Mariculture area bottom mud aging degree identification and restoration method

Abstract

The invention discloses a mariculture area bottom mud aging degree identification and restoration method, belongs to the technical field of aged bottom mud restoration, can quantitatively evaluate the aging degree of mariculture bottom mud by using sulfide, heavy metal and organic carbon as indexes, and solves the problem that the current aging judgment standard does not have a unified standard. A scientific basis is provided for repairing the aged bottom mud and evaluating the repairing effect; meanwhile, the developed iron-reducing flora loaded nZVI / S composite material (DIRB at nZVI / S) can be used for removing sulfides, heavy metals and organic matters in the mariculture bottom mud in an immobilization manner by utilizing a physical-chemical-biological combined effect, so that effective repair of the aged mariculture bottom mud is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of aging sediment repair, and in particular to a method for identifying the aging degree of sediment in a seawater aquaculture area and repairing the sediment. Background Art

[0002] With the continued expansion of global aquaculture, intensive, high-density aquaculture has become the mainstream. However, the sedimentation of large amounts of leftover bait, feces, and biological metabolites during the aquaculture process leads to excessive accumulation of sulfides, heavy metals, organic matter, and nutrients (nitrogen and phosphorus) in the mud at the bottom of aquaculture ponds or near the seabed, causing sediment "aging." This process is particularly prominent in enclosed or semi-enclosed aquaculture waters (such as ponds, cage areas, and harbors), and has become a key environmental bottleneck restricting the sustainable development of the marine aquaculture industry. Aged sediment transforms the bottom environment from aerobic to anaerobic, releasing pollutants into the overlying waters, reducing aquaculture efficiency, killing aquaculture products, and even leading to the abandonment of aquaculture areas.

[0003] There are many methods for repairing aged sediments, mainly including physical methods (tillage, dredging, etc.), chemical methods (addition of oxidants, passivators, etc.) and biological methods (addition of functional microorganisms, etc.).

[0004] However, physical methods such as plowing and dredging are costly and will disturb the ecosystem, easily causing the transfer of pollutants; the addition of chemical agents is effective in the short term but may have toxic effects and destroy microbial communities; the added functional microorganisms are easily inhibited by the environment, making colonization difficult and the restoration dimension relatively single.

[0005] In view of this, it is necessary to provide a new technical solution to solve the above problems. Summary of the Invention

[0006] In order to solve the above technical problems, the present application provides a method for identifying and repairing the degree of aging of seawater aquaculture sediments, which can quantitatively evaluate the degree of aging of seawater aquaculture sediments, and use the combined physical, chemical and biological effects to remove sulfides, heavy metals and organic matter in seawater aquaculture sediments in a fixed manner, thereby realizing the evaluation and effective repair of aged seawater aquaculture sediments.

[0007] A method for identifying and repairing the aging degree of bottom mud in a marine aquaculture area, comprising: Assess the aging degree of marine aquaculture sediments; The iron-reducing bacteria-loaded nZVI / S composite material is mixed with the aged sediment that needs to be repaired to repair the aged sediment; Among them, nZVI / S is sepiolite-loaded nano-zero-valent iron material.

[0008] Preferably, the preparation process of the iron-reducing bacteria-loaded nZVI / S composite material includes: Strains with an iron reduction rate greater than 70% were selected as target strains, and the target strains were prepared into bacterial liquids; The nZVI / S composite material is added to the prepared bacterial solution and cultured under oscillation, and microbial attachment is achieved through electrostatic interaction and physical adsorption to obtain an iron-reducing bacteria-loaded nZVI / S composite material.

[0009] Preferably, strains with an iron reduction rate greater than 70% are screened out as target strains, including: Taking fresh samples of marine aquaculture sediment and culturing them statically to obtain a microbial inoculum; The inoculum was inoculated on a ferric citrate solid medium for cultivation; Pick a single colony and transfer it to LB medium for propagation, and then centrifuge to obtain the bacterial cells; The collected bacteria were inoculated into ferric citrate liquid culture medium, and after deoxygenation, the medium was sealed and cultured at a constant temperature until the color of the medium changed from yellow-green to white; Strains with the ability to reduce ferric citrate were selected and transferred to ferric hydroxide liquid culture medium, and strains with an iron reduction rate greater than 70% were screened out as target strains.

[0010] Preferably, a strain with an iron reduction rate greater than 70% is selected as the target strain, and when the target strain is prepared into a bacterial solution, the obtained bacterial solution of the target strain has a concentration greater than 10 6 CFU / mL of the target bacterial strain.

[0011] Preferably, the nZVI / S composite material is added to the prepared bacterial solution and shaken and cultured, and microbial attachment is achieved through electrostatic interaction and physical adsorption to obtain an iron-reducing bacteria-loaded nZVI / S composite material, comprising: 1 g of nZVI / S composite material was added to 50-200 ml of the prepared bacterial solution and cultured under shaking to allow the target strain to be electrostatically and physically adsorbed onto the nZVI / S composite material. The concentration of the target strain loaded on the nZVI / S composite material was not less than 4 × 10 7 CFU / g, and the iron-reducing bacteria-loaded nZVI / S composite material was obtained.

[0012] Preferably, the preparation process of the nZVI / S composite material includes: The pretreated sepiolite was mixed with anhydrous ethanol, ferrous sulfate solution and sodium borohydride to prepare a solution containing nZVI / S composite material; The synthesized nZVI / S composite material was separated from the solution; The separated nZVI / S composite material was washed with ethanol and deionized water, and dried to constant weight to obtain the final nZVI / S composite material.

[0013] Preferably, the pretreatment process of sepiolite comprises: Remove large particles of impurities from sepiolite raw materials and remove suspended matter on the surface of sepiolite; Acid treatment of the sepiolite to remove impurities and suspended matter; The acid-treated sepiolite is calcined to obtain pretreated sepiolite.

[0014] Preferably, the aging degree of marine aquaculture sediment is assessed, including Determine the evaluation indicators of marine aquaculture sediments; Standardize each evaluation indicator; A comprehensive evaluation index for sediment aging was constructed to calculate the aging degree of aquaculture sediment and classify it into grades.

[0015] Preferably, the evaluation indicators of marine aquaculture sediments include: acid-volatile sulfur, bioavailable heavy metals and organic carbon in marine aquaculture sediments.

[0016] Preferably, the calculation formula for the comprehensive evaluation index of sediment aging degree is: ; Where η i is the weight of the i-th marine aquaculture sediment assessment index; Q i is the quality index of the i-th marine aquaculture sediment assessment indicator.

[0017] Compared with the prior art, this application has at least the following beneficial effects: 1. The iron-reducing bacteria-loaded nZVI / S composite material (DIRB@nZVI / S) developed in this invention can remove sulfides, heavy metals, and organic matter from marine aquaculture sediments in an immobilized manner through a combined physical, chemical, and biological action, thereby effectively repairing aged marine aquaculture sediments.

[0018] 2. The present invention uses sulfide, heavy metals, and organic carbon as indicators of sediment aging, and quantitatively evaluates the aging degree of marine aquaculture sediment through the constructed comprehensive assessment index of marine aquaculture sediment aging, solving the problem that there is no unified standard for current aging judgment criteria, and providing a scientific basis for carrying out aged sediment remediation and remediation effect evaluation. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Hereinafter, some specific embodiments of the present invention will be described in detail in an exemplary and non-limiting manner with reference to the accompanying drawings. The same reference numerals in the accompanying drawings indicate the same or similar components or parts. It should be understood by those skilled in the art that these drawings are not necessarily drawn to scale. In the accompanying drawings: Figure 1 It is a schematic diagram of the overall process of the present invention; Figure 2XRD spectra of sepiolite before and after loading nZVI; Figure 3 This is a scanning electron microscope photo of sepiolite before loading with nZVI; Figure 4 This is a scanning electron microscope photo of sepiolite loaded with nZVI; Figure 5 This is the infrared spectrum of sepiolite loaded with nZVI. DETAILED DESCRIPTION

[0020] To make the purpose, technical solutions, and advantages of this application more clear, the technical solutions of this application will be clearly and completely described below in conjunction with the specific embodiments of this application and the corresponding drawings. Obviously, the embodiments described are only part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0021] like Figure 1 As shown, a method for identifying and repairing the aging degree of sediment in a marine aquaculture area is characterized by comprising: S1. Assess the aging degree of marine aquaculture sediments; S2. mixing the iron-reducing bacteria-loaded nZVI / S composite material with the aged sediment to be repaired to repair the aged sediment; Among them, nZVI / S is sepiolite-loaded nano-zero-valent iron material.

[0022] The iron-reducing bacteria-loaded nZVI / S composite material (DIRB@nZVI / S) developed in the present invention can remove sulfides, heavy metals and organic matter from marine aquaculture sediments in an immobilized manner by utilizing the combined physical, chemical and biological effects.

[0023] Specifically, DIRB@nZVI / S can reduce sulfide through physical adsorption, nZVI converting sulfide into FeS and elemental sulfur, and then generating pyrite through chemical reactions, competing with sulfate reduction for organic matter, inhibiting the biological action of sulfate reduction, fixing heavy metals through adsorption, surface complexation and co-precipitation, and degrading organic matter.

[0024] Determining the degree of sediment aging is a prerequisite for remediation and a tool for evaluating remediation effectiveness. However, there is currently no unified understanding or quantitative indicators for determining aging. The existing "Technical Specification for Pollution Investigation and Assessment of Sediment in Rivers, Lakes, and Reservoirs" (DB11 / T 2396-2025) provides regulations for sediment pollution investigation, analysis, testing, and evaluation. However, it primarily applies to sediments in rivers, lakes, and reservoirs, and focuses on assessing pollution levels.

[0025] There are significant differences between marine aquaculture sediments and sediments from rivers, lakes, and reservoirs in terms of physical and chemical properties, biological characteristics, and environmental risks. Marine aquaculture sediments have finer particle sizes, generally consisting of silt and clay, and possess distinct sedimentary structures and stratification. In contrast, sediments from rivers, lakes, and reservoirs have varying particle sizes and complex stratification due to the influence of various factors. Marine aquaculture sediments have high salinity and organic matter content, and contain large amounts of Na⁺, Cl⁻, and SO₄²⁻. In contrast, sediments from rivers, lakes, and reservoirs have extremely low salinity. Furthermore, marine aquaculture sediments are dominated by anaerobic / facultative bacteria and experience high levels of bioturbation, while sediments from rivers, lakes, and reservoirs are generally dominated by aerobic / facultative bacteria and experience low levels of bioturbation. The primary pollutants in marine aquaculture sediments are sulfides, heavy metals, and organic matter accumulation, while the primary risks in sediments from rivers, lakes, and reservoirs are eutrophication and accumulation of organic matter and heavy metals. Therefore, freshwater system standards such as the "Technical Specifications for Investigation and Evaluation of Sediment Pollution in Rivers, Lakes and Reservoirs" (DB11 / T2396-2025) obviously cannot be used to evaluate the pollution of marine aquaculture sediments.

[0026] Furthermore, sediment aging and pollution are two separate concepts. Aquaculture sediment aging refers to the process of declining sediment ecosystem functions (which can be accelerated by natural or human factors) and focuses on the overall ecological risk of the sediment (the threat to seafood). Sediment pollution, on the other hand, refers to the accumulation of harmful substances exceeding standards, primarily due to human input, and focuses more on the environmental risks of a single pollutant. Therefore, using sediment pollution assessment criteria cannot effectively assess the extent of sediment aging.

[0027] In this plan, the aging degree of marine aquaculture sediment is assessed, including: S11. Determine the evaluation indicators for marine aquaculture sediments.

[0028] Specifically, in this scheme, acid-volatile sulfur, bioavailable heavy metals and organic carbon are used as indicators for evaluating sediment aging.

[0029] Considering aspects such as bioavailability, migration and transformation patterns in sediments, and sensitivity of aquatic products to their pollution, sulfide, heavy metals, and organic carbon are important factors leading to sediment aging.

[0030] Sulfide can easily cause poisoning to aquatic and benthic organisms. Not only can it combine with hemoglobin in the blood of organisms to produce sulfhemoglobin, which greatly reduces the oxygen-carrying capacity of the blood, but it can also pose multiple threats to aquaculture products through direct toxicity (such as cell division inhibition and abnormal development, organelle damage), metabolic inhibition (such as obstructed photosynthesis, respiratory disorders) and ecological chain effects (such as quality decline, reduced biodiversity, and food chain disruption).

[0031] Unlike freshwater systems like rivers, lakes, and reservoirs, marine aquaculture systems are characterized by high-density, high-feeding practices. These systems produce finer sediments, contain higher levels of sulfate and organic matter, and have lower dissolved oxygen concentrations. These conditions favor sulfate-reducing bacteria, which use organic matter as electron donors and carbon sources and the abundant sulfate in seawater as electron acceptors to carry out sulfate reduction, generating and accumulating large amounts of sulfide. Investigations have revealed that many marine aquaculture areas are severely contaminated by sulfide in the sediments, where it has become a major cause of biotoxicity.

[0032] Among different types of sulfides, acid-volatile sulfur (AVS) is the most active and bioavailable form of sulfide, with the greatest biotoxicity. Therefore, this proposal selects AVS as one of the indicators for evaluating sediment aging.

[0033] Heavy metals in sediments can not only directly harm benthic organisms, but also enter the bodies of seafood such as fish, shrimp, oysters, and mussels through biological uptake, enrichment, and amplification, and then enter the human body through the food chain, causing direct harm to human health. They can also re-enter the overlying water bodies, threatening the entire marine ecosystem.

[0034] In addition, the form of heavy metals in sediments directly determines their biotoxicity. Heavy metals can be divided into different forms according to different extraction methods. The commonly used modified BCR extraction method divides heavy metal forms into weakly acid-soluble, reducible, oxidizable, and residual forms, with their stability increasing in sequence. The first three forms are less stable and are the main forms that produce biotoxicity, often referred to as bioavailable forms. The residual form is stable and not easily released into the environment for bioutilization, so it basically does not cause harm to aquaculture products. Obviously, it is inappropriate to assess the risk of heavy metals based on the total amount of heavy metals. In addition, the migration and transformation of heavy metals in sediments are affected by factors such as sulfide, sediment particle size, organic matter, salinity, sediment disturbance, pH value, and redox conditions. The above-mentioned influencing factors vary significantly in sediments from different regions, so the proportion of each form also varies significantly. This plan uses the bioavailable form of heavy metals as one of the evaluation indicators for sediment aging.

[0035] Heavy metals include cadmium, chromium, lead, copper, zinc, and nickel, typical heavy metals that are closely related to sulfur and have strong biotoxicity. Heavy metals in bioavailable states include weakly acid-soluble, reducible, and oxidizable forms. Weakly acid-soluble, reducible, and oxidizable forms were chosen because residual heavy metals are stable, difficult to release into the environment, and generally non-toxic to organisms.

[0036] Compared to freshwater systems like rivers, lakes, and reservoirs, marine aquaculture areas experience significant accumulation of organic carbon due to uneaten feed, chemical additions, and waste products. Sediment organic carbon reflects the intensity and duration of aquaculture activities. High concentrations of organic matter provide a rich substrate for heterotrophic microorganisms such as bacteria. These microorganisms decompose organic matter in large quantities, consuming large amounts of dissolved oxygen, driving the formation of anaerobic conditions in the sediments. This leads to the death of aquaculture products due to lack of oxygen and affects the migration and transformation of indicators such as sulfide and heavy metals. Therefore, high organic matter levels fuel anaerobic sediments and the production of toxic and hazardous substances (such as sulfide). This proposal selects organic carbon as one of the indicators for evaluating sediment aging.

[0037] S12. Standardize each evaluation indicator.

[0038] The quality index method is used to standardize each indicator. The quality index is calculated for each indicator, that is, the ratio of the measured value to the standard limit to reflect the degree of exceeding the standard for each indicator. The calculation formula is as follows: ; in, Q i is the quality index of the ith marine aquaculture sediment assessment indicator; C i is the measured value of the ith marine aquaculture sediment assessment index; S i is the limit value of the ith marine aquaculture sediment assessment index.

[0039] The measured value of AVS refers to the content determined by improved cold diffusion. C AVS The measured value of organic carbon refers to the organic carbon content measured by element analyzer after pre-treatment. C TOC The measured value of bioavailable heavy metals refers to the sum of the weak acid extractable state, reducible state and oxidizable state of each heavy metal extracted in sequence using the improved BCR extraction method. C H有效 Expressed in (unit: mmol / kg).

[0040] In addition, although simultaneous extraction of heavy metals (SEM) / AVS is also often used to predict the toxicity of heavy metals in sediments, for marine aquaculture sediments, some residual states will also be extracted during the simultaneous extraction of heavy metals, resulting in an overestimation of the toxicity of heavy metals. Therefore, the bioavailable state of heavy metals is chosen to replace SEM in this method.

[0041] In this plan, the classification of sediment quality is based on the Marine Sediment Quality (GB 18668-2002). SAVS and S TOC The limits adopted are 300.0 mg / kg and 2.0%. AVS plays an important role in controlling the bioavailability of heavy metals because it can react with heavy metals to form insoluble metal sulfides, making them difficult for aquaculture products to absorb. AVS content can represent the safe loading capacity of sediments for toxic heavy metals. The influence of AVS was fully considered when selecting the heavy metal limits, and the measured AVS value (expressed as molar concentration, unit: mmol / kg) was selected as the limit.

[0042] S13. Construct a comprehensive evaluation index for the degree of sediment aging to calculate the degree of aging of aquaculture sediments and classify them into grades.

[0043] The calculation formula for the comprehensive evaluation index of sediment aging degree is as follows: ; in, It is a comprehensive evaluation index of sediment aging degree; η i is the weight of the i-th marine aquaculture sediment assessment indicator.

[0044] Based on the classification of sediment quality in Marine Sediment Quality (GB 18668-2002) and relevant literature, the risk level of each marine aquaculture sediment assessment indicator was graded, as shown in Table 1.

[0045] Table 1 Comparison table of risk levels of marine aquaculture sediment assessment indicators

[0046]

[0047] Weights are determined based on the impact of marine aquaculture sediment assessment indicators on aquaculture products. Sulfide is highly toxic, directly affecting the survival of aquaculture organisms, impairing physiological functions and posing a direct threat to the safety of aquaculture products. Heavy metals have direct toxic effects, and even low concentrations, if accumulated over a long period, can lead to chronic poisoning in organisms, affecting product quality and food safety. Excessive organic carbon leads to a decrease in redox potential, releasing toxic substances, indirectly affecting the health of aquaculture organisms and product quality. Therefore, in this proposal, the weights for acid-volatile sulfur, bioavailable heavy metals, and organic carbon are set at 0.50, 0.30, and 0.20, respectively.

[0048] Sediment aging is graded based on the SEI. Combined with the risk level of a single marine aquaculture sediment assessment indicator, the degree of aquaculture sediment aging is divided into four levels: unaged, slightly aged, moderately aged, and severely aged. The SEI values ​​corresponding to different aging levels are shown in Table 2.

[0049] Table 2 Comparison table of aging degree of marine aquaculture sediment

[0050] In step S2, the iron-reducing bacteria-loaded nZVI / S composite material is mixed with the aged sediment to be repaired. In repairing the aged sediment, the preparation process of the iron-reducing bacteria-loaded nZVI / S composite material includes: S21. Screen out a strain with an iron reduction rate greater than 70% as a target strain, and prepare the target strain into a bacterial liquid.

[0051] The bacterial solution prepared has a concentration greater than 10 6 CFU / mL of the target bacterial strain.

[0052] Specifically, strains with an iron reduction rate greater than 70% were selected as target strains, including: Fresh samples of marine aquaculture sediment were statically cultured to obtain a microbial inoculum; the inoculum was inoculated onto a ferric citrate solid culture medium for culture; a single colony was picked and transferred to LB culture medium for propagation, and the bacteria were obtained by centrifugation; the collected bacteria were inoculated into a ferric citrate liquid culture medium, which was sealed and cultured at a constant temperature after deoxygenation until the color of the culture medium changed from yellow-green to white; a strain with the ability to reduce ferric citrate was selected and transferred to a ferric hydroxide liquid culture medium, and a strain with an iron reduction rate greater than 70% was screened as the target strain.

[0053] It should be noted that strains with iron reduction rates below 70% should not be considered as target strains due to insufficient efficiency, high cost, or metabolic defects. Furthermore, strains with iron reduction rates below 70% have low reduction efficiency, requiring more time, nutrients, or bacterial strain volume to achieve the same effect, increasing costs.

[0054] S22. Add the nZVI / S composite material to the prepared bacterial solution and culture it under oscillation, so as to achieve microbial attachment through electrostatic interaction and physical adsorption, thereby obtaining an iron-reducing bacteria-loaded nZVI / S composite material.

[0055] Specifically, 1 g of nZVI / S composite material was added to 50-200 ml of the prepared bacterial solution and cultured with shaking, so that the target strain was electrostatically and physically adsorbed onto the nZVI / S composite material, and the concentration of the target strain loaded on the nZVI / S composite material was not less than 4 × 10 7 CFU / g, and the iron-reducing bacteria-loaded nZVI / S composite material was obtained.

[0056] The preparation process of nZVI / S composite materials includes: The pretreated sepiolite is mixed with anhydrous ethanol, ferrous sulfate solution and sodium borohydride to prepare a solution containing the nZVI / S composite material; the synthesized nZVI / S composite material is separated from the solution; the separated nZVI / S composite material is washed with ethanol and deionized water, and dried to a constant weight to obtain the final nZVI / S composite material.

[0057] The volume ratio of anhydrous ethanol: 0.23 mol / L FeSO4·7H2O solution: 0.48 mol / L NaBH4 solution is 3~6:1:2~4. 2+ The mass ratio of Fe is about 5:1, that is, when the mass of sepiolite is 5 g, the required Fe 2+ The mass of sepiolite determines the volume of the 0.23 mol / L FeSO4·7H2O solution, which in turn determines the volumes of anhydrous ethanol and 0.48 mol / L NaBH4 solution.

[0058] Among them, the pretreatment process of sepiolite includes: The method comprises the following steps: removing large particles of impurities from the sepiolite raw material and removing suspended matter on the surface of the sepiolite; performing acid treatment on the sepiolite from which the impurities and suspended matter have been removed; and calcining the acid-treated sepiolite to obtain pretreated sepiolite.

[0059] After the preparation of nZVI / S composite materials was completed, whether nZVI was successfully loaded on sepiolite was analyzed.

[0060] like Figure 2 As shown, X-ray diffraction analysis (XRD) revealed that there was no Fe in sepiolite (S). 0 characteristic peaks, while Fe 0 Characteristic peak (2 θ = 44.9°), indicating that nZVI was successfully loaded on sepiolite.

[0061] like Figure 3 and Figure 4 As shown in the figure, scanning electron microscopy images show that the surface of sepiolite becomes rougher after loading nZVI, and the nZVI particles are dispersed and do not aggregate on the surface of sepiolite, indicating that loading nZVI can increase the specific surface area of ​​sepiolite, and the nZVI loading is relatively uniform.

[0062] like Figure 5As shown in the figure, through infrared spectroscopy (FTIR), it was found that after the sepiolite was loaded with nZVI, oxygen-containing functional groups such as -C=O-, -CO- and -OH were distributed on the surface. The oxygen-containing functional groups can stabilize heavy metals by complexing with heavy metal ions, indicating that loading nZVI can improve the immobilization ability of sepiolite for heavy metals.

[0063] It should be noted that after the preparation of the nZVI / S composite material is completed, analyzing whether nZVI is successfully loaded on the sepiolite is not a necessary process in this scheme. It is to verify the preparation results of the nZVI / S composite material through information characterization to determine the preparation effect of the nZVI / S composite material.

[0064] In addition, more than 10 6 High bacterial concentrations at the CFU / mL level provide sufficient active cells, ensuring full contact with the nZVI / S material and effectively catalyzing iron reduction or pollutant degradation reactions. Insufficient biomass, however, can result in slow reaction rates or failure to achieve the desired conversion.

[0065] In addition, experiments have shown that nZVI materials have a certain degree of toxicity to microorganisms. 6 High bacterial concentrations of the order of CFU / mL can dilute toxic effects and maintain sufficient viable cells. 6 When the concentration of bacterial solution is at the CFU / mL level, it is easily completely inhibited by the nZVI material, and the iron-reducing bacteria-loaded nZVI / S composite material cannot be successfully prepared. Example

[0066] Two ponds DY1 and DY2 in Kenli District of Dongying City, a pond (DH) in Changdao Sea Area of ​​Yantai City, and aquaculture area (S1~S16) of Sishili Bay in Yantai were selected to conduct an assessment of the degree of aging of aquaculture sediments.

[0067] Two ponds in Kenli District are common coastal, enclosed ponds. They employ feed aquaculture, with feed added daily. Water is exchanged monthly, with one-third of the water replaced each time. The ponds are 1.5–2 m deep and experience minimal hydraulic disturbance. The aquaculture periods are five years (DY1) and one year (DY2), respectively. A pond in the Changdao area is a semi-open, enclosed pond, common in bays, with a history of over 20 years. Constructed by enclosing the sea, the ponds exchange water twice daily, receiving seawater via tidal range (locally known as semi-diurnal tides). With a water depth of 1.5–2 m and significant hydraulic disturbance, the ponds primarily source feed from organic detritus and natural bait introduced through water exchange. Sishili Bay, one of Yantai's major bays, is a key aquaculture area in northern my country. Shellfish aquaculture primarily occurs in the western part of Sishili Bay, while sea cucumber aquaculture predominates in the eastern part. Aquaculture once accounted for 70% of the bay's total area.

[0068] The contents of sulfide, heavy metals and organic carbon in sediments from different areas are shown in Table 3.

[0069] Table 3 Measured values ​​of sulfide, heavy metals and organic carbon in sediments from different regions

[0070] The indicator quality index method was used to standardize each indicator and calculate the comprehensive evaluation index. The results are shown in Table 4.

[0071] Table 4 Quality index and comprehensive evaluation index of sulfide, heavy metals and organic carbon in sediment

[0072] Using the Comprehensive Evaluation Index (SEI) and a comparison table for aging, we assessed the degree of sediment aging. The results showed that sediment in long-term aquaculture ponds (DY1) in Kenli District, Dongying City, was severely aged and in need of repair. Sediment in short-term aquaculture ponds (DY2) was mildly aged. Sediment in Changdao aquaculture ponds was not aged. Sediment in the sampled aquaculture area of ​​Sishili Bay was not aged. This indicates that sediment aging in enclosed ponds offshore is more severe than that in semi-open aquaculture ponds and open-sea aquaculture areas, which is consistent with actual conditions.

[0073] Aged aquaculture sediments were collected from aquaculture ponds in Dongying, and their basic physical and chemical parameters and pollutant contents were analyzed. The results are shown in Table 5.

[0074] Table 5 Basic physical and chemical parameters and pollutant contents of aged aquaculture sediments

[0075] Table 5 shows that the AVS content in aquaculture sediments far exceeds the Class I standard limit in the Marine Sediment Quality Standard (GB 18668-2002). While the total heavy metal content meets the Class I standard, heavy metal contamination is closely related to its occurrence form. The risk assessment coding method assesses the environmental risk of heavy metals by calculating the proportion of the F1 form of heavy metals in the total amount. Based on the results of the risk assessment coding method, cadmium (Cd) in the sediments is severely contaminated.

[0076] Pretreatment of sepiolite: The sepiolite was passed through a 100-mesh nylon sieve to remove large particles of impurities, and then washed with deionized water to remove surface suspended matter. The cleaned sepiolite was dried at 60°C to constant weight.

[0077] The sieved and cleaned sepiolite was mixed with hydrochloric acid solution in a mass ratio of 1:5, stirred at room temperature for 4 hours to remove impurities and widen the pore structure, and then the sepiolite was washed with deionized water several times until neutral, and dried at 60°C to constant weight.

[0078] The acid-treated sepiolite was placed in a muffle furnace and calcined at 300 °C for 2 h to enhance its surface active sites.

[0079] Preparation of nZVI / S composite materials: Under N2 protection, 2.50 g of pretreated sepiolite was placed in 160 ml of anhydrous ethanol, and then 40 mL of 0.23 mol / L FeSO4·7H2O solution was added and mixed, and stirred in a 500 ml three-necked flask for 30 min.

[0080] Under N2 protection and stirring, 100 ml of freshly prepared 0.48 mol / L NaBH4 solution was slowly added into the three-necked flask. After the addition, stirring was continued for 0.5 h. After stirring, the mixture was allowed to stand for a while.

[0081] The synthesized sepiolite-supported nano-zero-valent iron composite (nZVI / S) was separated from the solution by vacuum filtration. The separated nZVI / S was washed multiple times with ethanol and deionized water and then dried in a vacuum drying oven at 60°C to constant weight.

[0082] Among them, the mass ratio of nano-zero-valent iron (nZVI) to sepiolite in nZVI / S synthesized by the above process is about 1:5.

[0083] Preparation of iron-reducing bacteria-loaded nZVI / S composite materials: The nZVI / S composite material was added to the prepared bacterial solution and cultured under oscillation, and microbial attachment was achieved through electrostatic interaction and physical adsorption to obtain the iron-reducing bacteria-loaded nZVI / S composite material. The specific process is as follows: Weigh about 50 g of fresh marine aquaculture sediment sample, put it into a wide-mouth bottle, add 200 ml of artificial seawater with a salinity of 30‰, place it in a dark environment at room temperature and culture it for one week, and use the obtained supernatant as the microbial inoculum.

[0084] The inoculum was inoculated onto a solid ferric citrate culture medium (pH=7) prepared with ferric citrate, glucose, potassium dihydrogen phosphate, agar powder, dipotassium hydrogen phosphate, magnesium sulfate heptahydrate, calcium chloride dihydrate, and ammonium chloride by conventional dilution and spreading method, and the culture was sealed and cultured at a constant temperature of 30°C for 2-3 days.

[0085] A single colony was picked and transferred to a serum tube containing 50% LB medium (prepared by yeast extract, peptone, and sodium chloride, pH = 7), propagated for 24 hours, and then centrifuged to obtain the bacteria.

[0086] Add 1 ml of sterile water to the collected bacteria and inoculate it into a ferric citrate liquid culture medium (pH = 7) prepared with ferric citrate, glucose, potassium dihydrogen phosphate, dipotassium hydrogen phosphate, magnesium sulfate heptahydrate, calcium chloride dihydrate, and ammonium chloride. After nitrogen is introduced to deoxygenate, seal the culture medium and culture it at a constant temperature of 30°C until the color of the culture medium changes from yellow-green to white.

[0087] Strains with the ability to reduce ferric citrate were selected and transferred to a ferric hydroxide liquid culture medium prepared with ammonium chloride, glucose, and potassium phosphate buffer. The iron reduction rate was measured, and strains with an iron reduction rate greater than 70% were screened as target strains.

[0088] Collect wet cells and resuspend them to obtain high concentration bacterial solution (>10 6 CFU / mL), 1 g of nZVI / S composite material was added to 100 ml of high-concentration bacterial solution and cultured at 30°C and 150 r / min for 24 h. Microbial attachment was achieved through electrostatic interaction and physical adsorption, so that the concentration of the target strain loaded on the nZVI / S composite material was not less than 4×10 7 CFU / g, and the iron-reducing bacteria-loaded nZVI / S composite material (DIRB@nZVI / S) was obtained.

[0089] Aged aquaculture sludge collected from Dongying aquaculture ponds was spread evenly in a tall beaker with a thickness of 5 cm. Then the prepared DIRB@nZVI / S was evenly spread on the aged sludge with a thickness of 1 cm. Finally, ultrapure water was slowly added, and the solid-liquid phase height ratio in the beaker was about 1:2.

[0090] Overlying water samples were taken on the 1st, 5th and 10th day respectively to determine the AVS and Cd contents. The results showed that no AVS and Cd were detected in the overlying water, indicating that DIRB@nZVI / S has a good fixation effect on AVS and heavy metals in aged marine aquaculture sediments.

[0091] In addition, the long-term aquaculture ponds (DY1) in Kenli District, Dongying City do not need to be verified for organic carbon. The reason is that the organic carbon content in this area is only 0.87%, which is far below the first category limit (2.0%) of "Marine Sediment Quality" (GB18668-2002). There is no organic carbon pollution, so verification is not required.

[0092] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, tasks, devices, components and / or combinations thereof.

[0093] It should be noted that the terms "first," "second," and the like in the specification and claims of this application and the accompanying drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or precedence. It should be understood that the terms used in this manner are interchangeable where appropriate, so that the embodiments of the present application described herein can be implemented in an order other than that illustrated or described herein.

[0094] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for identifying and repairing the aging degree of sediment in a marine aquaculture area, characterized in that: include: Assess the aging degree of marine aquaculture sediments; The iron-reducing bacteria-loaded nZVI / S composite material is mixed with the aged sediment that needs to be repaired to repair the aged sediment; Among them, nZVI / S is sepiolite-loaded nano-zero-valent iron material.

2. The method for identifying and repairing the aging degree of bottom mud in a marine aquaculture area according to claim 1, characterized in that: The preparation process of the iron-reducing bacteria-loaded nZVI / S composite material includes: Strains with an iron reduction rate greater than 70% were selected as target strains, and the target strains were prepared into bacterial liquids; The nZVI / S composite material is added to the prepared bacterial solution and cultured under oscillation, and microbial attachment is achieved through electrostatic interaction and physical adsorption to obtain an iron-reducing bacteria-loaded nZVI / S composite material.

3. The method for identifying and repairing the aging degree of bottom mud in aquaculture areas according to claim 2, characterized in that: Strains with an iron reduction rate greater than 70% were selected as target strains, including: Taking fresh samples of marine aquaculture sediment and culturing them statically to obtain a microbial inoculum; The inoculum was inoculated on a ferric citrate solid medium for cultivation; Pick a single colony and transfer it to LB medium for propagation, and then centrifuge to obtain the bacterial cells; The collected bacteria were inoculated into ferric citrate liquid culture medium, and after deoxygenation, the medium was sealed and cultured at a constant temperature until the color of the medium changed from yellow-green to white; Strains with the ability to reduce ferric citrate were selected and transferred to ferric hydroxide liquid culture medium, and strains with an iron reduction rate greater than 70% were screened out as target strains.

4. The method for identifying and repairing the aging degree of bottom mud in a marine aquaculture area according to claim 2, characterized in that: The strain with an iron reduction rate greater than 70% was selected as the target strain. When the target strain was prepared into a bacterial solution, the obtained bacterial solution of the target strain had a concentration greater than 10 6 CFU / mL of the target bacterial strain.

5. The method for identifying and repairing the aging degree of bottom mud in a marine aquaculture area according to claim 4, characterized in that: The nZVI / S composite material is added to the prepared bacterial solution and shaken for cultivation, and microbial attachment is achieved through electrostatic interaction and physical adsorption to obtain an iron-reducing bacteria-loaded nZVI / S composite material, comprising: 1 g of nZVI / S composite material was added to 50-200 ml of the prepared bacterial solution and cultured under shaking to allow the target strain to be electrostatically and physically adsorbed onto the nZVI / S composite material. The concentration of the target strain loaded on the nZVI / S composite material was not less than 4 × 10 7 CFU / g, and the iron-reducing bacteria-loaded nZVI / S composite material was obtained.

6. The method for identifying and repairing the aging degree of bottom mud in a marine aquaculture area according to claim 2, wherein: The preparation process of nZVI / S composite materials includes: The pretreated sepiolite was mixed with anhydrous ethanol, ferrous sulfate solution and sodium borohydride to prepare a solution containing nZVI / S composite material; The synthesized nZVI / S composite material was separated from the solution; The separated nZVI / S composite material was washed with ethanol and deionized water, and dried to constant weight to obtain the final nZVI / S composite material.

7. The method for identifying and repairing the aging degree of bottom mud in a marine aquaculture area according to claim 6, characterized in that: The pretreatment process of sepiolite includes: Remove large particles of impurities from sepiolite raw materials and remove suspended matter on the surface of sepiolite; Acid treatment of the sepiolite to remove impurities and suspended matter; The acid-treated sepiolite is calcined to obtain pretreated sepiolite.

8. The method for identifying and repairing the aging degree of bottom mud in a marine aquaculture area according to claim 1, wherein: Assess the aging degree of marine aquaculture sediments, including Determine the evaluation indicators of marine aquaculture sediments; Standardize each evaluation indicator; A comprehensive evaluation index for sediment aging was constructed to calculate the aging degree of aquaculture sediment and classify it into grades.

9. The method for identifying and repairing the aging degree of bottom mud in a marine aquaculture area according to claim 8, characterized in that: The evaluation indicators of marine aquaculture sediments include: acid-volatile sulfur, bioavailable heavy metals and organic carbon in marine aquaculture sediments.

10. The method for identifying and repairing the aging degree of bottom mud in a marine aquaculture area according to claim 8, characterized in that: The calculation formula for the comprehensive evaluation index of sediment aging degree is: ； Where, η i is the weight of the ith marine aquaculture sediment assessment index; Q i is the quality index of the i-th marine aquaculture sediment assessment indicator.

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