CN115090668A - Method for artificially reinforcing natural attenuation of polycyclic aromatic hydrocarbon in soil - Google Patents
Method for artificially reinforcing natural attenuation of polycyclic aromatic hydrocarbon in soil Download PDFInfo
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Abstract
The invention discloses a method for artificially reinforcing the natural attenuation of polycyclic aromatic hydrocarbon in soil, which mixes high-efficiency degrading flora with inorganic salt culture solution and adds the mixture into the soil polluted by polycyclic aromatic hydrocarbon, wherein the high-efficiency anaerobic degrading flora is a mixed flora taking nitroreduction pseudomonas as a dominant strain; then adding a potassium nitrate solution with a certain concentration into the soil, and uniformly stirring and mixing the potassium nitrate solution with the soil; sealing the surface of the soil to keep the soil in an anoxic or anaerobic environment for biostimulation and bioaugmentation natural degradation; and (3) periodically supplementing the potassium nitrate solution with the same concentration into the soil, and stopping degradation when the degradation rates of the polycyclic aromatic hydrocarbons phenanthrene and pyrene in the soil respectively reach the requirements. According to the method, the exogenous high-efficiency degradation flora is added, and meanwhile, the electron acceptor used for microbial degradation in the soil is added for multiple times to strengthen the natural attenuation process of the polycyclic aromatic hydrocarbon in the soil, namely a promotion mode combining biostimulation and biological strengthening, so that the natural attenuation rate of the polycyclic aromatic hydrocarbon in the soil is greatly improved.
Description
Technical Field
The invention relates to the technical field of polycyclic aromatic hydrocarbon polluted soil treatment, in particular to a method for artificially reinforcing the natural attenuation of polycyclic aromatic hydrocarbon in soil.
Background
Polycyclic aromatic hydrocarbons are organic compounds composed of 2 or more aromatic fused rings in a direct, bent or aggregated manner, and mainly produce incomplete combustion with organic substances. Polycyclic aromatic hydrocarbon is a persistent organic matter which widely exists in the environment and has the effect of causing three, the toxicity of the polycyclic aromatic hydrocarbon is enhanced along with the increase of the number of benzene rings, the polycyclic aromatic hydrocarbon is stable in chemical property and difficult to degrade, and most of the polycyclic aromatic hydrocarbon enters soil and water in a sedimentation and migration mode and can enter human bodies through direct contact and food chains to harm public health, so that the study on treating the polycyclic aromatic hydrocarbon polluted soil is difficult and hot.
Polycyclic aromatic hydrocarbon widely exists in soil, and due to strong hydrophobicity and difficult water solubility, most of polycyclic aromatic hydrocarbon is adsorbed and enriched by organic matters in the soil after entering the soil, and then the polycyclic aromatic hydrocarbon in the soil is continuously and slowly released to surrounding environment media along with the lapse of time, thereby causing long-term secondary pollution to surrounding water and air. Therefore, the soil is an important hub or gathering station of the polycyclic aromatic hydrocarbon and bears more than 90 percent of the environmental load [1] . The natural attenuation process of polycyclic aromatic hydrocarbon in soil comprises various ways such as absorption, adsorption, volatilization, chemical degradation, photolysis, hydrolysis and biodegradation. Wherein, the natural attenuation of polycyclic aromatic hydrocarbon in soil mainly plays an important role in the aspects of preventing polycyclic aromatic hydrocarbon from further migrating to underground water, reducing pollution concentration and the like through the degradation of microorganisms [2] . The microbial degradation of polycyclic aromatic hydrocarbon can be divided into aerobic degradation and anaerobic degradationBy solving the two modes, researchers at home and abroad can more particularly study the degradation of the polycyclic aromatic hydrocarbon by microorganisms under aerobic conditions, and the corresponding biotransformation mechanism is also clarified. Although studies have shown that most polycyclic aromatic hydrocarbons are degraded by microorganisms, their natural decay rate is slow in practical environments. There are two main reasons:
1) most of polycyclic aromatic hydrocarbons are remained in environments with low oxygen concentration, such as subsurface layers of soil and marine sediments, and slowly accumulate over time, and under anoxic or anaerobic conditions, the activity of aerobic microorganisms is low, and the degradation efficiency is reduced.
2) The existing environmental factors can not provide proper external conditions for degrading polycyclic aromatic hydrocarbon by microorganisms.
Researches show that the water solubility of the polycyclic aromatic hydrocarbon can be improved by adding the surfactant, so that the bioavailability of the polycyclic aromatic hydrocarbon is increased, and the degradation efficiency of the polycyclic aromatic hydrocarbon by microorganisms is improved. Meanwhile, other environmental factors (such as temperature, pH, nutritive salt, oxygen content and humidity) which influence the natural decay of the polycyclic aromatic hydrocarbon are widely researched and summarized. At present, most of researches are carried out by artificially reinforcing aerobic microorganisms to degrade polycyclic aromatic hydrocarbons in soil, and most of the reinforcing measures belong to remote repair technologies, so that the repair cost is increased, and great disturbance and harm are caused to the surrounding environment. Due to the strong adsorption of polycyclic aromatic hydrocarbons by soil particles, most of the polycyclic aromatic hydrocarbons can be accumulated in soil, especially in deep soil. The oxygen content in the deep soil is extremely low, so that the soil environment is always in an anoxic state, even a strict anaerobic state is achieved. Therefore, aerobic microorganisms have difficulty in exerting their ability to degrade polycyclic aromatic hydrocarbons in deep soil (anaerobic or anoxic environments).
Research shows that the concentration of an electron acceptor is one of the main factors influencing the anaerobic degradation efficiency of microorganisms in soil, however, most of research on degradation of polycyclic aromatic hydrocarbons by anaerobic microorganisms from the aspect of the electron acceptor is in the initial stage.
[1] Natural degradation characteristics of polycyclic aromatic hydrocarbon phenanthrene in Tianhua, Liu hui, Zhao Lu, Li Huai, soil [ J ]. environmental engineering report, 2015,9(08): 4055-.
[2] Zhenglei, Tanjie, Ding ai, Cheng Li Rong, Liu Yulan, Cheng Chen and the migration characteristic of polycyclic aromatic hydrocarbon in soil under the action of microorganism [ J ] chemical science report 2010,61(01): 200-.
Disclosure of Invention
Aiming at the technical defects, the invention aims to provide a method for artificially reinforcing the natural attenuation of polycyclic aromatic hydrocarbon in soil, which is characterized in that an exogenous high-efficiency degradation flora is added, and an electron acceptor utilized by microbial degradation in soil is added for multiple times to reinforce the natural attenuation process of polycyclic aromatic hydrocarbon in soil, namely a promotion mode combining biostimulation and biological reinforcement is adopted, so that the natural attenuation rate of polycyclic aromatic hydrocarbon in soil is improved.
In order to solve the technical problems, the invention adopts the following technical scheme:
the invention provides a method for artificially reinforcing the natural attenuation of polycyclic aromatic hydrocarbon in soil, which comprises the following steps:
s1: mixing the high-efficiency degrading flora with an inorganic salt culture solution, and adding the mixture into soil polluted by polycyclic aromatic hydrocarbon, wherein the adding concentration range of the high-efficiency degrading flora in the soil is 40-60 mg/kg;
s2: adding potassium nitrate solution into the soil, and uniformly stirring and mixing the potassium nitrate solution with the soil, wherein the potassium nitrate addition concentration in the soil is 1500-2000 mg/kg;
s3: the soil is kept in an anoxic or anaerobic environment for biostimulation and biological enhanced natural degradation;
s4: and (4) periodically supplementing a potassium nitrate solution with the same concentration as that in the step S2 into the soil, wherein the supplement addition amount of potassium nitrate in each time is the same as that in the step S2, and the degradation is stopped when the degradation rates of the polycyclic aromatic hydrocarbons phenanthrene and pyrene in the soil reach more than 99% and 85% respectively.
Preferably, the composition of the inorganic salt medium comprises NaNO 3 4.0g、NH 4 Cl 2 2.0g、KH 2 PO 4 1.5g、Na 2 HPO 4 0.5g、CaCl 2 0.01g、MgCl 2 0.2g, 1ml of microelement solution and 1L of deionized water, adjusting the pH value to 7.0, and sterilizing at 121 ℃ for 20 min.
Preferably, the composition of the trace element solution is: FeSO 4 ·7H 2 O 2g、ZnSO 4 ·7H 2 O 0.03g、H 3 BO 3 0.3g、CoCl 3 ·6H 2 O 0.3g、NiCl 2 ·6H 2 O 0.02g、Na 2 MoO 4 ·2H 2 0.03g of O and 1L of deionized water, and the pH is adjusted to 7.0.
Preferably, the domestication method of the high-efficiency anaerobic degradation flora comprises the following steps:
standing an activated sludge sample to separate a supernatant and a lower layer of activated sludge, taking the lower layer of activated sludge, adding an inorganic salt culture medium taking phenanthrene and pyrene as carbon sources, transferring the mixture into an anaerobic bottle, introducing nitrogen into the anaerobic bottle, sealing the anaerobic bottle, and culturing the anaerobic bottle in a constant-temperature oscillation box, wherein the culture temperature is controlled at 30 ℃, and the oscillation rate is 180 rmp; the acclimation period is 10 days.
Preferably, the proportion of the pseudomonas nitroreducens in the high-efficiency degradation flora obtained by the domestication method is 77.0%.
Preferably, the method for artificially reinforcing the natural attenuation of the polycyclic aromatic hydrocarbon in the soil according to claim 4, wherein a plurality of groups of domesticated floras are arranged, the concentration gradients of phenanthrene in the inorganic salt culture medium are 50mg/L, 100mg/L and 200mg/L in sequence, and the concentrations of pyrene are 25mg/L, 50mg/L and 100mg/L in sequence; and selecting the domesticated flora with the optimal degradation effect for enrichment culture according to the growth condition of the flora and the degradation rate of the polycyclic aromatic hydrocarbon.
Preferably, before step S1, the content of polycyclic aromatic hydrocarbons in the contaminated soil is measured in advance, and the addition concentrations of the efficient degrading bacteria and the nitrate are determined according to the measured contents of phenanthrene and pyrene, and the relationship is shown in the following table:
preferably, the potassium nitrate solution is prepared at the concentration of 24 g/L.
The invention has the beneficial effects that:
1. according to the invention, a mode of adding electron receptors used for microbial degradation in soil for multiple times is adopted, and meanwhile, the natural attenuation process of polycyclic aromatic hydrocarbon in soil is enhanced by adding exogenous high-efficiency degrading flora, and under the enhancing condition, namely a promoting mode of combining biostimulation and biological enhancement, the natural attenuation rate of polycyclic aromatic hydrocarbon in soil is greatly improved;
2. compared with heavy metal ions such as ferric iron, high-valence manganese and the like, the nitrate is a safer and more environment-friendly electron acceptor additive, and can be used as an economic and feasible in-situ remediation technology by supplementing the electron acceptor and strengthening the anaerobic degradation of polycyclic aromatic hydrocarbon in soil;
3. the invention adopts artificial measures to strengthen the natural attenuation process of polycyclic aromatic hydrocarbon in soil, the attenuation rate of phenanthrene is improved to 95.72 percent from 50.70 percent when not strengthened, and is improved by 88.8 percent; the attenuation rate of pyrene is improved to 89.89% from 39.97% when not strengthened, 124.89% is improved, and the degradation time is greatly shortened.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.
FIG. 1 is a design drawing of a soil test column according to the present invention;
FIG. 2 is a diagram of a soil sample column according to the present invention;
FIG. 3 is a graph showing the concentration change of phenanthrene in the soil samples contaminated by the enhanced and non-enhanced groups of potassium nitrate and highly effective degrading microorganisms in example 1 of the present invention;
FIG. 4 is a graph showing the change in concentration of pyrene in the soil samples contaminated by the potassium nitrate and the enhanced and non-enhanced groups of the highly effective degrading bacteria in example 1 of the present invention;
FIG. 5 is a graph showing the concentration change of phenanthrene in soil samples contaminated with potassium nitrate reinforced groups and non-reinforced groups in comparative example 1 according to the present invention;
FIG. 6 is a graph showing the change in concentration of pyrene in the soil samples contaminated with the potassium nitrate-fortified group and the non-fortified group in comparative example 1 of the present invention;
FIG. 7 is a diagram showing the microbial diversity of the highly effective degrading bacteria obtained after acclimation in accordance with the present invention;
Detailed Description
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 only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The soil sample source is as follows: the soil sample used in the test is collected in the north square open space of the college of surveying and mapping of China mining university, and is sampled by a five-point method after surface vegetation is removed. Naturally air-drying the collected soil sample, removing impurities such as stones and branches, and sieving the soil sample by a 2mm sample sieve. And crushing the soil blocks larger than 2mm, sieving the crushed soil blocks by a sample sieve of 2mm, and uniformly mixing the crushed soil blocks for later use. Accurately weighing 2.000g of phenanthrene and 1.000g of pyrene, dissolving in 500ml of methanol, spraying the prepared methanol solution on the surface of 10kg of soil to ensure that the final concentration of phenanthrene and the final concentration of pyrene in the soil sample are 200mg/kg and 100mg/kg respectively, uniformly stirring and mixing, placing in a dark and ventilated place for aging for one week, and waiting until the methanol is completely volatilized.
The domestication method of the high-efficiency degradation flora comprises the following steps: the bacterial source of the experiment is from activated sludge in an aerobic pool of a sewage treatment plant in Xuzhou, the activated sludge is poured into a beaker and stands still for 30min, and supernatant liquid is separated from the activated sludge at the lower layer. Measuring 20ml of activated sludge on the lower layer, adding 80ml of inorganic salt culture medium taking phenanthrene and pyrene as carbon sources, transferring to a 250ml anaerobic bottle, introducing nitrogen into the inorganic salt culture medium with flora, quickly screwing a bottle cap after 10min, putting into a constant-temperature oscillation box, and carrying out shake culture, wherein the culture temperature is controlled at 30 ℃, and the oscillation rate is 180 rmp. Multiple groups of flora are cultured and domesticated in the same period, so as to ensure the success rate of the domesticated flora. According to the degradation condition of polycyclic aromatic hydrocarbon in the anaerobic bottle, the concentrations of phenanthrene and pyrene in the culture medium are gradually increased, the concentrations of phenanthrene are 50mg/L, 100mg/L and 200mg/L in sequence, and the concentrations of pyrene are 25mg/L, 50mg/L and 100mg/L in sequence. The domestication period of each concentration gradient is 10 days, floras with phenanthrene (concentration: 200mg/L) and pyrene (concentration: 100mg/L) degradation rates stably kept at more than 95% and 85% respectively are selected for enrichment culture according to the growth condition of the floras and the degradation rate of the polycyclic aromatic hydrocarbon, and finally the efficient anaerobic degradation floras of the polycyclic aromatic hydrocarbon are obtained for subsequent experiments. The obtained high-efficiency anaerobic degradation flora is a mixed flora taking Pseudomonas nitroreducens (77.0%) as dominant strains.
Mixing the domesticated high-efficiency degrading flora with an inorganic salt culture solution at a mixing ratio of 1:10, and adding the mixture into a soil sample polluted by polycyclic aromatic hydrocarbon; the inorganic salt culture solution comprises the following components: NaNO 3 4.0g、NH 4 Cl 2 2.0g、KH 2 PO 4 1.5g、Na 2 HPO 4 0.5g、CaCl 2 0.01g、MgCl 2 0.2g, 1ml of trace element solution and 1L of deionized water, adjusting the pH value to 7.0, and sterilizing at 121 ℃ for 20 min; the composition of the trace element solution is as follows: FeSO 4 ·7H 2 O 2g、ZnSO 4 ·7H 2 O 0.03g、H 3 BO 3 0.3g、CoCl 3 ·6H 2 O 0.3g、NiCl 2 ·6H 2 O 0.02g、Na 2 MoO 4 ·2H 2 0.03g of O and 1L of deionized water, and adjusting the pH value to 7.0;
meanwhile, potassium nitrate solutions with different concentrations are added into the soil, the mixture is uniformly stirred and mixed with the soil, and the treated soil is added into a customized soil column with the height of 1 m. In addition, the soil column is periodically supplemented with potassium nitrate solution with corresponding concentration, namely, electron acceptors needed by microorganisms are supplemented. As shown in figures 1-2, the soil column is height 1m, outside diameter 110mm, internal diameter 100mm, the cylinder of wall thickness 5mm, and the base is 160 mm's square, and the cylinder both sides all are equipped with the thief hole, and thief hole outside diameter 15mm, internal diameter 11mm, wall thickness 2mm, and length of extension 2mm is equipped with 5 thief holes on every side, totally 10 thief holes.
According to a national standard method, namely gas chromatography-mass spectrometry (HJ805-2016) for determination of polycyclic aromatic hydrocarbons in soil and sediments, the content of the polycyclic aromatic hydrocarbons in the polluted soil is determined, and then the adding concentration of flora and the adding concentration of potassium nitrate are adjusted, so that the degradation effect is improved, and the degradation time is shortened.
TABLE 1 reference standard for degradation artificial strengthening treatment of phenanthrene and pyrene with different concentrations in anoxic/anaerobic soil environment
*: the degradation rates of phenanthrene and pyrene in the concentration range cannot stably reach more than 99% and 85% respectively, but the method still has the effect of promoting degradation.
According to the invention, a mode of adding electron acceptors used for microbial degradation in soil for multiple times is adopted, and meanwhile, the natural attenuation process of polycyclic aromatic hydrocarbon in soil is strengthened by adding exogenous high-efficiency degrading flora, and under the strengthening condition, namely a promoting mode combining biostimulation and biological strengthening, the natural attenuation rate of polycyclic aromatic hydrocarbon in soil is greatly improved; under the anaerobic condition, the efficient degradation flora in the soil utilizes potassium nitrate as a terminal electron acceptor, and polycyclic aromatic hydrocarbons accumulated in the soil can be degraded through oxidation-reduction reaction. The nitrate electron acceptor is supplemented into the soil, so that the degradation capability of the high-efficiency degradation flora on the polycyclic aromatic hydrocarbon can be enhanced. Compared with heavy metal ions such as ferric iron, high-valence manganese and the like, the nitrate is a safer and more environment-friendly electron acceptor additive, and can be used as an economic and feasible in-situ remediation technology by supplementing an electron acceptor and strengthening the anaerobic degradation of polycyclic aromatic hydrocarbon in soil.
Example 1:
and (2) filling 8 kg of soil sample polluted by the polycyclic aromatic hydrocarbon into a customized soil experimental column, and adding an inorganic salt culture solution containing potassium nitrate and the high-efficiency degrading flora into the soil experimental column, so that the addition concentration of the potassium nitrate in the soil sample is 1500mg/kg, and the addition concentration of the high-efficiency degrading flora in the soil sample is 50mg/kg per kg of the soil sample. And sealing sampling ports on two sides of the soil by using a sealing film to keep an anoxic or anaerobic environment at a position of 30-100cm of the soil column. And adding potassium nitrate every 4 days, wherein the addition amount is 1500mg of nitrate per kg of soil, and the experimental operation cycle is 20 days, so that the process of strengthening the natural attenuation of the polycyclic aromatic hydrocarbon polluted soil is completed.
Collecting samples from a soil experimental column regularly, extracting, measuring the concentration of the polycyclic aromatic hydrocarbon by using a GCMS computer, and calculating the degradation rate, wherein the specific operation is as follows:
accurately weigh 1.000g of soil sample into a 10ml centrifuge tube, add 8ml of acetone: mixing the extraction liquid with n-hexane (1: 1), shaking to mix the soil sample and the extraction liquid thoroughly, performing ultrasonic treatment for 30min, centrifuging the sample at 5000rpm for 10min, and absorbing the upper organic phase into a round-bottom flask. Again 8ml of acetone were added: mixing the extraction liquid with n-hexane (1: 1), shaking to mix the soil sample and the extraction liquid thoroughly, performing ultrasonic treatment for 30min, centrifuging the sample at 5000rpm for 10min, and sucking the upper organic phase and combining the upper organic phase into a round-bottom flask. And (3) rotationally evaporating the extracted organic phase on a rotary evaporator to less than 0.5ml, washing the round-bottom flask with ethyl acetate for 3 times, transferring the ethyl acetate obtained by washing into a 2ml centrifuge tube, filtering the ethyl acetate through a 0.22 mu m organic phase filter membrane, transferring the organic phase into a gas phase to be detected on a machine.
GCMS detection program: the polycyclic aromatic hydrocarbon is quantitatively detected by a gas chromatograph-mass spectrometer GCMS (CLARUS SQ 8 of Perkin Elmer, USA).
The instrument parameters are as follows: the column was a 30m long HP-5 column (30X 0.25mm X0.25 μm). The ionization mode is Electron Impact (EI); ionization energy: 70 eV; the ion source temperature is 230 ℃; the temperature of a sample inlet is 250 ℃; the temperature rise conditions are as follows: the initial temperature is 80 ℃ (keeping for 2min), the temperature is increased to 200 ℃ at the speed of 15 ℃/min, the temperature is increased to 230 ℃ at the speed of 4 ℃/min, and the temperature is increased to 280 ℃ (keeping for 2min) at the speed of 10 ℃/min; the sample is injected without shunting, and the sample injection amount is 1 mu L. Program run time 24.5min, solvent delay 4 min; the carrier gas is helium, and the flow rate is 2.0 ml/min; the quantitative method is an external standard method.
Drawing a polycyclic aromatic hydrocarbon standard curve: taking 8 clean 25ml volumetric flasks, respectively adding 100. mu.L, 250. mu.L, 500. mu.L, 1ml, 2.5ml, 5ml, 7.5ml and 10ml of 1000mg/L phenanthrene ethyl acetate standard solution and 100. mu.L, 250. mu.L, 500. mu.L, 1ml, 2.5ml, 5ml, 7.5ml and 10ml of 500mg/L pyrene ethyl acetate standard solution, fixing the volume by using ethyl acetate, and fully mixing to obtain the final concentrations of phenanthrene, namely 4mg/L, 10mg/L, 20mg/L, 40mg/L, 100mg/L, 200mg/L, 350mg/L and 400 mg/L; the final concentration of pyrene is sequentially 2mg/L, 5mg/L, 10mg/L, 20mg/L, 50mg/L, 100mg/L, 150mg/L and 200mg/L, then 2ml of pyrene is respectively taken out of a sample injection bottle, and the concentration of polycyclic aromatic hydrocarbon is taken as a response axis, the response value is a y axis, wherein the linear relationship between phenanthrene and the response value is y-249979 x-188383, R2 is 0.999883, the linear relationship between pyrene and the response value is y-231050 x-289929, and R2 is 0.999369; the calculation method comprises the following steps: the attenuation rate [% initial concentration-concentration after reaction ]/initial concentration.
Test results and analysis: as shown in FIGS. 3 and 4, after 20 days, the attenuation rate of phenanthrene in the non-enhanced group was 50.70%, and the attenuation rate of pyrene was 39.97%; the attenuation rate of phenanthrene in the potassium nitrate and efficient degradation flora reinforced group is 95.72%, and the attenuation rate of pyrene is 89.89%. Compared with the non-reinforced group, the attenuation rates of phenanthrene and pyrene in the reinforced group are respectively increased by 88.8% and 124.89% within 20 days, and the attenuation rates of phenanthrene and pyrene in the soil are greatly increased under the condition of combining two measures of biostimulation and bioaugmentation.
Comparative example 1:
8 kg of soil samples polluted by polycyclic aromatic hydrocarbon are filled in a customized soil experiment column, and potassium nitrate with the preparation concentration of 24g/L is added into the soil samples, so that the addition concentration of the potassium nitrate in the soil samples is 1500 mg/kg. And sealing sampling ports on two sides of the soil by using a sealing film to keep an anoxic or anaerobic environment at a position of 30-100cm of the soil column. Electron acceptors were replenished every 7 days with 1500mg nitrate per kg soil. The experimental operation period is 70 days, and the strengthening process of the natural attenuation of the polycyclic aromatic hydrocarbon polluted soil is completed.
Samples are periodically collected from a soil experimental column, the concentration of the polycyclic aromatic hydrocarbon is measured by using a GCMS machine after extraction, the degradation rate is calculated, and the specific steps and the drawing method of the polycyclic aromatic hydrocarbon standard curve are the same as those in the example 1.
Test results and analysis: as shown in FIGS. 5 and 6, after 20 days, the attenuation rate of phenanthrene in the non-reinforced group was 46.24%, and the attenuation rate of pyrene was 47.92%; the attenuation rate of phenanthrene in the potassium nitrate reinforced group is 86.62%, and the attenuation rate of pyrene is 72.38%. Compared with the non-reinforced group, the attenuation rates of phenanthrene and pyrene in the potassium nitrate reinforced group are respectively improved by 87.3% and 51.04% within 20 days.
In conclusion, within 20 days, the attenuation rates of phenanthrene and pyrene in the potassium nitrate and high-efficiency degradation flora enhanced group are respectively increased by 88.8% and 124.89% compared with those of the non-enhanced group, and the attenuation rates of phenanthrene and pyrene in the potassium nitrate and high-efficiency degradation flora enhanced group are respectively increased by 10.50% and 24.32% compared with those of the potassium nitrate enhanced group.
From this, it is found that the decay rates of the potassium nitrate and the high-efficiency degradation flora enhanced group are both significantly improved compared with those of the non-enhanced group or the potassium nitrate enhanced group, and particularly, even if the enhancement time of the potassium nitrate enhanced group is prolonged from 20 days to 70 days, the decay rate of phenanthrene in the potassium nitrate enhanced group after 70 days is 94.77%, and the decay rate of pyrene is 87.34%, the degradation effect of the potassium nitrate and the high-efficiency degradation flora enhanced group at 20 days can not be achieved, and the potassium nitrate and the high-efficiency degradation flora enhanced group can also improve the degradation rate and shorten the degradation time.
Therefore, under the anoxic or anaerobic condition, the polycyclic aromatic hydrocarbon high-efficiency degradation flora can utilize inorganic salt ion nitrate as a final electron acceptor to oxidize and degrade organic matters such as polycyclic aromatic hydrocarbon, has an enhanced effect on degradation, shortens the degradation time, improves the degradation efficiency, and has a better degradation effect compared with natural degradation or only use of nitrate.
It will be apparent to those skilled in the art that various changes and modifications may be made in the present invention without departing from the spirit and scope of the invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include such modifications and variations.
Claims (10)
1. A method for artificially reinforcing polycyclic aromatic hydrocarbon natural attenuation in soil is characterized by comprising the following steps:
s1: mixing the high-efficiency degrading flora with an inorganic salt culture solution, and adding the mixture into soil polluted by polycyclic aromatic hydrocarbon, wherein the adding concentration range of the high-efficiency degrading flora in the soil is 40-60 mg/kg;
s2: adding potassium nitrate solution into the soil, and uniformly mixing with the soil under stirring, wherein the potassium nitrate addition concentration in the soil is 1500mg/kg-2000 mg/kg;
s3: the soil is kept in an anoxic or anaerobic environment for biostimulation and bioaugmentation natural degradation;
s4: and (4) periodically supplementing a potassium nitrate solution with the same concentration as that in the step S2 into the soil, wherein the supplement addition amount of potassium nitrate in each time is the same as that in the step S2, and the degradation is stopped after the degradation rates of the polycyclic aromatic hydrocarbons phenanthrene and pyrene in the soil respectively reach the requirements.
2. The method of claim 1, wherein the inorganic salt medium comprises NaNO 3 4.0g、NH 4 Cl 2 2.0g、KH 2 PO 4 1.5g、Na 2 HPO 4 0.5g、CaCl 2 0.01g、MgCl 2 0.2g, 1ml of trace element solution and 1L of deionized water, adjusting the pH value to 7.0, and sterilizing at 121 ℃ for 20 min.
3. The method for artificially reinforcing the natural attenuation of the polycyclic aromatic hydrocarbon in the soil as claimed in claim 2, wherein the composition of the microelement solution is as follows: FeSO 4 ·7H 2 O 2g、ZnSO 4 ·7H 2 O 0.03g、H 3 BO 3 0.3g、CoCl 3 ·6H 2 O 0.3g、NiCl 2 ·6H 2 O 0.02g、Na 2 MoO 4 ·2H 2 0.03g of O and 1L of deionized water, and the pH is adjusted to 7.0.
4. The method for artificially reinforcing the natural attenuation of the polycyclic aromatic hydrocarbon in the soil as claimed in claim 1, wherein the high efficiency degrading flora and the inorganic salt culture solution are mixed in a volume ratio of 1: 10-12.
5. The method for artificially reinforcing polycyclic aromatic hydrocarbon natural attenuation in soil according to claim 1, wherein degradation is considered to be in a stagnation state when degradation rates of polycyclic aromatic hydrocarbons phenanthrene and pyrene in soil reach 99% and 85% respectively after the degradation rates reach requirements.
6. The method for artificially reinforcing the natural attenuation of the polycyclic aromatic hydrocarbon in the soil according to claim 1, wherein the domestication method of the high-efficiency anaerobic degradation flora is as follows:
standing an activated sludge sample to separate supernatant and lower layer activated sludge, taking the lower layer activated sludge, adding an inorganic salt culture medium taking phenanthrene and pyrene as carbon sources, transferring the mixture into an anaerobic bottle, introducing nitrogen into the anaerobic bottle, sealing the anaerobic bottle, and placing the anaerobic bottle in a constant-temperature oscillation box for culture, wherein the culture temperature is controlled to be 25-30 ℃, and the oscillation rate is 160-200 rmp; the domestication period is 10 days to 14 days, and the high-efficiency anaerobic degradation flora of the polycyclic aromatic hydrocarbon is obtained.
7. The method for artificially reinforcing the natural attenuation of the polycyclic aromatic hydrocarbon in the soil according to claim 6, wherein a plurality of groups of domesticated floras are arranged, the concentrations of phenanthrene and pyrene in an inorganic salt culture medium are gradually increased according to concentration gradients, and floras with phenanthrene and pyrene degradation rates respectively maintained at 95% and 85% stably are selected for enrichment culture according to the growth conditions of the floras and the degradation rate of the polycyclic aromatic hydrocarbon, so as to obtain the high-efficiency anaerobic degradation floras of the polycyclic aromatic hydrocarbon.
8. The method for artificially reinforcing natural attenuation of polycyclic aromatic hydrocarbons in soil according to claim 6, wherein the high-efficiency degradation flora obtained by the domestication method is a mixed flora taking pseudomonas nitroreducens (77.0%) as dominant bacteria.
9. The method for artificially reinforcing polycyclic aromatic hydrocarbon natural attenuation in soil according to claim 1, wherein before step S1, the content of polycyclic aromatic hydrocarbon in the polluted soil is measured in advance, the adding concentration of the high efficiency degradation bacterial flora and the nitrate is determined according to the measured content of phenanthrene and pyrene, and the relationship is as follows:
10. the method for artificially reinforcing the natural attenuation of the polycyclic aromatic hydrocarbon in the soil according to claim 1, wherein the potassium nitrate solution is prepared at a concentration of 24 g/L.
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