CN112980456A

CN112980456A - Environment-friendly eluent for restoring organochlorine pesticide polluted soil and preparation method thereof

Info

Publication number: CN112980456A
Application number: CN202110256958.7A
Authority: CN
Inventors: 万金忠; 周艳; 王祥; 赵远超; 靳德成
Original assignee: Nanjing Institute of Environmental Sciences MEE
Current assignee: Nanjing Institute of Environmental Sciences MEE
Priority date: 2021-03-09
Filing date: 2021-03-09
Publication date: 2021-06-18

Abstract

The invention discloses an environment-friendly eluent for restoring organochlorine pesticide contaminated soil and a preparation method thereof, wherein the environment-friendly eluent takes water as a base liquid, and is added with 50-100 g/L of a biosurfactant, 5-10% of peanut oil leftovers by mass fraction and 3-5% of N/P nutrient particles by mass fraction. The method has low influence on the soil environment, does not cause additional soil pollution and the like, can reduce the risk of restoring the soil environment, and can improve the soil restoration effect.

Description

Environment-friendly eluent for restoring organochlorine pesticide polluted soil and preparation method thereof

Technical Field

The invention relates to the technical field of soil remediation, in particular to an environment-friendly eluent for remediation of soil polluted by organochlorine pesticides and a preparation method thereof.

Background

Organochlorine pesticide contamination is an environmental pollution caused by polychlorinated organically synthesized insecticides. The main varieties of the organochlorine pesticides include DDT (DDT), hexachloro cyclohexane, and the like, and the organochlorine pesticides are stable in chemical properties and difficult to decompose and can cause serious pollution to the environment; it is self-inoculated with contaminated crops and remains in large quantities in the soil. The pesticide enters human body through food, and is accumulated in tissues such as liver, kidney, heart, etc., and is accumulated in fat most. The accumulated pesticide can be discharged through breast milk, and poultry can be transferred into tissues such as eggs and eggs to influence the offspring. The residual of the organochlorine pesticide in food is controlled very severely in various countries.

Aiming at the remediation of soil polluted by organic chlorine, the concentration (activity) of soil pollutants can be reduced by adopting physical, chemical, biological and ecological principles and adopting artificial regulation and control measures, so that the harmless and stabilization of the pollutants are realized, and the technical measures of the detoxification effect expected by people are achieved.

However, the currently disclosed eluents are roughly classified into an environment-friendly eluent and a conventional chemical eluent, the environment-friendly eluent has low/no pollution to soil, but has a high price and a poor economy, the conventional chemical eluent has a high economy, but may cause secondary pollution after soil elution and remediation, and the ecological function diversity and the like of the soil of the polluted soil after multiple times of elution are reduced to a certain extent, so that a novel environment-friendly eluent is needed to solve the problems.

Disclosure of Invention

In order to solve the technical problems, the invention provides an environment-friendly eluent for restoring organochlorine pesticide polluted soil and a preparation method thereof.

The technical scheme of the invention is as follows: an environment-friendly eluent for restoring organochlorine pesticide contaminated soil and a preparation method thereof are disclosed, wherein the environment-friendly eluent takes water as a base liquid, and is added with 50-100 g/L of a biosurfactant, 5-10% of peanut oil leftovers by mass fraction and 3-5% of N/P nutrition particles by mass fraction. The problem that the market price of the novel environment-friendly eluent is relatively high at present can be effectively solved through the proportion, and the compounding of the peanut oil leftovers and the biosurfactant in the proportion not only maintains the high-efficiency removal of target pollutants, but also reduces the dosage of the eluent and the input energy consumption cost; meanwhile, N/P nutrient particles are added, so that organic matters, mineral elements or certain nutrient elements suitable for growth of microorganisms in part of soil can be effectively prevented from being removed together when target pollutants are removed by elution, and the eluted soil can be recovered to a certain degree.

Further, the biosurfactant is a cyclodextrin HPCD biosurfactant. The cyclodextrin HPCD biosurfactant has positive correlation between the treatment effect and the concentration when the organochlorine pesticide polluted soil is repaired, so that the cyclodextrin HPCD biosurfactant has smaller limited condition when used for treating the organochlorine pesticide polluted soil, and is favorable for being used under various use conditions.

Further, the cyclodextrin HPCD biosurfactant of the environment-friendly eluent and the peanut oil leftovers are added in the following amounts: 50g/L of biosurfactant and 10 percent of peanut oil leftovers by mass fraction. Through the optimized proportion, the use effect of the composite combination has no obvious difference with the compound combination of 100g/L HPCD + 5% peanut oil leftovers on the removal rate of DDTs (dichlorodiphenyltrichloroethane) in the total amount, and the removal rate is about 86%, and the cost of the peanut oil leftovers is far lower than that of the cyclodextrin HPCD biosurfactant, so that the adoption of the preparation not only maintains the high-efficiency removal of target pollutants, but also reduces the dosage of the eluent and the input energy consumption cost.

Further, the N/P nutrition addition source of the N/P nutrition granules is from inorganic nutrition salt containing nitrogen and phosphorus, and the preparation method comprises the following steps:

1) dissolving inorganic nutrient salt containing nitrogen and phosphorus in warm water until insoluble substances appear to obtain nutrient salt solution;

2) then, putting porous ceramic particles which account for 30-50% of the volume of the nutrient salt solution into the nutrient salt solution, wherein the particle size of the porous ceramic particles is about 1 mm;

3) heating and evaporating the nutrient salt solution, and slowly stirring until the nutrient salt solution is evaporated to dryness to obtain porous ceramic particles containing nutrient salt;

4) collecting porous ceramic particles containing nutrient salt, placing the porous ceramic particles into hot-melted gelatin liquid, stirring and coating, adding wood fiber powder accounting for 5-12% of the mass of the gelatin liquid, taking out the gelatin liquid, and naturally drying in the shade to obtain the N/P nutrient particles.

The N/P nutrient particles prepared by the method not only have high-load N/P nutrient salt, but also can be greatly remained in the soil during elution, and cannot be taken away by water to N, P ingredients, so that sufficient N, P nutrient substances are provided for self-recovery of the soil after elution, and the richness and uniformity of the microbial community of the soil after recovery can be effectively recovered and promoted.

Further, the environment-friendly eluent is mainly suitable for soil polluted by organochlorine pesticides polluted by DDTs. The environment-friendly eluent is cyclodextrin HPCD biosurfactant and is mainly used for repairing organochlorine pesticide polluted soil polluted by DDTs, but is not limited to the organochlorine pesticide polluted soil.

Furthermore, the liquid-solid ratio of the environment-friendly eluent to the organochlorine pesticide polluted soil polluted by the DDTs is 5-15: 1, and the use conditions are as follows: and (3) eluting the organochlorine pesticide polluted soil polluted by the DDTs at the rotating speed of 20-45 rpm and the elution temperature of 45-60 ℃, wherein the elution is carried out for 2-4 times, and each time of elution is 50-80 min. Through the limitation of the using conditions, the single maximum removal rate of the organochlorine pesticide contaminated soil polluted by DDTs can reach 95%, so that the efficient elution treatment of the organochlorine pesticide contaminated soil can be realized on the premise of meeting the limitation of the parameters, and the problems of cost increase and the like caused by resource waste and the like are avoided.

Furthermore, ultrasonic strengthening is also embedded in the elution treatment of the environment-friendly eluent and the organic chlorine pesticide polluted soil polluted by the DDTs, wherein the ultrasonic strengthening of 25-45 kH is used. By applying ultrasonic synergistic enhancement treatment with the parameters, the composition has extremely remarkable synergistic effect on the total amount of DDTs, and remarkably improves the peanut oil leftovers and the cyclodextrin HPCD biosurfactant.

The invention also provides a preparation method of the environment-friendly eluent for restoring the organochlorine pesticide contaminated soil, which is characterized by comprising the following steps of:

s1: selecting and matching the biosurfactant, the peanut oil leftovers, the N/P nutrient particles and the water according to the proportion;

s2: uniformly mixing the peanut oil leftovers and the N/P nutrient particles to obtain solution A, heating water to 25 +/-1 ℃ from room temperature, then adding a biosurfactant, uniformly mixing to obtain solution B, and storing for later use;

s3: when in preparation and use, the solution B is slowly stirred and then added with the solution A, and the mixture is uniformly mixed to obtain the environment-friendly eluent.

Further, the preservation temperature of the solution A is not higher than 35 ℃, and the environment-friendly eluent is suitable for being prepared. Through the limitation, the conditions that the N/P nutrient particles are unstable and the like caused by the overhigh temperature of the A liquid are prevented, and the like, and the conditions that the N/P nutrient particles in the A liquid are deposited and the like can be effectively prevented by adopting the existing preparation method, so that the using effect of the environment-friendly eluent is better.

The invention has the beneficial effects that:

(1) the environment-friendly eluent for restoring the soil polluted by the organochlorine pesticide provided by the invention has low influence on the environment, does not cause additional soil pollution and the like, and can reduce the risk of restoring the soil environment and improve the soil restoration effect.

(2) The environment-friendly eluent for restoring the organochlorine pesticide polluted soil provided by the invention maintains high-efficiency removal of target pollutants, simultaneously reduces the dosage of the eluent and the input energy consumption cost, and has good restoration effect and moderate restoration agent price.

(3) The environment-friendly eluent for restoring the organochlorine pesticide-contaminated soil can restore the eluted soil to a certain degree by adding N/P nutrient particles, and can effectively prevent the problems of nutrient loss and the like of the restored soil caused by soil elution.

Drawings

FIG. 1 shows the removal efficiency of total DDTs and 4 homologues in soil of Wujiang polluted site by a random compounding interaction experiment of 3 HPCD multiplied by 3 concentrations of peanut oil leftovers.

FIG. 2 shows the effect of 7 eluents on the removal of DDTs in Wujiang soil under different elution time conditions.

FIG. 3 shows the effect of 7 eluents on DDTs in Wujiang soil under different stirring speeds.

FIG. 4 shows the effect of 7 eluents on the removal of DDTs in Wujiang soil under different liquid-solid ratio conditions.

FIG. 5 shows the effect of the eluting agent on DDT removal in soil of Wujiang polluted site under different temperature conditions.

FIG. 6 shows the effect of 4 eluents on DDT removal in Wujiang soil under chimeric ultrasound conditions.

FIG. 7 shows the kinetics of OCPs desorption in Liyang field soil with different elution times.

FIG. 8 shows the variation of indexes of the diversity of the ecological functions of microorganisms in the soil polluted by Shijiazhuang after three times of elution.

Detailed Description

Example 1

Composition of environment-friendly eluent

An environment-friendly eluent for restoring organochlorine pesticide contaminated soil is prepared by taking water as a base liquid, and adding 50g/L of a biosurfactant, 10% of peanut oil leftovers by mass fraction and 4% of N/P nutrient particles by mass fraction;

wherein the biosurfactant is cyclodextrin HPCD biosurfactant. The cyclodextrin HPCD biosurfactant is adopted, and the treatment effect and the concentration of the cyclodextrin HPCD biosurfactant are positively correlated when the organochlorine pesticide polluted soil is repaired, so that the cyclodextrin HPCD biosurfactant is adopted to treat the organochlorine pesticide polluted soil under smaller limited conditions, and is favorable for being used under various use conditions;

the N/P nutrition addition source of the N/P nutrition particles is from inorganic nutrition salt containing nitrogen and phosphorus, and is selected from commercially available nitrogen and phosphorus nutrition salt, and the preparation method comprises the following steps: 1) dissolving inorganic nutrient salt containing nitrogen and phosphorus in warm water until insoluble substances appear to obtain nutrient salt solution; 2) then, putting porous ceramic particles accounting for 45% of the volume of the nutrient salt solution into the nutrient salt solution, wherein the particle size of the porous ceramic particles is about 1 mm; 3) heating and evaporating the nutrient salt solution, and slowly stirring until the nutrient salt solution is evaporated to dryness to obtain porous ceramic particles containing nutrient salt; 4) collecting porous ceramic particles containing nutrient salt, placing the porous ceramic particles into hot-melted gelatin liquid for stirring and coating, adding wood fiber powder accounting for 7.5% of the mass of the gelatin liquid, and then fishing out and naturally drying in the shade to obtain the N/P nutrient particles. The N/P nutrient particles prepared by the method not only have high-load N/P nutrient salt, but also can be greatly remained in the soil during elution, and cannot be taken away by water to N, P ingredients, so that sufficient N, P nutrient substances are provided for self-recovery of the soil after elution, and the richness and uniformity of the microbial community of the soil after recovery can be effectively recovered and promoted.

The problem that the market price of the novel environment-friendly eluent is relatively high at present can be effectively solved through the proportion, and the compounding of the peanut oil leftovers and the biosurfactant in the proportion not only maintains the high-efficiency removal of target pollutants, but also reduces the dosage of the eluent and the input energy consumption cost; meanwhile, N/P nutrient particles are added, so that organic matters, mineral elements or certain nutrient elements suitable for growth of microorganisms in part of soil can be effectively prevented from being removed together when target pollutants are removed by elution, and the eluted soil can be recovered to a certain degree.

Preparation of environment-friendly eluent

s2: uniformly mixing the peanut oil leftovers and the N/P nutrient particles to obtain solution A, heating water to 25 ℃ from room temperature, then adding a biosurfactant and uniformly mixing to obtain solution B, and storing for later use; the preservation temperature of the solution A is not higher than 35 ℃, so that the conditions that the N/P nutrient particles are unstable and the like caused by the overhigh temperature of the solution A are prevented;

s3: when the environment-friendly eluent is prepared and used, the solution B is slowly stirred and then added with the solution A, and the environment-friendly eluent is uniformly mixed to obtain the environment-friendly eluent, wherein the environment-friendly eluent is suitable for being prepared and used on site, and the N/P nutrient particles in the solution A can be effectively prevented from being deposited and the like by adopting the mode of being prepared and used on site, so that the environment-friendly eluent has better use effect.

Use of environment-friendly eluent

The environment-friendly eluent is mainly suitable for organochlorine pesticide polluted soil polluted by DDTs, and the application method comprises the following steps: the liquid-solid ratio of the environment-friendly eluent to the organochlorine pesticide polluted soil polluted by the DDTs is 10:1, and the use conditions are as follows: and (3) eluting the organochlorine pesticide polluted soil polluted by the DDTs at the rotating speed of 30rpm and the elution temperature of 50 ℃, wherein the elution is carried out for 60min each time. The environment-friendly eluent and the organic chlorine pesticide polluted soil polluted by DDTs are subjected to ultrasonic strengthening in the elution treatment, wherein 35kH of ultrasonic strengthening is used. By applying ultrasonic synergistic enhancement treatment with the parameters, the composition has extremely remarkable synergistic effect on the total amount of DDTs, and remarkably improves the peanut oil leftovers and the cyclodextrin HPCD biosurfactant, specifically 13% and 9% respectively. Through the limitation of the using conditions, the single maximum removal rate of the organochlorine pesticide contaminated soil polluted by DDTs can reach 95%, so that the efficient elution treatment of the organochlorine pesticide contaminated soil can be realized on the premise of meeting the limitation of the parameters, and the problems of cost increase and the like caused by resource waste and the like are avoided.

Example 2

The present example is substantially the same as example 1, except that the mixture ratio of the environment-friendly eluent is different, specifically: the environment-friendly eluent takes water as base liquid, and 100g/L of biosurfactant, 5% of peanut oil leftovers by mass fraction and 3% of N/P nutrition particles by mass fraction are added.

Example 3

The present example is substantially the same as example 1, except that the mixture ratio of the environment-friendly eluent is different, specifically: the environment-friendly eluent takes water as base liquid, and 50g/L of biosurfactant, 5% of peanut oil leftovers by mass fraction and 5% of N/P nutrition particles by mass fraction are added.

Example 4

The present example is substantially the same as example 1, except that the N/P nutrient granules are different, specifically: the N/P nutrition additive of the N/P nutrition granules is derived from inorganic nutrient salt containing nitrogen and phosphorus, and the preparation method comprises the following steps: 1) dissolving inorganic nutrient salt containing nitrogen and phosphorus in warm water until insoluble substances appear to obtain nutrient salt solution; 2) then, putting porous ceramic particles accounting for 30% of the volume of the nutrient salt solution into the nutrient salt solution, wherein the particle size of the porous ceramic particles is about 1 mm; 3) heating and evaporating the nutrient salt solution, and slowly stirring until the nutrient salt solution is evaporated to dryness to obtain porous ceramic particles containing nutrient salt; 4) collecting porous ceramic particles containing nutrient salt, placing the porous ceramic particles into hot-melted gelatin liquid for stirring and coating, adding wood fiber powder accounting for 5% of the mass of the gelatin liquid, and then fishing out the gelatin liquid and naturally drying in the shade to obtain the N/P nutrient particles.

Example 5

The present example is substantially the same as example 1, except that the N/P nutrient granules are different, specifically: the N/P nutrition additive of the N/P nutrition granules is derived from inorganic nutrient salt containing nitrogen and phosphorus, and the preparation method comprises the following steps: 1) dissolving inorganic nutrient salt containing nitrogen and phosphorus in warm water until insoluble substances appear to obtain nutrient salt solution; 2) then, putting porous ceramic particles accounting for 50% of the volume of the nutrient salt solution into the nutrient salt solution, wherein the particle size of the porous ceramic particles is about 1 mm; 3) heating and evaporating the nutrient salt solution, and slowly stirring until the nutrient salt solution is evaporated to dryness to obtain porous ceramic particles containing nutrient salt; 4) collecting porous ceramic particles containing nutrient salt, placing the porous ceramic particles into hot-melted gelatin liquid for stirring and coating, adding wood fiber powder accounting for 12% of the mass of the gelatin liquid, and then fishing out the gelatin liquid and naturally drying in the shade to obtain the N/P nutrient particles.

Example 6

This example is essentially the same as example 1, except that the environmentally friendly eluent is applied by the following method: the liquid-solid ratio of the environment-friendly eluent to the organochlorine pesticide polluted soil polluted by the DDTs is 5: 1, and the use conditions are as follows: and (3) carrying out elution treatment on the organochlorine pesticide polluted soil polluted by the DDTs at the rotating speed of 20rpm and the elution temperature of 45 ℃, and eluting for 2 times, wherein each elution is carried out for 50 min. The environment-friendly eluent and the organic chlorine pesticide polluted soil polluted by DDTs are subjected to ultrasonic strengthening in the elution treatment, wherein the ultrasonic strengthening of 25kH is used.

Example 7

This example is essentially the same as example 1, except that the environmentally friendly eluent is applied by the following method: the liquid-solid ratio of the environment-friendly eluent to the organochlorine pesticide polluted soil polluted by the DDTs is 15: 1, and the use conditions are as follows: and (3) carrying out elution treatment on the organochlorine pesticide polluted soil polluted by the DDTs at the rotating speed of 45rpm and the elution temperature of 60 ℃, and eluting for 4 times, wherein each elution time is 80 min. The environment-friendly eluent and the organic chlorine pesticide polluted soil polluted by DDTs are subjected to ultrasonic strengthening in the elution treatment, wherein the ultrasonic strengthening of 45kH is used.

Experimental exploration of environmentally friendly eluents

First, the repairing effect of the environment-friendly eluent in each embodiment is explored

The method comprises the following steps of selecting Liyang contaminated site soil as a restoration sample of each embodiment, and respectively carrying out experimental exploration on the following items:

1) explore the influence of different environment-friendly eluent ratios on soil remediation

The environmental friendly eluents provided in examples 1-3 were used as control eluents prepared by replacing N/P nutrient particles with the same amount of inorganic nutrient salts containing nitrogen and phosphorus based on example 1, and the results of soil remediation by each eluent are shown in Table 1 below,

table 1 results of the soil remediation efficiency of each eluent on contaminated site

	DDT removal Rate/%)	AWCD value after 12 weeks of culture
			Example 1	86	1.3
Example 2	86	1.15
			Example 3	67	1.25
Comparative example	85	0.9

And (4) conclusion: as can be seen from the results in table 1, by comparing examples 1 to 3 with the comparative example, the environment-friendly eluent in different ratios has a certain influence on the removal rate of DDT, while the removal rates of examples 1 and 2 are the same, but considering the cost factor, the cost of the peanut oil leftovers is far lower than the price of HPCD, so the scheme ratio of experimental example 1 is better, and meanwhile, the detailed description of the compounding effect of the cyclodextrin HPCD and the peanut oil leftovers is further demonstrated subsequently;

compared with the comparative example and the experimental example 1, the addition mode of only the N/P nutrient source is different, the DDT removal rate is not affected basically, but the soil recovery after the soil is cultured for 12 weeks is affected greatly, and probably because the N/P nutrient source part of the comparative example is less in soil remaining along with the water removal in the elution and remediation process.

2) Researches on influence of different N/P nutrition particle preparation methods on soil remediation

Eluents prepared from different N/P nutrient particles provided in examples 1, 4 and 5 were investigated only for their effect on the recovery ability of the soil after elution remediation, since the above investigation was conducted to verify that the nutrient source had no substantial effect on the removal rate of the contaminated soil, and the results of the remediation of the soil by each eluent are shown in table 2 below,

table 2 results of the soil remediation efficiency of each eluent for contaminated site

	AWCD value after 12 weeks of culture
		Example 1	1.3
Example 4	1.05
		Example 5	1.0

And (4) conclusion: as can be seen from the results of table 2 above, by comparing examples 4 and 5 with example 1, different addition amounts of the wood fiber powder have a greater effect on the use of the prepared N/P nutrient granules, which is likely to make it easier to satisfy the release of the nutrient source upon soil recovery after the elution remediation process due to the improved properties of the gelatin by the addition of the wood fiber powder.

3) Exploring the influence of the use parameters of different environment-friendly eluents on soil remediation

The sample soil is subjected to elution treatment according to different use parameters provided by example 1, example 6 and example 7, the effect of the soil remediation treatment under each use parameter is shown in the following table 3,

table 3 result table of soil remediation efficiency for contaminated site under each use parameter

	DDT removal Rate/%)
		Example 1	86
Example 6	64
		Example 7	88

And (4) conclusion: as can be seen from the results of table 3, by comparing examples 6 and 7 with example 1, different usage parameters of the eluent have certain influence on the soil remediation treatment, wherein the difference between the removal rate of example 6 and that of example 1 is large, and it may be that the removal rate is relatively low due to relatively insufficient elution, and the removal rate of example 7 is relatively high but almost no difference between that of example 1, so that the usage parameters of example 1 are relatively better in consideration of the treatment cost and other factors, and further demonstration is subsequently carried out on the influence of the application parameters on the soil remediation.

Secondly, the compounding effect of the cyclodextrin HPCD and the peanut oil leftovers is explored

The HPCD belongs to the field of environment-friendly novel eluents, so that the market price is relatively high at present, in order to try and explore the random interaction experiment (shown in table 4) of 3 concentrations of HPCD multiplied by 3 concentrations of peanut oil leftovers for reducing the dosage of the eluents and the input energy consumption cost while efficiently removing target pollutants, the formula of the compound eluents is screened and optimized under the conventional conditions.

Table 43 concentration HPCD x 3 concentration peanut oil leftover random interaction experimental design table

Note: the liquid-solid ratio is 10:1, 30rpm, stirring for 1 hour, and eluting at 25 ℃ at normal temperature.

FIG. 1 illustrates the removal efficiency of total DDTs and 4 homologues in soil of Wujiang polluted site by a compound interaction experiment of 3 concentrations of HPCD multiplied by 3 concentrations of peanut oil leftovers. The results show that the combination of HPCD with different concentrations and peanut oil leftovers has obvious promotion effect on the removal rate of DDTs and 4 homologues (p is less than 0.01).

The results of binary variance analysis of these two eluents are shown in table 4: the compounding experiment of the HPCD and the peanut oil leftovers has extremely obvious interaction on target pollutants (p <0.01), and the influence weight of the HPCD on the total DDTs removal rate is larger than that of the peanut oil leftovers on the DDTs removal rate (FHCD > F peanut oil leftovers, p < 0.01). Due to the strong water solubility of HPCD, the solubility of DDTs in the water phase is improved in the process of promoting DDTs to be desorbed from the soil particle solid phase to the eluent water phase; meanwhile, the added peanut oil leftovers provide an adsorption gradient which can promote pollutants to continuously migrate and accumulate from the water phase to the oil phase again, and finally the purposes of dissolution, coating and synergistic removal are achieved.

As can be seen from tables 4 and 5, the maximum removal rate of DDTs in total amount is about 92%, which occurs under the condition of compounding 100g/L HPCD + 10% peanut oil leftovers, but because the addition amounts of the two eluents are too high under the condition, the pollutants can not be efficiently removed in the research, and the requirement of reducing the dosage cost of the eluents is also taken into consideration, so that the formula is not suitable for application; and because the removal rate of total DDTs (DDTs removal rate) is not obviously different between the compound combination of 50g/L HPCD + 10% peanut oil leftovers and the compound combination of 100g/L HPCD + 5% peanut oil leftovers, namely about 86%, and the market price of HPCD is far higher than that of peanut oil leftovers by referring to the price of related eluent, the compound combination of 50g/L HPCD + 10% peanut oil leftovers is finally screened as the optimal selection under the conventional elution condition.

TABLE 5 binary analysis of variance the effect of HPCD and peanut oil leftovers on DDTs removal efficiency

Thirdly, exploring the application parameters of the environment-friendly eluent

(1) Effect of eluent concentration

When HPCD is selected as an eluent, the removal rate of DDTs in soil gradually rises as the concentration of HPCD gradually increases from 50g/L to 100 g/L; when the concentration of HPCD is 100g/L, the DDTs removal rate of Wujiang soil is the highest, and the total DDTs removal rate is about 63 percent; the maximum removal rate of p, p' -DDE is 72 percent; the maximum removal rate of p, p' -DDD is 65 percent; the maximum removal rate of o, p' -DDT is 61%; the maximum removal rate of p, p' -DDT is 58%. When the concentration of HPCD is gradually increased from 150g/L to 250g/L, the removal rate of DDTs is remarkably reduced (p < 0.01). The reason for this result is probably that in a certain concentration range, as the concentration of HPCD increases, the interfacial tension in the slurry system of the elution reaction gradually decreases, and the HPCD solution has good water phase solubilization capacity for DDTs, which can promote the removal rate of pollutants to be significantly increased; however, when the concentration of the HPCD solution rises to a certain limit value, the viscosity of the solution system sharply increases, and the effective desorption and release of pollutants from soil particles to a water phase are prevented, so that the removal rate does not rise or fall. Therefore, the concentration of HPCD used in the subsequent experiments was 100 g/L.

(2) Effect of elution time

Figure 2 illustrates the removal efficiency of total DDTs and 4 homologues in wujiang soil at different elution times for 7 particular concentrations of eluent (three fractions 10% petroleum ether, 10% peanut oil trim, 30% n-propanol, 50% ethanol, 100g/L HPCD). Analysis of the results from FIG. 2 yields: eluents of 7 specific concentrations all have similar laws on DDTs removal efficiency. Namely, the DDTs removal rate is gradually increased along with the increase of the elution time; when the elution time is in the stage of 0-60min, the removal rate of DDTs is rapidly increased; when the elution time was extended from 60min to 780min, the increase in DDTs removal rate was significantly slowed (p <0.01) and gradually leveled off.

In the process of soil ex-situ elution remediation, target pollutants are gradually desorbed and released from the surface or the interior of soil particles to an elution liquid phase along with the increase of elution time, and a substance distribution process is gradually carried out between solid and liquid, so that the removal rate of the pollutants tends to be stable when the distribution process of the pollutants is balanced again. In the research of the link, the elution efficiency factor and the running time cost factor are considered, and 60min is selected as the optimal parameter of the elution time.

(3) Influence of stirring speed

FIG. 3 illustrates the removal efficiency of total DDTs and 4 homologs from soil in Wu-Jiang contaminated site using 7 eluents (three fractions 10% petroleum ether, 10% peanut oil trim, 30% n-propanol, 50% ethanol, 100g/L HPCD) at different agitation speeds. It is readily seen that the removal rate of DDTs increases significantly (p <0.01) as the stirring speed is increased from 0rpm to 30 rpm; there was no significant change in DDTs removal (p <0.05) when the agitation speed was increased from 30rpm to 150 rpm. The test result shows that when the whole slurry reaction system is under the external force stirring intensity of 30rpm, the soil particles have more sufficient chances of dispersion, friction and collision in the eluent, and the target pollutants can be desorbed and released from the soil particles into the eluent phase more smoothly. Meanwhile, the electric energy power applied to the polluted site in the future and the actually available engineering stirring speed are considered. Therefore, 30rpm was selected as the optimum parameter for the stirring speed.

(4) Influence of liquid-solid ratio

Figure 4 illustrates the removal efficiency of total DDTs and 4 homologues in soil in wujiang contaminated site with 7 eluents (three fractions 10% petroleum ether, 10% peanut oil trim, 30% n-propanol, 50% ethanol, 100g/L HPCD) at different liquid-to-solid ratios. The total DDTs and 4 homolog removal rates also increased significantly with increasing liquid-to-solid ratio (p < 0.01); under the condition of fixed eluent concentration, the high liquid-solid ratio is favorable for the DDTs to be smoothly desorbed. For example, fig. 4 (a): when the liquid-solid ratio is 2: 1, the removal rate of DDTs by 50% ethanol, 30% n-propanol, 10% petroleum ether (30-60 ℃), 10% petroleum ether (60-90 ℃), 10% petroleum ether (90-120 ℃), 10% leftovers of peanut oil, 100g/L HPCD is respectively about: 27%, 31%, 30%, 25%, 28%, 25% and 33%; when the liquid-solid ratio is increased to 20:1, the removal rates of the total DDTs by the 7 eluents with specific concentrations are respectively about: 68%, 72%, 71%, 69%, 73%, 65% and 86%. Similar rules apply to the other 4 DDTs homologs.

Possible causes of the above result are: the high liquid-solid ratio is beneficial to the uniform dispersion of soil particles in a mud body system and the full contact with the eluent; and when the concentration of the eluent is fixed, the integral liquid-solid ratio is improved, namely, the actual adding amount of the eluent is increased, so that the removal of pollutants is obviously promoted. However, if only the elution efficiency factor is considered and an excessively high liquid-solid ratio is selected, on one hand, the cost of the added amount of the eluent is increased, and on the other hand, higher requirements are provided for designing and manufacturing the cavity of the elution equipment in the future. Considering both the elution efficiency factor and the operation cost factor, when the liquid-solid ratio is 10:1, the removal rate of the total DDTs by the 7 eluents with specific concentrations can reach over 50 percent, and the operation cost is relatively moderate. Therefore, the liquid-solid ratio of 10:1 is selected as the optimal parameter.

(5) Influence of temperature

FIG. 5 illustrates the removal efficiency of total DDTs and 4 homologs from soil in Wu-Jiang contaminated site using 7 eluents (three fractions 10% petroleum ether, 10% peanut oil trim, 30% n-propanol, 50% ethanol, 100g/L HPCD) at different temperatures. It can be found that, for 50% ethanol and 30% n-propanol, as the temperature gradually rises from 25 ℃ to 70 ℃, the removal rates of the total DDTs are respectively increased by 59%, 56% and 92%, 97% (p is less than 0.01), which indicates that the distribution coefficient of the pollutants on a solid-liquid interface can be reduced in the temperature rising process, and the elution reaction is favorably carried out towards the direction of improving the removal efficiency; for 10% petroleum ether (30-60 ℃), the total DDTs removal rate is remarkably reduced from 56% to 25% (p is less than 0.01) along with the gradual increase of the temperature from 25 ℃ to 70 ℃, which is probably caused by the fact that the effective components of the eluent are volatilized in large quantities at the water bath temperature of 25 ℃ to 70 ℃ due to the fact that the fraction is 30-60 ℃ petroleum ether, and the removal efficiency of target pollutants is low.

For 10% petroleum ether (60-90 ℃), the total DDTs removal rate is remarkably increased from 52% to 81% (p <0.01) along with the gradual increase of the temperature from 25 ℃ to 50 ℃, and the total DDTs removal rate is remarkably decreased from 81% to 63% (p <0.01) when the temperature is continuously and gradually increased from 50 ℃ to 70 ℃, the reason for the phenomenon is probably that molecular motion, friction and collision in a slurry system are gradually more severe at the water bath temperature of 25 ℃ to 50 ℃, pollutants are easier to desorb and release into an eluent water phase along with the increase of the temperature, and the distillate is 60-90 ℃ petroleum ether under the temperature condition, a large amount of effective components of an eluent are not volatilized yet, so the removal rate is remarkably increased (p <0.01), but the petroleum ether at 60-90 ℃ also has large volatilization loss along with the gradual increase of the temperature to 70 ℃, the removal rate does not rise or fall inversely. For 10% petroleum ether (90-120 ℃), the total DDTs removal rate is remarkably increased from 52% to 70% (p is less than 0.01) along with the gradual increase of the temperature from 25 ℃ to 70 ℃, and the temperature increase process is also beneficial to the synergistic removal of pollutants; for 10% of the peanut oil leftovers, the total DDTs removal rate is remarkably increased from 49% to 81% (p is less than 0.01) along with the gradual increase of the temperature from 25 ℃ to 70 ℃, and the boiling point of the peanut oil is generally higher than 200 ℃, so that the temperature rise process set by the research is also favorable for improving the removal efficiency of pollutants; for 100g/L HPCD, the total DDTs removal rate is remarkably increased from 63% to 88% (p is less than 0.01) along with the gradual increase of the temperature from 25 ℃ to 70 ℃, and the temperature rise process plays a positive role in the efficient removal of pollutants.

From the aspect of elution efficiency, under the condition of 50 ℃, 50 percent of ethanol, 30 percent of n-propanol, 10 percent of petroleum ether (60-90 ℃), 10 percent of petroleum ether (90-120 ℃), 10 percent of peanut oil leftovers and 100g/L of HPCD have remarkable synergistic results on the total amount of DDTs and the removal rate of 4 pollutant homologues. Meanwhile, the overall cost of elution repair is increased due to too high energy input, so that the temperature of 50 ℃ is finally used as a temperature parameter for subsequent research.

In addition, considering the price of the relevant eluent and analyzing the cost factor of the eluent, the cost price of 30 percent of n-propanol as the eluent is obviously lower than 50 percent of ethanol; although the removal of pollutants is obviously promoted by 10% petroleum ether (90-120 ℃) in the temperature rise process of 25-70 ℃, the removal effect of 10% petroleum ether (90-120 ℃) as an eluent is lower than that of 10% petroleum ether (60-90 ℃) and the potential recovery difficulty of petroleum ether (90-120 ℃) is higher than that of petroleum ether (60-90 ℃), so that in the research of the link, 4 eluents, namely 30% n-propanol, 10% petroleum ether (90-120 ℃), 10% peanut oil leftovers and 100g/L HPCD, are further screened as the eluents of the subsequent experiments.

(6) Influence of ultrasonic coupling

FIG. 6 illustrates the removal efficiency of total DDTs and 4 homologues in soil of Wujiang polluted site by 4 eluents under the condition of ultrasonic 30min by embedding a 35kHz ultrasonic transmitter in a slurry system. The removal rates of 4 eluents of specific concentrations were significantly improved by 22%, 14%, 13% and 9% (p <0.01) for the total amount of DDTs by 30% n-propanol, 10% petroleum ether (60-90 ℃), 10% peanut oil leftovers and 100g/L HPCD after chimerization compared to normal temperature processing conditions. The cavitation effect, high radiation pressure, sound microflow and other effects generated under the ultrasonic condition are utilized to reduce the tight combination degree of the pollutants and the soil particles and promote the desorption of the pollutants in the soil particles from a solid phase to a soil water phase, thereby enhancing the elution efficiency. It was also found in the figure that the maximum removal efficiency of contaminants was achieved using both the elevated temperature process and the treatment conditions of the embedded ultrasonic emission, with 30% n-propanol, 10% petroleum ether (60-90 ℃), 10% peanut oil offal, and 100g/L HPCD removal rates of about 97%, 89%, 83%, and 95% for the total DDTs, respectively. Similar rules apply to the other 4 DDTs homologs in the figure.

In addition, the influence of the temperature factor and the ultrasonic factor on the removal efficiency of the DDTs is analyzed through the binary variance shown in Table 6, and the weight effect of the applied temperature factor on the increase of the removal rate of the total DDTs is found to be significantly larger than the weight effect of the chimeric ultrasonic factor on the increase of the removal rate of the total DDTs (F temperature > F ultrasonic, p < 0.01); the simultaneous embedding of the temperature rise process and the ultrasonic emission process has extremely remarkable synergistic effect on the total amount of DDTs (F temperature x F ultrasonic is 101 +/-13, and p is less than 0.01). This result demonstrates that the simultaneous application of these 2 exogenous enhancements does contribute to the synergistic removal of contaminants.

TABLE 6 analysis of the Effect of temperature factors and ultrasound factors on DDTs removal efficiency by binary variance

(7) Effect of elution number

The screened 50g/L HPCD + 10% peanut oil leftover formula is selected as an eluent, and the Liyang contaminated site soil is continuously eluted for 5 times under the conditions of a liquid-solid ratio of 10:1, elution time of 1h, a stirring rotation speed of 30rpm and normal temperature of 25 ℃. And (3) carrying out desorption research on the soil after each elution by using a Tenax-TA resin time continuous extraction method.

Liyang contaminated soil removal efficiency of surface 750 g/L HPCD + 10% peanut oil leftovers under conventional conditions

As can be seen from Table 7, the single removal rate of the total amount of OCPs was about 55%, and the single removal rate of the 8 organochlorine pesticides was 52-81%. After the continuous elution method is adopted for elution, the removal rate of the OCPs in the soil is gradually increased, when the continuous elution is carried out for 5 times, the maximum removal rate of the total amount of the OCPs is about 86 percent, the maximum removal rate of the 8 organochlorine pesticides is about 79-94 percent, but after the continuous elution is carried out for 3 times, the removal rate of the OCPs in the soil is not obviously increased (p is more than 0.05).

FIG. 7 shows the desorption kinetics of various contaminants after different elution times, and it can be seen from FIG. 7 that about 20%, 27%, 17% and 12% of the total amount of OCPs, DDTs, Chlordanes and Mirex in the original Liyang soil sample can be extracted by Tenax resin during desorption within 400 h. However, the total amount of residual OCPs, DDTs, chlorends and Mirex desorbable extract in suzhou soils decreased significantly (p <0.01) as the number of consecutive elutions increased from 1 to 3 (p >0.05), and no significant change in total amount of residual OCPs, DDTs, chlorends and Mirex desorbable extract occurred after 3 consecutive elutions.

The analytic kinetic parameters of each pollutant in the soil after different elution times can be calculated through a three-section model. As can be seen from Table 7, F for the total amount of OCPs before elution_rAnd F_slThe sum of the proportions is about 17% of the total amount, but F is gradually increased from 1 to 3 times with continuous elution_rAnd F_slThe sum of the proportions is reduced to 2% of the total amount, F_vlThe ratio of the total amount of the elution reagent is increased to about 98 percent, and after 3 times of continuous elution, F_vlThe proportion has no significant change (p)>0.05) with similar laws for DDTs, chlorends and Mirex (table 8); furthermore, as the number of continuous elution increases, k of OCPs in the soil after remediation_r、k_slAnd k_vlRespectively, the desorption rate constant is also significantly reduced (p) compared to the corresponding desorption rate constant in the original soil<0.01). After 3 elutions, the total amount of OCPs F_vlThe component desorption rate constant has already been derived from the initial k_vlDecrease to k when 2.71X 10-5_vlThe result is that after 3 times of continuous elution, the ultra-slow desorption component OCPs which are the main component in the soil exist in the glassy organic matter of the soil and inside the granules with submicron and nanometer pores in a very tight combination form, and the time required for the part of the 'locked' OCPs to be completely released to the water phase of the soil again is quite long if no strong external physical, chemical and biological interference exists. By comprehensively considering the elution effect and the desorption kinetic parameters, the potential risk that residual OCPs in the soil are desorbed into the soil environment again after the formula is continuously eluted for 3 times can be considered to be remarkably reduced (p)<0.01). Therefore, the corresponding elution removal rate of 3 times of continuous elution can be used as the Liyang soil remediation terminal, namely the removal rate of the total OCPs needs to be about 82% of the total amount; the removal rate of the chlordane and the mirex is about 80 percent of the total amount.

TABLE 8 three-phase desorption parameters of OCPs in Liyang field soil after different elution times

Note: fr, Fsl and Fvl represent a fast desorbing component, a slow desorbing component and a non-desorbing component, respectively.

In conclusion, we found that, as the number of continuous elution times was gradually increased, the sum of the proportion of the fast-desorbing component of OCPs and the proportion of the slow-desorbing component of OCPs in the contaminated soil was also gradually decreased, while the proportion of the ultra-slow-desorbing component of OCPs was significantly increased (p < 0.01). Meanwhile, with the gradual increase of the continuous elution times, the rapid component desorption rate constant, the slow component desorption rate constant and the ultra-slow component desorption rate constant of the OCPs remained in the soil are all obviously reduced (p is less than 0.01). When the proportion of the ultra-slow desorption components of the OCPs in the soil is increased to 98 percent of the total residual amount of the OCPs in the soil, the proportion of the ultra-slow desorption components of the OCPs is not changed significantly any more with the increase of the continuous elution times (p is more than 0.01). Meanwhile, the calculation is carried out according to the desorption rate constant of the OCPs ultra-slow desorption components, and under the combined action of strong external physical chemistry and biology, the OCPs ultra-slow desorption components can be completely desorbed to the soil water phase after more than 1000 years. Then, the potential secondary risk of re-desorbing the OCPs remaining in the soil to the environment at this time has been greatly reduced.

Therefore, the repair end point can be judged according to the change conditions of the proportion of the ultra-slow desorption components of the OCPs in the soil and the desorption rate constant of the ultra-slow desorption components of the OCPs along with the continuous elution times. The technology can reduce the judgment error caused by different OCPs pollution field types according to the desorption equilibrium distribution principle of the OCPs in the aged soil in the soil particle phase, the soil water phase and the resin phase, and has simple and convenient operation and higher broad spectrum. Can provide scientific reference basis for the optimization management of the actual soil ectopic elution remediation technology in China.

Fourthly, researching the biological evaluation of the soil after elution by the environment-friendly eluent

Evaluation of the change of the Liyang field soil microbial community before and after elution is performed by using a BIOLOG plate analysis method. FIG. 8 illustrates how the change of the index of diversity of ecological functions of soil microorganisms after constant temperature cultivation for 12 weeks is achieved by adding appropriate N/P nutrient source to Liyang soil which is obtained by continuously eluting 3 times by using 50g/L HPCD + 10% peanut oil leftovers as eluent under the conditions of normal temperature of 25 ℃, liquid-solid ratio of 10:1, stirring speed of 30rpm and stirring for 1h

The average color change rate AWCD value reflects an indication of the amount of capacity of the culturable microbial community in the soil to utilize a sole carbon source or an indication of the strength of activity of the culturable microbial community in the soil. From fig. 8(a), it is clear that when the site soil contaminated with lithium was eluted 3 times consecutively, its AWCD value was significantly lower than that of the original site soil contaminated with lithium (p < 0.01). The method is characterized in that the target pollutants are obviously removed after the Liyang polluted soil is continuously eluted for 3 times, but part of soil organic matters, mineral elements or some nutrient elements suitable for the growth of microorganisms in the Liyang polluted soil can be removed together, so that the utilization capacity of the culturable microbial community in the Liyang polluted soil after 3 times of elution to a unique carbon source is reduced, and the activity of the culturable microbial community is gradually weakened. On the other hand, the Liyang soil after 3 times of elution was added with an appropriate N/P nutrient source, and after 12 weeks of incubation at constant temperature, the AWCD value was monitored and found to be significantly increased (P < 0.01). Indicating that the activity of the microbial community in the Liyang soil was restored to some extent under such treatment conditions.

The Shannon-Weaver index reflects the actual abundance and uniformity of microbial communities in the soil. The Simpson index reflects the number of relative populations. As can be seen from FIG. 8, when the Liyang contaminated soil was eluted 3 times consecutively, its Shannon-Weaver index value was significantly lower than the original Liyang soil AWCD value (p < 0.01). The method is characterized in that after the Liyang polluted soil is continuously eluted for the first 3 times, the original microbial community in the soil is possibly dissolved and wrapped by the eluent to remove a part of the microbial community, and the relative balance of a microbial ecosystem in the original soil is broken through. This resulted in a gradual decrease in the actual abundance, uniformity and relative population numbers of the microbial community in the Liyang soil after 3 elutions. After the Liyang contaminated soil after 3 times of elution is added with a proper N/P nutrient source and cultured for 12 weeks at constant temperature, the change of the Shannon-Weaver index value is monitored, and the obvious increase is found (P is less than 0.01). The abundance and the uniformity of the microbial community in the Liyang polluted soil are shown, and the recovery and the promotion are achieved to a certain degree under the treatment conditions.

Claims

1. The environment-friendly eluent for restoring the organochlorine pesticide-contaminated soil is characterized by being prepared by taking water as a base liquid, and adding 50-100 g/L of a biosurfactant, 5-10% of peanut oil leftovers and 3-5% of N/P nutrient particles.

2. The environment-friendly eluent for remediating organochlorine pesticide-contaminated soil as recited in claim 1, wherein the biosurfactant is a cyclodextrin HPCD biosurfactant.

3. The environment-friendly eluent for remedying the soil polluted by the organic chlorine pesticide as claimed in claim 2, wherein the addition amount of the cyclodextrin HPCD biosurfactant and the peanut oil leftovers in the environment-friendly eluent is as follows: 50g/L of biosurfactant and 10 percent of peanut oil leftovers by mass fraction.

4. The environment-friendly eluent for remedying the organochlorine pesticide-contaminated soil according to claim 1, wherein the N/P nutrient additive source of the N/P nutrient particles is from inorganic nutrient salts containing nitrogen and phosphorus, and the preparation method comprises the following steps:

5. The environment-friendly eluent for remediating organochlorine pesticide-contaminated soil as recited in claim 1, wherein the environment-friendly eluent is mainly suitable for organochlorine pesticide-contaminated soil contaminated with DDTs.

6. The environment-friendly eluent for remediating organochlorine pesticide-contaminated soil as claimed in claim 5, wherein the liquid-solid ratio of the environment-friendly eluent to the organochlorine pesticide-contaminated soil contaminated with DDTs is 5-15: 1, and the use conditions are as follows: and (3) eluting the organochlorine pesticide polluted soil polluted by the DDTs at the rotating speed of 20-45 rpm and the elution temperature of 45-60 ℃, wherein the elution is carried out for 2-4 times, and each time of elution is 50-80 min.

7. The environment-friendly eluent for remediating organochlorine pesticide-contaminated soil as claimed in claim 6, wherein the environment-friendly eluent further performs an ultrasonic strengthening effect in the elution treatment of the organochlorine pesticide-contaminated soil contaminated with DDTs, wherein the ultrasonic strengthening effect is 25-45 kH.

8. The environment-friendly eluent for remediating organochlorine pesticide-contaminated soil as claimed in claim 1, wherein the organochlorine pesticide-contaminated soil is mainly organochlorine pesticide-contaminated soil contaminated with DDTs.

9. The method for preparing the environment-friendly eluent for remediating the organochlorine pesticide-contaminated soil as set forth in claim 1, which comprises the following steps:

10. The method for preparing the environment-friendly eluent for remediating the soil contaminated by the organochlorine pesticide as claimed in claim 9, wherein the preservation temperature of the solution A is not higher than 35 ℃, and the environment-friendly eluent is suitable for being prepared.