An arsenic removal system for groundwater and a construction method and application thereof

Abstract

The application provides a groundwater arsenic removal system and a construction method and application thereof, and belongs to the technical field of groundwater treatment. The system comprises a trivalent arsenic biological oxidation reactor, a drop water oxygenation zone and a ferrous biological mineralization contact oxidation arsenic removal reactor connected in sequence. The filter material of the trivalent arsenic biological oxidation reactor contains a biological membrane formed by facultative arsenic oxidizing bacteria, which can selectively oxidize trivalent arsenic in groundwater to pentavalent arsenic, and relatively less oxidize ferrous iron in water; the filter material of the ferrous biological mineralization contact oxidation arsenic removal reactor contains iron oxidizing bacteria and hydroxyl iron oxide minerals, and arsenic removal is realized by biological mineralization contact oxidation of ferrous iron on the filter material. The trivalent arsenic biological oxidation reactor is used for biological pre-oxidation of trivalent arsenic, which significantly improves the arsenic removal efficiency of the subsequent ferrous biological mineralization contact oxidation stage, and can effectively treat different types of arsenic-containing groundwater.

Description

Technical Field

[0001] This invention belongs to the field of water treatment technology, specifically relating to a groundwater arsenic removal system, its construction method, and its application. Background Technology

[0002] Arsenic pollution in groundwater exhibits a significant regional clustering distribution, particularly prominent in the hydrogeological units of closed- to semi-closed sedimentary basins. Groundwater in these areas is typically in a strongly reducing environment with a pH between neutral and slightly alkaline (7.0–8.5), rich in dissolved organic matter and other reducing substances. This results in arsenic primarily originating from the reduction and dissolution of iron and manganese oxides, with trivalent arsenic (As(III)) being the dominant form. Compared to pentavalent arsenic (As(V)), As(III) is more toxic and more difficult to remove due to its electrically neutral chemical properties, further exacerbating drinking water safety risks. Ferrous contact oxidation for arsenic removal has great potential in groundwater arsenic removal due to its low cost and ease of operation. This technology utilizes the oxidative precipitation of native ferrous iron (Fe(II)) in groundwater to achieve co-precipitation removal of arsenic on the surface of activated filter media. However, the arsenic removal efficiency of this technology is significantly affected by the arsenic valence state, and its removal efficiency for As(III) is far lower than that for As(V). To achieve the desired arsenic removal effect, it is often necessary to add a large amount of Fe(II) from external sources. This not only increases the treatment cost, but may also cause Fe ion residue and secondary water quality problems such as increased color.

[0003] Traditional chemical oxidation methods oxidize As(III) in groundwater to As(V) to improve subsequent As removal efficiency. However, when Fe(II) is also present in the groundwater, chemical oxidants (such as hydrogen peroxide and potassium permanganate) may simultaneously or even preferentially oxidize Fe(II) during the oxidation of As(III), leading to the premature oxidation of a large amount of Fe(II) and interfering with subsequent As removal reactions, thus limiting the improvement in As removal efficiency. For example, Chinese invention patent CN107162273A discloses a method for treating arsenic-containing wastewater by adding hydrogen peroxide to accelerate the oxidation of As(III). However, this system cannot achieve selective oxidation of As(III) when Fe(II) and As(III) coexist. In contrast, microbial oxidation can selectively oxidize As(III) while having less impact on other substances, avoiding unnecessary oxidation reactions. Furthermore, the microbial oxidation process is environmentally friendly, requiring no large amounts of chemical reagents and reducing potential environmental hazards. However, the construction of a bioreactor for the selective oxidation of As(III) under the coexistence of Fe(II) and As(III) is still lacking. For example, Chinese invention patent CN108531373A discloses a biofilm reactor constructed from arsenic-oxidizing bacteria. Although this reactor has a good oxidation effect on As(III) in synthetic groundwater, it does not consider or analyze the oxidation of Fe(II) and As(III) when they coexist. The oxidation of As(III) when Fe(II) coexists is still unclear. Summary of the Invention

[0004] 1. The problem to be solved

[0005] To address the challenges of selective pre-oxidation of As(III) in traditional chemical oxidation methods when Fe(II) and As(III) coexist, and the low efficiency of arsenic removal through ferrous contact oxidation technology or the increased cost of adding large amounts of exogenous Fe(II), this invention provides a groundwater arsenic removal system. This system includes a trivalent arsenic biological oxidation reactor, a cascading aeration zone, and a ferrous biomineralization contact oxidation arsenic removal reactor. Specifically, the trivalent arsenic biological oxidation reactor is an anaerobic As(III) oxidation reactor constructed using arsenic-oxidizing bacteria capable of selectively oxidizing As(III). In an oxygen-deficient environment, it can selectively oxidize As(III) in groundwater to As(V), while oxidizing Fe(II) relatively less, thus maintaining a certain Fe(II) concentration in the groundwater. The ferrous biomineralization contact oxidation arsenic removal reactor is a biomineralization contact oxidation arsenic removal reactor constructed using iron-oxidizing bacteria and hydroxyl iron oxide minerals. Utilizing biomineralization and contact oxidation catalysis, it achieves efficient As(V) removal while oxidizing and precipitating Fe(II). This invention couples a trivalent arsenic bio-oxidation reactor with a ferrous biomineralization contact oxidation reactor for arsenic removal. By combining the selective oxidation of As(III) with the ferrous biomineralization contact oxidation process, the advantages of As(III) pre-oxidation can be fully utilized, significantly improving the removal efficiency of As in groundwater. This has important application value for the treatment of arsenic pollution in groundwater.

[0006] 2. Technical Solution

[0007] To solve the above problems, the technical solution adopted by the present invention is as follows:

[0008] This invention provides a groundwater arsenic removal system, comprising a trivalent arsenic bio-oxidation reactor, a cascade aeration zone, and a ferrous biomineralization contact oxidation arsenic removal reactor connected in sequence; wherein:

[0009] The trivalent arsenic bio-oxidation reactor is a first continuous flow reactor filled with a first solid particulate filter media containing a biofilm formed by facultative arsenic oxidizing bacteria; it has the selective oxidation function of As(III).

[0010] The ferrous biomineralization contact oxidation arsenic removal reactor is a second continuous flow reactor filled with a second solid particulate filter media containing neutral iron-oxidizing bacteria and hydroxyl iron oxide minerals; it has the dual functions of Fe(II) biomineralization and contact oxidation.

[0011] Furthermore, the aforementioned connections include pipe connections, etc.

[0012] Furthermore, the height of the drop in the above-mentioned drop aeration zone is 50-100cm, and the ferrous iron in the groundwater should not be oxidized before entering the ferrous biomineralization contact oxidation arsenic removal reactor after the drop aeration.

[0013] Furthermore, the height of the aforementioned cascade oxygenation zone is 60cm.

[0014] Furthermore, the height of the first continuous flow reactor is 15–20 cm. Even further, the height of the first continuous flow reactor is 17 cm.

[0015] Furthermore, the diameter of the aforementioned first continuous flow reactor is 5–10 cm. Even further, the diameter of the aforementioned first continuous flow reactor is 6 cm.

[0016] Furthermore, the height-to-diameter ratio of the aforementioned first continuous flow reactor is 1.5 to 4.

[0017] Furthermore, the aforementioned first solid particulate filter media includes any one or more of perlite, volcanic rock, anthracite, or other particulate filter media.

[0018] Furthermore, the first solid particulate filter material mentioned above is perlite.

[0019] Furthermore, the particle size of the first solid particulate filter material is 2 to 6 mm.

[0020] Furthermore, the packing thickness of the first solid particulate filter media is 10-30 cm. Even further, the packing thickness of the first solid particulate filter media is 10 cm.

[0021] Furthermore, the aforementioned facultative arsenic oxidizing bacterium is *Ensifer adhaerens* ST2, deposited at the China Center for Type Culture Collection (CCTCC) on December 31, 2019, with accession number CCTCCNO.M20191138, located at Wuhan University, Wuhan, China. This strain was previously screened by the inventors in arsenic-contaminated rice paddies in Shantou City, Guangdong Province, as detailed in Chinese Invention Patent Publication No. CN117247912A. ST2 can selectively oxidize trivalent arsenic. During anaerobic denitrification, the nitrite generated by ST2 can be rapidly reduced, resulting in extremely low nitrite accumulation in the system. This inhibits the abiotic oxidation reaction between ferrous iron and nitrite, thus producing less iron oxide. In summary, under anaerobic conditions, when trivalent arsenic and ferrous iron coexist, ST2 can achieve selective oxidation of trivalent arsenic using nitrate as an electron acceptor.

[0022] Furthermore, the height of the second continuous flow reactor is 100–150 cm. Even further, the height of the second continuous flow reactor is 135 cm.

[0023] Furthermore, the diameter of the aforementioned second continuous flow reactor is 5–10 cm. Even further, the diameter of the aforementioned second continuous flow reactor is 6 cm.

[0024] Furthermore, the height-to-diameter ratio of the aforementioned second continuous flow reactor is 10–30.

[0025] Furthermore, the aforementioned second solid particulate filter media includes any one or more of quartz sand, manganese sand, and anthracite.

[0026] Furthermore, the second solid particulate filter material mentioned above is manganese sand.

[0027] Furthermore, the particle size of the second solid particulate filter material is 0.6–2 mm.

[0028] Furthermore, the filling thickness of the second solid particle filter material is 50–150 cm.

[0029] Furthermore, the filling thickness of the aforementioned solid particulate filter media is 50 cm.

[0030] Furthermore, the aforementioned neutral iron-oxidizing bacteria include any one or more of Arthrobacter W1, Agrobacterium W2, and Delftia J; wherein:

[0031] Arthrobacter W1 is deposited at the China General Microbiological Culture Collection Center (CGMCC) on August 16, 2024, with accession number CGMCC NO.31596.

[0032] Agrobacterium W2 is deposited at the China General Microbiological Culture Collection Center (CGMCC) on August 16, 2024, with accession number CGMCC NO.31597;

[0033] Delftia J is deposited at the China General Microbiological Culture Collection Center (CGMCC) on August 16, 2024, with accession number CGMCC NO.31598.

[0034] Furthermore, the aforementioned neutral iron-oxidizing bacteria is Arthrobacter W1.

[0035] This invention also provides a method for constructing the above-mentioned trivalent arsenic bio-oxidation reactor, the method comprising the following steps:

[0036] S1, filling the first solid particulate filter media into the first continuous flow reactor;

[0037] S2, after filling the filter media, a culture medium containing facultative arsenic oxidizing bacteria is introduced into the first continuous flow reactor in batches, and the bacteria are circulated and attached at a certain flow rate to form a biofilm on the surface of the first solid particle filter media, thus obtaining a trivalent arsenic bio-oxidation reactor.

[0038] Furthermore, the culture medium containing the above-mentioned facultative arsenic oxidizing bacteria includes *Streptococcus adiposa* ST2 and the culture medium.

[0039] Furthermore, the above-mentioned culture medium components are: 66.5 mg / L CaCl2, 14.9 mg / L KCl, 47.6 mg / L MgCl2·7H2O, 10.1 mg / L NH4Cl and 1.64 g / L C2H3NaO2.

[0040] Furthermore, in the culture medium containing facultative arsenic oxidizing bacteria, the amount of bacterial solution added in the initial batch of culture medium is 10% to 30%. Even further, in the culture medium containing facultative arsenic oxidizing bacteria, the amount of bacterial solution added in the initial batch of culture medium is 15%.

[0041] Furthermore, the culture medium is introduced in batches, with each batch circulating for 12–36 hours to allow for biofilm formation. Even further, the culture medium is circulated for 36 hours per batch to allow for biofilm formation.

[0042] Furthermore, the aforementioned batch introduction of culture medium includes 3 to 5 batches. Even further, the aforementioned batch introduction of culture medium includes 4 batches.

[0043] Furthermore, in the above-mentioned batch-by-batch introduction of the culture medium, the amount of bacterial solution added gradually decreases, and the amount of bacterial solution added in the last batch of the culture medium is 0% (i.e., pure culture medium).

[0044] Furthermore, the above-mentioned culture medium also contains 10-20 mg / L As(III). Even further, the above-mentioned culture medium also contains 15 mg / L As(III). As a further explanation of the present invention, the purpose of adding As(III) is to provide feedback on the enrichment of facultative arsenic oxidizing bacteria on the surface of the solid particulate filter media by real-time measurement of the As(III) oxidation rate. When the last batch of culture medium with an addition of 0% is introduced, and the As(III) oxidation rate remains stable, it is considered that the facultative arsenic oxidizing bacteria have been stably enriched on the surface of the solid particulate filter media, that is, the trivalent arsenic bio-oxidation reactor has been successfully constructed.

[0045] Furthermore, the flow rate of the aforementioned circulating biofilm is 0.2–0.4 m / h. Even further, the flow rate of the aforementioned circulating biofilm is 0.3 m / h.

[0046] The present invention also provides a trivalent arsenic bio-oxidation reactor constructed by the above-described construction method.

[0047] The present invention also provides a method for constructing the above-mentioned ferrous biomineralization contact oxidation arsenic removal reactor, the method comprising the following steps:

[0048] M1, Filter media filling: Fill the second continuous flow reactor with the second solid granular filter media;

[0049] M2, Neutral Iron Oxidizing Bacteria Loading: The second solid particle filter media is soaked in a culture medium containing neutral iron oxidizing bacteria, the culture medium including neutral iron oxidizing bacteria and a culture medium for culturing neutral iron oxidizing bacteria; after soaking, the culture medium diluted with arsenic-containing groundwater after aeration by a cascade is introduced into the second continuous flow reactor in batches, and cyclic culture is carried out at a certain flow rate. The dilution ratio of the culture medium introduced in batches is gradually increased to gradually reduce the nutrient content in the culture medium, and at least the last batch is introduced with arsenic-containing groundwater after aeration by a cascade (without culture medium); as a further explanation of the present invention, the purpose of cyclic culture is to load neutral iron oxidizing bacteria, and the purpose of gradually reducing the nutrient content in the culture medium is to acclimate the neutral iron oxidizing bacteria loaded on the surface of the filter media to gradually adapt to the water quality characteristics of the groundwater;

[0050] M3, Maturation: Arsenic-containing groundwater, after being aerated by a cascade, is continuously fed into the second continuous flow reactor at a certain flow rate to mature the filter media, thereby obtaining a ferrous biomineralization contact oxidation arsenic removal reactor; as a further explanation of the present invention, the purpose of selecting arsenic-containing groundwater is to simultaneously utilize the native ferrous iron and its natural microbial community in the groundwater, thereby accelerating the maturation (coating of ferric hydroxide minerals) of the filter media and the development of the surface microbial community.

[0051] Furthermore, the soaking time is 24–72 hours. Even further, the soaking time is 48 hours.

[0052] Furthermore, the culture medium diluted with arsenic-containing groundwater after being aerated by a waterfall was introduced in batches of 5 to 10 batches, with each batch having a culture duration of 5 to 7 days.

[0053] Furthermore, the diluted culture medium introduced in batches as described above includes at least diluted culture medium with a ratio of arsenic-containing groundwater aerated by waterfalls to culture medium of 2:8, 4:6, 6:4, 8:2 and 10:0.

[0054] Furthermore, the above-mentioned culture medium components are: 10 g / L ferric ammonium citrate, 2 g / L MnSO4·H2O, 0.5 g / L K2HPO4, 0.5 g / L NaNO3, 0.5 g / L CaCl2, 0.5 g / L MgSO4·7H2O, and 0.1 g / L NaCl.

[0055] Furthermore, the flow rate in the above-mentioned circulating culture is 0.2–5 m / h. Even further, the flow rate in the above-mentioned circulating culture is 0.2 m / h.

[0056] Furthermore, the flow rate during the above-mentioned maturation is 0.5–5 m / h. Even further, the flow rate during the above-mentioned maturation is 2 m / h.

[0057] Furthermore, the above-mentioned maturation process also includes backwashing, which is carried out every 48–72 hours. Even further, the backwashing cycle is 72 hours.

[0058] Furthermore, the backwashing intensity is 10–18 L / (s·m). 2 Furthermore, the backwashing intensity is 10 L / (s·m). 2 ).

[0059] Furthermore, the backwashing time is 5–10 minutes. Even further, the backwashing time is 5 minutes.

[0060] Furthermore, the maturation time is 12–78 days. Even further, the maturation time is 21 days.

[0061] The present invention also provides a method for constructing the above-mentioned ferrous biomineralization contact oxidation arsenic removal reactor, which is a ferrous biomineralization contact oxidation arsenic removal reactor.

[0062] The present invention also provides a method for constructing the above-mentioned groundwater arsenic removal system, the method comprising sequentially connecting the above-constructed trivalent arsenic bio-oxidation reactor, the cascade oxygenation zone, and the ferrous biomineralization contact oxidation arsenic removal reactor via pipelines.

[0063] This invention also provides the application of the aforementioned groundwater arsenic removal system in groundwater arsenic removal. In this application, groundwater sequentially passes through a trivalent arsenic biological oxidation reactor, a cascade aeration zone, and a ferrous biomineralization contact oxidation arsenic removal reactor. After entering the trivalent arsenic biological oxidation reactor, the As(III) oxidizing bacteria ST2 in the reactor use nitrate as an electron acceptor to efficiently and selectively oxidize As(III) to As(V), completing the As(III) pre-oxidation treatment while maintaining a certain Fe(II) concentration. After cascade aeration, the water enters the ferrous biomineralization contact oxidation arsenic removal reactor, where Fe(II) undergoes biomineralization contact oxidation arsenic removal on a filter media coated with an iron-based active filter membrane (neutral iron-oxidizing bacteria and hydroxyl iron oxide minerals). The final effluent arsenic concentration can be lower than the maximum allowable concentration of arsenic in drinking water of 10 μg / L specified in the current Chinese "Standards for Drinking Water Quality" (GB5749-2022).

[0064] Furthermore, the operating filtration rate of the above-mentioned trivalent arsenic bio-oxidation reactor is 0.4–3 m / h. Even further, the operating filtration rate of the above-mentioned trivalent arsenic bio-oxidation reactor is 0.6 m / h.

[0065] Furthermore, the operating filtration rate of the aforementioned ferrous biomineralization contact oxidation arsenic removal reactor is 2–9 m / h. Even more specifically, the operating filtration rate of the aforementioned ferrous biomineralization contact oxidation arsenic removal reactor is 2 m / h.

[0066] Furthermore, the above applications include: using the above-mentioned trivalent arsenic bio-oxidation reactor to pre-oxidize trivalent arsenic (As(III)) in groundwater to pentavalent arsenic (As(V)), and then aerating it through a cascade aeration zone before flowing into a ferrous biomineralization contact oxidation arsenic removal reactor, with the final effluent being discharged from the ferrous biomineralization contact oxidation arsenic removal reactor.

[0067] The present invention also provides a method for removing arsenic from groundwater. The method uses the above-mentioned groundwater arsenic removal system to remove arsenic. Specifically, the groundwater passes sequentially through a trivalent arsenic bio-oxidation reactor, a cascade oxygenation zone, and a ferrous biomineralization contact oxidation arsenic removal reactor, and is finally discharged from the ferrous biomineralization contact oxidation arsenic removal reactor.

[0068] 3. Beneficial effects

[0069] Compared with the prior art, the advantages of this invention are as follows:

[0070] (1) This invention provides a groundwater arsenic removal system, its construction method, and its application, comprising a trivalent arsenic bio-oxidation reactor, a cascade aeration zone, and a ferrous biomineralization contact oxidation arsenic removal reactor. The trivalent arsenic bio-oxidation reactor is obtained by stably enriching facultative arsenic-oxidizing bacteria capable of selectively oxidizing trivalent arsenic on the filter media surface of a continuous flow reactor. This achieves pre-oxidation of trivalent arsenic in groundwater under anoxic conditions, while minimizing oxidation of ferrous (Fe(II)) in the water. This effectively avoids the problem of traditional chemical oxidation, which lacks selectivity and causes premature oxidation of Fe(II), thus failing to improve arsenic removal efficiency. Compared to the lack of oxidation selectivity in traditional chemical oxidation methods, this invention achieves highly efficient and selective oxidation of trivalent arsenic while maintaining a certain concentration of ferrous in the water, which is beneficial for subsequent arsenic removal reactions.

[0071] (2) This invention provides a groundwater arsenic removal system, its construction method, and its application. In this system, a trivalent arsenic bio-oxidation reactor is coupled with a ferrous biomineralization contact oxidation arsenic removal reactor. By adding an anaerobic As(III) bio-oxidation reactor before the ferrous biomineralization contact oxidation arsenic removal reactor, the former pre-oxidizes As(III) in groundwater to As(V) in an oxygen-deficient environment, greatly improving the arsenic removal efficiency of the subsequent ferrous biomineralization contact oxidation arsenic removal reactor. The latter, through the biomineralization and contact oxidation catalytic effect on the surface of the active filter media in its reactor, achieves efficient As(V) removal while oxidizing and precipitating Fe(II). Verification shows that the pre-oxidation treatment of the trivalent arsenic bio-oxidation reactor effectively improves the arsenic removal efficiency of the subsequent ferrous biomineralization contact oxidation arsenic removal reactor.

[0072] (3) The present invention provides a groundwater arsenic removal system and its construction method and application. The trivalent arsenic bio-oxidation reactor and the ferrous biomineralization contact oxidation arsenic removal reactor in the system are low in preparation cost and easy to operate. The two are coupled to remove arsenic. There is no need to add external chemical agents (such as Fe(II)) to the reactor, so as to achieve efficient and environmentally friendly arsenic removal. It has important application value and broad application prospects in the treatment of arsenic pollution in groundwater. Attached Figure Description

[0073] Figure 1 The results are the oxidation of As(III) in the trivalent arsenic bio-oxidation reactors corresponding to different batches of culture broth containing facultative arsenic oxidizing bacteria introduced in this invention.

[0074] Figure 2 This is the result of Fe(II) and As(III) removal in the ferrous biomineralization contact oxidation reactor of the present invention after the filter media has been matured for 21 days.

[0075] Figure 3 This is a schematic diagram of the groundwater arsenic removal system in this invention.

[0076] Figure 4 This is the result of the oxidation of Fe(II) and As(III) in groundwater by the trivalent arsenic bio-oxidation reactor in this invention.

[0077] Figure 5 The results of different groundwater arsenic removal systems in this invention on the removal of As from groundwater are shown. Detailed Implementation

[0078] The present invention will be further described below with reference to specific embodiments.

[0079] It should be noted that terms such as "upper", "lower", "left", "right", and "middle" used in this specification are only for clarity of description and are not intended to limit the scope of implementation. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of implementation of this invention.

[0080] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the term “and / or” as used herein includes any and all combinations of one or more of the associated listed items.

[0081] Unless otherwise specified in the examples, the procedures should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0082] As used herein, the term “about” is used to provide for the flexibility and imprecision associated with a given term, measure, or value. Those skilled in the art can readily determine the degree of flexibility for a particular variable.

[0083] As used herein, the term “at least one of…” is intended to be synonymous with “one or more of…”. For example, “at least one of A, B, and C” explicitly includes only A, only B, only C, and combinations thereof.

[0084] Concentration, amount, and other numerical data may be presented in range format herein. It should be understood that such range format is used solely for convenience and brevity and should be flexibly interpreted to include not only the values ​​explicitly stated as the limits of the range, but also all individual values ​​or subranges encompassed within the range, as if each value and subrange were explicitly stated. For example, a range of values ​​from about 1 to about 4.5 should be interpreted to include not only the explicitly stated limits of 1 to 4.5, but also individual numbers (such as 2, 3, 4) and subranges (such as 1 to 3, 2 to 4, etc.). The same principle applies to ranges that describe only a single value, such as “less than about 4.5,” which should be interpreted to include all the aforementioned values ​​and ranges. Furthermore, this interpretation should apply regardless of the breadth of the range or characteristic described.

[0085] Example 1

[0086] This embodiment provides a trivalent arsenic bio-oxidation reactor and its construction method.

[0087] In this embodiment, the trivalent arsenic bio-oxidation reactor is a first continuous flow reactor filled with a first solid granular filter media, which contains a biofilm formed by facultative arsenic-oxidizing bacteria; wherein:

[0088] The first continuous flow reactor is a cylindrical continuous flow reactor with a diameter of 6 cm and a height of 17 cm;

[0089] The first solid particulate filter media is perlite particles with a particle size of 2-6 mm; the perlite particles are filled to a thickness of 10 cm, serving as a carrier for the biofilm.

[0090] The facultative arsenic oxidizing bacterium is *Ensifer adhaerens* ST2, deposited at the China Center for Type Culture Collection (CCTCC) on December 31, 2019, with accession number CCTCC NO.M20191138, located at Wuhan University, Wuhan, China.

[0091] Its construction method includes the following steps:

[0092] S1, filling the first solid particulate filter media into the first continuous flow reactor;

[0093] S2, after filling the filter media, a culture medium containing facultative arsenic oxidizing bacteria is introduced into the first continuous flow reactor in batches, and the bacteria are circulated and attached at a certain flow rate to form a biofilm on the surface of the first solid particle filter media, thus obtaining a trivalent arsenic bio-oxidation reactor.

[0094] In this embodiment, it specifically includes:

[0095] S1, fill a cylindrical continuous flow reactor with a diameter of 6cm and a height of 17cm with perlite particles with a thickness of 10cm as a biofilm carrier.

[0096] S2, after filling the filter media, a culture medium containing *Streptococcus adiposa* ST2 was introduced in four batches at a flow rate of 0.3 m / h for biofilm formation. Specifically, a culture medium containing 15% (v / v) *Streptococcus adiposa* ST2 was introduced sequentially (OD... 600 =1.2) culture medium, after 36 h replaced with culture medium containing 10% culture medium, after 36 h replaced with culture medium containing 5% culture medium, and after 36 h replaced with culture medium containing 0% culture medium (i.e., pure culture medium). The culture medium was Modified Freshwater Basal Medium (MFWM), with the following specific components: 15 mg / L As(III), 66.5 mg / L CaCl2, 14.9 mg / L KCl, 47.6 mg / L MgCl2·7H2O, 10.1 mg / L NH4Cl and 1.64 g / L C2H3NaO2. During the cyclic biofilm formation process, the concentrations of total As and As(V) in the culture medium were determined by liquid chromatography-inductively coupled plasma mass spectrometry. Based on the proportion of As(V) concentration to total As, the oxidation rate of As(III) under different ST2 contents of *Streptococcus adipoptera* was calculated.

[0097] The results are as follows Figure 1 As shown, when the ST2 content of the fourth batch of Adhesive Archaeopterygium decreased to 0%, As(III) in the reactor could still be completely oxidized within 2 hours. The ST2 Adhesive Archaeopterygium had been stably enriched on the surface of the perlite carrier and formed a biofilm, indicating that the trivalent arsenic bio-oxidation reactor was successfully constructed.

[0098] Example 2

[0099] This embodiment provides a ferrous biomineralization contact oxidation arsenic removal reactor and its construction method.

[0100] In this embodiment, the ferrous biomineralization contact oxidation arsenic removal reactor is a second continuous flow reactor filled with a second solid granular filter media containing neutral iron-oxidizing bacteria and ferric hydroxide minerals; it possesses dual functions of Fe(II) biomineralization and contact oxidation. Wherein:

[0101] The second continuous flow reactor is a cylindrical continuous flow reactor with a diameter of 6 cm and a height of 135 cm;

[0102] The second solid particulate filter media is manganese sand particles with a particle size of 0.6 to 2 mm; the filling thickness of the manganese sand particles is 50 cm.

[0103] The neutral iron-oxidizing bacterium is Arthrobacter W1, which is deposited at the China General Microbiological Culture Collection Center (CGMCC) on August 16, 2024, with accession number CGMCC NO.31596.

[0104] Its construction method includes the following steps:

[0105] M1, Filter media filling: Fill the second continuous flow reactor with the second solid granular filter media;

[0106] M2, Neutral Iron Oxidizing Bacteria Loading: The second solid particle filter media is soaked in a culture medium containing neutral iron oxidizing bacteria. The culture medium includes neutral iron oxidizing bacteria and a culture medium for culturing neutral iron oxidizing bacteria. After soaking, the culture medium diluted with arsenic-containing groundwater after aeration by a cascade is introduced into the second continuous flow reactor in batches. The medium is circulated at a certain flow rate. The dilution ratio of the diluted culture medium introduced in batches is gradually increased to gradually reduce the nutrient content in the culture medium. At least the last batch is introduced with arsenic-containing groundwater after aeration by a cascade.

[0107] M3, maturation: Arsenic-containing groundwater, after being aerated by a cascade, is continuously fed into the second continuous flow reactor at a certain flow rate to mature the filter media, thus obtaining a ferrous biomineralization contact oxidation arsenic removal reactor.

[0108] In this embodiment, it specifically includes:

[0109] M1, Filter media filling: Manganese sand particles with a thickness of 50cm are filled into a cylindrical continuous flow reactor with a diameter of 6cm and a height of 135cm; In this embodiment, to facilitate subsequent testing, a water intake is set on the reactor every 10cm starting from 5cm down from the top of the filter media.

[0110] M2, Neutral iron-oxidizing bacteria load: using a culture medium (OD) containing the neutral iron-oxidizing bacterium Arthrobacter W1. 600 =0.6) The second solid particle filter media was soaked for 48 hours; culture medium diluted with arsenic-containing groundwater after aeration by a cascade was introduced into the second continuous flow reactor in 7 batches at a flow rate of 0.2 m / h. Specifically, arsenic-containing groundwater (Fe(II) concentration of about 5 mg / L and As concentration of about 140 μg / L) after aeration by a 60 cm cascade was introduced in sequence with a volume ratio of 0:10, 2:8, 4:6, 6:4, 8:2, 9:1 and 10:0 to culture medium, for a total of 7 batches, with each batch cultured for 7 days; among them, the culture medium used in the culture medium containing neutral iron oxidizing bacteria consisted of: 10 g / L ferric ammonium citrate, 2 g / L MnSO4·H2O, 0.5 g / L K2HPO4, 0.5 g / L NaNO3, 0.5 g / L CaCl2, 0.5 g / L MgSO4·7H2O, 0.1 g / L NaCl;

[0111] After the M3 maturation and cyclic culture were completed, arsenic-containing groundwater, aerated by a 60cm drop, was continuously fed into the second continuous flow reactor at a flow rate of 2 m / h, with a further flow rate of 10 L / (s·m) every 72 hours. 2 The reactor was backwashed for 5 minutes at a specific intensity to obtain the ferrous biomineralization contact oxidation arsenic removal reactor. After 21 days of maturation, effluent samples were taken from different depths of the filter media through the reactor's inlet. The ferrous content in the effluent was determined using the o-phenanthroline spectrophotometric method (HJ / T 345-2007), and the As content was determined using liquid chromatography-inductively coupled plasma mass spectrometry. The results are as follows: Figure 2 As shown, Fe(II) in groundwater can be completely oxidized and removed at the top of the filter media, and most of As is removed simultaneously with the oxidation and precipitation of Fe(II), marking the successful construction of the ferrous biomineralization contact oxidation arsenic removal reactor.

[0112] Example 3

[0113] This embodiment provides a groundwater arsenic removal system.

[0114] The groundwater arsenic removal system, such as Figure 3As shown, it includes a trivalent arsenic bio-oxidation reactor, a cascading oxygenation zone, and a ferrous biomineralization contact oxidation arsenic removal reactor connected in sequence.

[0115] In this embodiment, the trivalent arsenic bio-oxidation reactor is the trivalent arsenic bio-oxidation reactor constructed in Example 1; the height of the cascading oxygenation zone is 60 cm; and the ferrous biomineralization contact oxidation arsenic removal reactor is the ferrous biomineralization contact oxidation arsenic removal reactor constructed in Example 2.

[0116] This system is used for arsenic removal from groundwater. The groundwater sequentially passes through a trivalent arsenic bio-oxidation reactor, a cascade aeration zone, and a ferrous biomineralization contact oxidation arsenic removal reactor. After entering the trivalent arsenic bio-oxidation reactor, the As(III) oxidizing bacteria ST2 in the reactor use nitrate as an electron acceptor to efficiently and selectively oxidize As(III) to As(V), completing the As(III) pre-oxidation treatment while maintaining a certain Fe(II) concentration. After cascade aeration, the water enters the ferrous biomineralization contact oxidation arsenic removal reactor. Fe(II) undergoes biomineralization contact oxidation arsenic removal on the filter media coated with an iron-based active filter membrane (neutral iron oxidizing bacteria and hydroxyl iron oxide minerals). The final effluent arsenic concentration can be lower than the maximum allowable concentration of arsenic in drinking water of 10 μg / L specified in my country's current "Standards for Drinking Water Quality" (GB5749-2022).

[0117] Example 4

[0118] This embodiment provides a method for removing arsenic from high-arsenic groundwater.

[0119] Specifically, the arsenic removal system described in Example 3 was used for arsenic removal.

[0120] The composition of the high-arsenic groundwater to be treated is as follows: 5 mg / L Fe(II), 250 μg / L LAs, 1.3 mg / L NO3. - -N, 4 mg / L dissolved organic carbon (DOC), dissolved oxygen (DO) ≤ 0.1 mg / L, pH 6.9.

[0121] The specific methods for arsenic removal are as follows:

[0122] High-arsenic groundwater is fed into a trivalent arsenic bio-oxidation reactor via an upward flow at a filtration rate of 0.6 m / h. The pre-oxidation reaction is carried out at room temperature in an anaerobic environment. In the reactor, the facultative arsenic-oxidizing bacterium ST2, using nitrate as an electron acceptor, efficiently and selectively oxidizes As(III) to As(V). The effluent from the above trivalent arsenic bio-oxidation reactor is then aerated through a 60 cm cascade aeration zone and fed into a ferrous biomineralization contact oxidation arsenic removal reactor via a downward flow at a filtration rate of 2 m / h. Ferrous arsenic undergoes biomineralization contact oxidation on the filter media in the reactor to remove arsenic.

[0123] This embodiment verifies the highly efficient and selective oxidation of trivalent arsenic by *Strombus amygdalinus* ST2. The contents of trivalent arsenic, pentavalent arsenic, total arsenic, and ferrous iron in the effluent of the trivalent arsenic bio-oxidation reactor were measured. Ferrous iron was detected using the o-phenanthroline spectrophotometric method (HJ / T 345-2007), while trivalent, pentavalent, and total arsenic were detected using liquid chromatography-inductively coupled plasma mass spectrometry (LC-ICP-MS). Based on the detection results, the oxidation rate of trivalent arsenic (the proportion of As(V) concentration in the effluent to the total As) and the oxidation rate of ferrous iron were calculated. The results are as follows: Figure 4 As shown, the oxidation rate of As(III) in the effluent of the trivalent arsenic bio-oxidation reactor reached 78%, while only 33% of Fe(II) was oxidized. Furthermore, 47% of As in the groundwater was removed by co-precipitation through the treatment of the trivalent arsenic bio-oxidation reactor, indicating that the bio-oxidation reactor has high selectivity for the oxidation of trivalent arsenic.

[0124] The arsenic concentration in the effluent of the biomineralization contact oxidation arsenic removal reactor was detected using liquid chromatography-inductively coupled plasma mass spectrometry (LC-ICP-MS). The results are as follows: Figure 5 As shown, the As concentration in the effluent from the above-mentioned groundwater arsenic removal system is lower than the maximum allowable concentration of As in drinking water of 10 μg / L as specified in the current Chinese "Standards for Drinking Water Quality" (GB5749-2022). The results indicate that the arsenic removal system can achieve efficient removal of arsenic from high-arsenic groundwater.

[0125] Comparative Example 1

[0126] This comparative example provides the treatment of high-arsenic groundwater using only a ferrous biomineralization contact oxidation reactor.

[0127] This comparative example does not use a trivalent arsenic bio-oxidation reactor, but only a ferrous biomineralization contact oxidation arsenic removal reactor for the removal of arsenic from high-arsenic groundwater. The ferrous biomineralization contact oxidation arsenic removal reactor used is the same as in Example 2.

[0128] The water composition of the treated high-arsenic groundwater was the same as in Example 4.

[0129] Specifically, groundwater is directly aerated through a 60cm drop aeration zone and then flows downflow into the ferrous biomineralization contact oxidation arsenic removal reactor for reaction at a filtration rate of 2m / h. After the reaction is completed, the arsenic concentration in the reactor effluent is detected using liquid phase-inductively coupled plasma mass spectrometry.

[0130] The results are as follows Figure 5 As shown, the effluent As concentration using only the ferrous biomineralization contact oxidation arsenic removal reactor is still higher than the maximum allowable As concentration of 10 μg / L in drinking water specified in my country's current "Standards for Drinking Water Quality" (GB5749-2022). This highlights the necessity of the trivalent arsenic bio-oxidation reactor described in this invention for the efficient removal of arsenic from groundwater.

Claims

1. A groundwater arsenic removal system, wherein the groundwater composition includes nitrates, characterized in that, The system comprises a trivalent arsenic bio-oxidation reactor, a cascading oxygenation zone, and a ferrous biomineralization contact oxidation arsenic removal reactor connected in sequence; wherein: The trivalent arsenic bio-oxidation reactor is a first continuous flow reactor filled with a first solid granular filter media, the first solid granular filter media containing a biofilm formed by facultative arsenic-oxidizing bacteria; the facultative arsenic-oxidizing bacteria are *Arctium tumefaciens*. Ensifer adhaerens ST2 is deposited at the China Center for Type Culture Collection (CCTCC) on January 15, 2020, with accession number CCTCC NO.M20191138. The ferrous biomineralization contact oxidation arsenic removal reactor is a second continuous flow reactor filled with a second solid particulate filter media containing neutral iron-oxidizing bacteria and hydroxyl iron oxide minerals.

2. The groundwater arsenic removal system according to claim 1, characterized in that, The first solid particulate filter media includes any one or more of perlite, volcanic rock, and anthracite; the particle size is 2-6 mm; the packing thickness is 10-30 cm; and The second solid particulate filter media includes any one or more of quartz sand, manganese sand, and anthracite; the particle size is 0.6~2mm; the packing thickness is 50~150 cm; and The neutral iron-oxidizing bacteria include Arthrobacter. Arthrobacter W1, Agrobacterium Agrobacterium W2, Delford bacteria Delftia Any one or more of J; wherein: Arthrobacterium Arthrobacter W1 is deposited at the China General Microbiological Culture Collection Center (CGMCC) on August 16, 2024, with accession number CGMCC NO.31596; Agrobacterium. Agrobacterium W2 is deposited at the China General Microbiological Culture Collection Center (CGMCC) on August 16, 2024, with accession number CGMCC NO.31597; *Delfordia* Delftia J is deposited at the China General Microbiological Culture Collection Center (CGMCC) on August 16, 2024, with accession number CGMCC NO.31598.

3. The groundwater arsenic removal system according to claim 1 or 2, characterized in that, The height of the drop aeration zone is 50-100 cm.

4. A method for constructing a groundwater arsenic removal system according to any one of claims 1-3, characterized in that, The method includes sequentially connecting a trivalent arsenic bio-oxidation reactor, a cascading aeration zone, and a ferrous biomineralization contact oxidation arsenic removal reactor via pipelines, wherein... The construction method for a trivalent arsenic biooxidation reactor includes the following steps: S1, filling the first solid particulate filter media into the first continuous flow reactor; S2, after filling the filter media, a culture medium containing facultative arsenic oxidizing bacteria is introduced into the first continuous flow reactor in batches, and the bacteria are circulated and biofilm is attached at a certain flow rate, so that the bacteria form a biofilm on the surface of the first solid particle filter media, and a trivalent arsenic bio-oxidation reactor is obtained. and The method for constructing the ferrous biomineralization contact oxidation arsenic removal reactor includes the following steps: M1, Filter media filling: Fill the second continuous flow reactor with the second solid granular filter media; M2, Neutral iron oxidizing bacteria loading: The second solid particle filter media is soaked in a culture medium containing neutral iron oxidizing bacteria, the culture medium including neutral iron oxidizing bacteria and a culture medium for culturing neutral iron oxidizing bacteria; after soaking, the culture medium diluted with arsenic-containing groundwater after aeration by a cascade is introduced into the second continuous flow reactor in batches, and circulated at a certain flow rate. The dilution ratio of the culture medium introduced in batches gradually increases, and at least the last batch is introduced with arsenic-containing groundwater after aeration by a cascade. M3, maturation: Arsenic-containing groundwater, after being aerated by a cascade, is continuously fed into the second continuous flow reactor at a certain flow rate to mature the filter media, thus obtaining a ferrous biomineralization contact oxidation arsenic removal reactor.

5. The method for constructing a groundwater arsenic removal system according to claim 4, characterized in that, The culture medium containing facultative arsenic oxidizing bacteria includes *Streptococcus adoxoides* ST2 and culture medium; the amount of bacterial solution added in the initial batch culture medium is 10%~30% (v / v). The flow rate of the circulating biofilm is 0.2~0.4 m / h; The culture medium containing facultative arsenic oxidizing bacteria is introduced in batches of 3 to 5 batches, with each batch of culture medium circulating for 12 to 36 hours to allow biofilm formation.

6. The method for constructing a groundwater arsenic removal system according to claim 5, characterized in that, The culture medium includes 10-20 mg / L As(III); and the culture medium containing facultative arsenic oxidizing bacteria is introduced in batches, with the amount of bacterial solution gradually decreasing, and the amount of bacterial solution added in the last batch of culture medium is 0%.

7. The method for constructing a groundwater arsenic removal system according to any one of claims 4-6, characterized in that, The culture medium containing neutral iron-oxidizing bacteria is used to soak the second solid particulate filter media for 24-72 hours; and The flow rate for the circulating culture is 0.2~5 m / h; and The culture medium, diluted with arsenic-containing groundwater after being aerated by a waterfall, is introduced in batches of 5-10 batches, with each batch incubated for 5-7 days; and The flow rate during the ripening process is 0.5~5 m / h.

8. The method for constructing a groundwater arsenic removal system according to claim 7, characterized in that, The curing process also includes backwashing, which is carried out every 48-72 hours at a rate of 10-18 L / (s·m). 2 The backwashing time is 5-10 minutes.

9. The application of the groundwater arsenic removal system according to any one of claims 1-3 in groundwater arsenic removal, characterized in that, The application involves passing groundwater sequentially through a trivalent arsenic bio-oxidation reactor, a cascade oxygenation zone, and a ferrous biomineralization contact oxidation arsenic removal reactor.

10. A method for removing arsenic from groundwater, characterized in that, The method uses the groundwater arsenic removal system according to any one of claims 1-3, comprising groundwater sequentially passing through a trivalent arsenic bio-oxidation reactor, a cascade oxygenation zone, and a ferrous biomineralization contact oxidation arsenic removal reactor, and finally being discharged from the ferrous biomineralization contact oxidation arsenic removal reactor.

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