Method for removing polychlorinated biphenyl compound

Abstract

The invention provides a method for removing polychlorinated biphenyl compounds, and relates to the field of pollutant treatment. Comprising the following steps: adding nano zero-valent iron into soil, and planting myriophyllum spicatum in the soil. The myriophyllum spicatum and the nano zero-valent iron are combined for use, so that ammonia nitrogen compounds and polychlorinated biphenyl compounds in water and soil can be effectively removed.

Description

Technical Field

[0001] The invention relates to the field of pollutant treatment, and in particular to a method for removing polychlorinated biphenyl compounds. Background Art

[0002] Polychlorinated biphenyls (PCBs) are a type of persistent organic pollutants and a type 1 carcinogen by the World Health Organization's International Agency for Research on Cancer. They appear as flowing oily liquids, white crystalline solids or non-crystalline resins. They are highly accumulative and will accumulate in organisms and be transmitted to humans and other organisms through the food chain. They have a very long lifespan in the environment and are difficult to decompose. They can exist in water for decades and in soil for hundreds of years, causing multiple hazards to the environment and human health.

[0003] At present, the main treatment methods for PCB pollutants in water bodies are: (1) filtration and sedimentation: using activated carbon, sand, and iron powder as media to remove PCBs in water bodies through sedimentation and filtration; (2) chemical reagents, using oxidants and bioactive agents, such as oxidants such as chlorine dioxide, ozone, and hydrogen peroxide, can effectively remove PCBs in water bodies;

[0004] The main treatment methods for PCB pollutants in the soil are: (1) Physical method: mainly through thermal decomposition, distillation and physical adsorption to degrade PCBs, but it is difficult to degrade them completely and the scope of application is limited. (2) Chemical method: including chlorination, hydrodechlorination, Sunohio method, wet catalytic oxidation and other methods, which can effectively degrade PCBs, but the operation is complicated and the cost is high. (3) Biological method: using microorganisms or plants to degrade PCBs is an environmentally friendly and economically feasible degradation method. (4) Plant rhizosphere remediation method: using the interaction between plants and rhizosphere microorganisms to degrade PCBs, the effect is obvious. For other forms of PCBs, there are also landfill methods and incineration methods.

[0005] The plant rhizosphere remediation method can not only degrade PCBs, but also improve soil and air quality. It has little damage to the environment and is friendly to nature. However, the current effect of using plants to degrade PCBs is poor. Summary of the invention

[0006] The object of the present invention is to provide a method for removing polychlorinated biphenyl compounds, which uses foxtail algae and nano zero-valent iron in combination to effectively remove ammonia nitrogen compounds and polychlorinated biphenyl compounds in water and soil.

[0007] The present invention solves the technical problem by adopting the following technical solutions.

[0008] On the one hand, an embodiment of the present invention provides a method for removing polychlorinated biphenyl compounds, which includes: adding nano zero-valent iron into soil, and planting foxtail algae in the soil.

[0009] The central tube tissue of foxtail algae is well developed, and its root surface is an interface with strong dynamic redox characteristics. The oxygen released from the roots can increase the dissolved oxygen concentration in the root microenvironment to more than 5.00 mg / L, which can reduce the concentration of zero-valent iron or Fe 2+ It is converted into iron oxide and forms an iron film on the roots, which is beneficial for plants to absorb, transfer and transform trace elements and nutrients, thereby increasing the biomass and chlorophyll content of foxtail algae and promoting its growth;

[0010] In some embodiments of the present invention, the soil environment is a wetland, especially a wetland environment rich in ammonia nitrogen. Myriophyllum has a dual effect of removing ammonia nitrogen and PCBs, and ammonia nitrogen can significantly enhance the microbial degradation of PCBs, achieving the effect of "treating waste with waste".

[0011] In some embodiments of the present invention, the input amount of the nano zero-valent iron in the soil is 90-110 mg / kg. At this input amount, the combination of nano zero-valent iron and foxtail algae has the best effect in removing PCBs. Preferably, the input amount of the nano zero-valent iron in the soil is 100 mg / kg.

[0012] In some embodiments of the present invention, the particle size of the nano zero-valent iron is 60-90 nm. Nano-particle zero-valent iron has an adsorption effect and can adsorb organic matter in water. Preferably, the particle size of the nano zero-valent iron is 80 nm.

[0013] In some embodiments of the present invention, the process further includes mixing nano zero-valent iron into air in small amounts for multiple times for activation, so as to form a passivation layer on the surface of the nano zero-valent iron particles.

[0014] Compared with the prior art, the embodiments of the present invention have at least the following advantages or beneficial effects:

[0015] The method for removing polychlorinated biphenyl compounds provided by the present invention uses nano zero-valent iron and foxtail algae in combination, and can remove ammonia nitrogen compounds and polychlorinated biphenyl compounds at the same time, with good combined removal effect.

[0016] Among them, foxtail algae can dually remove ammonia nitrogen compounds and polychlorinated biphenyl compounds in water and soil, while nano zero-valent iron can promote photosynthesis of foxtail algae. Secondly, nano zero-valent iron will be oxidized at the roots of foxtail algae, forming iron oxide precipitation on the root surface, that is, forming an iron film. The iron film can adsorb a large amount of nutrients and pollutants, promote plants to absorb more nutrients, thereby accelerating plant growth, and can also adsorb hydrophobic organic pollutants. When the iron film adsorbs hydrophobic organic pollutants, the redox of iron and the oxidation of PCBs undergo electron transfer. At the same time, the bacteria involved in the redox of iron also participate in the dechlorination or oxidation of PCBs, thereby achieving the effective removal of organic pollutants such as PCBs. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0018] Figure 1 This is a graph of the dry weight of Myriophyllum and the iron film content in its roots;

[0019] Figure 2 Electron microscopic images (A and C) and energy spectrum analysis (B and D) of the root of Myriophyllum;

[0020] Figure 3 It is the concentration map of PCBs and PCB9;

[0021] Figure 4 It is a graph of microbial content in soil;

[0022] Figure 5 is the Shannon index graph;

[0023] Figure 6 This is the PCoA score graph. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0025] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other. The present invention will be described in detail below with reference to specific embodiments.

[0026] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0027] Example

[0028] The soil contaminated by PCBs was collected in the area of ​​electronic waste dismantling. The soil contained a high concentration of iron and manganese heavy metals. After testing, the concentration of PCBs in the soil was 510μg / kg. Isotope-labeled 12 C-PCB9 and 13 C-PCB9, in soil 12 C-PCB9 and 13 The concentration of C-PCB9 is 1020±20 μg / kg, wherein PCB9 is (2,5)-dichlorobiphenyl.

[0029] According to the input amount of nano zero-valent iron (nZVI) of 100 mg / kg, the amount of nano zero-valent iron and soil was determined, and then the slightly activated nano zero-valent iron was weighed and added to 50 g of soil, and mixed in a shaker (normal temperature, 120 rpm / min, 3 days), and then the remaining soil was added in sequence and mixed to obtain the planting soil.

[0030] 25 ml of soil was placed in a 50 ml glass measuring cylinder, and a Myriophyllum was planted in the measuring cylinder. Tap water was added to 50 ml, and the soil layer of the measuring cylinder was wrapped with tin foil to prevent photodegradation of PCBs. All experimental groups were placed in a static culture at room temperature (light condition was 12 h / day) in an unordered manner.

[0031] Among them, according to the above method, a blank control group (CK); a group only adding nano zero-valent iron (ZVI); a group only planting foxtail algae (P); and an experimental group with nano zero-valent iron and foxtail algae added at the same time (ZVI-P) were set up, as shown in Table 1.

[0032] Table 1 Group settings

[0033]

[0034] After culturing Myriophyllum for 45 days, all soil samples were collected and freeze-dried, ground through a 60-mesh sieve and stored at -20°C to obtain soil samples of each group for later use. Myriophyllum was rinsed clean (first wash off the sticky soil with tap water, then rinsed with deionized water 3 times, and dried with filter paper), divided into roots and aboveground parts, and the dry weight of Myriophyllum was recorded. It was then ground into powder with a grinder and stored at -20°C to obtain plant samples of each group for later use.

[0035] 1.PCBs analysis

[0036] A certain mass of soil or plant sample was weighed, extracted with an organic solvent (dichloromethane) three times, and then impurities were removed by an acidic silica gel column. Finally, the extract was concentrated to 500 μL under a nitrogen flow. An internal standard (13C12-PCB141) was added before the measurement. The measuring instrument was a GC-MS / MS (Agilent 7890 / 7000, California, USA) equipped with a CP-Sil 8CB capillary column (50m×0.25mm×0.12μm). The injection carrier gas was high-purity helium with a flow rate of 1.1mL / min. The transfer line temperature, injection interface temperature, and ion source temperature were set to 280℃, 290℃, and 230℃, respectively. A splitless injection mode with an injection volume of 1μL was used. The temperature program of GC was as follows: maintain at 100 °C for 0.5 min, increase from 100 °C to 160 °C at a rate of 10 °C / min, then increase from 160 °C to 250 °C at a rate of 3 °C / min, increase from 250 °C to 295 °C at a rate of 10 °C / min, and finally maintain at 295 °C for 10 min. 13 C 12 The recoveries of the labeled recovery indicators PCB9, 155, and 206 were 59.4±8.0%, 63.9±6.5%, and 79.1±6.2%, respectively.

[0037] The results are as follows Figure 3 As shown, the concentrations of PCBs decreased from 1570 μg / kg to 963 ± 20, 870 ± 11, 931 ± 10, and 822 ± 52 μg / kg in the control (CK), ZVI, Myriophyllum (P), and Myriophyllum treatment with nZVI addition (ZVI-P), respectively. Figure 3 A), the removal rates of PCBs were 38.7%, 44.6%, 40.7% and 47.7% respectively. The concentrations of PCB homologues of dichlorobiphenyl and heptachlorobiphenyl were significantly reduced, and the ZVI and ZVI-P treatments with the addition of nZVI material achieved the highest PCBs removal efficiency.

[0038] The initial concentration of PCB9 was 1020±20μg / kg. After 45 days of cultivation, the residual amounts of PCB9 in the control (CK), ZVI, Myriophyllum (P) and Myriophyllum treatment with nZVI addition (ZVI-P) were 717±22, 625±5, 710±12 and 599±13μg / kg, respectively, and the removal rates were 30.0%, 38.8%, 30.5% and 41.3%, respectively. Figure 3B). First, there was no significant difference in PCB9 removal rates between the P and CK treatments (p>0.05), indicating that foxtail algae cultivation had no significant phytoremediation effect in this experiment. The content of PCBs in the soil of this experiment was 500μg / kg contaminated soil (low-concentration contaminated soil), and foxtail algae cultivation did not significantly enhance the removal of PCBs. Secondly, the PCB9 removal rates in the ZVI and ZVI-P treatments were significantly higher than those in the corresponding treatments without nZVI: CK control and P treatment (p<0.05), while there was no significant difference in PCB9 removal rates between the ZVI-P and ZVI treatments (p>0.05). These results all indicate that the addition of nZVI (nano zero-valent iron) is the main reason for the significant increase in PCBs removal rate. Among them, in Figure 3 In the figure, (A) represents the attenuation of PCB homologues of dichlorobiphenyl-heptachlorobiphenyl, and (B) represents the attenuation of PCB9 (change in concentration and removal rate). The values ​​are mean ± standard deviation (n = 3), and the bars with different letters indicate significant differences (p < 0.05). Original soil represents original soil, CK represents the control without plants and nZVI, ZVI represents the treatment with only nZVI, P represents the treatment with Myriophyllum, and ZVI-P represents the treatment with Myriophyllum added with nZVI.

[0039] The ability of Myriophyllum to absorb PCB9 was analyzed, and it was found that the concentrations of PCB9 in the roots and aboveground parts of Myriophyllum in the P treatment were 136±4 and 38.5±0.1μg / kg, respectively, while in the ZVI-P treatment, they were 29.2±0.3 and 15.9±1.10μg / kg, respectively. The RCF (root enrichment factor) and TF (root transport factor) of Myriophyllum were calculated to determine the ability of Myriophyllum to absorb and transport PCB9 in different treatments. The RCF and IF in the P treatment reached 0.19 and 0.28, respectively, while in the ZVI-P treatment, they were 0.05 and 0.54, respectively. It can be seen that the RCF value in the ZVI-P treatment was much lower than that in the P treatment (p<0.05), indicating that the addition of nZVI prevented the roots of Myriophyllum from absorbing PCB9. However, the TF value in ZVI-P was higher than that in P treatment, and the stem and leaf enrichment coefficient in ZVI-P treatment (0.03) was significantly lower than that in P treatment (0.05), indicating that the addition of nZVI also reduced the enrichment of PCB9 in the aboveground part of Myriophyllum.

[0040] In the foxtail algae wetland system with nZVI addition, in addition to natural reduction, the main reduction pathways of PCBs include plant absorption, chemical reduction and oxidation, and microbial degradation. After calculation, the contribution of plant absorption in the P and ZVI-P treatments was only 0.34% and 0.21%, respectively. Therefore, the relevant chemical removal triggered by nZVI and the root microbial remediation driven by soil microbiota are the main reduction pathways of PCBs. nZVI plays a multiple effect of chemical and microbial pathways in promoting PCBs reduction, and the chemical pathway may play a dominant role.

[0041] 2. Qualitative analysis of iron film

[0042] After the cultivation of foxtail algae was completed, an obvious orange precipitate was observed on the root surface. After washing the foxtail algae roots three times with tap water and ultrapure water, they were wrapped in qualitative filter paper (Whatman No. 1 qualitative filter paper, USA) and frozen at -20°C for about 6 hours, and then freeze-dried. The freeze-dried foxtail algae roots were made into target samples, which were then analyzed and measured by a scanning electron microscope energy dispersive spectrometer (Scanning Electron Microscope-Energy Dispersive Spectrometer, SEM-EDS). The SEM-EDS instrument is composed of a cold field emission scanning electron microscope (SU-8010, Hitachi, Japan) and an X-ray energy spectrometer (EDAXTEAMTM, Massachusetts, USA). The target was made and measured on the machine. The scanning electron microscope can see the characteristics of the foxtail algae roots ( Figure 2 A and C), and then the elemental composition of the flocculent precipitate accumulated on the root surface was analyzed by energy spectrometer, as shown in Figure ( Figure 2 B and D), it was found that iron film was formed in the rhizosphere of both the P treatment group and the ZVI-P treatment group. The scanning electron microscope (SEM) image showed obvious floccules on the root surface (red circle), and the elemental composition of these floccules was identified as iron (white circle) by energy dispersive spectrometer analysis. Secondly, the preliminary results of SEM-EDS showed that the iron-containing floccules on the root surface of Myriophyllum in the ZVI-P treatment group were significantly more than those in the P treatment. It should be noted that in Figure 2Figures (B) and (D) are the elemental compositions of Figures (A) and (C) analyzed by X-ray energy spectrometer (EDAX TEAMTM, USA). In this paper, only the basic and abundant elements (C, O and K) and the Fe element that needs to be analyzed are selected. The C, O and K elements are basically distributed in the roots of Myriophyllum, while the iron film (Fe element) is mostly attached to the surface of the roots. The white circles in Figures (B) and (D) and the flocs in the red circle in Figure (C) are the iron films formed on the root surface of Myriophyllum. The units shown in the scanning electron microscope images (A and C) are 200μm, and the units shown in the corresponding energy spectrum analysis images (B and D) are 100μm. P represents Myriophyllum treatment, and ZVI-P represents Myriophyllum treatment with nZVI added.

[0043] 3. Quantitative Analysis of Iron Film

[0044] After the fresh roots of foxtail algae were washed three times with tap water and ultrapure water, 0.1 g of fresh roots were extracted with 20 mL of DBC solution (0.60 g of sodium dithionite, 0.03 mol / L of sodium citrate and 0.125 mol / L of sodium bicarbonate) at room temperature for 90 min. The DCB extraction solution was then centrifuged at 16000 g for 10 min, and the precipitate after centrifugation was used to extract DNA and determine iron film microorganisms. The supernatant after centrifugation was first filtered through a 0.45 μm hydrophilic polyethersulfone membrane filter, and then the Fe (total iron ion) concentration in the solution was determined by the o-phenanthroline spectrophotometry using an ultraviolet spectrophotometer (Youke N5000, Shanghai, China), thereby calculating the amount of iron film formed on the roots of foxtail algae (mg / g fresh root). The results are shown in the figure. Figure 1 As shown in Figure 2. The iron film content formed in the rhizosphere of Myriophyllum in the P treatment group and ZVI-P treatment group was 25.6 and 30.0 mg / g fresh root, respectively ( Figure 1 ). The iron film content in the rhizosphere of Myriophyllum in the ZVI-P treatment was significantly higher than that in the control group without nZVI (p<0.05), indicating that nZVI significantly promoted the formation of iron film in the rhizosphere of Myriophyllum. Figure 1 In the table, the values ​​are mean ± SD (n = 3). P represents the Myriophyllum treatment, and ZVI-P represents the Myriophyllum treatment with nZVI addition. The bar graphs represent the biomass of Myriophyllum shoots and roots (dry weight g / pot), respectively, and the green five-pointed star (Fe plaque) represents the iron plaque content of Myriophyllum roots (in terms of total iron ion mass, mg / g fresh root).

[0045] 4. Microbiological Analysis

[0046] The PowerSoil DNA isolation kit (Mo Bio Laboratories, California, USA) was used to extract DNA from soil samples, and the extraction steps were referred to the kit instructions. Among them, the DNA in the DNA-SIP centrifugation process was 8 μg, and the SIP treatment group was shown in Table 1. The DNA was added to the EDTA / CsCl solution to adjust the final buoyant density to 1.77 g / mL. The above solution was then transferred to a Quick-Seal ultracentrifuge tube (13×51 mm, 5.1 mL; Beckman) and ultracentrifuged at 20°C and 47500 rpm / min (Optima L-100XP; Beckman) for 48 hours. Subsequently, the DNA was evenly divided into 14 layers, and the buoyant density was measured using an AR200 digital refractometer. Finally, the DNA fraction was purified with glycogen and ethanol to remove CsCl. The results are shown in the figure. Figure 4 As shown. Figure 4 In the table, the values ​​are mean ± SD (n = 3), and the bars with different letters indicate significant differences (p < 0.05). Original represents original soil, CK represents the control without plants and nZVI, ZVI represents the treatment with nZVI, P and ZVI-P represent the treatment with Myriophyllum, and nZVI-P represents the treatment with Myriophyllum. Soil represents soil samples, and Fe plaque represents Fe plaque samples.

[0047] From the attached Figure 4 It can be concluded that the number of 16S rRNA genes in the Myriophyllum cultivation treatment is 2.14×10 9 The number of copies / g dry soil was significantly higher than that of the blank control group (4.76×10 8 The number of copies / g dry soil) (p<0.05) indicated that the cultivation of Myriophyllum promoted the growth of microorganisms in the soil. Secondly, the number of 16S rRNA genes in the soil with only nZVI addition was 2.01×10 8 At the same time, after adding nZVI, the number of 16S rRNA genes in the rhizosphere soil and iron film of Myriophyllum was increased (ZVI-P, 1.74×10 9 The number of copies / g dry soil) was also lower than that of Myriophyllum treatment (p<0.05). These results indicate that nZVI reduced the number of microorganisms in soil and Myriophyllum rhizosphere soil.

[0048] Attached Figure 5 is the α-diversity based on the Shannon index. After 45 days of cultivation, the Shannon index of the ZVI treatment alone (9.49) was significantly lower than that of the original soil and the other three treatments (CK, P, and ZVI-P), indicating that nZVI addition reduced the diversity of microbial communities in the soil, while planting foxtail algae improved the inhibition of nZVI. The PCoA score map was obtained based on the unweighted unifra distance ( Figure 6 ), PCoA1 and PCoA2 explained 15.5% and 8.12% of the total variance of the microbial community, respectively. PCoA analysis results showed that only the soil microbial community structure of the ZVI treatment was different from that of CK, P and ZVI-P. The above results indicate that nZVI leads to a decrease in the diversity and change in the structure of the microbial community in the unplanted soil.

[0049] Analysis of the differences in the diversity and structure of soil and ferrocoel microbial communities revealed that the Shannon index of ferrocoel in the P and ZVI-P treatments (8.94 and 9.10) was significantly lower than that of its soil microorganisms (9.83 and 10.21) (p < 0.05) ( Figure 5 ), and PCoA analysis also showed that there were significant differences in the microbial communities between the iron film and the soil ( Figure 6 ).exist Figure 5 In the table, the values ​​are mean ± SD (n = 3), and the bars with different letters indicate significant differences (p < 0.05). Original represents the original soil, CK represents the control without plants and nZVI, ZVI represents the treatment with nZVI, P and ZVI-P represent the treatment with Myriophyllum, and nZVI-P represents the treatment with Myriophyllum. Soil represents soil samples, and Fe plaque represents Fe plaque samples. Figure 6 In the data, Original soil represents the soil sample at the beginning of the experiment, Original soil represents the original soil, CK represents the control without plants and nZVI, ZVI represents the treatment with nZVI, P and ZVI-P represent the treatment with Myriophyllum, and Myriophyllum with nZVI. P-FeB and ZVI-P-FeB represent the iron film samples with Myriophyllum treatment and Myriophyllum plus nZVI treatment.

[0050] 5. Growth analysis of Myriophyllum

[0051] The dry weight of the roots and aboveground parts of Myriophyllum is shown in the following table. Figure 1 As shown. Figure 1 It can be concluded that in the treatment group with only Myriophyllum (P), the dry weight of the root and aboveground parts of Myriophyllum were 0.06 and 2.14 g / pot, respectively. In the Myriophyllum treatment with nZVI (ZVI-P), the dry weight of the root and aboveground parts of Myriophyllum were 0.16 and 2.91 g / pot, respectively, which were 2.67 and 1.36 times that of Myriophyllum alone. This result shows that the addition of nano zero-valent iron significantly promoted the growth of Myriophyllum (p<0.05).

[0052] In summary, the method for removing polychlorinated biphenyl compounds provided by the embodiment of the present invention, the addition of nZVI promoted the growth of foxtail algae, reduced the ability of plants to absorb PCBs, but increased the PCBs removal rate in the soil by 7.00%. The nZVI treatment did not significantly change the microbial community structure and diversity of the rhizosphere soil, but changed the composition of active PCBs degradation functional microorganisms, and reduced the number of functional microorganisms and functional genes. However, the nZVI treatment promoted the formation of rhizosphere iron film, thereby accelerating the transfer of PCBs degradation functional microorganisms and degradation genes from soil to the iron film, and significantly increased the abundance of functional microorganisms in the iron film. Therefore, nZVI enhances the chemical reduction of PCBs, promotes the formation of rhizosphere iron film in foxtail algae, and increases the microbial degradation rate of PCBs.

[0053] The embodiments described above are part of the embodiments of the present invention, rather than all of the embodiments. The detailed description of the embodiments of the present invention is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

Claims

1. A method for removing polychlorinated biphenyl compounds, characterized in that: include: Nano-zero-valent iron was added to the soil and foxtail algae was planted in the soil.

2. The method for removing polychlorinated biphenyl compounds according to claim 1, characterized in that: The soil environment is a wetland.

3. The method for removing polychlorinated biphenyl compounds according to claim 1, characterized in that: The input amount of the nano zero-valent iron in the soil is 90-110 mg / kg.

4. The method for removing polychlorinated biphenyl compounds according to claim 3, characterized in that: The input amount of the nano zero-valent iron in the soil is 100 mg / kg.

5. The method for removing polychlorinated biphenyl compounds according to claim 1, characterized in that: The particle size of the nano zero-valent iron is 60-90 nm.

6. The method for removing polychlorinated biphenyl compounds according to claim 5, characterized in that: The particle size of the nano zero-valent iron is 80 nm.

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