Equipment and method for repairing odor substances in pesticide sites

Abstract

The present invention discloses a device and a method for repairing odor substances in a pesticide site. The device includes a heating unit, a reagent preparation unit, a pumping and injection circulation unit, a monitoring and control unit, and a power control unit. The present invention organically combines chemical oxidation, thermal desorption, and hydrolysis, and can simultaneously treat the composite pollution of underground soil and groundwater by chlorinated olefins and chlorinated alkanes, solving the problem that single chemical oxidation cannot effectively degrade chlorinated alkanes, not only improving the treatment efficiency, but also saving the treatment cost.

Description

Technical Field

[0001] The present invention relates to an apparatus and method for repairing odor substances in pesticide sites, and belongs to the field of remediation of organic contaminated sites. Background Art

[0002] Halogenated hydrocarbons, especially chlorinated hydrocarbons, are commonly used organic solvents and raw materials or intermediates in industries such as pesticides. Such substances are both typical characteristic pollutants and odor substances causing malodors in the site, seriously threatening human health and the ecological environment. Chlorinated hydrocarbons in pesticide sites mainly include two categories: chlorinated alkane hydrocarbons and chlorinated olefins. Among them, chlorinated alkane hydrocarbons are mainly chloroform, carbon tetrachloride, 1,1,1-trichloroethane or 1,1,2,2-tetrachloroethane, etc., and chlorinated olefins are mainly trichloroethylene and tetrachloroethylene, etc.

[0003] In-situ chemical oxidation is a mainstream technology for treating organic contaminated sites. The principle is to oxidize and decompose pollutants into substances with low toxicity or non-toxicity. Usually, unsaturated chlorinated olefins containing covalent bonds are easily removed by chemical oxidation, while highly chlorinated saturated alkanes without covalent bonds are not easily chemically oxidized. Therefore, for pesticide sites contaminated with a mixture of chlorinated olefins and chlorinated alkanes, the efficiency of single chemical oxidation treatment is not ideal, and it is difficult to achieve the remediation goal. Adopting a method of first chemical reduction and then chemical oxidation may be a solution, but since the main reducing agents currently used in the market are nano-zero-valent iron or micro-zero-valent iron, the cost of the reducing agent is high, and subsequent chemical oxidation requires a large amount of oxidant to convert the remaining strongly reducing soil environment.

[0004] In-situ thermal desorption is an efficient remediation technology for treating organic contaminated sites that has gradually emerged in China in recent years. The principle is to heat the soil to promote the transformation of pollutants into the gas phase, and then combined with extraction, transfer the pollutants to the ground for centralized treatment. However, heating the soil, extraction, and treating the tail gas require a large amount of energy, and high energy consumption is the bottleneck restricting the further popularization of this technology.

[0005] Hydrolysis is a water substitution reaction that contributes to the decomposition of many organic molecules. Through hydrolysis reactions, organic compounds are mineralized or transformed into another organic compound that is less toxic or more degradable than its parent. Hydrolysis is very important for chlorinated and other halogenated compounds (especially halogenated alkanes). After the hydrolysis of highly chlorinated saturated alkanes, hydroxyl functional groups are introduced to generate alcohols, aldehydes, or olefins, etc., thereby reducing toxicity or making it easier to be oxidized. For example, after the hydrolysis of the fumigants dichloropropane and trichloropropane, propylene glycol and glycerol are formed, after the hydrolysis of 1,2-dichloroethane, acetaldehyde is formed, and after the hydrolysis of tetrachloroethane, trichloroethylene is formed, etc. However, the reaction rate under natural environmental conditions is too slow for the effective degradation of harmful organic compounds, and the application of hydrolysis in environmental remediation has been ignored. The main factors affecting the hydrolysis rate are temperature and pH. With the rise of in-situ thermal desorption technology, heat treatment technology provides the possibility for applying hydrolysis reactions to a part of the environmental remediation field. Summary of the Invention

[0006] To solve the deficiencies in the prior art, the present invention provides a device and method for repairing odor substances in pesticide sites. The present invention organically combines chemical oxidation, thermal desorption, and hydrolysis, and can simultaneously treat chlorinated olefins and chlorinated alkanes in contaminated underground soil and groundwater, solving the problem that single chemical oxidation cannot effectively degrade chlorinated alkanes, not only improving the treatment efficiency but also saving the treatment cost.

[0007] To achieve the above object, the present invention adopts the following technical means:

[0008] The present invention provides a device for repairing odor substances in pesticide sites, and the device includes a heating unit, a chemical agent preparation unit, a pumping and injection circulation unit, a monitoring and control unit, and a power control unit;

[0009] The heating unit includes a plurality of heating wells for low-temperature heating of underground soil and groundwater;

[0010] The chemical agent preparation unit includes a chemical agent stirring tank and a water pump connected to each other for preparing chemical agents;

[0011] The pumping and injection circulation unit includes a plurality of extraction wells, extraction water pumps, sedimentation tanks, injection water pumps, and a plurality of injection wells connected in sequence; the inlet pipe of the water pump in the chemical agent preparation unit is inserted into the sedimentation tank, and the outlet pipe is connected to the chemical agent stirring tank for pumping the water in the sedimentation tank and injecting it into the chemical agent stirring tank; the outlet pipe of the chemical agent stirring tank and the outlet pipe of the sedimentation tank converge and are jointly connected to the injection water pump; the pumping and injection circulation unit is used for extracting groundwater, pre-treating groundwater, and injecting water and drugs;

[0012] The monitoring and control unit includes monitoring wells, monitoring devices, and control devices; the monitoring devices are arranged in the monitoring wells and are used to monitor the changes in the underground temperature field and the migration and diffusion of the medicament; the control devices are connected to the monitoring devices and display, record, and regulate the operating parameters of the other unit devices according to the monitoring situation;

[0013] The power control unit is connected to the other unit devices and is used to supply power to them.

[0014] Preferably, the odor substances include halogenated hydrocarbons.

[0015] Preferably, the heating elements in each heating well are electrodes for resistance heating or heating rods for heat conduction heating, and more preferably, they are electrodes for resistance heating.

[0016] Preferably, each extraction well and each injection well are arranged in an equilateral triangle layout, and each heating well is located at the center of each equilateral triangle.

[0017] Preferably, each extraction well and each injection well can switch the extraction or injection function according to the monitoring results of the monitoring and control unit.

[0018] Preferably, the monitoring device includes probe instruments such as thermocouples, multi-parameter water quality analyzers (pH, ORP, EC, etc.), water level gauges, watt-hour meters, voltage / ammeter, flow meters, and pressure gauges.

[0019] The present invention also provides a method for repairing odor substances in a pesticide site using the above equipment, and the method includes the following steps:

[0020] (1) Turn on the heating unit and the power control unit, and heat the underground soil and groundwater at a low temperature through each heating well;

[0021] (2) While heating at a low temperature, operate the extraction and injection circulation unit. The groundwater is extracted by each extraction well and transported to the sedimentation tank for pretreatment of sedimentation and pH adjustment. The pretreated groundwater is used for water injection and medicine injection. The water injection and medicine injection adopt a low-flow intermittent operation mode. In the medicine injection link, open the outlet valve of the medicine stirring tank and close the outlet valve of the sedimentation tank. Part of the pretreated groundwater in the sedimentation tank is pumped by a water pump into the medicine stirring tank, and then driven by an injection water pump, the prepared medicament is injected into the ground through each injection well. In the water injection link, close the outlet valve of the medicine stirring tank and open the outlet valve of the sedimentation tank. Part of the pretreated groundwater in the sedimentation tank is driven by the injection water pump to inject water into the ground through each injection well to promote the diffusion of the medicament;

[0022] (3) While carrying out low-temperature heating and groundwater pumping and injection circulation, by using the monitoring and control unit, according to the changes in the underground temperature field and the migration and diffusion of the medicament, display, record and regulate the functional layout, pumping and injection flow rates of each of the extraction wells and each of the injection wells, and the operation time and input power of each of the heating wells, so as to improve the effect of underground mass transfer and heat transfer;

[0023] (4) After the underground is heated to the target temperature, reduce the input power of each of the heating wells and enter the heat preservation stage. By regularly sampling and detecting, evaluate the degradation effect of pollutants and the remaining content of the medicament, and adjust the dosage of the medicament according to the detection situation to keep the concentration of the medicament within an appropriate range, further accelerate the reaction rate, shorten the repair time, until the repair reaches the standard.

[0024] Preferably, the odor substances include halogenated hydrocarbons.

[0025] Preferably, in step (1), the low-temperature heating is to increase the underground temperature by 1-2 °C per day.

[0026] Preferably, the chemicals used to adjust the pH in step (2) are quicklime, NaOH or KOH, and the target pH value is 10.5-11. More preferably, the chemical used is quicklime.

[0027] Preferably, the medicament prepared in step (2) is an oxidant, selected from sodium persulfate, potassium permanganate, hydrogen peroxide, Fenton's reagent. Preferably, it is sodium persulfate; the concentration of the medicament in step (4) is 10-80 g / L. Preferably, it is 40 g / L.

[0028] Preferably, the target temperature in step (4) is 40-50 °C. More preferably, it is 50 °C.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0030] 1. By means of heating, on the one hand, the chloroalkanes are heated and hydrolyzed to generate products that are easily oxidized, avoiding the use of expensive reducing agents; on the other hand, the activation efficiency of the oxidant is improved (thermal activation of 1 persulfate ion can generate 2 sulfate radicals, while other activation methods can only generate 1 sulfate radical), the oxidation ability is improved, and some VOCs can be pyrolyzed under heating conditions, reducing the dosage of the oxidant and lowering the cost of the repair medicament. In addition, the hydrolysis products react with the oxidant, avoiding the accumulation of hydrolysis products, which is beneficial to maintaining a high reaction rate of the hydrolysis reaction and shortening the hydrolysis time, overcoming the bottleneck problems of the difficulty of directly oxidizing chloroalkanes and the slow hydrolysis reaction rate under conventional conditions.

[0031] Equation for the hydrolysis of halogenated hydrocarbons:

[0032] RX + H 2 O=ROH + XH

[0033] Persulfate activation equation:

[0034] ① Thermal activation:

[0035] ② Other activation:

[0036] 2. Compared with single thermal desorption, on the one hand, the present invention reduces the heating energy consumption by lowering the heating temperature (target temperature 40 - 50 °C). Especially for chlorinated alkanes with boiling points greater than 100 °C such as tetrachloroethane (boiling point 146.4 °C), trichloropropane (boiling point 156 °C), and tetrachloropropane (boiling point 179 °C), the target temperature for thermal desorption of treating such pollutants is usually 100 °C or above. On the other hand, due to the reduced heating temperature and the absence of steam extraction, the equipment investment and operation costs for tail gas extraction and treatment are avoided. Since the heating temperature is limited, for the materials of extraction wells and injection wells with large usage, materials such as PPR or PVC can be selected instead of expensive stainless steel materials, thus reducing the overall remediation cost.

[0037] 3. The present invention adopts the method of low - flow pumping and injection circulation, which can effectively improve the mass transfer and heat transfer effects of groundwater. Especially because the present invention adopts a low - temperature heating method, the thermal field is prone to be uneven. However, the extraction / injection wells can be switched in function, which is beneficial to optimizing the functional layout in space and eliminating dead corners in reagent transmission or heating.

[0038] 4. The present invention adopts a layout method where the heating wells are located at the center of an equilateral triangle formed by the extraction / injection wells. While meeting the demand for low - temperature heating to enhance hydrolysis - oxidation of the present invention, it can also reduce the number of heating wells, lower the hardware input cost (the construction cost of heating wells is higher), and moreover, increasing the number of extraction / injection wells can achieve multi - point drug injection and a more uniform effect.

[0039] 5. The present invention controls the concentration of the reagent at 10 - 80 g / L, preferably 40 g / L, which can ensure a high reaction rate and degradation rate, while avoiding reagent waste and saving reagent costs.

[0040] 6. The remediation equipment and method of the present invention, in addition to having a good removal effect on halogenated hydrocarbons, also have a good removal effect on other odor - producing substances that are easily oxidized or hydrolyzed in pesticide sites, such as sulfur - containing / nitrogen - containing compounds (sulfides and mercaptans / amines), benzene series, and aldehydes.

[0041] 7. Through the remediation equipment and method of the present invention, it can not only be used to inject oxidants underground, but also, in the later stage of remediation, be changed to inject microbial nutrient solution or microbial agents to achieve integration with enhanced microbial remediation technology, etc., which is flexible and maneuverable. Brief Description of the Drawings

[0042] Figure 1 It is a schematic flow chart of the equipment and method of the present invention;

[0043] Figure 2 It is a schematic layout diagram of the extraction well / injection well and the heating well of the present invention. Detailed Embodiments

[0044] The present invention will be further described below in conjunction with specific embodiments, and the advantages and features of the present invention will become clearer as the description proceeds. However, these embodiments are exemplary only and do not constitute any limitation to the scope of the present invention. Those skilled in the art should understand that modifications or substitutions can be made to the details and forms of the technical solutions of the present invention without departing from the spirit and scope of the present invention, but such modifications and substitutions all fall within the protection scope of the present invention.

[0045] Embodiment 1

[0046] Please refer to Figure 1 As shown, this embodiment provides a device for repairing odor substances in a pesticide site. The odor substances include halogenated hydrocarbons. The device includes a heating unit, a reagent preparation unit, a pumping and injection circulation unit, a monitoring and control unit, and a power control unit;

[0047] The heating unit includes a plurality of heating wells for low-temperature heating of underground soil and groundwater;

[0048] The reagent preparation unit includes a reagent stirring tank and a water pump connected to each other for preparing reagents;

[0049] The pumping and injection circulation unit includes a plurality of extraction wells, extraction water pumps, sedimentation tanks, injection water pumps, and a plurality of injection wells connected in sequence; the inlet pipe of the water pump in the reagent preparation unit is inserted into the sedimentation tank, and the outlet pipe is connected to the reagent stirring tank for pumping the water in the sedimentation tank and injecting it into the reagent stirring tank; the outlet pipe of the reagent stirring tank converges with the outlet pipe of the sedimentation tank and jointly connects the injection water pump; the pumping and injection circulation unit is used for extracting groundwater, pre-treating groundwater, and injecting water and medicine;

[0050] The monitoring and control unit includes monitoring wells, monitoring devices, and control devices; the monitoring devices are arranged in the monitoring wells for monitoring the change of the underground temperature field and the migration and diffusion of the medicine; the control devices are connected to the monitoring devices and display, record, and adjust the operating parameters of the other unit devices according to the monitoring situation;

[0051] The power control unit is connected to the other unit devices for supplying power to them.

[0052] Among them, the heating elements in each of the heating wells are resistance - heated electrodes.

[0053] Among them, each of the extraction wells and each of the injection wells are arranged in an equilateral triangle layout, and each of the heating wells is located at the center of each equilateral triangle.

[0054] Among them, each of the extraction wells and each of the injection wells can switch the extraction or injection function according to the monitoring results of the monitoring and control unit.

[0055] Among them, the monitoring device includes probe instruments such as thermocouples, multi - parameter water quality analyzers (pH, ORP, EC, etc.), water level gauges, watt - hour meters, voltage / ammeter, flow meters, and pressure gauges.

[0056] Embodiment 2

[0057] Please refer to Figure 1 As shown, this embodiment provides a method for repairing odor substances in a pesticide site using the equipment of Embodiment 1. The odor substances include halogenated hydrocarbons, and the method includes the following steps:

[0058] (1) Turn on the heating unit and the power control unit, and heat the underground soil and groundwater at a low temperature through each heating well, so that the underground temperature rises by 1 - 2 °C per day.

[0059] (2) While heating at a low temperature, operate the extraction - injection circulation unit. Groundwater is extracted by each extraction well and transported to the sedimentation tank. Quicklime is added to adjust the pH to 10.5 - 11, which is both most beneficial for hydrolysis and avoids premature activation of persulfate. At the same time, utilize the exothermic property of quicklime slaking to assist in heating the extracted groundwater to reduce heating costs. After adjusting the pH and sedimentation, the groundwater is used for water injection and medicine injection. The water injection and medicine injection adopt a low - flow intermittent operation mode. In the medicine injection link, open the outlet valve of the medicine stirring tank and close the outlet valve of the sedimentation tank. Part of the pre - treated groundwater in the sedimentation tank is pumped by a water pump to the medicine stirring tank to prepare sodium persulfate oxidant, and then driven by the injection water pump, the prepared medicine is injected into the ground through each injection well. In the water injection link, close the outlet valve of the medicine stirring tank and open the outlet valve of the sedimentation tank. Part of the pre - treated groundwater in the sedimentation tank is driven by the injection water pump to inject water into the ground through each injection well to promote the diffusion of the medicine.

[0060] (3) While heating at a low temperature and circulating the groundwater extraction - injection, by using the monitoring and control unit, according to the changes in the underground temperature field and the migration and diffusion of the medicine, display, record, and regulate the functional layout, extraction - injection flow rate of each extraction well and each injection well, and the operation time and input power of each heating well to improve the effect of underground mass transfer and heat transfer.

[0061] (4) After the underground is heated to 50 °C, reduce the input power of each of the heating wells and enter the heat preservation stage. Through regular sampling and detection, evaluate the degradation effect of pollutants and the remaining content of the medicament, and adjust the amount of medicament added according to the detection situation to keep the concentration of the medicament at 40 g / L, further accelerating the reaction rate and shortening the repair time until the repair reaches the standard.

[0062] Experimental example

[0063] In this experimental example, the degradation rates of different pollutants after reacting for 72 h by the conventional chemical oxidation method (reaction temperature is at room temperature condition, and other reaction conditions are the same) and the method of the present invention were compared under the same external conditions. The results are shown in Table 1. The specific steps are as follows:

[0064] (1) Weigh about 10 g of contaminated soil containing chlorinated hydrocarbons and put it into a 43 ml brown headspace bottle.

[0065] (2) Add a sodium persulfate solution with a concentration of 20 g / L to the headspace bottle and fill it up to a non-headspace state to prevent volatilization.

[0066] (3) Put the two groups of samples into two water baths at different temperatures respectively. One is at room temperature without heating (room temperature is about 20 °C), and the other is set at 50 °C.

[0067] (4) After reacting for 72 h, take out the two groups of samples and let them stand in an ice-water bath for 20 min.

[0068] (5) Centrifuge the samples to separate the soil from the water; measure the pollutants in the soil and the solution respectively.

[0069] Table 1 Degradation rates (%) of different chlorinated hydrocarbons after reacting for 72 h

[0070]

[0071] Since chloroalkanes are difficult to oxidize under natural conditions, the present invention utilizes their characteristics of being easily hydrolyzed to form alcohols, aldehydes, and olefins under heating conditions, and the toxicity of the hydrolysis products is reduced or they are easily oxidized (Table 2). Through measures such as low-temperature heating and pH adjustment, the hydrolysis is strengthened, thereby achieving efficient hydrolysis-oxidation coupling repair of the combined pollution of chloroalkanes and chloroolefins. And in this process, ① through low-flow pumping and injection circulation, the heat and mass transfer process is strengthened, making the heat and chemicals diffuse more evenly and quickly; ② through well layout, the number of heating wells constructed is reduced, saving well construction costs, increasing the number of extraction / injection wells, and making the chemical injection more uniform; ③ through the function switching of extraction / injection wells, the chemical diffusion is made more uniform, eliminating the dead corners of transmission; ④ the extracted water is treated, using quicklime to adjust the pH and heat, creating a more favorable environment for the hydrolysis of halogenated hydrocarbons, offsetting the adverse effects of pH reduction caused by chemical oxidation, reducing the heating cost, realizing the recycling of groundwater, and reducing external discharge.

[0072] Table 2 Hydrolysis rates and hydrolysis products of some chloroalkanes under heating conditions

[0073]

Claims

1. A method for repairing odor substances in a pesticide site, characterized in that, the method comprises the following steps: (1) Turn on the heating unit and the power control unit, and low-temperature heat the underground soil and groundwater through each heating well; (2) While low-temperature heating, operate the pumping and injection circulation unit. The groundwater is extracted by each extraction well and transported to the sedimentation tank for pretreatment of sedimentation and pH adjustment. The pretreated groundwater is used for water injection and medicine injection. The water injection and medicine injection adopt a low-flow intermittent operation mode. In the medicine injection link, open the outlet valve of the medicine stirring tank and close the outlet valve of the sedimentation tank. Part of the pretreated groundwater in the sedimentation tank is pumped by a water pump into the medicine stirring tank, and then driven by the injection water pump, the prepared medicine is injected into the ground through each injection well. In the water injection link, close the outlet valve of the medicine stirring tank and open the outlet valve of the sedimentation tank. Part of the pretreated groundwater in the sedimentation tank is driven by the injection water pump to inject water into the ground through each injection well to promote the diffusion of the medicine; (3) While low-temperature heating and groundwater pumping and injection circulation, by using the monitoring and control unit, according to the change of the underground temperature field and the migration and diffusion of the medicine, display, record and regulate the functional layout, pumping and injection flow rate of each extraction well and each injection well, and the operation time and input power of each heating well to improve the effect of underground mass transfer and heat transfer; (4) After the underground is heated to the target temperature, reduce the input power of each heating well and enter the heat preservation stage. Through regular sampling and detection, evaluate the degradation effect of pollutants and the remaining content of the medicine, and adjust the medicine addition amount according to the detection situation to keep the concentration of the medicine within a suitable range, further accelerate the reaction rate, shorten the repair time until the repair reaches the standard; wherein, the odor substances include halogenated hydrocarbons; wherein, the low-temperature heating in step (1) is to increase the underground temperature by 1-2 °C per day; the target temperature in step (4) is 40-50 °C; wherein, the medicines used for pH adjustment in step (2) are quicklime, NaOH or KOH, and the target pH value is 10.5-11; wherein, the prepared medicine in step (2) is an oxidant, selected from sodium persulfate, potassium permanganate, hydrogen peroxide or Fenton reagent; the concentration of the medicine in step (4) is 10-80 g / L; wherein, the method is carried out by using a device for repairing odor substances in a pesticide site, and the device includes a heating unit, a medicine preparation unit, a pumping and injection circulation unit, a monitoring and control unit and a power control unit; the heating unit includes a plurality of heating wells for low-temperature heating of underground soil and groundwater; the medicine preparation unit includes a medicine stirring tank and a water pump connected to each other for preparing medicine; The pumping and injection circulation unit includes a plurality of extraction wells, extraction water pumps, sedimentation tanks, injection water pumps, and a plurality of injection wells connected in sequence; in the chemical preparation unit, the inlet pipe of the water pump is inserted into the sedimentation tank, and the outlet pipe is connected to the chemical mixing tank for pumping the water in the sedimentation tank and injecting it into the chemical mixing tank; the outlet pipe of the chemical mixing tank converges with the outlet pipe of the sedimentation tank and is jointly connected to the injection water pump; the pumping and injection circulation unit is used for extracting groundwater, pre-treating groundwater, and injecting water and chemicals. The monitoring and control unit includes monitoring wells, monitoring devices, and control devices; the monitoring devices are arranged in the monitoring wells and are used for monitoring the changes in the underground temperature field and the migration and diffusion of chemicals; the control devices are connected to the monitoring devices and display, record, and regulate the operating parameters of the other unit devices according to the monitoring conditions. The power control unit is connected to the other unit devices and is used for supplying power to them.

2. The method according to claim 1, characterized in that, the target temperature in step (4) is 50 °C.

3. The method according to claim 1, characterized in that, the chemical used for adjusting the pH in step (2) is quicklime.

4. The method according to claim 1, characterized in that, the chemical prepared in step (2) is sodium persulfate; the concentration of the chemical in step (4) is 40 g / L.

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