CN115612500A - Method for fixing heavy metal based on biochar - Google Patents
Method for fixing heavy metal based on biochar Download PDFInfo
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- CN115612500A CN115612500A CN202211260030.7A CN202211260030A CN115612500A CN 115612500 A CN115612500 A CN 115612500A CN 202211260030 A CN202211260030 A CN 202211260030A CN 115612500 A CN115612500 A CN 115612500A
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- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
- C09K17/00—Soil-conditioning materials or soil-stabilising materials
- C09K17/40—Soil-conditioning materials or soil-stabilising materials containing mixtures of inorganic and organic compounds
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B09—DISPOSAL OF SOLID WASTE; RECLAMATION OF CONTAMINATED SOIL
- B09C—RECLAMATION OF CONTAMINATED SOIL
- B09C1/00—Reclamation of contaminated soil
- B09C1/002—Reclamation of contaminated soil involving in-situ ground water treatment
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B09—DISPOSAL OF SOLID WASTE; RECLAMATION OF CONTAMINATED SOIL
- B09C—RECLAMATION OF CONTAMINATED SOIL
- B09C1/00—Reclamation of contaminated soil
- B09C1/08—Reclamation of contaminated soil chemically
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B09—DISPOSAL OF SOLID WASTE; RECLAMATION OF CONTAMINATED SOIL
- B09C—RECLAMATION OF CONTAMINATED SOIL
- B09C1/00—Reclamation of contaminated soil
- B09C1/10—Reclamation of contaminated soil microbiologically, biologically or by using enzymes
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- 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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- C—CHEMISTRY; METALLURGY
- C05—FERTILISERS; MANUFACTURE THEREOF
- C05G—MIXTURES OF FERTILISERS COVERED INDIVIDUALLY BY DIFFERENT SUBCLASSES OF CLASS C05; MIXTURES OF ONE OR MORE FERTILISERS WITH MATERIALS NOT HAVING A SPECIFIC FERTILISING ACTIVITY, e.g. PESTICIDES, SOIL-CONDITIONERS, WETTING AGENTS; FERTILISERS CHARACTERISED BY THEIR FORM
- C05G3/00—Mixtures of one or more fertilisers with additives not having a specially fertilising activity
- C05G3/80—Soil conditioners
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F2101/00—Nature of the contaminant
- C02F2101/10—Inorganic compounds
- C02F2101/20—Heavy metals or heavy metal compounds
Abstract
The invention discloses a method for fixing heavy metal based on biochar, which comprises the following steps: (1) Mixing the biochar with a polluted water body or a polluted soil body to enable the biochar to capture heavy metals; (2) Mixing the bacterial liquid containing urease bacteria with the biochar which is captured with the heavy metals in the step (1) to enable the biochar to capture the urease-producing bacteria in the bacterial liquid; (3) And (3) mixing the cementing liquid with the biochar which is captured with the urease-producing bacteria in the step (2), standing for reaction, and enabling the urease-producing bacteria to react with the cementing liquid, wherein the cementing liquid comprises calcium chloride and urea. The invention improves the efficiency and long-term effectiveness of the heavy metal fixation by the biochar and reduces the risk of secondary pollution after the biochar fixes the heavy metal.
Description
Technical Field
The invention belongs to the technical field of heavy metal treatment, and particularly relates to a method for fixing heavy metals based on biochar
Background
The problem of heavy metal contamination in water, atmosphere, soil has been widely reported over the past decades. The migration of heavy metal pollutants to the biosphere on which organisms live through human production and living activities, such as mining, smelting, waste incineration, automobile exhaust and the like, has become an important part of the geochemical cycle process of heavy metal pollutants. Humans can acquire heavy metals in nature through a variety of pathways, and humans often lack the ability to biodegrade them, leading to accumulation of heavy metals in the body, further leading to health problems. Therefore, heavy metal pollutants can cause great harm to human beings and ecological environment, heavy metal pollution of water bodies and soil is urgently treated, and effective and long-term treatment methods are sought, and the attention of scientists and engineers all over the world is also attracted.
Under the epoch background of implementing the sustainable development concept, the biochar treatment effect is realized for a long time, the national investment cost for treating heavy metal pollution can be reduced, and meanwhile, the development concept of green and environmental protection is also met, so that the ecological and economic benefits are realized. Currently, the solidification/stabilization technique is most commonly used, originating in the end of the 20 th century 50 s, initially for sludge remediation and later for soil remediation. Since the 90 s of the 20 th century, it has emerged as a heavy metal remediation technology in the united states, canada, uk, france, and the netherlands. 2017 to date, the heavy metal remediation market in China is briskly developing, wherein the curing/stabilizing technology is in the leading position in the use occupation ratio. The effectiveness of this technology is highly dependent on the performance of the additives used to fix metals in the soil, with biochar being one of the most popular additives due to its high affinity for heavy metal adsorption, low carbon, low cost. The fixation of the heavy metal by the biochar is realized by physical adsorption and cation exchange, and the fixed heavy metal ions are easily utilized by organisms and have poor stability and are greatly influenced by the pH value of the environment. Therefore, how to further improve the fixing efficiency and long-term effectiveness of the biochar on the heavy metal is a research difficulty in the field.
Disclosure of Invention
Aiming at the technical problems, the invention provides a method for fixing heavy metals based on biochar, which improves the efficiency and long-term effectiveness of the biochar in fixing the heavy metals and reduces the risk of secondary pollution after the biochar fixes the heavy metals.
In order to achieve the purpose, the invention adopts the following technical scheme:
a method for fixing heavy metal based on biochar comprises the following steps:
(1) Mixing biochar with a polluted water body or a polluted soil body to enable the biochar to capture heavy metals;
(2) Mixing a bacterial liquid containing urease bacteria with the biochar which is captured with heavy metals in the step (1) to enable the biochar to capture the urease-producing bacteria in the bacterial liquid;
(3) And (3) mixing a cementing liquid and the biochar which is captured with the urease-producing bacteria in the step (2) to react the urease-producing bacteria with the cementing liquid, wherein the cementing liquid comprises calcium chloride and urea.
Wherein, the stability of the biochar for fixing the heavy metal is improved by utilizing a microorganism induced calcium carbonate precipitation (MICP) technology.
Preferably, in the step (3), the ratio of the weight of the biochar to the volume of the cementing liquid is 1g: (200-400) mL, preferably 1g: (250-300) mL. In a specific embodiment, the ratio of the weight of the biochar to the volume of the cementing liquid is 1 g.
Preferably, in the step (3), the cementing liquid is a mixed solution of calcium chloride and urea, the concentration of the calcium chloride is 0.05-0.5 mol/L, and the concentration of the urea is 0.25-0.5 mol/L. The cementing liquid is aqueous solution, the solute consists of calcium chloride and urea, and the higher concentration of urea and the moderate concentration of calcium chloride are proper concentrations of the cementing liquid, so that microorganisms can be promoted to generate a relatively ideal carbonate precipitation protective shell on the surface of the biochar. In a specific embodiment, the MICP technology is most effective at a calcium chloride concentration of 0.3mol/L and a urea concentration of 0.5mol/L.
Preferably, in the step (3), the biochar is soaked in the cementing solution and placed in a constant-temperature shaking table at 25-35 ℃ for shaking, the sum of the shaking time and the standing time is 12-24 h, the rotating speed of the constant-temperature shaking table is controlled to be 100-150 rpm, the temperature is preferably 30 ℃, and the shaking time is controlled to be 12h, so that the biochar can uniformly capture bacteria. Further, the activity of the sporosarcina pasteurii is the most ideal under the condition of 30 ℃, and if other strains are selected, the temperature in the soaking process needs to be adjusted according to the characteristics of the strains. And standing after the oscillation is finished, wherein the standing time is controlled to be 12h, so that bacteria are firmly attached to the biochar, the biochar sufficiently captures urease-producing bacteria in the bacterial liquid, the biochar is kept in situ, and the sum of the oscillation time and the standing time is less than or equal to 24h. Further, the oscillation and standing time can be properly adjusted according to the characteristics of the biochar and the types of heavy metals, but the total treatment time is not more than 24 hours, so that the situation that the activity of bacteria is greatly reduced and the subsequent effect of inducing calcium carbonate precipitation by microorganisms is influenced is prevented. Or, in the step (3), spraying the cementing liquid into the polluted soil body treated in the steps (1) and (2), stirring and standing for no more than 24 hours, and then carrying out the subsequent steps.
Preferably, in the step (2), the urease-producing bacteria in the bacterial liquid are selected from sarcina pasteurii, and the liquid culture medium of the bacterial liquid comprises ammonium sulfate, yeast extract powder and trihydroxymethyl aminotoluene, and specifically, the liquid culture medium comprises 10g/L ammonium sulfate, 20g/L yeast extract powder and 15.73g/L trihydroxymethyl aminotoluene. After the strains are inoculated to the liquid culture medium according to the volume fraction of 1-5%, aerobic culture is carried out for 24h by using a constant-temperature shaking incubator under the conditions of 30 ℃ and 200 rpm. The bacterial liquid is required to be used for the soaking process immediately after aerobic culture for 24 hours. The initial conductivity of the bacterial liquid is 9.6mmol/L/min, and the initial OD600 value is 1.1. The conductivity of the bacterial liquid after the soaking process is 9.9mmol/L/min, and the OD600 value is 1.2. Further, the concentration of heavy metal is moderate, so that good bacterial activity can be ensured, if the concentration of heavy metal is too high, the bacterial activity can be seriously influenced, even bacteria die, and if necessary, the soaking process of the bacterial liquid is carried out after the concentration of heavy metal is diluted.
Preferably, in the step (2), the biochar with the captured heavy metals is taken out of the polluted water body, the biochar is soaked in the bacterial liquid, the rotating speed of the constant-temperature oscillating table is controlled to be 100-150 rpm, the temperature is preferably 30 ℃, and the oscillating time is controlled to be 12 hours, so that the biochar is ensured to uniformly capture bacteria. Further, the activity of the sporosarcina pasteurii is most ideal at 30 ℃, and if other strains are selected, the temperature in the soaking process needs to be adjusted according to the characteristics of the other strains. And standing after the oscillation is finished, wherein the standing time is controlled to be 12h, so that bacteria are firmly attached to the biochar, the biochar sufficiently captures urease-producing bacteria in the bacterial liquid, the biochar is kept in situ, and the sum of the oscillation time and the standing time is less than or equal to 24h. Further, the oscillation and standing time can be properly adjusted according to the characteristics of the biochar and the types of heavy metals, but the total treatment time is not more than 24 hours, so that the situation that the activity of bacteria is greatly reduced and the subsequent effect of inducing calcium carbonate precipitation by microorganisms is influenced is prevented. Or, in the step (2), spraying the bacterial liquid into the polluted soil body treated in the step (1), stirring, standing for no more than 24 hours, and carrying out the step (3).
Preferably, in the step (1), biochar is added into the polluted water body, and the ratio of the weight of the biochar to the volume of the polluted water body is 1g: (150-300) mL, preferably 1g:200ml, and oscillating for 24 hours in a constant-temperature oscillating table, wherein the set temperature is 25 ℃, the rotating speed is 250rpm, so as to ensure that the biochar reaches fixed balance, and the biochar reaching the fixed balance is kept to the original position; or, in the step (1), uniformly scattering the biochar on the surface of the polluted soil body, wherein the ratio of the weight of the biochar to the area of the polluted soil body is 1g: (0.4-0.8) m 2 And uniformly mixing the biochar with the polluted soil by using a cultivator, and carrying out subsequent steps after the biochar and the polluted soil are fixed and balanced.
Preferably, the biochar is powder or granules obtained by pyrolyzing and grinding plant straws. Specifically, powder or particles obtained by pyrolyzing and grinding plant straws under a high temperature condition are prepared into biochar, in the embodiment, agricultural waste rice straws are preferably used as a biochar raw material, a muffle furnace is used for heating the dried and ground rice straws to a specified temperature (preferably 300-700 ℃) at a speed of 10 ℃/min under an anoxic environment, the temperature is kept for 1.5 hours, and the obtained biochar is ground and sieved by a 70-mesh sieve.
In a specific and preferred embodiment, the treatment of the polluted water body based on the above method is as follows:
s101, adding biochar into a polluted water body, and oscillating to enable the biochar to capture heavy metals in the water body;
s102, taking the biochar out of the water body, soaking the biochar in a bacterial liquid containing sporosarcina pasteurii, placing the biochar in a constant-temperature oscillating table at 25-35 ℃, oscillating, and standing for 24 hours or less, so that the biochar captures sporosarcina pasteurii;
s103, soaking the biochar in the cementing liquid, placing the biochar in a constant-temperature oscillation shaking table at 25-35 ℃ for oscillation, wherein the sum of oscillation time and standing time is 12-24 h, and reacting sporosarcina pasteurii in the biochar with the cementing liquid, wherein the cementing liquid is a mixed solution of calcium chloride and urea, the concentration of the calcium chloride is 0.05-0.5 mol/L, and the concentration of the urea is 0.25-0.5 mol/L.
In another specific and preferred embodiment, the treatment of contaminated soil based on the above method is as follows:
s201, uniformly scattering biochar on the surface of a polluted soil body, and stirring to enable the biochar to capture heavy metals in the soil body;
s202, spraying a bacterial liquid containing sporosarcina pasteurii into a polluted soil body, stirring, standing for no more than 24 hours, and enabling the biochar in the soil body to capture sporosarcina pasteurii;
s203, spraying a cementing liquid into the polluted soil, and stirring to enable Sporosarcina pasteurii in the biochar to react with the cementing liquid, wherein the cementing liquid is a mixed solution of calcium chloride and urea, the concentration of the calcium chloride is 0.05-0.5 mol/L, and the concentration of the urea is 0.25-0.5 mol/L.
The invention has the following beneficial effects:
according to the invention, the biochar is firstly placed in a heavy metal polluted water body or soil body, after the fixed balance is achieved, the biochar is treated by using bacterial liquid containing urease producing bacteria, the biochar absorbs the bacterial liquid, finally, the biochar which is fully fixed with heavy metals and fully absorbs the bacterial liquid is treated by using a cementing liquid, and the urease producing bacteria are introduced to induce the deposition of carbonate in micropores of the biochar, so that the heavy metals adsorbed in the micropores of the biochar are reinforced, the efficiency and the long-term effectiveness of the biochar for fixing the heavy metals are greatly improved, the secondary pollution risk after the biochar fixes the heavy metals is reduced, the biochar after the treatment in the water body can be recycled, the biochar after the treatment in the soil body can increase the soil fertility, and the ecological development concept of low carbon and environmental protection is met.
Drawings
In order to more clearly illustrate the technical solution of the present invention, the drawings needed to be used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on the drawings without creative efforts.
FIG. 1 is a schematic flow diagram of a process for treating a contaminated water body in accordance with an embodiment of the present invention;
FIG. 2 is a schematic flow chart of the method for treating the polluted soil mass according to the embodiment of the invention;
FIG. 3 is a schematic representation of the actual state of biochar with lead in fixed equilibrium before and after MICP treatment in example 1 of the present invention;
FIG. 4 is a graph of the results of lead extraction tests on biochar obtained from example 1 and example 2 without MICP treatment.
Detailed Description
Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings so that the advantages and features of the invention may be more readily understood by those skilled in the art. It should be noted that the description of the embodiments is provided to help understanding of the present invention, but the present invention is not limited thereto.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs; as used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.
The present embodiment provides a method for fixing heavy metals based on biochar, which improves the stability of fixing heavy metals by biochar using a microorganism-induced calcium carbonate precipitation (MICP)) technique. The MICP technology takes microorganisms and calcium ions which widely exist in the environment as raw materials, has the advantage of green ecological environment protection, and is mainly characterized in that urea is hydrolyzed and reacts with Ca through a series of reactions (formula (1-5)) by utilizing urease-producing bacteria (taking barbiers as an example) separated from natural soil environment 2+ A carbonate is formed.
CO(NH 2 ) 2 +2H 2 O→H 2 CO 3 +2NH 3 (1)
The main processes for immobilizing heavy metals by MICP include encapsulation and precipitation, which are significantly stronger for immobilizing heavy metals than for physical adsorption and cation exchange. The MICP technology can prepare a calcium carbonate surface layer which can resist the change of the external environment on the fixed and balanced biochar by means of the reaction process of microorganisms, so as to protect a barrier, thereby realizing the long-term fixation of heavy metals.
The method comprises the following steps:
the method comprises the following steps: mixing the biochar with a polluted water body or a polluted soil body to enable the biochar to capture heavy metals;
specifically, powder or particles obtained by pyrolyzing and grinding plant straws are prepared into biochar under a high temperature condition, in the embodiment, agricultural waste rice straws are preferably used as a biochar raw material, a muffle furnace is used for heating the dried and ground rice straws to a specified temperature (preferably 300-700 ℃) at a speed of 10 ℃/min under an anoxic environment, the temperature is kept for 1.5 hours, and the obtained biochar is ground and sieved by a 70-mesh sieve. Adding biochar into the polluted water body, wherein the ratio of the weight of the biochar to the volume of the polluted water body is 1g: (150 to 300) mL, preferably 1g:200ml, and shaking in a constant temperature shaking table for 24h, wherein the temperature is set at 25 ℃ and the rotating speed is 250rpm, so as to ensure that the biochar reaches the fixed balance, and the biochar reaching the fixed balance is kept to the original position.
If in the soil polluted environment, the biochar needs to be uniformly scattered on the soil surface, and the ratio of the weight of the biochar to the area of the polluted soil body is 1g: (0.4-0.8) m 2 And uniformly mixing the biochar with the polluted soil by using a cultivator, and carrying out subsequent steps after the biochar and the polluted soil are fixed and balanced.
In the embodiment, lead with strong hazard, great treatment difficulty and wide pollution range is selected as the heavy metal to be fixed, and the lead pollution solution contains Pb (NO) 3 ) 2 And NaNO 3 。Pb(NO 3 ) 2 The concentration of (A) is controlled to be 3-20 mmol/L, naNO 3 The concentration of (B) is preferably controlled to 0.01 mol/L. In the practical application process, the heavy metal pollution components and concentration are based on the practical pollution condition, the ability of the biochar to fix heavy metals is influenced by raw materials, pyrolysis temperature, heavy metal ion species and the like, and the appropriate biochar to fix heavy metals is required to be selected to ensure that the biochar achieves a good heavy metal capturing effect, so that the subsequent steps of MICP treatment can be smoothly carried out.
Step two: mixing the bacterial liquid containing urease bacteria with the biochar which is captured with the heavy metals in the step one to enable the biochar to capture the urease-producing bacteria in the bacterial liquid;
in the embodiment, the urease-producing bacteria in the bacterial liquid are selected from Sporosarcina pasteurii, and the liquid culture medium used for the bacterial liquid comprises 10g/L ammonium sulfate, 20g/L yeast extract powder and 15.73g/L trihydroxymethyl aminotoluene. Inoculating the strains to a liquid culture medium which is fully sterilized at high temperature according to the volume fraction of 1-5%, and then carrying out aerobic culture for 24h by using a constant-temperature oscillation incubator at the temperature of 30 ℃ and the speed of 200 rpm. The bacterial liquid is required to be used for the soaking process immediately after aerobic culture for 24 hours. The initial conductivity of the bacterial liquid is 9.6mmol/L/min, and the initial OD 600 The value was 1.1. The conductivity of the bacterial liquid after the soaking process is 9.9mmol/L/min and OD 600 The value was 1.2. Further, the concentration of heavy metal is moderate, so that good bacterial activity can be ensured, if the concentration of heavy metal is too high, the bacterial activity can be seriously influenced, even bacteria die, and if necessary, the soaking process of the bacterial liquid is carried out after the concentration of heavy metal is diluted.
And taking the biochar trapped with the heavy metals out of the polluted water body, soaking the biochar in a bacterial liquid, and oscillating in a constant-temperature oscillating table at 25-35 ℃, wherein the rotating speed of the constant-temperature oscillating table is controlled to be 100-150 rpm, the temperature is preferably 30 ℃, and the oscillating time is controlled to be 12 hours, so that the biochar is ensured to uniformly trap bacteria. Further, the activity of the sporosarcina pasteurii is most ideal at 30 ℃, and if other strains are selected, the temperature in the soaking process needs to be adjusted according to the characteristics of the other strains. And standing after oscillation is finished, wherein the standing time is controlled to be 12h, so that bacteria are firmly attached to the biochar, the biochar sufficiently captures urease-producing bacteria in the bacterial liquid, the biochar is kept in the original position, and the sum of the oscillation time and the standing time is less than or equal to 24h. Further, the oscillation and standing time can be properly adjusted according to the characteristics of the biochar and the types of heavy metals, but the total treatment time is not more than 24 hours, so that the situation that the activity of bacteria is greatly reduced and the subsequent effect of inducing calcium carbonate precipitation by microorganisms is influenced is prevented.
And if the soil is in a polluted environment, spraying the bacterial liquid into the polluted soil treated in the step one, stirring and standing for no more than 24 hours, and then carrying out the subsequent steps.
Step three: and D, mixing the cementing liquid with the biochar which is captured with the urease-producing bacteria in the step two, and standing for reaction to enable the urease-producing bacteria to react with the cementing liquid.
The cementing solution is a mixed solution consisting of a calcium chloride solution and a urea solution, wherein the concentration of the calcium chloride solution is 0.05-0.5 mol/L, and the concentration of the urea solution is 0.25-0.5 mol/L. Further, the higher urea concentration and the moderate calcium chloride concentration are proper cementing liquid concentrations, which can promote microorganisms to generate a relatively ideal carbonate precipitation protective shell on the surface of the biochar. The most preferred concentration of calcium chloride is 0.3mol/L and urea is 0.5mol/L, at which MICP technology is most effective.
The ratio of the weight of the biochar to the volume of the cementing liquid is 1g: (200-400) mL, preferably 1-300, soaking the biochar after the bacteria are captured in the second step in the cementing solution, and placing the biochar in a constant-temperature shaking table at 25-35 ℃ for shaking, wherein the rotating speed of the constant-temperature shaking table is controlled to be 100-150 rpm or even lower, so as to ensure that calcium carbonate is stably precipitated on the biochar, and the temperature is preferably 30 ℃ so as to ensure the activity of the bacteria. Further, the activity of the sporosarcina pasteurii is the most ideal under the condition of 30 ℃, and if other strains are selected, the temperature in the soaking process needs to be adjusted according to the characteristics of the strains. The total sum of the oscillation time and the standing time is 12-24 h, and if the activity of bacteria on the biochar is stronger or the cementation speed is faster, the oscillation time and the standing time can be shortened. Taking a specific embodiment as an example, sporosarcina pasteurii is selected, the concentration of urea is controlled to be 0.25mol/L, the concentration of calcium chloride is controlled to be 0.3mol/L, the oscillation time is controlled to be 12 hours, and the standing time is 12 hours.
If the soil is polluted, the bacterial liquid and the cementing liquid are sprayed on the surface of the soil in sequence, and the bacterial liquid and the cementing liquid are mixed with the polluted soil uniformly by matching with a cultivator. After the cementation is finished, the calcium carbonate precipitate generated on the surface of the biochar can effectively help the biochar to resist the change of the external environment, particularly acid rain leaching, so that the long-term effectiveness of the biochar in fixing heavy metals is improved. In addition, the biochar can improve the soil fertility in the soil environment, and the cementation effect of the calcium carbonate can also improve the strength of the soil.
Further, the bacterial liquid in the second step and the cementing liquid in the third step may cause the heavy metals fixed on the biochar to migrate into the solution, so that a certain pollution risk is caused, and controlling the concentration of the cementing liquid is one of the methods for reducing the risk. The mobility of lead in known implementations can be controlled to a minimum of 5.72%.
In summary, the polluted water body can be treated based on the above method, the heavy metals in the polluted water body are removed, and the heavy metals are fixed in the biochar through MICP strengthening. As shown in fig. 1, the treatment process of the polluted water body based on the method specifically includes:
s101, adding biochar into a polluted water body, and oscillating to enable the biochar to capture heavy metals in the water body;
s102, taking the biochar out of the water body, soaking the biochar in a bacterial liquid containing sporosarcina pasteurianus, placing the biochar in a constant-temperature oscillating table at the temperature of 25-35 ℃, oscillating, and standing, wherein the sum of oscillation time and standing time is less than or equal to 24 hours, so that the biochar captures sporosarcina pasteurianus;
s103, soaking the biochar in a cementing solution, placing the biochar in a constant-temperature oscillation shaking table at the temperature of 25-35 ℃ for oscillation, wherein the sum of oscillation time and standing time is 12-24 h, and reacting sporosarcina pasteurii in the biochar with the cementing solution, wherein the cementing solution is a mixed solution of calcium chloride and urea, the concentration of the calcium chloride is 0.05-0.5 mol/L, and the concentration of the urea is 0.25-0.5 mol/L.
The method can be used for treating the polluted water body, removing the heavy metals in the polluted water body and fixing the heavy metals in the biochar.
As shown in fig. 2, the treatment process of the polluted water body based on the above method specifically includes:
s201, uniformly scattering biochar on the surface of the polluted soil body, and stirring to enable the biochar to capture heavy metals in the soil body;
s202, spraying a bacterial liquid containing sporosarcina pasteurii into a polluted soil body, stirring, standing for no more than 24 hours, and enabling biochar in the soil body to capture sporosarcina pasteurii;
s203, spraying the cementing liquid into the polluted soil body, and stirring to enable sporosarcina pasteurii in the biochar to react with the cementing liquid, wherein the cementing liquid is a mixed solution of calcium chloride and urea, the concentration of the calcium chloride is 0.05-0.5 mol/L, and the concentration of the urea is 0.25-0.5 mol/L.
The above scheme is further explained by combining with specific embodiments; it is to be understood that these embodiments are provided to illustrate the general principles, essential features and advantages of the present invention, and the present invention is not limited in scope by the following embodiments; the implementation conditions used in the examples can be further adjusted according to specific requirements, and the implementation conditions not indicated are generally the conditions in routine experiments. In the following, all starting materials are either commercially available or prepared according to methods conventional in the art, unless otherwise indicated.
Example 1
The embodiment adopts MICP technology to carry out surface treatment on the rice straw biochar with fixed and balanced lead, and comprises the following specific steps:
1) Fixation of lead by rice straw biochar: adding 0.1g of rice straw biochar into a mixture containing Pb (NO) with the concentration of 5mmol/L 3 ) 2 And 0.01mol/L NaNO 3 The solution was shaken at 25 ℃ and 250rpm for 24 hours in a centrifuge tube containing 20mL of the solution, and after the solution was equilibrated by fixation, the solution was centrifuged to remove the supernatant.
2) Soaking the biochar in bacterial liquid: soaking the biochar obtained in the step 1) in 30mL of the liquid of the sporosarcina pasteurianum inoculated for 24 hours, oscillating the mixed liquid of the liquid and the biochar in a constant-temperature oscillating table at the constant temperature of 30 ℃ at the rotating speed of 150rpm for 12 hours, standing for 12 hours again, ensuring that the biochar sufficiently captures bacteria in the liquid, and removing supernatant.
3) Soaking the biochar in the cementing solution: immediately soaking the biochar obtained in the step 2) in 30mL of cementing solution (the concentration of urea is 0.5mol/L, the concentration of calcium chloride is 0.3 mol/L), placing the biochar in a constant-temperature shaking table at 30 ℃ and shaking the mixed solution of the cementing solution and the biochar at the rotating speed of 100rpm for 12h, and standing for 12h to ensure that microorganisms can fully and stably react with each component in the cementing solution.
After the cementing solution is soaked in the biochar, a calcium carbonate surface barrier is formed on the surface of the biochar, and the barrier is helpful for improving the capability of the biochar for resisting environmental changes. FIG. 3 is a schematic diagram showing the actual state of the rice straw biochar with lead fixed in balance before and after MICP treatment according to this embodiment.
And (3) carrying out a step-by-step lead extraction experiment on the obtained biochar dried sample through a simplified continuous extraction method to measure the content of exchangeable-state lead, acid-soluble-state lead and stable non-bioavailable lead on each biochar. In the first step, 8mL of 0.5mol/L MgCl was added to 0.1g of biochar 2 Solution (pH = 7.0) and shaking at room temperature for 20min to extract exchangeable form lead; the second step was to add 8ml of 1mol/L NaOAc solution (pH = 5.0) to another 0.1g of biochar and shake for 5h at room temperature to extract exchangeable and acid-soluble lead. The extraction solution supernatant was collected and diluted and acidified, and the lead concentration in the solution was detected using an inductively coupled plasma optical emission spectrometer (ICP-OES). The content q of exchangeable lead is obtained in the first step 1 (mg/g); the total amount q of exchangeable and acid-soluble lead is obtained in the second step 2 ，q 1 And q is 2 The difference is the content of acid-soluble lead. The content of non-bioavailable lead can be determined from the total fixed quantity Q e Subtracting q 2 And (4) calculating. Fig. 4 shows the change in the ratio of lead in each form on the biochar before and after MICP treatment, from which it can be determined whether the stability of the biochar fixing lead is improved after MICP treatment.
The test result shows that: as can be seen from fig. 4, the stability of the biochar to fix lead is significantly improved after the biochar is treated by the MICP technology according to the above steps. The proportion of each lead form is changed as follows: 1.8 percent of exchangeable state lead is reduced to 0.2 percent, 94.7 percent of acid soluble state lead is reduced to 7.5 percent, and 3.5 percent of stable state lead is improved to 92.3 percent.
Example 2
This example differs from example 1 in the cementing liquid. Specifically, in the embodiment, the biological carbon is soaked in the cementing solution with the urea concentration of 0.25mol/L and the calcium chloride concentration of 0.1 mol/L. The urease-producing bacteria, the biochar types and the heavy metal types are the same as those in example 1, and the processing steps of fixing the heavy metal by the biochar and MICP and the test means for testing the proportion of each form are completely the same as those in example 1.
The results of the distributed lead extraction experiments after the biochar is treated by MICP in the embodiment show that the stability of the biochar for fixing lead is remarkably improved after the biochar is treated by MICP. The proportion of lead in each form is as follows: 1.78% of exchangeable state lead is reduced to 1.5%, 94.73% of acid soluble state lead is reduced to 39%, and 3.49% of stable state lead is improved to 52.5%. The reason for the improved long-term effectiveness of biochar in examples 1 and 2 is mainly due to the physical encapsulation and chemical buffer buffering of the calcium carbonate surface barrier on the biochar.
In summary, compared with the prior art, the invention has the beneficial effects that:
(1) The invention has obvious advantages particularly in the aspect of improving the long-term effectiveness of the biochar in fixing heavy metals, and the calcium carbonate surface layer with the resistance to the external environment change is prepared on the biochar by means of the biological reaction process of urease-producing bacteria, so that the defects of insufficient mechanicalness and biochar fixing stability of the existing biochar modification technology are overcome, and the biochar treated by the MICP technology is not easily influenced by the pH value of the environment and has good fixing efficiency and long-term effectiveness.
(2) The invention belongs to a soil mass solidifying technology which accords with the sustainable development concept, and the used urease-producing bacteria are widely distributed in the soil mass in the nature, thereby causing no pollution to the ecological environment; the used biochar raw material is rice straw, the source is wide, the cost is low, a large amount of non-standard incineration of agricultural wastes is avoided to a certain extent, and the energy consumption and carbon emission are reduced.
(3) Compared with the conventional biochar modification technology, the technology for fixing heavy metals by MICP reinforced biochar can have higher strengthening speed and a simpler strengthening process, generally speaking, only about 48 hours are needed from bacteria capture to completion of calcium carbonate precipitation, and the fixation of exchangeable heavy metals and acid-soluble heavy metals on the biochar can be strengthened after short-time microbial treatment, so that the heavy metals in a stable part are dominant.
(4) The invention can meet the treatment of heavy metal pollution places of soil bodies and water bodies, and has the advantages of low construction difficulty, low equipment demand, low investment cost, long maintenance period and obvious treatment effect.
The above-mentioned embodiments are merely illustrative of the technical concepts and features of the present invention, and are preferred embodiments, which are intended to enable those skilled in the art to understand the contents of the present invention and implement the present invention, and not to limit the scope of the present invention. All equivalent changes or modifications made according to the spirit of the present invention should be covered within the protection scope of the present invention.
Claims (10)
1. A method for fixing heavy metal based on biochar is characterized by comprising the following steps:
(1) Mixing biochar with a polluted water body or a polluted soil body to enable the biochar to capture heavy metals;
(2) Mixing a bacterial liquid containing urease bacteria with the biochar which is captured with heavy metals in the step (1) to enable the biochar to capture the urease-producing bacteria in the bacterial liquid;
(3) And (3) mixing a cementing liquid and the biochar with the urease-producing bacteria captured in the step (2) to react the urease-producing bacteria and the cementing liquid, wherein the cementing liquid comprises calcium chloride and urea.
2. The biochar-based heavy metal fixation method as claimed in claim 1, wherein in the step (3), the ratio of the weight of the biochar to the volume of the cementing liquid is 1g: (200 to 400) mL.
3. The method for fixing heavy metals based on biochar as claimed in claim 1 or 2, wherein in the step (3), the cementing liquid is a mixed solution of calcium chloride and urea, the concentration of calcium chloride is 0.05 to 0.5mol/L, and the concentration of urea is 0.25 to 0.5mol/L.
4. The method for fixing the heavy metal based on the biochar as claimed in claim 1, wherein in the step (3), the biochar is soaked in the cementing liquid and is placed in a constant-temperature shaking table at 25 to 35 ℃ for shaking, and the sum of the shaking time and the standing time is 12 to 24h; or, in the step (3), spraying the cementing liquid into the polluted soil body treated in the steps (1) and (2), and stirring.
5. The biochar-based heavy metal fixation method as claimed in claim 1, wherein in the step (2), urease-producing bacteria in the bacterial liquid are selected from sporosarcina pasteurii, a liquid culture medium of the bacterial liquid comprises ammonium sulfate, yeast extract powder and trihydroxymethyl aminotoluene, the bacterial species are inoculated into the liquid culture medium according to the volume fraction of 1 to 5%, aerobic culture is carried out to obtain the bacterial liquid, and the OD of the bacterial liquid is 600 The value is greater than or equal to 1.1.
6. The method for fixing heavy metals based on biochar according to claim 1, wherein in the step (2), the biochar with the captured heavy metals is taken out of a polluted water body, the biochar is soaked in the bacterial liquid, the biochar is placed in a constant-temperature shaking table at 25-35 ℃ for shaking and standing, and the sum of the shaking time and the standing time is less than or equal to 24 hours; or, in the step (2), spraying the bacterial liquid into the polluted soil body treated in the step (1), stirring, standing for no more than 24 hours, and carrying out the step (3).
7. The biochar-based heavy metal fixation method according to claim 1, wherein in the step (1), biochar is added into the polluted water body, and the ratio of the weight of the biochar to the volume of the polluted water body is 1g: oscillating at 150 to 300 mL; or, in the step (1), the biochar is uniformly scattered on the surface of the polluted soil body, and the ratio of the weight of the biochar to the area of the polluted soil body is 1g: (0.4 to 0.8) m 2 And stirring.
8. The biochar-based heavy metal fixation method as claimed in claim 1, wherein the biochar is powder or granules obtained by pyrolyzing and grinding plant straws.
9. The biochar-based heavy metal fixation method as claimed in claim 1, wherein the polluted water body is treated as follows:
s101, adding biochar into a polluted water body, and oscillating to enable the biochar to capture heavy metals in the water body;
s102, taking the biochar out of a water body, soaking the biochar in a bacterial liquid containing sporosarcina pasteurii, oscillating the biochar in a constant-temperature oscillating table at 25-35 ℃, standing the biochar, and enabling the biochar to capture sporosarcina pasteurii, wherein the sum of oscillation time and standing time is less than or equal to 24 hours;
s103, soaking the biochar in the cementing liquid, placing the biochar in a constant-temperature oscillation shaking table at 25-35 ℃ for oscillation, wherein the sum of oscillation time and standing time is 12-24h, and reacting sporosarcina pasteurii in the biochar with the cementing liquid, wherein the cementing liquid is a mixed solution of calcium chloride and urea, the concentration of the calcium chloride is 0.05-0.5 mol/L, and the concentration of the urea is 0.25-0.5 mol/L.
10. The biochar-based heavy metal fixation method as claimed in claim 1, wherein the polluted soil body is treated as follows:
s201, uniformly scattering biochar on the surface of a polluted soil body, and stirring to enable the biochar to capture heavy metals in the soil body;
s202, spraying a bacterial liquid containing sporosarcina pasteurii into a polluted soil body, stirring, standing for no more than 24 hours, and enabling the biochar in the soil body to capture sporosarcina pasteurii;
s203, spraying a cementing liquid into a polluted soil body, and stirring to enable Sporosarcina pasteurii in the biochar to react with the cementing liquid, wherein the cementing liquid is a mixed solution of calcium chloride and urea, the concentration of the calcium chloride is 0.05-0.5 mol/L, and the concentration of the urea is 0.25-0.5 mol/L.
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN116274343A (en) * | 2023-03-14 | 2023-06-23 | 四川农业大学 | Efficient, green and permanently fixed soil heavy metal cadmium repairing method |
| CN116274344A (en) * | 2023-03-14 | 2023-06-23 | 四川农业大学 | Repairing method for rapidly fixing heavy metal cadmium and improving soil quality |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN116274343A (en) * | 2023-03-14 | 2023-06-23 | 四川农业大学 | Efficient, green and permanently fixed soil heavy metal cadmium repairing method |
| CN116274344A (en) * | 2023-03-14 | 2023-06-23 | 四川农业大学 | Repairing method for rapidly fixing heavy metal cadmium and improving soil quality |
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