. The cadmium-contaminated soil and groundwater remediation agent of claim 1, wherein the hydrogen autotrophic denitrifying bacteria use domesticated species, the domestication of hydrogen autotrophic denitrifying bacteria comprising:
screening denitrifying bacteria from sludge, and domesticating the strains in an anaerobic reactor by using hydrogen as a main electron donor and adopting a cadmium concentration gradient method; during domestication, the sludge concentration is 5-20g/L, the glucose concentration is 50-150mg/L, the cadmium concentration is 1-10mg/L, the nitrate concentration is 62-248mg/L, the hydraulic retention time of the anaerobic reactor is 20-30h, and when the consumption rate of the nitrate in the liquid of the anaerobic reactor is stable to reach more than 95%, the domesticated hydrogen autotrophic denitrifying bacteria are obtained.
4. The cadmium-polluted soil and groundwater remediation agent of claim 3, wherein in the anaerobic reactor, the cadmium concentration is gradually increased from 1-10mg/L, and is gradually increased once every 40-50h, and is gradually increased by 0.5-1.5mg/L each time until the cadmium concentration is 10 mg/L; the gas atmosphere of the anaerobic reactor is a mixed atmosphere of nitrogen, hydrogen and carbon dioxide; the volume ratio of the nitrogen to the hydrogen to the carbon dioxide is as follows: n is a radical of2：H2：CO2＝85％：10％：5％。
5. The cadmium-contaminated soil and groundwater remediation agent of claim 1, wherein when the remediation agent is used for soil remediation, the amount of the zero-valent iron powder added is 1-10g/kg and the amount of the hydrogen autotrophic denitrifying bacteria suspension added is 50-200 mg/kg.
6. The cadmium-contaminated soil and groundwater remediation agent of claim 1, wherein when the remediation agent is used for groundwater remediation, the zero valent iron is added in an amount of 1 to 500g/L and the bacterial suspension is added in an amount of 50 to 400 mg/L.
7. A method for remediation of cadmium contaminated soil or groundwater using the cadmium contaminated soil and groundwater remediation agent of any one of claims 1 to 6, comprising ex situ remediation and in situ remediation;
the ectopic repair comprises: taking a cadmium-polluted soil or underground water sample to be repaired, adding the cadmium-polluted soil and underground water repairing agent to obtain a mixture, and then placing the mixture in an anaerobic reactor for ectopic repair treatment;
when the sample to be repaired is cadmium contaminated soil, the in-situ repair comprises the following steps: the cadmium-polluted soil and underground water remediation agent is sprayed to cadmium-polluted soil to be remedied in a rotating mode, and then in-situ remediation treatment is carried out in an anaerobic environment;
when the sample to be repaired is cadmium-polluted underground water, the in-situ repair comprises the following steps: the cadmium-polluted soil and groundwater remediation agent are uniformly mixed with quartz sand, then the mixture is filled into a permeable reactive barrier, the permeable reactive barrier is contacted with groundwater, and then in-situ remediation treatment is carried out in an anaerobic environment.
8. The method for remediating cadmium-contaminated soil or groundwater using the cadmium-contaminated soil and groundwater remediation agent as defined in claim 7, wherein the cadmium-contaminated soil has a particle size of 0.1 to 3mm, a water content of 50 to 65%, and a cadmium concentration of 1 to 15 mg/kg; the cadmium concentration in the cadmium-polluted underground water is 1-10 mg/L.
9. The method for remediating cadmium-contaminated soil or groundwater using a cadmium-contaminated soil or groundwater remediation agent as claimed in claim 7, wherein the ex-situ remediation treatment and the in-situ remediation treatment are performed for 5-15 days, and the temperature of the ex-situ remediation treatment and the in-situ remediation treatment is 25-35 ℃; the volume ratio of the cadmium-polluted soil and groundwater remediation agent to the quartz sand is 0.5-1.5: 1.
10. the method for remediating cadmium-contaminated soil or groundwater using a cadmium-contaminated soil and groundwater remediation agent as defined in claim 7, wherein the cadmium-contaminated soil and cadmium-contaminated groundwater has a pH of 5.0 to 8.0; the concentration of nitrate in the cadmium polluted soil and the cadmium polluted underground water is 62-248 mg/L.
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