CN110258439B - Multi-target environment-friendly dredging method for composite pollutants based on 4R theory - Google Patents
Multi-target environment-friendly dredging method for composite pollutants based on 4R theory Download PDFInfo
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- E—FIXED CONSTRUCTIONS
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- E02B3/00—Engineering works in connection with control or use of streams, rivers, coasts, or other marine sites; Sealings or joints for engineering works in general
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Abstract
The invention discloses a multi-target environment-friendly dredging method for composite polluted sediment based on a 4R theory, which comprehensively evaluates the Release (Release) of pollutants in the sediment before and after dredging, the ecological Risk (Risk) of harmful pollutants, the Resuspension (Resuspension) of the sediment and the pollutants during the dredging process and the dredging residues (Residual) aiming at the sediment with complex pollution sources and diversified pollutants in rivers and lakes, provides an accurate dredging depth, a dredging range and a dredging mode aiming at the comprehensive control of multiple pollution targets, can obviously improve the control effect of environment-friendly dredging on the endogenous pollution of the sediment, reduces the times of repeated dredging, and improves the environment-friendly dredging environment and the economic benefit.
Description
Technical Field
The invention belongs to the field of environmental protection, and relates to a composite polluted sediment multi-target environment-friendly dredging method based on a 4R theory.
Background
The sediment environment-friendly dredging technology is widely applied to the treatment of sediment polluted by water bodies such as rivers, lakes and the like since the 20 th century and the 60 th century, and is applied to the treatment of a plurality of water bodies such as rivers, lakes and the like in the world due to the fact that various pollutants enriched in the sediment can be rapidly and directly removed. However, the pollution control effect of sediment dredging has been controversial because the effect of sediment dredging is disturbed by a number of factors:
firstly, the understanding of the composite pollution state of the bottom mud is not comprehensive enough, and the evaluation work of ecological risks (Risk) of pollutants is not enough. As the bottom mud receives various pollutants from pollution sources of industry, agriculture, life and the like for a long time, the bottom mud generally suffers from composite pollution of various pollutants, mainly comprising nutrient salts, heavy metals, Persistent Organic Pollutants (POPs) and the like, and the comprehensive action of various pollutants causes the bottom mud to present a complex pollution condition. Wherein, the nutrient salts mainly comprise nutrient substances such as nitrogen, phosphorus and the like, and are main pollutants causing water eutrophication. Nitrogen and phosphorus are main limiting factors for the growth of phytoplankton such as blue algae in water, release of endogenous nitrogen and phosphorus in bottom sediment after long-term accumulation is one of important reasons for aggravating water eutrophication, and a plurality of eutrophic water bodies face serious endogenous nitrogen and phosphorus load problems. Heavy metal pollutants generally include toxic and harmful metals and metalloids such As arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), mercury (Hg), nickel (Ni), lead (Pb), and zinc (Zn). In water bodies such as rivers, lakes and the like, the bottom sediment is usually the main collection place of heavy metals, and the heavy metals accumulated in the bottom sediment can enter a food chain through the utilization of benthonic animals, thereby threatening the water ecosystem and the human health. In addition, heavy metals in the bottom mud can be released to an overlying water body or re-suspended to the overlying water body in a particle form under certain conditions (such as wind wave disturbance, change of oxidation-reduction environment, overwater operation, shipping and the like), and the ecological safety of the water is threatened. Persistent organic pollutants mainly comprise pollutants such as Polycyclic Aromatic Hydrocarbons (PAHs), Organic Chlorides (OCPs) and polychlorinated biphenyls (PCBs), the excessive use of pesticides such as herbicides and insecticides and the industrial production are main source ways of POPs, the POPs entering bottom mud through the processes of adsorption, sedimentation and the like after entering a water body can enter a food chain through benthos to be enriched, migrated and converted in aquatic organisms, and the persistent organic pollutants have a biological amplification effect. A plurality of POPs are listed as toxic and harmful pollutants to be immediately disposed by the environmental planning agency of the United nations. The prior dredging work is mostly aimed at a single pollution target and is insufficient for considering the compound pollution of the sediment.
Secondly, the polluted sediment is re-suspended (Resuspension) in the dredging process, namely, the loose polluted sediment is suspended and diffused into the water body due to the disturbance of the dredging engineering. The characteristics of the sediment, the environmental characteristics of the water area being dredged, and the dredging operation itself may result in resuspension of the sediment, and the dredging area and sediment should be investigated in detail before the dredging process is performed to determine in what manner the dredging is performed.
And thirdly, the Release of the pollutants at the interface of the newly generated mud water after the dredging (Release) causes the Release of the pollutants after the dredging, on one hand, the pollution to the composite polluted bottom mud and the unreasonable judgment on the dredging depth, and on the other hand, the dredging quality can not meet the requirements. In addition, different pollutants will show different release characteristics after dredging the sediment, for example, the release flux of ammonia nitrogen in the sediment may increase within 4-6 months after dredging, while the release of phosphate usually stops immediately or the release flux is reduced rapidly at a proper dredging depth. The phenomenon is not taken into consideration in the current environment-friendly dredging engineering, and the optimal dredging depth is determined by detailed investigation before dredging.
Fourthly, residues (Residual) generated in the dredging process are generally bottom mud with high surface pollution degree, relatively high water content and small particle size, and the residues are high in pollution and are important factors influencing the dredging quality.
The factors are main factors influencing the removal and control effects of dredging on endogenous pollution of the sediment, so that the dredging engineering is disputed for a long time, the evaluation and the solution of the factors have important significance on the effect of the environment-friendly dredging engineering, and the factors are researched, evaluated and analyzed in detail before the dredging engineering is carried out so as to determine whether the dredging is needed and how the dredging is carried out. However, the existing sediment dredging technologies pay more attention to the improvement, research and development and operation of dredging equipment (CN 2016100747678, CN 207452977U, CN 207211233U, CN 104005441B, etc.) or the disposal of dredging sludge (CN 106082903B, CN 102229485B, etc.), and some technologies consider a dredging method (CN 101962961B) for heavy metals, nutrient salts, etc. in the sediment, however, all of the related dredging technologies are not systematically evaluated and analyzed for Resuspension (Resuspension), pollutant Release (Release), pollutant residue (Residual), and ecological Risk (Risk) of the sediment in the dredging engineering on the basis of the sediment composite pollution evaluation, thereby causing the control effect of environmental protection dredging on the endogenous pollution of the sediment to be less than ideal and questioned in many ways.
Disclosure of Invention
In view of the defects of the prior sediment dredging technology and the disputes of the dredging engineering effect, the invention aims to provide a composite pollution sediment multi-target environment-friendly dredging method based on the 4R theory, aims to take the analysis and evaluation of the composite pollutant condition of the sediment as the basis, by establishing a 4R (Release, Risk, Resuspension and Residual) evaluation system for dredging the composite polluted bottom sediment, aiming at the bottom sediment with complex pollution sources and diversified pollutants in rivers and lakes, comprehensively evaluating the Release (Release) of the pollutants in the bottom sediment before and after dredging, the ecological Risk (Risk) of harmful substances, the Resuspension (Resuspension) of the bottom sediment and the pollutants in the bottom sediment dredging process and the dredging residues (Residual), providing an accurate dredging method system for controlling multiple pollution targets, and solving the problems that the dredging effect in the endogenous pollution regulation process cannot reach the expected target and the economic and environmental benefit loss caused by repeated dredging.
In order to solve the technical problems, the invention adopts the following technical scheme: a multi-target environment-friendly dredging method of composite polluted sediment based on a 4R theory is characterized by comprising the following steps:
(1) firstly, establishing an evaluation system of the bottom mud combined pollution condition based on multiple targets, wherein the evaluation system comprises:
evaluating the release of nitrogen and phosphorus pollutants in the sediment at different depths, and determining the dredging depth D1 according to the release flux of the nitrogen and phosphorus pollutants;
respectively evaluating the ecological risks of the heavy metals in the sediment, the persistent organic pollutants and the water body black and odor risk induced by the sediment, and respectively determining dredging depths D2, D3 and D4 according to the heavy metals in the sediment, the persistent organic pollutants and the ecological risks of the sediment induced water body black and odor;
then, the final dredging depth D is determined according to the pass D Max (D1, D2, D3, D4);
(2) then taking the dredging point as the center of a circle, sampling and analyzing the instantaneous particle content m in the water at intervals for the surrounding water body, determining the resuspension quantity Rs of the dredged sediment through the following formula,
Rs＝m/M
wherein M is the total dredging amount;
when the Rs is more than 1%, dredging the water body sediment by adopting a cutter-suction dredging method;
(3) taking the dredging point as the center of a circle, collecting columnar sediment samples at intervals for the sediment around the water body after dredging, analyzing the capacity, the water content and the TOC of the columnar sediment samples, comparing the capacity, the water content and the TOC with the sediment at the same depth before dredging,
when the error of the comparison result is within 10 percent, the dredging residue is considered to be the dredging residue, and the treatment is not needed;
when the error of the comparison result is more than 10 percent and the ratio Re of the capacity of the columnar sediment sample to the total sediment dredging amount is less than 2 percent, the sample is still considered as the dredging residue and does not need to be processed;
when the error of the comparison result is more than 10 percent and the ratio Re of the capacity of the columnar sediment sample to the total sediment dredging amount is more than 2 percent, the supplementary dredging is carried out.
Further, the method for determining the release flux of the nitrogen and phosphorus pollutants in the bottom sludge in the step (1) is as follows:
pumping the overburden water of the columnar sediment sample collected in situ, simulating dredging at equal intervals until the depth below a sediment sludge layer is d1, adding the water sample collected in situ along the sidewall of the residual sediment column sample obtained by simulating dredging without disturbance, wherein the depth of the water sample is d2, culturing for more than 72 hours in a constant-temperature water bath, respectively taking the overburden water sample at 0, 12, 24, 36, 48, 60 and 72 hours, supplementing the same amount of the in-situ water sample after taking the water, and then calculating the release flux of the sediment nitrogen and the phosphorus by the following formula:
in the formula: r is nitrogen and phosphorus release flux, and the dimension is mg/(m)2D); v is the total volume of the overlying water in the sediment column sample in the process of acquiring the release flux of nitrogen and phosphorus, and the dimension is L; cn、C0And Cj-1Respectively the concentrations of nitrogen and phosphorus in the overlying water during the nth sampling, the initial sampling and the j-1 sampling, and the dimension is mg/L; caThe concentration of nitrogen and phosphorus in the added raw water sample is mg/L in dimension; vj-1Sample volume (50mL) at j-1, dimension L; a is the area and amount of mud-water interface in the bottom mud column sampleLine is m2(ii) a t is the time for the release experiment to be carried out, and the dimension is d;
and when r is less than 0, the corresponding depth of the data is D1, nitrogen and phosphorus at the bottom of the dredging depth are not released to the overlying water body any more, and finally the dredging depth is determined to be D1, and D1 is more than or equal to D1.
Further, in the method for determining the release flux of the nitrogen and phosphorus pollutants in the bottom sediment, the depth d1 of the columnar bottom sediment sample dredged to the position below the bottom sediment sludge layer is 20cm, and the depth of the added water sample is also 20 cm; the columnar sediment samples simulate dredging at intervals of every 5cm during dredging.
Further, the ecological risk of the heavy metal in the bottom mud in the step (1) is determined by the following formula,
wherein, RI represents the potential ecological risk index of heavy metal;
as, Cd, Cr, Cu, Hg, Ni, Pb and Zn are 10, 30, 2, 5, 40, 5 and 1, respectively, which is the toxicity response coefficient of the metal i; ciThe measured concentration of metal i;
background content for metal i;
when RI <135, it means that the ecological risk of heavy metals in the bottom sludge is low;
when RI is more than or equal to 135 and less than 265, the heavy metal of the bottom sediment has moderate ecological risk;
when RI is less than or equal to 265 and less than 525, the heavy metal of the sediment is serious ecological risk, and the regulation work such as dredging is determined to be needed;
when RI is more than or equal to 525, serious ecological risks exist in the bottom sludge heavy metals;
the dredging depth is determined as the depth D2 of the sediment when the potential ecological risk index RI of the heavy metal is greater than or equal to 265.
Further, the ecological risk of the persistent organic pollutants in the step (1) is evaluated by adopting an ecological exposure risk low value (ERL) -ecological exposure risk median value (ERM) method; when the sediment sample depth is the persistent organic contaminant content > ERL value at D3, D3 is determined to be the dredging depth.
The ecological risk assessment of the persistent organic pollutants in the sediment composite pollution assessment method system is carried out by taking the obtained background content as reference and assessing the ecological risk of the persistent organic pollutants in the sediment by using an ecological exposure risk low value (ERL) -ecological Exposure Risk Median (ERM) method (Long et al, Environmental management,1995.19: 81-97).
Preferably, the ecological exposure risk low value (ERL) -the ecological exposure risk median value (ERM) of persistent organic pollutants in the sediment is shown in the following table (refer to Long et al, Environmental management,1995.19: 81-97):
further, the risk evaluation of the black and odorous water body induced by the sediment in the step (1) takes the content of Acid Volatile Sulfur (AVS) in the sediment and the porosity as judgment indexes,
when AVS >31.9mg/kg and porosity >0.60 in the sediment with the depth of D4 or more, the risk of inducing the black and odorous water exists, and the sediment dredging depth is determined to be more than or equal to D4.
Further, in the process of determining the dredged sediment resuspension chain Rs in the step (2), sampling of the water body is performed at equal intervals of 10m within a radius of 500m by taking the dredging point as a circle center.
Further, in the evaluation process of the dredged sediment dredged residues in the step (3), the cylindrical sediment sample is collected by taking a dredging point as a circle center and sampling at equal intervals of 50m within a radius of 500 m.
Further, the persistent organic pollutants are polycyclic aromatic hydrocarbons, organic chlorine or polychlorinated biphenyl.
Further, in the evaluation of the dredged sediment dredged residue in the step (3), the control amount of the dredged residue should be less than 2% of the total dredged sediment amount.
Has the advantages that: compared with the prior art, the invention comprehensively considers the composite pollution condition of the sediment, the release and ecological risks of pollutants before and after the sediment is dredged, the sediment and pollutant resuspension caused by the dredging engineering and the residual polluted sediment of the dredging engineering. On one hand, the pollution control effect can be maximized aiming at the bottom mud composite pollution condition, the inhibition on the release of various pollutants in the bottom mud and the removal effect on the risks of various harmful pollutants can be obviously improved, and the method has important environmental significance; on the other hand, the method can obviously reduce the times of repeated dredging aiming at the problems of repeated release of the dredged sediment pollution, repeated recovery of the sediment pollution and the like, and has important significance for reducing the loss of manpower and material resources caused by a large amount of repeated dredging and improving the control effect of the environmental-friendly dredging on the water body pollution.
Drawings
FIG. 1 is a schematic diagram of sediment deposition before the implementation of a certain lake bay dredging project of a nested lake, which is obtained by the investigation of a sediment composite pollution assessment method system;
FIG. 2 is a schematic diagram of a multi-target environment-friendly dredging method of composite polluted sediment based on a 4R theory;
FIG. 3 is a dredging control effect diagram for the black and odorous water body obtained by the system research of the sediment composite pollution assessment method;
FIG. 4 is a diagram of the effect of sediment dredging residues on the endogenous release after dredging in the multi-target accurate dredging method establishment system;
FIG. 5 is a diagram showing the change of water content of the sediment after the implementation of a certain bay dredging project of a nested lake after the composite polluted sediment multi-target environment-friendly dredging method based on the 4R theory is used for dredging;
FIG. 6 is a graph of the change of the phosphate release flux of the sediment after dredging by the composite polluted sediment multi-target environmental protection dredging method based on the 4R theory;
FIG. 7 is a graph showing the ammonia nitrogen release flux change of the sediment after dredging by the composite polluted sediment multi-target environment-friendly dredging method based on the 4R theory;
FIG. 8 is a graph showing the change of heavy metal content in the sediment after dredging by the composite polluted sediment multi-target environment-friendly dredging method based on the 4R theory;
FIG. 9 is a graph showing the content change of persistent organic pollutants in the sediment after dredging by the composite polluted sediment multi-target environmental-friendly dredging method based on the 4R theory;
in fig. 2, 1 is a mud-water interface, 2 is a dredging interface which must be reached based on pollutant release ecological Risk (Risk in the figure), 3 is a dredging interface which must be reached based on persistent organic pollutant ecological exposure control, 4 is a dredging interface which must be reached based on body water black and odor Risk control, 5 is a dredging interface which must be reached based on heavy metal potential ecological Risk control, 6 is a dredging depth which must be reached based on pollutant release, 7 is a dredging depth which must be reached based on persistent organic pollutant ecological exposure Risk, 8 is a dredging depth which must be reached based on body water black and odor Risk control, 9 is a dredging depth which must be reached based on heavy metal potential ecological Risk control, 10 is body water Resuspension particulate matter (Resuspension) during dredging, and 11 is dredging engineering residue (Residual).
Detailed Description
The invention will be further elucidated with reference to the following description of an embodiment in conjunction with the accompanying drawing. It is to be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention, which is to be given the full breadth of the appended claims and any and all equivalent modifications thereof which may occur to those skilled in the art upon reading the present specification.
The invention provides an accurate dredging method aiming at the comprehensive control of multiple pollution targets, and particularly aims at the sediment with complex pollution sources and diversified pollutants in rivers and lakes, comprehensively evaluates the Release of pollutants (Release) in the sediment before and after dredging, the ecological Risk (Risk) of harmful pollutants, the Resuspension (Resuspension) of the sediment and the pollutants during the dredging process and the dredging residues (Residual), and improves the environmental-friendly dredging efficiency and the pollution control effect aiming at the composite polluted sediment.
1) According to the sediment composite pollution assessment method system, sediment deposition depth distribution conditions of a target area and a control area without dredging are obtained, survey density is 100m multiplied by 100m, specific deposition conditions are shown in figure 1, the deposition depth of polluted sediment in a lake inlet is 10-50 cm, and the deposition depth of a central area of the lake inlet is the maximum.
2) According to the sediment composite pollution evaluation method system, on the basis of the sediment sedimentation of the polluted sediment, a columnar sample is collected, the density of the sampling point is 500m multiplied by 500m, the depth of the columnar sample reaches the depth of 20cm of a background layer, and the maximum sampling depth reaches 70 cm.
3) According to the sediment composite pollution evaluation method system, the dredging depth D1 (6 in figure 2) for the nitrogen and phosphorus release inhibition in the sediment is 15cm and is obtained by simulating the dredging investigation, and the dredging interface 2 is required to be reached. Namely, when the dredging depth reaches 15cm, the release flux of nitrogen and phosphorus in the sediment is rapidly reduced to be below 0 after dredging, and the release of nitrogen and phosphorus in the sediment to an overlying water body can be effectively inhibited. Wherein, the release inhibition effect of ammonia nitrogen in the sediment can be achieved after 4 months of dredging, namely the inhibition effect can be achieved after the newly-generated mud-water interface is stable, which is related to the conversion of the ammonia nitrogen under the oxidation-reduction condition. The sediment of the control area which is not dredged keeps the release state of nitrogen and phosphor all the time.
3) According to the sediment composite pollution assessment method system, the potential ecological risk index method is used for assessing, when the depth D2 (9 in figure 2) reaches 30cm, the dredging interface 5 needs to be reached, and the potential ecological risk index RI of toxic and harmful heavy metals in the sediment is reduced to below 265.
4) According to the sediment composite pollution assessment method system, when the depth D3 (7 in FIG. 2) reaches 20cm, namely reaches the dredging interface 3, the content of each persistent organic pollutant in the sediment is reduced to be lower than the ecological exposure low value through the assessment of an ecological exposure low value (ERL) -ecological exposure median value (ERM) method.
5) According to the sediment composite pollution evaluation method system, when the depth D4 (8 in figure 2) reaches 25cm, namely the dredging interface 4 is reached, the AVS content in the sediment can be reduced to be below 31.9mg/kg, and the porosity of the sediment can be reduced to be below 60.5% by a simulation control experiment mode. At this dredging depth, S in the body of water2-The concentration is obviously reduced (as shown in figure 3), the water body does not generate black odor, and the water body does not generate black odorThe water body under the dredging depth of the river is black and smelly.
6) Determining an accurate dredging depth judgment method in a system according to the multi-target accurate dredging method, wherein the final dredging depth D is as follows: max (D1, D2, D3, D4) 30 cm.
7) According to the multi-target accurate dredging method, a system is established, and 10000m is carried out in the lake bay by using cutter suction type dredging2While a control area without dredging was set at a distance of 1km from the demonstration area. In the region with the dredged residues above 2%, the dredged residues are found to cause the sediment flux after dredging to be kept at a high level (as shown in figure 4), and the endogenous release inhibition effect cannot be achieved.
8) The water content of the dredging area is significantly reduced while the water content of the control area which is not dredged is kept unchanged (as shown in figure 5), the water particle content of the dredging area (10 in figure 2) is similar to that of the control area, and the resuspension of the sediment is less than 1 percent.
9) Through the evaluation of the dredged residues (11 in figure 2), the amount of the dredged residues is about 1 percent, and the requirement of the dredged residues is met.
10) After the dredging project is implemented, the release of phosphate in the sediment is rapidly inhibited, the release of phosphorus in the sediment is effectively controlled (figure 6), and the sediment of the non-dredging area is still in a phosphorus release state.
11) After the dredging engineering is implemented, the ammonia nitrogen flux of the sediment in the dredging area is higher just after the dredging is finished, the ammonia nitrogen flux can be effectively controlled about 4 months after the dredging is finished (figure 7), and the ammonia nitrogen flux of the sediment in the non-dredging area is always at a higher release level.
12) After the dredging engineering is implemented, the heavy metal content in the sediment is obviously reduced, the potential ecological risk of the heavy metal is reduced to below 265 (figure 8), and the potential ecological risk of the heavy metal in the sediment in an unclogged area is still high.
13) After the dredging engineering is implemented, the content of persistent organic pollutants in the sediment is obviously reduced, the content of persistent organic pollutants is reduced to be lower than the ecological exposure risk low value, and the ecological risk is controlled (figure 9).
Claims (10)
1. A multi-target environment-friendly dredging method of composite polluted sediment based on a 4R theory is characterized by comprising the following steps:
(1) firstly, establishing an evaluation system of the bottom mud combined pollution condition based on multiple targets, wherein the evaluation system comprises:
evaluating the release of nitrogen and phosphorus pollutants in the sediment at different depths, and determining the dredging depth D1 according to the release flux of the nitrogen and phosphorus pollutants;
respectively evaluating the ecological risks of the heavy metals in the sediment, the persistent organic pollutants and the water body black and odor risk induced by the sediment, and respectively determining dredging depths D2, D3 and D4 according to the heavy metals in the sediment, the persistent organic pollutants and the ecological risks of the sediment induced water body black and odor;
then, the final dredging depth D is determined according to the pass D Max (D1, D2, D3, D4);
(2) then taking the dredging point as the center of a circle, sampling and analyzing the instantaneous particle content m in the water at intervals for the surrounding water body, determining the resuspension quantity Rs of the dredged sediment through the following formula,
Rs＝m/M
wherein M is the total dredging amount;
when the Rs is more than 1%, dredging the water body sediment by adopting a cutter-suction dredging method;
(3) taking the dredging point as the center of a circle, collecting columnar sediment samples at intervals for the sediment around the water body after dredging, analyzing the capacity, the water content and the TOC of the columnar sediment samples, comparing the capacity, the water content and the TOC with the sediment at the same depth before dredging,
when the difference value of the comparison result is within 10%, the dredging residue is considered to be the dredging residue, and the treatment is not needed;
when the difference value of the comparison result is more than 10 percent and the ratio Re of the capacity of the columnar sediment sample to the total sediment dredging amount is less than 2 percent, the sample is still considered as the dredging residue and does not need to be treated;
when the difference value of the comparison result is more than 10 percent and the ratio Re of the capacity of the columnar sediment sample to the total sediment dredging amount is more than 2 percent, the supplementary dredging is carried out.
2. The multiple-target environment-friendly dredging method for the composite polluted bottom mud based on the 4R theory as claimed in claim 1, is characterized in that: the method for determining the release flux of the nitrogen and phosphorus pollutants in the bottom sludge in the step (1) comprises the following steps:
pumping the overburden water of the columnar sediment sample collected in situ, simulating dredging at equal intervals until the depth below a sediment sludge layer is d1, adding the water sample collected in situ along the sidewall of the residual sediment column sample obtained by simulating dredging without disturbance, wherein the depth of the water sample is d2, culturing for more than 72 hours in a constant-temperature water bath, respectively taking the overburden water sample at 0, 12, 24, 36, 48, 60 and 72 hours, supplementing the same amount of the in-situ water sample after taking the water, and then calculating the release flux of the sediment nitrogen and the phosphorus by the following formula:
in the formula: r is nitrogen and phosphorus release flux, and the dimension is mg/(m)2D); v is the total volume of the overlying water in the sediment column sample in the process of acquiring the release flux of nitrogen and phosphorus, and the dimension is L; cn、C0And Cj-1Respectively the concentrations of nitrogen and phosphorus in the overlying water during the nth sampling, the initial sampling and the j-1 sampling, and the dimension is mg/L; caThe concentration of nitrogen and phosphorus in the added raw water sample is mg/L in dimension; vj-1Sample volume (50mL) at j-1, dimension L; a is the area of the mud-water interface in the bottom mud column sample, and the dimension is m2(ii) a t is the time for the release experiment to be carried out, and the dimension is d;
and when r is less than 0, the corresponding depth of the data is D1, nitrogen and phosphorus at the bottom of the dredging depth are not released to the overlying water body any more, and finally the dredging depth is determined to be D1, and D1 is more than or equal to D1.
3. The multiple-target environment-friendly dredging method for the composite polluted bottom mud based on the 4R theory as claimed in claim 2, characterized in that: in the method for determining the release flux of the nitrogen and phosphorus pollutants in the bottom sediment, the depth d1 of a columnar bottom sediment sample dredged to be below a bottom sediment sludge layer is 20cm, and the depth of an added water sample is also 20 cm; the columnar sediment samples simulate dredging at intervals of every 5cm during dredging.
4. The multiple-target environment-friendly dredging method for the composite polluted bottom mud based on the 4R theory as claimed in claim 1, is characterized in that: the ecological risk of the heavy metals in the bottom sludge in the step (1) is determined by the following formula,
wherein, RI represents the potential ecological risk index of heavy metal;
as, Cd, Cr, Cu, Hg, Ni, Pb and Zn are 10, 30, 2, 5, 40, 5 and 1, respectively, which is the toxicity response coefficient of the metal i; ciThe measured concentration of metal i;
background content for metal i;
when RI <135, it means that the ecological risk of heavy metals in the bottom sludge is low;
when RI is more than or equal to 135 and less than 265, the heavy metal of the bottom sediment has moderate ecological risk;
when RI is less than or equal to 265 and less than 525, the heavy metal of the sediment is serious ecological risk, and the regulation work such as dredging is determined to be needed;
when RI is more than or equal to 525, serious ecological risks exist in the bottom sludge heavy metals;
the dredging depth is determined as the depth D2 of the sediment when the potential ecological risk index RI of the heavy metal is greater than or equal to 265.
5. The multiple-target environment-friendly dredging method for the composite polluted bottom mud based on the 4R theory as claimed in claim 1, is characterized in that: evaluating the ecological risk of the persistent organic pollutants in the step (1) by adopting an ecological exposure risk low value (ERL) -ecological exposure risk median value (ERM) method;
when the sediment sample depth is the persistent organic contaminant content > ERL value at D3, D3 is determined to be the dredging depth.
6. The multiple-target environment-friendly dredging method for the composite polluted bottom mud based on the 4R theory as claimed in claim 1, is characterized in that: assessing the risk of water body black and odor induced by the sediment in the step (1), taking the content of Acid Volatile Sulfur (AVS) in the sediment and the porosity as judgment indexes,
when AVS >31.9mg/kg and porosity >0.60 in the sediment with the depth of D4 or more, the risk of inducing the black and odorous water exists, and the sediment dredging depth is determined to be more than or equal to D4.
7. The multiple-target environment-friendly dredging method for the composite polluted bottom mud based on the 4R theory as claimed in claim 1, is characterized in that: in the process of determining the dredged sediment resuspension chain Rs in the step (2), sampling of the water body is performed at equal intervals of 10m within the radius of 500m by taking the dredging point as the center of a circle.
8. The multiple-target environment-friendly dredging method for the composite polluted bottom mud based on the 4R theory as claimed in claim 1, is characterized in that: in the evaluation process of the dredged sediment dredged residues in the step (3), the collection of the columnar sediment samples takes a dredging point as the center of a circle, and the sampling is carried out at equal intervals of 50m within the radius of 500 m.
9. The multiple-target environment-friendly dredging method for the composite polluted bottom mud based on the 4R theory as claimed in claim 5, is characterized in that: the persistent organic pollutants are polycyclic aromatic hydrocarbons, organic chlorine or polychlorinated biphenyl.
10. The multiple-target environment-friendly dredging method for the composite polluted bottom mud based on the 4R theory as claimed in claim 1, is characterized in that: in the evaluation process of the dredged sediment dredged residue in the step (3), the control amount of the dredged residue is less than 2% of the total dredged sediment.
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