CN112342025A

CN112342025A - Compost composite modifier for Pb-polluted soil passivation remediation, method and application

Info

Publication number: CN112342025A
Application number: CN202011080438.7A
Authority: CN
Inventors: 田光明; 曾凡健; 王凯迪; 高毛; 徐欣韵
Original assignee: Zhejiang University ZJU
Current assignee: Zhejiang University ZJU
Priority date: 2020-10-10
Filing date: 2020-10-10
Publication date: 2021-02-09

Abstract

The invention discloses a compost composite modifier for Pb-polluted soil passivation and restoration, and a method and application thereof. The preparation steps of the organic fertilizer are as follows: firstly, properly air-drying the aerobic fermentation finished fertilizer, crushing the aerobic fermentation finished fertilizer to 20 meshes for later use, then adding a certain amount of lime and calcium magnesium phosphate fertilizer, fully mixing the mixture, and applying the mixture into polluted soil according to a certain proportion. The method has rich compost resources, so the raw materials of the method are low in price, the operation steps are simple and easy to implement, the method is favorable for large-scale popularization, and the condition of heavy metal micro-pollution in agricultural lands in China is met. The invention not only has good passivation effect on heavy metal Pb in soil, but also can improve the physical and chemical properties of the soil, increase the soil fertility, improve the crop yield, increase the added value of compost and be beneficial to solving the resource problem of compost products in China.

Description

Compost composite modifier for Pb-polluted soil passivation remediation, method and application

Technical Field

The invention belongs to the technical field of soil improvement, and particularly relates to a compost composite improver for passivating and restoring Pb-polluted soil, and a method and application thereof.

Background

The soil heavy metal pollution refers to the phenomenon that heavy metal elements in soil exceed the soil background value and the soil environment quality standard and threaten the production and life of people due to human activities or natural factors.

The compost refers to organic compost prepared by processing livestock and poultry manure, straws, solid wastes of agricultural and sideline products and food processing, organic garbage, municipal sludge and the like after microbial fermentation, deodorization and decomposition. The compost returning is one of compost recycling ways, and researches show that the compost which is applied to soil and is thoroughly decomposed is rich in humus with rich nutrition, so that the activity of heavy metal of the compost can be reduced, the compost can be used as a curing agent for repairing the heavy metal pollution of the soil, the physicochemical property of the soil can be improved while the activity of the heavy metal of the polluted soil is reduced, and the soil fertility is increased.

As a big country of livestock and poultry breeding and agriculture in the world, the resources of livestock and poultry manure and straws in China are particularly rich and tend to increase year by year. Composting is one of the effective ways to treat organic waste. If the compost is used as a passivation material for passivating and restoring the Pb pollution of the soil, the compost not only can passivate and restore the Pb pollution of the soil, but also can provide nutrition for the soil, improve the physicochemical property of the soil, simultaneously can consume excessive agricultural wastes, and has double meanings of waste utilization and ecological restoration.

However, it has also been found that the application of compost to soil increases the heavy metal content of the soil and enhances the migration, bioavailability and phytotoxicity of the heavy metals. Meanwhile, the use of compost as a passivating agent is limited due to the low quality, complex components and low passivation efficiency of compost products.

Therefore, it is highly desirable to provide a compost improver for Pb-contaminated soil.

Disclosure of Invention

Aiming at the existing problems, the invention considers that other heavy metal passivation materials are added on the basis of the existing compost product to develop a high-efficiency and durable composite modifier, and provides a compost composite modifier for Pb-polluted soil passivation and restoration, a method and application thereof, so as to achieve the purposes of improving soil fertility and increasing crop yield.

The invention adopts the following specific technical scheme:

the invention aims to provide a compost composite modifier for passivating and restoring Pb-polluted soil, which comprises 74-87% of compost products, 5-10% of lime and 8-16% of calcium magnesium phosphate fertilizer in percentage by mass.

Preferably, the compost product is obtained by composting chicken manure.

Preferably, the compost product is formed by mixing and composting 50% of chicken manure and 50% of wood dust respectively in percentage by mass.

Furthermore, the mass of organic matters in the compost product calculated by a drying base accounts for more than 50%, the mass of total nutrients in the compost product calculated by the drying base accounts for more than 5%, the mass of water accounts for 15-20%, and the pH value is 6-7.

Further, the total nutrient comprises nitrogen, phosphorus pentoxide and potassium oxide, and the mass ratio of N, P to K in the total nutrient on a drying basis is not less than 2%.

Preferably, the mass ratio of CaO in the lime is more than 90%, and the mass ratio of P in the calcium magnesium phosphate fertilizer is more than 12%.

The second purpose of the invention is to provide a preparation method of the compost composite improver, which comprises the following steps:

naturally drying the compost product under the condition of avoiding insolation, then crushing and sieving, uniformly mixing the compost product, lime and calcium-magnesia phosphate fertilizer according to the mass ratio of 74-87%, 5-10% and 8-16%, and stabilizing for 2-3 days at room temperature to obtain the compost composite modifier.

Preferably, the natural air drying refers to that the compost product is placed in a shade for natural air drying until the moisture content of the compost product is 15-20% by mass.

Preferably, the sieving means sieving with a 20-mesh sieve.

The third purpose of the invention is to provide an application of the compost composite modifier in passivation restoration of Pb-polluted soil, which specifically comprises the following steps:

adding the compost composite modifier into soil to be restored, and uniformly mixing; the mass of the added compost composite modifier is 2.5-10% of the mass of the soil to be repaired on a dry basis.

Compared with the prior art, the invention has the following beneficial effects:

1) the raw materials used by the method are wide in source and easy to obtain, low in price, convenient to operate, capable of realizing large-scale production and suitable for most of Pb micro-polluted farmland soil.

2) The invention combines the compost product with lime and calcium magnesium phosphate fertilizer, has the passivation effect of organic and inorganic passivators, and can ensure that the passivation effect is more efficient, more stable and more durable.

3) The invention is an improvement on the basis of compost products, can improve the soil fertility, improve the physicochemical property of the soil and improve the yield of crops while repairing the Pb-polluted soil, and particularly has more obvious effect on slightly-polluted barren soil.

4) According to the invention, chicken manure compost is adopted, and the pH value of the obtained compost composite modifier is close to the background value of soil, so that the soil is less disturbed after the compost composite modifier is added into the soil.

5) Aiming at Pb micro-polluted farmland soil, the invention combines compost products with other passivation materials, provides a high-efficiency compound modifying agent based on compost, can obviously reduce the activity of heavy metal Pb in soil, and reduces the influence of Pb on the growth of crops.

Drawings

FIG. 1 is a graph showing the content of available Pb in the treated soil and the passivation efficiency thereof with respect to a blank control in each of the indoor culture experiments in example 2; in the figure, CK, CC, L, F and CLF respectively represent a blank control, chicken manure compost, lime, calcium magnesium phosphate fertilizer and a compound modifier, a to E represent significant differences (P <0.05), and E represents a passivation rate;

FIG. 2 is a graph showing the appearance of Pb in the soil treated in each of the indoor culture experiments of example 2; in the figure, F1 to F4 respectively represent an acid extractable state, a reducible state, an oxidizable state and a residual state of heavy metal Pb;

FIG. 3 shows the fresh weight of the aerial parts of each processed pakchoi in the pot cultivation experiment of example 3;

FIG. 4 shows the Pb content in the aerial parts of the processed pakchoi and the decrease in Pb content (in fresh weight) from the blank control group in the potting experiment in example 3.

Detailed Description

The invention will be further elucidated and described with reference to the drawings and the detailed description. The technical features of the embodiments of the present invention can be combined correspondingly without mutual conflict.

Example 1

The soil to be tested is paddy soil, the surface layer (0-20 cm) of an experiment base in the region of Hangzhou city, Hangzhou, Zhejiang is adopted, large-particle impurities are removed, the soil is naturally dried and ground, and the soil is sieved by a sieve of 10 meshes and stored for later use, so that clean soil is obtained. According to the risk control value of lead in the soil environment quality agricultural land soil risk control standard (GB 15618-2018), adding Pb (NO3)₂Adding the solution into the soil for contamination, adding water until the water capacity of the soil is 70% of the field capacity, stably aging for three months at room temperature, air-drying, grinding, sieving with a 10-mesh sieve, and storing for later use to obtain contaminated soil. The basic physicochemical properties of the contaminated soil are shown in Table 1.

TABLE 1 basic physicochemical Properties of contaminated soil

Preparing a compost composite modifier as follows:

and (3) placing the chicken manure compost product after aerobic fermentation in a shade place for natural air drying until the water mass ratio of the compost product is 15-20% (facilitating crushing and grinding), and then crushing and sieving by a 20-mesh sieve to obtain a standby compost product. Wherein, the chicken manure compost product is formed by mixing and composting 50% of chicken manure and 50% of wood dust respectively by mass. The mass of organic matters in the compost product calculated on a drying basis is more than 50%, the mass of total nutrients in the compost product calculated on the drying basis is more than 5%, the mass of water is 15-20%, and the pH value is 6-7. In addition, the total nutrient comprises nitrogen, phosphorus pentoxide and potassium oxide, and the mass ratio of N, P and K in the total nutrient on a drying basis is not less than 2%.

Fully and uniformly mixing the standby compost product, lime (the mass ratio of CaO is more than 90%) and calcium magnesium phosphate (the mass ratio of P is more than 12%) according to the mass ratio of 87%, 5% and 8%, and stabilizing for 3 days at room temperature to obtain the compost composite modifier.

Example 2

In this example, the contaminated soil and compost composite modifier in example 1 were used for indoor culture tests, which were as follows:

200g of polluted soil is taken and added into a culture tank, and then the compost composite modifier is taken and added into the culture tank according to the proportion of 5 percent of the soil (dry basis) and is fully mixed with the polluted soil. And then deionized water is added by adopting a weighing method, so that the water content of the soil is kept at 70% of the field water capacity. Sealing with plastic wrap film with several small holes, culturing at 25 + -2 deg.C for 30 days, air drying the soil sample, grinding, and sieving. And (4) determining the content and occurrence form of the available Pb in the soil sample. This experimental group was designated as CLF.

At the same time, one blank and three control experiments were performed. The blank control group (CK) was performed as above, but no compost compound improver was added to the contaminated soil; the procedure of the three comparative groups is the same as above, but the chicken manure compost product, lime and calcium magnesium phosphate fertilizer are respectively added into the polluted soil instead of the compost compound modifier. The three control groups are respectively marked as CC (chicken manure compost product is added), L (lime is added) and F (calcium magnesium phosphate fertilizer is added). Wherein the chicken manure compost product, the lime and the calcium magnesium phosphate fertilizer are the same products used in example 1.

As can be seen from FIG. 1, the content of available Pb in CK soil is 306.52mg/kg, which is significantly lower than that of CK in the other groups of soils. Wherein the soil available Pb content of CLF is lowest, 176.64mg/kg, and the passivation rate is 42.37%; 11.89% higher than CC, 19.68% higher than L and 16.35% higher than F. Therefore, compared with a single material, the composite modifier has higher Pb passivation performance.

As can be seen from fig. 2, Pb in the soil exists mainly in a reducible state (71.83%) without adding any material (i.e., CK). After the compound modifier is added, the Pb in the soil in an acid extractable state and a reducible state is obviously reduced, and the Pb in an oxidizable state and a residue state is obviously improved. Compared with CC, the acid extractable Pb and the reducible Pb of the CLF are respectively reduced by 1.35 percent and 2.19 percent, and the acid extractable Pb and the reduced Pb of the CLF are respectively improved by 1.54 percent and 1.99 percent, which shows that the passivation of the compost on Pb can be more stable due to the addition of lime and calcium magnesium phosphate fertilizer.

Example 3

In this example, the contaminated soil and the compost composite modifier in example 1 were used for potting experiments, which were as follows:

after the polluted soil is diluted by one time by clean soil (namely the polluted soil is mixed with the clean soil in a ratio of 1: 1), the prepared composite modifier (5 percent of the polluted soil in terms of dry basis) is added into 1000g of the polluted soil and fully mixed. Placing in a pot, adding water (70% of field water capacity of the soil), and standing for 3 days to fully wet the soil. Then, 5 small holes (the depth is about 1cm) are dug in the surface layer of each pot of soil by a 5-point method, 2-3 Chinese cabbage seeds which are subjected to pregermination in advance are sown in each small hole, soil is added for covering, and a small amount of water is used for wetting. The pot plants were placed in a greenhouse for cultivation, and the soil was kept moist by weighing each day (70% of the field capacity of the soil). Thinning after the seedling emergence of the Chinese cabbage (about 14 days), reserving 5 plants (one plant at each point) in each pot, culturing for 30 days, and harvesting. The fresh weight of the overground part of the pakchoi and the content of Pb in the overground part tissue (calculated by the fresh weight) are measured. This experimental group was designated as CLF.

At the same time, one blank and three control experiments were performed. The blank control group (CK) was performed as above, but no compost improver was added; the procedure of the three comparative groups is the same as above, but the chicken manure compost product, lime and calcium magnesium phosphate fertilizer are respectively added instead of the compost compound modifier. The three control groups are respectively marked as CC (chicken manure compost product is added), L (lime is added) and F (calcium magnesium phosphate fertilizer is added). Wherein the chicken manure compost product, the lime and the calcium magnesium phosphate fertilizer are the same products used in example 1.

As can be seen from FIG. 3, the fresh weights of the overground parts of the pakchoi of the experimental group and the comparative group are obviously higher than those of the control group, and the fresh weights of the overground parts of the pakchoi of the CC and CLF groups added with compost products are higher, so that the abundant nutrition in the compost improves the yield of the pakchoi. Meanwhile, compared with CC, the fresh weight of the overground part of the CLF pakchoi is reduced by 21.94 percent, which indicates that the compost product of the compound lime and the calcium magnesium phosphate fertilizer has a certain inhibition effect on the growth of the pakchoi, but is still obviously higher than CK, L and F.

As can be seen from FIG. 4, the Pb content of the aerial parts of the pakchoi in the control group was 0.349 mg/kg. Compared with the control group, the Pb content of the overground part of the pakchoi of the other groups is obviously reduced, wherein the CLF content is the lowest and is 0.092mg/kg, compared with the control group, the CLF content is reduced by 73.65%, the reduction amplitude is higher than that of CC by 18.33%, compared with L by 28.24% and is higher than that of F by 27.21%. Therefore, the composite modifier can obviously reduce the Pb content of the overground part of the pakchoi and reduce the absorption of the lost Pb of the pakchoi, and the performance of the composite modifier is superior to that of any single material.

Example 4

This example prepared three comparative improvers A1, A2 and A3, all prepared in the same manner as the compost improver A0 of example 1. However, A1 is obtained by fully mixing the ready-to-use compost product with lime, A2 is obtained by fully mixing the ready-to-use compost product with calcium magnesium phosphate, and A3 is obtained by fully mixing the lime with the calcium magnesium phosphate. Wherein, the mass ratio of the standby compost products used in A1, A2 and A3, lime and calcium magnesium phosphate fertilizer is the same as that of A0, and the shortage part is replaced by clean soil.

200g of the contaminated soil of example 1 was taken and added to four culture pots, respectively, and then A0, A1, A2 and A3 were added to the culture pots, respectively, in a proportion of 5% of the soil (dry basis), to each culture pot, and mixed well with the contaminated soil. And then deionized water is added by adopting a weighing method, so that the water content of the soil is kept at 70% of the field water capacity. Sealing with plastic wrap film with several small holes, culturing at 25 + -2 deg.C for 30 days, air drying the soil sample, grinding, and sieving. The content of available Pb in each soil sample was measured, and the results are shown in table 2:

TABLE 2 content of available Pb in soil and passivation rate of amendment

Note: the available Pb data in the table are mean ± sd (n ═ 3), and different lower case letters in the same column indicate significant difference (P <0.05), and the same is as below

As shown in Table 2, after 4 conditioners A0, A1, A2 and A3 are respectively added into the polluted soil, the content of the available Pb in the soil is remarkably reduced, wherein the content of the available Pb in the soil added with A0 is the lowest and is only 182.86mg/kg, and the passivation rate of A0 is the highest and is 41.18%. It can be seen that the passivation effect of the modifier compounded by three materials (A0) is far better than that of the modifier compounded by two materials (A1, A2 and A3).

After the contaminated soil was diluted one time with clean soil (i.e., contaminated soil was mixed with clean soil at 1: 1), a0, a1, a2 and A3 (5% of contaminated soil on a dry basis) were added to four groups of 1000g of contaminated soil, respectively, and mixed thoroughly. Placing in a pot, adding water (70% of field water capacity of the soil), and standing for 3 days to fully wet the soil. Then, 5 small holes (the depth is about 1cm) are dug in the surface layer of each pot of soil by a 5-point method, 2-3 Chinese cabbage seeds which are subjected to pregermination in advance are sown in each small hole, soil is added for covering, and a small amount of water is used for wetting. The pot plants were placed in a greenhouse for cultivation, and the soil was kept moist by weighing each day (70% of the field capacity of the soil). Thinning after the seedling emergence of the Chinese cabbage (about 14 days), reserving 5 plants (one plant at each point) in each pot, culturing for 30 days, and harvesting. The Pb content (in terms of fresh weight) of the overground part tissues of the pakchoi is respectively measured. The results are shown in Table 3:

TABLE 3 Pb content and relative reduction of the same in the aerial parts of pakchoi

Note: the Pb content of overground part of the Chinese cabbage in the table is calculated by fresh weight

As can be seen from Table 3, the Pb content of the overground part of the pakchoi was significantly reduced by adding 4 kinds of the improving agents A0, A1, A2 and A3 to the contaminated soil, respectively, as compared with the control group. The Pb content of the overground parts of the pakchoi among A1, A2 and A3 is not obviously different, and A0 is greatly different from A1, A2 and A3, so that the reduction range of the pakchoi is the largest compared with a control group. Therefore, compared with the modifier compounded by two or more of the three materials of the compost, the lime and the calcium-magnesia phosphate fertilizer, the modifier compounded by two or more of the three materials has more obvious effect of inhibiting the celery cabbage from absorbing Pb.

Therefore, the invention combines the compost product with lime and calcium magnesium phosphate fertilizer, and has the passivation mechanism of organic and inorganic passivators, which is as follows: the compost product of the invention can adsorb and fix Pb by complexation/chelation²⁺(ii) a Lime can increase the pH value of soil and induce the formation of hydroxide or carbonate combined-state precipitate or coprecipitation; the calcium magnesium phosphate fertilizer can provide P element for soil and can form lead phosphate ore compounds such as phosphorus-chlorine-lead ore and the like with Pb. However, due to the complexity of the ingredients of the compost product, the compost product inevitably contains a part of small molecular organic acids which are mixed with Pb²⁺In combination, the mobility of Pb is enhanced. The addition of lime and calcium magnesium phosphate can neutralize the small molecular organic acid and reduce the activation effect on Pb caused by the complexity of the components of the compost product. Meanwhile, the pH value of the soil is adjusted by adding lime, the solubility of Pb-containing compounds such as phosphorus-chlorine-lead ore and the like is reduced, and the precipitation reaction is promoted to move towards the positive direction. Thus, the combination of the three may make the passivation effect more efficient, more stable and longer lasting.

In addition, the invention explores the application of the existing compost products on the basis of compost, has low price, convenient operation and wide application range, and is suitable for the heavy metal pollution condition of soil in agricultural lands in China.

The method has rich compost resources, so the raw materials of the method are low in price, the operation steps are simple and easy to implement, the method is favorable for large-scale popularization, and the condition of heavy metal micro-pollution in agricultural lands in China is met. The invention not only has good passivation effect on heavy metal Pb in soil, but also can improve the physical and chemical properties of the soil, increase the soil fertility, improve the crop yield, increase the added value of compost and be beneficial to solving the resource problem of compost products in China.

The above-described embodiments are merely preferred embodiments of the present invention, which should not be construed as limiting the invention. Various changes and modifications may be made by one of ordinary skill in the pertinent art without departing from the spirit and scope of the present invention. Therefore, the technical scheme obtained by adopting the mode of equivalent replacement or equivalent transformation is within the protection scope of the invention.

Claims

1. A compost composite modifier for passivating and restoring Pb-polluted soil is characterized by comprising 74-87% of compost products, 5-10% of lime and 8-16% of calcium magnesium phosphate fertilizers in percentage by mass.

2. A compost improver according to claim 1, wherein said compost product is obtained by composting chicken manure.

3. A compost improver according to claim 1, wherein said compost product is obtained by mixing and composting 50% by mass of chicken manure and 50% by mass of wood chips, respectively.

4. A compost composite improver as claimed in claim 2 or 3, wherein the compost product contains organic matter in an amount of 50% or more by mass on a dried basis, total nutrients in an amount of 5% or more by mass on a dried basis, water in an amount of 15 to 20% by mass, and a pH of 6 to 7.

5. A compost improver as claimed in claim 4, wherein said total nutrients include nitrogen, phosphorus pentoxide and potassium oxide, and the mass ratios of N, P and K in the total nutrients on an oven dried basis are not less than 2%.

6. A compost improver as claimed in claim 1, wherein the mass proportion of CaO in said lime is > 90%, and the mass proportion of P in a calcium magnesium phosphate fertilizer is > 12%.

7. A preparation method of a compost composite modifier according to any one of claims 1 to 6, which is characterized by comprising the following steps:

8. The preparation method of the compost composite improver as claimed in claim 7, wherein the natural air drying means that the compost product is naturally air-dried in a shade until the moisture content of the compost product is 15-20% by mass.

9. A method of producing a compost improver as claimed in claim 7, wherein said sieving means 20-mesh sieving.

10. An application of a compost composite modifier for passivation remediation of Pb-contaminated soil based on any one of claims 1 to 6 is characterized by comprising the following specific steps: