Sulfur conversion driven chlorinated hydrocarbon polluted underground water treatment method

Abstract

The invention belongs to the technical field of sewage treatment, and particularly relates to a sulfur conversion driven chlorohydrocarbon polluted underground water treatment method. According to the method, the multifunctional biochar is prepared through high-temperature ammonia gas modification, PS can be activated to oxidize and remove chlorinated hydrocarbon, then sulfide reduction is catalyzed to remove residual chlorinated hydrocarbon, a porous structure of BC provides pollutant adsorption and fixation functions, and after MFBC, PS and sulfate reducing bacteria are sequentially added into a chlorinated hydrocarbon pollution medium, the pollution medium is subjected to high-temperature ammonia gas modification to remove the residual chlorinated hydrocarbon. The sulfur-containing species undergo a cyclic conversion process from PS-sulfate ion-sulfide-elemental sulfur-sulfate ion. In the conversion process, various oxidation and reduction active substances can be used for effective detoxification of chlorinated hydrocarbon, and MFBC and sulfate reducing bacteria play a key role in mediating sulfide conversion. According to the method, the chlorohydrocarbon in the high-permeability medium can be rapidly removed firstly, and then the chlorohydrocarbon slowly released by the low-permeability medium can be slowly removed at low cost. And the method is low-carbon and environment-friendly, has no secondary pollution such as heavy metals and has obvious application advantages.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, specifically relating to a method for treating groundwater contaminated with chlorinated hydrocarbons driven by sulfur conversion. Background Technology

[0002] Groundwater is a crucial component of drinking water resources, and groundwater pollution prevention and control plays a vital role in ensuring the well-being of urban and rural residents. Chlorinated hydrocarbons (CHHs) are among the most frequently detected organic pollutants in groundwater, exhibiting carcinogenic, teratogenic, and mutagenic effects, and their natural decay and neutralization processes often take hundreds or even thousands of years. Furthermore, CHHs are highly biotoxic and have low inhibition factors on their underground migration; once leaked into groundwater, they easily migrate, causing long-term pollution of groundwater at significant depths and across broad areas. Therefore, the remediation of CHH-contaminated groundwater is a critical aspect of groundwater pollution prevention and control.

[0003] Currently, the main technologies for remediation of water and soil contaminated with chlorinated hydrocarbons include ex-situ remediation technologies such as extraction treatment and thermal desorption treatment, and in-situ remediation technologies such as in-situ microbial / abiotic reaction zones and permeable reactive barriers.

[0004] The practical application of ex-situ remediation technology for chlorinated hydrocarbon-contaminated water suffers from inherent problems such as tailing, rebound, and back diffusion. This is mainly because chlorinated hydrocarbon-contaminated aquifers are often heterogeneous and contain low-permeability media that are infiltrated by the contaminants.

[0005] Compared to ex-situ remediation technologies, in-situ remediation technologies have relatively lower treatment costs and can minimize the exposure of contaminants. In-situ chemical oxidation / reduction reaction zone technologies (such as in-situ persulfate reaction zone technologies) have significant advantages in terms of rapid dechlorination and stable effects; however, they face the challenge of high remediation costs when dealing with low-concentration contaminants slowly released into the aquifer by contaminated low-permeability media. Maintaining the stable removal effect of in-situ abiotic / microbial reaction zone technologies on the slow release of chlorinated hydrocarbons into low-permeability media also increases subsequent operation and maintenance costs.

[0006] The inconsistency in the migration characteristics and removal processes of chlorinated hydrocarbons (CHPs) in high-permeability and low-permeability aquifers is the main reason for the unsatisfactory results of existing remediation technologies. In high-permeability aquifers, the concentration of CHPs is relatively high, the migration and diffusion process is relatively rapid, and the short-term environmental risk is relatively higher, thus requiring rapid treatment. In contrast, in low-permeability aquifers, CHPs do not readily come into direct contact with reagents; their pollution is characterized by slow release, lower concentrations, and long-term environmental risks, thus requiring long-term, stable control and remediation, with lower requirements for reaction rates.

[0007] A remediation technology that can simultaneously meet the removal requirements of chlorinated hydrocarbons in both high-permeability and low-permeability aquifers will be significantly competitive in terms of risk control and cost savings. Furthermore, low-carbon and environmental friendliness is also an important goal of this new technology.

[0008] Therefore, designing an efficient, economical, and environmentally friendly method to simultaneously meet the removal requirements of chlorinated hydrocarbons in aquifers with both high and low permeability media is an urgent technical problem that needs to be solved. Summary of the Invention

[0009] To overcome the shortcomings of existing technologies, this invention provides a sulfur conversion-driven method for treating chlorinated hydrocarbon-contaminated groundwater. This invention utilizes a multi-functional biochar (MFBC) material, developed through continuous optimization, to simultaneously perform two functions: activated persulfate (PS) oxidation for chlorinated hydrocarbon removal and catalytic sulfide reduction for chlorinated hydrocarbon removal. Furthermore, the inherent porous structure of the biochar provides adsorption and fixation capabilities for certain pollutants. After sequentially adding MFBC, PS, and sulfate-reducing bacteria (SRB) to the chlorinated hydrocarbon-contaminated medium, sulfur-containing substances undergo a cyclic transformation process from PS—sulfate ions—sulfides—elemental sulfur—sulfate ions. Various oxidizing and reducing active substances in this transformation process can be used for effective detoxification of chlorinated hydrocarbons, with MFBC and sulfate-reducing bacteria playing a key role in mediating sulfide conversion. This invention's treatment method can first rapidly remove chlorinated hydrocarbons from highly permeable media, and then slowly remove chlorinated hydrocarbons released from low-permeability media at low cost. This technology is low-carbon, environmentally friendly, and produces no secondary pollution such as heavy metals, offering significant application advantages.

[0010] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0011] The first aspect of this invention provides a method for treating groundwater contaminated with chlorinated hydrocarbons driven by sulfur conversion, the method comprising the following steps:

[0012] (1) Adding BC and persulfate (PS) to groundwater and soil contaminated with chlorinated hydrocarbons creates an in-situ reaction zone. After 2-4 days of reaction, the persulfate is activated by BC to produce various oxidizing substances (such as SO42-). ·- ,·OH,O2 ·- and 1 O2) is used to oxidize and detoxify dissolved and residual chlorinated hydrocarbons in the aquifer. This detoxification process is rapid, and persulfate is ultimately converted into sulfate.

[0013] (2) When a certain amount of sulfate-reducing bacteria (SRB) and sodium acetate, a carbon source, are added to the chlorinated hydrocarbon contaminated medium, the sulfate generated by PS is quickly converted into sulfides (HS) by SRB under anaerobic / anoxic conditions. - / S2- Under the catalysis of MFBC, sulfides can achieve the reductive dechlorination of chlorinated hydrocarbons, and they are oxidized to elemental sulfur (S). Although the dechlorination process is relatively slow, considering that sulfides can be continuously generated by the microbial reduction of sulfate ions, the treatment cost of chlorinated hydrocarbons will be much lower than that of continuing to add PS. In addition, the dissolution and diffusion process of residual chlorinated hydrocarbons will be effectively intercepted by the adsorption of BC. Therefore, the relatively slow reduction process is sufficient to control the long-term risks caused by the low-permeability slow-release medium.

[0014] (3) As the redox conditions in the medium change continuously, sulfides and S may be oxidized into sulfates during migration, thereby enabling the sulfur-containing substances in the medium to circulate and achieve the effect of controlling medium pollution in a long-term and low-cost manner. In this invention, BC has a certain electron transfer capability, which can play a certain role in promoting the microbial-driven circulation process of S.

[0015] A conceptual diagram of the sulfur conversion-driven method for treating chlorinated hydrocarbon-contaminated groundwater of this invention is shown below. Figure 1 As shown.

[0016] Preferably, in step (1), the dosage of the multifunctional biochar material is 0.1-5 g / L, and the dosage of persulfate is 20-50 times the chemical oxygen demand of the target chlorinated hydrocarbon-contaminated groundwater.

[0017] Preferably, in step (2), the amount of sulfate-reducing bacteria added is 10-20 ml of SRB bacterial suspension with absorbance of 0.3 per liter of groundwater, and the amount of carbon source sodium acetate added is 0.01-0.03 g / L.

[0018] Preferably, the preparation method of the multifunctional biochar material includes the following steps:

[0019] Step S1: Heat and pre-carbonize the biomass raw material to obtain pre-made biochar;

[0020] Step S2: Grind and sieve the pre-made biochar, then treat it at high temperature in an ammonia atmosphere, cool it, and then grind and sieve it again.

[0021] Preferably, the biomass raw material is at least one of corn stalks, alfalfa, and grapefruit peel.

[0022] Preferably, the heating and pre-carbonization temperature is 250-300℃, and the heating and pre-carbonization time is 20-40 minutes.

[0023] More preferably, the heating pre-carbonization temperature is 300°C, and the heating pre-carbonization time is 30 minutes.

[0024] Preferably, the grinding and sieving of the pre-made biochar refers to passing it through a 100-mesh sieve.

[0025] Preferably, the cooling and grinding process refers to passing the material through a 200-mesh sieve.

[0026] Preferably, the high-temperature treatment temperature is 750-850℃, and the high-temperature treatment time is 30 minutes to 2 hours.

[0027] Preferably, the high-temperature treatment is performed at a temperature of 800°C for 1 hour.

[0028] Compared with the prior art, the beneficial effects of the present invention are:

[0029] (1) This invention has continuously optimized the preparation of a multifunctional biochar material (MFBC). The preparation method of the MFBC in this invention can complete nitrogen doping in a short time. An oxygen-free atmosphere is necessary because a large number of oxygen-containing functional groups in the MFBC will affect the catalytic effect. This invention uses ammonia instead of nitrogen, which not only isolates oxygen but also provides a nitrogen source. Ammonia modification is convenient, easy to scale up and operate continuously, and the material has good performance stability. The use of ammonia modification avoids the problem of water content affecting the stability of material performance caused by the drying process after soaking in ammonia water in the ammonia water modification path. High-temperature ammonia modification gives the MFBC excellent electron transfer ability, which can promote the microbial-driven cycle of sulfur. It also satisfies the two functions of activating persulfate (PS) oxidation to remove chlorinated hydrocarbons and catalytic sulfide reduction to remove chlorinated hydrocarbons. In addition, the inherent porous structure of biochar itself will provide a certain function of pollutant adsorption and fixation.

[0030] (2) In this invention, after sequentially adding MFBC, PS, and sulfate-reducing bacteria (SRB) to a chlorinated hydrocarbon contaminated medium, sulfur-containing substances will undergo a cyclic transformation process from PS—sulfate ions—sulfides—elemental sulfur—sulfate ions. Various oxidizing and reducing active substances in this transformation process can be used for the effective detoxification of chlorinated hydrocarbons, and MFBC and sulfate-reducing bacteria play a key role in mediating the sulfide transformation.

[0031] (3) This invention can first quickly remove chlorinated hydrocarbons from highly permeable media, and then slowly remove chlorinated hydrocarbons released from low-permeability media at low cost. The multifunctional coupling is perfectly suited to solving the problem of chlorinated hydrocarbons in polluted water and soil. This technology is low-carbon, environmentally friendly, and free from secondary pollution such as heavy metals, and has obvious application advantages. Attached Figure Description

[0032] Figure 1 This is a conceptual diagram of the sulfur conversion-driven method for treating chlorinated hydrocarbon-contaminated groundwater according to the present invention.

[0033] Figure 2This is a schematic diagram of the remediation of a heterogeneous aquifer contaminated with trichloroethylene in a two-dimensional simulation tank in Example 2. Detailed Implementation

[0034] The specific embodiments of the present invention will be further described below. It should be noted that these descriptions are for the purpose of aiding understanding the present invention, but do not constitute a limitation thereof. Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0035] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods, and the experimental materials used in the following embodiments are all available through conventional commercial channels.

[0036] Example 1: Experiments on the catalytic oxidation of hexachlorobutadiene by persulfate and the catalytic reduction of hexachlorobutadiene by sodium sulfide using multifunctional biochar materials.

[0037] Preparation of alfalfa-based multifunctional biochar material: Alfalfa was pre-carbonized in a muffle furnace at 300℃ for 30 minutes to obtain pre-carbonized biochar; subsequently, it was ground through a 100-mesh sieve; then, it was heated in a tube furnace at 800℃ for 1 hour in an ammonia atmosphere; after cooling, it was removed and ground again through a 200-mesh sieve. The obtained alfalfa-based multifunctional biochar material had a nitrogen content of 4.5% and a bulk resistivity of 0.18 Ω·mm.

[0038] Experiment on the oxidation of hexachlorobutadiene by persulfate catalyzed by multifunctional biochar material: 2 mmol / L sodium persulfate solution and 500 mg / L multifunctional BC were added to 100 mL of hexachlorobutadiene solution with a concentration of 20 mg / L; stirring was continued for 30 minutes. The removal effect of hexachlorobutadiene at different reaction times is shown in Table 1. As can be seen from Table 1, alfalfa-based multifunctional biochar (MFBC) can remove more than 99% of hexachlorobutadiene by catalyzing sodium persulfate.

[0039] Table 1

[0040]

[0041] Experiment on the catalytic reduction of hexachlorobutadiene by sodium sulfide using multifunctional biochar (MFBC) material: 1 mmol / L sodium sulfide solution and 500 mg / L MFBC were added to 100 mL of hexachlorobutadiene solution with a concentration of 10 mg / L; the solution was continuously shaken in a shaker at 20℃ for 2 days. The removal effect of hexachlorobutadiene at different reaction times is shown in Table 2 below. As can be seen from Table 2, 98.2% of hexachlorobutadiene can be removed.

[0042] Table 2

[0043]

[0044] Example 2: Two-dimensional simulation tank for remediation of trichloroethylene-contaminated heterogeneous aquifers

[0045] The alfalfa-based multifunctional biochar material used in Example 1 also has the functions of catalytic oxidation of persulfate and catalytic reduction of trichloroethylene (TCE).

[0046] A heterogeneous aquifer contaminated with TCE was constructed using a two-dimensional simulation tank (made of stainless steel and glass). A schematic diagram of the two-dimensional simulation tank simulating the remediation of a heterogeneous aquifer contaminated with trichloroethylene is shown below. Figure 2 As shown, the high-permeability medium is quartz sand (sterilized), with a medium sand particle size and a permeability coefficient of 30 m / d; the low-permeability medium for TCE contamination is clay, with a permeability coefficient of 0.011 m / d. The simulated groundwater design flow velocity is 0.01 m / d, the hydraulic retention time of the simulation tank is about 11 days, the average water content of the simulation tank medium is 0.41%, and the water volume is 32.7 L.

[0047] Simulated TCE back-diffusion contamination stage: Sterile simulated groundwater was continuously pumped in. Due to the back-diffusion of TCE-contaminated clay, the TCE concentration in the simulation tank continuously increased. After three hydraulic retention times, the TCE concentration at the sampling port was found to remain at approximately 15±3 mg / L. Subsequently, a simulated remediation comparative experiment was initiated.

[0048] Simulated TCE remediation stage 1: Utilizing the excellent reagent transport properties in highly permeable media, a pre-mixed suspension of MFBC and PS was rapidly pumped in at once using a high-pressure pump to form an in-situ black reaction zone in the highly permeable medium. The inlet and outlet water were then shut off. The pre-mixed suspension of MFBC and PS was prepared as follows: MFBC was thoroughly dispersed using mechanical stirring, followed by the addition of PS and stirring for another minute, then immediately pumped into the simulation tank. In this case, approximately 3 L of the pre-mixed reagent was pumped in, with an MFBC concentration of 1 g / L and a PS concentration of 2 mmol / L. In the control simulation tank experiment, no in-situ reaction zone was set up; all other conditions were the same as the experimental group.

[0049] Simulated TCE remediation stage 2: Two days after pumping in the reagent, another 500 mL of SRB bacterial suspension (containing 0.8 g / L sodium acetate as a carbon source, with an absorbance of approximately 0.3) is pumped in. At this point, theoretically, most of the residual and dissolved TCE phases have been removed, and PS has been catalytically decomposed into sulfate ions. After pumping in the suspension, the TCE removal reaction in the remediation simulation tank slowly transitions to a reduction removal stage.

[0050] The effluent from each of the above remediation stages was sampled periodically to monitor the concentrations of TCE, TCE products, persulfate (PDS), and sulfides. The results are shown in Table 3 below.

[0051] Table 3

[0052]

[0053] The results showed that, following the strategy described in this invention, the TCE concentration at the sampling port was 51 μg / L on day 9, meeting the Class III groundwater standard (less than 70 μg / L); and on day 40, the TCE concentration at the sampling port was 6 μg / L, meeting the Class II groundwater standard (less than 7 μg / L). In contrast, the TCE concentration at the sampling port in the control group remained high due to the back-diffusion of TCE-contaminated clay. Therefore, the technology provided by this invention achieves both rapid short-term removal of TCE from the simulated tank and long-term control of TCE contamination at low concentrations.

[0054] The embodiments of the present invention have been described in detail above, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and these variations still fall within the protection scope of the present invention.

Claims

1. A method for treating groundwater contaminated with chlorinated hydrocarbons driven by sulfur conversion, characterized in that, The processing method includes the following steps: (1) Add multifunctional biochar material and persulfate to groundwater and soil contaminated with chlorinated hydrocarbons to form an in-situ reaction zone, and react for 2-4 days; (2) Continue to add sulfate-reducing bacteria and sodium acetate, a carbon source, to groundwater and soil contaminated with chlorinated hydrocarbons.

2. The method for treating sulfur-converted chlorinated hydrocarbon-polluted groundwater driven by sulfur conversion according to claim 1, characterized in that, In step (1), the dosage of the multifunctional biochar material is 0.1-5 g / L, and the dosage of persulfate is 20-50 times the chemical oxygen demand of chlorinated hydrocarbon-contaminated groundwater.

3. The method for treating sulfur-converted chlorinated hydrocarbon-polluted groundwater driven by sulfur conversion according to claim 1, characterized in that, In step (2), the amount of sulfate-reducing bacteria added is 10-20 ml of SRB bacterial suspension with an absorbance of 0.3 per liter of groundwater, and the amount of carbon source sodium acetate added is 0.01-0.03 g / L.

4. The method for treating sulfur-converted chlorinated hydrocarbon-polluted groundwater driven by sulfur conversion according to claim 1, characterized in that, The preparation method of the multifunctional biochar material includes the following steps: Step S1: Heat and pre-carbonize the biomass raw material to obtain pre-made biochar; Step S2: Grind and sieve the pre-made biochar, then treat it at high temperature in an ammonia atmosphere, cool it, and then grind and sieve it again.

5. The method for treating sulfur-converted chlorinated hydrocarbon-polluted groundwater driven by sulfur conversion according to claim 4, characterized in that, The biomass raw material is one of corn stalks, alfalfa, or grapefruit peel.

6. The method for treating sulfur-converted chlorinated hydrocarbon-polluted groundwater driven by sulfur conversion according to claim 4, characterized in that, The heating and pre-carbonization temperature is 250-300℃, and the heating and pre-carbonization time is 20-40 minutes.

7. The method for treating sulfur-converted chlorinated hydrocarbon-polluted groundwater driven by sulfur conversion according to claim 4, characterized in that, The grinding and sieving of pre-made biochar refers to passing it through a 100-mesh sieve.

8. The method for treating sulfur-converted chlorinated hydrocarbon-polluted groundwater driven by sulfur conversion according to claim 4, characterized in that, The cooling and grinding process refers to passing the material through a 200-mesh sieve.

9. A method for treating sulfur-converted chlorinated hydrocarbon-polluted groundwater driven by sulfur conversion according to claim 4, characterized in that, The high-temperature treatment is performed at a temperature of 750-850℃ for a duration of 30 minutes to 2 hours.

10. A method for treating sulfur-converted chlorinated hydrocarbon-polluted groundwater driven by sulfur conversion according to claim 9, characterized in that, The high-temperature treatment is performed at a temperature of 800°C for 1 hour.

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