CN103771674B - A kind of in-situ remediation method of polluted bed mud - Google Patents

Abstract

The invention discloses a kind of in-situ remediation method of polluted bed mud, belong to in-situ sediment remediation technical field, the method is that cladding thickness is the loess formation of 10 ~ 15cm on polluted bed mud, loess formation and polluted bed mud interface place establish polarity carbon electrode I, polarity carbon electrode II is established at loess formation and water interface place, polarity carbon electrode I is connected as negative electrode with power cathode, and polarity carbon electrode II is connected as anode with positive source, and energising hydrolysis carries out in-situ immobilization to polluted bed mud.The present invention adds electrode in covering material, and during energising hydrolysis, pollutent in bed mud of can effectively degrading, creates a redox gradient rapidly, provide electron donor and acceptor in bed mud tectum, stimulates microorganism growth, strengthens the biological degradation of pollutent.

Description

An in-situ remediation method for polluted sediment

technical field

The invention belongs to the technical field of in-situ restoration of bottom mud, and in particular relates to an in-situ restoration method of polluted bottom mud.

Background technique

Water pollution is an important environmental problem that exists worldwide. In the process of river pollution control, the control of polluted sediment has always been the main difficulty. Pollutants enter the water body through atmospheric deposition, rainwater leaching, wastewater discharge, soil erosion and erosion, and gradually settle and accumulate in the bottom mud of the water body. Through physical, chemical and biological exchanges with the overlying water body, the pollutants in the sediment will be re-released and become an important internal pollution source that affects and restricts the quality of the overlying water.

The U.S. Environmental Protection Agency (EPA) proposed "Guidelines for Remediation of Contaminated Sediment" in 2004, which proposed three main methods: dredging, natural restoration under monitoring, and capping. Contaminated sediments often contain complex mixtures of toxic anthropogenic organic and inorganic pollutants. If these mixtures are directly degraded, not only the cost is high but the efficiency is extremely limited, and if they are allowed to recover naturally, the rate is very slow. In this case, use in-situ cover to treat the contaminated sediment. By covering, the bottom mud is separated from the overlying water, and the release of bottom mud pollutants to the overlying water is prevented. At the same time, the covering material can stabilize the polluted sediment, prevent it from resuspension or migration, and has an adsorption effect, which can reduce the flux of pollutants diffusing to the overlying water to a certain extent. The in-situ covering method is simply to cover the surface of the sediment with a layer of material to isolate the pollutants of the aquatic ecosystem. However, the risk to human and environmental health from contaminated sediment resurfaces when the cover material becomes saturated. Remedial measures based on electrochemical techniques have been developed, where electrodes may be placed in groundwater or sediments to treat pollutants from chlorinated solvents and reactive compounds, mixed organic-inorganic wastes and heavy metals. Electrodes in these cases can be used directly to degrade pollutants, sequester pollutants at the electrodes, or collect pollutants for further processing through electrokinetic processes; both of these processes require high voltages or a large number of electrodes, adding to the cost. Obviously, these methods cannot fully meet the usage requirements at present.

Contents of the invention

Purpose of the invention: In view of the deficiencies in the prior art, the purpose of the present invention is to provide an in-situ remediation method for polluted sediment, which can not only stimulate the degradation of pollutants in the sediment, but also create a redox environment in the sediment cover layer. Gradient and provide electron donors and acceptors for the degradation of pollutants, and enhance the degradation efficiency of pollutants in the sediment.

Technical solution: In order to realize the above-mentioned purpose of the invention, the technical solution adopted in the present invention is:

An in-situ restoration method for polluted bottom mud: covering the polluted bottom mud with a loess layer with a thickness of 10-15 cm, setting a polar carbon pole I at the interface between the loess layer and the polluted bottom mud, and setting a polar carbon pole I at the interface between the loess layer and water The polar carbon pole II is set, the polar carbon pole I is connected to the negative pole of the power supply as the cathode, and the polar carbon pole II is connected to the positive pole of the power supply as the anode, and the contaminated sediment can be repaired in situ by electrification and hydrolysis.

The loess has a density of 2-3 g·cm ^-3 and an average particle size of 0.1-0.2 mmol/L.

For the electrified hydrolysis, the output voltage of the power supply is 3-4V.

Working principle: The bottom mud in-situ covering technology provided by the present invention is to place a certain thickness of loess on the mud-water interface as a barrier to isolate pollutants from diffusing to the overlying water layer, and place electrodes in it. When energized and hydrolyzed, the cathode generates H ₂ to stimulate biological The reduction reaction of degradation, the anode produces O ₂ , which stimulates the oxidation reaction of biodegradation; overcoming the natural conditions can not provide continuous redox conditions for the complete mineralization of pollutants, nor can it provide enough electron donors and Acceptor limiting conditions rapidly create a redox gradient while providing electron donors and acceptors to stimulate microbial growth and enhance the biodegradation of pollutants.

Beneficial effects: Compared with the prior art, the in-situ restoration method of polluted sediment of the present invention is not only simple and reasonable, but also can effectively degrade the pollutants in the sediment when the electrode is added to the covering material, and the pollutants in the sediment can be covered in the sediment. Rapidly create a redox gradient in the layer, while providing electron donors and acceptors, stimulating microbial growth and enhancing the biodegradation of pollutants.

Description of drawings

Figure 1 is a schematic diagram of the principle of electrokinetic remediation of polluted sediment;

Fig. 2 is T-cell reactor schematic diagram;

Figure 3 is a diagram of the redox potential change of T-cell 1;

Figure 4 is a diagram of the redox potential change of T-cell 2;

Figure 5 is a diagram of the redox potential change of T-cell 3;

Fig. 6 is a schematic diagram of a laboratory test reactor;

Fig. 7 is a relation diagram between applied voltage and nitrobenzene reduction rate constant;

Fig. 8 is a relation diagram of initial nitrobenzene concentration and nitrobenzene reduction rate constant;

Figure 9 is a graph showing the relationship between the presence of organic pollutants and the reduction rate constant of nitrobenzene.

Detailed ways

The present invention will be further described below in conjunction with specific examples, and the present invention is not limited to the following examples.

Example 1

As shown in Figure 1, the in-situ remediation method of polluted sediment includes the following steps:

1) Place a polar carbon electrode I at the mud-water interface perpendicular to the pollutant transmission path, and connect the polar carbon electrode I to the negative pole of the power supply as the cathode;

2) Cover the polar carbon electrode I with a covering material with a thickness of 10~15cm (loess layer, the density of loess is 2~3g·cm ^-3 , and the average particle size is 0.1~0.2mmol/L);

3) Another polar carbon pole II is placed at the interface between the loess layer and the water perpendicular to the pollutant transmission path, and the polar carbon pole II is connected to the positive pole of the power supply as an anode;

4) Power hydrolysis, the output voltage of the power supply is 3V.

The in-situ remediation method of polluted bottom mud is to place a certain thickness of loess on the mud-water interface as a barrier to isolate pollutants from diffusing to the overlying water layer, and place electrodes in it. When energized and hydrolyzed, the cathode generates H ₂ to stimulate the reduction reaction of biodegradation. The anode produces O ₂ to stimulate the oxidation reaction of biodegradation; it overcomes the limitation that natural conditions cannot provide continuous redox conditions for the complete mineralization of pollutants, nor can they provide sufficient electron donors and acceptors for the biodegradation of pollutants , rapidly creating a redox gradient while providing electron donors and acceptors to stimulate microbial growth and enhance the biodegradation of pollutants.

Example 2

The T-cell reactor shown in Figure 2 is used as a laboratory device to evaluate the ability of the carbon electrode to create a redox gradient, thereby reflecting the biodegradability of pollutants in this environment. A 4cm-thick sediment (taken from the Confucius Temple section of the Qinhuai River in Nanjing) was placed in the lower layer of the reactor, and a 14×7 cm woven carbon cloth was placed on the upper layer of the sediment as the polar carbon electrode I. Place a 10cm thick loess layer (density 2~3g·cm ^-3 , average particle size 0.1~0.2mmol/L) on the cathode. A 14 × 7 cm woven carbon cloth was placed on the loess layer as the polar carbon pole II. Add water from the same section as the above-mentioned sediments to the reactor. The polar carbon pole I is connected to the negative pole of the power supply as the cathode, and the polar carbon pole II is connected to the positive pole of the power supply as the anode.

In the experiment, three of the above-mentioned reactors were used as comparative experiments, respectively marked as T-cell 1 reactor, T-cell 2 reactor, and T-cell 3 reactor. The electrodes in T-cell 1 and T-cell 2 reactors were respectively connected to two 4 V Huayi 382202 DC power supplies with copper wires. Power supply 1 outputs 4V to the T-cell 1 reactor and supplies power continuously for 100 days. The power supply 2 outputs 4V to the T-cell 2 reactor for 30 days, and then disconnects the power supply. The T-cell 3 reactor is not connected to a power source. Observe the above three reactors, and use Pt microelectrodes to measure the oxidation-reduction potentials of the three reactors at different stages and at different depths (the interface between the loess and the water layer is 0, and the depth increases sequentially), which reflects that the carbon pole creates a redox gradient. Ability. The results are shown in Figures 3~5. In Figures 3~5, d represents the depth in meters.

As shown in Figure 3, the redox potential change diagram of T-cell 1. Before the output voltage of the T-cell 1 reactor was 4V, the redox potential difference between the anode and the cathode was 90mV, and when the output voltage continued for 98 days, the redox potential difference between the anode and the cathode was 700mV, which was much larger than that of the anode and the cathode before the output voltage of the reactor redox potential difference.

As shown in Figure 4, the redox potential change diagram of T-cell 2 . Before the output voltage of the T-cell 2 reactor was 4V, the redox potential difference between the anode and the cathode was 80mV. When the output voltage continued for 28 days, the redox potential difference between the anode and the cathode was 700mV, which was much larger than that of the anode and the cathode before the output voltage of the reactor. redox potential difference. After the power is turned off, the redox potential difference gradually decreases.

As shown in Figure 5, the redox potential change diagram of T-cell 3 . In the T-cell 3 reactor, the initial redox potential difference between the anode and the cathode was 65mV. On the 98th day, the redox potential difference between the anode and the cathode was 5mV, and the redox potential difference basically remained unchanged.

It can be concluded that the addition of electrode output voltage in the reactor can quickly create a redox gradient, which overcomes the limitation that natural conditions cannot provide continuous redox conditions for the complete mineralization of pollutants, thereby enhancing the microbial oxidation of organic pollutants Ability.

Example 3

As shown in Figure 6, it is a laboratory test reactor, which contains two glass chambers connected by cation exchange membranes, and carbon cloths of 12.6×6.25 cm are placed in the glass chambers as electrodes; the two electrodes pass through the diameter 0.64cm, length 15.2cm graphite rod is connected to an E3620A DC power supply; each chamber has 60ml headspace and 250ml buffer solution, the buffer solution contains 20mmol/L NaHCO ₃ and 20mmol/L NaCl, and with 5% concentration The NaOH was used to adjust the pH to 6.5, matching the strength of the sediment pore water. This device simulates the conventional water environment and is used to test the influence of voltage, initial pollutant concentration and natural organic matter concentration on the degradation of pollutants, so as to provide reference data for the design of the in-situ covering layer containing electrodes and make the best design scheme.

Nitrobenzene is a relatively common pollutant in general waters. Taking nitrobenzene as a pollutant, the effects of applied voltage, initial pollutant concentration and the presence of natural organic matter on the degradation of pollutants were studied respectively. Add nitrobenzene to one of the chambers, connect to the negative pole of the power supply as the cathode in the reduction reaction, and then switch to the positive pole as the anode in the oxidation reaction. In this reactor, nitrobenzene is theoretically reduced to aniline at the cathode, the intermediate product is nitrosobenzene, and aniline is subsequently removed at the anode.

As shown in Figure 7, the effect of the applied voltage on the reduction rate of nitrobenzene was tested. When the voltage is from 2V to 3.5V, the reduction rate of nitrobenzene increases from 0.3 h?1 to 1.6 h?1, and the reduction rate of nitrosobenzene increases from 0.04 h ^?1 to 0.64 h ^?1 ; the voltage is higher than 3.5V When , the reduction rate of nitrobenzene and nitrosobenzene did not increase with the increase of voltage; when the voltage was less than 2V, the reaction would not occur.

As shown in Figure 8, the effect of the initial nitrobenzene concentration on the reduction rate of nitrobenzene was tested. If the initial nitrobenzene concentration was reduced from 100 μM to 5 μM, the reduction rate of nitrobenzene increased from 0.88 h ⁻¹ to 7.9 h ⁻¹ , and that of nitrosobenzene increased from 0.36 h ⁻¹ to 1.7 h ⁻¹ .

As shown in Figure 9, the influence of the presence of natural organic matter on the reduction rate of nitrobenzene was tested. Test with humic acid solution (containing 14.4 mg/L DOC). When no natural organic matter exists, the rate constant of nitrobenzene reduction is 2.2 h ^-1 . When humic acid solution was added, the reduction rate constant of nitrobenzene was 0.8 h ⁻¹ . The reduction rate constants of nitrosobenzene were all around 0.4 h ⁻¹ .

The bottom mud in-situ covering technology provided by the present invention is to place loess with a thickness of 10 to 15 cm on the sediment water interface as a barrier to isolate pollutants from diffusing to the overlying water layer; due to natural conditions, continuous redox cannot be provided for the complete mineralization of pollutants conditions, and cannot provide sufficient electron donors and acceptors for the biodegradation of pollutants. The invention arranges electrodes in the loess covering layer, quickly creates a redox gradient, and at the same time provides electron donors and acceptors to stimulate the growth of microorganisms and enhance the biodegradation of pollutants. From the above experiments, it can be concluded that the reduction rate constants of nitrobenzene and nitrosobenzene all increase with the increase of the applied voltage when the voltage is between 2V and 3.5V, and stop increasing when the voltage is higher than 3.5V, so the preferred voltage is 3~4V. When the initial nitrobenzene concentration decreased from 100 μM to 5 μM, the reduction rate constant of nitrobenzene became 9 times of the original, and the reduction rate constant of nitrosobenzene became 5 times of the original. The presence of natural organic matter decreased the reduction rate of nitrobenzene, but the reduction rate of nitrosobenzene was basically unchanged.

Claims (3)

1. An in-situ remediation method for polluted bottom mud, characterized in that: the polluted bottom mud is covered with a loess layer with a thickness of 10 to 15 cm, a polar carbon pole I is set at the interface between the loess layer and the polluted bottom mud, and the loess A polar carbon pole II is set at the interface between the layer and the water, and the polar carbon pole I is connected to the negative pole of the power supply as the cathode, and the polar carbon pole II is connected to the positive pole of the power supply as the anode, and the polluted sediment can be repaired in situ by power-on hydrolysis; The polar carbon pole I and the polar carbon pole II are both arranged in the loess layer. 2. The method for in-situ remediation of polluted bottom mud according to claim 1, characterized in that the density of the loess is 2-3 g·cm ^-3 and the average particle size is 0.1-0.2 mmol/L. 3. The method for in-situ remediation of polluted bottom mud according to claim 1, characterized in that: for the electrified hydrolysis, the output voltage of the power supply is 3-4V.