Method for repairing copper-polluted water body by using corn straw biochar to strengthen hydrocotyle verticillata

Abstract

The invention relates to the field of phytoremediation of heavy metals, in particular to a method for repairing a copper-polluted water body by using corn straw biochar to strengthen hydrocotyle verticillata. The method comprises the following specific operation steps: carrying out pyrolysis on agricultural waste corn straws to produce corn straw biochar, and carrying out secondary utilization on the wastes; the method comprises the following steps: transplanting hydrocotyle vulgaris in a copper-polluted water body needing to be repaired, and applying corn straw biochar for culture; and removing the hydrocotyle vulgaris from the copper-polluted water body after the remediation period is finished, and repeatedly planting and operating until the content of copper in the water body meets the national water quality standard requirement. Compared with the traditional phytoremediation scheme, the method disclosed by the invention effectively solves the problems of low tolerance of plants to heavy metals, long remediation time and poorer water quality purification effect in the traditional phytoremediation.

Description

Technical Field

[0001] The invention relates to the field of plant remediation of heavy metals, and in particular to a method for remediating copper-contaminated water bodies by utilizing corn straw biochar to strengthen pennywort. Background Art

[0002] When the concentration of heavy metals exceeds the tolerance of the natural environment, it will destroy the balance of the ecosystem and pose a risk to human health. At present, finding more efficient and greener technologies to control and reduce heavy metal pollution has become an urgent issue. When a large amount of heavy metals enter the environment, the self-cleaning function of the environment alone cannot effectively reduce the content and toxicity in a short period of time, so it has a long-term impact on the ecological environment. Heavy metals have the characteristics of being non-biodegradable and highly toxic. They are absorbed from water bodies by organisms in a bioavailable state and accumulate along the food chain, causing oxidative stress and toxic damage to organisms. Human intake of foods that accumulate heavy metals can cause health problems, such as damage to human organs, lung diseases, and osteoporosis. Therefore, it is very important to develop technologies for the remediation of heavy metal-contaminated soil.

[0003] At present, the remediation technologies for heavy metal pollution are divided into three categories: physical, chemical and biological. Physical remediation methods include flushing soil, thermal desorption, replacing or partially replacing contaminated soil with clean soil to reduce the degree of pollution. The remediation effect is relatively thorough, but the physical method of migrating heavy metals in the contaminated environment and disposing them in landfills is expensive, laborious and time-consuming. Chemical remediation mainly includes vitrification technology, chemical leaching, chemical fixation and electrokinetic method, etc., using liquids or gases that can remove heavy metals from sediments or soil to repair the environment, and heavy metals are transferred to the liquid phase through precipitation, ion exchange, chelation, adsorption and other effects. However, the above technologies are relatively complex and expensive, so their application range is relatively narrow. In situ bioremediation is considered to be an eco-friendly, easy-to-operate and inexpensive technology. Among them, phytoremediation is a highly anticipated bioremediation technology. Due to its potential cost-effectiveness, simple engineering operation and environmentally friendly characteristics, it has become a hot topic in the field of pollution remediation. Among the remediation technologies for copper pollution, phytoremediation is an environmentally friendly, easy-to-operate and cost-effective method. Among them, plants mainly participate in the long-term remediation of copper pollution through plant extraction and plant stabilization. However, under high copper stress, the damaged plant growth state makes the restoration work ineffective. When heavy metals accumulate in plants to a certain level, the plant's growth physiological activities such as photosynthesis, nutrient absorption and stomatal movement will be inhibited and destroyed. High concentrations of heavy metals may lead to plant chlorophyll degradation, stomatal closure and oxidative damage, and in severe cases, plant death.

[0004] Hydrocotyle vulgaris L. has the advantages of fast reproduction, high population density, few pests and diseases, relatively low fertilizer requirements, evergreen, and high landscape value, so it is often used as a means to remove environmental pollutants. However, when the concentration of heavy metals is too high, it leads to slow plant growth and root development, which in turn makes phytoremediation inefficient. At present, various types of biochar have been used to remediate heavy metal-contaminated water bodies, which is closely related to its own unique physical and chemical properties. Biochar is a substance made from biomass such as plant residues, animal manure, and sludge, which is made by heating it to high temperatures and exposing it to a low-oxygen environment. It has special properties such as high specific surface area, high porosity, alkalinity, high cation exchange capacity, and rich types and quantities of surface functional groups. In addition, the type of raw materials used and the production temperature will affect these properties. Although there have been many previous studies on the remediation of heavy metals by biochar, the role of assisting in situ phytoremediation is often overlooked. Summary of the invention

[0005] The purpose of the present invention is to provide a method for using corn straw biochar to enhance the use of pennywort to repair copper pollution in water bodies, further solving the problems of poor growth of repair plants, low efficiency in removing copper from water bodies and long repair cycle, thereby achieving efficient and relatively safe water body repair, and can be applied on a large scale in actual repair.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows: a method for repairing copper-contaminated water bodies by using corn straw biochar to strengthen copper pennywort, comprising the following steps:

[0007] 1) Pyrolysis of agricultural waste corn straw to produce corn straw biochar, so that the waste can be reused for the second time.

[0008] 2) Planting Copper Coin Grass in the copper-contaminated water body that needs to be repaired and applying corn straw biochar for cultivation;

[0009] 3) After the restoration period, the copper coin grass is removed from the copper-contaminated water body, and the copper content in the water body reaches the national water quality standard through repeated planting and operation.

[0010] The above-mentioned method of using corn straw biochar to strengthen copper pennywort to repair copper-contaminated water bodies, the corn straw biochar described in step 1) is recycled corn straw from agricultural waste and sintered under anaerobic pyrolysis at 700°C. The finished product is black powder with a pH of 10.14, and is added to the contaminated water body in the form of solid powder.

[0011] In the above-mentioned method of using corn straw biochar to enhance the use of pennywort to repair copper-contaminated water bodies, the pennywort is first cultivated in soil to a height of 12-15 cm and a fresh weight of 23-25 ​​g before being transplanted, the roots are washed, and after hydroponic acclimation, they are cultivated in copper-contaminated water bodies.

[0012] The above-mentioned method of using corn straw biochar to enhance the use of pennywort to repair copper-contaminated water bodies, hydroponic domestication is to place the pennywort with washed roots in 1 / 600 modified Hoagland nutrient solution for 14 days.

[0013] In the above-mentioned method of using corn straw biochar to enhance pennywort to repair copper-contaminated water bodies, the amount of biochar added is 0.5g / 300mL.

[0014] In the above-mentioned method of using corn straw biochar to enhance pennywort to repair copper-contaminated water bodies, the copper ion concentration in the copper-contaminated water bodies is 10-50 mg / L.

[0015] The above-mentioned method of using corn straw biochar to enhance the use of pennywort to repair copper-contaminated water bodies is as follows: when the leaves of the pennywort turn yellow and fade to green on a large scale, and the water content of the plant is significantly reduced, and the stems become shriveled and soft, the plants are recovered from the polluted water body, and a new batch of pennywort is planted, and the above-mentioned operation is repeated to make the copper content in the polluted water body meet the national water quality standards.

[0016] The beneficial effects of the present invention are:

[0017] (1) The present invention strengthens the restoration of copper-contaminated water bodies by establishing a corn straw biochar and pennywort coupling system, and through the measurement of the growth and development and physiological characteristics of pennywort, it is found that pennywort strengthened with corn straw biochar can alleviate the weakening of plant photosynthesis under heavy metal stress, reduce the concentration of malondialdehyde in pennywort, effectively improve the plant restoration efficiency of copper pollution, and has good environmental and economic benefits.

[0018] (2) The restoration plant Copper Coin Grass selected by the present invention has the advantages of fast growth rate and strong stress resistance. On the one hand, it can repair copper-contaminated water bodies while on the other hand, it plays a role in beautifying the environment and has good environmental benefits.

[0019] (3) The biochar used in the present invention can be produced by recycling agricultural waste corn stalks to achieve the effect of secondary utilization.

[0020] (4) The present invention safely disposes of the treated plants, reducing the secondary pollution to the environment caused by the restored plants. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The copper removal rate changes before and after adding corn straw biochar under different copper concentrations.

[0022] Figure 2 The changes of malondialdehyde before and after adding corn straw biochar under different concentrations of copper treatment.

[0023] Figure 3 The changes in total chlorophyll before and after adding corn straw biochar under different concentrations of copper treatment. DETAILED DESCRIPTION

[0024] In order to better understand the present invention, the scheme of the present invention will be further illustrated by specific examples below.

[0025] Example 1

[0026] (I) A method for using corn straw biochar to enhance copper coin grass to repair copper-contaminated water bodies is as follows:

[0027] 1. Wash the soil-cultured Hydrocotyle vulgaris L. seedlings with a height of 12-15 cm and a fresh weight of 23-25 ​​g with distilled water for more than 3 times to ensure that the soil at the roots of the seedlings is clean. Then transplant the seedlings into a spherical hydroponic basket with a height of 13.5 cm and a maximum diameter of 18 cm, and culture them with deionized water. Plant a group of seedlings in each hydroponic basket. Cultivate in a light incubator for 7 days. The culture conditions are set to a light duration of 16 h and a light intensity of 350 μmol / m 2 / S, temperature was 25°C. Subsequently, the deionized water was replaced with 1 / 600 Hoagland modified nutrient solution, pH value was adjusted to 6.5 and culture was continued for 7 days. Plants with similar growth were selected for subsequent culture.

[0028] 2. After the corn stalks were crushed, they were pyrolyzed at 700℃ for 2h in anoxic environment to generate corn stalk biochar. The plants were subjected to copper stress experiment after 7 days of cultivation. The copper concentration gradient was set to: 0, 10, 20, 30, 40, 50 mg / L. Copper was added in the form of CuSO4·5H2O aqueous solution. 2+ 300mL of aqueous solution and 0.5g of corn straw biochar were added evenly to the roots of the plants. The specific groups were: (1) a group without biochar and cultured with 1 / 600 Hoagland nutrient solution under 0, 10, 20, 30, 40, and 50mg / L copper stress; (2) a group with 0.5g corn straw biochar and cultured with 1 / 600 Hoagland nutrient solution under 0, 10, 20, 30, 40, and 50mg / L copper stress. The treatment time was 7 days, and each treatment was repeated three times for parallel experiments.

[0029] (II) Determination of changes in growth physiological indicators and copper ion removal rate of Copper Pennisetum under copper stress after adding corn straw biochar:

[0030] The copper coin grass was cultured according to step (a) in a nutrient solution containing the above-mentioned culture concentration for 7 days and then harvested to measure relevant indicators.

[0031] The growth parameters of P. cyrtonema before and after application of biochar under different levels of copper stress are shown in Table 1.

[0032] Table 1 Growth parameters of pennywort under different treatments

[0033]

[0034] BC is the abbreviation of biochar, and different letters indicate significant differences among different treatment groups. One-way analysis of variance (Duncan test) was used for significance test.

[0035] The change of biomass is the most direct response of plants to various environmental stimuli. As can be seen from Table 1, in the range of 0-50 mg / LCu 2+ Under the treatment, stem length and leaf area gradually decreased with the increase of stress degree, reaching the minimum value at 50 mg / L, and dry weight and fresh weight showed an overall downward trend. For example, compared with the stem length and fresh weight under no stress, 50 mg / L decreased by 29.07% and 30.34%, respectively. With the addition of corn straw biochar, the reduction of the overall biomass of copper coin grass was alleviated. Although the biomass of copper coin grass still showed a downward trend with the increase of stress concentration, it was significantly alleviated compared with the absence of biochar. Under low stress concentration, the addition of biochar can even promote plant stem length and leaf growth. Compared with the stem length and fresh weight under no stress, the addition of biochar at 50 mg / L decreased by 19.96% and 26.42%, respectively. It shows that corn straw biochar effectively increases the resistance of copper coin grass to copper stress, weakens the harm of copper stress to copper coin grass, and thus promotes the absorption of copper by copper coin grass.

[0036] Under different degrees of copper stress, the addition of corn straw biochar significantly increased the removal rate of copper by Copper Pennisetum ( Figure 1 ). The removal rate is often closely related to the state of the plant. As the degree of copper stress increases, the overall removal rate gradually decreases, which may be because the state of the plant deteriorates, affecting the absorption of copper. The addition of biochar significantly improves the state of the plant and can reduce environmental toxicity by adsorbing copper, thereby improving plant growth and increasing copper removal rate. Under high stress, the degree to which biochar improves the removal rate is more obvious.

[0037] The increase in MDA content under copper stress indicates that the leaves of the copper coin grass accumulate a large amount of reactive oxygen, indicating that the degree of lipid peroxidation increases, which will induce chlorophyll degradation in plants ( Figure 2). In this study, as the degree of copper stress increased, the concentration of malondialdehyde in the copper coin grass also increased, indicating that lipid peroxidation caused by free radicals occurred in plant cells, destroying plant photosynthesis, causing oxidative damage, and affecting the effect of plant restoration. After adding biochar, except for 10 mg / L, the concentration of malondialdehyde in the copper coin grass under the five levels of stress was significantly lower than that without biochar. Among them, the decrease was the most obvious at 40 mg / L (43.72%), indicating that the application of biochar effectively alleviated the oxidative damage to the copper coin grass and helped to better remove copper pollution.

[0038] Determining the relative content of chlorophyll in living leaves can be used to evaluate plant growth, physiological changes and nitrogen nutrition status. As the degree of stress increases, the total chlorophyll content tends to decrease gradually ( Figure 3 ). After adding corn straw biochar, the total chlorophyll in plant leaves was significantly higher than that in the group without biochar, and there was a significant difference between the 20 and 30 mg / L treatments. The total chlorophyll content increased the most under 20 mg / L (47.81%), followed by 30 mg / L (34.07%). This shows that adding biochar can increase the relative content of total chlorophyll and promote chlorophyll formation. However, under high stress, the ability of biochar to alleviate the reduction of total chlorophyll was weakened, probably because the high stress caused serious damage to the plants.

Claims

1. A method for repairing copper-contaminated water bodies by using corn straw biochar to strengthen copper coin grass, characterized in that: The steps include: 1) Pyrolysis of agricultural waste corn stalks to produce corn stalk biochar, so that the waste can be reused for the second time; 2) Transplanting copper coin grass in the copper-contaminated water body that needs to be repaired and applying corn straw biochar for cultivation; 3) After the restoration period, the copper coin grass is removed from the copper-contaminated water body, and the copper content in the water body reaches the national water quality standard through repeated planting and operation.

2. The method for repairing copper-contaminated water bodies by using corn straw biochar to strengthen pennywort according to claim 1, characterized in that: In step 1), the pyrolysis is carried out at 700° C. for 2 hours in anoxic pyrolysis. The corn straw biochar after pyrolysis is in the form of black powder with a pH of 10.

14.

3. The method for repairing copper-contaminated water bodies by using corn straw biochar to strengthen pennywort according to claim 2, characterized in that: In step 2), when the copper coin grass is cultivated in soil to a height of 12-15 cm and a fresh weight of 23-25 ​​g, the roots are washed, acclimated through hydroponics, and then transplanted into a copper-contaminated water body.

4. The method for repairing copper-contaminated water bodies by using corn straw biochar to strengthen pennywort according to claim 3, characterized in that: In step 2), the hydroponic domestication is to place the cleaned pennywort roots in 1 / 600 improved Hoagland nutrient solution and culture for 14 days.

5. The method for repairing copper-contaminated water bodies by using corn straw biochar to strengthen pennywort according to claim 1, characterized in that: In step 2), the amount of corn straw biochar added is 0.5 g / 300 mL.

6. The method for repairing copper-contaminated water bodies by using corn straw biochar to strengthen pennywort according to claim 1, characterized in that: In step 2), the copper ion concentration in the copper-contaminated water is 10-50 mg / L.

7. The method for repairing copper-contaminated water bodies by using corn straw biochar to strengthen pennywort according to claim 1, characterized in that: Step 3) Specifically, when a large area of ​​the leaves of the copper coin grass turn yellow and fade to green, the water content of the plant is significantly reduced, and the stems become shriveled and soft, the plants are removed from the polluted water body, and a new batch of copper coin grass is planted, and the above operation is repeated to make the copper content in the polluted water body meet the national water quality standards.

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